t^r-- -,m. M' to >o *.f {" I 0 '■ ;' v. V, 4 NATIONAL LIBRARY OF MEDICINE Bethesda, Maryland 4 . *- fe»lW: *• 4 TEXT BOOK ^— OF CHEMICAL PHILOSOPHY. ON THE BASIS OF DR. TURNER'S ELEMENTS OF CHEMISTRY j > CO s o fa hermom. Sinks. r to —5° Degree of Cold produced. Muriate of Soda . 2 Muriate of Ammonia . 1 Snow . . .5 to —12° Muriate of Soda . 10 Muriate of Ammonia . 5 Nitrate of Potash . 5 Snow . . .24 to —18° Muriate of Soda . 5 Nitrate of Ammonia . 5 Snow . . .12 to —25° f Diluted Sulphuric Acid 2 Snow . . .3 from+32° to —23° 55 deg. Concentrated Muriatic Acid 5 Snow . . .8 from+32° to —27° 59 Concentrated Nitrous Acid 4 Snow . . .7 from+32° to —30° 62 Muriate of Lime . 5 Snow . . .4 from+32° to —40° 72 Crystallized Muriate of Lime 3 Snow . . .2 from+32° to —50° 82 Fused Potash . . 4 Snow . . . 3| from+32° to —51° 83 But freezing mixtures may be made by the rapid solution of salts, without the use of snow or ice; and the following table includes the most important of them. The salts must be finely powdered and dry. * The snow should be freshly fallen, dry, and uncompressed. If snow can- not be had, finely pounded ice may be substituted for it. t Made of strong acid, diluted with half its weight of snow or distilled water. H 58 CALORIC. Mixtures. Parts by Muriate of Ammonia Nitrate of Potash Water Weight. 5 5 . 16 Temperature Falls. from+50° to+10° Degree of Uold produced. 40 -deg. Muriate of Ammonia Nitrate of Potash Sulphate of Soda Water 5 5 8 16 from + 50° to +4° 46 Nitrate of Ammonia Water 1 1 from+50° to +4° 46 Nitrate of Ammonia Carbonate of Soda Water 1 1 I from+50° to —7° 57 Sulphate of Soda Diluted Nitrous Acid* 3 2 from+50° to —3° 53 Sulphate of Soda Muriate of Ammonia Nitrate of Potash Diluted Nitrous Acid 6 4 2 4 from+50° to—10° 60 Sulphate of Soda Nitrate of Ammonia Diluted Nitrous Acid 6 5 4 from+50° to—14° 64 Phosphate of Soda Diluted Nitrous Acid 9 4 from+50° to—12° 62 Phosphate of Soda Nitrate of Ammonia Diluted Nitrous Acid 9 6 4 from+50° to—21° 71 Sulphate of Soda Muriatic Acid 8 5 from+50° to —0° 50 Sulphate of Soda . 5 Diluted Sulphuric Acidf 4 from+50° to +3° 47 * Composed of fuming nitrous acid 2 parts in weight and one of water the mixture being allowed to cool before being used. ' f Composed of equal weights of strong acid and water, being allowed to cool before use. CALORIC. 59 These artificial processes for generating cold are much more effectual when the materials are previously cooled by immersion in other frigorific mixtures. One would at first suppose that an unlimited degree of cold might be thus produced ; but it is found that when the difference between the mixture and the air becomes very great, caloric is so rapidly communicated from one to the other as to limit the reduction to a certain point. The greatest cold produced does not exceed 100 degrees below the zero of Fahrenheit. Though it is unlikely that we shall ever succeed in depriving any substance of all its caloric, it is presumed that bodies do contain a certain definite quantity of this principle, and various attempts have been made to calculate the amount of it. To be satisfied that such calculations cannot be trusted, it is sufficient to know, that the estimates made by different chemists respecting the absolute quantity of caloric in water vary from 900 to nearly 8000. Vaporization. Aeriform substances are commonly divided into vapours and gases. The character of the former is, that they can be readily converted into liquids or solids, either by a moderate increase of pressure, the temperature at which they were formed remaining the same, or by a diminution of temperature, the pressure being unchanged. Gases, on the contrary, retain their elastic state more obstinately; they are always such at common temperatures, and cannot be made to change their form, except by being sub- jected to much greater pressure than they are naturally exposed to. Several of them, indeed, have hitherto resisted every effort to compress them into liquids. Caloric appears to be the cause of vaporization, as well as of liquefaction, and it is a general opinion that a sufficiently intense heat would convert every liquid and solid into vapour. A con- siderable number of bodies, however, resist the strongest heat of our furnaces without vaporizing. These are said to be fixed in the fire; those which, under the same circumstances, are con- verted into vapour, are called volatile. The disposition of different substances to form vapour is very different; and the difference depends doubtless on the relative power of cohesion with which they are endowed. Fluids are, in general, more easily vaporized than solids, as would be expected from the weaker cohesion ofthe former. Some solids, as arsenic and sal-ammoniac, pass at once into vapour without being lique- fied ; but most of them become liquid before assuming the elastic condition. Vapours occupy more space than the substance from which they were produced. According to the experiments of Gay- 60 CALORIC. Lussac, water in passing into vapour expands to 1696 times its volume, alcohol to 659 times, and ether to 443 times. Inis shows that vapours differ in density. Watery vapour is lighter than air in the proportion of 1000 to 1604; or the density of air being 1000, that of watery vapour is 623. The vapour of alco- hol, on the contrary, is half as heavy again as air ; and that of ether is more than twice and a half as heavy. As alcohol boils at a lower temperature than water, and ether than alcohol, it was conceived that the density of vapours might be in the direct ratio of the volatility ofthe liquids which produced them. But Gay- Lussac has shown that this law does not hold generally. The dilatation of vapours by heat was found by Gay-Lussac to follow the same law as gases, that is, for every degree of Fahren- heit, they increase by 1 -480th of the volume they occupied at 32°. But the law does not hold unless the quantity of vapour con- tinues the same. If the increase of temperature cause a fresh portion of vapour to rise, then the expansion will be greater than l-480th, for each degree; because the heat not only dilates the vapour previously existing to the same extent as if it were a real gas, but augments its bulk by adding a fresh quantity of vapour. The contraction of a vapour on cooling will likewise deviate from the above law, whenever the cold converts any of it into a liquid—an effect which must happen, if the space had originally contained its maximum of vapour. Vaporization is conveniently studied under two heads,—Ebul- lition and Evaporation. In the first, the production of vapour is so rapid that its escape gives rise to a visible commotion in the liquid ; in the second, it passes off insensibly. Ebullition. The temperature at which vapour rises with sufficient freedom for causing the phenomena of ebullition, is called the boiling point. The heat requisite for this effect varies with the nature of the fluid. Thus, sulphuric ether boils at 96° F., alcohol at 173°, and pure water at 212°; while oil of turpentine must be raised to 316°, and mercury to 660° before either exhibits marks of ebullition. The boiling point of the same liquid is constant, so long as the necessary conditions are preserved; but it is liable to be affected by several circumstances. The nature ofthe ves- sel has some influence upon it. Thus, Gay-Lussac observed that pure water boils precisely at 212° in a metallic vessel, and at 214° in one of glass. It is likewise affected by the presence of foreign particles. The same accurate experimenter found, that when a few iron filings are thrown into water boiling in a glass vessel, its temperature quickly falls from 214° to 212°, and re- mains stationary at the last point. But the circumstance which has the greatest influence over the boiling point of fluids is varia- CALORIC. 61 tion of pressure. All bodies upon the earth are constantly ex- posed to considerable pressure; for the atmosphere itself presses with a force equivalent to a weight of 15 pounds on every square inch of surface. Liquids are exposed to this pressure as well as solids, and their tendency to take the form of vapour is very much counteracted by it. In fact, they cannot enter into ebullition at all, till their particles have acquired such an elastic force as en- ables them to overcome the pressure upon their surfaces ; that is, till they press against the atmosphere with the same force as the atmosphere against them. Now the atmospheric pressure is variable, and hence it follows that the boiling point of liquids must also vary. The only time at which the pressure ofthe atmosphere is equal to a weight of 15 pounds on every square inch of surface, is when the barometer stands at 30 inches, and then only does water boil at 212° F. If the pressure be less, that is, if the barometer fall below 30 inches, then the boiling point of water, and every other liquid will be lower than usual ; or if the barometer rises above 30 inches, the temperature of ebullition will be proportionally increased. This is the reason why water boils at a lower tem- perature on the top of a hill than in the valley beneath it; for as the column of air diminishes in length as we ascend, its pressure must likewise suffer a proportional diminution. The ratio be- tween the depression ofthe boiling point and the diminution of the atmospherical pressure is so exact, that it has been proposed as a method for determining the heights of mountains. An elevation of 530 feet makes a diminution of one degree of Fahrenheit. The influence ofthe atmosphere over the point of ebullition is best shown by removing its pressure altogether. Professor Robi- son found that fluids boil in vacuo at a temperature 140 degrees lower than in the open air. Thus water boils at 72° F. alcohol at 33° F. and ether at—44° F. This proves that a liquid is not necessarily hot, because it boils. The heat of the hand is suffi- cient to make water boil in vacuo, as is exemplified by the com- mon pulse-glass ; and ether, under the same circumstances, will enter into ebullition, though its temperature is low enough for freezing mercury. Water cannot be heated under common circumstances beyond 212° F., because it then acquires such an expansive force as ena- bles it to overcome the atmospheric pressure, and to fly off in the form of vapour. But if subjected to sufficient pressure, it may be heated to any extent without boiling. This is best done by heat- ing water while confined in a strong copper vessel, called Papin's Digester. A large quantity of vapour collects above the water, which checks the ebullition by the pressure it exerts upon the surface of the liquid. There is no limit to which water might not be heated in this way, provided the vessel is strong enough to 62 CALORIC. confine the vapour; but the expansive force of steam under these circumstances is so enormous as to overcome the greatest re- sistance. In estimating the power of steam, it should be remembered that vapour, if separated from the liquid which produced it, does not possess a greater elasticity than an equal quantity of air. If, for example, the digester was full of steam at 212°, no water in the liquid state being present, it may be heated to any degree, even to redness, without danger of bursting. But if water be pre- sent, then each addition of caloric causes a fresh portion of steam to rise, which adds its own elastic force to that of the vapour pre- viously existing; and in consequence an excessive pressure is soon exerted against the inside of the vessel. Professor Robison found that the tension of steam is equal to two atmospheres at 244° F., and to three at 270°. F. The results of Mr. Southern's experi- ments, fix upon 250.3° F. as the temperature at which steam has the force of two atmospheres, on 293.4° F. for four, and 343.6° F. for eight atmospheres. The elasticity of steam is employed as a moving power in the steam-engine. The construction of this machine depends on two properties of steam, namely, the expansive force communinated to it by caloric, and its ready conversion into water by cold. The effect of both these properties is well shown by a little instrument devised by Dr. Wollaston. It consists of a cylindrical glass tube, six inches long, nearly an inch wide, and blown out into a little ball at one end. A piston is accurately fitted to the cylinder, so as to move up and down the tube with freedom. When the piston is at the bottom ofthe tube, it is forced up by causing a portion of water, previously placed in the ball, to boil by means of a spirit-lamp. On dipping the ball into cold water, the steam which occupies the cylinder is suddenly condensed, and the pis- ton is forced down by the pressure of the air above it. By the alternate application of heat and cold, the same movements are reproduced, and may be repeated for any length of time. The moving power of the steam-engine is the same as in this apparatus. The only essential difference between them is in the mode of condensing the steam. In the steam-engine, the steam is condensed in a separate vessel, where there is a regular supply of cold water for the purpose. By this contrivance, which con- stitutes the great inprovement of Watt, the temperature of the cylinder never falls below 212°. The formation of vapour is attended, like liquefaction, with a loss of sensible caloric. This is proved by the well-known fact that the temperature of steam is precisely the same as that of the boiling water from which it rises; so that all the caloric which enters into the liquid is solely employed in converting a portion of it into vapour, without affecting the temperature of either in the slightest degree, provided the latter is permitted to escape CALORIC. 63 with freedom. The caloric which then becomes latent, to use the language of Dr. Black, is again set free when the vapour is condensed into water. The exact quantity of caloric absorbed, may therefore be ascertained by condensing the steam in cold water, and observing the rise of temperature occasioned by it. From the experiments of Dr. Black and Mr. Watt, conducted on this principle, it appears that steam of 212°, in being condensed into water of 212°, gives out as much caloric as would raise the temperature of an equal weight of water by 950 degrees, all of which had previously existed in the vapour without being sensi- ble to a thermometer. The latent heat of steam and several other vapours has been examined by Dr. Ure, whose results are contained in the follow- ing table. Latent Heat. Vapour of water at its boiling point . 967° Ether 302.379 Petroleum 177.87 Oil of turpentine . 177.87 Nitric acid 531.99 Liquid ammonia . 837.28 Vinegar . 875 The disappearance of caloric that accompanies vaporization was explained by Dr. Black and Dr. Irvine, in the way already mentioned, under the head of liquefaction, and the objections then urged against each theory are likewise applicable on the present occasion. Evaporation. Evaporation, as well as ebullition, consists in the formation of vapour, and the only assignable difference between them is, that the one takes place quietly, the other with the appearance of boiling. Evaporation takes place at common temperatures, as may be proved by exposing water in a shallow vessel to the air for a few days, when it will gradually diminish, and at last dis- appear entirely. Most fluids, if not all of them, are susceptible of this gradual dissipation; and it may also be observed in some solids, as for example in camphor. Evaporation is much more rapid in some fluids than in others, and it is always found that those liquids, whose boiling point is lowest, evaporate with the greatest rapidity. Thus alcohol, which boils at a lower tem- perature than water, evaporates also more freely; and ether, whose point of ebullition is yet lower than that of alcohol, eva- porates still more rapidly. The chief circumstances that influence the process of evapora- 64 CALORIC. tion are extent of surface, and the state of the air as to tempera- ture, dryness, stillness, and density. 1. Extent of surface. Evaporation proceeds only from the surface of fluids, and therefore, cceteris paribus, must depend upon the extent of surface exposed. 2. Temperature. The effect of heat in promoting evaporation may easily be shown by putting an equal quantity of water into two saucers, one of which is placed in a warm, the other in a cold situation. The former will be quite dry before the latter has suffered an appreciable diminution. 3. State of the air as to dryness or moisture. When water is covered by a stratum of dry air, the evaporation is rapid even when its temperature is low. Thus in some dry cold days in winter, the evaporation is exceedingly rapid ; whereas it goes on very tardily, if the atmosphere contains much vapour, even though the air be very warm. 4. Evaporation is far slower in still air than in a current, and for an obvious reason. The air immediately in contact with the water soon becomes moist, and thus a check is put to evapora- tion. But if the air is removed from the surface of the water when it has become charged with vapour, and its place sup- plied with fresh dry air, then the evaporation continues without interruption. 5. Pressure over the surface of liquids has a remarkable in- fluence over evaporation. This is easily proved by placing ether in the vacuum of an air pump, when vapour rises so abundantly as to produce ebullition. As a large quantity of caloric passes from a sensible to an in- sensible state during the formation of vapour, it follows that cold should be generated by evaporation. A very simple experiment will prove it. If a few drops of ether be allowed to fall upon the hand, a strong sensation of cold will be excited during the evapo- ration ; or if the bulb of a thermometer, covered with lint, be moistened with ether, the production of cold will be marked by the descent of the mercury. But to appreciate the degree of cold which may be produced by evaporation, it is necessary to render it very rapid and abundant by artificial processes ; and the best means of doing so, is by removing pressure from the surface of volatile liquids. Water placed under the exhausted receiver of an air-pump, evaporates with great rapidity, and so much cold is generated as would freeze the water, did the vapour continue to rise for some time with the same velocity. But the vapour it- self soon fills the vacuum, and retards the evaporation by press- ing upon the surface ofthe water. This difficulty may be avoid- ed by putting under the receiver a substance, such as sulphuric acid, which has the property of absorbing watery vapour, and consequently of removing it as quickly as it forms. Such is the CALORIC. 65 principle of Mr. Leslie's method for freezing water by its own evaporation. The action ofthe cryophorus, an ingenious contrivance of Dr. Wollaston, depends on the same principle. It consists of two glass balls, perfectly free of air, and joined together by a tube. One of the balls contains a portion of distilled water, while the other parts of the instrument, which appear empty, are full of aqueous vapour, which checks the evaporation from the water by the pressure it exerts upon it. But when the empty ball is plunged into a freezing mixture, all the vapour within it is con- densed ; evaporation commences from the surface of the water in the other ball, and it is frozen in two or three minutes by the cold thus produced. Liquids which evaporate more rapidly than water, cause a still greater reduction of temperature. The cold produced by the evaporation of ether in the vacuum ofthe air-pump, is so in- tense as to freeze mercury. Scientific men have differed concerning the cause of evapora- tion. It was once supposed to be owing to a chemical attraction between the air and water, and the idea is at first view plausible, since a certain degree of affinity does, to all appearance, exist be- tween them. But it is nevertheless impossible to attribute the effect to this cause. For evaporation takes place equally in vacuo as in the air; nay, it is an established fact, that the at- mosphere positively retards the process, and that one of the best means of accelerating it, is by removing the air altogether. The experiments of Mr. Dalton prove that caloric is the true and only cause ofthe formation of vapour. He finds that the actual quantity of vapour which can exist in any given space, is depen- dant solely upon the temperature. If, for instance, a little water be put into a dry glass flask, a quantity of vapour will be formed proportional to the temperature. If a thermometer placed in it stands at 32° F. the flask will contain a very small quantity of vapour. At 40°, more vapour will exist in it; at 50° it will contain still more; and at 60°, the quantity will be still farther augmented. If, when the thermometer is at 60°, the tempera- ture of the flask is suddenly reduced to 40°, then a certain por- tion of vapour will be converted into water; the quantity which retains the elastic form being precisely the same as when the temperature was originally at 40° F. It matters not with regard to these changes, whether the flask is full of air, or altogether empty; for in either case, it will even- tually contain the same quantity of vapour, when the thermome- ter is at the same height. The only effect of a difference in this respect, is in the rapidity of evaporation. The flask, if pre- viously empty, acquires its full complement of vapour, or, in com- mon language, becomes saturated with it in an instant; whereas the presence of air affords a mechanical impediment to its pas- 66 CALORIC. sage from one part of the flask to another, and therefore an ap- preciable time elapses before the whole space is saturated. Mr. Dalton found that the tension or elasticity of vapour is al- ways the same, however much the pressure may vary, so long as the temperature remains constant, and liquid enough is present for preserving the state of saturation proper to the temperature. If, for example, in a vessel containing a liquid the space occupied by its vapour should suddenly dilate, the vapour it contains will dilate also, and consequently suffer a diminution of elastic force; but its tension will be quickly restored, because the liquid yields an additional quantity of vapour, proportional to the increase of space. Again, if the space be diminished, the temperature re- maining constant, the tension of the confined vapour will still continue unchanged; because a quantity of it will be condensed proportional to the diminution of space, so that, in fact, the re- maining space, contains the very same quantity of vapour as it did originally. The same law holds good whether the vapour is pure or mixed with air or any other gas. The presence of watery vapour in the atmosphere is owing to evaporation. All the accumulations of water upon the surface ofthe earth are subjected by its means to a natural distillation ; the impurities with which they are impregnated remain behind, while the pure vapour ascends into the air, gives rise to a multi- tude of meteorological phenomena, and after a time descends again upon the earth as rain. As evaporation goes on to a certain ex- tent even at low temperatures, it is probable that the atmosphere is fiever absolutely free of vapour. The quantity of vapour present in the atmosphere is very varia- ble, in consequence of the continual change of temperature to which the air is subject. But even when the temperature is the same, the quantity of vapour is still found to vary ; for the air is not always in a state of saturation. At one time it is excessively dry, at another it is fully saturated; and at other times it varies between these extremes. This variable condition of the atmos- phere as to saturation is ascertained by the hygrometer. A great many hygrometers have been invented; but they may all be referred to two principles. The construction of the first kind of hygrometer is founded on the property possessed by[some substances of expanding in a humid atmosphere, owing to a depo- sition of moisture within them ; and of parting with it again to a dry air, and in consequence contracting. Almost all bodies have the power of attracting moisture from the air, though in different proportions. A piece of glass or metal weighs sensibly less when carefully dried, than after exposure to a moist atmosphere; though neither of them is dilated, because the water cannot penetrate into their interior. Dilatation from the absorption of moisture ap- pears to depend on a deposition of it within the texture of a body, the particles of which are moderately soft and yielding. The CALORIC. 67 hygrometric property therefore belongs chiefly to organic sub- stances, such as wood, the beard of grain, whalebone, hair, and animal membranes. Of these, none is better than the human hair, which not only elongates freely from imbibing moisture, but, by reason of its elasticity, recovers its original length on drying. The second kind of hygrometer points out the opposite states of dryness and moisture by the rapidity of evaporation. Water does not evaporate at all when the atmosphere is completely sa- turated with moisture ; and the freedom with which it goes on at other times, is in proportion to the dryness of the air. The hy- grometric condition of the air may be determined, therefore, by observing the rapidity of evaporation. The most convenient method of doing this, is by covering the bulb of a thermometer with a piece of silk or linen, rnoistening it with water, and expos- ing it to the air. The descent of the mercury, or the cold produc- ed, will correspond to the quantity of vapour formed in a given time. Mr. Leslie's hygrometer is of this kind. A very elegant instrument for determining the dew-point, or the temperature at which dew is deposited, has been lately in- vented. It consists of a common mercurial thermometer, with a bulb of black glass, the upper half of which is covered with mus- lin. When sulphuric ether is dropped upon the muslin, the tem- perature ofthe whole bulb sinks rapidly, and a deposition of dew soon becomes visible on the lower and exposed part of it. The degree indicated by the thermometer at that instant is the dew-point. It is desirable, on some occasions, not merely to know the hygrometric condition of air or gases, but also to deprive them entirely of their vapour. This may be done to a great extent by exposing them to an intense cold ; but the method now generally preferred is by bringing the moist gas in contact with some sub- stance which has a powerful chemical attraction for water. Of these none is preferable to muriate of lime in a state of perfect dryness. Constitution cf the Gases with respect to Caloric. Tf* ingenious experiments of Mr. Faraday on ttie liquefac- tiofi of gaseous substances appear to justify the opinion that gases are merely the vapours of extremely volatile liquids. These liquids, however, are so volatile, that their boiling point, under the atmospheric pressure, is lower than any natural tem- perature; and this is the reason why they are always found in the gaseous state. By subjecting them to great pressure, their elas- ticity is so far counteracted that they become liquid. But even when thus compressed, a very moderate heat is sufficient to make them boil; and on the removal of pressure they re-assume the elastic form, most of them with such violence as to cause a 68 CALORIC. report like an explosion, and others with the appearance of brisk ebullition. An intense degree of cold is produced at the same time, in consequence of caloric passing from a sensible to an in- sensible state. The process for condensing the gases, consists in exposing them to the pressure of their own atmospheres. The materials for producing them are put into a strong glass tube, which is after- wards sealed hermetically, and bent in the middle. The gas is generated, if necessary, by the application of heat, and when the pressure becomes sufficiently great, the liquid forms and collects in the free end of the tube, which is kept cool to facilitate the condensation. Most of these experiments are attended with danger from the bursting ofthe tubes, against which the operator must protect himself by the use of a mask. The pressure required to liquefy the gases is very variable, as will appear from the following table. The results were obtained by Mr. Faraday. Sulphurous acid gas 2 atmosphi 2res at4£°F Sulphuretted hydrogen gas 17 - - 50°F. Carbonic acid gas 36 - - 32°F. Chlorine gas - 4 - - 60°F. Nitrous oxide gas - 50 - - 45°F. Cyanogen gas - 3.6 - - 45°F. Ammoniacal gas - 6.5 - - 50°F. Muriatic acid gas - - 40 - - 50°F. SECTION II. Light. Light is similar to caloric in many of its properties. They are both emitted in the form of rays, traverse the air in straight lines, and are subject to the same laws of reflection. The intensity of each diminishes as the square of the distance from their source. They often accompany each other; and on some occasions seem to be actually converted into one another. It has been supposed, from this circumstance, that they might be modifications of the same agents, and though most persons regard them as indepen- dent principles, yet they are certainly allied in a way which is at present quite inexplicable. There are two kinds of light, natural and artificial; the former proceeding from the sun and stars, the latter from bodies which are strongly heated. The light derived from these sources is so different, that it is necessary to speak of them separately. The solar rays come to us either directly, as in the case of sun- shine, or indirectly, in consequence of being diffused through the atmosphere, constituting day-light. They pass freely through LIGHT. 69 some solid and liquid bodies, hence called transparent, such as glass, rock-crystal, water, and many others, which, if clear and in moderately thin layers, intercept a portion of light that is quite in- appreciable when compared to the quantity transmitted. Opaque bodies, on the contrary, intercept the rays entirely, absorbing some of them and reflecting others. In this respect, also, there is a close analogy between light and caloric; for every good re- flector ofthe one, reflects the other also. Though transparent substances permit the light to pass through them, they nevertheless exert a considerable influence upon it in its passage. All the rays which fall obliquely are refracted, that is, are made to deviate from their original direction. It was this property of transparent media which enabled Sir Isaac Newton to discover the compound nature of the solar light, and to resolve it into its constituent parts. The substance commonly employed for this purpose is a triangular piece of glass called the prism. Its action depends upon the different refrangibility ofthe seven- coloured rays which compose a colourless one. The violet ray suffers the greatest refraction, and the red the least; while the other colours ofthe rainbow lie between them, disposed in regu- lar succession according to the degree of deviation, which they have individually experienced. The coloured figure so produced is called the prismatic spectrum, which is always bounded by the violet ray on one side, and by the red on the other. The prismatic colours, according to the experiment of Sir W, Herschell, differ in their illuminating power. The orange pos- sesses this property in a higher degree than the red; and the yellow rays illuminate objects still more perfectly. The maxi- mum of illumination lies in the brightest yellow or palest green. The green itself is nearly equally bright with the yellow ; but from the full deep grelen, the illuminating power decreases very sensibly. That of the blue is nearly equal to that of the red; the indigo has much less than the blue; and the violet is very deficient. The solar rays, both direct and diffused, possess the property of exciting heat as well as light. This effect takes place only when the rays are absorbed; for the temperature of transparent substances through which they pass, or of opaque ones by which they are reflected, is not affected by them. Hence it happens that the burning glass and concave reflector are themselves nearly or quite cool, at the very moment of producing a strong heat by collecting the sun's rays into a focus. The extreme coldness that prevails in the higher strata of the air arises from the same cause. The rays pass on unabsorbed through the atmosphere; and the lower parts of it would be as cold as the upper, did they not receive caloric by communication from the earth. The absorption of light is much influenced by the nature of the surface on which it falls; and it is remarkable that those sub- 70 LIGHT. stances which absorb radiant non-luminous caloric most power- fully, are likewise the best absorbers of light. But there is one property of surfaces, namely, colour, which has a great influence over the absorption of light, but exceedingly little, if any, over that of pure radiant caloric. That dark-coloured substances acquire a higher temperature in the sunshine than light ones, may be inferred from the general preference given to the latter as articles of dress during summer; and this practice, founded on the experience of mankind, has been justified by direct experi- ment. Dr. Hooke, and subsequently Dr. Franklin, proved the fact by placing pieces of cloth of the same texture and size, but of different colours, upon snow, and allowing the sun's rays to fall upon them. The dark-coloured specimens always absorbed more caloric than the light ones, the snow beneath the former having melted to a greater extent than under the others; and it was remarked that the effect was nearly in proportion to the depth of shade. Sir H. Davy has recently examined the subject, and arrived at the same conclusions. The rays of the prismatic spectrum differ from one another in their heating power as well as in colour. Their difference in this respect was first noticed by Herschell, who was induced to direct his attention to the subject by the following circumstance. In viewing the sun by means of large telescopes through differently coloured darkening glasses, he sometimes felt a strong sensation » of heat with very little light, and at other times he had a strong light with little heat,—differences which appeared to depend on the colour ofthe glasses which he used. This observation led to his celebrated researches on the heating power of the prismatic colours, which were published in the Philosophical Transactions for 1800. The experiments were made by transmitting a solar beam through a prism, receiving the spectrum on a table, and placing the bulb of a very delicate thermometer successively in the dif- ferent parts of it. While engaged in this inquiry, he observed, not only that the red was the hottest ray, but that there was a point a little beyond the red, altogether out of the spectrum, where the thermometer stood higher than in the red itself. By repeating and varying the experiment, he discovered that the most intense heating power was always beyond the red ray, where there was no light at all; and that the heat progressively diminished in passing from the red to the violet, where it was least. He hence inferred that there exists in the solar beam a distinct kind of ray, which causes heat, but no light; and that these rays, from being less refrangible than the luminous ones, deviate in a less degree from their original direction in passing through the prism. All succeeding experiments confirm the statement of Sir W. Herschell, that the prismatic colours have very different heatin« LIGHT. 71 powers; but they are at variance with respect to the spot at which the heat is at a maximum. Some assert with Sir W. Herschell that it is beyond the red ray; while others, and in particular Pro- fessor Leslie, contend that it is in the red itself. This question has been decided by the recent observations of M. Seebeck. He found that the point of greatest heat was variable according to the kind of prism which was employed for refracting the rays. When he used a prism of fine flint glass, the greatest heat was constantly beyond the red. With a prism of crown glass, the greatest heat was in the red itself. When he employed a prism externally of glass, but containing water within, the maximum was neither in the red, nor beyond it, but in the yellow. It is difficult to account for these phenomena, except on the supposi- tion that the different kinds of prisms differ in their power of refracting caloric. These experiments therefore confirm the opi- nion of Sir W. Herschell, that the sun-beam contains calorific rays, distinct from the luminous ones; and render it highly pro- bable, that the heating effect imputed to the latter, is solely owing to the presence of the former. It has been long known that the solar light is capable of pro- ducing powerful chemical changes. One of the most striking instances of it is its power of darkening the white muriate of silver, which takes place slowly in the diffused light of day, but in the course of one or two minutes by exposure to the sun-beam. This effect was once attributed to the influence of the luminous rays; but it appears from the observations of Ritter and Wollas- ton, that it is owing to the presence of certain rays that excite neither heat nor light, and which, from their peculiar agency, are termed chemical rays. It is found that the greatest chemical action is exerted just beyond the violet ray ofthe prismatic spec- trum ; that the spot next in energy is occupied by the violet ray itself; and that the property gradually diminishes as we advance to the green, beyond which it seems wholly wanting. It hence follows that the chemical rays are still more refrangible than the luminous ones, in consequence of which they are dispersed in part over the blue, indigo, and violet, but in the greatest quantity at a point which is even beyond the latter. The more refrangible rays of light possess the property of ren- dering steel or iron .magnetic. This property was discovered in the violet ray by Dr. Morichini of Rome; but as some experi- mentalists of eminence had repeated the experiments without success, the subjectPwas involved in some degree of uncertainty. The fact, however, has been established by Mrs. Somerville of London, who recently gave an account of her researches to the Royal Society. Sewing needles were rendered magnetic by exposure for two hours to the violet ray; and the magnetic pro- perty was communicated in a still shorter time, when the violet rays were concentrated by a lens. The indigo rays posse ss the 72 LIGHT. magnetizing power almost to the same extent as the violet; and the blue and green possess the same power, though in a less de- gree. It is wanting in the yellow, orange, and red. Needles were also rendered magnetic by the sun's rays, transmitted through green and blue glass. The second kind of light is that which is emitted by substances when strongly heated. All bodies begin to emit light when caloric is accumulated within them in great quantity; and the appearance of glowing or shining, which they then assume, is called incan- descence. The temperature at which solids in general begin to shine in the dark, is between 600° and 700° F.; but they do not appear luminous in broad day-light, till they are heated to about 1000° F. The colour of incandescent bodies varies with the in- tensity ofthe heat. The first degree of luminiousness is an ob- scure red. As the heat augments, the redness becomes more and more vivid, till at last it acquires a full red glow. Should the temperature still continue to increase, the character of the glow changes, and by degrees becomes white, shining with increasing brilliancy as the intensity of the heat augments. Liquids and gases likewise become incandescent when strongly heated ; but a very high temperature is required to make a gas luminous, more than is sufficient for heating a so/id body even to whiteness. The different kinds of flame, as ofthe fire, candles, and gas light, are instances of incandescent gaseous matter. All artificial lights are procured by the combustion or burning of inflammable matter. So large a quantity of caloric is evolved during the process that the body is made incandesent in the moment of being consumed. Those substances are preferred for the purposes of illumination that yield gaseous products when strongly heated, which, by becoming luminous while they burn, constitute flame. The light derived from such sources differs from the solar light in being accompanied by free radiant caloric similar to that emitted by a non-luminous heated body. The free radiant caloric may be separated by a screen of moderately thick glass; but the light so purified still heats any body that absorbs it, whence it would appear that it retains some calorific rays which, like those in the solar beam, accompany the luminous ones in their passage through solid transparent media. Terres- trial light has been supposed to contain no chemical rays. It is probable, however, that the attempts hitherto made to detect their presence, have failed rather from a want of delicacy in our tests than from their non-existence. This supposition is sup- ported, or rather confirmed, by the chemical effects recently oc- casioned by phosphorescent lime. Light is emitted by some substances at common temperatures, giving rise to an appearance which is called phosphorescence! This phenomenon seems owing, in some instances, to a direct ab- sorption of light which is afterwards slowly emitted. A compo- LIGHT. 73 sition made by heating to redness a mixture of calcined oyster shells and sulphur, known by the name of Canton's Phosphorus, possesses this property in a very remarkable degree. It shines so strongly for a few minutes after exposure to light, that when removed to a dark room the hour on a watch may be distinctly seen by it. After some time it ceases to be luminous, but it regains the property when exposed during a short interval to light. No chemical change attends the phenomenon. Another kind of phosphorescence is observable in some bodies when they are strongly heated. A piece of marble, for example, heated to a degree which would only make other bodies red, emits a brilliant white light of such intensity that the eye cannot support the impression of it. A third species of phosphorescence is observed in the bodies of some animals, either in the dead or living state. Some marine animals, and particularly fish, possess it in a remarkable degree. It may be witnessed in the body of the herring, which begins to phosphoresce a day or two after death, and before any visible sign of putrefaction has set in. Sea-water is capable of dissolv- ing the luminous matter; and it is probably from this cause that the waters of the ocean sometimes appear luminous at night when agitated. This appearance is also ascribed to the pre- sence of certain animalcules, which, like the glow-worm of this country, or the fire-fly of the West Indies, are naturally phos- phorescent. It is sometimes of importance to measure the comparative in- tensities of light, and the instrument by which this is done is called a photometer. The only photometer which is employed for estimating the relative strength of the sun's light is that of Mr. Leslie. It consists of his differential thermometer, with one ball made of black glass. The clear ball transmits all the lumin- ous rays that fall upon it, and therefore its temperature is not affected by them; they are all absorbed, on the contrary, by the black ball, and by heating and expanding the air within it, cause the liquid to ascend in the opposite stem. The whole instrument is covered with a case of thin glass, the object of which is to prevent the balls from being affected by currents of cold air. The action of this photometer depends on the heat produced by the absorption of light. Mr. Leslie conceives that light when absorbed is converted into heat; but according to the experi- ments already referred to, the effect must'be attributed, not so much to the light itself, as to the absorption ofthe calorific rays which accompany it. Mr. Leslie recommends his photometer also for determining the relative intensities of artificial light, such as that emitted by candles, oil, or gas. This application of it differs from the fore- going, because the light proceeding from terrestrial sources con- tains caloric under two forms. One is analogous to that emitted K 74 LIGHT. by a body which is not luminous ; the other is similar to that which accompanies the solar light. It is presumed that the first form of caloric will not prove a source of error: that these rays are wholly intercepted by the outer case of glass ; or that should a few of them penetrate into the interior, they will be absorbed equally by both balls, and will therefore heat them to the same extent. It is probable that this reasoning is not wide of the truth; and, consequently, the photometer will give correct in- dications so far as regards the new element—non-luminous caloric. But it is not applicable to lights which differ in colour; for their heating power is out of all proportion to their light. Thus, the light emitted by burning cinders or red-hot iron, even after pass- ing through glass, contains a quantity of calorific rays, which is out of all proportion to the luminous ones; and, consequently, they may and do produce a greater effect on the photometer than some lights whose illuminating powers are far greater. The second kind of photometer is on a totally different prin- ciple. It determines the comparative strength of lights by a comparison of their shadows. This instrument was invented by Count Rumford. It is susceptible of great accuracy when em- ployed with the requisite care; but, like the foregoing, its in- dications cannot be trusted when there is much difference in the colour ofthe lights. In this case, the best mode of obtaining an approximative result, is by observing the distance from each light at which any given object, as a printed page, ceases to be dis- tinctly visible. The illuminating power of the lights so compared is as the squares ofthe distance. SECTION III. Electricity. When certain substances, such as amber, glass, sealing-wax, or sulphur, are rubbed, and then brought near small fragments of paper, cork, or other light bodies, the latter move rapidly to- wards the former, and adhere during a longer or shorter interval to their surface. If the body which is thus excited by friction is light and freely suspended, it will move towards the substances in its vicinity. After a while the excited body looses its in- fluence ; but it may be renewed for any number of times by fric- tion. The movement observed in these instances are attributed to a peculiar kind of attraction, and the unknown cause of this attraction is called Electricity, from the Greek word *i%sxte:ov, amber, because the electric property was first noticed in this substance. The ancients were aware that amber and the lyncurium, (sup- posed to be our tourmalin,) may be rendered electric by friction, but it was not known that other bodies may be simlarly excited ELECTRICITY. 75 until the commencement of the 17th century, when Dr. Gilbert of Colchester detected the same property in a variety of other substances. Of those which he has enumerated in his treatise de Magnete, the principal are the diamond, rock crystal, and seve- ral of the precious stones, glass, sulphur, mastic, sealing-wax, and resin; and in making this discovery he laid the foundation ofthe science of Electricity. A few additional facts were noticed during the course of the same century by Boyle, Otto de Gue- ricke and Dr. Wall, and in 1709 Mr. Hawkesbee published an ac- count of ma/iy curious electrical experiments; but no material progress was made in this department of knowledge till between the years of 1729 and 1733, when the discovery of new and im- portant facts by Mr. Stephen Grey in England, and M. Dufay in France, attracted general attention to the subject, and spee- dily acquired for it the regular form of a science. The most important fact established by Mr. Grey was the fun- damental one, that electricity passes freely along certain sub- Btances, and that its progress is more or less entirely arrested by others. M. Dufay, in repeating the experiments of Grey, ob- served that an electrified substance not only attracts light bodies, but causes them after contact to fly off from its surface as if by a principle of repulsion. This singular phenomenon, which is termed electrical repulsion, had been previously noticed by Otto de Gue- ricke, but the merit of original observation seems also justly due to the French philosopher. Dufay likewise noticed that the elec- tricity excited on glass is different from that of resin, and hence inferred the existence of two kinds of electricity, the vitreous and resinous, the former belonging to glass, and the latter to resin. He established an excellent mode of distinguishing them, by finding] that substances possessed of the same kind of electricity always repel each other; and that attraction is as uniformly ex- erted between substances which are in opposite states of electri- cal excitement. Another fact of consequence, relative to the excitement of elec- tricity by friction, was discovered in 1759 by Mr. Symmer, who found that when two bodies are rubbed together, both are ex- cited, and that one always possesses vitreous and the other resinous electricity. This induced Symmer to modify the doctrine of the two electricities. Dufay conceived the vitreous electricity to be peculiar to some substances and the resinous electricity to others. Symmer, on the contrary, maintained, that bodies in their ordi- nary unexcited condition contain both kinds of electricity in a state of combination; and as they then neutralize or counteract each other's effects, no electrical phenomena are apparent; that friction produces excitement by separating the two principles; and excitation continues until that kind of electricity which has been withdrawn is restored. Dufay's doctrine of the two electricities, as modified by Sym- 76 ELECTRICITY. mer, is consistent with all the facts which subsequent observation has brought to light, and is adopted alrrfbst universally in France and other parts ofthe continent. It is found that all substances, when electrified by friction, are thrown into opposite states of excitement; that electrical repulsion is never observed but be- tween bodies similarly electrified ; and that electrical attraction is as uniformly owing to the substances possessing different kinds of electricity. For these phenomena, however, Dr. Franklin pro- posed a different explanation, founded on the supposition of there being only one kind of electricity. According to«this philoso- pher, when bodies contain their natural quantity of electricity, they do not manifest any electrical properties ; but they are ex- cited either by its increase or diminution. On rubbing a tube of glass with a woollen cloth, the electrical condition of both sub- stances is disturbed; the former acquires more, oris overcharged, the other less than its natural quantity, or is undercharged. These opposite states he expressed by the terms positive and negative, the first corresponding to the vitreous, the second to the resinous electricity of Dufay. Electrical repulsion, according to Franklin, takes place between substances which contain either more or less than their natural quantity; and electrical attraction is only exerted between two bodies, one of which contains more than its natural quantity and the other less. The excess of elec- tricity has a strong tendency to pass from a positively to a nega- tively excited surface, so as to restore the equilibrium in both ; and this always happens either by contact, or from such prox- imity that the electricity is able to pass from one to the other through the intervening stratum of air. The phenomena of elec- tricity are explicable by both these theories ; but as that of Dr. Franklin is commonly adopted in this country, we shall employ it in this treatise. It has been objected to this hypothesis that it does not ac- count satisfactorily for the repulsion observed between bodies negatively electrified. The separation of two positive electric bodies is easily accounted for by the repulsive power supposed to be exerted among the .particles ofthe electricity accumulated upon them; while substances which are negative, or possess less than their natural quantity of electricity, cannot be influenced by such a power, and therefore it is argued, ought not to diverge or separate. This mode of reasoning, however, is entirely hypothe- tical. There is no proof that the divergence observed in simi- larly electrified bodies is owing to actual repulsion ; and the phenomenon may be explained equally well on the principle, that the two excited substances are attracted in opposite directions, in consequence of the contiguous strata of air being rendered op- positely electrical by induction. In this way all the phenomena of electrical attraction and repulsion, are referable to the attrac- tive power exerted between bodies in opposite states of excite- ELECTRICITY. 77 ment. The term repulsion, according to this view, is used merely to express the act of separation or divergence. Nothing certain is known concerning the principle or cause of the phenomena of electricity. It may possibly be only a pro- perty of matter, called into action by particular circumstances ; but the phenomena accord much better with the opinion, which is now almost universally received by philosophers, that it is a highly subtile elastic fluid, too light to affect the most delicate balances, capable of moving with extreme velocity, and present in all bodies. Its influence, in excited bodies, is diffused uni- formly in every direction; and like light and other principles which are subject to this law, its power diminishes as the squares of the distance. It is one of the most energetic principles in nature. It is the cause of thunder and lightning; the pheno- mena of galvanism, and probably of magnetism, are produced by it; and the influence which it exerts over chemical changes is so great, that some philosophers regard it as the cause of chemical attraction. The particles ofthe electric fluid are supposed to be highly repulsive to each other, and to be powerfully attracted by other material substances. The tendency to pass from over- charged surfaces to those that are in a negative state, may be ascribed to one or other of these properties, or perhaps to their conjoint operation. Electricity may be excited in all solid substances by friction. This assertion seems at first view contrary to fact. It is well known that a metallic substance, if held in the hand, may be rubbed for any length of time without exhibiting the least sign of electricity ; an observation which led to the division of bodies into such as may be excited by friction, and into those that, un- der the same circumstances, give no sign of electrical excite- ment. The former were called Electrics, the latter Non-electrics. But the distinction is not founded in nature. A metallic sub- stance does not indeed exhibit any trace of electricity when rub- bed in the same way as a piece of glass; but if, while it is rubbed with the dry fur of a cat, it is supported by a glass handle, it will then evince signs of electrical excitement. The difficulty and apparent impossibility of exciting metallic bodies, receives an explanation from the fact observed by Grey, that the electric fluid passes with great facility along the surface of some substances, and with difficulty over that of others; and this discovery has led to the division of bodies into conductors and non-conductors of electricity. If an excited conductor, such as a metallic wire, be made to communicate with the earth at one of its extremities, the electricity will pass to it from the op- posite end in an instant, even though it were several miles in length; so that when the equilibrium is disturbed, it will be at once restored along the whole wire, just as effectually as if every point of it communicated with the ground. But an excited stick 78 ELECTRICITY. of glass or resin is not affected in the same manner; for as elec- tricity does not obtain a free passage along them, the equilibrium is restored in those parts only, which are actually touched. For this reason a non-conductor of electricity, though held in the hand, may be readily excited; but a good conducting body can- not be brought into that state, unless it be insulated, that is, cut off from communication with the earth by means of some non- conductor. This is generally effected either by supporting a body with a handle of glass, or by placing it on a stool made with glass feet. To the class of conductors belong the metals, charcoal, plum- bago, water, and most substances which contain water in its liquid state, such as animals and plants. The conductibility of these substances is different. Of the metals, according to the experiments of Mr. Harris, silver and copper are the best con- ductors of electricity; then gold, zinc, platinum, iron, tin, and lead. To the list of non-conductors belong glass, resins, sulphur, the diamond, dried wood, precious stones, silk, hair, and wool. Atmospheric air is also a non-conductor. If it were not so, no substance could retain its electricity when surrounded by it. Aqueous vapour suspended in the air injures the non-conducting property of the latter, and hence electrical experiments do not succeed so well when the air is charged with moisture as when it is dry. The presence of a little moisture communicates con- ducting properties to the most imperfect conductor; and hence it is impossible to excite glass by rubbing it with a moist sub- stance. A knowledge of the different conducting power of bodies is required for explaining some circumstances which appear con- tradictory to a preceding statement. It is above mentioned that when two bodies are excited by friction, they are rendered op- positely electrical; but if a tube of glass is rubbed by a person communicating with the ground, the glass will become positively electrical, while the hand of the operator manifests no sign what- ever of excitement. The cause of this is obvious. The operator is not electrified, because the earth restores the electric fluid as soon as it is withdrawn by the glass; but if he is insulated, the indications of negative electricity will immediately appear. Hence it is a rule to insulate a conductor, whenever it is wished to examine its electrical condition. The experiments which have been made concerning the effects of friction, have demonstrated that the same substance is not always similarly electrified. Its electricity is influenced partly by the state of its surface, and partly by the nature of the body with.which it is rubbed. Thus smooth glass is rendered posi- tive by friction with woollen cloth ; whereas, if its surface is rough, it becomes negative from the same treatment. Smooth glass which is positive with woollen cloth, is rendered negatively ELECTRICITY. 79 electrical by being rubbed with a cat's fur. The following table from Cavallo's Complete Treatise on Electricity, shows the kind of excitement produced by the friction of various substances. The back of a cat Smooth glass . . Rough glass . . Tourmalin , . , Hare's skin . . , White silk . . , Black silk . . . Sealing-wax . , Baked wood Is rendered By Friction with 7 r, •..• C Every substance with which it has been i Positive } hitJ;erto tried. 7 p ... C Every substance hitherto tried, except the 5 t back of a cat. / Positive < Dry oiled silk, sulphur, and metals. \ N t' ? Woollen cloth, quills, wood, paper, seal- ) XNeSauve £ ing wax, white wax, the human hand. / Positive k Amber, a current of air. \ Negative j Diamond, the human hand. } -a ... C Metals, silk, loadstone, leather, the hand, / positive | paper, baked wood. ( Negative < Other finer furs. ) Positive j Black silk, metals, black cloth. ( Negative < Paper, hand, hair, weasel's skin. f Positive < Sealing-wax. IN t" ? The skin of the hare, weasel, and ferret, j negative £ loadstone.brass, silver, iron, and the hand. ) Positive j Metals. C "N" t" p £ "^ne s^'n °^ ^e hare> weasel, and ferret, ) Sa 1V i the hand, leather, woollen cloth, paper. ) Positive £silk. C Negative < Flannel. Mr. Singer states that sealing-wax is not rendered positive by friction with all metals:—iron, steel, lead, and bismuth, as also plumbago, leave it negative. The foregoing remarks on the effects of friction will render intelligible the principle of the electrical machine. In the time of Grey, a supply of electricity was obtained for experimental purposes by rubbing a glass tube with the dry hand. Glass globes made to revolve by machinery were afterwards substituted for the tube, the friction being at first produced with the hand, and subsequently by means of a fixed rubber. As now con- structed the electrical machine is formed either with a cylinder or plate of glass, which is pressed during its rotation by cushions stuffed with hair. The cushion is usually covered with an amal- gam of tin and zinc, which, partly by increasing the friction, and partly by the oxidation of the metals, materially assists the action of the machine. The electricity developed on the glass is con- ducted away by an insulated bar of brass placed close to it, called 80 ELECTRICITY. the prime conductor, on which it is collected in considerable quantity. By this means the electricity spread over the whole surface of the prime conductor may be carried off at the same instant, and thus act with far greater power than if accumulated on glass or any other imperfectly conducting substance. The electricity which is so freely and unceasingly evolved during the action of a good electrical machine, is derived from the great reservoir of electricity, the earth. This is obvious from the fact, that if the whole apparatus is insulated, the evolu- tion of electricity immediately ceases; but the supply is as instantly restored, when the requisite communication is made with the ground. In the state of complete insulation the glass and prime conductor are positive as usual, and the rubber is nega- tively excited; but as the electricity then developed is derived solely from the machine itself, its quantity is exceedingly small. When the machine is used, therefore, the rubber is made to com- municate with the earth. As soon as friction is begun, the glass becomes positive, and the rubber negative; but as the latter com- municates with the ground, it instantly recovers the electricity which it had lost, and thus continues to supply the glass with an uninterrupted current. If the rubber is insulated, and the prime conductor communicates with the ground, the electricity of the former, and all conductors connected with it, is carried away into the earth, and they are negatively electrified. Friction is not the only cause of electrical excitement. The electric equilibrium is often disturbed by chemical action; and frequently by the mere contact of two substances of a different kind, as when a plate of zinc is made to touch a plate of copper. The same body is sometimes excited by its different parts being unequally heated. Some substances are excited by mere eleva- tion of temperature. This is noticed in certain crystallized minerals, as in tourmalin, which do not possess that symmetrical arrangement of parts commonly existing in crystals. Electricity is often developed during a change of form. Fused sulphur be- comes electrical in pooling, and other liquids exhibit the same appearance in the act of congealing. Evaporation and the con- densation of vapour are accompanied by a similar change, and it is probable that the electricity excited by these and other analo- gous processes is the cause of the electrical phenomena of the atmosphere. Another cause of excitement is proximity to an electrified body; and as the explanation of many electrical phenomena depends on a knowledge of this fact, it is of importance to understand it clearly. When a substance excited positively is brought near another in its natural state and insulated, the electric equilibrium of the latter is instantly disturbed; the parts nearest to the for- mer become negative, and the distant ones positive. If the bodv is not insulated, its electricity passes into the earth, and it be- ELECTRICITY. 81 comes negatively electrical. If, on the contrary, the exciting substance is negative, it causes the contiguous parts of a body in its vicinity to become positive. Hence it may be established as a law, that an electrified body tends to produce in contiguous substances an electric state opposite to its own. The electricity developed in this way is said to be induced, or to be excited by induction. The movement of light bodies towards an excited stick of sealing-wax or glass tube is accounted for on this princi- ple. Thus, the vicinity of the negative sealing-wax renders the surrounding objects positive, and therefore a mutual attraction is exerted. When the inside of a glass bottle is rendered positive by contact with the prime conductor of the electrical machine, the outside, if in communication with the earth, parts with elec- tricity and becomes negative. Both surfaces, therefore, are elec- trified and are in opposite states ; and if a communication be established between them by means of a good conductor, the excess of electricity instantly passes along it, and both sides of the glass return to their natural condition. That the experi- ment may succeed in the most perfect manner, it is necessary to cover the bottle externally and internally, except to within three or four inches of its summit, with tinfoil or some other good con- ductor, in order that every point of both sides ofthe glass may be brought into communication at the same moment. For without this precaution, the electric equilibrium ofthe two surfaces of the bottle, owing to the imperfect conducting power of glass, will be restored on those points only which are touched. The apparatus thus described is much employed by electricians, and has receiv- ed the name of Leyden phial, in consequence of its remarkable effects having been first exhibited at the University of Leyden. To render it more convenient for use, the aperture of the glass jar or phial is closed by some imperfect conductor, such as dry wood, through the centre of which passes a metallic rod that commu- nicates with the tinfoil in the inside of the jar. The phial is electrified or charged by holding the outside in the hand, or plac- ing it on the ground, while the metallic rod is made to receive sparks from the prime conductor of an electrical machine. If the jar is insulated, no charge will be received, or at least very slight indications of excitement will be manifested. By arrang- ing a number of Leyden phials in a box lined with tinfoil so that they may all communicate freely by their outer surfaces, and then bringing their inner surfaces into communication by wires, the whole series may be charged and discharged in the same man- ner as a single phial. This arrangement is known by the name of the electrical battery. Some of the phenomena of lightning are explained on the prin- ciple of induced electricity. When, for instance, a negatively electrified cloud approaches the earth, all objects in its vicinity are positively excited; and when it comes within what is called 82 ELECTRICITY. the striking distance, that is, so near that the tendency of the electricity to pass from the positive to the negative body, overcomes the resistance ofthe intermediate stratum of air, the equilibrium is restored with a report and flash of light, exactly as in the discharge of a Leyden phial. A similar effect is pro- duced by an electrified cloud on other clouds within the sphere of its influence. The passage of electricity is frequently attended with the pro- duction of heat and light, effects which invariably ensue when it meets with an impediment to its progress, a3 in passing through an imperfect conductor. The most familiar illustration of this is afford- ed by its passage through the air, when it gives rise to a spark ac- companied with a peculiar snapping noise, if in small quantity; or to the phenomena of thunder and lightning, when it takes place on a large scale. On the contrary, it passes along perfect con- ductors, such as the metals, without any perceptible warmth or light, provided the extent of their surface is in proportion to the quantity of electricity to be transmitted by them ; but if the charge is too great in relation to the extent of the conducting surface, an intense degree of heat will be produced. Electricity acts with surprising energy on the animal system. When a large quantity of the electric fluid passes through the body, the vital functions cease on the instant, as is exemplified by the numerous accidents on record of persons being killed by lightning. Even the small quantity of electricity contained in a Leyden phial gives a very powerful shock, exciting a sudden spasm of the muscles along which it passes, so violent as to pro- duce a disagreeable or even painful sensation. The shock from a large electrical battery is much more severe, and smaller ani- mals, such as rabbits and fowls, are destroyed by its action. It is very important, in conducting electrical experiments, to possess an easy method of discovering when any substance is electrified, of ascertaining its intensity or the degree to which it is excited, and of distinguishing the kind of excitement. The mode of effecting these objects is founded on electrical attraction and repulsion, and the instruments employed for the purpose are called Electroscopes and Electrometers, the latter denoting the intensity of electricity, the former merely indicating excitement, and the electrical state by which it is produced. The term elec- trometer, however, is often indiscriminately applied to all such instruments, since the methods of ascertaining the kind of excite- ment, give, at the same time, some idea of its intensity. A body is known to be excited by its power of attracting light substances, and a small ball made of the pith of elder, suspended on a silk thread, affords a convenient material for the experiment. Ano- ther mode of acquiring the same information is by means of two pith balls suspended from the same point by silk threads of equal length. When all the surrounding objects are unexcited, the ELECTRICITY. S3 pith balls remain in contact; but on the approach of any elec- trified body, the two balls are excited by induction, and, having the same electricity, diverge or retreat from each other. A more delicate contrivance, but of a similar kind, was invented by Mr. Bennett, and is known by the name of the Gold Leaf Electro- meter. It consists essentially of a cylindrical glass bottle, with its aperture closed by a brass plate, from the centre of which two slips of gold leaf are suspended. The brass plate, with its slips of gold leaf, are thus insulated, and the latter prevented from being moved by currents of air by the glass with which they are surrounded. The approach of any electrified body, even though feebly excited, to the brass plate, is immediately detected by the divergence ofthe leaves. A very simple method of distinguishing the kind of excitement is the following : If a piece of white silk be drawn a few times rapidly between the fingers, it will become negative ; and if in this state it is suspended in the air, it will be attracted by a body positively excited, and repelled by one which is negative. When rubbed on black cloth the silk is rendered positive, and will then of course retreat from a substance similarly electrified, and be attracted by one in an opposite state. The indications of the gold leaf electrometer are still more delicate. If the leaves are diverging with positive electricity, the approach of a positively excited body to the brass plate increases the divergence; because the electric equilibrium is immediately disturbed, and while the plate becomes negative, the gold leaves acquire a still greater degree of electricity. The approach of a negatively excited body would of course be productive of a change precisely opposite, and the divergence, if produced by positive electricity, would be diminished, or even entirely destroyed. To prepare the electro- meter for an observation, it is however necessary to communicate to it a known state of excitement. This may be done by touch- ing the electrometer with an electrified body, such as an excited glass tube or stick of sealing-wax, when the whole metallic sur- face of the electrometer is electrified in the same manner as the substance by which it was touched. A more convenient method is to communicate electricity permanently by induction. Thus, on placing a negatively excited body, as for example a stick of sealing-wax after friction on woollen cloth, near the brass plate of the electrometer, the electric equilibrium of its whole metallic surface is disturbed; the brass plate becomes positive, and the slips of gold leaf diverge from being negative. On withdrawing the sealing-wax, the excess of electricity accumulated on the plate returns to the leaves, and the equilibrium is restored ; but if, while the sealing-wax is near the top of the instrument, the plate is touched with the finger, a portion of electricity is sup- plied to the gold leaves from the earth, and the divergence ceases more or less completely, while the excess of electricity is pre- 84 ELECTRICITY. served on the plate by the vicinity of the sealing-wax. On re- moving first the finger, and then the sealing-wax, the brass is left with an excess of electricity, which extends over the whole me- tallic surface ofthe electrometer, and thus produces a divergence which continues for a considerable time if the glass is dry, and the atmosphere moderately free from moisture. The electrometer most frequently employed for estimating the intensity of electricity is that invented by Mr. Henley, and com- monly called the quadrant electrometer. It consists of a smooth round stem of wood, about seven inches long, terminated above by a ball, immediately below which, and projecting from the side of the stem, is attached a semicircular piece of ivory. In the centre ofthe semicircle is fixed a pin, from which is suspended, to serve as an index, a slender piece of wood or cane four inches in length, and terminated by a small ball. When the apparatus is screwed on the prime conductor, or placed on any electrified body, it indicates the intensity ofthe electricity by the extent to which the index is repelled by the stem. In order to mark the divergence accurately, the lower half of the semicircle, which is traversed by the index, is divided into 90 equal parts or degrees. But this instrument is not well adapted to researches of delicacy. The only electrometer suited for such purposes is the electrical balance invented by Coulomb, which measures the intensity of an excited body by its power of twisting a thread of silk or a fine metallic wire. In some of the preceding remarks a term has been employed, which perhaps will not be understood without an explanation. By electric tension or intensity is meant that state of a body which is estimated by an electrometer. When a body acts feebly on the electrometer its intensity is low, and it differs but little from its natural state; and on the contrary if it affects the elec- trometer powerfully, its electric tension is great. The higher the intensity of a body, the more it is removed from its natural state, and the greater its tendency to return to an equilibrium. Intensity is distinct from quantity of electricity. That intensity is not dependant on quantity alone, is proved by the tension of a charged Leyden phial being equal to that of a large battery con- taining twenty times more electricity. The tension appears to depend on the quantity of electricity accumulated or deficient in a given space ; so that the intensity of those substances is great- est, which have the greatest excess or deficiency of electricity in proportion to their surface. Electricity appears to diffuse itself over the surface of bodies, and the quantity contained on the same substance, all other cir- cumstances being the same, depends on the extent of surface, and is not connected with quantity of matter. Thus a solid sphere of brass cannot contain more electricity than a hollow sphere of the same diameter. ELECTRICITY. 85 Galvanism. The science of Galvanism owes its name and origin to the experiments on animal irritability made by Galvani, Professor of Anatomy at Bologna, about the year 1790. In the course ofthe investigation, he discovered the fact that muscular con- tractions are excited in the leg of a frog recently killed, when two metals, such as zinc and silver, one of which touches the crural nerve, and the other the muscles to which it is dis- tributed, are brought into contact with one another. Gal- vani imagined that the phenomena were owing to electricity present in the muscles, and that the metals only served the purpose of a conductor. He conceived that the animal elec- tricity originated in the brain, was distributed to every part ofthe system, and resided particularly in the muscles. He was of opinion that the different parts of each muscular fibril were in opposite states of electrical excitement, like the two surfaces of a charged Leyden phial, and that contractions took place whenever the' electric equilibrium was restored. This he sup- posed to be effected during life through the medium of the nerves, and in his experiments by the intervention of metallic conductors. The views of Galvani had several opponents, one of whom, the celebrated Volta, Professor of Natural Philosophy at Pavia, succeeded in pointing out their fallacy. Volta maintained that the electricity was excited by the contact of the metals; that the animal substances merely acted as conductors in restor- ing the electric equilibrium at the moment of its being dis- turbed ; and that the contraction was produced by the stimu- lus arising from the passage of electricity along the nerves and muscular fibres. He proved that electricity was excit- ed in the way he supposed, by bringing plates of different metals, as zinc and silver, in contact with one another, and ex- amining their electrical state, at the moment of separation, by means of a delicate electrometer. For this purpose, it is ne- cessary to insulate each of the metallic discs, by supporting them on a handle of glass or resin. On taking this precaution, it was found that both the metals were excited, the silver nega- tively, and the zinc positively. As the quantity of electricity excited by any two metals is small, Volta endeavoured to increase the effect by employing several pairs of metals, connecting them in such a manner that the electricity excited by each pair should be diffused through the whole series; and this attempt led him to the construction of the Voltaic pile, a description of which was published in the Philosophical Transactions for 1800. It consists of any number 86 ELFCTRICITY. of pairs of zinc and copper, or zinc and silver plates, each pair being separated from the adjoining one by pieces of cloth, near- ly of the same size as the plates, and moistened in a saturated solution of salt. The relative position ofthe metals in each pair must be the same in the whole series; that is, if the copper is placed below the zinc in the first combination, the same order must be preserved in all the others. The pile is contained in a proper frame, formed of glass pillars, fixed into a space of thick wood, which both supports and insulates it. The apparatus so formed is in the same state of excitement as the insulated metallic discs after contact, and affects the elec- trometer and excites muscular contractions in a similar manner, but in a much greater degree. The opposite ends of the pile are also differently excited, the side which begins with a zinc plate being positive and the other negative ; and hence, when they are made to communicate by means of a good conductor, electricity must pass from the one to the other, precisely as is supposed to happen in the discharge of a Leyden phial. But the apparatus is not thereby rendered inactive; for as the conditions which originally excited it are still maintained, the equilibrium is no sooner restored than it is again disturbed, and therefore a continued current must pass from one end or pole to the other along the wire that connects them. The Voltaic pile is now rarely employed, because we possess other modes of forming galvanic combinations which are far more powerful and convenient. The galvanic battery, proposed by Mr. Cruickshank, consists of a trough of baked wood, about thirty inches long, in which are placed at equal distances fifty pairs of zinc and copper plates previously soldered together, and so arranged that the same metal shall always be on the same side. Each pair is fixed in a groove cut in the sides and bottom of the box, the points of junction being made water-tight by cement. The apparatus thus constructed is always ready for use, and is brought into action by filling the cells left between the pairs of plates with some convenient solution, which serves the same pur- pose as the moistened cloth in the pile of Volta. Other modes of construction are now in use which facilitate the employment of it, and increase its energy. The trough, made either of baked wood or glazed earthen ware, is divided into partitions of the same material. Each cell contains a plate of zinc and another of copper, which do not touch each other, but communicate merely through the medium of the fluid in which they are immersed. The zinc plate of one cell is con- nected with the copper of the adjoining one by means of a slip of copper. All the plates are attached to a piece of wood, and may thus be introduced into the liquid ofthe trough, or removed from it at pleasure. This method was suggested by the Couronne des Tasses of Volta, an arrangement which was described by ELECTRICITY. 87 him, together with his pile, in the paper already alluded to. The following is a figure of the instrument : An additional improvement was suggested by Dr. Wollaston, who recommends that each cell should contain one zinc and two copper plates, so that both surfaces of the first metal are opposed to one of the second. In consequence of this arrangement, the plates of copper communicate with each other, and the zinc be- tween them with the copper of the adjoining cell. An increase of one half the power is obtained by this method. The size and number ofthe plates may be varied at pleasure. The largest battery ever made is that of Mr. J. G. Children, of the British Museum, the plates of which are six feet long, and two feet eight inches broad. The common and most con- venient size for the plates is four or six inches square; and when great power is required, a number of different batteries are united by establishing a metallic communication between the positive pole of one battery and the negative pole of the adjoin- ing one. The great battery of the Royal Institution is composed of 2000 pairs of plates, each plate having 32 square inches of surface. It was by this that Sir H. Davy was enabled to effect the decomposition and determine the constitution of substances which were previously supposed to be elementary bodies. The action of the galvanic trough is always attended by chemical changes between the liquid ofthe cells* and one of the metals with which it is in contact. It has indeed been main- tained by one ofthe most profound philosophers ofthe age, that such changes are essential to the production of galvanism ; and it is certain that the action of the pile or battery is neither per- manent nor energetic without their occurrence. The energy of a galvanic trough is, in fact, proportional to the degree of chemical action which takes place. When pure water is put into the cells, ELECTRICITY. the action is feeble, because the accompanying chemical changes are feeble; but still the zinc is observed to rust more rapidly than it would do, were it not in contact with copper. A solution of some saline substance increases the energy of the pile; and the zinc is also found to oxidize more rapidly than in the first case. An acid fluid corrodes the metal with still greater rapidity, and augments the activity of the battery in the same proportion. In constructing a galvanic battery, each member of the series must consist either of one imperfect and two perfect conductors, or of one perfect and two imperfect. The annexed tables, from Sir H. Davy's Elements of Chemical Philosophy, contain some series of both kinds, arranged in the order of their powers; the substance which is most active being named first in each column. Among the good or perfect conductors are the metals and char- coal. The imperfect conductors are water, and saline or acid solutions. Table of some electrical arrangements, which, by combination, form Voltaic batteries, composed of two conductors and one imperfect conductor. Zinc Iron Tin Lead Copper Silver Gold Platinum Charcoal Each of these is the posi- tive pole to allthe metals below it, and negative with respect to the metals above it in the column. Solutions of Nitric Acid Muriatic Acid Sulphuric Acid Sal Ammoniac Nitre other Neutral Salts Table of some electrical arrangements, consisting of one con- ductor, and two imperfect conductors. Solution of Sulphur and potash Potash Soda Copper Silver Lead Tin Zinc other Metals Charcoal Nitric Acid Sulphuric Acid Muriatic Acid Any solutions containing Acid In all combinations in which fluids act chemically by affording oxygen, the positive pole is always attached to the metal which has the strongest affinity for oxygen ; but when the fluid menstrua afford sulphur to the metals, the metal which has the strongest affinity for sulphur will be positive. Thus, in a series of copper and iron plates introduced into a porcelain trough, the cells of which are filled with water or acid solutions, the iron is positive, and the copper negative; but when the cells are filled with solu- tion of sulphur and potash, the copper is positive, and the iron negative. In all combinations in which one metal is concerned, the sur- ELECTRICITY. 89 face opposite to the acid is negative, and that in contact with the solution of alkali and sulphur, or of alkali, is positive. The more remarkable effects of the galvanic battery may be conveniently considered under four heads. 1st. Its electrical phe- nomena ; 2d. Its chemical agency; 3d. Its power of igniting the metals. I. A galvanic battery may be made to produce all the phe- nomena occasioned by the common electrical machine. It will cause the gold leaves of the electrometer to diverge, and a Ley- den phial, or even an electrical battery, may be charged by it. When conductors, connected with the opposite poles of an active galvanic trough, are brought near each other, a spark is seen to pass between them; and on establishing the communication by means ofthe hands, previously moistened, a distinct shock is per- ceived, though of a peculiar nature. These properties naturally gave rise to the belief, that the agent or power excited by the Voltaic apparatus, is identical with that which is called into ac- tivity by the electrical machine, and the arguments in favour of this opinion seem quite satisfactory. For not only may all the common electrical experiments be performed by means of galva- nism; but it has been shown by Dr. Wollaston, that all the che- mical effects of the galvanic battery may be produced by elec- tricity. For producing intense heat and light, a battery composed of large plates is preferable. Small ones, on the contrary, should be employed when the object is to give shocks, to charge a Ley- den phial, or affect an electrometer; for the power of a battery, in this point of view, depends upon the number, rather than on the size of its plates. The apparatus should be excitpd by an acid solution when it is wished to draw sparks or produce a shock; but for charging a Leyden phial, or affecting the electrometer, the cells should be filled by preference with water only. II. The chemical agency of the Voltaic apparatus^ to which chemists are indebted for their most powerful instrument of analysis, was discovered by Messrs. Carlisle and Nicholson, soon after the invention was made known in England. The sub- stance first decomposed by it was water. When two wires are connected with the opposite poles of a battery, and their free extremities are plunged into the same cup of water, but without touching each other, the water is decomposed, one of its con- stituents being attracted by the positive wire, and the other by the negative. •This important discovery led many able experimenters to make similar trials'. Other compound bodies, such as acids and salts, were exposed to the action of galvanism, and all of them were decomposed without exception, one of their elements appearino- at one side ofthe battery, and the other at its opposite extremity. An exact uniformity in the circumstances attending the decora- 90 ELECTRICITY. position was also remarked. Thus, in decomposing water or other compounds, the same kind of body was always disengaged at the same side of the battery. In performing some of these experiments, Sir H. Davy observed, that if the conducting wires were plunged into separate vessels of water, which were made to communicate by some moist fibres of cotton or amianthus, the two gases were still disengaged in their usual order, the hydrogen in one vessel, and the oxygen in the other, just as if the wires had been dipped into the same por- tion of that liquid. This singular fact, and another of the like kind observed by Hisinger and Berzelius, induced him to operate in the same way with other compounds, and thus gave rise to his celebrated experiments on the transfer of chemical substances from one vessel to another. Two agate cups, N and P, were employed in them, the first communicating with the negative, the second with the positive pole of the battery, and connected to- gether by moistened amianthus. On putting a solution of sul- phate of potash or soda into N, and distilled water into P, the acid very soon passed over to the latter, while the liquid in the former, which was at first neutral, became distinctly alkaline. The process was reversed by placing the saline solution in P, and the distilled water in N, when the alkali went over to the nega- tive cup, leaving pure acid in the positive. That the acid in the first experiment, and the base in the second, actually passed along the amianthus, was obvious; for, on one occasion, when nitrate of silver was substituted for the sulphate of potash, the amianthus leading to N, was coated with a film of metal. A similar trans- fer may be effected by putting distilled water into N and P, and a saline solution in a third cup placed between the two others, and connected with each of them by moistened amianthus. In a short time the acid ofthe salt appears in P, and the alkali in N. The galvanic action not only separates the elements of com- pound bodies, but suspends the operation of affinity so entirely as to enable an acid to pass through an alkaline solution, or an alkali through water containing a free acid, without combination taking place between them. The three cups being arranged as in the last experiment, Sir H. Davy put a solution of sulphate of potash in N, pure water in P, and a weak solution of an alkali in the intermediate cup, so that no sulphuric acid could find its way to the distilled water in P, without passing through the alkaline liquid on its passage. A battery composed of 150 pairs of 4 inch plates was set in action, and in five minutes free acid appeared at the positive pole, and, on reversing the experiment, alkalies were transmitted directly through acid liquids without entering into combination with them. The analogy between the preceding phenomena and the at- tractions and repulsions exerted by ordinary electricity is too close to escape observation. If an acid or an alkali passes from Electricity. 91 one vessel to another in opposition to gravity and chemical affini- ty, it is clear that it must arise from its being under the influence of a still stronger attraction ; and the only power to which such an effect can in the present case be attributed, is electricity. Now, in all instances of common electrical attraction, the bodies attract one another in consequence of being in opposite states of excitement; and, in like manner, the tendency of acids towards the zinc, and of alkalies towards the copper extremity of the V oltaic apparatus, can be accounted for, consistently with our present knowledge, only on the supposition that the former are negatively, and the latter positively electric, at the moment of being separated from one another. To explain how the elements of compounds may be in such a state, Sir H. Davy conceives that all bodies possess natural electric energies, which are inherent in them whether they are in a state of combination or not; and that some of them, such as oxygen, chlorine, iodine, and acids in general, are naturally negative, while hydrogen, metals, and me- tallic oxides, are naturally positive. The facts on which this opinion is founded are very remarkable. On bringing dry acids in contact with a metallic plate properly insulated, it was found, after separation, that the former were excited with negative and the latter with positive electricity. On touching the same metal with earthy and alkaline substances, the latter became positive and the former negative. It might hence be expected that acid and alkaline bodies would exhibit opposite electrical energies if directly compared together; and this was proved by the contact of lime with crystals of oxalic acid, when the lime exhibited the character of positive, and the acid of negative electricity. It ap- pears, therefore, that the electric equilibrium of bodies which have a strong affinity for each other, is readily disturbed by mere contact; and Sir H. Davy conceives that the opposite energies which are then manifested are inherent in them at all times. The author of this ingenious view not only applies it to explain the chemical agency ofthe Voltaic apparatus, but has founded upon it an hypothesis concerning the nature of affinity. He sug- gests that chemical attraction and the phenomena of electricity are owing to the same cause, that the same power which commu- nicates attractive and repellent properties to masses of matter, will, when acting upon the ultimate particles of different bodies, induce them either to separate or combine, according as their natural electric energies are the same or different. But, though this hypothesis applies to chemical changes very satisfactorily, and coincides with the laws of affinity, it would nevertheless be premature, as Sir H Davy himself admits, to place entire confidence in it. For there is no proof that chemi- cal attraction is owing to the cause supposed ; nor is it establish- ed with certainty that bodies do possess natural electric energies. It does not follow, because they exhibit signs of electric excite- 92 ELECTRICITY. ment after contact, that they naturally possess one kind of elec- tricity rather than another. As well might it be argued that a common stick of sealing wax is naturally negative, because it is excited negatively by friction, a mode of reasoning which is in opposition to the facts exhibited by electrical action. Another circumstance which seems unfavourable to the hypothesis, is the well known fact, that one and the same substance is positive to some bodies and negative to others. The best arrangement for exhibiting the chemical agency of galvanism is a battery composed of an extensive series of small plates. No advantage is derived from using plates of a large size, since the decomposing power of the Voltaic apparatus is dependant on the number of the plates rather than on their di- mensions. The enormous battery of Mr. Children decomposed water very slowly. An acid solution should be employed for ex- citing the battery, and its strength should be such as to cause a moderate, long-continued action, in preference to a violent and temporary one. Any of the stronger acids, as the nitric, sulphuric and muriatic, may be used for the purpose ; but the last produces the most permanent effect, and is therefore preferable. The pro- portion should be one part of acid to 16 or 20 of water; or if the series is extensive, the acid may be still farther diluted with ad- vantage. III. The conditions necessary for igniting metallic wires or char- coal by the battery are different from those which have been re- commended for procuring its other effects. Their ignition seems to arise from the electricity passing along them with difficulty; which, as they are perfect conductors, can take place only when the quantity to be transmitted is out of proportion to the extent of surface along which it has to pass. It is therefore an object to excite as large a quantity of electricity in a given time as pos- sible, and for this purpose a very few large plates answer better than a great many small ones. A strong acid solution may also be used; for an energetic ac- tion, though of short duration, is more important than a moderate one of greater permanence. With this intention nitric acid may be employed with advantage. On the Theory of the Pile. There are three theories concerning the action ofthe Voltaic pile or battery. The first originated with Volta, who conceived that the electricity was set in motion, and the supply kept up, solely by the contact of the metals. He regarded the interposed solu- tions merely as conductors, by means of which the electricity, developed by each pair of plates, was conveyed from one part of the apparatus to the other. ELECTRICITY. 93 Volta, in forming his theory, left out of view the chemical changes going on between the metals and the fluids in contact with them; whereas, it was apparent that these changes consti- tuted an important, if not an essential, part of the process. For it was observed that no sensible effects were produced by a combination formed of substances which have no chemical action on each other ; that the action of the pile is always accompanied by the oxidation of the zinc ; and that its energy is almost in exact proportion to the rapidity with which the oxidation takes place. These observations induced Dr. Wollaston to conclude that the process begins with the oxidation ofthe zinc—that the oxidation is the primary cause of the electric phenomena ; and he published several ingenious experiments in the Philosophical Transactions for 1801 in support of his opinion. This forms the second theory of the pile, and is in direct opposition to that of Volta. The third theory is intermediate between the two others, and was proposed by Davy. He inferred from numerous experiments, that there is no reason to question the fact, originally stated by Volta, that the electric equilibrium is disturbed by the contact of different substances without any chemical action taking place between them ; and his conclusions appear to be justified by sub- sequent observers. But he perceived, at the same time, that the chemical changes, though not the primary cause of the pheno- mena, are an essential part of the process; that without them no considerable degree of galvanic excitement can ever be produc- ed. In his opinion, therefore, the action is commenced by the contact of the metals, and kept up by the chemical pheno- mena. The mode in which Davy conceives the chemical changes act, is by restoring the electric equilibrium whenever it is disturbed. By the contact of the zinc and copper plates, the former is ren- dered positive throughout the whole series, and the latter nega- tive ; and by means ofthe conducting fluid with which the cells are filled, the positive electricity accumulates on one side ofthe battery, and the negative electricity on the other. But the quan- tity of electricity, thus excited, would not be sufficient, as is maintained, for causing an energetic action. For this effect, the electric equilibrium of each pair of plates must be restored as soon as it is disturbed, in order that they should be able to furnish an additional supply of electricity. The chemical substances of the solution are supposed to effect that object in the following manner. The negative ingredients ofthe liquid, pass over to the zinc; while those which are positive, go to the copper; in con- sequence of which, both the metals are for the moment restored to their natural condition. But as the contact between them continues, the equilibrium is no sooner restored than it is again disturbed; and when, by a continuance ofthe chemical changes, 94 MAGNETISM. the zinc and copper recover their natural state, electricity is again developed by a continuance of the same condition by which it was excited in the first instance. In this way Davy explains why chemical action, though not essential to the first development of electricity, is necessary for enabling the Voltaic apparatus to act with energy. It will be useless to pursue any further this recondite part of the subject; whatever view is taken, active powers must be sup- posed to be bestowed upon some species of matter, and the im- pulse must be ultimately derived from the same source. In the universe, nothing can be said to be automatic, as nothing can be said to be without design. An imperfect parallel may be found in human inventions; springs may move springs, and wheels, in- dexes ; but the motion and the regulation must be derived from the artist; sounds may be produced by undulations in the air, undulations of the air by vibrations of musical strings; but the impulse and the melody must arise from the master. SECTION IV. Magnetism. There is a mineral substance, called the loadstone, which possesses the property of attracting iron filings, and these ad- here to different parts of it in greater or less quantities : they are particularly accumulated at two opposite points, and stand, as it were, on end. The mineral, an ore of iron, which possesses this property, is said to be magnetic, and its properties to depend on magnetism. The points around which the iron filings are ac- cumulated, are called magnetic poles. We are entirely ignorant of the nature of magnetism. The phenomena presented by magnetized bodies have been explained on the supposed existence of a magnetic fluid or fluids. The magnetic influence may be communicated by the load- stone to some metallic bodies, particularly to iron and steel, and it is exerted through water, glass, metals, flame, &c. &c. A steel bar, which has been rendered magnetic by the loadstone, or by other methods, is called a magnet; and if it be suspended by a filament of silk, so as to. move easily in a horizontal plane, it does not turn indifferently to every part of space, but takes a direction nearly north and south. A small magnetized steel bar, delicately mounted on a central pivot, is called a magnetic needle. In some places, the north end of the needle deviates from the true meridian towards the east, and in other places towards the west, and sometimes to a very great degree; this deviation is called the declination of the magnetic needle, or variation. MAGNETISM. 95 The vertical plane in which the needle directs itself is called the magnetic meiidian. If the north extremity of one needle be presented to the north extremity of another, it repels it; but if to the south extremity, it attracts it; and the south extremity of one needle repels the south, but attracts the north extremity of another. Hence the two polar extremities of a magnet or needle are dissimilar; the one attracts what the other repels, and vice versa. When a magnet or loadstone is brought near a magnetic needle, the two poles act at once on it; but the pole which is nearest acts most powerfully, and the needle turns towards the magnet that pole which is most strongly attracted, and averts the one which is repelled. After the needle has taken a position of equilibrium, if we turn it ever so little from its place, it re- turns to it again, by a series of oscillations, in the same manner as a pendulum, pushed from the perpendicular line, returns to it again by the attraction of gravitation. A similar motion takes place in a magnetic needle turned ever so little from its mag- netic meridian, so that the earth acts on a magnetic needle like a true magnet or loadstone ; and the magnetism residing in the southern hemisphere is called austral magnetism, and that in the northern hemisphere boreal magnetism. Hence, as dissimilar magnetisms attracts each other, we must suppose that the ex- tremity of the needle which points to the north is charged with austral magnetism, and the opposite pole with boreal mag- netism. Take a steel bar, and suspend it delicately by an axis in the middle between the two ends, so that it may move easily, but in a vertical plane only; if the bar be now carefully magnetized, it will not in this latitude remain any longer in a horizontal posi- tion ; but the end whrch possesses the austral magnetism will de- cline downwards, and after a few oscillations will rest at a de- terminate angle with the horizon : this angle is called the dip of the needle, and is very different in different places ; the apparatus by which it is ascertained, is called the dipping needle, in which the needle probably points to the magnetic pole of the earth. Near the equator is a zone where there is no dip; to the north of this zone, the extremity of the needle charged with the austral magnetism declines from the horizontal; and to the south of this zone the opposite extremity declines. The poles of the earth and of a magnet can be considered only as centres of action. A piece of soft iron held near a magnet, becomes itself a tem- porary magnet; this phenomenon is analogous to electrical ex- citement by induction ; and that part ofthe iron which is nearest the magnet assumes the opposite magnetic state. Take a little bar of soft iron and attach one end of it to a magnet, it immedi- ately acquires all the magnetic properties; and to its opposite end another little bar will adhere, which in its turn becomes 96 MAGNETISM. « magnetic and capable of supporting a third bar. Other bars may be attached till their total weight exceeds that which the magnet is capable of sustaining. As soon as the first bar detaches itself, the others all separate and fall: and if we try to unite them, they will be found incapable of supporting each other, although they retain some feeble remains of magnetism. It is not necessary that the first bar should be in contact with the magnet; it may be kept at a distance by the intervention of paper, or glass ; but then the total weight thus supported at a distance will be less than when in contact. If bars of steel be employed instead of soft iron, their adherence to each other is less readily effected ; but it is more durable, and they retain more perfectly the magnetic states they have acquired by being in contact with each other, and with the magnet. A soft unmagnetized bar of iron, three or four feet long, held in the direction of the dipping needle, becomes a temporary magnet by the action of the earth's magnetism. Its lower ex- tremity acquires an austral, and its upper a boreal magnetism. The latter will repel the south end and attract the north extre- mity of a needle; and the former presents the reverse phenomena. That these effects are due to the sudden development of mag- netism by position, is readily shown by reversing the ends ofthe bar, for they instantly assume the reverse magnetic states. The same loadstone or magnet may successively render mag- netic any number of bars, without losing any of its own power : it seems only to develop a hidden principle. In the same manner an electrified body loses nothing of its electricity in exciting electricity by induction. If a wire of platinum or silver, be placed horizontally in the direction of the magnetic meridian, and a delicately suspended magnetic needle be placed under it, no effect is noticed; but if the wire be made to connect the two extremities of a powerful voltaic battery, the needle instantly declines from its position: one end goes to the west, the other to the east, the north end being slightly elevated, the south a little depressed. The posi- tion ofthe needle depends on the direction ofthe supposed elec- trical current through the conjunctive wire. The power of lightning in destroying and reversing the polarity of a magnet, and of communicating magnetic properties to pieces of iron which did not previously possess them, has been known for some years, and had led to the supposition that similar effects might be produced by the common electrical or galvanic appa- ratus. Attempts were accordingly made to communicate the magnetic virtue by means of electricity or galvanism ; but no re- sults of importance were obtained till the winter of 1S19, when Professor Oersted of Copenhagen made his famous discovery, which forms the basis of a new branch of science called electro- magnetism. MAGNETISM. 97 • The fact observed by Professor Oersted was, that an electric current, such as is supposed to pass from the positive to the nega- tive pole of a Voltaic battery along a wire which connects them, causes a magnetic needle placed near it to deviate from its natu- ral position, and assume a new one, the direction of which de- pends upon the mode of conducting the experiment. On placing the wire above the magnet and parallel to it, the pole next the negative end of the battery always moves westward, and when the wire is placed under the needle, the same pole goes towards the east. If the wire is on the same horizontal plane with the needle, no inclination whatever takes place; but the magnet shows a disposition to move in a vertical direction, the pole next the negative side of the battery being depressed when the wire is to the west of it, and elevated when it is placed on the east side. The extent of the declination occasioned by a battery depends upon its power, and the distance of the connecting wire from the needle. If the apparatus is powerful, and the distance small, the declination will amount to an angle of 45°. But this deviation does not give an exact idea of the real effect which may be pro- duced by galvanism ; for the motion of the magnetic needle is counteracted by the magnetism of the earth. When the influ- ence of this power is destroyed by means of another magnet, the needle will place itself directly across the connecting wire; so that the real tendency of a magnet is to stand at right angles to an electric current. The communicating wire is also capable of attracting and re- pelling the poles of a magnet. If, when the magnet and con- necting wire are at right angles to each other, the latter passing across the centre of the former, the wire be moved along the needle towards either extremity, attraction will take place be- tween the wire and the adjacent pole: and this will occur though the same point of the wire should be presented in succession to both of the poles. Again, if the position of the poles of the needle be reversed, they will be repelled by the same point of the wire which had previously attracted them. This discovery was no sooner announced, than the experiments were repeated and varied by philosophers in all parts of Europe, and, as was to be expected, new facts were speedily brought to light. Among the most, successful labourers in this field, M. M. Ampere, Arago, Biot, Sir II. Davy and Mr. Faraday deserve to be particularly mentioned. M. Ampere observed that the Voltaic apparatus itself acted on a magnetic needle placed upon or near it in the same manner as the wire which united its two extremities. But the declination was found to occur only when the opposite ends of the battery were in communication, and ceased entirely as soon as the circuit was interrupted,—a difference which was supposed to arise from the passage of an uninterrupted electric current through the ap- N 98 MAGNETISM. paratus, as along the connecting wire, taking place in the first case, and not in the second. M. Ampere therefore proposed the magnetic needle as an instrument for discovering the existence and direction of an electric current, (or currents, according to the theory of the two electricties) as well as for pointing out the proper state and fitness of a galvanic apparatus for electro-mag- netic experiments in general. M. Ampere soon after discovered tnat a power of attraction and repulsion might be communicated by an electric current alone, without the use of a magnet. Two wires of copper, brass, or any other metal, placed parallel to one another, and suspended so as to move freely, were connected with the opposite poles of a gal- vanic apparatus. If the electric current passed along both wires in the same direction, they attracted one another : if in an op- posite direction, they repelled each other. The result of this experiment gave rise to the supposition that the magnetic pro- perty was actually communicated to the wires by the electric current; and this supposition was confirmed by M. Arago who found that iron filings were attracted by a wire placed in the Voltaic circuit, and that they all fell off when the communica- tion between the poles was interrupted. This fact was also dis- covered about the same time by Sir H. Davy. The communication of temporary magnetic properties to the common metals naturally led to an attempt to magnetize steel and iron permanently by the same agent. The experiment was made by Arago and Davy about the same time, and both of them were successful. Davy attached steel needles to the connecting wire, some parallel to it, and others transversely. The former merely acted as a part of the circuit; they did not possess poles, and lost their power of attracting iron filings as soon as the elec- tric current ceased to circulate through them. But the latter acquired a north and south pole, and preserved the property after separation from the wire. Arago at first operated in a similar manner; but, at the suggestion of Ampere, he made the connect- ing wire in the form of a spiral or helix, and placed the needle to be magnetized in the centre of it. By this arrangement the maximum effect was obtained in a shorter time than by any other method. Davy also rendered a needle magnetic by placing it across a wire, along which a charge from a common Leyden bat- tery was transmitted. This series of experiments was completed by Ampere's discovery, that a connecting wire, suspended so as to have perfect freedom of motion, was influenced by the magne- tic attraction ofthe earth. For the next fact of importance, science is indebted to the researches of Mr. Faraday. He ascertained that the action of the connecting wire on the direction of a magnet, was not owing to any attraction or repulsion exerted between them, but to a tendency they have to revolve round each other. He contrived MAGNETISM. 99 an apparatus, by means of which either pole of a magnet was made to revolve round the wire as a fixed point; and then, by fixing the wire, and giving free motion to the magnet, both poles ofthe lat- ter were made to revolve in succession round the former. He was also successful in causing the wire to revolve by the influence ofthe magnetism ofthe earth. These magnetic properties of the Voltaic apparatus, were dis- covered soon after the original experiments of Oersted were made known to the public. Other facts of interest have since been observed, and some ingenious general views have been proposed to account for all the phenomena; but a full discussion of electro-magnetism would lead into details too minute for an ele- mentary treatise. We must refer the reader who may wish for further information to our treatise entitled Electro-Magnetism. PART III. OF PONDERABLE BODIES. Preliminary Remarks. From the laws and agencies of the imponderable substances which we have just examined, it will be readily perceived that they have an extensive influence over all chemical phenomena. The electrical relations which bodies sustain towards each other have furnished us with a convenient, if not a natural method of classification, for all substances in nature are either electro- positive or electro-negative, that is, they are all attracted by the positive or negative pole of a galvanic battery. There are but five simple electro-negative substances known : oxygen, chlorine, iodine, bromine, and fluorine, and these five substances, by com- bining with the electro-positive elements, produce a vast variety of characteristic compounds. For the purpose of rendering our subject as perspicuous as possible, we shall first investigate the properties of but one of the electro-negative bodies, and then examine its combinations with each of the electro-positive sub- stances, after first describing their characteristic properties. This will form our first division. In the next division we shall treat ofthe properties and combinations of another electro-nega- tive body in the same way, and so on of the whole series. The foundation of our less comprehensive sub-divisions will be stated, whenever they are made. Besides some other important advan- tages which we think will result from our present method of classi- fication, it makes the student acquainted in the early period of his 6tudy with the properties of acids and alkalies, substances con- nected with a range of chemical affinities the most extensive and important, and which we should be forced to anticipate, by fol- lowing the ordinary mode of treatment. DIVISION I.—CHAPTER I. In this chapter we shall treat of the properties and combina- tions of oxygen, nitrogen, hydrogen, and carbon. The three first bodies are only known to us in the state of gas, the fourth as a solid. They are classed together on account of their mutual affinities for each other. Thus hydrogen will combine with OXYGEN. 101 oxygen and nitrogen, and carbon with oxygen, nitrogen, and hydrogen. There is no other electro-positive solid, as far as our present knowledge extends, which can combine in the same man- ner. We commence the examination of ponderable bodies with oxygen gas from the important part which it performs in the economy of nature; it not only unites with every other known substance, but the compounds which it thus forms, are by far the most important. SECTION I. Oxygen, Oxygen gas was discovered by Priestley in 1774, and by Scheele a year or two after, without any previous knowledge of Priestley's discovery. Several appellations have been given to it. Priestley named it Dephlogisticated air; it was called Em- pyreal air by Scheele, and Vital air by Condorcet. The name it now bears, derived from the Greek words o|u$ acid, and y*j>iroperties in an eminent degree. A NITROGEN. 121 few drops of it diluted with a considerable quantity of water form an acid solution, which reddens litmus paper permanently. It unites with and neutralizes alkaline substances, forming salts with them which are called nitrates. In its purest and most concentra- ted state it is colourless and has a specific gravity of 1.50 or 1.510. It still contains a considerable quantity of water, from which it cannot be separated without decomposition, or by uniting with some other body. An acid ofthe density 1.50 contains 25 per cent. of water according to the experiments of Mr. Philips; and 20.3 per cent, according to those of Dr. Ure. Nitric acid of this strength emits dense, white, suffocating vapours when exposed to the atmosphere. It attracts watery vapour from the air, whereby its specific gravity is diminished. A rise of temperature is oc- casioned by mixing it with a certain quantity of water. Dr. Ure found that when 58 measures of nitric acid, of specific gravity 1.5, are suddenly mixed with 42 of water, the temperature rises from 60 to 140° F.; and the mixture, on cooling to 60°, occupies the space of 92.65 measures instead of 100. From its strong affinity for water, it occasions snow to liquefy with great rapidity; and an intense degree of cold is generated if the mixture be made in due proportion. Nitric acid boils at 248° F., and may be distilled without suf- fering material change. An acid of less specific gravity than 1.42 becomes stronger by being heated, because the water evapo- rates more rapidly then the acid. An acid, on the contrary, which is stronger than 1.42 is weakened by the application of heat. Nitric acid may be frozen by cold. The temperature at which congelation takes place varies with the strength of the acid. The strongest acid freezes at about 50 degrees below zero. When diluted with half its weight of water, it becomes solid at —\h° F. By the addition of a little more water its freezing point is lowered to—45° F. Nitric acid acts powerfully on substances which are disposed to unite with oxygen ; and hence it is much employed by che- mists for bringing bodies to their maximum of oxidation. Nearly all the metals are oxidized by it; and some of them, such as tin, copper, and mercury, are attacked with great violence. If thrown on burning charcoal, it increases the brilliancy of its com- bustion in a high degree. Sulphur and phosphorus are convert- ed into acids by its action. All vegetable substances are decom- posed by it. In general the oxygen ofthe nitric acid enters into direct combination with the hydrogen and carbon of those com- pounds, forming water with the first, and carbonic acid with the second. This happens remarkably in those compounds in which hydrogen and carbon are predominant, as in alcohol and the oils. It effects the decomposition of animal matters also. The cuticle and nails receive a permanent yellow stain when touched with Q 122 NITROGEN. it; and if applied to the skin in sufficient quantity it acts as a powerful cautery, destroying the organization of the part entirely. When oxidation is effected through the medium of nitric acid, the acid itself is commonly converted into the deutoxide of nitro- gen. This gas is sometimes given off nearly quite pure; but in general some nitrous acid, protoxide of nitrogen, or pure nitrogen is disengaged at the same time. The direct solar light deoxidizes nitric acid, resolving a portion of it into oxygen and nitrous acid. The former separates; the latter is absorbed by the nitric acid, and converts it into the mixed nitrous acid ofthe shops. When the vapour of nitric acid is passed through red-hot porcelain tubes it suffers complete decomposition, and a mixture of oxygen and nitrogen gases is the product. Nitric acid may also be deoxidized by passing a current ofthe deutoxide of nitrogen through it. Tliat gas, by taking oxygen from the nitric acid, is converted into nitrous acid ; and a portion of nitric acid, by losing oxygen, passes into the same compound. The nitrous acid, thus derived from two sources, gives a colour to the nitric acid, the depth and kind of which depend upon the quantity of the deutoxide of nitrogen which has been employed. The first portion communicates a pale straw colour, which gra- dually deepens as the absorption of the deutoxide continues, till the nitric acid has acquired a deep orange hue, together with all the characters of the strong forming nitrous acid. But the solu- tion still continues to absorb the deutoxide; and in doing so, its colour passes through different shades of olive and green, till it becomes greenish blue. By applying heat to the blue liquid, the deutoxide of nitrogen is evolved; and in proportion as it es- capes, the colour ofthe solution changes to green, olive, orange, and yellow, at length becoming pale as at first. Nitrous acid vapours are likewise disengaged as well as the deutoxide. These phenomena are very favouable to the view that the conversion of the orange colour into olive, green, and blue, is owing to the for- mation of hyponitrous acid. All the salts of nitric acid are soluble in water, and therefore it is impossible to precipitate that acid by any reagent. The presence of nitric acid, when uncombined, is readily detected by its strong action on copper and mercury, and by its forming with potassa a neutral salt, which crystallizes in prisms, and which has all the properties of nitre. The combining proportion of nitric acid is 54. ( 123 ) SECTION III. Hydrogen. This gas was formerly termed inflammable air from its com* bustibility, and phlogiston from the supposition that it was the matter of heat; but the name hydrogen, derived from iSue,, water, has now become general. Its nature and leading properties were first pointed out in 1766, by Mr. Cavendish. Hydrogen gas may be easily prepared in two ways. The first consists in passing the vapour of water over metallic iron heated to redness. This is done by putting iron wire into a gun-barrel open at both ends, to one of which is attached a flask containing pure water, and to the other a bent tube. The gun-barrel is placed in a furnace, and when it has acquired a full red heat, the water in the flask is made to boil briskly. The gas, which is copiously disengaged as soon as the steam comes in contact with the glowing iron, passes along the bent tube and may be collect- ed in convenient vessels, by dipping the free extremity of the tube into the water of a pneumatic trough. The second and most convenient method consists in putting pieces of iron or zinc into dilute sulphuric acid, formed of one part of strong acid to four or five of water. Zinc is generally preferred. These materials are to be put into a plain or untubulated retort, a figure of which is here represented, and the gas is to be caught in receivers over water. Hydrogen is a colourless gas, and has neither odour nor taste when perfectly pure. It is a powerful refractor of light. Like oxygen, it cannot be resolved into more simple parts, and, like that gas, has hitherto resisted all attempts to compress it into a liquid. It is the lightest body in nature, and is consequently the best material for filling balloons. It is ex- actly 16 times lighter than oxygen, and therefore 100 cubic inches of it at 60° F. and 30 Bar. must weigh 5||5* or 2.118 grains. Its specific gravity is consequently 0.0694, as stated some years ago by Dr. Prout. Hydrogen does not change the blue colour of vegetables. It is sparingly absorbed by water,100 cubic inches of that liquid dis- solving about one and a half of the gas. It cannot support re- spiration; for an animal soon perishes when confined in it. Death ensues from deprivation of oxygen rather than from any noxious quality ofthe hydrogen, since an atmosphere composed of a due proportion of oxygen and hydrogen gases may be respired without inconvenience. Nor is it a supporter of combustion; for when a 124 HYDROGEN. lighted candle fixed on wire is passed up into an inverted jar full of hydrogen, the light disappears on the instant. Hydrogen gas is inflammable in an eminent degree. Its com- bustion, is attended with a yellowish blue flame and a very feeble light. The phenomena are different when the hydrogen is pre- viously mixed with a due quantity of atmospheric air. The ap- proach of flame not only sets fire to the gas near it, but the whole is kindled at the same instant ; a flash of light passes through the mixture, which is followed by a violent explosion. The best proportion for the experiments is two measures of hy- drogen, to five or six of air. The explosion is far more violent when pure oxygen is used instead of atmospheric air, particularly when the gases are mixed together in the ratio of one measure of oxygen to two of hydrogen. Compounds of Oxygen and Hydrogen. Protoxide of Hydrogen or Water. Oxygen and hydrogen gases cannot combine at ordinary tem- peratures, and may, therefore, be kept in a state of mixture with- out even gradual combination taking place between them. Hy- drogen may be set on fire, when in contact with air or oxygen gas, by flame, by a solid body heated to bright redness, and by the electric spark. If a jet of hydrogen be thrown upon recently prepared spongy platinum, this metal almost instantly becomes red-hot, and then sets fire to the gas, a discovery which was made three years ago by Professor Doeberiner of Jena. The power of flame and electricity in causing a mixture of hydrogen with air or oxygen gas to explode, is limited. Mr. Cavendish found that flame occasions a very feeble explosion when the hy- drogen is mixed with nine times its bulk of air ; and that a mix- ture of four measures of hydrogen to one of air does not explode at all. An explosive mixture formed of two measures of hydro- gen to one of oxygen, explodes from all the causes above enu- merated. M. Biot found that sudden and violent compression likewise causes an explosion, apparently from the heat emitted during the operation; for an equal degree of condensation, slowly produced, has not the same effect. The electric spark ceases to cause a detonation when the explosive mixture is dilu- ted with twelve times its volume of air, fourteen of oxygen, or nine-of hydrogen, or when it is expanded to sixteen times its bulk by diminished pressure. Spongy platinum acts just as rapidly as flame or the electric spark in producing an explosion, provided the gases are quite pure and mixed in the exact ratio of two to one. When the action of heat, the electric spark, and spongy plati- num no longer cause an explosion, a silent and gradual combina- tion between the gases may still be occasioned by them. Sir H. HYDROGEN. 125 Davy observed that oxygen and hydrogen gases unite slowly with one another, when they are exposed to a temperature above the boiling point of mercury, and below that at which glass begins to appear luminous in the dark. An explosive mixture diluted with air to too great a degree to explode by electricity, is made to unite silently by a succession of electric sparks. Spongy platinum causes them to unite slowly, though mixed with one hundred times their bulk of oxygen gas. A large quantity of caloric is evolved during the combustion of hydrogen gas. Lavoisier concludes from experiments made with his calorimeter, that one pound of hydrogen occasions so much heat in burning as is sufficient to melt 295.6 pounds of ice. Mr. Dalton fixes the quantity of ice at 320 pounds, and Dr. Craw- ford at 480. The most intense heat that can be produced, is caused by the combustion of hydrogen in oxygen gas. Dr. Hare who first burned hydrogen for this purpose, collected the gases in separate gas-holders, from which a stream was made to issue through tubes communicating with one another, just before their termination. At this point the jet of the mixed gases was in- flamed. The effect of the combustion, though very great, is materially increased by forcing a proper mixture of the two gases into a strong metallic syringe, and burning them as they escape from it. An apparatus of this kind, now known by the name of the oxy-hydrogen blowpipe, was contrived by Mr. Newman, and was employed by the late Professor Clarke in his experiments on the fusion of refractory substances. On opening a stopcock which confines the condensed gases, a jet of the explosive mix- ture issues with force through a small blowpipe tube, at the ex- tremity of which it is kindled. In this state, however, the ap- paratus should never be used; for, as the reservoir is itself full of an explosive mixture, there is great danger of the flame run- ning, back along the tube and setting fire to the whole gas at once. To prevent the occurrence of such an accident, which would most probably prove fatal to the operator, Professor Cum- ming proposed that the gas, as it issues from the reservoir, should be made to pass through a cylinder full of oil or water before reaching the point at which it is to burn; and Dr. Wollaston suggested the additional precaution of fixing successive layers of fine wire gauze within the exit tube, each of which tends to inter- cept the communication of flame. But this apparatus is rarely necessary in chemical researches. A very intense heat, quite sufficient for most purposes, may be safely and easily procured by passing a jet of oxygen gas through the flame of a spirit lamp, as proposed by the late Dr. Marcet. Water is the sole product of the combustion of hydrogen gas. For this important fact, we are indebted to Mr. Cavendish. He demonstrated it by burning oxygen and hydrogen gases in a dry glass vessel, when a quantity of pure water was generated exactly 126 HYDROGEN. equal in weight to that of the gases which had disappeared. This experiment, which is the synthetic proof of the composition of water, was afterwards made on a much larger scale in Paris, by Vauquelin, Fourcroy, and Seguin. Lavoisier first demonstrated its nature analytically, by passing a known quantity of watery vapour over metallic iron heated to redness in a glass tube. Hy- drogen gas was disengaged, the metal in the tube was oxidized, and the weight of the former, added to the increase which the iron had experienced from combining with oxygen, exactly cor- responded to the quantity of water which had been decomposed. It will soon appear that a knowledge of the exact proportions in which oxygen and hydrogen gases unite to form water, is a necessary element in many chemical reasonings. Its composi- tion by volume was demonstrated very satisfactorily by Messrs. Nicholson and Carlisle, in their researches on the chemical agency of galvanism. On resolving water into its elements by this agent, and collecting them in separate vessels, they obtained precisely two measures of hydrogen to one of oxygen,—a result which has been fully confirmed by subsequent experimenters. The same fact was proved synthetically by Gay-Lussac and Humboldt. They found that when a mixture of oxygen and hy- drogen is inflamed by the electric spark, those gases always unite in the exact ratio of one to two, whatever may be their relative quantity in the mixture. When one measure of oxygen is mixed with three of hydrogen, one measure of hydrogen is the residue after the explosion; and a mixture of two measures of oxygen and two of hydrogen leaves one measure of oxygen. When one volume of oxygen is mixed with two of hydrogen, both gases, if quite pure, disappear entirely on the electric spark being passed through them. The composition of water by weight was de- termined with great care by Berzelius and Dulong; and we can- not hesitate, considering the known dexterity of the operators, and the principle on which their method of analysis was founded, to regard their result as a nearer approximation to the truth than that of any of their predecessors. They state as a mean of three careful experiments, that 100 parts of pure water consist of 88.9 of oxygen and 11.1 of hydrogen. Now, 11.1 : 88.9 :: 1 : S.009 which is so near the proportion of 1 to 8 as to justify the adop- tion of that ratio. Hence, the constitution of water by weight and measure, may be thus stated : By Weight. By Volume. Oxygen 8 . . 1 Hydrogen . 1 . . 2 These are the data from which it was inferred that oxygen gas is just 16 times heavier than hydrogen. The processes for forming hydrogen gas will now be intelligi- ble. The first is the method by which Lavoisier made the analy- HYDROGEN. 127 sis of water. It is founded on the fact that iron at a red heat de- composes water, the oxygen of that liquid uniting with the metal, and hydrogen gas being set free. That the hydrogen which is evolved when zinc or iron is put into dilute sulphuric acid must be derived from the same source, is obvious from the considera- tion that ofthe three substances, iron, sulphuric acid, and water, the last is the only one which contains hydrogen. The action of diluted sulphuric acid on metallic zinc affords an instance of what was once called Disposing Affinity. Zinc cannot decompose water at common temperatures ; but as soon as sulphuric acid is added, the decomposition of the water takes place rapidly, though the acid merely unites with the oxide of zinc. The former explanation was, that the affinity of the acid for the oxide of zinc disposed the metal to unite with the oxygen, and thus enabled it to decompose water; that is, the oxide of zinc was supposed to produce an effect previous to its existence. The obscurity of this explanation arises from regarding changes as consecutive, which are in reality simultaneous. There is no appearance of succession in the process; the oxide of zinc is not formed previously to its combination with the acid, but at the same instant. There is, as it were, only one chemical change, which consists in the combination, at one and the same moment, ofthe zinc with the oxygen, and the oxide of zinc with the acid; and this change occurs because these two affinities, acting to- gether, overcome the attraction of oxygen and hydrogen for one another. Water is a transparent colourless liquid, which has neither smell nor taste. It is a powerful refractor of light, conducts heat very slowly, and is an imperfect conductor of electricity. It is compressible by very strong pressure. This fact was long disputed; but Mr. Perkins finds that the pressure of 2000 atmos- pheres occasions a diminution of 1-12 of its bulk. The relations of water, with respect to caloric, are highly important, but have already been discussed in a former part of the work. The spe- cific gravity of water is 1, the density of all solid and liquid bodies being referred to it as a term of comparison. One cubic inch at 60° F. and 30 Bar., weighs 252.525 grains, so that it is 828 times heavier than atmospheric air. Water is one of the most powerful chemical agents which we possess. Its agency is owing partly to the extensive range of its own affinity, and partly to the nature of its elements. The effect of the last circumstance has already appeared in the formation of hydrogen gas; and indeed there are few complex chemical changes which do not give rise either to the production or de- composition of water. But, independently of the elements of which it is composed, it combines directly with many bodies. Sometimes it is contained in a variable ratio, as in ordinary solu- tion ; in other compounds it is present in a fixed definite propor- 128 HYDROGEN. tion, as is exemplified by its union with several ofthe acids, the alkalies, and all salts that contain water of crystallization. These combinations are termed hydrates; thus, the strongest liquid sul- phuric acid, is a compound of one atom ofthe real dry acid and one atom of water; and its proper name is hydrous sulphuric acid, or hydrate of sulphuric acid. The adjunct hydro has been sometimes used to signify the presence of water in definite pro- portion : but it is advisable, to prevent mistakes, to limit its em- ployment to the compounds of hydrogen. The purest water which can be found as a natural product, is procured by melting freshly fallen snow, or by receiving rain in clean vessels in an open situation. But this water is not abso- lutely pure ; for if it is placed under the exhausted receiver of an air pump, or boiled briskly for a few minutes, bubbles of gas es- cape from it. The air obtained in this way from snow water, is much richer in oxygen gas than atmospheric air. According to the experiments of Gay-Lussac and Humboldt, it contains 34.8 per cent, of oxygen, and the air separated by ebullition from rain- water contains 32 per cent, of that gas. All water which has once fallen on the ground, becomes impregnated with more or less earthy or saline matters, and it can be separated from them only by distillation. The distilled water, thus obtained, and preserved in clean well-stopped bottles, is absolutely pure. Recently boil- ed water has the property of absorbing a portion of all gases when its surface is in contact with them; and the absorption is promoted by brisk agitation. Deutoxide of Hydrogen. The deutoxide, or peroxide of hydrogen, was discovered by M. Thenard in the year 1818. Before describing the mode of pre- paring this compound, it must be observed that there are two oxides of barium, and that when the peroxide of that metal is put into water containing free muriatic acid, oxygen gas is set at liberty, and the peroxide is converted into the protoxide of barium or baryta, which combines with the acid. When this process is conducted with the necessary precautions, the oxygen which is set free, instead of escaping in the form of gas, unites with the hydrogen ofthe water, and brings it to a maximum of oxidation. The peroxide of hydrogen of sp. gr. 1.452 is a colourless transparent liquid without odour. It whitens the surface of the skin when applied to it, causes a prickling sensation, and even destroys its texture if the application is long continued. It acts in a similar manner on the tongue, in addition to which it thickens the saliva, and tastes like certain metallic solutions. Brought into contact with litmus and turmeric paper, it gradually destroys their colour and makes them white. It is slowly volatilized in vacuo, which shows that its vapour is much less elastic than that HYDROGEN. 129 of water. It preserves its liquid form at all degrees of cold to which it has hitherto been exposed. At the temperature of 59° F. it is decomposed, being converted into water and oxygen gas. For this reason it ought to be preserved in glass tubes surrounded with ice. The most remarkable property of the peroxide of hydrogen is the facility with which it is decomposed. The diffused day-light does not seem to exert any influence over it, and even the direct solar rays act upon it tardily. It effervesces from the escape of oxygen at 59° F., and the sudden application of a higher tem- perature, as of 212° F., gives rise to such a rapid evolution of gas as to cause an explosion. Water, apparently by combining with the peroxide, renders it more permanent; but no degree of dilution can enable it to bear the heat of boiling water, at which temperature it is decomposed entirely. All the metals except iron, tin, antimony, and tellurium, have a tendency to decompose the peroxide of hydrogen, converting it into oxygen and water. A state of minute mechanical division is essential for producing rapid decomposition. If the metal is in mass, and the peroxide diluted with water, the action is slow. It is a singular fact, that some oxides decompose the peroxide of hydrogen without pass- ing into a higher degree of oxidation. While the tendency of metals and metallic oxides is to decom- pose the peroxide of hydrogen, acids have the property of ren- dering it more stable. In proof of this, let a portion of that liquid, somewhat diluted with water, be heated till it begins to effervesce from the escape of oxygen gas; let some strong acid, as the nitric, or sulphuric, be then dropped into it, and the effervescence will cease on the instant. When a little gold in a state of fine divi- sion is put into a weak solution of the peroxide of hydrogen, con- taining only 10, 20, or 30 times its bulk of oxygen, a brisk effer- vescence ensues; but on letting one drop of sulphuric acid fall into it, the effervescence ceases instantly ; it is reproduced by the addition of potash, and is again arrested by adding a second por- tion of acid. The only acids that do not possess this property are those that have a low degree of acidity, as the carbonic and boracic acids; or those which suffer a chemical change when mixed with the peroxide of hydrogen. Acids appear to increase the stability of the peroxide in the same way as water does, namely, by combining chemically with it. Several compounds of this kind were formed by Thenard, before he was aware ofthe existence ofthe peroxide of hydrogen. They were made by dis- solving the peroxide of barium in some diluted acid, such as the nitric, and then precipitating the baryta by sulphuric acid. As the nitric acid was supposed under these circumstances to com- bine with an additional quantity of oxygen, Thenard applied the term oxygenized nitric acid to the resulting compound, and described several other new acids under a similar title. But the R 130 HYDROGEN. subsequent discovery ofthe peroxide of hydrogen put the nature of the oxygenized acids in a clearer light; for their properties are easily explicable on the supposition that they are composed, not of acids and oxygen gas, but of acids united with the peroxide of hydrogen. The peroxide of hydrogen was analyzed by diluting a known weight of it with water, and then decomposing it by boiling the solution. According to two careful analyses, conducted on this principle, 864 parts ofthe peroxide of hydrogen are composed of 466 of water, and 398 of oxygen gas. The 466 of water contain 414 of oxygen, whence it may be inferred that the peroxide of hydrogen contains twice as much oxygen as water. A small deficiency of oxygen in the experiment was to be expected, owing to the difficulty of obtaining the peroxide of hydrogen per- fectly free from water. The peroxide consists, therefore, of Hydrogen 1 1 proportion. Oxygen 16 2 proportions. Hydrogen and Nitrogen.—Ammoniacal Gas. Ammonia was known to the alchymists, though not in a state of purity. They sometimes called it hartshorn, because it was frequently obtained by distilling the horns of the hart; and some- times the spirit of sal ammoniac, when they procured it from that salt. The existence of ammonia as a gas, was first noticed by Dr. Priestley, and he described it under the name of alkaline air; Scheele, also, appears to be entitled to the merit of discovering this gas, but the composition of ammonia by the union of hydro- gen and nitrogen, was first ascertained by Berthollet. As ammonia possesses all those properties which we have here- tofore described sb constituting an alkali, it is therefore called, from its volatility, the volatile alkali, in most of the Phar- macopoeias. The most convenient method of preparing ammoniacal gas for the purposes of experiment, is by applying a gentle heat to the concentrated solution of ammonia, contained in a glass vessel. It soon enters into ebullition, and a large quantity of pure am- monia is disengaged. The gas must be caught in vessels filled with mercury, as it is rapidly absorbed by water. The following figure represents a section of a small mercurial trough, used for this and similar purposes. It represents a block of hard wood or marble 14 inches long, 7 broad, and 6 deep. This is to be hollowed out, as represented in the drawing. This trough is then to be filled with mercury to the height of? of an inch above the level ofthe hori- zontal line or shelf, upon which the receivers which contain the HYDROGEN. 131 lii^lllillii 11, gas are placed. This rude kind of mercurial trough will do for ordinary experiments. The most convenient form of the mecurio-pneu- matic apparatus, is one contrived by Mr. Newman of London, a figure of which may be seen in the Quarterly Jour. vol. 1. p. 185. Ammonia is a colourless gas, which has a strong pungent odour, and acts powerfully on the eyes and nose. It is quite ir- respirable in its pure form, but when diluted with air, it may be taken into the lungs with safety. Burning bodies are extinguish- ed by it, nor is the gas inflamed by their approach. Ammonia, however, is inflammable in a low degree. For when a lighted candle is immersed in it, the flame is somewhat enlarged, and tinged of a pale yellow colour at the moment of being extin- guished ; and a small jet of the gas will burn in an atmosphere of oxygen. A mixture of ammoniacal and oxygen gases detonates by the electric spark ; water is formed, and nitrogen remains. A little nitric acid is generated at the same time, except when less oxygen is employed than is sufficient for combining with all the hydrogen of the ammonia. Ammoniacal gas, at the temperature of 50° F. and under a pres- sure equal to 6.5 atmospheres, becomes a transparent colourless liquid. It is also liquefied, according to Guyton-Morveau, under the common pressure, by a cold of 70 degrees below zero of Fahrenheit; but it is more probable that the liquid he obtained was a solution of ammonia in water. Hydrogen and nitrogen gases no not unite directly, and there- fore chemists have no synthetic proof ofthe constitution of am- monia. Its composition, however, has been determined analyti- cally with great exactness. When a succession of electric sparks is passed through ammoniacal gas, it is resolved into its elements; and the same effect is produced by conducting am- monia through porcelain tubes heated to redness. The late A. Berthollet analyzed ammonia in both ways, and ascertained that 200 measures of that gas, on being decomposed, occupy the space of 400 measures, 300 of which are hydrogen, and 100 nitrogen. The specific gravity of ammonia, is 0.5902, and its atomic weight 17. Ammoniacal gas a powerful affinity for water. Owing to this attraction, a piece of ice, when introduced into a jar full of am- monia, is instantly liquefied, and the gas disappears in the course of a few seconds. Sir H. Davy, states that water at 50° F. and when the barometer stands at 29.8 inches, absorbs 670 times its volume of ammonia; and that the solution has a specific gravity of 0.875. Water, at the common temperature and pressure, takes up 780 times its bulk. By strong compression, water absorbs the gas in still greater quantity. Caloric is evolved during the absorption, and a considerable expansion, independently of the increased temperature, occurs at the same time. 132 HYDROGEN. The concentrated solution of ammonia commonly, though incor- rectly, termed liquid ammonia, is made by passing^ current of the gas, a long as it continues to be absorbed, into distilled water, which is kept cool by means of ice or moist cloths. The gas may be prepared from any salt of ammonia by the action of any pure alkali or alkaline earth ; but muriate of ammonia and lime, from economical considerations, are always employed. The best proportions are equal parts of the muriate of ammonia and well- burned quicklime, a considerable excess of lime being taken, in order to decompose the muriate more expeditiously and com- pletely. The lime is slaked by the addition of water, and as soon as it has fallen into powder, it should be placed in an ear- then pan and be covered to protect it from the carbonic acid of the air, till it is quite cold. It is then mixed in a mortar with the muriate of ammonia, previously reduced to a fine powder, and the mixture is put into a retort or other convenient glass vessel. Heat is then applied, and the temperature gradually increased as long as a free evolution of gas continues. The ammonia should be conducted by means of a Welter's safety tube into a quantity of distilled water equal to the weight ofthe salt employ- ed. The residue consists of lime and muriate of lime. The concentrated solution of ammonia, as thus prepared, is a clear colourless liquid, of specific gravity 0.936. It possesses the peculiar pungent odour, taste, alkalinity, and other properties of the gas itself. On account of its great volatility it should be pre- served in well-stopped bottles, a measure which is also required to prevent the absorption of carbonic acid. At a temperature of 130° F. it enters into ebullition, owing to the rapid escape of pure ammonia; but the whole of the gas cannot be expelled by this means, as at last the solution itself evaporates. It freezes at about the same temperature as mercury. The following table shows the quantity of real ammonia con- tained in 100 parts of solutions of different densities, at 59° F. and when the barometer stands at 30 inches. The specific gravity of water is supposed to be 10,000: Table ofthe quantity of real Ammonia in solutions of different densities. 100 parts of Of real i 100 parts of Of real sp. gravity. £ Ammonia. sp. gravity. £! Ammonia. .8750 32.5 9435 14.53 .8875 <3 29.25 9476 a 13.46 .9000 "^ 26.00 9513 e 12.40 9054 s 25.37 9545 s 11.56 9166 22.07 9573 10.82 9255 19.54 9597 10.17 9326 17.52 9619 9.60 9385 15.88 9692 9.50 ---- HYDROGEN. 133 The presence of free ammoniacal gas may always be detected by its odour, by its temporary action on the yellow turmeric pa- per, and by forming dense white fumes, the muriate of ammonia, when a glass red moistened with muriatic acid is brought near it. Of Chemical Equivalents. Before describing the combination of ammonia with the nitric acid, we will offer a brief explanation of a law of chemical com- bination to which we have not hitherto adverted. It has been shown that water is composed of 1 part of hydro- gen, combined with 8 parts of oxygen, now it has been found that the same quantity of any substance which will combine with I part of hydrogen, will also combine with 8 parts of oxygen; thus 16 parts of sulphur will combine with 1 of hydrogen and with 8 of oxygen; 12 parts of phosphorus will combine with 1 of hydrogen and with 8 of oxygen, and what is very remarkable the only known compound of sulphur and phosphorus is composed of 16 parts of the former combined with 12 ofthe latter. It is manifest, from these and other examples, that bodies unite according to proportional numbers; and hence has arisen the use of certain terms as Proportion, Combining Proportion, or Equi- valent, to express them. Thus the combining proportions of the substances just alluded to, are Hydrogen ----- 1 Oxygen _____ 8 Phosphorus 12 Sulphur - - - - - 16 When one body combines with another in more than one pro- portion, then the law of multiples, already explained, comes into action. Thus, Sulphur. Oxygen. Hyposulphurous Acid is composed of 16orlpr. + 8 or 1 pr. Sulphurous Acid - - 16 or 1 pr. + 16 or 2 pr. Sulphuric Acid - - 16 or 1 pr. + 24 or 3 pr. The most common kind of combination is one proportion of one body either with one or with two proportions of another. Combinations of 1 to 3, or 1 to 4, are very uncommon, unless the more simple compounds likewise exist. Ammonia, however, is a singular instance of the reverse. It is composed of 14 parts of nitrogen, and three of hydrogen. Now 14 is the precise quan- tity of nitrogen that unites with 8 of oxygen, and therefore 14 is considered as one proportion of nitrogen, which is consequently combined with three proportions of hydrogen. It is probable that compounds of 1 to 1, and 1 to 2, will hereafter be discovered, but they are quite unknown at present. 134 HYDROGEN. But this law does not apply to elementary substances only, since compound bodies have their combining proportion which may likewise be expressed in numbers. Thus, since water is composed of one proportion or 8 of oxygen, and one proportion or 1 of hydrogen, its combining proportion is 9. The propor- tion of sulphuric acid is 40, because it is a compound of one pro- portion or 16 of sulphur, and three proportions or 24 of oxygen; and in like manner, the combining proportion of nitric acid is 54; because it is a compound of 5 proportions or 40 of oxygen, and 1 proportion or 14 of nitrogen. The combining proportion of ammonia is 14+3=17. Now when these compounds unite, one proportion of the one combines with one, two, three, or more of the other, precisely as simple substances do. The nitrate of ammonia, for example, is constituted of 54 nitric acid and 17 am- monia, its combining proportion is consequently 54+17=71. Since the proportional numbers merely express the relative quan- tities of different substances which combine together, it is in itself immaterial what figures are employed to express them. The only essential point is, that the relation should be strictly observed. Thus, we may make the combining proportion of hy- drogen 10 if we please ; but then oxygen must be 80, phosphorus 120, and sulphur 160. We may call hydrogen 100 or 1000, or, if it were desirable to perplex the subject as much as .possible, some high uneven number might be selected, provided the due relation between the different numbers is faithfully preserved. As the opinion of different chemists concerning the simplicity of numbers is somewhat at variance, we possess several series of them. Dr. Thomson, for example, makes oxygen 1, so that hy- drogen is eight times less than unity, or 0.125, phosphorus 1.5 and sulphur 2. Dr. Wollaston, in his scale of chemical equi- valents, fixes oxygen at 10, by which hydrogen is 1.25, sulphur 20, and so on. According to Berzelius, oxygen is 100. And lastly, several other chemists, such as Dalton, Davy, Henry, and others, call hydrogen unity, and therefore oxygen 8. One of these series may easily be reduced to either of the others by an obvious and simple arithmetical process; and excepting that of Berzelius, whose numbers are inconveniently high for practice, it is not very material to which of them the preference is given. We have adopted the last, because, as it contains no fractional parts, it appears best adapted to the purpose of teaching. The utility of being acquainted with these important laws is almost too manifest to require mention. Through their aid, and by renumbering the proportional numbers of a few elementary substances, the composition of an extensive range of compound bodies may be calculated with facility. The exact quantity of substances required to produce a given effect can be determined with certainty, thus affording informa- tion which is often necessary to the success of chemical process- HYDROGEN. 135 es, and of vast consequence, both in the practice of the chemi- cal arts, and in the operations of pharmacy. The same knowledge affords a good test to the analyst, by which he may judge ofthe accuracy of his result, and even sometimes cor- rect an analysis which he has not the means of performing with rigid precision. Thus a powerful argument for the accuracy of an analysis is derived from the correspondence of its result with the laws of chemical union. On the contrary, if it form an ex- ception to them, we are authorized to regard it as doubtful, and may hence be led to detect an error, the existence of which might not otherwise have been suspected. If an oxidized body is found to contain one proportion ofthe combustible with 7.99 of oxygen, then the inference is unavoidable that 8, or one pro- portion of oxygen, would have been the result, had the analysis been perfect. From the same cause, the discovery of a new compound, whether it has been formed by the chemist, or exists as a mineral in the earth, is always interesting ; curiosity is ex- cited to ascertain the ratio of its constituents, and see if it be such as reasoning from the established data would have led us to con- jecture. Taking it for granted, that combination takes place between the atoms of matter only, the combining proportion of a substance represents the relative weight of its atom—hence atomic weight and combining proportion are synonymous. Nitrate of Ammonia. The nitrate of ammonia may be formed by neutralizing dilute nitric acid by the carbonate of ammonia, and evaporating the solution. This salt may be procured in three different states, which have been described by Sir H. Davy. If the evapora- tion is conducted at a temperature not exceeding 100° F., the salt is obtained in prismatic crystals which are composed, ac- cording to the experiments of Davy, and Berzelius, of 67 parts, or one proportion of the neutral nitrate of ammonia, and 9 parts, or one proportion of water. If the solution is evaporated at 212° F., fibrous crystals are procured ; and if the heat be gradually increased to 300° F., it forms a brittle compact mass on cooling. The fibrous and compact varieties still contain water, the former 8.2 per cent, and the latter 5.7. All these varieties are deliques- cent, and very soluble in water. When this salt is exposed to a temperature of 400° or 500° F. it liquefies, bubbles of gas begin to rise from it, and in a short time a brisk effervescence ensues, which continues till the whole of the salt disappears. The nitrate of ammonia should be con- tained in a glass retort, and the heat applied by means of a lamp placed at such a distance below it as to maintain a moderately rapid evolution of gas. 136 HYDROGEN. The sole products of this operation, when carefully conducted, are water and the protoxide of nitrogen. The theory of the pro- cess is as follows :— Nitrate of ammonia is composed of Nitric acid 54 one proportion or atom, Ammonia 17 one proportion or atom. 71 The nitric acid consists of Nitrogen 14 one proportion or atom, Oxygen 40 five proportions or atoms. 54 And the ammonia of Nitrogen 14 one proportion or atom, Hydrogen 3 three proportions or atoms. 17 By the action of heat, these elements arrange themselves in a new order. The hydrogen takes so much oxygen as is sufficient for forming water, and the residual oxygen converts the nitrogen both of the nitric acid and of the ammonia into the protoxide of nitrogen. The decomposition of 71 grains ofthe salt will there- fore yield Water 27 or 3 pr. J °xpn 2! or % Pr* v \ Hydrogen 3 or 3 pr. Protoxide of nitrogen 44 or 2 pr. \ °X/Sen \\ or ? Pr' b I Nitrogen 28 or 2 pr. When the nitrate of ammonia is heated to 600°, it explodes with violence, being resolved into water, nitrous acid, the deut- oxide of nitrogen, and nitrogen. The fibrous variety was found by Sir II. Davy to yield the largest quantity of the protoxide of nitrogen. From one pound of this salt he procured nearly three cubic feet of the gas. General remarks on Salts. By the term salt, chemists mean a definite compound of an acid, and an alkaline or salifiable base, both of which are, in every case, composed of at least two simple substances. Nitrate of ammonia, for example, is a salt, the acid of which consists of oxygen and nitrogen, and the salifiable base of hydrogen and nitrogen. The names by which the salts are designated, are so constitut- ed, as to indicate the substances contained in them. If the aci- dified substance contains a maximum of oxygen, the name termi- nates in ate, if a minimum, the termination ite is employed, and the name of the base is added for the specific distinction of HYDROGEN. 137 the salt. The nitrate and sulphate of ammonia, are combina- tions of nitric and sulphuric acids with ammonia; and the sul- phite and hyponitrite of potassa, are formed by the union of sulphurous and hyponitrous acids with potassa. The different salts formed of the same constituents were for- merly divided into neutral, super, and swo-salts. They were called neutral if the acid and alkali are in the proportion for neu- tralizing one another ; super-salts, if the acid prevails ; and sub- salts, if the alkali is in excess. The name is now regulated by the atomic constitution of the salt. If it be a compound of one atom ofthe acid to one atom ofthe alkali or base, the generic name ofthe salt is employed without any addition ; but if two or more atoms ofthe acid be attached to one ofthe base, or two or more atoms ofthe base to one ofthe acid, a numeral is prefixed so as to indicate its composition. The two salts of sulphuric acid and potash are called sulphate and 6i-sulphate ; the first containing one atom of the acid to one atom of the alkali, and the latter, two ofthe former to one ofthe latter. The three salts of oxalic acid and potash are termed the oxalate, oinoxalate, and qua- rtYoxalate, of potash ; because one atom of the alkali is united with one atom of acid in the first, with two in the second, and with four in the third salt. As the numerals which denote the atoms of the acid in a super-salt are derived from the Latin language, it has been proposed to employ the Greek numerals, dis, tris, tetrakis, to signify the atoms of alkali in a sub-salt. In studying the salts, it is important to set out with correct ideas concerning the nature of an acid and of an alkaline base, and we shall therefore make a few preliminary remarks in addi- tion to what we have already said, concerning the nature and characteristic properties of these two classes of compounds. An acid is commonly regarded as a substance which has a sour taste, reddens litmus paper, and neutralizes alkalies. But these properties, though very conspicuous in all the powerful acids, are not altogether general, and therefore cannot serve the purpose of a definition. Thus insoluble acids, owing to their insolubility, do not taste sour, nor redden litmus paper; and some bodies, the title of which to be placed among the acids cannot be called in question, are unable to destroy the alkaline reaction of potassa. The most correct definition of an acid, is the following :—an acid is a compound which is capable of uniting in definite proportion with alkaline bases, and which, when liquid or in a state of solu- tion, has either a sour taste, or reddens litmus paper. Most of the acids contain oxygen as one of their elements, a circumstance which induced Lavoisier to suppose that oxygen possesses some specific power of causing acidity, and for this reason he regarded it as the acidifying principle. The acquisi- tion of new facts, however, has»shown the fallacy of his opinion. Acids may and do exist which contain no trace of oxygen, nor S 138 HYDROGEN. does its presence necessarily give rise to acidity. The com- pounds of oxygen are frequently alkaline instead of acid ; and in many instances they are neither acid nor alkaline. No substance contains a larger proportional quantity of oxygen than water, and yet this fluid does not possess the slightest degree of acidity. The progress of science, indeed, seems to justify the opinion that there is no body to which the term acidifying principle is strictly applicable. The acidity of any substance cannot be referred to one of its elements rather than another; but is a new property peculiar to the compound, and to which its constituents equally contribute. An alkali is characterized by a peculiar pungent taste, by its alkaline reaction on vegetable colours, and by neutralizing acids. There are many salifiable bases, however, which do not possess these characters. Thus pure magnesia, though it is a strong alka- line base and forms neutral salts with acids, is insipid, and barely produces an appreciable effect on yellow turmeric paper,—an inaction obviously owing to its insolubility. Some compounds neutralize the properties of acids in an imperfect manner, although they form perfect salts. For these reasons it is desirable to define precisely what is meant by a salifiable base, and the following definition appears to me to answer the purpose. Every com- pound may be regarded as an alkaline or salifiable base, which forms definite compounds with acids, and which, when liquid or in a state of solution, has an alkaline reaction. All alkaline bases, with the exception of ammonia, and the vegetable alkalies, are metallic oxides. The insufficiency of the division into neutral, super, and sub- salts will be made apparent by the following remarks. In the first place, some alkaline bases form more than one super-salt, in which case two or more different salts would be included under the same name. Secondly, some salts have an acid reaction, and might therefore be denominated super-salts, although they do not contain an excess of acid. The nitrate of lead, for instance, has the property of reddening litmus paper; whereas it consists of one atom of the oxide of lead and one atom of nitric acid, and therefore in composition is precisely analogous to the nitrate of potassa, which is a neutral salt. This fact was noticed some years ago by Berzelius, who accounted for the circumstance in the following manner. The colour of litmus is naturally red, and it is only rendered blue by the colouring matter combining with an alkali. If an acid be added to the blue compound, the colouring matter is deprived of its alkali, and thus, being set free, resumes its red tint. Now on bringing litmus paper in con- tact with a salt, the acid and base of which have a weak attrac- tion for each other, it is possible that the alkali contained in the litmus paper may have a stronger affinity for the acid of the salt than the base has with which it was combined, and in that case HYDROGEN. 139 the alkali ofthe litmus being neutralized, its red colour would necessarily be restored. It is hence apparent that a salt may have an acid reaction without having an excess of acid. As every acid with few exceptions, is capable of uniting with every alkaline base, and frequently in two or more proportions, it is manifest that the salts must constitute a very numerous class of bodies. Nearly all salts are solid, and most of them assume crystalline forms when their solutions are spontaneously evaporated. The colour of salts is very variable. Those that are composed of a colourless base and acid are always colourless. There is no necessary connexion between the colour of an oxide or an acid and that of its salts. A salt, though formed of a coloured oxide or acid, may be colourless; and if it is coloured, the tint may differ from that of both its constituents. All soluble salts are more or less sapid, while those that are in- soluble in water are insipid. Few salts are possessed of odour: the only one which is remarkable for this property is the carbo- nate of ammonia. Salts differ remarkably in their affinity for water. Thus some salts, are deliquescent, that is, attract moisture, from the air and become liquid. Others, which have a less powerful attraction for water, undergo no change when the air is dry, but become moist in a humid atmosphere; and others may be exposed with- out change to an atmosphere loaded with watery vapour. Salts differ likewise in the degree of solubility in water. Some dissolve in less than their weight of water; while others require several hundred times their weight of this liquid for solution, and others are quite insoluble. This difference depends on two cir- cumstances, namely, on the degree of their affinity for water, and on their cohesion ; their solubility being in direct ratio with the first, and in inverse ratio with the second. One salt may have a greater affinity for water than another, and be less soluble ; an effect which may be produced by the cohesive power ofthe salt, which has the stronger attraction for water, being greater than that ofthe salt which has a less powerful affinity for that liquid. The method proposed by Gay-Lussac for estimating the relative degrees of affinity of salts for water, is by dissolving equal quan- tities of salts in equal quantities of water, and applying heat to the solutions. That salt which has the greatest affinity for the menstruum will retain it with most force, and will therefore re- quire the highest temperature for boiling. Salts which are soluble in water crystallize more or less re- gularly when their solutions are evaporated. If the evaporation is rendered rapid by heat, the salt is usually deposited in a con- fused crystalline mass; but if it take place slowly, regular crystals are formed. The best mode of conducting the process, is to dis- solve a salt in hot water, and, when it has become quite cold, to 140 HYDROGEN. pour the saturated solution into an evaporating basin, which is to be set aside for several days or weeks without being moved. As the water evaporates, the salt assumes the solid form ; and the slower the evaporation, the more regular are the crystals. Some salts which are much more soluble in hot than in cold water, crystallize with considerable regularity when a boiling saturated solution is slowly cooled. The form which salts assume in crys- tallizing is constant under the same circumstances, and constitutes an excellent character by which they may be distinguished from one another. Many salts, during the act of crystallizing, unite chemically with a definite portion of water, which forms an essential part of the crystal, and is termed the water of crystallization. The quan- tity of combined water is very variable in different saline bodies, but is uniform in the same salt. A salt may contain more than half its weight of water, and yet be quite dry. On exposing a salt of this kind to heat, it is dissolved, if soluble, in its own water of crystallization, undergoing what is termed the watery fusion. By a strong heat, the whole ofthe water is expelled; for no salt can retain its water of crystallization when heated to redness. Some salts, such as the sulphate and phosphate of soda, lose a portion of their water, and crumble down into a white powder, by mere exposure to the air, a change which is called efflores- cence. Salts, in crystallizing, frequently inclose mechanically within their texture particles of water, by the expansion of which, when heated, the salt is burst with a crackling noise into smaller frag- ments. This phenomenon is known by the name of decrepita- tion. Berzelius has correctly remarked that those crystals de- crepitate most powerfully, such as the nitrates of baryta and of lead, which contain no water of crystallization. The atmospheric pressure is said to have considerable influence on the crystallization of salts. If, for example, a concentrated solution, composed of about three parts of sulphate of soda in crystals to two of water, is made to boil briskly, and the flask which contains it is then tightly corked, while its upper part is full of vapour, the solution will cool down to the temperature of the air without crystallizing, and may in that state be preserved for months without change. Before removal of the cork, the liquid may often be briskly agitated without losing its fluidity; but on re-admitting the air, crystallization commonly commences, and the whole becomes solid in the course of a few seconds. The admission of the air sometimes, indeed, fails in causing the effect; but it may be produced with certainty by agitation or the in- troduction of a solid body. The theory of this phenomenon is not very apparent. Gay-Lussac has shown that it does not de- pend on atmospheric pressure ; for he finds that the solution may HYDROGEN. 141 be cooled in open vessels without becoming solid, provided its surface be covered with a film of oil. The same quantity of water may hold several different salts in solution, provided they do not mutually decompose each other. The solvent power of water with respect to one salt is, indeed, sometimes increased by the presence of another, owing to com- bination taking place between the two salts. Most salts produce cold during the act of dissolving in water, especially when they are dissolved rapidly and in large quantity. The greatest reduction of temperature is occasioned by those which contain water of crystallization. All salts are decomposed by Voltaic electricity, provided they are either moistened or in solution. The acid appears at the positive pole of the battery, and the oxide at its opposite ex- tremity ; or, if the oxide is of easy reduction, the metal itself goes over to the negative side, and its oxygen accompanies the acid to the positive wire. The composition of the salts affords a very neat illustration of the law of combination in definite proportions. The following list contains the proportional numbers of a few acids and alkalies. Phosphoric 28 Soda 32 Sulphuric 40 Potassa 48 Nitric 54 Baryta 78 The proportion of each base expresses the precise quantity required to neutralize a proportion of each of the acids. Thus, 32 of soda, 48 of potassa, and 78 of baryta combine with 40 of sulphuric acid, forming the neutral sulphates of soda, potassa, and baryta. The same fact occurs with the acids; for 28 of phos- phoric, 40 of sulphuric, and 54 of nitric acid, unite with 32 of soda, forming a neutral, phosphate, sulphate, and nitrate of soda. These circumstances afford a ready explanation of a curious fact, first noticed by the Saxon Chemist Wenzel;—when two neutral salts mutually decompose one another, the resulting compounds are likewise neutral. The cause of this fact is now obvious. If 88 parts of neutral sulphate of potassa are mixed with 132 ofthe nitrate of baryta, the 78 baryta unite with the 40 sul- phuric acid, and the 54 nitric acid of the nitrate combine with the 48 potassa ofthe sulphate, not a particle of acid or alkali re- maining in an uncombined condition. Sulphate of Potash, Nitrate of Baryta. Sulphuric acid 40 54 Nitric acid. Potassa 48 78 Baryta. 88 132 It matters not whether more or less lhan 88 parts of sulphate of potassa are added; if more, a small quantity of sulphate of pot- 142 HYDROGEN. assa will remain in solution ; if less, nitrate of baryta will be in excess; but in either case the neutrality will be unaffected. Aerates. The nitrates are prepared by the action of nitric acid on metals, on the salifiable bases themselves, or on carbonates. As nitric acid forms soluble salts with all alkaline bases, the acid of the nitrates cannot be precipitated by any re-agent. They are readily distinguished from other salts, however, by the three following characters :—1st. By deflagrating with red-hot charcoal; 2d. By their power of dissolving gold leaf on the addition of muriatic acid; 3. By the evolution of dense, white, acid vapours, which are easily recognised to be nitric acid by their odour, when mixed with strong sulphuric acid. All the nitrates are decomposed without exception by a high temperature, various results are obtained according to the che- mical relations of the different ingredients in the salt employed. There are but two acid compounds of nitrogen, which com- bine with the salifiable bases, and form salts. When nitrous acid is added to a base, it is decomposed, and the result is a nitrate and hyponitrite, or a hyponitrite alone. SECTION IV. Carbon. When wood is heated to a certain degree in the open air, it takes fire and burns till the whole of it is consumed. A small portion of ashes is the sole residue. But if the wood be heated to redness in close vessels, so that the atmospheric air cannot have free access to it, a large quantity of gaseous and other vola- tile matters is expelled, and a black, hard, porous substance is left, called charcoal. Charcoal may be procured from other sources. When the volatile matters are driven off from coal, as in the process for making coal gas, a peculiar kind of charcoal, called coke, remains. Most animal and vegetable substances yield it when ignited in close vessels. Thus, a very pure charcoal may be procured from starch or sugar, and from the oil of turpentine, or spirits of wine, by passing their vapours through tubes heated to redness. When bones are made red hot in a covered crucible, a black mass re- mains, which consists of charcoal mixed with the earthy matters of the bone. It is called ivory black or animal charcoal. Charcoal is hard and brittle, conducts heat very slowly, but is a good conductor of electricity. It is quite insoluble in water, is attacked with difficulty by nitric acid, and is little affected by CARBON. 143 any of the other acids, or by the alkalies. It undergoes little change from exposure to air and moisture. The beams of the theatre at Herculaneum were converted into charcoal by the lava which overflowed that city; and during the lapse of seventeen hundred years the charcoal has remained as entire as if it had been formed but yesterday. It is exceedingly refractory in the fire, if excluded from the air, supporting the most intense heat which chemists are able to produce without change. Charcoal possesses the property of absorbing a large quantity of air or other gases at common temperatures, and of yielding the greater part of them again when it is heated. It appears from the researches of Saussure, that different gases are absorbed by it in different proportions. His experiments were performed by plunging a piece of red-hot charcoal under mercury, and intro- ducing it when cool into the gas to be absorbed. He found that charcoal prepared from box-wood, absorbs, during the space of 24 or 30 hours, of Ammonical gas - - 90 times its volume. Muriatic acid - - 85 Sulphurous acid - - 65 Sulphuretted hydrogen - 55 Nitrous oxide 40 Carbonic acid - - 35 Olefiant gas 35 Carbonic oxide - - 9.42 Oxygen - - - 9.25 Nitrogen - - 7.5 Hydrogen - - 1.75 The absorbing power of charcoal, with respect to gases, can- not be attributed to chemical action ; for the quantity of each gas, which is absorbed, bears no relation whatever to its affinity for charcoal. The effect is in reality owing to the peculiar po- rous texture of that substance, which enables it, in common with most spongy bodies, to absorb more or less of all gases, vapours, and liquids, with which it is in contact. This property is most remarkable in charcoal prepared from wood, especially in the compact varieties of it, the pores of which are numerous and small. It is materially diminished in reducing the charcoal to powder ; and in plumbago, which has not the requisite degree of porosity, it is wanting altogether. The porous texture of charcoal accounts for the general fact of absorption only; its power of absorbing more of one gas than of another, must be explained on a different principle. This ef- fect, though modified to all appearance by the influence of che- mical attraction, seems to depend chiefly on the natural elasticity of the gases. Those which possess such a great degree of elasticity as to have hitherto resisted all attempts to condense them into 144 CARBON. liquids, are absorbed in the smallest proportion j while those that admit of being converted into liquids by compression, are absorb- ed more freely. For this reason, charcoal absorbs vapours more easily than gases, and liquids than either. Messrs. Allen and Pepys determined experimentally the increase in weight experienced by different kinds of charcoal, recently ignited, after a week's exposure to the atmosphere. The char- coal from fir gained 13 per cent.; that from lignum vitae, 9.6; that from box 14; from beech 16.3; from oak, 16.5; and from mahogany, 18. The absorption is most rapid during the first 24 hours. The substance absorbed is both water and atmospheric air, which the charcoal retains with such force, that it cannot be completely separated from them without exposure to a red heat. Vogel has observed that charcoal absorbs oxygen in a much greater proportion from the air than nitrogen. Thus, when re- cently ignited charcoal, cooled under mercury, was put into a jar of atmospheric air, the residue contained only 8 percent, of oxygen gas ; and if red-hot charcoal be plunged into water, and then in- troduced into a vessel of air, the oxygen disappears almost en- tirely. It is said that pure nitrogen may be obtained in this way. Charcoal likewise absorbs the odoriferous and colouring prin- ciples of most animal and vegetable substances. When coloured infusions of this kind are digested with a due quantity of charcoal, a solution is obtained, which is nearly, if not quite, colourless. Tainted flesh may be rendered sweet and eatable by this means, and foul water may be purified by filtering through charcoal. The substance commonly employed to decolourize fluids is animal charcoal reduced to a fine powder. It loses the property of ab- sorbing colouring matters by use, but recovers it by being heated to redness. Charcoal is highly combustible. When strongly heated in the open air, it takes fire, and burns slowly. In oxygen gas, its com- bustion is lively, and accompanied with the emission of sparks. In both cases it is consumed without flame, smoke, or residue, if quite pure; and carbonic acid gas is the product of its com- bustion. The pure inflammable principle, which is the characteristic ingredient of all kinds of charcoal, is called carbon. Wood- charcoal contains about l-50th its weight of alkaline and earthly salts, which constitute the ashes when this species of charcoal is burned. Charcoal derived from spirit of wine is almost quite pure ; and the diamond is carbon in a state of absolute purity. The diamond appears to be the hardest substance in nature. Its texture is crystalline in a high degree, and its cleavage very perfect. Its primary form is the octahedron. It has a specific gravity of 3.520. Acids and alkalies do not act upon it; and it bears the most intense heat in close vessels without fusing or undergoing any perceptible change. Heated to 14° W., in the CARBON. 145 open air, it is entirely consumed. Newton first suspected it to be combustible from its great refracting power, a conjecture which was rendered probable by the experiments of the Floren- tine academicians in 1694, and which was subsequently confirmed by several philosophers. Lavoisier first proved it to contain carbon by throwing the sun's rays, concentrated by a powerful lens, upon a diamond contained in a vessel of oxygen gas. The diamond was consumed entirely, oxygen disappeared, and car- bonic acid was generated. The combining proportion or atomic weight of carbon is 6. Carbon and Oxygen. There are two compounds of carbon and oxygen; carbonic oxide and carbonic acid. No compound of carbon and oxygen is known which contains a less quantity of oxygen than carbonic oxide. For this reason it is regarded as a combination of one proportion1 of carbon=6 and one of oxygen=8; and carbonic acid of one atom of carbon=6 and two of oxygen=16. The combining proportion of carbonic oxide is therefore 14, and that of carbonic acid 22. Carbonic Oxide Gas. When two parts, by weight, of well-dried chalk and one of pure iron filings are mixed together, and exposed in a gun- barrel to a red heat, a large quantity of uniform matter is evol- ved, which may be collected over water. On examination, it is found to contain two compounds of carbon and oxygen, one of which is carbonic acid, and the other carbonic oxide. By washing the mixed gases with lime water, the carbonic acid is absorbed, and the carbonic oxide gas is left in a state of purity. Carbonic oxide gas is colourless and insipid. It does not affect the blue colour of vegetables in any way; nor does it combine with lime or any of the pure alkalies. It is very spa- ringly dissolved by water. Lime-water does not absorb it, nor is its transparency affected by it. Carbonic oxide is inflammable. When a lighted taper is plunged into ajar full of that gas, the taper is extinguished; but the gas itself is set on fire, and burns calmly at its surface with a lambent blue flame. The sole product of its combustion, when the gas is quite pure, is carbonic acid. The blue flame which appears upon the surface of a charcoal fire, is caused by this gas. Carbonic oxide gas cannot support respiration. It acts inju- riously on the system; for if diluted with air, and taken into the lungs, it very soon occasions headache and other unpleasant feelings; and when breathed pure, it almost instantly causes pro- found coma. The specific gravity of carbonic oxide is 0.9721. T 146 CARBON. Carbonic Acid. Carbonic acid was discovered by Dr. Black in 1757, and de- scribed by him in his inaugural dissertation de Magnesia Alba, under the name of fixed air. He observed the existence of this gas in common limestone and magnesia, and found that it might be expelled from these substances by the action of heat or of acids. He also remarked that the same gas was formed during respiration, fermentation, and combustion. Its composition was first demonstrated synthetically by Lavoisier, who burned carbon in oxygen gas, and obtained carbonic acid as the product. The late Mr. Smithson Tennant illustrated its nature analytically by passing the vapour of phosphorus over chalk, or the carbonate of lime, heated to redness in a glass tube. The phosphorus took oxygen from the carbonic acid, charcoal in the form of a light black powder was deposited. Carbonic acid is most conveniently prepared for the purposes of experiment by the action of muriatic acid, diluted with two or three times its weight of water, on fragments of marble. The muriatic acid unites with the lime, forming a muriate of lime, and carbonic acid gas escapes with effervescence. Carbonic acid, as thus procured, is a colourless, inodorous, elastic fluid, which possesses all the physical characters of the gases in an eminent degree, and requires a pressure of 36 atmos- pheres to condense it into a liquid, its specific gravity is 1.5277. Carbonic acid extinguishes burning substances of all kinds. Bodies, when immersed in it, do not cease to burn from a want of oxygen only. It exerts a positive influence in checking combus- tion, as appears from the fact, that a candle cannot burn in a gaseous mixture composed of four measures o£ atmospheric air, and one of carbonic acid. It is not better qualified to support the respiration of animals, its presence, even in moderate proportion, being soon fatal. An animal cannot live in air which contains sufficient carbonic acid for extinguishing a lighted candle ; and hence the practical rule of letting down a burning taper into old wells or pits before any one ventures to descend. When an attempt is made to inspire pure carbonic acid, a violent spasm of the glottis takes place, which prevents the gas from entering the lungs. If it be so much diluted with air as to admit of its passing the glottis, it acts as a narcotic poison on the system. It is this gas which has often proved destructive to persons sleeping in a confined room with a pan of burning charcoal. Carbonic acid is quite incombustible, and cannot be made to unite with an additional portion of oxygen. Lime water becomes turbid when brought into contact with carbonic acid. Hence lime water is not only a valuable test of CARBON. 147 the presence of carbonic acid, but is frequently used to withdraw it altogether from any gaseous mixture that contains it. Carbonic acid is absorbed by water. This may be easily de- monstrated, by agitating the gas with that liquid, or by leaving a jar full of it inverted over water. In the first case the gas disap- pears in the course of a minute ; in the latter it is absorbed gradually. Recently boiled water dissolves its own volume of carbonic acid at the common temperature and pressure ; but it will take up much more if the pressure be increased. The quan- tity ofthe gas absorbed is in exact ratio with the compressing force ; that is, water dissolves twice its volume when the pressure is doubled, and three times its volume, when the pressure is trebled. A saturated solution of carbonic acid may be made by passing a stream of the gas through a vessel of cold water during the space of half an hour, or still better by the use of a Woulfe's bottle or Nooth's apparatus, so as to aid the absorption by pres- sure. Water and other liquids which have been charged with carbonic acid under great pressure, lose the greater part of the gas when the pressure is removed. Water, which is fully satu- rated with carbonic acid gas, sparkles when it is poured from one vessel into another.* The solution has an agreeable acidulous taste, and gives to litmus paper a red stain which is lost on ex- posure to the air. On the addition of lime-water to it, a cloudi- ness is produced, which at first disappears, because the carbonate of lime is soluble in an excess of carbonic acid; but a perma- nent precipitate ensues when the free acid is neutralized by an additional quantity of lime water. The water which contains carbonic acid in solution is wholly deprived of the gas by boil- ing. Removal of pressure from its surface by means of the air- pump has a similar effect. The agreeable pungency of beer, porter, and ale, is in great measure owing to the presence of carbonic acid, by the loss of which, on exposure to the air, they become stale. All kinds of spring and well water contain carbonic acid, which they absorb from the atmosphere, and to which they partly are indebted for their pleasant flavour. Boiled water has an insipid taste from the absence of carbonic acid. A knowledge of the exact composition of carbonic acid gas is of very great importance. Oxygen gas, in combining with car- bon, so as to form carbonic acid, suffers no change of volume; or, in other words, carbonic acid contains its own volume of oxygen. It hence follows lhat 100 cubic inches, or 46.597 grains of car- bonic acid, consist of 100 cubic inches, or 33.888 grains of oxy- gen, united with 12.709 grains (46.597—33.8SS) of carbon. Now, 12.709 : 33.88S : : 6 : 16. * This is the common soda water of the shops. 148 CARBON. and since, 6 is the combining proportion of carbon, carbonic acid is composed of Carbon . 6.1 proportion, Oxygen . 16 . 2 proportions. By a rule which is given hereafter, it may be calculated that carbon, if supposed to exist in the form of vapour, would have a specific gravity of 0.4166 ; from which it follows, that 100 cubic inches of the vapour of carbon, at 60° F., and when the baro- meter stands at 30 inches, would weigh 12.709 grains. Conse- quently, 100 cubic inches of carbonic acid gas are composed of Oxygen gas . 100 cubic inches. Vapour of Carbon 100 cubic inches. Carbonic acid is always present in the atmosphere, even at the summit ofthe highest mountains, or at a distance of several thou- sand feet above the ground. Its presence may be demonstrated by exposing lime water in an open vessel to the air, when its sur- face will soon be covered with a pellicle, which is carbonate of lime. The orign ofthe carbonic acid is obvious. Besides being formed abundantly by the combustion of all substances which contain carbon, the respiration of animals is a fruitful source of it, as may be proved by breathing for a few minutes into lime water: and it is also generated in all the spontaneous changes to which dead animal and vegetable matters are subject. The car- bonic acid proceeding from such sources, is commonly diffused equably through the air; but when any of these processes occur in low confined situations, as at the bottom of old wells, the gas is then apt to accumulate there, and form an atmospher called choke damp, which is fatal to any animals that are placed in it. These accumulations happily never take place, except when there is some local origin for the carbonic acid ; for example, when it is generated by fermentative processes going on at the surface of the ground, or when it issues directly from the earth, as happens at the Grotto del Cane in Italy, and at Pyrmont in Westphalia. There is no real foundation for the opinion that carbonic acid can separate itself from the great mass of the atmosphere, and accumulate in a low situation merely by the force of gravity. Such a supposition is contrary to the well-known tendency of gases to diffuse themselves equally though one another. It is also contradicted by observation ; for many deep pits, which are free from putrefying organic remains, though otherwise favoura- bly situated for such accumulations, contain good atmosphe- ric air. Though carbonic acid is the product of many natural opera- tions, chemists have not hitherto noticed any increase in the quantity which is contained in the atmosphere. The only known process which tends to prevent an increase in its proportion, is that of vegetation. Growing plants purify the air by withdraw- CARBON. 149 ing carbonic acid, and yielding an equal volume of pure oxygen in return ; but whether a full compensation is produced by this cause, has not yet been satisfactorily determined. Carbonic acid is contained in the earth. Many mineral springs are highly charged with it. In combination with lime, it forms extensive masses of rock, which geologists have found to occur in all countries, and in every formation. Carbonic acid unites with alkaline substances, and the salts so constituted are called carbonates. Its acid properties are feeble. When a succession of electric sparks is passed through carbonic acid confined over mercury, a portion of that gas is converted into carbonic oxide and oxygen. When a mixture of hydrogen and carbonic acid gases is electrified, a portion of the latter yields one half of its oxygen to the former; water is generated, and car- bonic oxide produced. Compounds of Carbon with Nitrogen. Bicarburet of Nitrogen, or Cyanogen Gas. Cyanogen gas was discovered in]1815 by M. Gay-Lussac; it is prepared by heating the cyanuret of mercury, carefully dried, in a small glass retort, by means of a spirit lamp. The retort, at the close of the process, contains a small residue of charcoal, derived from the cyanogen itself, a portion of which is decom- posed by the temperature employed in its formation ; but no free nitrogen is disengaged till towards the close ofthe process. Cyanogen gas is colourless, and has a strong pungent and very peculiar odour. At the temperature of 45° F., and under a pressure of 3.6 atmospheres, it is a limpid liquid, which resumes the gaseous form when the pressure is removed. It extinguishes burning bodies ; but is inflammable, and burns with a beautiful and characteristic purple flame. It can support a strong heat without decomposition. Water, at the temperature of 60° F., absorbs 4.5 times, and alcohol 23 times, its volume of the gas. The aqueous solution reddens litmus paper; but this is not to be ascribed to the gas itself, but to the presence of acids which are generated by the decomposition of cyanogen and water. Cyanogen consists by weight of Nitrogen - 29.652 - 14 - one atom. Carbon - 25.418 - 12 - two atoms. The specific gravity is 1.8054. Cyanogen, from this view of its composition, is a bicarburet of nitrogen ; but for the sake of convenience we shall employ the term cyanogen, proposed by its discoverer ; from xvavos, blue, and ytn'oco, I generate ; because it is an essential ingredient of Prussian blue. All the compounds of cyanogen, which are not acid, are called cyanurets or cyanides. 150 CARBON. Cyanogen, though a compound body, has a remarkable ten- dency to combine with elementary substances. Thus it is capa- ble of uniting with the simple non-metallic bodies, and evinces a strong attraction for metals. When potassium, for instance, is heated in cyanogen, such an energetic action ensues, that the metal becomes incandescent, and a cyanuret of potassium is generated. The affinity of cyanogen for metallic oxides, on the contrary, is comparatively feeble. It enters into direct combi- nation with a few alkaline bases only, and these compounds are by no means permanent. From these remarks it is apparent that cyanogen has no claim to be regarded as an acid. Cyanogen and Oxygen.—Cyanic Acid. Chemists are acquainted with two acid compounds of cyanogen and oxygen ; and it is remarkable, that though the properties of these acids are quite different, their elements, according to the best analyses we possess, are united in the same proportion. That two or more different substances may be composed of the same elements combined in the same ratio, is a fact which can hardly be questioned. But since examples of the kind are as yet exceedingly rare, it will be proper, before admitting this similarity of composition in the present instance, to suspend our judgment till the analysis of the two cyanic acids shall have been repeated and confirmed by other chemists. In the mean time, however, we shall describe each under the term of cyanic add. Cyanic acid of M. Wohler. It is stated by Gay-Lussac, that cyanogen gas is freely absorbed by pure alkaline solutions ; and he expresses the opinion that the alkali combines directly with the cyanogen. It appears, however, from the experiments of M. Wohler, that, by decomposition of water, hydrocyanic and cyanic acids are formed under these circumstances; and, consequently, that alkaline solutions act upon cyanogen in the same manner as on chlorine, iodine, and sulphur. But the salts of cyanic acid cannot conveniently be procured in this way owing to the diffi- culty of separating the cyanate from the hydrocyanate that accompanies it. M. Wohler finds that the cyanate of potassa may be procured in large quantity by mixing the ferrocyanate of potassa with an equal weight of the peroxide of manganese, in fine powder, and exposing the mixture to a low red heat. The cyanogen of the ferrocyanic acid receives oxygen from the manganese, and is converted into cyanic acid, which unites with the potassa. The ignited mass is then boiled in alcohol of 86 per cent.; and, as the solution cools, the cyanate is deposited in small tabular crystals. The only precaution necessary in this process is to avoid too high a temperature. The cyanic acid is characterized by the facility with which it CARBON. 151 is resolved by water into carbonic acid and ammonia. This change is effected merely by boiling an aqueous solution of the cyanate of potassa; and it takes place still more rapidly when an attempt is made to decompose the cyanate by means of another acid. If the acid is diluted, the cyanic acid is instantly decomposed, and the carbonic acid escapes with effervescence. But, on the contrary, if a concentrated acid is employed, then the cyanic acid resists decomposition for a short time, and emits a stong odour of vinegar. The cyanic acid forms a soluble salt with baryta, but insoluble ones with the oxides of lead, mercury, and silver. If the cyanate of potassa is quite pure, it gives a white precipitate with nitrate of silver, and the cyanate of silver so formed dissolves without residue in dilute nitric acid. Cyanic acid, according to the analysis of M. Wohler, is com- posed of 26 parts or one atom of cyanogen, and eight parts or one atom of oxygen. The existence of cyanic acid was suspected by M. Vauquelin before it was actually discovered by Wohler. The experiments of the former chemist led him to the opinion that a solution of cyanogen in water is gradually converted into hydrocyanic, cyanic, and carbonic acids, and ammonia; and he supposed alkalies to produce a similar change. He did not establish the fact, however, in a satisfactory manner. Cyanic acid of M. Liebig. A powerfully detonating compound of mercury was described in the Philosophical Transactions for 1800, by Mr. E. Howard. It is prepared by dissolving 100 grains of mercury in a measured ounce and a half of nitric acid of spe- cific gravity 1.3; and adding, when the solution has become cold, two ounces, by measure, of alcohol, the density of which is 0.849. The mixture is then heated till a moderately brisk effervescence takes place, during which the fulminating compound is generated. A similar substance may be made by treating silver in the same manner. The conditions necessary for forming these compounds are, that the silver or mercury be dissolved in a fluid which con- tains so much free nitric acid and alcohol, that, on the applica- tion of heat, nitric ether shall be freely disengaged. Fulminating silver and mercury bear the heat of 212°, or even of 260° F., without detonating; but a higher temperature, or slight percussion between two hard bodies, causes them to ex- plode with violence. The nature of these compounds was dis- covered in 1823 by M. Liebig, who demonstrated that they are salts, composed of a peculiar acid, which he termed fulminic acid, in combination with the oxide of mercury or of silver. Ac- cording to an analysis of fulminating silver, made by M. Liebig and Gay-Lussac, the acid of the salt is composed of 26 parts or one atom of cyanogen, and eight parts or one atom of oxygen. It is therefore a real cyanic acid, and its salts may with propriety be 152 CARBON. termed cyanates. The fulminating silver is a cyanate of the oxide of silver; and is found to contain one atom of each element. It is remarkable that the oxide of silver cannot be entirely se- parated from cyanic acid by means of an alkali. On digesting the cyanate of silver in potassa, for example, one atom of the ox- ide of silver is separated, and a double cyanate is formed, which consists of two atoms of cyanic acid, one atom of the oxide of silver, and one atom of potassa. Similar compounds may be pro- cured by substituting other alkaline substances, such as baryta, lime or magnesia, for the potassa. These double cyanates are capable of crystallizing; and they all possess detonating pro- perties. From the presence of the oxide of silver in the double cyanates, it was at first imagined that this oxide actually constitutes a part of the acid; but since several other substances, such as the ox- ides of mercury, zinc, and copper, may be substituted for that of silver, this view can no longer be admitted. From some very recent experiments of M. Serullas the cyanic acid appeared to have been obtained in a separate state, his pro- cess is to dissolve the protochlorite of cyanogen in water, and after evaporating the solution to dryness, to continue the heat as long as muriatic acid vapours are given off. By this operation the water is decomposed, its hydrogen combines with the chlorine and forms muriatic acid, and its oxygen unites to the cyanogen and forms the cyanic acid, the former is driven of by the heat, and the latter remains in the vessel. Cynogen and Hydrogen. Hydrocyanic or Prussic Acid. The prussic acid was discovered in 1782 by Scheele, and Berthollet afterwards ascertained that it contains carbon, ni- trogen, and hydrogen ; but Gay-Lussac first procured it in a pure state, and by the discovery of cyanogen was enabled to determine its real nature. Pure hydrocyanic or prussic acid may be prepared by heating the cyanuret of mercury in a glass retort with two thirds of its weight of concentrated muriatic acid. By an intercharge of ele- ments, the cyanogen ofthe cyanuret unites with hydrogen, form- ing hydrocyanic acid, while a muriate of the peroxide of mercu- ry remains in the retort. The vapour ofthe hydrocyanic acid, as it rises, is mixed with moisture and muriatic acid. It is separa- ted from the latter by being conducted through a narrow tube over fragments of marble, with the lime of which the muriatic acid unites. It is next dried by means ofthe chloride of calcium, and is subsequently collected in a tube surrounded with ice or snow. CARBON. 153 Vauquelin proposes the following process as affording a more abundant product than the preceding. It consists in filling a narrow tube, placed horizontally, with fragments of the cy- anuret of mercury, and causing a current of sulphuretted hydro- gen gas to pass slowly along it. The instant that gas comes in contact with the cyanuret, dou- ble decomposition ensues, and hydrocyanic acid and the black sulphuret of mercury are generated. The progress of the sul- phuretted hydrogen along the tube may be distinctly traced by the change of colour, and the experiment may be closed as soon as the whole ofthe cyanuret has become black. It then only re- mains to expel the hydrocyanic acid by a gentle heat, and collect it in a cool receiver. This process is elegant, easy of execution, and productive. Pure hydrocyanic acid is a limpid colourless fluid, of a strong odour, similar to that of peach-blossoms. It excites at first a sensation of coolness on the tongue, which is soon followed by beat; but when diluted, it has the flavour of bitter almonds. Its specific gravity at 45° F. is 0.7058. It is so exceedingly volatile, that its vapours during warm weather may be collected over mercury. Its point of ebullition is 79° F., and at zero it congeals. When a drop of it is placed on a piece of glass, it becomes solid, because the cold produced by the evaporation of one portion is such as to freeze the remainder. It unites with water and alcohol in every proportion. Pure hydrocyanic acid is a powerful poison. A single drop of it placed on the tongue of a dog causes death in the course of a very few seconds ; and small animals, when confined in its vapour, are rapidly destroyed. On inspiring the vapour, diluted with atmospheric air, head ache and giddiness supervene ; and for this reason the pure acid should not be made in close apartments during warm weather. The distilled water from the leaves ofthe Prunus lauro-cerasus owes its poisonous quality to the presence of this acid. Pure hydrocyanic acid, even when excluded from air and mois- ture, is very liable to spontaneous changes, owing to the tendency of its elements to form new combinations. These changes some- times commence within an hour after the acid is made, and it can rarely be preserved for more than two weeks. The commence- ment of decomposition is marked by the liquid acquiring a reddish brown tinge. The colour then gradually deepens, a matter like charcoal subsides, and ammonia is generated. On analyzing the black matter, it was found to contain carbon and nitrogen. The acid may be preserved for a longer period if diluted with water, but even then it undergoes gradual decomposition. Hydrocyanic acid reddens litmus paper feebly, and unites with most alkaline bases, forming salts which are termed prussiates or hydrocyanates. It is a weak acid ; for it does not decompose the 154 CARBON. carbonates, and no quantity of it can destroy the alkaline re-ac- tion of potassa. Its salts are poisonous ; they are all decompos- ed by carbonic acid, and have the odour of hydrocyanic acid, a character by which the hydrocyanates may easily be recog- nised. Hydrocyanic acid is resolved by galvanism into hydrogen and cyanogen, the former of which appears at the negative, and the latter at the positive pole. When its vapour is conducted through a red-hot porcelain tube, partial decompositon ensues. Charcoal is deposited, and nitrogen, hydrogen, and cyanogen gases are set at liberty; but the greater part of the acid passes over unchanged. Electricity produces a similar effect. The vapour of hydrocyanic acid takes fire on the approach of flame; and with oxygen gas it forms a mixture which detonates with the electric spark. The pro- ducts of the combustion are nitrogen, water, and carbonic acid. The composition of hydrocyanic acid is shown by the following simple but decisive experiment of Gay-Lussac. If a quantity of potassium, precisely sufficient for absorbing 50 measures of pure cyanogen gas, is heated in 100 measures of hydrocyanic acid vapour, the cyanuret of potassium is generated, a diminution of 50 measures takes place, and the residue is pure hydrogen. From this it appears that hydrocyanic acid vapour is composed of equal volumes of cyanogen and of hydrogen, united without any condensation ; and, consequently, these two gases combine, by weight, according to the ratio of their densities. The com- position of hydrocyanic acid may, therefore, be thus stated :— By Volume. By Weight. Cyanogen 50 - - 1.8054—26, one atom. Hydrogen 50 - - 0.0694 1, one atom. 100 acid vapour. The atomic weight of hydrocyanic acid is 27. The specific gravity of its vapour is, of course, the mean of its constituents, or 0.9374; as determined directly by Gay-Lussac, its density is 0.9479. From the powerful action of hydrocyanic acid on the animal economy, this substance, in a diluted form, is sometimes em- ployed medicinally. It may be procured of any given strength by dissolving the cyanuret of mercury in water, and passing a current of sulphuretted hydrogen gas through the solution till the whole of the cyanuret is decomposed. The excess of sul- phuretted hydrogen is removed by agitation with carbonate of lead, and the hydrocyanic acid is then separated from the inso- luble matters by filtration. The quality of dilute hydrocyanic acid, however prepared, is very variable, owing to the volatility of the acid, and its ten- CARBON. 155 dency to spontaneous decomposition. On this account, it should be made only in small quantities at a time, kept in well-stopped bottles, and excluded from the light. The best way of estimat- ing the strength of any solution is that proposed by Dr. Ure. To 100 grains, or any other convenient quantity of the acid, con- tained in a phial, small quantities of the peroxide of mercury in fine powder are successively added, till it ceases to be dissolved. The weight of the peroxide which is dissolved, divided by four, gives the quantity of real hydrocyanic acid present. The presence of free hydrocyanic acid is easily recognised by its odour. Chemically, it may be detected by agitating the fluid, supposed to contain it, with the oxide of mercury in fine powder. Double decomposition ensues, by which water and the cyanuret of mercury are generated; and on evaporating the solution slowly, the latter is obtained in the form of crystals. Compounds of Hydrogen and Carbon. Chemists have for several years been acquainted with two dis- tinct compounds of carbon and hydrogen, the carburetted hydro- gen and defiant gas; but the researches of M. Faraday have recently enriched the science by the discovery of two new sub- stances of a similar nature, and the same able chemist has de- monstrated the existence of others, though he has hitherto been unable to obtain them in an insulated form. According to Dr. Thomson, naphtha and naphthaline are likewise pure carburets of hydrogen. Light Carburetted Hydrogen. This gas is sometimes called heavy inflammable air, the inflam- mable air of marshes, hydro-carburet, and proto-carburet of hy- drogen. Dr. Thomson proposed the term of bi-hydroguret of carbon; but it is more generally known by the name of light car- buretted hydrogen. It is formed abundantly in stagnant pools during the spontaneous decomposition of dead vegetable matter; and it may readily be procured by stirring the mud at the bot- tom of them, and collecting the gas, as it escapes, in an inverted glass vessel. In this state it is found to contain l-20th of car- bonic acid gas, which may be removed by means of lime water or a solution of pure potassa, and l-15th or I-20th of nitrogen. This is the only convenient method of obtaining it. Light carburetted hydrogen is tasteless, and nearly inodorous, and it does not change the colour of litmus or turmeric paper. Water absorbs about l-60th of its volume. It extinguishes all burning bodies, and is of course unable to support the respiration of animals. It is highly inflammable, and when a jet of it is set on fire, it burns with a yellow flame, and with a much stronger 156 CARBON. light than is occasioned by hydrogen gas. With a due propor- tion of atmospheric air or oxygen gas, it forms a mixture which detonates powerfully with the electric spark, or by the contact of flame. The sole products of the explosion are water and car- bonic acid. When 100 measures are detonated with rather more than twice their volume of oxygen, the whole of the inflammable gas, and precisely 200 measures of 'the oxygen, disappear, water is con- densed, and 100 measures of carbonic acid are produced. From this it maybe inferred, that 100 cubic inches of light carburetted hydrogen contain 100 cubic inches ofthe vapour of carbon and 200 cubic inches of hydrogen; and that it is composed by weight of Carbon 6 or one atom. Hydrogen 2 or two atoms. Its atomic weight is consequently 8. From the same data it follows that 100 cubic inches of light carburetted hydrogen, at 60° F., and when the barometer stands at 30 inches, must weigh 16.939 grains, and its specific gravity is therefore 0.5554. This calculated result is almost identical with the density ofthe gas, as determined directly by experiment. Light carburetted hydrogen is not decomposed by electricity, or by being passed through red-hot tubes, unless the temperature is very great. It may be inferred from the experiments of Ber- thollet, and from the phenomena that attend the formation of oil gas at high temperatures, that light carburetted hydrogen is re- solved into its elements, at least in part, when the heat is very intense. It follows, from the nature of the gas, that for each volume so decomposed, two volumes of hydrogen must be set free. Chlorine and light carburetted hydrogen do not act on each other at common temperatures, when quite dry, even if they are exposed to the direct solar rays. If the gases are moist, and the mixture is kept in a dark place, still no action ensues; but if light be admitted, particularly sunshine, then decomposition fol- lows. The nature of the product depends upon the proportion ofthe gases. If four measures of chlorine and one of light car- buretted hydrogen are present, carbonic and muriatic acid gases will be produced,—effects which may be thus explained. Two volumes of chlorine combine with two volumes of hydrogen con- tained in the carburetted hydrogen, and the other two volumes of chlorine decompose so much water as will likewise give two volumes of hydrogen,—which forms muriatic acid ; while the oxygen of the water unites with the carbon, and converts it into carbonic acid. If there are three instead of four volumes of chlorine, then carbonic oxide will be generated instead of car- bonic acid, because one-half less water will be decomposed. If a mixture of chlorine and light carburetted hydrogen is electrified CARBON. 157 or exposed to a red heat, muriatic acid is formed, and charcoal is deposited. It was first ascertained by Dr. Henry, and his conclusions have been fully confirmed by the subsequent researches of Sir H. Davy, that the fire-damp of coal mines consists almost solely of light carburetted hydrogen. This gas often issues in enormous quantity from between beds of coal, and by collecting in mines, owing to deficient ventilation, gradually mingles with atmos- pheric air, and forms an explosive mixture. The first unprotected light which then approaches, sets fire to the whole mass, and a dreadful explosion ensues. These accidents, which were formerly so frequent and so fatal, are now comparatively rare, owing to the employment of the safety lamp ; and we conceive it to be de- monstrable, on the view that light carburetted hydrogen is the sole constituent of fire-damp, that accidents of the kind cannot occur at all, provided the gauze lamp is in a due state of repair, and is employed with the requisite precautions. For this inven- tion we are indebted to Sir H. Davy; and we must in justice remember that it is not, like many discoveries, the offspring of chance, but the fruit of elaborate experiment and close induc- tion, which originated solely with that philosopher, and which may be regarded as one of the happiest efforts of his genius. Sir H. Davy commenced the inquiry by determining the best proportion of air and light carburetted hydrogen for forming an explosive mixture. When the inflammable gas is mixed with three or four times its volume of air, it does not explode at all. It detonates feebly when mixed with five or six times its bulk of air, and powerfully when one to seven, or one to eight, is the pro- portion. With 14 times its volume, it still forms a mixture which is explosive; but if a larger quantity of air be admitted, a taper burns in it only with an enlarged flame. The temperature which is required for causing an explosion was next ascertained. It was found that the strongest explosive mixture might come in contact with iron or other solid bodies heated to redness, or even to whiteness, without detonating, pro- vided they are not in a state of actual combustion; whereas the smallest point of flame, owing to its higher temperature, instantly causes an explosion. The last important step in the inquiry, was the observation that flame cannot pass through a narrow tube. This led Sir H. Davy to the discovery that the power of tubes in preventing the trans- mission of flame is not necessarily connected with any particular length; and that a very short one will have the effect, provided its diameter is proportionally reduced. Thus a piece of fine wire gauze, which may be regarded as an assemblage of short small tubes, is quite impermeable to flame; and consequently if a com- mon oil lamp be completely surrounded with a cage of such gauze, it may be introduced into an explosive atmosphere of fire- 158 CARBON. damp and air, without kindling the mixture. This simple con- trivance, which is appropriately termed the safety-lamp, not only prevents explosion, but indicates the precise moment of danger. When the lamp is carried into an atmosphere charged with fire- damp, the flame begins to enlarge; and the mixture, if highly explosive, takes fire as soon as it has passed through the gauze and burns on its inner surface, while the light in the centre of the lamp is extinguished. Whenever this appearance is observed, the miner must instantly withdraw; for though the flame cannot communicate to the explosive mixture on the outside of the lamp, as long as the texture of the gauze remains entire, yet the heat emitted during the combustion is so great, that the wire, if ex- posed to it for a few minutes, would suffer oxidation, and fall to pieces. The peculiar operation of small tubes in obstructing the pas- sage of flame admits of a very simple explanation. Flame is gaseous matter heated so intensely as to be luminous; and Sir H. Davy has shown that the temperature necessary for producing this effect is far higher than the white heat of solid bodies. Now when flame comes in contact with the sides of very minute aper- tures, as when wire gauze is laid upon a burning jet of coal gas, it is deprived of so much caloric that its temperature instantly falls below the degree at which gaseous matter is luminous; and consequently, though the gas itself passes freely through the interstices, and is still very hot, it is no longer incandescent. Nor does this take place when the wire is cold only ;—the effect is equally certain at any degree of heat which the flame can com- municate to it. For since the gauze has a large extent of sur- face, and from its metallic nature is a good conductor of caloric, it loses heat with great rapidity. Its temperature, therefore, though it may be heated to whiteness, is always so far below that of flame, as to exert a cooling influence over the burning gas, and thus deprive it of its property of emitting light. defiant Gas. This gas was discovered in 1796 by some associated Dutch chemists, who gave it the name of Olefiant gas, from its property of forming an oily-like liquid with chlorine. It is sometimes called bi-carburetted or per-carburetted hydrogen, and hydroguret of carbon; but as none of these terms convey a precise idea of its nature, we shall employ the appellation proposed by its dis- coverers. Olefiant gas is prepared by mixing in a capacious retort six measures of strong alcohol with sixteen of concentrated sulphuric acid, and heating the mixture as soon as it is made by means of an Argand lamp. The acid soon acts upon the alcohol, effer- vescence ensues, and olefiant gas passes over. The chemical CARBON. 159 changes which take place are of a complicated nature, and the products numerous. At the commencement of the process, the olefiant gas is mixed only with a little ether; but in a short time the solution becomes dark, the formation of ether declines, and the odour of sulphurous acid begins to be perceptible; and to- wards the close of the operation, though olefiant gas is still the chief product, sulphurous acid is freely disengaged, some carbo- nic acid is formed, and charcoal in large quantity is deposited. The olefiant gas may be collected either over water or mercury. The greater part of the ether condenses spontaneously, and the sulphurous and carbonic acids may be separated by washing the gas with lime water, or a solution of pure potassa. The olefiant gas in this process is derived solely from the alco- hol ; and its production is owing to the strong affinity of sulphuric acid for water. Alcohol is composed of carbon, hydrogen, and oxygen; and from the proportion of its elements, it is inferred to be a compound of 14 parts or one atom of olefiant gas, united with 9 parts or one atom of water. It is only necessary, there- fore, in order to obtain olefiant gas, to deprive alcohol of the water which is essential to its constitution, and this is effected by sulphuric acid. The formation of ether, which occurs at the same time, will be explained hereafter. The other phenomena are altogether extraneous. They almost always ensue when sub- stances derived from the animal and vegetable kingdoms are sub- jected to the action of sulphuric acid. They occur chiefly at the close of the preceding process, in consequence of the excess of acid which is then present. Olefiant gas is a colourless elastic fluid, which has no taste, and scarcely any odour when pure. Water absorbs about one- eighth of its volume. Like the preceding compound, it extin- guishes flame, is unable to support the respiration of animals, and is set on fire when a lighted candle is presented to it, burn- ing slowly with the emission of a dense white light. With a proper quantity of oxygen gas, it forms a mixture which may be kindled by flame or the electric spark, and which explodes with great violence. To burn it completely, it should be detonated with four or five times its volume of oxygen. On conducting this experiment with the requisite care, Dr. Henry finds that for each measure of olefiant gas, precisely three of oxygen disappear, a deposition of water takes place, and two measures of carbonic acid are produced. From these data the proportion of its con- stituents may easily be deduced in the following manner. Two measures of carbonic acid contain two measures ofthe vapour of carbon, which must have been present in the olefiant gas, and two measures of oxygen. Two-thirds of the oxygen which had disappeared are thus accounted for, and the other third must have combined with hydrogen. But one measure of oxygen requires for forming water precisely two measures of hydrogen, 160 CARBON. which must likewise have been contained in the olefiant gas. It hence follows that 100 cubic inches contain, Grains. 200 cubic inches ofthe vapour of carbon, which weigh 25.418 200 - - hydrogen gas, which weigh 4.236 and consequently 100 cubic inches of olefiant gas must weigh - 29.654 Its specific gravity, accordingly, is 0.9722; whereas its density, as taken directly by Saussure, is 0.9852; by Henry, 0.967, and by Thomson, 0.97. Olefiant gas, by weight, consists of Carbon - 25.418 - 12 or two atoms. Hydrogen - 4.236 - 2 or two atoms. and therefore 14 is the weight of its atom. Olefiant gas, when a succession of electric sparks is passed through it, is resolved into charcoal and hydrogen ; and the latter of course occupies twice as much space as the gas from which it was derived. Olefiant gas is decomposed by being passed through red-hot tubes of porcelain. The nature ofthe products depends upon the temperature. By employing a very low degree of heat, it may probably be converted solely into carbon and light car- buretted hydrogen; and in this case no increase of volume can occur, because these two gases, for equal bulks, contain the same quantity of hydrogen. But if the temperature is high, then a great increase of volume takes place, a circumstance which indi- cates the evolution of free hydrogen, and consequently the total decomposition of some of the olefiant gas. On the New Carburets of Hydrogen discovered by Mr. Faraday. In the process of compressing oil gas in Gordon's conden- sing apparatus, during which the gas is subjected to a force equal to thirty atmospheres, a considerable quantity of liquid collects, which retains its fluidity at the common atmospheric pressure. This liquid, when recently received from the conden- ser, boils at 60°F. But as soon as the more volatile portions are dissipated, which happens before one tenth is thrown off, the point of ebullition rises to 100°F.; and the temperature gradually ascends to 250°F. before all the liquid is volatilized. This indi- cated the presence of several compounds, which differ in their degree of volatility ; and Mr. Faraday remarked that the boiling point was more constant between 176° and 190°F. than at any other temperature. He was hence led to search for a definite compound in the fluid which came over at that period ; and at length, by repeated distillations, and exposing the distilled liquid to a temperature of zero, he succeeded in obtaining a substance to which he has applied the term of bi-carburet of hydrogen. CARBON. 161 The bi-carburet of hydrogen, at common temperatures, is a colourless transparent liquid, which smells like oil gas, and has also a slight ordour of almonds. Its specific gravity is nearly 0.85 at ' OF. At 32°F. it congeals, and forms dentritic crystals on the sides of the glass. At zero it is transparent, bitter, and pulverulent, and is nearly as hard as loaf sugar. When exposed to the air at the ordinary temperature it evaporates, and it boils at 186°F. the density of its vapour, at 60°F. and when the baro- meter stands at 29.98 inches, is nearly 2.7760. The bi-carburet of hydrogen is very slightly soluble in water, but it dissolves freely in fixed and volatile oils, in ether, and in alcohol, and the alcoholic solution is precipitated by water. It is not acted on by alkalies. It is combustible, and burns with a bright flame and much smoke. When admitted to oxygen gas, so much vapour arises as to make a powerfully detonating mix- ture. Potassium heated in it does not lose its lustre. On pass- ing its vapour through a red-hot tube, it gradually deposits char- coal, and yields carburetted hydrogen gas. Chlorine, by the aid of sunshine, decomposes it with evolution of muriatic acid. Two triple compounds of chlorine, carbon, and hydrogen, are formed at the same time, one of which is a crystalline solid, and the other a dense thick fluid. The bi-carburet of hydrogen was analyzed in two ways. In the first, its vapour was passed over oxide of copper heated to redness; ana*in the second, it was detonated with oxygen gas. Carbonic acid and water were the sole products : and as the ab- sence of oxygen is established by the inaction of potassium, it follows that the bi-carburet consists of carbon and hydrogen only. Mr. Faraday infers from his analyses, that 100 measures ofthe inflammable vapour require 750 of oxygen for complete combus- tion ; that 150 measures of oxygen unite with 300 of hydrogen ; and that the remaining 600 combine with 600 of the vapour of carbon, forming 600 measures of carbonic acid gas. Consequently, 100 measures ofthe vapour are composed of Carbon - (0.4166x6) - 2.4996 - 36 - 6 atoms. Hydrogen - (0.0694x3) - 0.2082 - 3 - 3 atoms. The weight of its atom is therefore 39 ; and its specific gravi- ty, by calculation, is 2.7078. The second carburet of hydrogen discovered by Mr. Faraday, to which he has not given a name, was derived from the same source as the preceding. It is obtained by heating with the hand the condensed liquid from oil gas, and conducting the vapour which escapes through tubes cooled artificially to zero. A li- quid then condenses, which boils from a slight elevation of tem- perature, and before the thermometer rises to 32° F. is wholly reconverted into vapour. This vapour is highly combustible, and burns with a brilliant flame. Its specific gravity, at 60°F. and 29.94 of the barometer, X 162 CARBON. is about 1.9065. On being cooled to zero, it again condenses, and the specific gravity of this liquid at 54° is 0.627 ; so that among solids and liquids it is the lightest body known. Water absorbs the vapour sparingly; but alcohol takes it up in large quantity, and the solution effervesces on being diluted with water. Alkalies and muriatic acid do not affect it. Sul- phuric acid, on the contrary, absorbs more than 100 times its vol- ume of the vapour. A dark-coloured solution is formed, but no sulphurous acid is disengaged. From the analysis of this vapour, made by detonating it with oxygen gas, Mr. Faraday infers that each volume requires six of oxygen for complete combustion, and yields four volumes of car- bonic acid. It hence follows that 100 measures of the vapour contain 400 measures ofthe vapour of carbon and 400 of hydro- gen gas, and that this carburet of hydrogen consists, by weight, of Carbon - (0.4166x4) - 1.6664 - 24 - 4 atoms. Hydrogen - (0.0694x4) - 0.2776 - 4 - 4 atoms. The weight of its atom is therefore 28. Its density must be 1.9440; and Mr. Faraday regards this estimate of its specific gravity as nearer the truth than that above stated. The compo- sition of this substance was calculated by Dr. Thomson before the compound itself had been obtained in an insulated form. He terms it quadro-carburetted hydrogen, and is of opinion that it exists in sulphuric ether, combined with one atom of water. This view is justified by the proportion in which the elements of ether are united. The discovery of this substance has established a fact which is altogether new to chemists. The elements of the new car- buret are united in the proportion of 24 to 4, and those of olefiant gas in that of 12 to 2; that is, the carbon and hydrogen in both are in the ratio of 6 to 1, and therefore each may be regarded as a compound of one atom of its component principles. Hence it appears, that two substances may be identical with respect to the proportion of their constituents, and yet be quite distinct in their physical and chemical properties. This peculiarity is explicable on the supposition that the ulti- mate atoms of such compounds are differently disposed. It is to be presumed, that the smallest possible particle of olefiant gas contains two atoms of carbon and two atoms of hydrogen ; and that, in like manner, an integrant particle ofthe new compound of Mr. Faraday contains four atoms of each element. Neither of these substances could, perhaps, be formed by direct union of a single atom of carbon and a single atom of hydrogen. If a combination of the kind were to occur, a new conpound, dif- ferent from any known at present, would be the result. Such appears to be the only satisfactory mode of accounting for the phenomena. CARBON. 163 Naphtha from Coal Tar. This substance is obtained by the distillation of coal tar, and is termed Naphtha from its similarity to mineral naphtha. It has a strong and peculiar empyreumatic odour, and is highly inflam- mable. Potassium may be preserved in it without losing its lus- tre, which is a sufficient proof that it contains no oxygen. Ac- cording to Dr. Thomson, one measure of the vapour of naphtha contains six measures ofthe vapour of carbon, and six of hydro- gen gas ; or, by weight, that it consists of 36 or six atoms of car- bon, and 6 or six atoms of hydrogen. Naphthaline. This compound is likewise derived from coal tar. If the dis- tillation is conducted at a very gentle heat, the naphtha, from its greater volatility, first passes over; and afterwards the naphtha- line rises in vapour, and condenses in the neck of the retort as a white crystalline solid. Pure naphthaline is heavier than water, has a pungent aromatic taste, and a peculiar, faintly aromatic, odour, not unlike that of the narcissus. It is smooth and unctuous to the touch, is per- fectly white, and has a silvery lustre. It fuses at 180°, and as- sumes a crystalline texture in cooling. It volatilizes slowly at common temperatures, and boils at 410° F. Its vapour, in con- densing, crystallizes with remarkable facility in thin transparent laminae. Naphthaline is not very readily inflammed ; but when set on fire it burns rapidly, and emits a large^quantity of smoke. It is insoluble in cold, and dissolves very sparingly in hot water. Its proper solvents are alcohol and ether, and especially the latter. Olive oil, the oil of turpentine, and naphtha, likewise dissolve it. The alkalies do not act upon naphthaline. The acetic and oxalic acids dissolve it, forming pink-coloured solutions. Sul- phuric acid enters into direct combination with it, and forms a new and peculiar acid, which Mr. Faraday has described in the Philosophical Transactions for 1826, under the name of Sulpho- naphthalic acid. Naphthaline, according to the analysis of Dr. Thomson, is a sesquicarburet of hydrogen; that is, a compound of nine or an atom and a half of carbon, and one atom of hydrogen. It is de- sirable, however, that this- analysis should be repeated. On Coal and Oil Gas. The nature ofthe inflammable gases derived from the destruc- tive distillation of coal and oil was first ascertained by Dr. Henry, who showed, in several elaborate and able essays, that these 164 CARBON. gaseous products do not differ essentially from one another, but consist of a few well-known compounds, mixed in different and very variable proportions'. The chief constituents were found to be light carburetted hydrogen and olefiant gas, besides which they contain an inflammable vapour, free hydrogen, carbonic acid, carbonic oxide, and nitrogen gases. The discoveries of Mr. Faraday have elucidated the subject still farther, by proving that there exists in oil gas, and by inference in coal gas also, the vapour of several definite compounds of carbon and hydrogen, the presence of which, for the purposes of illumination, is ex- ceedingly important. The illuminating power of the ingredients of coal and oil gas is very unequal. Thus the carbonic oxide and carbonic acid are positively hurtfult; that is, the other gases would give more light without them. The nitrogen, of course, can be of no service. The hydrogen is actually prejudicial; because, though it evolves a large quantity of caloric in burning, it emits an exceedingly feeble light. The carburets of hydrogen are the real illuminating agents, and the degree of light emitted by these is dependant on the quantity of carbon which they contain. Thus olefiant gas illuminates much more powerfully than the light carburetted hy- drogen; and, for the same reason, the dense vapour of the qua- drocarburet of hydrogen emits a far greater quantity of light, for equal volumes, than the olefiant gas. From these facts, it is obvious that the comparative illuminat- ing power of different kinds of coal and oil gas may be estimated, approximately at least, by determining the relative quantities of the denser carburets of hydrogen which enter into their com- position. This may be done in three ways. 1. By their specific gravity. 2. By the quantity of oxygen required for their com- plete combustion. 3. By the quantity of gaseous matter con- densible by chlorine in the dark ; for chlorine, when light is excluded, condenses all the hydro-carburets, excepting the light carburetted hydrogen. Of these methods, the last is, perhaps, the least exceptionable. The formation of coal and oil gas is a process of considerable delicacy. Coal gas is prepared by heating coal to redness in iron retorts. The quality ofthe gas, as made at different places or at the same place at different times, is very variable, the density of some specimens having been found so low as 0.443, and that of others so high as 0.700. These differences arise in part from the nature of the coal, and partly from the mode in which the pro- cess is conducted. The regulation ofthe degree of heat is the chief circumstance in the mode of operating, by which the quality of the gas is affected. That the quality of the gas may be in- fluenced by this cause is obvious from the fact, that all the dense hydro-carburets are resolved by a strong red heat either into charcoal and light carburetted hydrogen, or into charcoal and CARBON. 165 hydrogen. Consequently, the gas made at a very high tempera- ture, though its quantity may be comparatively great, has a low specific gravity, and illuminates feebly. It is therefore an object of importance that the temperature should not be greater than is required for decomposing the coal effectually, and that the re- torts be so contrived as to prevent the gas from passing over a red-hot surface subsequently to its formation. These remarks apply with still greater force to the manufac- ture of oil gas, because oil is capable of yielding a much larger quantity of the heavy hydrocarburets than coal. The quality of oil gas from the same material is liable to so great variation from the mode of manufacture, that the density of some specimens has been found so low as 0.464, and that of others so high as 1.110. The average specific gravity of good oil gas is 0.900, and it should never be made higher. The true interest of the manu- facturer is to form as much olefiant gas as possible, with only a small proportion of the heavier hydrocarburets. If the latter predominate, the quantity of gas derived from a given weight of oil is greatly diminished ; and a subsequent loss is experienced by the condensation of the inflammable vapours when the gas is compressed, or while it is circulating through the distributing tubes. Coal gas, when first prepared, always contains sulphuretted hydrogen, and for this reason must be purified before being dis- tributed for burning. The process of purification consists in passing the gas under strong pressure through milk of lime, by which means the sulphuretted hydrogen may be entirely re- moved. But coal gas, after being treated in this manner, still retains some compound of sulphur, most probably, as Mr. Brande conjectures, the sulphuret of carbon, owing to the presence of which, sulphurous acid is generated during its combustion. Oil gas, on the contrary, needs no purification ; and as it is free from all compounds of sulphur, it yields in burning no sulphurous acid, and is therefore better fitted for lighting dwelling-houses than coal gas. With respect to the relative economy ofthe two gases, we may observe that the illuminating power of oil gas, of specific gravity 0.900, is about double that of coal gas of 0.600. In good coal districts, however, oil gas is fully three times the price of coal gas, and therefore in such situations, the latter is considerably cheaper. Salts. Carbonate of Ammonia.—The only method of procuring this salt is by mixing dry carbonic acid over mercury, with twice its volume of ammoniacal gas. It is a dry white volatile powder, of an ammoniacal odour, and alkaline reaction. From the propor- 166 CARBON. tion of its constituents by volume, it is easy to infer that it is com- posed, by weight, of 22 parts or one atom of carbonic acid, and 17 parts or one atom of ammonia. Bicarbonate of Ammonia.—This salt was formed by Berthol- let, by transmitting a cunent of carbonic acid gas through a so- lution of the common carbonate of ammonia of the shops. On evaporating the liquid by a gentle heat, the bicarbonate is depo- sited in small six-sided prisms, which have no smell, and very little taste. Berthollet ascertained that li; contains twice as much acid as the carbonate. Sesqui-carbonate of Ammonia.—The common carbonate of ammonia ofthe shops, the sub-carbonas ammoniac ofthe pharma- copoeia, is different from both the above compounds. It is prepared by heating a mixture of one part of muriate of ammonia, with one part and a half of the carbonate of lime, carefully dried. Double decomposition ensues during the process; muriate of lime re- mains in the retort, and the sesqui-carbonate of ammonia is sub- limed. The carbonic acid and ammonia are, indeed, in proper proportion in the mixture for forming the real carbonate; but from the heat employed in the sublimation, a part of the ammonia is disengaged in a free state. The salt thus formed, consists of 33 parts or an atom and a half of carbonic acid, of 17 parts or one atom of ammonia, and 9 parts or one atom of water. When recently prepared it is hard, compact, semi-transparent, of a crystalline texture, and pungent ammoniacal odour; but if exposed to the air, it loses w eight rapidly, and is converted into an opaque brittle mass, which is the bicarbonate. Carbonates. Carbonic acid combines with bases in different proportions forming carbonates, bi-carbonates, and sesqui-carbonates. The carbonates are formed by one proportion of the acid and one of the base; the bi-carbonates two ofthe acid and one of the base; and the sesqui-carbonates of one and a half of the acid and one ofthe base. The carbonates are distinguished from other salts by being de- composed with effervescence, owing to the escape of carbonic acid gas, by nearly all the acids. All the carbonates, excepting those of potassa, soda, and lithia, may be deprived of their acid by heat. The carbonates of baryta and strontia, and especially the former, require an intense white heat for decomposition ; those of lime and magnesia are reduced to the caustic state by a full red heat; and the other carbonates part with their carbonic acid when heated to dull redness. All the carbonates, excepting those of potassa, soda, and am- monia, are of sparing solubility in pure water; but all of them CARBON. 167 are more or less soluble in an excess of carbonic acid, owing doubtless to the formation of super-salts. The former nomenclature ofthe salts is peculiarly exceptiona- ble as applied to the carbonates. The two well-known carbo- nates of potassa, for example, are distinguished by the preposi- tions sub and super, as if the one had an alkaline, and the other an acid re-action; whereas, in fact, according to their action on test paper, they are both sub-salts. We shall adopt the nomen- clature which has been employed with other salts, applying the generic name of carbonate to those salts which contain one atom of carbonic acid, and one atom ofthe base,—compounds which may be regarded as neutral in composition, however they may act on the colouring matter of plants. Several of the carbonates occur native. Cyanate of Ammonia, is an interesting salt. From some late researches of Dr. Wohler, it appears to be precisely identical in its composition with purified urea, an animal product which we shall examine hereafter. It is obtained by acting on the cyanate of lead by liquid ammonia. It is composed of 1. Cyanic Acid • - 34 1. Ammonia - 17 1. Water - 9=G0 Hydro Cyanate of Ammonia, appears in cubical, or prismatic crystals, which are exceedingly volatile, and undergo rapid spon- taneous decomposition. As this is the first salt formed by the union* of a base with an hydracid, it will be proper to say a word on that subject. By the expression, salts of the hydracids, is meant those saline compounds, the acid of which contains hydro- gen as one of its elements. Most of the salts which are composed of a hydracid and a metallic oxide are so constituted, that the oxygen of the oxide contains a quantity of oxygen precisely sufficient for forming water with the hydrogen of the acid. This is true of all the neutral compounds containing a protoxide, without exception, and it likewise holds good in many other cases. CHAPTER II. In this chapter, we shall notice the chemical history of boron, silicon, zirconion, phosphorus, sulphur, selerium, tellunium, arse- nic, tin, and potassium. All these substances, except silicon and zirconion, agree in producing acids by combining with oxygen, and in forming analagous and peculiar compounds by uniting with hydrogen. The oxide of silicon seems also to possess some acid powers. Though experiment has not yet demonstrated that silicon and zirconion are capable of uniting to hydrogen, this, it 168 BORON. is probable, may yet be effected, and in a chain of substances, arranged according to their resemblances, their natural place is between boron and phosphorus. Carbon, it will be observed, stands between hydrogen and boron; with hydrogen it agrees in uniting to nitrogen, and in a number of other qualities, and with boron it is connected by many distinct analogies. The whole series of simple and compound substances noticed in this chapter, though in many respects very unlike each other, are nevertheless distinguished by certain, similar, and characteristic properties; but concerning these resemblances we shall speak more at large in another part of our work. When substances are classed according to their analogies, we suggest the propriety of changing the names of sulphur, phospho- rus, and selenium, to those of sulphuron, phosphoron, and sele- nion, as these are the only simple solid elements not metallic, which do not terminate in on. SECTION I. Boron. Sir H. Davy discovered the existence of Boron] in 1807, by exposing boracic acid to the action of a powerful galvanic battery; but he did not obtain a sufficient supply of it for determinifig its properties. It was procured in greater quantity by Gay-Lussac and Thenard in 1808, by heating boracic acid with potassium. The boracic acid is by this means deprived of its oxygen, and boron is set free. Boron is a dark olive-coloured substance, which has neither taste nor smell, and is a non-conductor of electricity. It is in- soluble in water, alcohol, ether, and oils. It does not decompose water, whether hot or cold. It bears an intense heat in cold ves- sels, without fusing or undergoing any other change, except a slight increase of density. Its specific gravity is about twice as great as that of water. It may be exposed to the atmosphere at common temperatures without change; but if heated to 600° F., it suddenly takes fire, oxygen gas disappears, and boracic acid is generated. It experiences a similar change when heated in nitric acid, or with any substance that yields oxygen with facility. Boracic acid.—This is the only known compound of boron and oxygen. As a natural product it is found in the hot springs of Lipari, and in those of Sasso in the Florentine territory. It is a constituent of several minerals, among which the datolite and boracite may in particular be mentioned. It occurs much more abundantly under the form of borax, a native compound of bo- racic acid and soda. It is prepared for chemical purposes by ad- BORON. 169 ding sulphuric acid to a concentrated solution of purified borax in boiling water, till the liquid acquires a distinct acid reaction. The sulphuric acid unites with the soda; and the boracic acid is deposited, when the solution cools, in a confused group of crys- tals, which are sometimes scaly, and sometimes assume the form of minute irregular prisms. It is then thrown on a filter, and edulcorated with cold water till the sulphate of soda and excess of sulphuric acid are entirely removed. Boracic acid in this state is a hydrate. Its precise degree of solubility in water has not been determined with accuracy ; but it is much more soluble in hot than in cold water. Boiling al- cohol dissolves it freely, and the solution, when set on fire, burns with a beautiful green flame ; a test which affords the surest indi- cation of the presence of boracic acid. Its specific gravity is 1.479. It has no odour, and its taste is rather bitter than acid. It reddens litmus paper feebly, renders turmeric paper brown like the alkalies, and effervesces with alkaline carbonates. From the weakness of its acid properties, all the borates, when in solution, are decomposed by the stronger acids. When hydrous boracic acid is exposed to a gradually increas- ing heat in a platinum crucible, its water of crystallization is wholly expelled, and a fused mass remains which bears a white heat without volatilizing. On cooling, it forms a hard, colour- less, transparent glass, which is anhydrous boracic acid. If the water of crystallization be driven off by the sudden application of a strong heat, a large quantity of boracic acid is carried away during the rapid escape of watery vapour. The same happens, though in a less degree, when a solution of boracic acid in water is boiled briskly. Vitrified boracic acid should be preserved in well stopped vessels ; for if exposed to the air, it absorbs water, and gradually loses its transparency. Its specific gravity is 1.803. It is exceedingly fusible, and communicates this property to the substances with which it unites. For this reason borax is often used as a flux. The most obvious mode of determining the composition of bo- racic acid is to burn a known quantity of boron, and ascertain its increase of weight when the combustion ceases. This method, however, though apparently simple, is very difficult of execution ; for the boracic acid fuses at the moment of being generated, and by glazing the surface ofthe unconsumed boron, protects it from oxidation. Hence it was that the experiments performed by Gay-Lussac and Thenard on this subject, led to results widely different from those which Sir H. Davy obtained by a similar pro- cess. The atomic weight of boron is 8, and boracic acid is composed of Boron - - 8, or one atom. Oxygen - - 16, or two atoms. Consequently, the combining proportion of boracic acid is 24. Y 170 BORON. Crytallized boracic acid, is probably composed of Boracic acid - - 24, or one atom. Water - - 18, or two atoms Borruretted Hydrogen. This gas was first produced by Gmelin. He mixed together four parts of iron filings and one part of boracic acid, and ex- posed them in a crucible to a strong heat for half an hour. When the resulting mass was dissolved in muriatic acid, the borruretted hydrogen gas was produced. It burns with a reddish yellow flame surrounded by a green border; during the combustion white fumes are formed, and a garlicy odour is produced. The affinity of boron for hydrogen appears, however, to be exceedingly feeble. Salt. Boracic acid combines with ammonia, and forms the Borate of Ammonia, which is an unimportant salt. Borates. As the boracic is a feeble acid, it neutralizes the alkalies in an imperfect manner, and on this account the borates of soda, potas- sa, and ammonia, have always an alkaline reaction. For the same reason, when the borates are digested in any of the more powerful acids, such as the sulphuric, nitric, or muriatic, the bo- racic acid is separated from its base. This does not happen, however, at high temperatures ; for boracic acid, owing to its fixed nature, decomposes at a red heat all salts, not excepting sulphates, the acid of which is volatile. The borates of the alkalies are soluble in water, but all the other salts of this acid are of sparing solubility. They are not decomposed by heat, and the alkaline and earthy borates resist the action of heat and combustible matter. They are remark- ably fusible, a property obviously owing to the great fusibility of boracic acid itself. The borates are distinguished by the following character:— By digesting any borate in a slight excess of strong sulphuric acid, evaporating to dryness, and boiling the residue in strong alcohol, a solution is formed, which has the property of burning with a green flame. ( 171 ) SECTION II. Silicon. That silica^ or siliceous earth, is composed of a combustible body united with oxygen, was demonstrated by Sir H. Davy ; for on bringing the vapour of potassium in contact with pure silica, heated to whiteness, a compound of silica and potassa*resulted, through which was diffused the inflammable base of silica in the form of black particles like plumbago. To this substance, on the supposition of its being a metal, the term silicium was applied. But though this view has been adopted by most chemists, there is now little doubt that the base of silica is a non-metallic body, analogous to carbon and boron. The recent researches of Ber- zelius appear decisive of this question. A substance which wants the metallic lustre, and is a non-conductor of electricity, cannot be regarded as a metal. Pure silicon was procured by Berzelius in the year 1824, by the action of potassium on fluosilicic acid gas. The most con- venient method of preparing it is by heating potassium with the dry fluate of silica and potassa. The residue, after being well washed with hot water, is heated to redness to expel a little hy- drogen which was united to the silicon, and it is then digested in dilute fluoric acid, with the view of dissolving adherent particles of silica. Silicon obtained in this manner has a dark nut-brown colour, without the least trace of metallic lustre. It is a non-conductor of electricity. It is incombustible in air and in oxygen gas ; and may be exposed to the flame of the blow-pipe without fusing or undergoing any other change. It is neither dissolved nor oxidiz- ed by the sulphuric, nitric, muriatic, or fluoric acids ; but a mix- ture ofthe nitric and fluoric acids dissolves it readily even in the cold. Silicon is not changed by ignition with chlorate of potassa. In nitre it does not deflagrate until the temperature is raised so high that the acid is decomposed; and then the oxidation is affected by the affinity of the disengaged alkali for silica co-operating with the attraction of oxygen for silicon. For a similar reason it burns vividly when brought into contact with the carbonate of potassa or soda, and the combustion ensues at a temperature con- siderably below redness. It explodes, in consequence of a co- pious evolution of hydrogen, when it is dropped upon the fused hydrates of potassa, soda, or baryta. 172 SILICON. Oxide of Silicon or Silica. Silica exists in the earth in great quantity. It enters into the composition of most of the earthy minerals; and under the name of quartz rock, forms independent mountainous masses. It is the chief ingredient in sand-stones; and flint, calcedony, rock crys- tal, and other analogous substances, consist almost solely of silica. Siliceous earth of sufficient purity for most purposes may, indeed, be procifred by igniting transparent specimens of rock crystal, throwing them while red hot into water, and then reducing them to powder. Pure silica, in this state, is a light white powder, which feels rough and dry when rubbed between the fingers, and is both in- sipid and inodorous. It is fixed in the fire, and is very infusible; but fuses before the oxy-hydrogen blowpipe with greater facility than lime or magnesia. In its solid form it is quite insoluble in water; but Berzelius has shown that, when silica in the nascent state is in contact with that fluid, it is dissolved in large quantity. On evaporating the solution gently, a bulky gelatinous substance separates, which is the hydrate of silica. This hydrate is partially decomposed by a very moderate temperature; but a red heat is required for ex- pelling the whole ofthe water. Silica unites with water in seve- ral proportions. Silica, most likely from its insolubility, does not change the blue vegetable colours. It appears to possess the properties of an acid rather than of an alkali. Thus, no acid acts upon silica except the fluoric acid; whereas it is dissolved by solutions ofthe fixed alkalies, and combines with many of the metallic oxides. On this account silica is termed silicic acid by some chemists, and its compounds with alkaline bases silicates. The compound earthy minerals that contain silica may be regarded as native silicates. Silicates.—The combination of silica with the fixed alkalies is best effected by mixing pure sand with the carbonate of potassa or soda, and heating the mixture to redness. During the process, carbonic acid is expelled, and a silicate of the alkali is generated. The nature ofthe product depends upon the proportions which are employed. On igniting one part of silica with three ofthe carbonate of potassa, a vitreous mass is formed, which is deliques- cent, and may be dissolved completely in water. This solution, which was formerly called liquor silicum, has an alkaline reac- tion, and absorbs carbonic acid on exposure to the atmosphere, by which it is partially decomposed. Concentrated acids preci- pitate the silica as a gelatinous hydrate; but if a considerable quantity of water is present, and the acid is added gradually, the alkali may be perfectly neutralized without any separation of silica. When a solution of this kind is evaporated to dryness, « SILICON. 173 the silica is rendered quite insoluble, and may thus be obtained in a pure form. But if the proportion of silica and alkali is reversed, a transpa- rent brittle compound results, which is insoluble in water^is attacked by none of the acids except the fluoric, and possesses the well-known properties of glass. Every kind of glass is com- posed of silica and an alkali, and all its varieties are owing either to differences in the proportion ofthe constituents, to the nature of the alkali, or to the presence of foreign matters. Thus the green bottle glass is made of impure materials, such as river sand, which contains iron, and the most common kind of kelp or pearl ashes. Crown glass for windows is made of a purer alkali, and sand which is free from iron. Plate glass, for looking glass- es, is composed of sand and alkali in their purest state ; and in the formation of flint glass, besides these pUre ingredients, a considerable quantity of litharge or red lead is employed. A small portion of the peroxide of manganese is also used, in order to oxidize carbonaceous matters contained in the materials of the glass ; and nitre is sometimes added with the same intention. Berzelius ascertained the composition of silica by oxidizing a known quantity of silicon, and weighing the product carefully; and according to this synthetic experiment, 100 parts of silica are composed of 48 parts of silicon and 52 parts of oxygen. The atomic weight of silica, deduced apparently with great care, is precisely 16. Admitting, therefore, that an atom of silica con- tains 8 parts or one atom of oxygen, (and it manifestly, if 16 is its equivalent, cannot contain more than one atom,) it follows that the remaining 8 parts must be silicon, an inference which ac- cords very nearly with the experimental result of Berzelius. Consequently, 8 must be the atomic weight of silicon, and silica is its protoxide. It has not yet been ascertained that silicon combines with hydrogen. SECTION III. Zirconion. This substance occurs in nature in the state of an oxide—the minerals from which it is obtained are zircon and the hyacinth, two substances frequently employed in jewellery. Zircon, though originally brought from Ceylon, where it is called jargon, is by no means an uncommon mineral in the United States. The production of zirconion from the zircon, was first effected by Berzelius in 1824. It is procured by heating a mixture of po- tassium with the fluate of zirconia and potassa, carefully dried, in a tube of glass or iron, by means of a spirit-lamp. The re- 174 ZIRCONION. duction takes place at a temperature below redness, and without emission of light. The mass is then washed with boiling water, and afterwards digested for some time in dilute muriatic acid. The residue is pure zirconion. Zirconion, thus obtained, is in the form of a black powder, which may be boiled in water without being oxidized, and is attacked with difficulty by the sulphuric, muriatic, or nitro- muriatic acids ; but is dissolved readily and with disengagement of hydrogen by fluoric acid. Heated in the open air, it takes fire at a temperature far below luminOusness, burns brightly, and is converted into zirconia. Zirconia was discovered in 1789, by Klaproth in the jargon or zircon of Ceylon, and has since been found in the hyacinth from Expailly in France. It is an earthy substance, resembling alumina in appearance, of specific gravity 4.3, having neither taste nor odour, and quite insoluble in water. Its colour, when pure, is white ; but it has frequently a tinge of yellow, owing to the presence of iron, from which it is separated with great diffi- culty. Its salts are distinguished from those of alumina or glucina by being precipitated by all the pure alkalies, in an excess of which it is insoluble. The alkaline carbonates preci- pitate it as the carbonate of zirconia, and a small portion of it is re-dissolved by an excess ofthe precipitant. The composition of zirconia has not been satisfactorily ascer- tained. Berzelius thinks its atomic weight somewhere between 30 and 33. He has examined with great attention the properties of zirconia and several ofthe compounds into which it enters ; it is therefore probable that he is nearer the truth than those who make the atomic weight of zirconion 40, and zirconia 48. SECTION IV. Phosphorus, or Phosphoron. Phosphorus was discovered about the year 1669 by Brandt, an alchemist of Hamburgh. Scheele first described a method of obtaining it from bones. The object of his process is to bring phosphoric acid in contact with charcoal at a strong red heat. The charcoal takes oxygen from the phosphoric acid ; carbonic acid is disengaged, and phosphorus is set free. The bones should first be ignited in an open fire till they become quite white, so as to destroy all the animal matter they contain, and oxidize the carbon proceeding from its decomposition. The calcined bones, of which phosphate of lime constitutes nearly four-fifths, should be reduced to a fine powder, and be digested for a day or two with half their weight of concentrated sulphuric acid, so much water being added to the mixture as to give it the PHOSPHORUS. 175 consistence of a thin paste. The phosphate of lime is decom- posed by the sulphuric acid, and two new salts are generated,— the insoluble neutral sulphate, and the soluble biphosphate of lime. On the addition of boiling water the biphosphate is dis- solved, and may be separated by filtration from the sulphate of lime. The solution is then evaporated to the thickness of syrup, mixed with one-fourth of its weight of charcoal in powder, and is heated in an earthen retort well luted with clay. The beak of the retort is put into water, in which the phosphorus, as it passes over in the form of vapour, is collected. When first obtained, it is frequently of a reddish-brown colour, owing to the presence of the phosphuret of carbon, which is generally formed during the process. It may be purified by being put into hot water, and pressed while liquid through chamois leather; or the puri- fication maybe rendered still more complete by a second dis- tillation. Pure phosphorus is transparent and almost colourless. It is so soft that it may be cut with a knife, and the cut surface has a waxy lustre. At the temperature of 108° F. it fuses, and at 550° F. it is converted into vapour. It is soluble by the aid of heat in naptha, in mixed and volatile oils, and in the chloride, carburet, and phosphuret of sulphur. On cooling from its solution in the latter, Professor Mitscherlich obtained it in regular dodecahedral crystals. By the fusion and slow cooling of a large quantity of phosphorus, M. Frantween has obtained very fine crystals of an octahedral form, and as large as a cherry-stone. Phosphorus is exceedingly inflammable. Exposed to the air at common temperatures, it undergoes a slow combustion; emits a white vapour of a peculiar alliaceous smell, appears distinctly luminous in the dark, and is gradually consumed. On this ac- count phosphorus should always be kept under water. The dis- appearance of oxygen which accompanies these changes is shown by putting a stick of phosphorus in ajar full of air, inverted over water. The volume of the gas gradually diminishes, and if the temperature of the air is at 60°F., the whole ofthe oxygen will be withdrawn in the course of 12 or 24 hours. The residue is nitrogen, containing about l-40th of its bulk of the vapour of phosphorus. It is remarkable that the slow combustion of phos- phorus does not take place in pure oxygen, unless its tempera- ture be about 80°F.; but if the oxygen is rarefied by diminished pressure, or diluted with nitrogen, hydrogen, or carbonic acid, then the oxidation occurs at 60°F. A very slight degree of heat is sufficient to inflame phospho- rus. Gentle pressure between the fingers, friction, or a tempera- ture not much above its point of fusion, kindles it readily. It burns rapidly even iii the air, emitting a splendid white light, and causing an intense heat. Its combustion is far more rapid in 176 PHOSPHORUS. oxygen gas, and the light proportionably more vivid. The ato- mic weight of phosphorus has been estimated at 12. Compounds of Phosphorus and Oxygen. Oxides of phosphorus.—Chemists have not yet succeeded in proving the existence of any oxide of phosphorus. When phos- phorus is kept under water for some time, a white film forms upon its surface, which some have regarded as an oxide of phosphorus. The red-coloured matter, which remains after the combustion of phosphorus, is also supposed to be an oxide. The nature of these substances has not, however, been determined in a satisfactory manner. Hypophosphorous acid.—This acid was discovered in 1816 by M. Dulong, and is produced by the action of wateron the phos- phuret of baryta. The water suffers decomposition ; its elements unite with different portions of phosphorus, by which three com- pounds, phosphuretted hydrogen, phosphoric acid, and hypophos- phorous acid, are generated. The first escapes in the form of gas; the two latter combine with the baryta. The hypophosphite of baryta, being soluble, dissolves in the water, and may conse- quently be separated by filtration from the phosphate of baryta, which is insoluble. On adding a sufficient quantity of sulphuric acid for precipitating the baryta, the hypophosphorus acid is ob- tained in a free state. On evaporating the solution, a viscid li- quid remains, highly acid and even crytallizable, which is a hy- drate of hypophosphorous acid. When an attempt is made to ex- pel the water by heat, the acid itself, and some of the water, are decomposed ; phosphuretted hydrogen gas is disengaged, a little phosphorus sublimes, and phosphoric acid is left. The hypophosphorous acid is a powerful deoxidizing agent. It unites with alkaline bases ; and it is remarkable that all its salts are soluble in water. The hypophosphites of potash, soda, and ammonia, dissolve in every proportion in rectified alcohol; and the hypophosphite of potash is even more deliquescent than the chloride of calcium. They are all decomposed by heat, and yield the same products as the acid itself. M. Dulong infers from his analysis that it contains 27.25 per cent, of oxygen ; but, accordingjto Sir H. Davy, it has exactly one half less oxygen than the phosphorous acid, and is therefore composed of Phosphorus 24 - 2 atoms. Oxygen - 8 - ] atom. More recent experiments*throw doubt on this analysis. Phosphorus acid.—When phosphorus is heated in highly rare- fied air, an imperfect oxidation ensues, and the phosphoric and phosphorous acids are both generated, the latter being obtained in the form of a white volatile powder. In this state it is anhydrous. PHOSPHORUS. 177 Heated inTthe open air, it takes fire, and forms phosphoric acid ; but if exposed to heat in close vessels, it is resolved into phos- phoric acid and phosphorus. It dissolves readily in water, has a sour taste, and smells somewhat like garlic. It unites with alka- lies, and forms salts which are termed phosphites. The solution of phosphorous acid absorbs oxygen slowly from] the air, and is converted into phosphoric acid. From its tendency to unite with an additional quantity of oxygen, it is a powerful deoxidizing agent; and, hence, like sulphurous acid, precipitates mercury, silver, platinum, and gold, from their saline combinations in the metallic form. Nitric acid, of course, converts it into phospho- ric acid. Phosphorous acid is also generated during the slow oxidation of phosphorus in atmospheric air. The product attracts moisture from the air, and forms an oily-like liquid. M. Dulong .thinks that a distinct acid is generated in this case, which he calls phos- phalic acid; but it is the opinion of Sir H. Davy, that it is merely a mixture of phosphoric and phosphorous acids. With respect to the composition of phosphorous acid, Sir H. Davy ascertained, by careful experiment, that it contains one half less oxygen than phosphoric acid; from which it follows that it is composed of Phosphorus . 12 . one atom. Oxygen . 8 . one atom. But the composition of this, like that of the hypophosphorous acid, seems doubtful. Phosphoric Acid.—Of the compounds of phosphorus and oxy- gen, phosphoric acid is by far the most interesting and important. This acid may be obtained in a state of perfect purity by burning phosphorus in air or oxygen gas. Copious white vapours are produced, which fall to the bottom of the vessel like flakes of snow. In this state it is the solid anhydrous phosphpric acid. From its powerful affinity for water, it attracts watery vapour rapidly from the atmosphere, and in the course of two or three minutes appears in the form of minute drops of liquid, which is a solution of phosphoric acid in water. Phosphoric acid may be conveniently formed by the action of nitric acid on phosphorus. The phosphorus takes oxygen from the nitric acid, and a large quantity ofthe deutoxide of nitrogen is disengaged; but as the reaction is apt to be very violent, the process ought to be conducted with caution. It is best done by adding fragments of phosphorus to concentrated nitric acid con- tained in a platinum capsule. A gentle heat is applied so as to commence, and, when necessary, to maintain a moderate effer- vescence; and when one portion of the phosphorus disappears, another is added, till the whole of the nitric acid is exhausted. The solution is then evaporated to dryness. Phosphoric acid may be prepared at a much cheaper rate from 178 PHOSPHORUS. bones. For this purpose, the biphosphate of lime, obtained in the way already described, should be boiled for a few minutes with an excess of the carbonate of ammonia. The lime is thus precipitated as a carbonate, and the solution contains phosphate, together with a little sulphate of ammonia. The liquid, after filtration, is evaporated to dryness, and then ignited in a platinum crucible, by which the ammonia and sulphuric acid are ex- pelled. Solid phosphoric acid unites with water in every proportion, and forms, if concentrated, a dense oily liquid. On heating the solution in a platinum vessel, the greater part of the water is driven off; the residue fuses at a low red heat, and concretes on cooling into a brittle glass, called glacial phosphoric acid. This substance is a hydrate of phosphoric acid, which cannot be de- composed by the fire; for on exposing it to a strong red heat, with the view of expelling the water, the compound itself is volatilized. According to Dulong, it is composed of 84 or three atoms of phosphoric acid, and nine or one atom of water. Phosphoric acid is intensely sour to the taste, reddens litmus paper strongly, and neutralizes the alkalies. It is therefore a powerful acid; but it does not destroy the texture of the skin like the sulphuric and nitric acids. It may be distinguished from all other acids by the following circumstances :—that when carefully neutralized by pure carbonate of soda or potash, it forms a solution, in which no precipitate or change of colour is produced when a stream of sulphuretted hydrogen gas is passed through it; but which is precipitated white by a solution of the acetate of lead, and yellow by the nitrate of silver. The first precipitate, the phosphate of lead, dissolves completely on the addition of nitric or phosphoric acid; the second, the phosphate of silver, is dissolved by both those acids, and also by ammonia. The composition of phosphoric acid has been investigated by Sir H. Davy, Berzelius, and M. Dulong. The subject is one of much difficulty, and the results differ widely. Berzelius considers it a composition of 2 atoms of phosphorus, and 5 of oxygen. Phosphorus and Hydrogen. Perphosphuretted Hydrogen.—Perphosphuretted hydrogen was discovered in 1783, by M. Gengembre. This gas may be pre- pared in several ways. The first is by heating phosphorus in a strong solution of pure potassa. The second consists in heating a mixture made of small pieces of phosphorus, and recently 6laked lime, to which a sufficient quantity of water is added to give it the consistence of a thick paste. The third method is by the action of dilute muriatic acid, aided by a moderate heat, on the phosphuret of lime. In these processes, three compounds of PHOSPHORUS. 179 phosphorus are generated ;—phosphoric acid, hypo-phosphorous acid, and perphosphuretted hydrogen,—all of which are produced by the decomposition of water, and the combination of its ele- ments with separate portions of phosphorus. The gas should be generated at as low a temperature as possible; for otherwise some free hydrogen is apt to pass over. Perphosphuretted hydrogen gas has a strong peculiar odour, and a bitter taste. Its specific gravity has not been determined precisely. Recently boiled water absorbs about l-50th of its volume, and acquires the peculiar odour of the gas. The solu- tion does not redden litmus paper, nor does the gas itself possess acid properties. The most remarkable property of this compound, by which it is distinguished from all other gases, is the sponta- neous combustion which it undergoes on mixing with air or oxy- gen gas. If the beak of the retort from which it issues is plunged under water, so that successive bubbles of the gas may rise through the liquid, a very beautiful appearance takes place. Each bubble, on reaching the surface of the water, bursts into flame, and forms a ring of dense white smoke, which enlarges as it ascends, and retains its shape, if the air be very tranquil, till it disappears. If the gas is received in a vessel of oxygen gas, the entrance of each bubble is instantly followed by a strong con- cussion, and a flash of white light of extreme intensity. The products of the combustion in both cases are phosphoric acid and water. Mr. Dalton observed that it might be mixed with pure oxygen in a tube of three-tenths of an inch in diameter without taking fire; but the mixture detonates when an electric spark is passed through it. From the combustibility of phosphuretted hydrogen, it would be hazardous to mix jt in any quantity with air or oxygen in close vessels. For the same reason, care is required, in making the gas, to allow it to form very slowly at first, in order that the oxy- gen within the apparatus may be gradually consumed. A very simple method of averting all danger consists in moistening the interior of the retort with one or two drops of ether, the vapour of which, when mixed with atmospheric air, even in small propor- tion, effectually prevents the combustion of phosphuretted hy- drogen. Perphosphuretted hydrogen is resolved into its elements by exposure to a strong heat. The same effect is produced by pass- ing through it a succession of electric sparks, pure hydrogen remaining, which occupies the same space as the gas from which it was derived. The analysis of perphosphuretted hydrogen gas has been attempted by a number of chemists, but no satisfactory results have yet been obtained. Protophosphuretted Hydrogen.—The protophosphuretted hy- drogen, discovered in 1812, by Sir H. Davy, is a colourless gas, which has the following properties: Its odour, though disagree- 180 PHOSPHORUS. able, is less fetid than that of the preceding compound. Water absorbs about one-eighth of its volume of the gas. It does not take fire when mixed with air or oxygen at common temperatures ; but the mixture detonates with the electric spark, or when heated to the temperature of 300° Fahrenheit. Admitted into chlorine gas, it inflames instantly, and emits a white light, a property which it possesses in common with the perphosphuretted hy- drogen. The protophosphuretted hydrogen is prepared by heating the solid hydrate of phosphorus acid in close vessels. The chemical changes which give rise to its production, are explained by Sir H. Davy in the following manner : For every four atoms of phosphorus acid two of water are decomposed. The six atoms of oxygen unite with three of phosphorus, forming three atoms of phosphoric acid ; while the remaining atom of phosphorus attaches itself to the two atoms of hydrogen, and forms one atom of pro- tophosphuretted hydrogen. Great uncertainty exists with respect to the composition of this substance, indeed all the compounds of phosphorus with hydrogen and oxygen, require further investigation before we can draw any accurate conclusions respecting them. Phosphuret of Carbon.—This compound is a soft powder, of a yellowish colour, without taste or smell: exposed to air it slowly imbibes moisture, and acquires an acid flavour. Exposed to a red heat, it burns and gradually gives out its phosphorus, the charcoal being prevented from burning by a coating of phosphoric acid. It consists, probably, of one atom of carbon and one of phosphorus. Salts. Phosphate of Ammonia.—Is a common ingredient in the urine of carnivorous animals. It may be obtained pure by saturating phosphoric acid with ammonia : it forms permanent octahedral crystals soluble in two parts of water at 68°, and of a bitterish saline taste; its specific gravity is 1.8051. k hosphite of Ammonia.—This salt is very soluble in water, and cry talizes with difficulty. Hypophosphite of Ammonia.—Is very soluble in water and equally so in alcohol. These salts of ammonia are unimportant. Phosphates. The neutral salts of phosphoric acid with fixed bases sustain a a red heat without decomposition, but they are all fusible at a high temperature. The phosphates of the common metals, at least the greater part of them, are converted into phosphurets by the combined agencyof heat and charcoal. The alkaline phosphates PHOSPHORUS. 181 are only partially decomposed under these circumstances, and the phosphates of lime, baryta, and strontia, undergo no change. The neutral phosphates, excepting those of potassa, soda, and ammonia, are of sparing solubility in pure water; but they are all dissolved without effervescence in an excess of phosphoric or nitric acid, and precipitated, for the most part unchanged, from the acid solutions by pure ammonia. Of all the phosphates, those of baryta, lime, and lead, and especially the latter, are the most insoluble. The presence of a neutral phosphate in solution may be dis- tinguished by the tests which have been already mentioned. The insoluble phosphates are decomposed when boiled with a strong solution of carbonate of potassa or soda, the acid uniting with the alkali, so as to form a soluble phosphate. The earthy phosphates yield to this treatment with some difficulty, and re- quire continued ebullition. Several phosphates are met with in the native state, such as those of lime, manganese, iron, uranium, copper, and lead. Phosphites and Hypophosphites.—These compounds have been little examined, and as they are of no material importance they do not require a particular description. SECTION V. Sulphur, or Sulphuron. Sulphur occurs as a mineral production in some parts of the earth, particularly in the neighbourhood of volcanoes, as in Italy and Sicily. It is commonly found in a massive state; but is sometimes met with crystallized in the form of an oblique rhom- bic octahedron. It exists much more abundantly in combination with several metals, such as silver, copper, antimony, lead, and iron. It is procured in large quantity by exposing the common iron pyrites to a red heat in close vessels. Sulphur is a brittle solid, of a greenish yellow colour, emits a peculiar odour when rubbed, and has little taste. It is a non- conductor of electricity, and is excited negatively by friction. Its specific gravity is 1.99. At the temperature of 190° F., it begins to liquefy ; it is in a state of perfect fusion at 220° F., and if then cast into cylindrical moulds, forms the common roll sul- phur of commerce. It becomes viscid and acquires a reddish- brown colour when the heat is raised to 300° or 350° F.; and if poured at that temperature into water, it becomes a ductile mass, which may be used for taking the impression of seals. Fused sulphur has a tendency to crystallize in cooling. A crystalline arrangement is perceptible in the centre of the com- mon roll sulphur; and by good management regular crystals may be obtained. For this purpose, several pounds of sulphur 182 SULPHUR. should be melted in an earthen crucible ; and when partially cooled, the outer solid crust should be pierced, and the crucible quickly inverted, so that the inner and as yet fluid parts may gradually flow out. On breaking the solid mass, when quite cold, crystals of sulphur will be found in its interior. Sulphur is very volatile. It begins to rise slowly in vapour even before it is completely fused. At 550° or 600° F., it vola- tilizes rapidly, and condenses again unchanged in close vessels. Common sulphur is purified by this process ; and if the sublima- tion be conducted slowly, the sulphur collects in the receiver in the form of detached crystalline grains, called flowers of sulphur. In this state, however, it is not quite pure; for the oxygen of the air within the apparatus combines with a portion of sulphur dur- ing the process, and forms sulphurous acid. The acid may be removed by washing the flowers repeatedly with water. Sulphur is insoluble in water, but unites with it under favour- able circumstances, forming the white hydrate of sulphur, termed Lac Sulphuris. It dissolves readily in boiling oil of turpentine. The solution has a reddish-brown colour like melted sulphur, and if fully saturated deposits numerous small crystals in cooling. Sulphur is also soluble in alcohol, if both substances are brought together in the form of vapour. The sulphur is precipitated from the solution by the addition of water. Sulphur, like charcoal, retains a portion of hydrogen so obsti- nately that it cannot be wholly freed from it, either by fusion or sublimation. Sir H. Davy detected its presence by exposing sulphur to the strong heat of a powerful galvanic battery, when some sulphuretted hydrogen gas was disengaged. The hydro- gen, from its minute quantity, can only be regarded in the light of an accidental impurity, and as no wise essential to the nature of sulphur. When sulphur is heated in the open air to 300° F., or a little higher, it kindles spontaneously, and burns with a faint blue light. In oxygen gas, its combustion is far more vivid ; the flame is much larger, and of a bluish-white colour. Sulphurous acid is the product in both instances;—no sulphuric acid is formed, even in oxygen gas, unless moisture is present. Compounds of Sulphur and Oxygen. Chemists are at present acquainted with four compounds of sulphur and oxygen, all of which have acid properties. Their composition is shown by the following table : Hyposulphurous acid Sulphurous acid Sulphuric acid Hyposulphuric acid Sulphur. Oxygen. S. Ox. 16 8 1 1 16 16 . 1 2 16 24 1 3 32 40 2 5 SULPHUR. 183 Sulphurous Acid Gas. Pure sulphurous acid, at the common temperature and pres- sure, is a colourless transparent gas, which was first obtained in a separate state by Priestley. It is the sole product when sulphur burns in air or in dry oxygen gas, and is the cause of the peculiar odour emitted by that substance during its combustion. It may also be prepared by depriving sulphuric acid of one proportion of its oxygen. This may be done in several ways. If chips of wood, straw, or cork, oil, or other vegetable matters, be heated in strong sulphuric acid, the carbon and hydrogen of those sub- stances deprive the acid of a part of its oxygen, and convert it into sulphurous acid. Nearly all the metals, with the aid of heat, have a similar effect. One portion of sulphuric acid yields oxygen to the metal, and is thereby converted into sulphurous acid ; while the metallic oxide, at the moment of its formation, unites with some of the undecomposed sulphuric acid. The best method of obtaining pure sulphurous acid gas, is by putting two parts of mercury and three of sulphuric acid into a glass retort, the beak of which is received under mercury, and heating the mixture by an Argand lamp. Effervescence soon takes place, a large quantity of pure sulphurous acid is disengaged, and the sulphate ofthe oxide of mercury remains in the retort. Sulphurous acid gas is distinguished from all other gaseous fluids by its suffocating pungent odour. All burning bodies, when immersed in it, are extinguished, without setting fire to the gas itself. It is fatal to all animals which are placed in it. A violent spasm of the glottis takes place, by which the entrance of the gas into the lungs is prevented; and even when diluted with air, it excites cough, and causes a peculiar uneasiness about the chest. Recently boiled water dissolves about 33 times its volume of sulphurous acid, at 60° F. and 30 inches ofthe barometer, form- ing a solution which has the peculiar odour of that compound, and from which the gas may be expelled by ebullition, without change. Sulphurous acid has considerable bleaching properties. It reddens litmus paper, and then slowly bleaches it. Most-vegetable colouring matters, such as that of the rose and the violet, are speedily removed, without being first reddened by it. It is re- markable that the colouring principle is not destroyed by the sulphurous acid ; it may be restored either by a stronger acid or by an alkali. Sir H. Davy inferred from his experiments on the combustion of sulphur in dry oxygen gas, that the volume of the oxygen is not altered during the process, a fact which is now admitted by most chemists ; so that 100 cubic inches of sulphurous acid con- tain 100 cubic inches of oxygen, sulphurous acid gas is just twice 184 SULPHUR. as heavy as oxygen. It follows, therefore, that sulphurous acid consists of equal weights of sulphur and oxygen; and conse- quently that 100 cubic inches weigh 67.776 grains, and contain 33.S88 grains of sulphur. This proportion is established by the researches of Berzelius. The specific gravity of sulphurous acid gas is double that of oxygen, or 2.2222. It is inferred from the composition of hyposulphurous acid, sulphuretted hydrogen, and other compounds of sulphur, that 16 is the number which expresses the combining proportion of that substance. Hence sulphurous acid is composed of 16 or 1 pro- portion of sulphur, and 16 or 2 proportions of oxygen. Its atomic weight is therefore 32. Though sulphurous acid cannot be made to burn by the ap- proach of flame, it has a very strong attraction for oxygen, unit- ing with it under favourable circumstances, and forming sulphuric acid. The presence of moisture is essential to this change. A mixture of sulphurous acid and oxygen gases, if quite dry, may be preserved over mercury for any length of time without acting on each other. But if a little water be admitted, the sulphurous acid gradually unites with oxygen, and disappears entirely. For this reason, a solution of sulphurous acid in water cannot be kept unless the atmospheric air is carefully excluded. Many of the chemical properties of sulphurous acid are owing to its affinity for oxygen. On being added to a solution of the peroxide of iron, it takes oxygen, and thus converts the peroxide into the protoxide of that metal. The solutions of metals which have a weak affinity for oxygen, such as gold, platinum, and mercury, are completely decomposed by it, those substances being pre- cipitated in the metallic form. Nitric acid converts it instantly into sulphuric acid by yielding some of its oxygen. The peroxide of manganese causes a similar change, and is itself converted into the protoxide of manganese, which unites with the sul- phuric acid. Sulphurous acid gas may be passed through red-hot tubes without decomposition. Several substances which have a strong affinity for oxygen, such as hydrogen, carbon, and potassium, de- compose it at the temperature of ignition. Of all the gases, sulphurous acid is most readily liquefied by compression. According to Mr. Faraday, it is condensed by a force equal to the pressure of two atmospheres. M. Bussy, has obtained it in a liquid form under the usual atmospheric pres- sure, by passing it through tubes surrounded by a freezing mix- ture of snow and salt. The anhydrous liquid acid has a density of 1.45. It boils at 14° F. From the rapidity of its evaporation at common temperatures, it may be used advantageously for pro- ducing an intense degree of cold. M. Bussy succeeded in freez- SULPHUR. 185 ing mercury, and liquefying several of the gases, by employing it with this intention. Sulphurous acid combines with metallic oxides, and forms salts which are called sulphites. Sulphuric Acid.—Sulphuric acid was discovered by Basil Valentine towards the close ofthe 15th century. It is procured for the purposes of commerce by two methods. The first is the process which has been pursued many years in the manufactory at Nordhausen in Germany, and consists in decomposing the sul- phate ofthe protoxide of iron (green vitriol) by heat. The crys- tallized protosulphate of iron contains seven atoms of water of crystallization; and when strongly dried by the fire, it crumbles down into a white powder, which, contains one atom of water. On exposing this dried protosulphate of iron to a red heat, the whole of the sulphuric acid is expelled, the greater part of it passing over unchanged into the receiver, in combination with the water of the salt. One portion of the acid is resolved by the strong heat employed in the distillation into sulphurous acid and oxygen. The former escapos as gas throughout the whole pro- cess ; the latter only in the middle and latter stages, being re- tained, in the beginning of the distillation, by the protoxide of iron. The peroxide of iron is the sole residue. The acid, as procured by this process, is a dense, oily, colour- less liquid, which emits copious white vapours on exposure to the air, and is hence called fuming sidphuric acid. Its specific gravity is stated at 1.896 and 1.90 and it is composed of Anhydrous sulphuric acid 80 2 proportions. Water . . . . 9 . 1 On putting this acid into a glass retort, to which a receiver, surrounded by snow, is securely adapted, and applying a very gentle heat to it, a transparent colourless vapour passes over, which condenses into a white crystalline solid. This substance is pure anhydrous sulphuric acid. It is tough and elastic; lique- fies at 66° F. and boils at a temperature between 104° and 122° F., forming, if no moisture is present, a transparent vapour. Ex- posed to the air, it unites with watery vapour, and flies off in the form of dense white fumes. The residue ofthe distillation is no longer fuming, and is in every respect similar to the common acid of commerce. The second process for forming sulphuric acid, which is prac- tised in America, and in most parts of Europe, is by burning sulphur previously mixed with one-eighth of its weight of nitrate of potassa. The mixture is burned in a furnace so contrived that the current of air which supports the combustion, conveys the gaseous products into a large leaden chamber, the bottom of which is covered to the depth of several inches with water. The nitric acid yields oxygen to a portion of sulphur, and converts it into sulphuric acid, which combines with the potassa of the A a 186 SULPHUR. nitre ; while the greater part of the sulphur forms sulphurous acid by uniting with the oxygen of the air. The nitric acid, in losing oxygen, is converted into the deutoxide of nitrogen, which, by mixing with air at the moment of its separation, gives rise to the red nitrous acid vapours. The gaseous substances present in the leaden chamber, are therefore sulphurous and nitrous acids, atmospheric air, and watery vapour. The explanation of the mode in which these substances re-act on one another, so as to form sulphuric acid, was suggested by Clement and D6sormes, and the subject has been put in a still clearer light by Sir H. Davy. On mixing together dry sulphurous acid gas and nitrous acid vapour in a glass vessel, quite free from moisture, no change ensues; but if a drop of water be added, so as to fill the space with vapour, a white crystalline solid is formed, which is com- posed of water and the two acids. When these crystals come into contact with water, the sulphurous acid takes oxygen from the nitrous acid, the deutoxide of nitrogen escapes with efferves- cence, and the sulphuric acid is dissolved by the water. A similar change takes place within the leaden chamber. The crystalline solid is decomposed by the water at the bottom of the chamber, by which sulphuric acid is generated, and the deutoxide of nitrogen set free. That gas, in mixing with atmospheric air, is again converted into nitrous acid, and thus gives rise to the formation of a second portion of the crystalline solid, which is resolved, like the preceding, into sulphuric acid and the deut- oxide of nitrogen. These successive combinations and decom- positions continue till the water is sufficiently charged with sul- phuric acid, when it is drawn off and concentrated by evaporation. It hence appears that the oxygen by which the sulphurous is converted into the sulphuric acid, is in reality supplied by the air; and that the combination is effected, not directly, but through the medium ofthe nitrous acid. The decomposition of the crystalline solid by water, seems owing to the affinity ofthe water for sulphuric acid. Sulphuric acid, as thus prepared, is never quite pure. It con- tains some sulphate of potash and of lead, the former derived from the nitre employed in making it, the latter from the leaden cham- ber. To separate these impurities, the acid should be distilled from a glass or platinum retort. The former may be used with safety by putting some fragments of platinum leaf into it, which causes the acid to boil freely on the application of heat without danger of breaking the vessel. Pure sulphuric acid, as obtained by the second process, is a dense, colourless, oily fluid, which boils at 620° F., and has a specific gravity, in its most concentrated form, of 1.847 or a little higher, never exceeding 1.850. It is one ofthe strongest acids with which chemists are acquainted. When undiluted it is powerfully corrosive. It decomposes all animal and vegetable SULPHUR. .b7 substances by the aid of heat, causing deposition of charcoal and formation of water. It has a strong sour taste, and reddens lit- mus paper, even though greatly diluted. It unites with alkaline substances, and separates all other acids more or less completely from their combinations with the alkalies. Sulphuric acid has a very great affinity for water, and* unites with it in every proportion. The combination takes place with the production of an intense heat. When four parts, by weight, of the acid are suddenly mixed with one of water, the tempera- ture of the mixture rises, to 300° F. By its attraction for water it causes the sudden liquefaction of snow; and if mixed with it in due proportion, an intense degree of cold is generated. It ab- sorbs watery vapour with avidity from the air, and on this ac- count is employed in the process for freezing water by its own evaporation. The operation of sulphuric acid in destroying the texture ofthe skin, in forming ethers, and in decomposing animal and vegetable substances in general, seems dependant on its affi- nity for water. The sulphuric acid of commerce, freezes at—15° F. Diluted with water, so as to have a specific gravity of 1.78, it congeals even above 32° F., and remains in the solid state, till the tem- perature rises to 45° F. When mixed with rather more than its weight of water, its freezing point is lowered to—36° F. When sulphuric acid is passed through a small porcelain tube heated to redness, it is entirely decomposed; and Gay-Lussac found that it is resolved into two measures of sulphurous acid and one of oxygen. Hence it follows that real sulphuric acid is com- posed of By Weight. By Volume. Sulphur - 16 - 1 p. or vapour of sulphur 100 Oxygen - 24 - 3 p. oxygen gas - 150 and its atomic weight is 40. Berzelius ascertained its composi- tion by converting a known weight of sulphur into sulphuric acid ; and his result confirms the conclusion of Gay-Lussac. Chemists possess an unerring test ofthe presence of sulphuric acid. If a solution of muriate of baryta is added to a liquid con- taining sulphuric acid, it causes a white precipitate, the sulphate of baryta, which is characterized by its insolubility in acids and alkalies. Sulphuric acid does not often occur free in nature, except in the neighbourhood of volcanoes. In combination, particu- larly with lime and baryta, it is very abundant. Hyposulphurous acid.—This acid may be formed in several ways:—1. By digesting sulphur in a solution of any sulphite; 2. by the digestion of iron filings in a solution of sulphurous acid; 3. by passing a current of sulphurous acid into a solution ofthe 188 SULPHUR. hydrosulphuret of lime or strontia. In the first case, the sulphu- rous acid takes up an additional quantity of sulphur, and a salt of hyposulphurous acid is obtained; in the second, the sulphurous acid yields one half of its oxygen to the iron, and a hyposulphite of the protoxide of iron is generated ; and in the third, the sul- phurous acid is deprived of one half of its oxygen by the hydro- gen of the sulphuretted hydrogen, pure sulphur is precipitated, and a hyposulphite of lime or of strontia remains in solution. The salts of hyposulphurous acid were first described by Gay- Lussac under the name of the Sulphuretted Sulphites. On ex- posing the hyposulphite of lime to a red heat, Mr. Herschel found that free sulphur is given off, and that a sulphite of lime remains, the acid of which contains a quantity of sulphur equal to what is expelled during the experiment. It hence follows, that the hyposulphurous contains twice as much sulphur as the sul- phurous acid, or is composed of Sulphur . 16 . one p. Oxygen . 8 . one p. and therefore the weight of its atom is 24. From recent experiments, Dr. Thomson infers, that this acid consists of two parts of sulphur and one of oxygen. Its combin- ing proportion would therefore be 40. Hyposulphurous acid cannot exist permannently in a free state. On decomposing a hyposulphite by any stronger acid, such as the sulphuric or muriatic, the hyposulphurous acid, at the moment of quiting the base, resolves itself into sulphurous acid and sul- phur. All hyposulphites may be known by this character. Mr. Herschel succeeded in obtaining free hyposulphurous acid, by adding a slight excess of sulphuric acid to a diluted solution ofthe hyposulphite of strontia; but its decomposition very soon took place, even at common temperatures, and was instantly effected by heat. Hyposulphuric acid.—The hyposulphuric acid was discovered in 1819, by Welter and Gay-Lussac. It is formed by passing a current of sulpurous acid gas through water containing peroxide pf manganese in fine powder. The manganese yields oxygen to the sulphurous acid, thus converting one part of it into sulphuric, and another part into the hyposulphuric acid, both of which unite with the protoxide of manganese. To the liquid, after filtration, a solution of pure baryta is added in slight excess, which preci- pitates the protoxide of manganese, and forms an insoluble sul- phate of baryta with the sulphuric, and a soluble hyposulphate with the hyposulphuric acid. The hyposulphate of baryta is then decomposed by a quantity of sulphuric acid exactly sufficient for precipitating the baryta, and the hyposulphuric acid is left in solution. SULPHUR. 189 This compound reddens litmus paper, has a sour taste, and forms neutral salts with the alkalies. It has no odour, by which circumstance it is distinguished from sulphurous acid. It cannot be confounded with the sulphuric acid; for it forms soluble salts with baryta, strontia, lime, and the oxide of lead, whereas the com- pounds which sulphuric acid forms with those bases are all inso- luble. The hyposulphuric acid cannot be obtained free from water. Its solution, if confined with a vessel of sulphuric acid under the exhausted receiver of an air-pump, may be concentrated till it has density of 1.347 ; but if an attempt is made to condense it still further, the acid is decomposed, sulphurous acid gas escapes; and sulphuric acid remains in solution. A similar change is still more readily produced if the evaporation is conducted by heat. Welter and Gay-Lussac analyzed the hyposulphuric acid by applying heat to the neutral hyposulphate of baryta. At a tem- perature a little above 212° F., this salt suffers complete decom- position ; sulphurous acid gas is disengaged, and a neutral sul- phate of baryta is obtained. They ascertained in this way, that 72 grains of hyposulphuric acid yield 32 grains of sulphurous, and 40 of sulphuric acid; from which it is probable that the hyposul- phuric acid is composed of an atom of each of those acids, com- bined directly with one another. Regarded as a definite com- pound of sulphur and oyxgen, its composition is Sulphur 32 2 atoms. Oxygen 40 5 atoms. Its combining proportion, which ever opinion is adopted, is 72. Compounds of Sulphur and Hydrogen. Sulphuretted Hydrogen.—The best method of preparing pure sulphuretted hydrogen is by heating sulphuret of antimony in a retort, or any convenient glass flask, with four or five times its weight of strong muriatic acid. An interchange of elements takes place between water and the sulphuret of antimony, in con- sequence of which, sulphuretted hydrogen, and the protoxide of antimony, are generated. The former escapes with effervescence, while the latter unites with muriatic acid. The affinities which determine these changes are the attraction of hydrogen for sul- phur, of oxygen for antimony, and of muriatic acid for the pro- toxide of antimony. Sulphuretted hydrogen is also formed by the action of sulphuric or muriatic acid, diluted with three or four parts of water, on the proto-sulphuret of iron; and the theory of the phenomena is similar to that just mentioned. The protosulphuret procured from iron filings and sulphur, always contains some uncombined iron, and therefore the gas obtained from it is never quite pure, being mixed with a little 190 SULPHUR. free hydrogen. This, however, for many purposes, is quite im- material. Sulphuretted hydrogen is a colourless gas, and is distinguished from all other gaseous substances by its offensive taste and odour, which is similar to that of putrefying eggs, or the water of sul- phurous springs. Under a pressure of 17 atmospheres, at 50° F., it is compressed into a limpid liquid, which resumes the gaseous state as soon as the pressure is removed. Sulphuretted hydrogen is very injurious to animal life. Ac- cording to the experiments of Dupuytren and Thenard, the pre- sence of 1-1500th of sulphuretted hydrogen in air, is instantly fatal to a small bird; 1-800th killed a middle sized dog, and a horse died in an atmosphere which contained l-250th of its volume. Sulphuretted hydrogen extinguishes all burning bodies: but the gas takes fire when a lighted candle is immersed in it, and burns with a pale blue flame. Water and sulphurous acid are the products of its combustion, and sulphur is deposited. With oxygen gas it forms a mixture which detonates by the application of flame or the electric spark. If 100 measures of sulphuretted hydrogen are exploded with 150 of oxygen, the former is com- pletely consumed, the oxygen disappears, water is deposited, and 100 measures of sulphurous acid gas remain. From the result of this experiment, the composition of sulphuretted hydrogen may be inferred; for it is clear, from the composition of sulphurous acid, that two-thirds of the oxygen must have combined with sul- phur ; and, therefore, that the remaining one-third contributed to the formation of water. Consequently, sulphuretted hydrogen contains its own volume of the vapour of sulphur and of hydro- gen gas; its specific gravity is 1.1805. Sulphuretted hydrogen is composed, by weight, of Sulphur - 33.888 - 16 - one atom. Hydrogen - 2.118 - 1- one atom. Sulphuretted hydrogen has decided acid properties; for it red- dens litmus paper, and forms salt with alkalies. It is hence sometimes called hydro-sulphuric acid. Its salts are termed hydro-sulphurets or hydro-sulphates. All the hydro-sulphurets are decomposed by muriatic or sulphuric acid, and sulphuretted hydrogen is disengaged with effervescence. Recently boiled water absorbs its own volume of sulphuretted hydrogen, and acquires the peculiar taste and odour of sulphur- ous springs. The gas is expelled without change by boiling. The elements of sulphuretted hydrogen may easily be separated from one another. Thus, on putting a solution of sulphuretted hydrogen into an open vessel, the oxygen absorbed from the air gradually unites with the hydrogen ofthe sulphuretted hydrogen, water is formed, and sulphur is deposited. Sulphuretted hydro- SULPHUR. 191 gen and sulphurous acid mutually decompose each other, with formation of water and deposition of sulphur. If a drachm of fuming nitric acid is poured into a bottle full of sulphuretted hydrogen gas, a bluish-white flame passes rapidly through the vessel, sulphur and nitrous acid fumes make their appearance, and of course water is generated. Chlorine and iodine decom- pose sulphuretted hydrogen, with separation of sulphur, and for- mation either of muriatic or hydriodic acid. An atmosphere charged with sulphuretted hydrogen gas may be purified by means of chlorine in the space of a few minutes. Sulphuretted hydrogen, from its affinity for metallic substances, is a chemical agent of great importance. It tarnishes gold and silver powerfully, forming with them metallic sulphurets. White paint, owing to the lead which it contains, is blackened by it; and the salts of nearly all the common metals are decomposed by its action. In most cases, the hydrogen of the sulphuretted hydrogen combines with the oxygen of the oxide, and the metal unites with the sulphur. Sulphuretted hydrogen is readily distinguished from other gases by its odour. The most delicate chemical test of its presence is carbonate of lead (white paint) mixed with water and spread upon a piece of white paper. So minute a quantity of sulphuretted hydrogen may by this means be detected, that one measure of the gas mixed with 20,000 times its volume of air, hydrogen, or carburetted hydrogen, gives a brown stain to the whitened sur- face. Bisulphuretted Hydrogen.—Though Scheele discovered this compound, it was first particularly described by Berthollet. It may be made conveniently by boiling equal parts of recently slaked lime and flowers of sulphur with five or six of water, when a deep orange-yellow solution is formed, which contains a hy- drosulphuret of lime with excess of sulphur. On pouring this liquid into strong muriatic acid, a copious deposition of sulphur takes place ; and the greater part of the sulphuretted hydrogen, instead of escaping with effervescence, is retained by the sulphur. After some minutes, a yellowish semifluid matter, like oil, collects at the bottom ofthe vessel, which is bisulphuretted hydrogen. From the facility with which this substance resolves itself into sulphur and sulphuretted hydrogen, its history is imperfect, and in some respects obscure. It is viscid to the touch, and has the peculiar odour and taste of sulphuretted hydrogen, though in a slighter degree. It appears to possess the properties of an acid ; for it unites with alkalies and the alkaline earths, forming salts which are termed sulphuretted hydro-sulphurets. According to Mr. Dalton, the bisulphuretted hydrogen consists of one atom of hydrogen and two atoms of sulphur; and consequently its combining proportion is 33. 192 SULPHUR. The salts of the bisulphuretted hydrogen may be prepared by digesting sulphur in solutions of the alkaline or earthy hydro- sulphurets. They are also generated when alkalies or alkaline earths are boiled with sulphur and water ; but in this case, ano- ther salt is formed at the same time. Thus, on boiling together lime and sulphur, as in the preceding process, the only mode by which sulphuretted hydrogen can be formed at all, is by the de- composition of water; but since no oxygen escapes during the ebullition, it is manifest that the elements of that liquid must have combined with separate portions of sulphur, and have formed two distinct acids. One of these, in all probability, is hyposulphurous acid ; and the other is sulphuretted hydrogen. The salts of bisulphuretted hydrogen, absorb oxygen from the air, and pass gradually into hyposulphites. A similar change is speedily effected by the action of sulphurous acid. Dilute mu- riatic and sulphuric acids produce in them a deposition of sul- phur, and evolution of sulphuretted hydrogen gas. Bisulphuret of Carbon. Sulphur and Carbon.—This substance was discovered acci- dentally in 1796, by Professor Lampadius, who regarded it as a compound of sulphur and hydrogen, and termed it alcohol of sulphur. Clement and Desormes first declared it to be a sul- phuret of carbon, and their statement was fully confirmed by the joint researches of Berzelius and the late Dr. Marcet. The sulphuret of carbon may be obtained by heating in close vessels the native bisulphuret of iron, (iron pyrites) with one-fifth of its weight of well-dried charcoal; or by passing the vapour of sulphur over fragments of charcoal heated to redness in a lube of porcelain. The compound, as it forms, should be conducted by means of a glass tube into cold water, at the bottom of which it is collected. To free it from moisture and adhering sulphur, it should be distilled at a low temperature in contact with the chloride of calcium. The bisulphuret of carbon is a transparent colourless liquid, which is remarkable for its high refractive power. Its specific gravity is 1.272. It has an acrid, pungent, and somewhat aro- matic taste, and a very fetid odour. It is exceedingly volatile; —its vapour at 63°.5 F. supports a column of mercury, 7.36 inches long; and at 110° F. it enters into brisk ebullition. From its great volatility it may be employed for producing an intense degree of cold. The bisulphuret of carbon is very inflammable, and kindles in the open air at a temperature scarcely exceeding that at which mercury boils. It burns with a pale blue flame. Admitted into SULPHUR. 193 a vessel of oxygen gas, so much vapour rises as to form an explo- sive mixture. It dissolves readily in alcohol and ether, and is precipitated from the solution by water. It dissolves phosphorus. The pure acids have little action upon it. With the alkalies it unites slowly, forming compounds which Berzelius calls carbo- sulphurets. It is converted by strong nitro-muriatic acid into a white crystalline substance like camphor, which Berzelius con- siders to be a compound of muriatic, carbonic, and sulphurous acid gases. From some recent experiments, itseems probable that pure crys- tallized carbon, or diamonds may be precipitated from the bisul- phuret of carbon, by the action of phosphorus upon it. The dia- monds are said to be small, and the process requires some months before it is completed. Xanthogen and Hydroxanthic.—M. Zeise, professor of che- mistry in Copenhagen, has lately discovered some novel and inte- resting facts, relative to the bisulphuret of carbon. When this fluid is agitated with a solution of pure potassa in strong alcohol, the alkaline properties ofthe potassa disappear entirely; and on ex- posing the solution to a temperature of 32°F. numerous acicular crystals are deposited. M. Zeise attributes these phenomena to the formation of a new acid, the elements of which are derived, in his opinion, partly from the alcohol, and partly from the bi- sulphuret of carbon. He regards the acid as a compound of car- bon, sulphur, and hydrogen. He supposes it to be a hydracid, and that its radical is a sulphuret of carbon. To the radical of this hydracid he applies the term Xanthogen, (from ^avOos yellow, and ytwacj I generate,) expressive ofthe fact that its combinations with several metals have a yellow colour. The acid itself is call- ed hydroxanthic acid, and its salts hydroxanthates. The crystals deposited from the alcoholic solution are the hydroxanthate of potassa. There is no doubt of a new acid being generated under the circumstances described by M. Zeise ; but since he has not pro- cured xanthogen in an insulated form, nor even determined with certainty the constituent principles of the hydroxanthic acid, there exists considerable uncertainty as to its real nature. Sulphocyanic Acid. The sulphocyanic acid was discovered in 1808 by Mr. Porrett, who ascertained that it is a compound of sulphur, carbon, hydro- gen, and nitrogen, and described it under the name of sulphuret- ted chyazic add. It is now more commonly called sulpho-cyanic acid, and its salts are termed sulpho-cyanates. The sulphocyanic acid is obtained by mixing so much sulphur- ic acid with a concentrated solution of the sulpho-cyante of po- tassa as is sufficient to neutralize the alkali, and then distilling 194 SULPHUR. the mixture. An acid liquor collects in the recipient, which is sulphocyanic acid dissolved in water, and the sulphate of potassa remains in the retort. The sulphocyanic acid, as thus prepared, is a transparent li- quid, which is either colourless or has a slight shade of pink. Its odour is somewhat similar to that of vinegar. The strongest so- lution of it which Mr. Porrett could obtain had a specific gravity of 1.022 It boils at 216°.5 F.; and at 54°.5 F. crystallizes in six- sided prisms. The sulphocyanic acid reddens litmus paper, and forms neutral compounds with alkalies. Its presence, whether free or combined, is easily detected by a per-salt of iron, with the oxide of which it unites, forming a soluble salt of a deep blood-red colour. With the protoxide of copper it yields a white salt, which is insoluble in water. The sulpho-cyanic acid is composed of Cyanogen - 26 one atom. Sulphur - .32 - two atoms. Hydrogen - 1 - one atom. or of • Bisulphuret of Cyanogen 58 - or one atom. Hydrogen - 1 - or one atom. The sulphocyanic acid is, therefore, a hydracid; and though its radical, the bisulphuret of cyanogen, has not been obtained in a separate state, it is capable, like the radicals of all the other hydracids, of combining with metallic substances. Sulphuret of Boron.—Boron takes fire and burns when strong- ly ignited in the vapour of sulphur. The sulphuret thus formed is a white opaque mass, which is converted by'water into sulphu- reted hydrogen and boracic acid. Sulphuret of phosphorus.—When sulphur is brought into con- tact with fused phosphorus, they unite readily, but in proportions which have not been precisely determined. They frequently re-act on each other with such violence as to cause an explosion ; for this reason the experiment should be made with a quantity of phosphorus not exceeding thirty or forty grains. The phos- phorus is placed in a glass tube, five or six inches long, and about half an inch wide, and when by a gentle heat it is liquefied, the sulphur is added to it in successive small portions. Caloric is evolved at the moment of combination, and sulphuretted hydro- gen and phosphoric acid, owing to the presence of moisture, are generated. This compound may also be made by agitating the flowers of sulphur with fused phosphorus under water. The tem- perature should not exceed 160° F. ; for otherwise sulphuretted hydrogen and phosphoric acid would be evolved so freely as to prove dangerous, or at least to interfere with the success of the process. The sulphuret of phosphorus, from the nature of its elements, is highly combustible. It is much more fusible than phosphorus. SULPHUR. 195 A compound made by Mr. Faraday, with about five parts of sul- phur to seven of phosphorus, was quite fluid at 32° F., and did not solidify at 20° F. Salts. Sulphate of Ammonia.—This salt is easily prepared by neutra- lizing the carbonate of ammonia with dilute sulphuric acid. It crystallizes in long flattened six-sided prisms. It dissolves in two parts of water at 60°, and in an equal weight of boiling water. It is sublimed by heat, but is partially decomposed at the same time. The crystals are composed of 40 parts or one atom of acid, and 17 parts or one atom of ammonia, combined according to Dr. Thomson with one atom, and according to Berzelius with two atoms of water. Sulphite of Ammonia.—Crystallizes in six-sided prisms, termi- nated by six-sided pyramids; or in four-sided rhomboidal prisms, terminated by three-sided pyramids. It is soluble in its own weight of water; its solubility is increased by heat. When ex- posed to the air, it attracts moisture, and is soon converted into a sulphate. It is composed of 32 parts or one atom of acid, and 17 parts or one atom of ammonia. The crystals consist of two atoms ofthe salt united to one atom of water. Sulphate of Zirconia.—Burzelius enumerates three compounds of sulphuric acid and zirconia, none of which require particular notice. Sulphates. The salts of sulphuric acid in solution may be detected by the muriate of baryta. A white precipitate, the sulphate of baryta, in- variably subsides, which is insoluble in all the acids and alkalies, a character by which the presence of sulphuric acid, whether free or combined, may always be recognised. An insoluble sulphate, such as the sulphate of baryta or strontia, may be detected by mixing it, in fine powder, with three times its weight ofthe carbo- nate of potassa or soda, and exposing the mixture in a platinum crucible for half an hour to a red heat. Double decomposition ensues ; and on digesting the residue in water, filtering the solu- tion, neutralizing the free alkali by pure muriatic, nitric, or acetic acids, and adding the muriate of baryta, the insoluble sulphate of that base is precipitated. Several of the sulphates exist in nature, but the only ones which are abundant are the sulphates of lime and baryta. All of them may be formed by the action of sulphuric acid on the me- tals themselves, on the metallic oxides or their carbonates, or by way of double decomposition. The solubility of the sulphates is very variable. There are six 196 SULPHUR. only which may be regarded as really insoluble ; namely, the sul- phates of baryta, tin, antimony, bismuth, lead, and mercury. The sparingly soluble sulphates are those of strontia, lime, zirconia, yttria, cerium, and silver. All the others are soluble in water. AH the sulphates, those of potassa, soda, lithia, baryta, strontia, and lime excepted, are decomposed in a white heat. One part ofthe sulphuric acid of the decomposed sulphate escapes un- changed, and another portion is resolved into sulphurous acid and oxygen. Those which are easily decomposed by heat, such as the sulphate of iron, yield the largest quantity of undecomposed sulphuric acid. When a sulphate, mixed with carbonaceous matter, is ignited, the oxygen both of the acid and of the oxide, unites with carbon, carbonic acid is disengaged, and a metallic sulphuret remains. A similar change is produced by hydrogen gas at a red heat, with formation of water, and frequently of some sulphuretted hydro- gen. In some instances the hydrogen entirely deprives the me- tal of its sulphur. The composition of the sulphates, so far as they are subject to general laws has already been described. Sulphites. The salts of sulphurous acid have not hitherto been minutely examined. The sulphites of potassa, soda, and ammonia, which are made by neutralizing those alkalies with sulphurous acid, are soluble in water; but most of the other sulphites, so far as is known, are of sparing solubility. The sulphites of baryta, strontia, and lime, are very insoluble, and consequently the soluble salts of these earths decompose the alkaline sulphites. The stronger acids, such as the sulphuric, muriatic, phosphoric, and arsenic acids, decompose all the sulphites with effervescence, owing to the escape of sulphurous acid, which may easily be re- cognised by its odour. The nitric acid, by yielding oxygen, con- verts the sulphites into sulphates. When the sulphites of the fixed alkalies and alkaline earths are heated strongly in close vessels, a sulphate is generated, and a portion of sulphur sublimes. In open vessels, at a high tem- perature, they absorb oxygen, and are converted into sulphates, and a similar change takes place even in the cold, especially when they are in solution. M. Gay-Lussac has remarked, that a neutral sulphite always forms a neutral sulphate wtoen its acid is oxidized; a fact from which it may be inferred, that neutral sul- phites consist of one atom ofthe acid and one atom ofthe base. The hyposulphates and hyposulphites are of little importance, and their general character has already been sufficiently des- cribed. Hydrosulphate of Ammonia.—This salt may be procured in SULPHUR. 197 white acicular crystals by mixing together sulphuretted hydrogen and ammoniacal gases in a dry vessel. As the crystals are very volatile, the vessel in which the combination is effected should be kept cool by ice. It is of much use as a test for the metals. It is composed of 17 sulphuretted hydrogen, and 17 ammonia, or one atom of each. Hydrosulphurets or Hydrosulphates. Sulphuretted hydrogen forms soluble salts with the alkalies, alkaline earths', and magnesia, most of which are capable of crys- tallizing. With the alkalies, indeed, if not with other bases, this acid unites in two proportions, forming a hydrosulphate and a bi-hydrosulphate. It may be doubted if sulphuretted hydrogen is capable of uniting with any of the oxides of the common metals; for when their salts are mixed with the hydrosulphate of potassa, a precipitate takes place, which in most, if not in all cases, is the sulphuret of a metal, and not the hydrosulphate of its oxide. Thus, by the action of the hydrosulphate of potassa on the nitrate of lead, copper, bismuth, silver, or mercury, a nitrate of potassa is formed, water is generated, and a metallic sulphuret subsides. The precipitates occasioned by hydrosul- phate of potassa, in a salt of iron, zinc, and manganese, may also be regarded as sulphurets; for though sulphuric acid decomposes these compounds with evolution of sulphuretted hydrogen, it does not follow that that acid had previously existed in them. As sulphuretted hydrogen is a weak acid, and is naturally gaseous, its salts are decomposed by most other acids, such as the sulphuric, muriatic, and acetic acids, with disengagement of sulphuretted hydrogen gas, a character by which all the hydro- sulphates are easily recognised. They are decomposed, likewise, by chlorine and iodine, with separation of sulphur, and forma- tion of a muriate or hydriodate. When recently prepared, they form solutions which are colourless, or nearly so ; but on ex- posure to the air, oxygen gas is absorbed, a portion of its acid is deprived of its hydrogen, and a sulphuretted hydrosulphate of a yellow colour is generated. By continued exposure, the whole of the sulphuretted hydrogen is decomposed, water and hypo-sul- phurous acid being produced. The hydrosulphates of baryta and strontia, prepared by dissolv- ing the sulphurets of barium and strontium in water, are some- times used in preparing the salts of those bases. The hydrosul- phates of potassa and ammonia are employed as re-agents. Sulphocyanate of Ammonia.—This is a soluble salt which does not crystallize. ( 198 ) SECTION VI. Selenium or Selenion. Selenium has hitherto been found in very small quantity. It occurs for the most part in combination with sulphur in some kinds of iron pyrites. Stromeyer has also detected it, as a sul- phuret of selenium, among the volcanic products of the Lip*ari isles. It is found likewise at Clausthal, in the Hartz mountains, combined, according to Stromeyer and Rose, with several metals, such as lead, cobalt, silver, m«rcury, and copper. It was discovered in 1818 by Berzelius in the sulphur obtained by sub- limation from the iron pyrites of Fahlun. In a manufactory of sulphuric acid at which this sulphur was employed, it was observ- ed that a reddish-coloured matter always collected at the bottom ofthe leaden chamber; and on burning this substance, Berzelius perceived a strong and peculiar odour, similar to that of decayed horse-radish, which induced him to submit it to a careful examina- tion, and this led to the discovery of selenium. Selenium, at common temperatures, is a brittle opaque solid body, without taste or odour. It has a metallic lustre and the aspect of lead, when in mass ; but is of a deep red colour when reduced to powder. Its specific gravity is between 4.3 and 4.32. At 212° it softens, and is then so tenacious that it may be drawn out into fine threads which are transparent, and appear red by transmitted light. It becomes quite fluid at a temperature some- what above that of boiling water. It boils at about 650°, forming a vapour which has a deep yellow colour, but emitting no odour. It may be sublimed in close vessels without change, and con- denses again into dark globules of a metallic lustre, or as a cin- nabar red powder, according as the space in which it collects is small or large. Berzelius at first regarded it as a metal; but, since it is an imperfect conductor of caloric and electricity, it more properly belongs to the class ofthe simple non-metallic bodies. Selenium is insoluble in water. It suffers no change from mere exposure to the atmosphere ; but if heated in the open air it com- bines readily with oxygen, and two compounds, the oxide of selenium and selenious acid, are generated. If the experiment is made by throwing upon it the oxidizing part ofthe blow-pipe flame, it tinges the flame of a light-blue colour, and exhales so strong an odour of decayed horse-radish, that l-50th of a grain is said to be sufficient to scent the air of a large apartment. By this character the presence of selenium, whether alone or in com- bination, may always be detected. Oxide of Selenium.—This compound is formed in greatest abundance by heating selenium in a limited quantity of atmos- pheric air, and washing the product to separate the selenious SELENIUM. 199 acid. It is a colourless gas, which is very sparingly soluble in water, and does not possess any acid properties. It is the cause ofthe peculiar odour which is emitted during the oxidation of se- lenium. Its composition has not been determined, but it proba- bly contains an atom of each of its elements. Selenious Acid.—This acid is most conveniently prepared by digesting selenium in nitric or nitro-muriatic acid till it is com- pletely dissolved. On evaporating the solution to dryness, a white residue is left, which is selenious acid. By increase of tem- perature, the acid itself sublimes, and condenses again unchang- ed into long four-sided needles. It attracts moisture from the air, whereby it suffers imperfect liquefaction. It dissolves in alcohol and water. It has distinct acid properties, and its salts are called selenites. Selenious acid is readily decomposed by all substances which have a strong affinity for oxygen, such as sulphurous and phos- phorous acids. When sulphurous acid, or an alkaline sulphite, is added to a solution of selenious acid, a red-coloured powder, pure selenium, is thrown down, and the sulphurous is converted into sulphuric acid. Sulphuretted hydrogen also decomposes it; and an orange-yellow precipitate subsides, which is a sulphuret of selenium. The atomic weight of selenium, deduced chiefly from the ex- periments of Berzelius, is 40; and the selenious acid, according to the analysis ofthe same chemist, consists of Selenium - 40 - one equivalent. Oxygen - 16 - two equivalents. 56 Selenic acid.—The preceding compound, discovered by Ber- zelius, was, till lately, the only known acid of selenium, and has hitherto been described in elementary works under the name of selenic acid; but the recent discovery of another acid of selenium containing more oxygen than the other, has rendered necessary a change of nomenclature. The existence of the selenic acid was first noticed by M. Nitzsch, assistant of Professor Mitscher- lich, and its properties have been examined and described by the Professor himself. This acid is prepared by fusing nitrate of potassa or soda with selenium, a metallic seleniuret, or with selenious acid or any of its salts. The seleniuret of lead, as the most common ore of selenium, will generally be employed; but it is very difficult to obtain pure selenic acid by its means, because it is commonly associated with metallic sulphurets. The ore is first treated with muriatic acid to remove any carbonate that may be present; and the insoluble part, which is about a third of the mass, is mixed with its own weight of nitrate of soda, and thrown by successive 200 SELENIUM. portions into a red-hot crucible. The lead is thus oxidized, and the selenium converted into selenic acid, which unites with soda. The fused mass is then acted on by hot water, which dissolves only the seleniate of soda, together with nitrate and hyponitrite of soda; while the insoluble matter, when well washed, is quite free from selenium. The solution is next made to boil briskly, when anhydrous seleniate of soda is deposited; while, on cooling, ni- trate of soda crystallizes. On renewing the ebullition and sub- sequent cooling, fresh portions of the seleniate and nitrate are procured ; and these successive operations are repeated, until the former salt is entirely separated. This process is founded on the fact, that seleniate of soda, like the sulphate ofthe same base, is more soluble in water of about 90° F. than at higher or lower temperatures. The hyponitrite of soda, formed during the fusion, is purposely reconverted into nitrate by digestion with nitric acid. The seleniate of soda thus procured always contains a little sulphuric acid, derived from the metallic sulphurets of the ore; and it is not possible to separate this acid by crystallization. All attempts to separate it by means of baryta were likewise fruitless ; and the only method of effecting this object is by reducing the selenic acid into selenium. This is done by heating a mixture of the seleniate of soda and sal-ammoniac ; when mutual decom- position ensues, the soda unites with muriatic acid, the hydrogen ofthe ammonia combines with the oxygen of the selenic acid, and selenium and nitrogen are set free. The selenium thus ob- tained is quite free from sulphur. It is then converted by nitric acid into selenious acid, neutralized with soda, the seleniate gene- rated by fusion with nitre or nitrate of soda, and separated ac- cording to the foregoing process. The pure seleniate of soda is subsequently dissolved in water, and obtained in. crystals by spontaneous evaporation. To procure the acid in a free state, the seleniate of soda is de- composed by nitrate of lead. The seleniate of lead, which is as insoluble as the sulphate, after being well washed, is exposed to a current of sulphuretted hydrogen gas, which precipitates all the lead as a sulphuret, but does not decompose the selenic acid. The excess of sulphuretted hydrogen is driven off by heat, and pure selenic acid remains diluted with water. The absence of fixed substances may be proved by its being volatilized by heat without residue; and if free from sulphuric acid, it gives no pre- cipitate with muriate of baryta after being boiled with muriatic acid. Any nitric acid which may be present is expelled by con- centrating the solution by means of heat. Selenic acid is a colourless liquid, which may be heated to 576° F. without appreciable decomposition ; but above that point decomposition commences, and becomes rapid at 554° giving rise to disengagement of oxygen and selenious acid. When concen- trated by a temperature of 329° its specific gravity is 2.524; at SELENIUM. 201 512° it is 2.60, and at 545° it is 2.625, but a little selenious acid is then present. When procured by the process above described, selenic acid always contains water, but it is very difficult to as- certain its precise proportion. Some acid which had been heated higher than 576°, contained, subtracting the quantity of selenious acid present, 15.75 per cent, of water, which approximates to the ratio of one equivalent of water and one ofthe acid. It is certain that selenic acid is decomposed by heat before parting with all the water which it contained. Selenic acid has a powerful affinity for water, and emits as much heat in uniting with it as sulphuric acid does. Like this acid, it is not decomposed by sulphuretted hydrogen, and hence this gas may be employed for decomposing the seleniate of lead or copper. With muriatic acid the'change is peculiar; for on boiling the mixture mutual decomposition ensues, water and selenious acid are formed, and chlorine set free ; so that the so- lution, like aqua regia, is capable of dissolving gold and platinum. Selenic acid dissolves zinc and iron with disengagement of hydro- gen gas, and copper with formation of selenious acid. It dis- solves gold also, but not platinum. Sulphurous acid has no action on selenic acid, whereas selenious acid is easily reduced by it. Consequently, when it is wished to precipitate selenium from selenic acid, it must be boiled with muriatic acid before sulphurous acid is added. Selenic acid, in its affinity for alkaline bases, is little inferior to sulphuric acid ; so much so, indeed, that the seleniate of baryta cannot be completely decomposed by sulphuric acid. It is there- fore an acid of great power. From the analysis of this acid and of the seleniates of potassa and soda by Professor Mitscherlich, it is established that the oxygen ofthe selenious and selenic acids, combined with the same quantity of selenium, is in the ratio of 2 to 3, as is the case with sulphurous and sulphuric acids. Hence the 'selenic acid is a compound of 40 parts or one equivalent of selenium, and 24 parts or three equivalents of oxygen; and its equivalent is 64. . Professor Mitscherlich has observed, that the selenic and sul- phuric acids are not only analogous in composition and many of their properties, but that the similarity runs through their com- pounds with alkaline substances, their salts resembling each other in chemical properties, constitution, and form. Hydrogen and Selenium. Hydro-Selenic Acid.—Selenium, like sulphur, forms a gaseous compound with hydrogen, which has distinct acid properties, and is termed selenuretted hydrogen, or hydro-selenic acid. This gas is disengaged when muriatic acid is added to a concentrated solution of any hydro-seleniate. It may also be procured by C 202 SELENIUM. heating the selenuret of iron in muriatic acid. By the decom- position of water, oxide of iron and hydro-selenic acid are gene- rated ; and while the former unites with the muriatic acid, the latter escapes in the form of gas. Hydro-selenic acid gas is colourless. Its odour is at first similar to that of sulphuretted hydrogen; but it afterwards irri- tates the lining membrane of the nose powerfully, excites catarrhal symptoms, and destroys for some hours the sense of smelling. It is absorbed freely by water, forming a colourless solution, which reddens litmus paper, and gives a brown stain to the skin. The acid is soon decomposed by exposure to the atmosphere, for the oxygen of the air unites with the hydrogen of the hydro-selenic acid, and selenium, in the form of a red powder, subsides. All the salts of the common metals are decomposed by hydro- selenic acid. The hydrogen of that acid combines with the oxygen of the oxide, and a selenuret ofthe metal is generated. The hydro-selenic acid gas is composed, according to the analysis of Berzelius, of one atom of each of its constituents. Selenio-cyanic Acid.—Berzelius also succeeded in proving the existence of a selenio-cyanic acid, though he could not separate it from its combination with potassa. It is a hydracid, and its radical is a selenuret of cyanogen. Phosphuret of Selenium.—The phosphuret of selenium may be prepared in the same manner as the sulphuret of phosphorus ; but as selenium is capable of uniting with phosphorus in several proportions, the compound formed by fusing them together can hardly be supposed to be of a definite nature. This phosphuret is very fusible, sublimes without change in close vessels, and is inflammable. It decomposes water gradually when digested in it, giving rise to selenuretted hydrogen, and one of the acids of phosphorus. Sulphuret of Selenium.—When sulphuretted hydrogen gas is conducted into a solution of selenic acid, an orange-coloured precipitate subsides, which is a sulphuret of selenium. It fuses at a heat a little above 212° F., and at a still higher temperature may be sublimed without change. In the open air it takes fire when heated, and sulphurous, selenius, and selenic acids are the products of its combustion. The alkalies and alkaline hydro- sulphurets dissolve it. Nitric acid acts upon it with difficulty; but nitro-muriatic acid converts it into sulphuric and selenic acids. According to Berzelius, this sulphuret is composed of Selenium . 40 . one atom. Sulphur . 24 . one atom and a half. Selenium and sulphur combine readily by the aid of heat, but it is difficult in this way to obtain a definite compound. TELLURIUM, 203 Hydro-seleniates.—These salts have been little examined, owing to the scarcity of selenium. The researches of Berzelius have demonstated, however, that hydroselenic acid forms with the alkalies soluble compounds, which are very analogous in their chemical relations to the hydrosulphates, and which preci- pitate the salts ofthe common metals, giving rise in most, if not in all cases, to the formation of a metallic selenuret. SECTION VII. Tellurium. # Tellurium is a rare metal, hitherto found only in the gold mines of Transylvania, and even there in very small quantity. Its ex- istence was inferred by Midler in 1782, and fully established in 1798 by Klaproth. It occurs in the metallic state, chiefly in combination with gold and silver. Tellurium has a tin-white colour running into lead-gray, a strong metallic lustre, and lamellated texture. It is very brittle, and its density is 6.115., fuses at a temperature below redness, and at a red heat, is volatile. When heated before the blow pipe it takes fire, burns rapidly with a blue flame bordered with green, and is dissipated in gray coloured pungent inodorous fumes. The odour of decayed horse raddish is sometimes emitted during the combustion, and was thought by Klaproth to be peculiar to tellurium; but Berzelius ascribes it solely to the presence of selenium. Oxide of Tellurium.—Tellurium is rapidly oxidized by nitric acid, and a soluble nitrate of the oxide results. The oxide is likewise formed during the combustion ofthe metal. It is of a gray colour, fuses at a red heat, and at a temperature still higher sublimes. When heated before the blow-pipe on charcoal it is decomposed with violence. It has the property of forming salts both with acids and alkalies. It is precipitated from its solution in acids, as a hydrate, by all the alkalies both pure and carbona- ted ; but it is re-dissolved by an excess of the precipitant. Alka- line hydrosulphurets occasion a black precipitate, which is pro- bably a sulphuret of tellurium. It is reduced to the metallic state, and thrown down as a black powder, by insertion of a rod of zinc, tin, antimony, or iron. According to Berzelius, the oxide of tellurium is composed of nearly 32 parts ofthe metal, and 8 parts of oxygen; so that 32 may be regarded as the atomic weight of tellurium, and 40 of its oxide. This result, however, differs considerably from that of Klaproth, and therefore requires comfirmation. Tellurium with Hydrogen.—Tellurium forms two distinct compounds with hydrogen, one of which is solid the other gas- 204 TELLURIUM. eous. By making tellurium the negative surface in water, in the galvanic circuit, a brown powder is formed which is a solid hydruret of tellurium. By acting with dilute sulphuric upon the alloy of tellurium and potassium we obtain a peculiar gas. This gas is colourless, has an odour similar to that of sulphuretted hydrogen, and is absorbed by water, forming a claret-coloured so- lution. As it unites with alkalies, it may be regarded as a feeble acid. It reddens litmus paper at first; but loses this property after being washed with water. Sulphuret of Tellurium.—Tellurium may be combined with sulphur by fusion. The sulphuret has a leaden gray colour and a radiated texture, on red hot coals it burns with a green flame. Salts. Telluriate of Ammonia.—When oxide of tellurium is digested in ammonia it dissolves, as the solution cools it deposits a white powder which is telluriate of ammonia. Nitrate of Tellurium.—Nitric acid dissolves tellurium with fa- cility. The solution is colourless and not rendered turbid by water. It yields, when concentrated, small, white light needle formed deudritical crystals. Sulphate of Tellurium.—When one part of tellurium is con- fined with 100 parts of sulphuric acid, in a close vessel, it dis- solves and gives the acid a crimson colour. When water is drop- ped into the acid, the red colour disappears and the metal is pre- cipitated. Diluted sulphuric acid, mixed with a little nitric acid dissolves a considerable portion of tellurium, the solution is colour- less, and no precipitate is produced in it by water. SECTION VIII. Arsenic or Arsenicum. Metallic arsenic sometimes occurs native, but more frequently it is found in combination with other metals, and especially with cobalt and iron. On roasting these arsenical ores in a rever- berating furnace, the arsenic, from its volatility, is expelled, com- bines with oxygen as it rises, and condenses into thick cakes on the roof of the chimney. The sublimed mass, after being purified by a second sublimation, is the virulent poison known by the name of arsenic or ivhite oxide of arsenic. From this substance the metal itself is procured by heating it with charcoal. Arsenic is an exceedingly brittle metal, of a strong metallic lustre, and white colour, running into steel gray. Its structure is crystalline, and its density 8.3. When heated to 356° F. it sublimes without previously liquefying; for its point of fusion is ARSENIC. 205 far above that of its sublimation, and has not hitherto been de- termined. Its vapour has a strong odour of garlic, a property which is possessed by no other metal, and therefore forms a dis- tinguishing character for metallic arsenic. In close vessels it may be sublimed without change, but if atmospheric air be ad- mitted, it is rapidly converted into the white oxide. It soon tarnishes by exposure to the atmosphere at common temperatures, acquiring a dark film upon its surface. This crust, which is ex- ceedingly superficial, was supposed by Berzelius to be a distinct oxide ; but it is more generally regarded as a mixture of white oxide and metallic arsenic. Compounds of Arsenic and Oxygen. Chemists are acquainted with two compounds of arsenic and oxygen, and as they both possess the properties of an acid, the terms arsenious and arsenic acid have been properly applied to them. Considerable difference of opinion exists as to their com- position. Berzelius maintains that the oxygen of the former is to that of the latter as 3 to 5, while Dr. Thomson contends that the ratio is as 2 to 3. To decide the question an appeal to direct experiment by other chemists is necessary. According to Dr. Thomson, whose data are more generally adopted in this country than those of Berzelius, 38 is the atomic weight of arsenic, and its two acids are thus constituted :— Arsenic. Oxygen. Arsenious acid . 38 or one atom. . 16 or two atoms. Arsenic acid . 38 or one atom. . 24 or three atoms. Arsenious acid.—This compound, frequently called white oxide of arsenic, is always generated when arsenic is heated in open vessels, and may be prepared by digesting the metal in dilute nitric acid. At 380° it is volatilized, yielding vapours which do not possess the odour of garlic, and which condense unchanged on cold surfaces. If the sublimation is conducted slowly, the vapour is deposited in the form of distinct octahedral crystals of an adamantine lustre and perfectly transparent. If the arsenious acid is suddenly heated beyond its subliming point, it fuses into a transparent brittle glass, which gradually becomes opaque by keeping. The specific gravity of this glass is about 3.7. Arsenious acid has an acrid taste, followed by an impression of sweetness. It reddens vegetable blue colours feebly, an effect which is best shown by placing the acid in powder on moistened litmus paper. It combines with salifiable bases, forming salts which are termed arsenites; 1000 parts of boiling water dissolve 77.75 of arsenious acid; and the solution, after having cooled to 60° F., contains only 30 parts. The same quantity of water at 206* ARSENIC. 60° F., when mixed with the acid in powder, dissolves only two parts and a half. The tests which are commonly recommended for detecting the presence of arsenious acid are four in number; namely, lime water, the ammoniacal nitrate of silver, the ammoniacal sulphate of copper, and sulphuretted hydrogen. 1. When lime water is added in excess to a solution of arsenious acid, a white precipitate subsides, which is the arsenite of lime. On drying this salt, mixing it with powdered charcoal or black flux, and heating the mixture contained in a glass tube to redness by means of a spirit-lamp, the arsenic is reduced, sublimes, and condenses in a cool part of the tube. The process of reduction is absolutely necessary, since several other acids as well as the arsenious, such as the carbonic, phosphoric, oxalic, and tartaric acids, yield white precipitates with lime water. The arsenite of lime is soluble in all acids which are capable of dissolving lime itself. Indeed all the arsenites are dissolved by those acids with which their bases do not form insoluble compounds. Lime water is of little service for discovering arsenious acid in mixing fluids. For the arsenite of lime is so light a powder, that when formed in gelatinous or oleaginous solutions, such as in broth or tea made with milk, it remains suspended in the liquid, and cannot be separated from it. 2. Arsenious acid is not precipitated by nitrate of silver unless an alkali be present, which may unite with the nitric acid. Am- monia is commonly employed for the purpose; but as the arsenite of silver is very soluble in ammonia, and excess of the alkali might retain the arsenite of silver in solution. To remedy this inconvenience, Mr. Hume proposes to employ the ammoniacal nitrate of silver, which is made by dropping ammonia into a solution of lunar caustic till the oxide of silver at first thrown down is nearly all dissolved. The liquid thus prepared contains the precise quantity of ammonia which is required; and when mixed with arsenious acid, two neutral salts result, the soluble nitrate of ammonia, and the insoluble yellow arsenite of silver. The ammoniacal nitrate of silver likewise diminishes the risk of fallacy that might arise from the presence of phosphoric acid. The phosphate of silver is so very soluble in ammonia, that when a neutral phosphate is mixed with the ammoniacal nitrate of silver, the resulting phosphate of silver is held almost entirely in solution by the free ammonia. The test of nitrate of silver, however, even in its improved state, is still liable to objection. For when arsenious acid in small proportion is mixed with salts of muriatic acid, or animal and vegetable infusions, the arsenite of silver either does not sub- side at all, or is precipitated in so impure a state that its charac- teristic colour cannot be distinguished. Several methods have been proposed for obviating this source of fallacy ; but Dr. Chris- ARSENIC. 207 tison has shown, in manner quite satisfactory, that this test cannot be relied on in practice. 3. The ammoniacal sulphate of copper, which is made by add- ing sulphate of copper to ammonia till it ceases to be dissolved, occasions with arsenious acid a green precipitate, which has been long used as a pigment under the name of Scheele's green. This test, though well adapted for detecting arsenious acid dissolved in pure water, is very fallacious when applied to mixed fluids. Dr. Christison has proved that the ammoniacal sulphate of cop- per produces in some animal and vegetable infusions, containing no arsenic, a greenish precipitate, which may be mistaken for Scheele's green ; whereas in other mixed fluids, such as tea and porter, to which arsenic has been previously added, it occasions none at all, if the arsenious acid is in small quantity. In some of these liquids, a free vegetable acid is doubtless the solvent; but the arsenite of copper is also dissolved by tannin, and per- haps by other vegetable as well as some animal principles. 4. When a current of sulphuretted hydrogen gas is conducted through a solution of arsenious acid, the fluid immediately ac- quires a yellow colour, and in a short time becomes turbid, owing to the formation of orpiment, or the yellow sulphuret of arsenic. The precipitate is at first partially suspended in the liquid; but as soon as the free sulphuretted hydrogen is expelled by boiling, it subsides perfectly, and may easily be collected on a filter. One condition, however, must be observed in order to insure suc- cess, namely, that the liquid does not contain a free alkali; for the sulphuret of arsenic is dissolved with remarkable facility by pure potassa or ammonia. To avoid this source of fallacy, it is necessary to acidulate the solution with a little acetic or muriatic acid. Sulphuretted hydrogen likewise acts on arsenic in all vegetable and animal fluids if previously boiled, filtered, and acidulated. But it does not necessarily follow, because sulphuretted hy- drogen causes a yellow precipitate, that arsenic is present; for there are no less than four other substances, namely, selenium, cadmium, tin, and antimony, the sulphurets of which, judging from their colour alone, might be mistaken for orpiment. From these and all other substances whatever, the sulphuret of arsenic may be thus distinguished.—When heated with black flux in the manner described for reducing the arsenite of lime, a metallic crust of an iron-gray colour externally, and crystalline on its inner surface, is deposited on the cool part of the tube; and by converting a portion of this crust into vapour, its alliaceous odour will instantly be perceived. Besides these circumstances, which alone are quite satisfactory, it is easy to procure additional evi- dence by reconverting the metal into arsenious acid, so as to obtain it in the form of resplendent octahedral crystals. This is done by holding that part of the tube to which the arsenic adheres 208 ARSENIC. about three-fourths of an inch above a very small spirit-lamp flame, so that the metal may be slowly sublimed. As it rises in vapour it combines with oxygen, and is deposited in crystals within the tube. The character of these crystals with respect to volatility, lustre, transparency, and form, is so exceedingly well marked, that a practised eye may safely identify them, though their weight should not exceed the 100th part of a grain. This experiment does not succeed unless the tube be quite clean and dry. It hence appears, that of the various tests for arsenic, the only one which gives uniform results, and is applicable to every case, is sulphuretted hydrogen :—all the rest may be dispensed with. For this great improvement in the mode of testing for arsenious acid, we are indebted to Dr. Christison. By this process he dis- covered the presence of arsenious acid when mixed with complex fluids, such as tea, porter, and the like, in the proportion of one- fourth of a grain to an ounce; and more recently he has twice obtained so small quantity as the 20th of a grain from the stomachs of people who had been poisoned with arsenic. The black flux employed in the processes for reducing arsenic, is prepared by deflagrating a mixture of the bitartrate of potassa with half its weight of nitre. The nitric and tartatric acids un- dergo decomposition, and the solid product is pure carbonate of potassa and charcoal. When this substance is employed in the reduction of arsenious acid or its salts, the charcoal is of course the chief ingredient; but the alkali is of use in retaining the arsenious acid until the temperature is sufficiently high for its decomposition. With sulphuret of arsenic, on the contrary, the alkali is the active ingredient, the potassium of which unites with sulphur and liberates the arsenic; but the charcoal operates use- fully by facilitating the decomposition ofthe alkaline carbonate. Arsenic acid.—This compound is made by dissolving the arse- nious acid in concentrated nitric, mixed with a little muriatic acid, and distilling the solution to perfect dryness. The acid, thus prepared, has a sour metallic taste, reddens vegetable blue colours, and with alkalies forms neutral salts, which are termed arseniates. It is much more soluble in water than arsenious acid, dissolving in five or six times its weight of cold, and in a still smaller quantity of hot water. It forms irregular grains when its solution is evaporated, but does not crystallize. If strongly heated it fuses into a glass which is deliquescent. When urged by a very strong red heat it is converted into oxygen and arse- nious acid. It is an active poison. Arsenic acid is slowly reconverted by sulphuretted hydrogen gas into arsenious acid, and is then precipitated as orpiment. The soluble arseniates, when mixed with the nitrates of lead or silver, form insoluble arseniates, the former of which has a white, and the latter a brick-red colour. They dissolve readily ia ARSENIC. 209 dilute nitric acid, and when heated with charcoal yield metallic arsenic. Arseniuretted hydrogen.—This gas, which was discovered by Scheele, is most conveniently prepared by digesting an alloy of tin and arsenic in muriatic acid. It is a colourless elastic fluid, of a fetid odour, resembling that of garlic. Its specific gravity is about 0.5. It extinguishes bodies in combustion, but is itself kindled by them, and burns with a blue flame. It instantly destroys small animals that are immersed in it, and is poisonous in a high degree, having proved fatal to a German philosopher, the late Mr. Gehlen. With oxygen gas, it forms an explosive mixture, and is decomposed by chlorine with deposition of arse- nic. It is not absorbed by water, nor does it possess acid pro- perties. It has not hitherto been obtained in a pure state, being always mixed with hydrogen, and consequently its composition has not been exactly determined. A solid compound of arsenic and hydrogen, of a brownish colour, was discovered by Sir H. Davy, and Gay-Lussac, and The- nard. It is formed by the action of waiter on an alloy of potas- sium and arsenic; and it is also generated by attaching a piece of arsenic to the negative wire during the decompositions of water by a galvanic battery. Its composition is unknown. Phosphuret of Arsenic.—May be formed by distilling equal parts of its ingredients over a moderate fire. It is black and brilliant; it should be preserved in water. Metallic Phosphurets. Chemists are acquainted with several metallic phosphurets ; and it is probable that phosphorus, like sulphur, is capable of uniting with all the metals. Little attention however has hith- erto been devoted to their compounds ; and for the greater part of our knowledge concerning them, we are indebted to the re- searches of Pelletier. The metallic phosphurets may be prepared in several ways. The most direct method is, by bringing phosphorus in contact with metals at a high temperature, or, what amounts to the same thing, by igniting metals in contact with phosphoric acid and charcoal. Many of the phosphurets may be formed by passing a current of phosphuretted hydrogen gas over metallic oxides heat- ed to redness in a porcelain tube. Water is generated, and a phosphuret ofthe metal remains. Phosphorus unites also with some of the metallic oxides. The phosphurets of lime and baryta, for example, may be made by conducting the vapour of phosphorus over those earths at a red heat. Sulphurets of Arsenic.—Sulphur unites with arsenic in two proportions, forming compounds which are known by the names Dd 210 ARSENIC. of realgar and orpiment. They both occur native, and may be made artificially by heating mixtures of arsenious acid and sul- phur, the nature of the product depending on the quantity of sul- phur employed. They are both fusible by heat, and may be sublimed in close vessels without change. Realgar, which is the protosulphuret, is of a red colour, and is composed of 38 parts or one atom of metallic arsenic, and 16 or one atom of sulphur. Orpiment has a rich yellow colour, and consists of 38 parts or one atom of arsenic, and 24 parts or an atom and a half of sulphur. It is therefore a sesquisulphuret of arsenic. Berzelius has proved, that the precipitate formed by the action of sulphuretted hydro- gen on a solution of arsenious acid, is constituted in a similar manner. Orpiment is employed as a pigment, and is the colouring prin- ciple ofthe paint called King's yellow. M. Braconnot has pro- posed it likewise for dyeing silk, woollen, or cotton stuffs of a yellow colour. For this purpose the cloth is soaked in a solution of orpiment in ammonia, and then suspended in a warm apart- ment. The alkali evaporates, and leaves the orpiment perma- nently attached to the fibres ofthe cloth. The experiments of Orfila have proved that the sulphurets of arsenic are poisonous, though in a much less degree than arsenious acid. The precipitated sulphuret is more injurious than native orpiment. Metallic Sulphurets. Sulphur, has a strong tendency to unite with metals. The combination may be effected in several ways: 1. By heating the metal directly with sulphur. The metal, in the form of powder or filings, is mixed with a due proportion of sulphur, and the mixture is then heated in an earthen crucible, which is covered to prevent the access of air. Or if the metal can sustain a red heat without fusing, the vapour of sulphur may be passed over it while heated to redness, in a tube of porcelain. The act of combination, which frequently ensues below the tem- perature of ignition, is attended by a free disengagement of calo- ric ; and in several instances the heat evolved is so great, that the whole mass becomes luminous, and shines with a vivid light. This appearance of combustion, which occurs quite indepen- dently of the presence of oxygen, is exemplified by the sulphurets of potassium, sodium, copper, iron, lead, and bismuth. 2. By igniting a mixture of a metallic oxide and sulphur. The sulphurets of the common metals may be made by this process. The elements of the oxide unite with separate portions of sul- phur, forming sulphurous acid gas, which is disengaged, and a metallic sulphuret which remains in the retort. 3. By depriving the sulphate of an oxide of its oxygen by ARSENIC. 211 means of heat and combustible matter. Charcoal or hydrogen gas may be employed for the purpose, as will be described im- mediately. 4. By sulphuretted hydrogen, or an alkaline hydrosulphuret. Nearly all the salts ofthe common metals are decomposed when a current of sulphuretted hydrogen gas is conducted into their solutions. The salts of uranium, iron, manganese, cobalt, and nickel, are exceptions ; but these also are precipitated by the hydrosulphuret of ammonia or potassa. The sulphurets are opaque brittle solids, many of which, such as the sulphurets of lead, antimony, and iron, have a metallic lustre. They are all fusible by heat, and commonly assume a crystalline texture in cooling. Most of them are fixed in the fire; but the sulphurets of mercury and arsenic are remarkable for their volatility. All the sulphurets, excepting those which are formed of the. metallic bases ofthe alkalies and earths, are inso- luble in water. Most of the protosulphurets are capable of supporting an in- tense heat without decomposition ; but those which contain more than one atom of sulphur, lose a part of it when strongly heated. They are all decomposed without exception by exposure to the combined agency of heat and air or oxygen gas ; and the pro- ducts depend entirely on the degree of heat and the nature of the metal. The sulphuret is converted into the sulphate of an oxide, prqvided the sulphate is able to support the temperature employ- ed in the operation. If this is not the case, then the sulphur is evolved under the form of sulphurous acid, and a metallic oxide is left; or if the oxide itself is decomposed by heat, the pure metal remains. The action of heat and air in decomposing metallic sulphurets is the basis of several metallurgic processes. Many of the metallic sulphurets were formerly believed to be compounds of sulphur and a metallic oxide ; this was first shown to be an error by Proust. He demonstrated that the sulphuret of iron, (magnetic pyrites,) as well as the common cubic pyrites or bisulphuret, are compounds of sulphur and metallic iron with- out any oxygen. He showed the same also with respect to the sulphurets of other metals, such as those of mercury and copper. He was of opinion, however, that in some instances sulphur does unite with a metallic oxide. Thus, when sulphur and the pe- roxide of tin are heated together, sulphurous acid is disengaged, and the residue, according to Proust, is a sulphuret of the prot- oxide. It was the general belief at that time, also, that the compounds formed by heating sulphur with an alkali or earth, are sulphurets of a metallic oxide. Thus, the old hepar sulphuris, which is made by fusing together a mixture of sulphur and dry carbonate of potassa, was regarded as a sulphuret of potassa. In the year 1817, M. Vauquelin published some experiments, the object of 212 ARSENIC. which was to determine the state ofthe alkali in that compound. The late Count Berthollet had observed, that when the hepar sul- phuris is dissolved in water, the solution always contains a con- siderable portion of sulphuric acid, which he conceived to be generated at the moment of solution. He supposed that water is then decomposed ; and that its elements combine with dif- ferent portions of sulphur, the oxygen giving rise to the forma- tion of sulphuric acid, and the hydrogen to sulphuretted hydro- gen. The accuracy of this explanation was called in question by Vauquelin, who contended that the sulphuric acid is gene- rated, not during the process of solution, but by the action of heat during the formation of the sulphuret. One portion of potassa, according to him, yields its oxygen at a high tempera- ture to some of the sulphur, converting it into sulphuric acid, while the potassium unites with pure sulphur. Two combina- tions therefore result—sulphuret of potassium and sulphate of potassa, which are mixed together. Though the experiments adduced in favour of this opinion were not absolutely convincing, yet they made it the more probable of the two; and M. Vauque- lin, admitting, however, the want of actual proof, inferred from them that when an alkaline oxide is heated to redness with sul- phur, the former loses oxygen, and a sulphuret of the metal itself is produced. M. Gay-Lussac, offered additional arguments in favour of Vau- quelin's opinion, and most chemists held them to be satisfactory. But the more recent labours of MM. Berthier and Berzelius have given still greater insight into the nature of these compounds. One of Vauquelin's chief arguments was drawn from the action of charcoal on the sulphate of potassa. When a mixture of this salt with powdered charcoal is ignited without exposure to the air, carbonic oxide and carbonic acid gases are formed, and a sulphuret is left, analogous both in appearance and properties to that which may be made by igniting carbonate of potassa directly with sulphur. They are both essentially the same substance, and Vauquelin conceived, from the strong attraction of carbon for oxygen, that both the sulphuric acid and the potassa would be decomposed by charcoal at a high temperature ; and that, con- sequently, the product must be a sulphuret of potassium. M. Berthier has proved, in the following manner, that these changes do actually occur. He put a known weight of sulphate of baryta into a crucible lined with a mixture of clay and char- coal, defended it from contact with the air, and exposed it to a white heat for the space of two hours. By this treatment it suf- fered complete decomposition, and it was found that in passing into a sulphuret, it had suffered a loss in weight precisely equal to the quantity of oxygen originally contained in the acid and earth. This circumstance, coupled with the fact that there had been no loss of sulphur, is decisive evidence that the baryta, as ARSENIC. 213 well as the acid, had lost its oxygen, and that a sulphuret of barium had been formed. He obtained the same results also with the sulphates of strontia, lime, potassa, and soda; but from the fusi- bility of the sulphurets of potassium and sodium, their loss of weight could not be determined with such precision as in the other instances. The experiments of Berzelius, performed about the same time, are exceedingly elegant, and still more satisfactory than the fore- going. He passed a stream of dry hydrogen gas over a known quantity of sulphate of potassa, heated to redness. It was ex- pected from the strong affinity of hydrogen for oxygen, that the sulphate would be decomposed; and, accordingly, a considera- ble quantity of water was formed, which was carefully collected and weighed. The loss of weight which the salt had experienc- ed, was precisely equivalent to the oxygen ofthe acid and alkali; and the oxygen of the water was exactly equal to the loss in weight. A similar result was obtained with the sulphates of soda, baryta, strontia, and lime. It is demonstrated, therefore, that the metallic bases ofthe alka- lies and alkaline earths agree with the common metals in their dis- position to unite with sulphur. It is now certain that, whether we decompose a sulphate by hydrogen or charcoal, or whether we ignite sulphur with an alkali or an alkaline earth, a metallic sul- phuret is always the product. Direct combination between sul- phur and a metallic oxide is a rare occurrence, and it may be almost doubted if it ever happens. Gay-Lussac indeed states that, when an alkali or an alkaline earth is heated with sulphur in such a manner that the temperature is never so high as a low red heat, the product is really the sulphuret of an oxide. But the facts adduced in favour of this opinion are not altogether satisfac- tory, and we must leave it therefore to be decided by future ob- servation. Several of the metallic sulphurets occur abundantly in nature. Those that are most frequently met with, are the sulphurets of lead, antimony, copper, iron, zinc, molybdenum, and silver. Salts. Arseniate of Ammonia.—When arsenic acid is saturated with ammonia, the solution yields, by evaporation, crystals of arseniate of ammonia in rhomboidal prisms, which give a green colour to syrup of violets. With an excess of acid, it yields needle-form crystals of bi-arseniate of ammonia which deliquesce when ex- posed to the air. Arsenite of Ammonia.—This salt may be prepared by dissolv- ing arsenious acid in liquid ammonia, a viscid yellow coloured liquid is obtained, which does not crystallize. Arseniates.—All the arseniates are sparingly soluble in water 214 ARSENIC. except those of potassa, soda, ammonia, and perhaps of lithia; but all are dissolved without effervescence by dilute nitric acid, as well as mosf other acids, which do not precipitate the base of the salt, and are thrown down again unchanged by pure ammonia. Most of them bear a red heat without decomposition ; but they are all decomposed by being heated to redness with charcoal, metal- lic arsenic being set at liberty. The arseniates ofthe fixed alka- lies and alkaline earths require a rather high temperature for re- duction ; while the arseniates of the common metals, such as those of lead and copper, are easily reduced in a glass tube by means of a spirit-lamp without danger of melting the glass. Of all the arseniates, that of lead is the most insoluble. The soluble arseniates are easily recognised by the tests al- ready described, and the insoluble arseniates, when boiled in a strong solution of the fixed alkaline carbonates, are deprived of their acid, which may then be detected in the usual manner. The free alkali, however, should first be exactly neutralized by pure nitric acid. The arseniates of lime, nickel, cobalt, iron, copper, and lead, are natural productions. M. Mitscherlich has ascertained that a close analogy exists be- tween the salts of phosphoric and arsenic acid. So far as his re- searches have extended, it appears, that for every arseniate there is a corresponding phosphate ; and that these corresponding salts are analogous in composition, and identical in form. Arsenites. The only soluble compounds of arsenious acid and salifiable bases known to chemists, are the arsenites of potassa, soda, and ammonia, which may be prepared by boiling a solution of these alkalies in arsenious acid. The other arsenites are insoluble, or, at most sparingly soluble in pure water; but they are dissolved by an excess of their own acid, with great facility by nitric acid, and by most other acids with which their bases do not form inso- luble compounds. The insoluble arsenites are easily formed by the way of double decomposition. On exposing the arsenites to heat in close vessels, the arsenious acid is either dissipated in vapour or converted, with disengage- ment of some metallic arsenic, into arseniates. Heated with charcoal or black-flux, the acid is reduced with facility. The soluble arsenites, if quite neutral, are characterized by forming a yellow arsenite of silver when mixed with the nitrate of that base, and a green arsenite of copper, Scheele's green, with the sulphate of copper. When acidulated with acetic or muriatic acid, sulphuretted hydrogen causes the formation of orpiment, an effect which it likewise produces, though slowly, in the arseniates. PROPERTIES OF METALS. 215 The insoluble arsenites are all decomposed when boiled in a so- lution of the carbonate of potassa or soda. General properties of Metals. As tellurium and arsenic, the two last simple substances de- scribed, belong to a class of bodies usually denominated the metals, it will be proper in this place to introduce some general remarks upon the nature and properties of these important sub- stances. Metals are distinguished from other substances by the follow- ing properties. They are all conductors of electricity and calo- ric. When combined with oxygen, chlorine, iodine, or sulphur, and the resulting compounds are submitted to the action of gal- vanism, the metals always appear at the negative side of the battery, and for this reason are said to be positive electrics. They are quite opaque, refusing a passage to light, though re- duced to very thin leaves. They are in general good reflectors of light, and possess a peculiar lustre, which is termed the me- tallic lustre. Every substance in which these characters reside may be regarded as a metal. The number of metals, the existence of which is admitted by chemists, amounts to forty. The following table contains the names of those that have been procured in a state of purity, together with the date at which they were discovered, and the names of the chemists by whom the discovery was made. Table of the discovery of Metals. Names of Metals. Authors of the Discovery, Dates of the Discovery. Gold - Silver - Iron - Copper Mercury Lead - Tin - Antimony - Zinc - Bismuth Arsenic Cobalt Platinum - Nickel Manganese Tungsten - Tellurium - Molybdenum Uranium - Titanium - Chromium - Columbium )> Known to the Ancients J Described by Basil Valentine ■ Described by Agricola in First mentioned by Paracelsus Brandt in Wood, Assay Master, Jamaica Cronstedt - Gahn and Scheele - M. M. D'Elhuyart - Muller..... Hielm - - • - Klaproth - Gregor - Vauquelin - Hatchett - 15th century 1520 16th century 1733 1741 1751 1774 1781 1782 1782 1789 1791 1797 1802 I 216 PROPERTIES OF METALS. Names of Metals. Authors of the Discovery. Dates ofthe Discovery. Palladium -Rhodium -Iridium -Osmium -Cerium -Potassium -Sodium -Barium -Strontium -Calcium -Cadmium -Lithium -Pluranium -Aluminum -Glucinum -Yttrium - \ Dr. Wollaston Descotils and Smjthson Tennant Smithson Tennant -Hisinger and Berzelius -y Sir H. Davy -1 J Arfwedson - 1803 1803 1803 1804 1807 1818 1818 1828 1828 1828 1828 Most of the metals are remarkable for their great specific gra- vity, some of them, such as gold and platinum, which are the densest known bodies in nature, being more than nineteen times heavier than an equal bulk of water. Great density was once supposed to be an essential character of metals ; but the disco- very of potassium and sodium, which are so light as to float on the surface of water, has shown that this supposition is erroneous. Some metals experience an increase of density to a certain extent when hammered, their particles being permanently approximated by the operation. On this account the specific gravity of some of the metals contained in the following table, is represented as varying between two extremes :— Table of the specific gravity of Metals, at 60° Fahr. compared to water as unity. Platinum Gold Tungsten Mercury Palladium Lead Silver Bismuth Uranium Copper Cadmium Cobalt Arsenic Nickel Iron Molybdenum Tin Zinc Manganese Antimony Tellurium 20.98 Brisson 19.257 Do. 17.6 D'Elhuhart 13.568 Brisson 11.3 to 11.8 Wollaston 11.352 Brisson 10.474 Do. 9.822 Do. 9.000 Bucholz 8.895 Hatchett 8.604 Stromeyer 8.538 Hauy 8.308 Bergmann 8.279 Richter 7.788 Brisson 7.400 Hielm * 7.291 Brisson 6.861 to 7.1 Do. 6.850 Bergmann 6.702 Brisson 6.115 Klaproth PROPERTIES OF METALS. 217 Titanium Cerium Sodium Potassium 5.3 4.489 to 4.619 0.972? 0.865 5 Wollaston C Heisinger and £ Berzelius C Gay-Lussac dand Thenard. Some metals possess the property of malleability, that is, ad- mit of being beaten into thin plates or leaves by hammering. The malleable metals are gold, silver, copper, tin, platinum, pal- ladium, cadmium, lead, zinc, iron, nickel, potassium, sodium, and frozen mercury. The other metals are either malleable in a very small degree only, or, like antimony, arsenic, and bismuth, are actually brittle. Gold surpasses all metals in malleability :—one grain of it may be extended so as to cover about 52 square inches of surface, and to have a thickness not exceeding 1-282,020th of an inch. Nearly all malleable metals may be drawn out into wires, a property which is expressed by the term ductility. The only metals which are remarkable in this respect are gold, silver, platinum, iron, and copper. Dr. Wollaston has described a method by which gold wire may be obtained so fine,that its diameter shall be only l-5000th of an inch, and that 550 feet of it are required to weigh one grain. He has obtained a platinum wire so small, that its diameter did not exceed l-30,000th of an inch. It is singular that the ductility and malleability of the same metal are not always in proportion to one another. Iron, for example, cannot be made into fine leaves, but it may be drawn into very small wires. The tenacity of metals is measured by ascertaining the greatest weight which a wire of a certain thickness can support, without breaking. According to the experiments of Guyton-Morveau, whose results are comprised in the following table, iron, in point of tenacity, surpasses all other metals. The diameter of each wire was 0.7S7th of a line. Pounds, Iron wire supports Copper Platinum 549.25 302.278 274.32 Silver 187.137 Gold..... 150.753 Zinc . . . 109.54 Tin .... • 34.63 Lead . 27.621 Ee 21S PROPERTIES OF METALS. The metals differ also in hardness, but we are not aware that their exact relation to one another, under this point of view, has been determined by experiment. In the list of hard metals may be placed titanium, manganese, iron, nickel, copper, zinc, and palladium. Gold, silver, and platinum are softer than these ; lead is softer still, and potassium and sodium yield to the pres- sure of the fingers. The properties of elasticity and sonorous- ness are allied to that of hardness. Iron and copper are in these respects the most conspicous. Many ofthe metals have a distinctly crystalline texture. Iron, for example, is fibrous; and zinc, bismuth, and antimony, are lamellated. Metals are sometimes obtained also in crystals; and when they do crystallize, they always assume the figure of a cube, the regular octahedron, or some form allied to it. Gold, silver, and copper occur naturally in crystals, while others crys- tallize when they pass gradually from the liquid to the solid con- dition. Crystals are most readily procured from those metals which fuse at a low temperature ; and bismuth, from conducting caloric less perfectly than other metals, and therefore cooling more slowly, is best fitted for the purpose. The process should be conducted in the way already described for forming crystals of sulphur. The metals, with the exception of mercury, are solid at com- mon temperatures ; but they may all be liquefied by heat. The degree at which they fuse, or their point of fusion, is very diffe- rent for different metals, as will appear by inspecting the follow- ing table : Table of the fusibility of different Metals. Fusible below a< red heat Potassium Sodium . Tin Bismuth Lead Fahr. f Mercury , . 39° Different Chemists. . 136 ") Gay-Lussac and . 190 5 Thenard. 4g3 > Newton. . 500 Biot. Tellurium—rather less fu- sible then lead . Klaproth. Arsenic—undetermined. Zinc . . .698 Brongniart. Antimony—a little below a red heat. .Cadmium . . Stromeyer. PROPERTIES OF METALS. 219 rSilver Copper Gold Cobalt—rather less fusible than iron. Iron Manganese Nickel—the same as Man- Infusible below a red heat. Pyrometer of Wedgwood. . 20° Kennedy. 27°} 32° S Wed§wood. 130 158 160 Wedgwood. Mackenzie. Guy ton. Richter. ganese Palladium. ^ Molybdenum ("Almost invisible, and"l Fusible before Uranium Tungsten Chromium Titanium Cerium Osmium •Iridium Rhodium Platinum Columbium J ^Pluranium J not to be procured in I the oxy-hy- "S buttons by the heat (drogen blow- Lof a smith's forge. J pipe. Infusible in the heat of a smith's forge, ^■but fusible before the oxy-hydrogen I blow-pipe. The metals differ also in volatility. Some are readily volatiliz- ed by caloric, while others are of so fixed a nature that they may be exposed to the most intense heat of a wind furnace without being dissipated in vapour. There are seven metals the volatility of which has been ascertained with certainty; namely, cadmium mercury, arsenic, tellurium, potassium, sodium and zinc. The metals cannot be resolved into more simple parts, and there- fore, in the present state of chemistry, they must be regarded as elementary bodies. It was formerly conceived that they might be converted into one another; and this notion led to the vain at- tempts of the alchemists to convert the baser metals into gold. The chemist has now learned that his sole art consists in resolv- ing compound bodies into their elements, and causing substances to unite which were previously uncombined. There is not a single fact in support of the opinion that one elementary principle can assume the properties peculiar to another. Metals have an extensive range of affinity, and on this account few of them are found in the earth native, that is, in an uncom- bined form. They commonly occur in combination with other bodies, especially with oxygen and sulphur, in which state they are said to be mineralized. It is a singular fact in the chemical history of the metals that they are little disposed to combine in the metallic state with compound bodies. Chemists are not ac- quainted with any instance of a metal combining either with a metallic oxide or with an acid. They unite readily, on the contrary, with elementary substances. Thus, under favourable circum- stances, they combine with one another, forming compounds 220 PROPERTIES OF METALS. termed alloys, which possess all the characteristic properties of the pure metals. They unite likewise with the simple substances not metallic, such as oxygen, chlorine, and sulphur, giving rise to new bodies in which the metallic character is wholly wanting. In all these combinations the tendency to unite in a few definite proportions is conspicuous. Metals are of a combustible nature, that is, they are not only susceptible of slow oxidation, but, under favourable circum- stances, they unite rapidly with oxygen, giving rise to *all the phenomena of real combustion. Zinc burns with a brilliant flame when heated to full redness in the open air; iron emits vivid scintillations on being inflamed in an atmosphere of oxygen gas; and the least oxidable metals, such as gold and platinum, scintillate in a similar manner when heated by the oxy-hydrogen blow-pipe. The product either of the slow or rapid oxidation of a metal, when heated in the air, has an earthy aspect, and was called a calx by the older chemists, the process of forming it being ex- pressed by the term calcination. Another method of oxidizing metals is by deflagration; that is, by mixing them with the nitrate or.chlorate of potassa, and projecting the mixture into a red-hot crucible. Most metals may be oxidized by digestion in nitric acid ; and nitro-muriatic acid is an oxidizing agent of still greater power. Some metals unite with oxygen in one proportion only, but most of them have two or three degrees of oxidation. Metals differ remarkably in their relative forces of attraction for oxygen. Potassium and sodium, for example, are oxidized by mere expo- sure to the air; and they decompose water at all "temperatures the instant they come in contact with it. Iron and copper may be preserved in dry air without change, nor can they decompose water at common temperatures; but they are both slowly oxi- dized by exposure to a moist atmosphere, and combine rapidly with oxygen when heated to redness in the open air. Iron has a stronger affinity for oxygen than copper; for the former de- composes water at a red heat, whereas the latter cannot produce that effect. Mercury is less inclined than copper to unite with oxygen. Thus it may be exposed without change to the influence of a moist atmosphere. At a temperature of 650° or 700° F. it is oxidized ; but at a red heat it is reduced to the metallic state, while the oxide of copper can. sustain the strongest heat of a blast furnace, without losing its oxygen. The affinity of silver is still weaker than that of mercury for oxygen ; for it cannot be oxidized by the sole agency of caloric at any temperature. Metallic oxides suffer reduction, or may be reduced to the me- tallic state in several ways : 1. By heat alone. By this method, the oxides of gold, silver, mercury, and platinum, may be decomposed. PROPERTIES OF METALS. 221 2. By the united agency of heat and combustible matter. Thus, by conducting a current of hydrogen gas over the oxides of copper or of iron heated to redness in a tube of porcelain, water is generated, and the metals- are obtained in a pure form. Carbonaceous matters are likewise used for the purpose with great success. Potassa and soda, for example, may be decom- posed by exposing them to a white heat after being intimately mixed with charcoal in fine powder. A similar process is em- ployed in metallurgy for procuring the metals from their ores, the inflammable materials being wood, charcoal, coke, or coal. In the more delicate operations of the laboratory, charcoal and the black flux are preferred. 3. By the galvanic battery. This is a still more powerful agent than the preceding; since some oxides, such as baryta and strontia, which resist the united influence of heat and char- coal, are reduced by the agency of galvanism. 4. By the action of deoxidizing agents on metallic solutions. The phosphorons acid, for example, when added to a liquid con- taining the oxide of mercury, deprives the oxide of its oxygen, metallic mercury subsides, and phosphoric acid is generated. In like manner, one metal may be precipitated by another, pro- vided the affinity of the latter for oxygen exceeds that of the former. Thus, when mercury is added to a solution ofthe nitrate ofthe oxide of silver, metallic silver is thrown down, and oxide of mercury is dissolved by the nitric acid. On placing metallic copper in the liquid, pure mercury subsides, and a nitrate ofthe oxide of copper is formed ; and from this solution metallic cop- per may be precipitated by means of iron. Metals, like the simple non-metallic bodies, may give rise to oxides or acids by combining with oxygen. The former are the most frequent products. Many metals form oxides, which are not acidified by oxygen ; whereas one metal only, arsenic, is capable of forming an acid and not an oxide. All the other metals which are convertible into acids by oxygen, such as chromium, tungsten, and molybdenum, are also susceptible of yielding one or more oxides. In these instances, the acids always contain a larger quantity of oxygen than the oxides of the same metal. The distinguishing feature of the metallic oxides is the pro- perty possessed by many of them of entering into combination with acids. All salts, those of ammonia excepted, are composed of an acid and a metallic oxide. In some instances, all the oxides of the same metal are capable of forming salts with acids, as is exemplified by the oxides of iron. More commonly, how- ever, the protoxide is the sole alkaline or salifiable base. Most of the metallic oxides are insoluble in water; but all those that are soluble, have the property of giving a brown stain to the 222 TIN. yellow turmeric paper, and of restoring the blue colour of red- dened litmus. Oxides sometimes unite with each other, and form definite compounds. The most abundant ore of chronium, commonly called chromate of iron, is an instance of this kind; and the red and deutoxide of manganese, and the red oxide of lead, appear to belong to the same class of bodies. SECTION IX. Tin, or Stannum. Tin has been known since the earliest periods of civilization. It was used in the time of Moses; it is mentioned by Homer, and was brought from Cornwall (England,) by the Phoenicians and Greeks, centuries before the birth of our Saviour. Some of the mines in that country are excavated so far under the bed of the ocean, that the workmen often hear the rolling ofthe pebbles and the washing of the waves, over their heads. The tin of commerce, called by the names of block and grain tin, is procured from the native oxide by means of heat and char- coal. The best grain tin is almost chemically pure, containing very minute quantities of copper and iron, and occasionally of arsenic. Tin has a white colour, and a lustre resembling that of silver. The brilliancy of its surface is soon impaired by exposure to the atmosphere, though it is not oxidized even by the combined agency of air and moisture. Its malleability is very considerable ; for the thickness of common tin-foil does not exceed 1-1000 of an inch. In ductility and tenacity it is inferior to several metals. It is soft and inelastic, and when bent backwards and forwards, emits a peculiar crackling noise. Its specific gravity is about 7.9. At 442° F. it fuses, and if exposed at the same time to the air, its surface tarnishes, and a gray powder is formed. When heated to whiteness, it takes fire and burns with a white flame, being converted into the peroxide of tin. Tin and Oxygen. Oxides of Tin.—Tin is susceptible of two degrees of oxidation. Both the oxides of tin form salts by uniting with acids; they are likewise capable of combining with alkalies. These oxides are inferred to be thus constituted :— Tin. Oxygen. Protoxide 58 or one atom. 8 or one atom. Peroxide 58 16 or two atoms. TIN. 223 The protoxide is of a gray colour, and is formed when tin is kept for some time in a state of fusion in an open vessel. It may also be procured by precipitation from the protomuriate of tin. This salt is made by boiling tin in strong muriatic acid, when the metal is oxidized by the decomposition of water ; and if atmos- pheric air be carefully excluded, a pure protomuriate results. From this solution the hydrate of the protoxide may be precipi- tated either by pure potassa or the carbonate of that alkali; but an excess of the former must be carefully avoided, as otherwise the precipitate would be re-dissolved. It is essential likewise to the success of the process that the protoxide should be both washed and dried without being exposed to the air. The protoxide of tin is remarkable for its powerful affinity for oxygen. When heated in open vessels, it is converted into the peroxide with evolution of heat and light. Its salts not only at- tract oxygen from the air, but act as powerful deoxidizing agents. Thus the protomuriate of tin converts the peroxide of copper or iron into protoxides, and it precipitates silver, mercury, and pla- tinum from their solutions in the metallic state. It is thrown down by sulphuretted hydrogen as the black protosulphuret of tin. The peroxide of tin is most conveniently prepared by the action of nitric acid on metallic tin. Nitric acid, in its most concen- trated state, does not act easily upon tin; but when a small quantity of water is added, violent effervescence takes place ow- ing to the evolution of nitrous acid and the deutoxide of nitrogen, and a while powder, the hydrated peroxide, is produced. On edulcorating this substance, and heating it to redness, watery vapour is expelled, and the pure peroxide, of a straw yellow colour, remains. In this process ammonia is generated, a cir- cumstance which proves water as well as nitric acid to have been decomposed. The peroxide of tin has a very feeble affinity for acids. With nitric acid it does not unite at all; and as prepared by the pre- ceding method, it is dissolved by muriatic acid, even before being ignited, with great difficulty. The peroxide of tin, when melted with glass, forms white enamel. Both these oxides of tin have, in a certain degree, acid pow- ers, though their affinities for the different bases are exceedingly feeble. The protoxide is, therefore, sometimes called the stannous acid, and the peroxide the stannic acid. Tin and Hydrogen. During the solution of tin in muriatic acid, hydrogen gas, of an alleacfeous odour, is produced. This has been supposed by some chemists, to arise from the presence of arsenic in the tin used in the experiment; but Bayen seems to have proved that this is not the case—for the tin of commerce very rarely con- 224 TIN. tains arsenic, and when it is found in it, the proportion is so small that it can have no influence in producing the odour of garlic. For this reason, we have considered stannuretted hydro- gen as a chemical compound. Phosphuret of Tin.—This is formed by dropping small pieces of phosphorus into melted tin. Sulphurets of Tin.—The protosulphuret is best formed by heating sulphur with metallic tin. A brittle compound of a bluish gray colour and metallic lustre results, which is fusible at a red heat, and assumes a lamellated structure in cooling. It is dissolved by muriatic acid, with disengagement of sulphuretted hydrogen. According to the analysis of Dr. Davy and Berzelius, it is composed of one atom of tin and one atom of sulphur. The bisulphuret, formerly called aurum musivum, has a golden yellow colour, and is made by heating a mixture of sulphur and the oxide of tin in close vessels. The elements of the latter unite with separate portions of sulphur, forming sulphurous acid and bisulphuret of tin. This compound was supposed by Proust to be the hydrosulphuret of the peroxide of tin, and its real nature was first made known by Dr. Davy. It consists of one atom of tin and two atoms of sulphur. By exposing a mixture of sulphur and the protosulphuret of tin to a low red heat, Berzelius obtained a compound, consisting of 58 parts, or one atom of tin, and 24 parts or one atom and a half of sulphur. If it is really a definite compound, it should be termed a sesquisulphuret. Salts. Tin combines with the nitric, carbonic, boracic, and phos- phoric acids, and forms compounds which do not crystallize. The sulphate of tin is a white acicular crystaline solid. The phos- phite, sulphite, hyposulphite, and hydrosulphate, have been formed, but have as yet been slightly examined. The salts of tin are mostly soluble in water, and are precipi- tated of an orange colour, by the hydrosulphate of ammonia pro- vided no excess of acid be present. The alloy of tin and arsenic is employed for forming arsenu- retted hydrogen gas. The tin of commerce sometimes contains a minute quantity of this alloy. On Metallic Combinations. We shall treat briefly in the present section of the combina- tions of the metals with one another. These compounds are called alloys; and to those alloys of which mercury is a consti- tuent, the term amalgam is applied. It is probable that each metal is capable of uniting in one or more proportions with every METALLIC COMBINATIONS. 225 other metal, and on this supposition the number of alloys would be exceedingly numerous. This department of chemistry, how- ever, owing to its having been cultivated with less zeal than most other branches of the science, is as yet limited, and our knowledge concerning it imperfect. Metals do not combine with one another in their solid state, owing to the influence of chemical affinity being counteracted by the force of cohesion. It is necessary to liquefy at least one of them, in which case they always unite, provided their mutual attraction is energetic. Thus brass is formed when pieces of copper are put into melted zinc; and gold unites with mercury at common temperatures by mere contact. Metals appear to unite with one another in every proportion, precisely in the same manner as sulphuric acid and water. Thus there is no limit to the number of alloys of gold and copper. It is certain, however, that metals have a tendency to combine in definite proportion ; for several atomic compounds of this kind occur native. The crystallized amalgam of silver, for example, is composed, according to the analysis of Klaproth, of 64 parts of mercury and 3G of silver, numbers which are so nearly in the ratio of 200 to 110, that there can be no doubt of the amalgam containing one atom of each of its elements. It is indeed pos- sible, that the variety of proportion is rather apparent than real, arising from the mixture of a few definite compounds with one another, or with uncombined metal, an opinion not only sug- gested by the mode in which alloys are prepared, but in some measure supported by observation. Thus on adding successive small quantities of silver to mercury, a great variety of fluid amalgams are apparently produced; but, in reality, the chief, if not the sole compound, is a solid amalgam, which is merely dif- fused throughout the fluid mass, and may be separated by pressing the liquid mercury through a piece of thick leather. Alloys are analagous to metals in their chief physical proper- ties. They are opaque, possess the metallic lustre, and are good conductors of electricity and caloric. They often differ mate- rially in some respects from the elements of which they consist. The colour of an alloy is sometimes different from that of its con- stituents, of which brass is a remarkable example. The hard- ness of a metal is in general increased by being alloyed, and for this reason its elasticity and sonorousness are frequently improv- ed. The malleability and ductility of metals, on the contrary. are usually impaired by combination. Alloys formed of two brittle metals are always brittle ; and an alloy composed of a ductile and a brittle metal is generally brittle, especially if the latter predominates. An alloy of two ductile metals is sometimes brittle. The density of alloys is sometimes less, sometimes greater, than the mean density of the metals of which it is composed. Ff 226 POTASSIUM. The fusibility of metals is greatly increased by being alloyed. Thus pure platinum, which cannot be completely fused in the most intense heat of a wind furnace, forms a very fusible alloy with arsenic. The tendency of metals to unite with oxygen is considerably augmented by being alloyed. This effect is particularly conspi- cuous when dense metals are liquefied by combination with quicksilver, and is manifestly owing to the loss of their cohesive power. Lead and tin, for instance, when united with mercury, are soon oxidized by exposure to the atmosphere ; and even gold and silver combine with oxygen, when the amalgams of those metals are agitated with air. The oxidability of one metal in an alloy appears in some instances to be increased in consequence of a galvanic action. Thus Mr. Faraday observed, that an alloy of steel with 100th of its weight of platinum was dissolved with effervescence in dilute sulphuric acid, which was so weak that it scarcely acted on common steel;—an effect which he ascribes to the steel in the alloy being rendered positive by the presence of the platinum. SECTION X. Potassium. If a sufficient quantity of wood be burnt to ashes, and these ashes be afterwards repeatedly washed with water till it comes off free from any taste, and if this liquid be filtered, and then evapo- ted to dryness, the substance which remains behind is potash. That potash was known to the ancient Gauls and Germans cannot be doubted, as they were the inventors of soap, which, Pliny, informs us, they composed of ashes and tallow ; these ashes were nothing else than potash, not, however, in a state of purity. The alchimists were well acquainted with it; and it has been in every period very much employed in chemical re- searches. It may be said however, with justice, that till Ber- thollet published the process in the year 1786, chemists had never examined potash in a state of complete purity. When potash is perfectly dry it is a non-conductor of electricity, but it becomes a conductor when slightly moistened on the sur- face, a degree of moisture which it acquires by being exposed for a few seconds to the atmosphere. When pieces of potash in this state are placed upon a disc of platinum attached to the ne- gative end of a powerful galvanic battery, and a platinum wire from the positive extremity is made to touch its upper surface, the potash is gradually decomposed, oxygen gas separating at the extremity ofthe positive wire, while globules of a white metal, like mercury, appear at the side in contact with the platinum disc, POTASSIUM. 227 a number of accurate experiments by Sir H. Davy, demonstrated that the globules were the basis of potash, and that they were converted into potash by absorbing oxygen. This brilliant dis- covery was made in the year 1807. To the metallic basis thus discovered, Davy gave the name of potassium. By this process potassium is obtained in small quantity only; but Gay-Lussac and Thenard invented a method by which a more abundant supply of it may be procured. Their process consists in bringing fused hydrate of potassa in contact with turnings of iron heated to whiteness in a gun-barrel. The iron, under these circumstances, deprives the water and potassa of oxygen, hydro- gen gas combined with a little potassium is evolved, and pure potassium sublimes, and may be collected in a cool part of the apparatus. Potassium may also be prepared, as first noticed by M. Curau- dau, by mixing dry carbonate of potassa with half its weight of powdered charcoal, and exposing the mixture, contained in a gun-barrel or spheroidal iron bottle, to a strong heat. An im- provement on both processes has been made by M. Brunner, who decomposes potassa by means of iron and charcoal. From eight ounces of fused carbonate of potassa, six ounces of iron filings, and two ounces pf charcoal, mixed intimately, and heated in an iron bottle, he obtained 140 grains of potassium. Berzelius has observed, that the potassium thus made, though fit for all the usual purposes for which it is required, contains a minute quan- tity of carbon; and therefore, if required to be quite pure must be rendered so by distillation in a retort of iron or green glass; a modification of this process has been since described by Wohler, who effects the decomposition of the potash solely by means of charcoal. The material employed for this purpose is carbonate of potassa prepared by heating cream of tartar to redness in a co- vered crucible. Potassium is solid at the ordinary temperature of the atmos- phere, at 70° F.; it is somewhat fluid, though its fluidity is not per- fect till it is heated to 150° F. At 50° F. it is soft and malleable, and yields like wax to the pressure of the fingers ; but it becomes brittle when cooled to 32° F. It sublimes at a red heat without undergoing any change, provided the atmospheric air be com- pletely excluded. Its texture is crystalline, as may be seen by breaking it across while brittle. In colour and lustre it is pre- cisely similar to mercury. At 60° F. its density is 0.865, so that it is considerably lighter than water. It is quite opaque, and is a good conductor of electricity and caloric. The most prominent chemical property of potassium is its affinity for oxygen gas. It oxidizes rapidly in the air, or by contact with fluids which contain oxygen. On this account it must be preserved either in glass tubes hermetically sealed, or under the surface of liquids, such as naphtha, of which oxygen is 228 POTASSIUM. not an element. If heated in the open air, it takes fire, and burns with a white flame and great evolution of caloric. It decompo- ses water on the instant of touching it, and so much heat is dis- engaged, that the potassium is inflamed, and burns vividly while swimming upon its surface. The hydrogen unites with a little potassium at the moment of separation ; and this compound takes fire as it escapes, and thus augments the brilliancy of the com- bustion. When potassium is plunged under water, violent action ensues, but without the emission of light, and pure hydro- gen gas is evolved. Potassium and Oxygen. Potassium unites with oxygen in two proportions. The pro- toxide, commonly called potash or potassa, is always formed when potassium is put into water, or when it is exposed at com- mon temperatures to dry air or oxygen gas. By the first me- thod, the protoxide is obtained in combination with water ; in the latter, it is anhydrous. In performing the last mentioned pro- cess, the potassium should be cut into very thin slices ; for other- wise the oxidation is incomplete. The product, when partially oxidized, was once suspected to be a distinct oxide ; but it is now admitted to be a mixture of potassa and potassium. As potassa is the protoxide of potassium, it is supposed to con- tain one atom of each of its elements. Its composition is best determined by collecting and measuring the quantity of hydrogen which is evolved when potassium is plunged underwater. From the experiments of Sir H. Davy, and Gay-Lussac, and Thenard, it appears that 40 grains of potassium decompose precisely 9 grains of water; and that while one grain of hydrogen escapes in the gaseous form, the 8 grains of oxygen combine with the metal. The protoxide of potassium is therefore composed of Potassium . . . 40, or one atom. Oxygen . . . 8, or one atom. And 48 is its combining proportion. When potassium burns in the open air or in oxygen gas, it is converted into an orange-coloured substance, which is the per- oxide of potassium. It may likewise be formed by conducting oxygen gas over potassa at a red heat. When this peroxide is put into water, it is resolved into oxygen and potassa, the former of which escapes with effervescence, and the latter is dissolved- It consists of Potassium ... 40, or one atom. Oxygen ... 24, or three atoms. Anhydrous potassa may be prepared either by the slow oxida- tion of potassium, as already mentioned, or by decomposing nitrate of potassa by a red heat in a vessel of gold. In its pure state, it is a white solid substance, highly caustic, which fuses at POTASSIUM. 229 a temperature somewhat above that of redness, and bears the strongest heat of a wind furnace without being decomposed or volatilized. It has a powerful affinity for water, and intense heat is disengaged during the act of combination. With a certain portion of that liquid it forms a solid hydrate, the elements of which are united by an affinity so energetic that, no degree of heat hitherto employed can effect their separation. This sub- stance was long regarded as the pure alkali, but it is in reality the hydrate of potassa. It is composed of 48 parts, or one atom of potassa, and 9 parts, or one atom of water. The hydrate of potassa is solid at common temperatures. It fuses at a heat rather below redness, and assumes a somewhat crystalline texture in cooling. It is highly deliquescent, and re- quires about half its weight of water for solution. It is soluble, likewise, in alcohol. It destroys all animal textures, and on this account is employed in surgery as a caustic. It was formerly called lapis causticus, but it is now termed potassa and potassa fusa. This preparation is made by evaporating the aqueous solu- tion of potassa in a silver or clean iron capsule to the consistency of oil, and then pouring it into moulds. In this state it is im- pure, containing oxide of iron, together with the muriate, car- bonate, and sulphate of potassa. It is purified from these sub- stances by dissolving it in alcohol, and evaporating the solution to the same extent as before, in a silver vessel. The operation should be performed expeditiously, in order to prevent, as far as possible, the absorption of carbonic acid. When common caustic potash is dissolved in water, a number of small bubbles of gas are disengaged, which are pure oxygen, the quantity of gas is variable in different specimens. The aqueous solution of potassa, the aqua potassa, of the Phar- macopoeia, is prepared by decomposing the carbonate of potassa by lime. To effect this object completely, it is advisable to employ equal parts of quicklime and carbonate of potassa. After slaking the lime in an iron vessel, the carbonate of potassa, dis- solved in its own weight of hot water, is added, and the mixture is boiled briskly for about ten minutes. The liquid, after sub- siding, is filtered through a funnel, the throat of which is ob- structed by a piece of clean linen. This process is founded on the fact that lime deprives the car- bonate of potassa of its acid, forming an insoluble carbonate of lime, and setting the pure alkali at liberty. If the decomposi- tion is complete, the filtered solution should not effervesce with muriatic acid. The solution of potassa is highly caustic, and its taste intensely acrid. It possesses alkaline properties in an eminent degree, converting the vegetable blue colours to green, and neutralizing the strongest acids. It absorbs carbonic acid gas rapidly, and is consequently employed for withdrawing that substance from 230 POTASSIUM. gaseous mixtures. For the same reason it should be excluded from the atmosphere during the process of filtering, and preserved in well-closed bottles. Potassa is employed as a re-agent in detecting the presence of bodies, and in separating them from one another. The solid hy- drate, owing to its strong affinity for water, is used for depriving gases of hygrometric moisture, and is admirably fitted for forming frigorific mixtures. Potassa may be distinguished from all other substances by the following characters: 1. If tartaric acid be added in excess to a salt of potassa dissolved in water, and the solution be stirred with a glass rod, a white precipitate, the bitartrate of potassa, soon appears, which forms peculiar white streaks upon the glass by the pressure of the rod in stirring. 2. A solution of the muriate of platinum causes a yellow precipitate, the muriate of platinum and potassa. This is the most delicate test, provided the mixture be gently evaporated to dryness, and a little cold water be after- wards added. The muriate of platinum and potassa then remains in the form of small shining yellow crystals. 3. By being pre- cipitated by no other substance. Potassium and Hydrogen. These substances unite in two proportions, forming in one case a solid, and in the other a gaseous compound. The latter is produced when the hydrate of potassa is decomposed by iron at a white heat, and it appears also to be generated when potassium burns on the surface of water. It inflames spontaneously in air or oxygen gas; but on standing for some hours over mercury, the greater part, if not the whole ofthe potassium, is deposited. The solid hydroguret of potassium was made by Gay-Lussac and Thenard, by heating potassium in hydrogen gas. It is a gray solid substance, which is readily decomposed by heat or contact with water. It does not inflame spontaneously in oxygen gas. Cyanide of Potassium.—When potassium is heated in hydro- cyanic vapour, the acid is decomposed, the hydrogen is driven off, and the cyanogen combines with the potassium, and forms a cya- nide of that metal. The cyanides are very analagous to the sul- phurets; we shall describe those only which are the most impor- tant. Phosphuret of Potassium.—This compound may be formed by the action of potassium on phosphorus with the aid of a moderate heat. It is converted by water into potassa and phosphuretted hydrogen gas, which inflames at the moment of its formation. Sulphuret of Potassium.—Sulphur unites readily with potassium by the aid of heat; and so much caloric is evolved at the moment of combination, that the mass becomes incandescent. The best method of obtaining a sulphuret in definite proportion, is by de- POTASSIUM. 231 composing the sulphate of potassa according to the process of Berthier or Berzelius. This sulphuret is composed of one atom of sulphur and one atom of potassium. It has a red colour, fuses below the temperature of ignition, and assumes a crystalline tex- ture in cooling. It is dissolved by water, being converted, with evolution of caloric, into the hydrosulphuret of potassa. Besides this protosulphuret, Berzelius has described four other compounds, which he obtained by igniting carbonate of potassa with different proportions of sulphur. These are composed of one atom of potassium to 2, 3, 4, and 5 atoms of sulphur. Selenuret of Potassium.—Selenium combines with potassium with great energy, producing a grayish compound, with metallic lustre, and which, when thrown into water, evolves selenuretted hydrogen gas. Salts. Nitrate of Potassa.—This salt is generated spontaneously in the soil, and crystallizes upon its surface, in several parts of the world, and especially in the East Indies. In France and Ger- many, it is prepared artificially from a mixture of common mould, or porous calcareous earth, with animal and vegetable remains containing nitrogen. When a heap of these materials, preserved moist and in a shaded situation, is moderately exposed to the air, nitric acid is gradually generated, and unites with the potassa, lime and magnesia, which are commonly present in the mixture. On dissolving these salts in water, and precipitating the two earths by carbonate of potassa, a solution is formed, which yields crystals of nitre by evaporation. The nitric acid is doubtless generated under these circumstances by the nitrogen of the or- ganic matters combining during putrefaction with oxygen of the atmosphere, a change which must be attributed to the affinity of oxygen for nitrogen, aided by that of the nitric acid for alkaline bases. The nitrate of potassa is a colourless salt, which crystallizes readily in six-sided prisms. Its taste is saline, accompanied with an impression of coolness. It requires for solution seven parts of water at 60° F., and its own weight of boiling water. It con- tains no water of crystallization, but its crystals are never quite free from water lodged mechanically within them. At 616° it undergoes the igneous fusion, and like all the nitrates, is decom- posed by a red heat. Nitre is chiefly employed in chemistry as an oxidizing agent, and in the formation of nitric acid. Its chief use in the arts is for making gunpowder, which is a mixture of nitre, charcoal, and sulphur. In the East Indies it is employed for the preparation of cooling mixtures ;—an ounce of powdered nitre dissolved in 232 POTASSIUM. five ounces of water reduces its temperature by fifteen degrees. It possesses powerful antiseptic properties, and is therefore much employed in the preservation of meat and animal matters in general. Hyponitrite of Potassa.—This salt appears to form a part of the residuum, left in the retort after the decomposition of the nitre used in making oxygen gas. Carbonate of Potassa.—This salt is procured in an impure form by burning land plants, lixiviating their ashes, and evapo- rating the solution to dryness, a process which is performed on a large scale in Russia and America. The carbonate of potassa, thus obtained, is known in commerce by the names of potash and pearlash, and is employed in many of the arts, especially in the formation of soap and the manufacture of glass. When derived from this source it always contains other salts, such as the sul- phate and muriate of potassa; and therefore, for chemical pur- poses, should be prepared from cream of tartar, the bitartrate of potassa. On heating this salt to redness, the tartaric acid is decomposed, and a pure carbonate of potassa mixed with char- coal remains. The carbonate is then dissolved in water, and, after filtration, is evaporated to dryness in a capsule of platinum or silver. Pure carbonate of potassa has a taste strongly alkaline, is slightly caustic, and communicates a green to the blue colour of the violet. It dissolves in less than an equal weight of water at 60° F., deliquesces rapidly on exposure to the air, and crystal- lizes with much difficulty from its solution. In pure alcohol it is insoluble. It fuses at a full red heat, but undergoes no other change. According to the analysis of Dr. Wollaston, it is com- posed of 22 parts or one atom of carbonic acid, and 48 parts or one atom of potassa. The purity of any given specimen of this salt is conveniently ascertained by means of sulphuric acid of specific gravity 1.141. Of this acid, 355 grains neutralize 100 grains of pure carbonate of potassa. The bicarbonate of potassa is made by transmitting a current of carbonic acid gas through a solution of the carbonate of potassa. By slow evaporation, the bicarbonate is deposited from the liquid in regular prismatic crystals. The bicarbonate of potassa, though far milder than the carbo- nate, is alkaline both to the taste and to test paper. It does not deliquesce on exposure to the air. It requires four times its weight of water at 60° F. for solution, and is much more soluble at 212° F.; but it parts with some of its acid at that temperature. At a low red heat it is converted into the carbonate. From the analysis of Dr. Wollaston, the crystals consist of one atom of potassa, two atoms of acid, and one atom of water. POTASSIUM. 233 Sequi-Carbonate of Potassa was discovered by Dr. Nimmo of Glasgow. Its crystals are composed of one atom of potassa, an atom and a half of carbonic acid, and six atoms of water. Cyanate of Potassa.—This is an unimportant salt, first pro- duced by Wohler, during his interesting researches on the com- pounds cyanogen. Hydrocyanate of Potassa, is generated by the decomposition of water, when the cyanide of potassium is put into that fluid, and may be made directly by mixing hydrocyanic acid with a solution of potassa. This salt in a short time undergoes de- composition. The hydrocyanate of potassa appears to exist-only in solution; for when evaporated to dryness, it is converted into the cyanuret of potassium, a compound which is far less liable to spontaneous decomposition than hydrocyanic acid, and is capable of support- ing a very high temperature in close vessels without change. It is deliquescent, and highly soluble in water. The solution gives a green colour to violets, and has an alkaline taste, accompanied with the flavour and a faint odour of hydrocyanic acid. It is de- composed by nearly all the acids, even by the carbonic, and on this account should be preserved in well-closed vessels. It acts upon the animal system in the same manner as hydrocyanic acid, and MM. Robiquet and Villerme have proposed its employment in medical practice, as being more uniform in strength, and less prone to decomposition, than hydrocyanic acid. Borate of Potassa—May be prepared by calcining a mixture of boracic acid and nitre. The heat drives off the nitric acid, and leaves a white saline mass, which, when dissolved in water, yields crystals of borate of potassa in four sided prisms. Silicate of Potassa—May be formed by fusing three parts of potash by weight, with one part of silica. A transparent colourless liquid is formed which, on cooling, congeals into glass. Silica seems capable of combining with potassa, in a great number of proportions. Glass may be considered as a supersilicate of potassa in which the proportion of silica is very considerable. Phosphate of Potassa, is a soluble difficultly crystallizable salt, it may be obtained in four sided prisms and octahedrons. It has little taste, by the action of heat it undergoes fusion. It is not decomposed by lime, unless the lime be added in considerable excess, and then a compound is formed of phosphoric acid with potassa and lime. Bi-phosphate of Potassa, is formed by dissolving the neutral phosphate in phosphoric acid, and evaporating till crystals are obtained, which are prismatic and very soluble. Di-phosphate of Potassa.—When phosphate of potassa, is fused in a platinum crucible with potassa, it is converted into di-phosphate of potassa, which is insoluble in cold and very diffi- cultly soluble in hot water. It is fusible before the blow-pipe 234 POTASSIUM. yielding a globule, which is opaque when cold, but transparent whilst in fusion. Phosphite of Potassa, is a soluble deliquescent salt, not hith- erto accurately examined. Hypophosphite of Potassa, is very deliquescent, and soluble in water and alcohol, nearly in all proportions; when heated, it evolves phosphuretted hydrogen and phosphorus, and is convert- ed into phosphate of potassa. Sulphate of Potassa.—This salt is easily prepared artificially by neutralizing the carbonate of potassa with sulphuric acid, and it is procured abundantly as a product of the operation for prepar- ing nitric acid. Its taste is saline and bitter. It crystallizes in six-sided prisms, bounded by pyramids with six sides. The crys- tals contain no water of crystallization, and suffer no change by exposure to the air. They decrepitate when heated, and enter into fusion at a red heat. They require 16 times their weight of water at 60° F. and five of boiling water for solution. The sulphate of potassa is composed of 40 parts or one atom of sulphuric acid, to 48 parts or one atom of potassa. The Bisulphate of Potassa, which contains twice as much acid as the foregoing salt, is easily formed by digesting 88 parts, or one atom ofthe neutral sulphate, with water containing about 50 parts of concentrated sulphuric acid, and evaporating the solution. It has a strong sour taste, and reddens litmus paper. It is much more soluble than the neutral sulphate, requiring for solution only twice its weight of water at 60°, and less than an equal weight at 212° F. It is resolved by heat into sulphuric acid and the neu- tral sulphate. Sulphite of Potassa—Is formed by passing sulphurous acid into a solution of carbonate of potassa, till all effervescence ceases, and evaporating out of the contact of air. Rhomboidal plates are obtained, white, of a sulphurous taste, and very soluble; by exposure to air they pass into sulphate of potassa. Hypo-sulphite of Potossa.—This salt is formed by exposing the sulphuretted hydrosulphate of potassa to the atmosphere, till it has lost its colour, after which, on evaporation, it crystallizes in the form of fine needles. It has a taste, at first, not unlike that of nitre, succeeded by bitterness. It is deliquescent. When care- fully dried, it takes fire on raising the heat, and burns somewhat like tinder, but with a feeble blue flame. Hydrosulphate of Potassa—May be formed by transmitting a current of sulphuretted hydrogen gas, through liquid hydrate of potassa the salt crystallizes in six sided prisms, which are deliques- cent and soluble in water and alcohol. If the alkali is completely saturated, the resulting compound is the sulphuretted hydrosul- phate of potassa. Ammonio—sulphate of Potassa is a double salt, formed by add- POTASSIUM. 235 ing ammonia to bi-sulphate of potassa. It crystallizes in bril- liant plates of a bitter taste. The Sulphocyanate of Potassa, (and most of the salts of sulphocyanic acid have probably a similar constitution,) contains one atom of the acid, and one atom of the oxide ; so that the oxy- gen and hydrogen are in due proportion for combining. This salt, indeed, exists only in a liquid state; for the crystals which are deposited from a concentrated solution, when separated from the adhering moisture by bibulous paper, do not contain either water or its elements, but are a pure sulphocyanuret of potassium. The crystals are very deliquescent on exposure to the air, and dissolve freely in water, yielding a solution which is quite neutral. In form, taste, and fusibility, they are very analogous to nitre. The sulphocyanate of potassa is employed in preparing the sulphocyanic acid, and as a test for detecting the presence ofthe peroxide of iron. Tellurate of Potassa, may be formed by heating oxide of tellu- rium with nitre and dissolving the residuum in boiling water, which, on cooling, deposits an imperfectly crystallized white powder, difficultly soluble in water. Arseniate of Potassa.—When arsenic acid is saturated with potassa, it forms an uncrystallizable salt, which deliquesces in the air, renders syrup of violets green, but does not alter the infusion of turnsole. Bi-narseniate of Potassa.—This salt was first obtained by Macquer, hence it was termed, Macquefs neutral arsenical salt. It is soluble in water, and gives a red colour to vegetable blues. It crytallizes in four sided prisms, terminated by four sided pyramids. Arsenite of Potassa, is a yellow viscid liquid, which does not crystallize. It forms the active ingredient in Fowler's mineral solution. Alloys of Potassium.—Arsenic combines readily with potassium by the application of a moderate heat. Light is evolved during the combination. The alloy has a brown colour and little ofthe metallic lustre. Tin and potassium are easily alloyed by heating them together, a weak light is emitted at the instant of combina- tion. The alloy is brittle, not so white as tin, and pretty fusible. It is speedily destroyed either in the air or under water by the conversion of the potassium into potassa. ( 23G ) CHAPTER III. In this part of our work we have arranged all the solid elemen- tary bodies, except potash, which, by uniting with oxygen, have an alkaline re-action on vegetable colours ; converting the blues to green, and the yellows to brown. These substances are six in number, sodium, lithium, barium, strontium, calcium, and magnesium. Potassium, from its powerful alkaline functions, very properly stands at the head of this list, though we have placed it at the close of our last chapter, on account of its combination with hydrogen. It thus beautifully links together, in a natural arrangement, the two series of substances. SECTION I. Sodium. Soda, called also the fossil or mineral alkali, was known to the ancients, though not in a state of purity, under the name of ni- trum or natron. It was confounded with potassa, which it closely resembles, till Duhamel published a dissertation on common salt, in 1736. He first proved that the base of common salt is soda, and that soda is different from potassa. Sir H. Davy succeeded in decomposing soda by the same pro- cess, which enabled him to obtain the base of potassa. Like that alkali, its basis is a metal, and Davy distinguished it by the name of sodium. The first portions of it were obtained by means of galvanism; but it may be procured in much larger quantity by chemical pro- cesses, precisely similar to those described in the last section for obtaining potassium. Sodium has a strong metallic lustre, and in colour is very ana- logous to silver. It is so soft at common temperatures, that it may be formed into leaves by the pressure of the fingers. It fuses at 200° F. and rises in vapour at a full red heat. Its speci- fic gravity is 0.972. Sodium soon tarnishes on exposure to the air, though less ra- pidly than potassium. When thrown into water it swims upon its surface, occasions violent effervescence and a hissing noise,. and is rapidly oxidized ; but no light is visible. The action is stronger with hot water, and a few scintillations appear ; but still there is no flame. In each case, soda is generated, owing to SODIUM. 237 which, the water acquires an alkaline re-action, and pure hydro- gen gas is disengaged. Oxides of Sodium.—Chemists are acquainted with two definite compounds only of sodium and oxygen. The protoxide or soda is a gray white solid, difficult of fusion, which is obtained by burning sodium in dry atmospheric air. It is also formed when sodium is oxidized by water; and its composition may be de- termined by collecting the hydrogen which is then disengaged. According to the experiments of Sir H. Davy, the results of which differ little from those of Gay-Lussac and Thenard, soda consists of 24 parts of sodium and 8 parts of oxygen. For this reason, 24 is regarded as the atomic weight of sodium, and 32 the combin- ing proportion of soda. When sodium is strongly heated in an excess of pure oxygen, an orange-coloured substance is formed, which is the peroxide of sodium. It is resolved by water into oxygen and soda ; and is composed, according to Gay-Lussac and Thenard, of two atoms of sodium and three atoms of oxygen. With water soda forms a solid hydrate, easily fusible by heat, which is very caustic, is soluble in water and alcohol, has power- ful alkaline properties, and in all its chemical relation is exceed- ingly analogous to potassa. It is prepared from the solution of pure soda, exactly in the same manner as the corresponding pre- parations of potassa. The solid hydrate is composed of 32 parts, or one atom of soda, and 9 parts or one atom of water. Soda is readily distinguished from the other alkaline bases by the following characters : 1. It yields with sulphuric acid a salt, which, by its taste and form, is easily recognized as glauber salt or sulphate of soda. 2. All its salts are soluble in water, and are not precipitated by any re-agent. 3. On exposing its salts by means of a platinum wire to the blowpipe flame, they communi- cate to it a rich yellow colour. Phosphuret of Sodium.—Sodium combines readily with phos- phorus, when heat is applied; a feeble light appears during the combination. The phosphuret has the colour and appearance of lead. When brought in contact with water, or heated in the open air, it is converted into phosphate of soda. Sulphuret of Sodium.—Sodium combines with sulphur when heated with it in close vessels, with great vividness, much heat and light being evolved, the sulphuret has a deep gray colour; when heated in the open air, it takes fire and is converted into sulphate of soda. Salts. Nitrate of Soda—May be formed by saturating carbonate of soda with nitric acid, it crystallizes in rhombs, soluble in three parts of water at 60° and in less than its weight at 212°. It has 238 SODIUM. a cool sharp flavour, and is somewhat deliquescent; it is often found in crude nitre ; it is the cubic nitre of old writers. Carbonate of Soda.—The carbonate of soda of commerce is obtained by lixiviating the ashes of sea-weeds. The best variety is known by the name of barilla, and is derived chiefly from the salsola soda and salicornia herbacea. A very inferior kind, known by the name of kelp, is prepared from sea-weeds on the northern shores of Scotland. The purest barilla, however, though well fitted for making soap and glass, and for other purposes in the arts, always contains the sulphates and muriates of potassa and soda, and on this account is of little service to the chemist. A purer carbonate is prepared by heating a mixture of sulphate of soda, saw-dust, and lime, in a reverberatory furnace. By the action of the carbonaceous matter, the sulphuric acid is decom- posed ; its sulphur partly uniting with lime and partly being dis- sipated in the form of sulphurous acid, while the carbonic acid, which is generated during the process, unites with soda. The carbonate of soda is then obtained by lixiviation and crystalliza- tion. It is difficult to obtain this salt quite free from sulphuric acid. The quantity of real carbonate in the soda of commerce may be conveniently estimated by its neutralizing power. One hun- dred grains of pure carbonate of soda is neutralized by 460 grains of sulphuric acid of density 1.141. The carbonate of soda crystallizes in octahedrons with a rhom- bic base, the acute angles of which are generally truncated. The crystals effloresce on exposure to the air, and, when heated, dissolve in their water of crystallization. By a continued heat they are rendered anhydrous without loss of carbonic acid. They dissolve in about two parts of cold, and in rather less than their weight of boiling water, and the solution has a strong alkaline taste and reaction. The crystals are composed of 22 parts or one atom of carbonic acid, 32 parts or one atom of soda, and 90 parts or ten atoms of water. The water of crystallization is apt to vary according to the temperature at which the crystals are formed. Bicarbonate of Soda.—This salt is made by transmitting a current of carbonic acid gas through a solution ofthe carbonate, and is deposited in crystalline grains by evaporation. Though still alkaline, it is much milder than the carbonate, and far less soluble, requiring about"ten times its weight of water at 60° F. for solution. It is decomposed partially at 212° F. and is con- verted into the carbonate by a red heat. It is composed, ac- cording to Thomson, of two atoms of acid, one atom of the base, and one atom of water. Sesqui-carbonate.—This compound occurs native on the banks of the lakes of soda in the province of Sukena in Africa, whence it is exported under the name of Trona. It was first SODIUM. 239 distinguished from the two other carbonates by Mr. Phillips, whose analysis corresponds with that of Klaproth. It consists of one atom of soda, an atom and a half of acid, and two atoms of water. Borate of Soda.—This salt may be formed by saturating borax with boracic acid; it is unimportant. Biborale of Soda.—This salt, the only borate of importance, occurs native in some of the lakes of Thibet and Persia, and is extracted from this source by evaporation. It is, imported from India in a crude state, under the name of Tincal, which, after being purified, constitutes the refined borax of commerce. It is frequently called sub-borate of soda, a name suggested by the inconsistent and unphilosophical practice, now quite inadmissible, of regulating the nomenclature of salts merely by their action on vegetable colouring matter. It crystallizes in hexahedral prisms, which effloresce on exposure to the air, and require twenty parts of cold, and six of boiling water, for solution. When exposed to heat, the crystals are first deprived of their water of crystal- lization, and are then fused, forming a vitreous transparent sub- stance called glass of borax. The crystals, are composed of 48 parts or two atoms of boracic acid, 32 or one atom of soda, and 72 or eight atoms of water. The chief use of borax is as a flux, and for the preparation of boracic acid. Silicate of Soda.—This salt may be easily formed by fusing two parts by weight of soda with one part of silica. It is ana- logous in its chemical propreties to the silicate of potassa. Phosphate of Soda.—Of the alkaline phosphates, that with the base of soda is the one generally employed, owing to the facility with which it is obtained in crystals It is prepared on a large scale in chemical manufactories, by neutralizing the super-phosphate of lime, procured by the action of sulphuric acid on burned bones, with carbonate of soda. The phosphate of lime is separated by filtra- tion, and the clear liquid, after being duly concentrated by evapo- ration, deposits crystals ofthe phosphate of soda in cooling. It commonly contains traces of sulphuric acid, from which it may be purified by repeated crystallization. It is customary in this process to employ a slight excess of the alkali, the presence of which facilitates the formation of crystals. On this account the phosphate of soda has commonly an alkaline reaction ; but when carefully prepared, it is quite neutral. This salt crystallizes in rhombic prisms, which effloresce on exposure to the air, and require four parts of cold or two of boil- ing water for solution. The crystals are composed of 28 parts or one atom of phosphoric acid, 32 or one atom of soda, and 108 or twelve atoms of water. This salt is employed in medicine as a laxative, and in che- mistry as a re-agent. 240 SODIUM. Phosphate of Soda and Ammonia.—This salt is easily prepared by dissolving one atom of muriate of ammonia and two atoms of phosphate of soda in a small quantity of boiling water. As the li- quid cools, prismatic crystals of the double phosphate are depo- sited, while muriate of soda remains in solution. This salt has been long known by the name ofmicrocosmic salt, and ismuch employed as a flux in experiments with the blow-pipe. When heated it parts with its water and ammonia, and a very fusible biphosphate of soda remains. It is composed of one atom of the phosphate of soda, and one atom ofthe phosphate of ammonia, united with 16 atoms of water. Phosphite of Soda, and hypophosphite of soda are unimpor- tant salts. Sulphate of Soda.—The sulphate of soda, commonly called Glauber's salt, is occasionally met with on the surface of the earth, and is frequently contained in mineral springs. It may be made by the direct action of sulphuric acid on the carbonate of soda; and it is procured in large quantity as a residue in the pro- cesses for forming muriatic acid and chlorine. The sulphate of soda has a cooling, saline, and bitter taste. It forms four and six-sided prismatic crystals, but its primary form is a rhombic octahedron; its crystals effloresce rapidly when ex- posed to the air, and are composed of 72 parts or one atom of the neutral sulphate, and 90 parts or ten atoms of water. The crystals readily undergo the watery fusion when heated; and dis- solve in three times their weight of water at 60° Fahr. The bisulphate of soda, may be formed in the same manner as the analogous salt of potassa. Sulphite of Soda, is crystallizable in transparent four and six sided prisms, soluble in four parts of water at 60°. It consists of 32 soda+32 sulphurous acid. The crystals contain 12 atoms of water=108. Hyposulphite of Soda, is formed in the same manner as the hyposulphite of potassa. It is difficultly crystallizable, deliques- cent, of an intensely bitter taste, and insoluble in alcohol. Hydrosulphate of Soda, may be prepared by the same process as the hydrosulphate of potassa. Its taste is alkaline and intense- ly bitter. It is very soluble, both in water and alcohol. When exposed to the air, it deliquesces and assumes a green colour. Arseniate of Soda, is formed by saturating a solution of car- bonate of soda with arsenic acid; on evaporation, crystals are ob- tained. It has a cooling taste, resembling that of carbonate of soda, but less strong. It requires more than ten times its weight of cold water for solution, and the liquid has alkaline properties. It undergoes the watery fusion. Arsenite of Soda.—A yellow viscid liquor, with a nauseous odour. It does not crystallize. Alloys of Sodium.—The alloy with arsenic is either brown or of an earthy aspect, or gray and metallic, according to the pro- LITHIUM. 241 portions of the metals. Sodium with tin' forms a brittle white alloy. Three parts of sodium and one part of potassium form an alloy, which remains fluid at 32°. Equal parts of these metals form a brittle crystallizable alloy. SECTION II. Lithium. In the year 1818, M. Arfwedson, of Sweden, in analyzing the mineral called petalite, discovered the existence of a new alkali, and its presence has since been detected in spodumene, lepido- lite, and in several varieties of mica. Berzelius has found it also in the waters of Carlsbad in Bohemia. From the circumstance of its having been first obtained from an earthy mineral, Arfwed- son gave it the name of lithion (from uestos lapideus), a term since changed to lithia. It has hitherto been procured in small quan- tity only, because spodumene and petalite are rare, and do not contain more than 6 or 8 per cent, of the alkali. It is combined in these two minerals with silica and alumina, whereas potassa is likewise present in lepidolite and lithion-mica, and therefore lithia should be prepared solely from the former. The best process for preparing lithia is that which was sug- gested by Berzelius. One part of petalite or spodumene, in fine powder, is mixed intimately with two parts of fluor-spar, and the mixture is heated with three or four times its weight of sulphuric acid, as long as any acid vapours are disengaged. The silica of the mineral unites with fluoric acid, and is dissipated in the form of fluosilicic acid gas, while the alumina and lithia unite with sul- phuric acid. After dissolving these salts in water, the solution is boiled with pure ammonia to precipitate the alumina, filtered, evaporated to dryness, and then heated to redness to expel the sulphate of ammonia. The residue is sulphate of lithia. Sir H. Davy succeeded, by means of galvanism, in obtaining a white coloured metal like sodium from lithia; but it was oxidized, and thus reconverted into the alkali, with such rapidity that it could not be collected. Lithia may therefore be regarded as the protoxide of lithium; and, according to the analysis of the sul- phate of lithia by Stromeyer and Thomson, lithia is inferred to be composed of Lithium - 10 or one proportional. Oxygen - 8 or one proportional. Consequently, 18 is its combining proportion. Lithia is distinguished from potassa and soda by ifs greater neutralizing power* by forming sparingly soluble salts with car- bonic and phosphoric acids, and by the circumstance of the chloride of lithium being highly deliquescent, and dissolving H h 242 LITHIUM. freely in strong alcohol. This alcoholic solution burns with a red flame ; and all the salts of lithia, when heated on platinum wire before the blowpipe, tinge the flame of a red colour. Further, when lithia is fused on platinum foil, it attacks that metal, and leaves a dull yellow trace round the spot on which it lay. Lithia is distinguished from the alkaline earths by forming soluble salts with sulphuric and oxalic acids ; and by the circum- stance that the carbonate of lithia, though sparingly soluble in water, forms with it a solution which gives a brown stain to tur- meric paper. Sulphuret of Lithium.—The action of sulphur on lithium af- fords a very soluble yellow compound, which is decomposed by acids, and, from the abundance of the precipitate, appears to con- tain a large proportion of sulphur. Salts. Lithia forms salts with all of the acids, but the following have been more particularly described. Carbonate of Lithia.—When a strong solution of carbonate of potassa is added to sulphate of lithia, a white precipitate of car- bonate of lithia is formed. It requires about 100 parts of water at 60° for its solution. It is fusible, alkaline, effervesces with acids, and absorbs carbonic acid from the air. Phosphate of Lithia, may be obtained by adding phosphoric acid to sulphate of lithia ; no precipitate is at first formed, but on adding excess of ammonia, an insoluble phosphate of lithia falls. This property enables us to separate lithia from potassa and soda. The phosphate of lithia may be decomposed by dissolving it in acetic acid, and adding acetate of lead, acetate of lithia remains in solution. Sulphate of Lithia.—This salt is very soluble in water, fuses by heat more readily than the sulphates ofthe other alkalies, and crystallizes in prisms, which resemble the sulphate of soda in appearance, but do not effloresce on exposure to the air. Its taste is saline, without being bitter. SECTION III. Barium. Sir H. Davy discovered barium, the metallic base of baryta, in 1808, by a process suggested by Berzelius and Pontin. It con- sists in forming carbonate of baryta into a paste with water, and placing a globule of mercury in a little hollow made in its sur- face. The paste was laid upon a platinum tray which commu- BARIUM. 243 nicated with the positive pole of a galvanic battery of 100 double plates, while the negative wire was brought into contact with the mercury. The baryta was decomposed, and the barium entered into combination with the mercury. This amalgam was then heated in a vessel free of air, by which the mercury was expelled, and the barium obtained in a pure form. Barium, thus procured, is of a dark gray colour, with a lustre inferior to cast iron. Its density is far greater than water, for it sinks rapidly in strong sulphuric acid. It attracts oxygen with avidity from the air, and in doing so forms a white powder which is baryta. It effervesces strongly from the escape of hydrogen when it is thrown into water, and a solution of baryta is produced. It has hitherto been obtained in very minute quantities, and con- sequently its properties have not been determined with precision. Oxides of Barium.—Barytes, or Baryta, so called from the great density of its compounds, (from j3a^s heavy,) was discovered in 1774 by Scheele. It is the sole product of the oxidation of barium in air or water. It may be prepared by decomposing the nitrate of baryta at a red heat; or, as was ascertained by Dr. Hope, by exposing the carbonate of baryta contained in a black lead crucible to an intense white heat; a process which succeeds much better, when the carbonate is intimately mixed with char- coal. Baryta is a gray powder, the density of which is about 4. It requires a very high temperature for fusion. It has a sharp caustic alkaline taste, converts vegetable blue colours to green, and neutralizes the strongest acids. Its alkalinity, therefore, is equally distinct as that of potassa or soda ; but it is much less caustic and less soluble in water than those alkalies. In pure alcohol it is insoluble. It has an exceedingly strong affinity for water. When mixed with that liquid it slakes in the same man- ner as quicklime, but with the evolution of a more intense heat, which, according to Dobereiner, sometimes amounts to luminous- ness. The result is a white bulky hydrate, fusible at a red heat, which bears the highest temperature of a smith's forge without parting with its water. It is composed of 78 parts, or one atom of baryta, and 9 parts, or one atom of water. The hydrate of baryta dissolves in twice its weight of boiling water, and in twenty parts of water at the temperature of 60° F. A saturated solution of baryta in boiling water deposits, on cool- ing, transparent, flattened prismatic crystals, which are composed of 78 parts, or one atom of baryta, and 180 parts, or 20 atoms of water. • The aqueous solution of baryta is an excellent test ofthe pre- sence of carbonic acid in the atmosphere or in other gaseous mixtures. The carbonic acid unites with the baryta, and a white insoluble precipitate, the carbonate of baryta, subsides. Seventy-eight is regarded as the combining proportion of baryta; and the earth, assuming it to be the protoxide of barium, 244 BARIUM. is composed of 70 parts or one atom of barium, and one atom of oxygen. The deutoxide of Barium may be formed by conducting dry oxygen gas over pure baryta at a low red heat. . This deutoxide, according to Thenard, contains twice as much oxygen as baryta; or is composed of one atom of barium and two atoms of oxygen. This is the substance employed by Thenard in the formation of the deutoxide of hydrogen. Baryta is distinguished by the following characters : 1. By dissolving in water and forming an alkaline solution. 2. By all its soluble salts being precipitated as the white carbonate of baryta by alkaline carbonates, and forming the sulphate of baryta, which is insoluble, both in acid and alkaline solutions, by sul- phuric acid or any soluble sulphate. The readiest method of forming the salts of baryta is by the action of acids on the native or artificial carbonate. All the soluble salts of baryta are poisonous. The carbonate of baryta, from being dissolved by the juices of the stomach, likewise acts as a poison. The sulphate, from its perfect insolu- bility, is inert. By dissolving peroxide of barium in muriatic acid, and precipi- tating by sulphuric acid, M. Thenard succeeded in obtaining the peroxide of hydrogen. For a full detail of all the minutiae of the process, the reader may consult the original memoir of M. Thenard; the general directions are the following :—To six or seven ounces of water, add so much pure concentrated muriatic acid as is sufficient to dissolve 230 grains of baryta, and after having placed the mixed fluids in a glass vessel surrounded with ice, add, in successive portions, 185 grains of the deutoxide of barium reduced to powder, and stir with a glass rod after each addition. When the solution, which takes place without effer- vesence, is complete, sulphuric acid is added in sufficient quantity for precipitating the whole of the baryta in the form of an in- soluble sulphate, so that the muriatic acid which had been com- bined with that earth, is completely separated from it. Another portion of the deutoxide of barium, amounting to 185 grains, is then put into the liquid; the free muriatic acid instantly acts upon it, and as soon as it is dissolved, the baryta is again con- verted into a sulphate by the addition of sulphuric acid. The solution is then filtered, to separate the insoluble sulphate of baryta, and fresh quantities of the peroxide of barium are added in succession, till about three ounces of it have been employed. The liquid then contains from 25 to 30 times its volume of oxy- gen gas. The muriatic, acid which has served to decompose the peroxide of barium during the whole process, is now removed by the cautious addition ofthe sulphate of silver, and the sulphuric acid is afterwards separated by solid baryta. The peroxide of hydrogen, as thus prepared, is still diluted BARIUM. 245 with a considerable quantity of water. To separate the latter, the mixed liquids are placed under the exhausted receiver of an air pump, with a vessel of strong sulphuric acid. As the water evaporates, the density of the residue increases, till at last it acquires the specific gravity of 1.452. The concentration can- not be pushed farther ; for if kept under the receiver after reach- ing this point, the peroxide itself gradually, but slowly, volati- lizes without change. Phosphuret of Barium is produced by passing phosphorus over heated baryta, there is an intense action, and a phosphuret of a metallic lustre is obtained, which acts upon water, and affords a solution containing hypophosphite of baryta. Sulphuret of Barium.—The protosulphuret of barium may be prepared from the sulphate of baryta, by the action of charcoal or hydrogen gas, at a high temperature. It dissolves readily in hot water, forming the hydrosulphuret of baryta. By means of this so- lution all the chief salts of baryta may be procured. Thus, by add- ing an alkaline carbonate, the carbonate of baryta is precipitated. A solution of pure baryta may also be obtained from the hydro- sulphuret, by boiling it with oxide of copper, until the filtered solution no longer gives a dark precipitate with acetate of lead. The crystallized hydrate of baryta is easily procured by means of this solution. The combinations of barium with the other non-metallic sub- stances, have not yet been carefully examined. Salts. Nitrate of Baryta may be formed by dissolving the native carbonate in nitric acid, evaporating to dryness, re-dissolving and crystallizing. It forms permanent octahedral crystals. Its taste is acrid and astringent. It is soluble in 12 parts of cold and 4 of boiling water; it is decomposed by a bright red heat, furnishing pure baryta. It consists of 78 baryta 4- 54 nitric acid. The crystals contain no water of crystallization. The Carbonate of Baryta occurs abundantly in the lead mines ofthe north of England, where it was discovered by Dr. Wither- ing, and has hence received the name of Witherite. It may be prepared by way of double decomposition, by mixing a soluble salt of baryta with any of the alkaline carbonates or bicarbo- nates. It is exceedingly insoluble in distilled water, requiring 4300 times its weight of water at 60° F., and 2300 of boiling water for solution ; but when recently precipitated, it is dissolved much more freely by a solution of carbonic acid. It is highly poisonous. The artificial carbonate contains 22 carbonic acid + 78 baryta = 100. 246 BARIUM, Borate of Baryta is an insoluble white powder. Silicate of Baryta is formed by pouring barytic water into a solution of silicate of potassa ; silicate of baryta precipitates in the state of a white powder. Phosphate of Baryta is insoluble in water, and therefore form- ed by adding a solution of phosphoric acid, or phosphate of soda, to nitrate or muriate of baryta. It consists of one atom phos- phoric acid and one of baryta. Berzelius has described a crystallizable bi-phosphate of baryta obtained by digesting the phosphate in phosphoric acid, and a sesqui-phosphate of baryta, obtained by pouring the bi-phosphate into alcohol, which occasions a precipitate of a white tasteless powder, composed of 1 proportion of baryta + H of acid. Phosphite of Baryta.—Berzelius prepared this salt by pouring muriate of baryta into phosphite of ammonia; in 24 hours, the glass was covered with a crust of phosphite of baryta. Hypo-phosphite of Baryta is a very soluble salt, which crys- tallizes with difficulty. Sulphate of Baryta.—The native sulphate of baryta, com- monly called heavy spar, occurs abundantly in nature, chiefly massive, but sometimes in anhydrous crystals, the form of which is variable, being sometimes prismatic and sometimes tabular ; its primary form is a right rhombic prism. Its density is about 4.4. It is easily formed artificially by the way of double decom- position. This salt bears an intense heat without fusing or un- dergoing any other change, and is one of the most insoluble substances with which chemists are acquainted. It is sparingly dissolved by hot and Concentrated sulphuric acid, but is preci- pitated by the addition of water. It is composed of 78 parts or one atom of baryta, and 40 parts or one atom of sulphuric acid. Sulphite of Baryta is insoluble in water, and formed by adding sulphite of potassa to muriate of baryta. When prepared by precipitation, it is in the state of a white powder : but it may be obtained crystallized, by dissolving it in sulphurous acid, and evaporating slowly. It has but very little taste. When heated strongly, sulphur is disengaged, and sulphate of baryta remains. Hyposulphite of Baryta.—This salt is thrown down on pour- ing muriate of baryta into a solution not too dilute, of hyposul- phite of lime ; it is a white powder, soluble without decomposi- tion, in muriatic acid ; at a low heat it takes fire, and the sul- phur burns off. When the solutions from which it is precipitated are dilute, it falls, after some minutes, in small crystalline grains, followed by a copious separation ofthe salts. Hydrosulphate of Baryta.—When sulphate of baryta is con- verted into sulphuret of barium by mixing it with charcoal, and keeping it red-hot in a crucible, if boiling water be poured upon the black mass, and filtered while hot, the green coloured solu- tion thus obtained yields crystals of hydrosulphate of baryta. STRONTIUM. 247 This compound is soluble in water and the solution has a very slight tinge of green, its taste is acid and sulphurous; and when exposed to the air, it is readily decomposed. Seleniate of Baryta.—Selenic acid is capable of combining with baryta into two proportions. The neutral salt is insoluble : the biseleniate is soluble in water, and crystallizes in round trans- parent grains. Arseniate of Baryta, may be formed by mixing arseniate of potassa with nitrate of baryta. This salt is insoluble in water, except there be an excess of acid ; when exposed to a violent heat it shows a tendency to melt, but is not decomposed. SECTION IV. Strontium. The metallic base of strontia, called strontium, was discovered by Sir H. Davy by a process analogous to that described in the last section. All that is known respecting its properties is, that it is a heavy metal, similar in appearance to barium, that it de- composes water with evolution of hydrogen, and oxidizes quickly in the air, being converted in both cases into strontia. From the close resemblance between baryta and strontia, these substances were once supposed to be identical. Dr. Crawford, however, and M. Sulzer noticed a difference between them ; but the existence of strontia was first established with certainty in the year 1792 by Dr. Hope, and the same discovery was made about the same time by Klaproth. It was originally extracted from strontianite, the native carbonate of strontia, a mineral found at Strontian in Scotland ; and hence the origin of the term Stron- tities or Strontia, by which the earth itself is designated. Oxides of Strontium.—Pure strontia may be prepared from the nitrate and carbonate of strontia, in the same manner as baryta. It resembles this earth in appearance, in infusibility, and in pos- sessing distinct alkaline properties. It slakes when mixed with water, causing an intense heat, and forming a white solid hydrate, which consists of 52 parts or one atom of strontia, and 9 parts or one atom of water. The hydrate of strontia fuses readily at a red heat, but sustains the strongest heat of a wind furnace with- out decomposition. It is insoluble in alcohol. Boiling water dissolves it freely, and a hot saturated solution, on cooling, de- posits transparent crystals in the form of thin quadrangular tables. These crystals are composed, according to the analysis of Dr. Hope, of 52 parts or one atom of strontia and 108 parts or 12 atoms of water. They are converted by heat into the proto- hydrate. They require 50 times their weight of water at 60° F. for solution, and twice their weight at 212° F. 248 STRONTIUM. The solution of strontia has a caustic taste and alkaline reac- tion. Like the solution of baryta it is a delicate test of the pre- sence of carbonic in air or other gaseous mixtures, forming with it the insoluble carbonate of strontia. The atomic weight of strontia, as deduced from the analyses of Berzelius, Stromeyer, and Thomson, is 52; and consequently strontia, regarded as the protoxide of strontium, is composed of Strontium . . . 44 or one atom. Oxygen . . . 8 or one atom. The deutoxide of Strontium is prepared in the same manner as the corresponding preparation of baryta. It may likewise be formed by pouring an aqueous solution of strontia into the deut- oxide of hydrogen. According to Thenard, it contains twice as much oxygen as the protoxide. The soluble salts of strontia, like those of baryta, are pre- cipitated by alkaline carbonates, and by sulphuric acid or soluble sulphates. Strontia is distinguished from baryta by forming with muriatic acid a salt, which crystallizes in the form of slender hexagonal prisms, deliquesces in a moist atmosphere, and dis- solves freely in pure alcohol. The alcoholic solution, when set on fire, burns with a blood-red flame; and the salts of strontia, when exposed to the blow-pipe flame on platinum wire, impart to it a red tinge. The salts of strontia are most conveniently made from the carbonate. These compounds are not poisonous. Phosphuret of Strontium—May be prepared in the same way as the phosphuret of baryta. Its properties are similar. Sulphuret of Strontium—May be formed by fusing the ingredi- ents in a green glass tube, or by exposing the powdered sulphate to a red heat with charcoal. It may be advantageously employ- ed for forming the solution and salts of strontia, in the same man- ner as those of baryta are prepared from the sulphuret of barium. Salts. Nitrate of Strontia—May be obtained in the same manner as the nitrate of baryta, to which it is exceedingly analogous; like all the soluble salts of strontia, it gives a blood red colour to flame. The Carbonate of Strontia, which occurs native at Strontian in Argyleshire, and is known by the name of Strontianite, may be prepared in the same manner as the carbonate of baryta. It is very insoluble in pure water, but is dissolved by an excess of carbonic acid. Borate of Strontia,—Is a white powder, soluble in about 130 parts of boiling water. Silicate of Strontia,—Is formed by pouring strontic water into a solution of silicate of potassa, a white powder precipitates, which is the silicate of strontia. CALCIUM. 249 Phosphate of Strontia.—May be formed by mixing solutions of muriate of strontia and phosphate of soda. It is insoluble in water, but soluble in an excess of phosphoric acid (which is not the case with phosphate of baryta.) It is fusible by the blow-pipe into a white enamel, and decomposible by sulphuric acid. By igniting it with charcoal, phosphuret of strontium is obtained. Phosphite of Strontia.—Is a difficultly soluble crystalline solid. Hypophosphite of Strontia.—A very soluble salt which crys- tallizes with difficulty. Sulphate of Strontia.—The sulphate of strontia, the celestine of mineralogists, is less abundant than heavy spar. It occurs in prismatic crystals of peculiar beauty in Sicily. Its density is 3.858. As obtained by the way of double decomposition, it is a white heavy powder, very similar to the sulphate of baryta. It requires about 3840 times its weight of boiling water for solution. It consists of 52 parts or one atom of strontia, and one atom of sulphuric acid. Sulphite of Strontia.—Is an unimportant compound. Hyposidphite of Strontia.—Is formed by passing sulphurous acid into the liquid sulphuret; it crystallizes in rhomboids; per- manent at common temperatures, and soluble in 5 parts of water at 60°, it is insoluble in alcohol. Its taste is bitter. Hydrosulphate of Strontia.—May be procured by the same process as the hydrosulphate of baryta, to which it is very analo- gous. • Arseniate of Strontia.—A white insoluble powder obtained by pouring arsenic acid into strontia. Arsenite of Strontia.—Is soluble in water but does not crystal- lize. SECTION V. Caldum. The existence of calcium, the metallic base of lime, was de- monstrated by Sir H. Davy by a process similar to that described in the section on barium. It is of a whiter colour than barium or strontium and is converted into lime by being oxidized. Its other properties are unknown. When carbonate of lime is exposed to a white or even to a very strong red heat, carbonic acid is expelled, and pure lime, commonly called quicklime, remains. If lime of great purity is required, it should be prepared from pure carbonate of lime, such as Iceland-spar or Carrara marble; but in burning lime-kilns for making mortar, common lime-stone is employed. The expulsion of carbonic acid' is facilitated by mixing the carbonate with I i 250 CALCIUM. combustible substances, in which case carbonic oxide is gene- rated. Lime is a brittle white earthy solid, the specific gravity of which is about 2.3. It phosphoresces powerfully when heated to full redness, a property which it possesses in common with strontia and baryta. It is one ofthe mostin fusible bodies known; fusing with difficulty, even by the heat of the oxy-hydrogen blow- pipe. It has a powerful affinity for water, and the combination is attended with great increase of temperature, and formation of a white bulky hydrate, which is composed of 2S parts or one atom of lime, and 9 parts or one atom of water. The process of slaking lime consists in forming this hydrate, and the hydrate itself is called slaked lime. It differs from the hydrates of strontia and baryta in parting with its water at a red heat. The hydrate of lime is dissolved very sparingly by water, and it is a singular fact, that it is more soluble in cold than in hot water. Thus Mr. Dalton found that one grain of lime requires for solution 778 grains of water . at 60° F. 972 ... 130° 1270 .... 212° And, conseqently, on heating a solution of lime, or lime-water, which has been prepared in the cold, a deposition of lime ensues. This fact was determined experimentally by Mr. Phillips, who has likewise observed that water at 32° F. is capable of dissolv- ing twice as much lime as at 212 F. Owing to this circumstance pure lime cannot be made to crystallize in the same manner as baryta or strontia. Gay-Lussac succeeded, however, in obtaining crystals of lime by evaporating lime water under the exhausted receiver of an air-pump by means of sulphuric acid, small transparent crystals, in the form of regu- lar hexaedrons are deposited, which consist of water and lime in the same proportion as the hydrate above mentioned. Lime water is prepared by mixing the hydrate of lime with water, agitating the mixture repeatedly, and then setting it aside in a well-stopped bottle until the undissolved parts shall have sub- sided. The substance called milk or cream of lime, is made by mix- ing the hydrate of lime with sufficient quantity of water to give it the liquid form;—it is merely lime water in which hydrate of lime is mechanically suspended. Lime water has a harsh acrid taste, and converts vegetable blue colours to green.—It agrees, therefore, with baryta and strontia in possessing distinct alkaline properties. Like the solution of these earths, it has a strong affinity for carbonic acid, and forms with it an insoluble carbonate. On this account lime water should be / carefully protected from the air. For the same reason, lime water is rendered turbid by a solution of carbonic acid ; but on adding a large quantity of the acid, the transparency of the solution is CALICUM. 251 completely restored, because carbonate of lime is soluble in an excess of carbonic acid. The action of this acid on the solutions of baryta and strontia is precisely similar. The atomic weight of lime, is 28 ; and therefore lime, regarded as the protoxide of calcium, is composed of 20 parts or one atom of calcium, and one atom of oxygen. The deutoxide of calcium may be formed in the same way as the deutoxide of strontium; it consists of one atom of calcium and two atoms of oxygen. The salts of lime, which are easily prepared by the action of acids on pure marble, are in many respects similarly affected by reagents, as those of baryta and strontia. They are precipitated, for example, by alkaline carbonates. Sulphuric acid and soluble sulphates likewise precip.ate lime from a moderately strong solu- tion. But the sulphate of lime has a considerable degree of solubility. Thus, a dilute solution of salt of lime is not precipi- tated at all by sulphuric acid ; and when the sulphate of lime is separated, it may be redissolved by the addition of nitric acid, The most delicate test of the presence of lime is oxalate of am- monia ; for of all the salts of lime, the oxalate is the most insolu- ble in water. This serves to distinguish lime, from most sub- stances, though not from baryta and strontia ; because the oxala- tes of baryta and strontia, especially the latter, are likewise spar- ingly soluble.—All these oxalates dissolve readily in water acidu- lated with the nitric acid. The best characters for distinguishing lime from the two other alkaline earths are the following. Nitrate of lime yields pris- matic crystals by evaporation, is deliquescent in a high degree, and is very soluble in alcohol. The nitrates of baryta and strontia crystallize in regular octahedrons or segments of an octahedron, undergo no change on exposure to the air, and do not dissolve in pure alcohol. The salts of lime, when heated before the blow-pipe, or when. their solutions in alcohol are set on fire, communicate to the flame a dull brownish-red colour. Phosphuret of Lime.—This compound is formed by passing the vapour of phosphorus over fragments of quicklime at a red heat. The true nature of the product is not known with cer- tainty. It is either a phosphuret of lime, or a mixture of phos- phuret of lime and phosphuret of calcium. When it is put into water, mutual decomposition ensues, and phosphuretted hydro- gen, hypophosphorous acid, and phosphoric acid are generated. The protosulphuret of calcium is procured by processes similar to those for forming the sulphuret of barium. The phosphorescent substance, called Canton's phosphorus, which is made by exposing a mixture of calcined oyster shells and sulphur to a red heat, is supposed to be a sulphuret of lime; but its real composition has not been determined. 252 CALCIUM. Salts. Nitrate of Lime is a deliquescent salt, soluble in four parts of water. It is a very abundant natural production in the calcareous caverns, in the western parts of the United States, where it com- monly occurs, combined with the nitrate of potash. Much ofthe nitre of commerce is derived from these two salts by the following process. A quantity of the earth taken from the bottom of these caverns, is lixivated and the lixivium is then passed through wood ashes, the potash of which decomposes the nitrate of lime, by combining with the nitric acid, evaporation and crystalliza- tion then give us the nitrate of potash. One bushel ofthe earth, in some of these caves, will yield nearly two pounds of nitre. Small portions ofthe salt have been found to exist in these caves, at the depth of 15 feet from the surface; even the clay, is impregnated with the nitrate of lime. Carbonate of Lime.—This salt is a very abundant natural pro- duction, and occurs under a great variety of forms, such as com- mon lime-stone, chalk, marble, and Iceland spar, and in regular crystals. It may also be formed by precipitation. Though sparingly soluble in pure water, it is dissolved by carbonic acid in excess. On this account the spring water of lime-stone dis- tricts always contains carbonate of lime, which is deposited when the water is boiled. Borate of Lime, is a white tasteless powder of very difficult solubility in water. Silicate of Lime.—The mineral called shalstein, or table 6par, is a bi-silicate of lime, it is composed, according to the analysis of Klaproth, of silica 50, lime 45, water 5. Borosilicate of Lime.—The mineral called datholite is a bo- rosilicate of lime. Klaproth found it composed of silica 36.5, boracic acid 24, lime 35.5, water 4. Phosphate of Lime.—Chemists differ exceedingly as to the number of compounds which phosphoric acid is capable of form- ing with lime. There seems no doubt, however, from the re- searches of Berzelius and others, that the phosphate of lime, as it exists in bones, or as obtained by mixing muriate of lime with neutral phosphate of soda in excess, is composed of one atom of phosphoric acid, and one atom of lime. This is the com- pound of which many urinary concretions consist. The biphosphate of lime may be prepared by adding one atom of phosphoric acid to one atom ofthe phosphate of lime. It is very soluble in water, but does not crystallize. A super-phos- phate is also formed by the action of sulphuric acid on phosphate of lime ; but whether it is really a biphosphate, or some super- salt, with a still larger proportion of acid, is as yet uncertain. The biphosphate exists in the urine. CALCIUM. 253 Phosphite of Lime is an unimportant compound, which has been but partially examined. Hypophosphite of Lime, is one of the products formed in the process used for obtaining the phosphuret of lime. Sulphate of Lime.—This salt is easily formed by mixing a solu- tion ofthe muriate of lime with any soluble sulphate. It occurs abundantly as a natural production. The mineral called anhy- drite is the anhydrous sulfonate of lime; and all the varieties of gypsum arc composed ofthe same salt, united with water. The pure crystallized specimens of gypsum are sometimes called selenite; and the white compact variety is employed in statuary under the name of alabaster. The anhydrous compound consists of one atom of acid, and 28 parts or one atom of lime; and pure gypsum, is composed of 68 parts or one atom ofthe sulphate of lime, and 18 parts or two atoms of water. The hydrous salt is deprived of its water by a low red heat, and in this state forms plaster of paris. Its property of becoming hard, when made into a thin paste with water, is owing to the anhydrous sulphate com- bining chemically with that liquid, and thus depriving it of its fluidity. The sulphate of lime has hardly any taste. It is considerably more soluble than the sulphates of baryta or strontia, requiring for solution about 500 parts of cold, and 450 of boiling water. Owing to this circumstance, and to its existing so abundantly in the earth, it is frequently contained in spring water, to which it communicates the property called hardness. When freshly pre- cipitated, it may be dissolved completely by dilute nitric acid. It is commonly believed to sustain a white heat without decom- position ; but Dr. Thomson states, that it parts with some of its acid when heated to redness. Sulphite of Lime, is formed by passing sulphurous acid into a mixture of lime and warm water. It is a white powder, soluble by excess of sulphurous acid, and then separating in prismatic crystals of difficult solubility, efflorescent, and passing into sul- phate of lime by exposure to air. Hyposulphite of Lime may be formed by passing sulphurous acid through an aqueous solution of sulphuret of lime, if the so- lution be filtered and evaporated at a temperature not exceeding 140°, it furnishes crystals, the temperature of ebullition decom- poses it. The crystals are little altered by air, very soluble in water, and insoluble in alcohol. Hydrosulphite of Lime, is easily prepared by passing sulphuret- ted hydrogen gas through lime suspended in water; the solution is colourless and has an acrid and bitter taste. Arseniate of Lime.—When arsenic acid is dropped into lime water, arseniate of lime is precipitated; but if an excess of acid be added, the salt is re-dissolved and yields, when evaporated, 254 CALCIUM. small crystals of arseniate of lime, which are soluble in water and decomposed by sulphuric acid. Arsenite of Lime is a white insoluble powder. SECTION VI. Magnesiunt. The galvanic researches of Sir H. Davy have demonstrated the existence of magnesium, though he obtained it in a quantity too minute for determining its properties. He ascertained, however, that it decomposes water, and is converted by combining with oxygen into magnesia. Oxide of Magnesium.—Magnesia, the only known oxide of magnesium, is obtained by exposing the carbonate of magnesia to a very strong red heat, by which the carbonic acid is expelled. It is a white powder, of an earthy appearance ; when pure, it has neither taste nor odour. Its specific gravity is about 2.3. It is exceedingly infusible. It has a weaker affinity than lime for water; for, though it forms a hydrate when moistened, the com- bination is effected with hardly any disengagement of caloric, and the product is readily decomposed by a red heat. There probably exist several different compounds of water and magne- sia, but the native hydrate is the only one known with certainty. According to the analysis of Stromeyer, this hydrate contains one atom of each of its constituents ; and the results of the analyses of Berzelius and Dr. Fyfe accord very nearly with this proportion. Magnesia dissolves very sparingly in water. According to Dr. Fyfe, it requires 5142 times its weight of water at 60°, and 36,000 of boiling water for solution. The resulting liquid does not change the colour of violets; but when pure magnesia is put upon moistened turmeric paper, it causes a brown stain. From this, there is no doubt that the inaction of magnesia with respect to vegetable colours, when tried in the ordinary mode, is owing to its insolubility. It possesses the still more essential character of alkalinity, that, namely, of forming neutral salts with acids, in an eminent degree. It absorbs both water and carbonic acid when exposed to the atmosphere, and therefore should be kept in well-closed phials. The atomic weight of magnesia is 20. Consequently, this alkaline base, regarded as the protoxide of magnesium, is com- posed of Magnesium 12 or one atom. Oxygen 8 or one atom. Magnesia is characterized by the following properties. With the nitric and muriatic acids it forms salts which are soluble in MAGNESIUM. 255 alcohol, and exceedingly deliquescent. The sulphate of mag- nesia is very soluble in water, a circumstance by which it is dis- tinguished from the alkaline earths. Magnesia is precipitated from its salts as a bulky hydrate by the pure alkalies. It is pre- cipitated as carbonate of magnesia, by the carbonates of potassa and soda; but the hicarbonates, and the common carbonate of ammonia, do not precipitate it in the cold. If moderately diluted, the salts of magnesia are not precipitated by oxalate of ammonia. By means of this reagent, magnesia may be both distinguished and separated from lime. Salts. Nitrate of Magnesia, may be prepared by dissolving carbo- nate of magnesia in dilute nitric acid. The solution, when evaporated, yields crystals, in the shape of prisms, with four oblique faces, truncated at their summits. Most commonly, however, it forms a shapeless mass, consisting of an immense number of small needle-shaped crystals, crossing each other irre- gularly. These crystals deliquate in the air, and are soluble in half their weight of water. When exposed to the heat of igni- tion, they fuse, a few bubbles of oxygen gas first escape, and the nitric acid then passes undecomposed. This salt contains, ex- clusive of water, magnesia 20-facid 54. Nitrate of Magnesia and Ammonia, may be obtained by eva- porating a mixed solution of nitrate of ammonia and nitrate of magnesia; it forms prismatic crystals of a bitter acid taste, solu- ble in about 11 parts of water at 60°, and less deliquescent than their component salts separately. Carbonate of Magnesia.—This salt is easily prepared by add- ing carbonate of potassa in slight excess to a hot solution of sulphate of magnesia, and edulcorating the precipitated carbo- nate with warm water. It requires 2493 parts of cold, and 9000 of hot water for solution. It is so soluble in an excess of car- bonic acid that the sulphate of magnesia is not precipitated at all in the cold by the alkaline bicarbonates, or by the sesqui-car- bonate of ammonia. On allowing a solution ofthe carbonate of magnesia in carbonic acid to stand in an open vessel, minute crystals are deposited, which consist of 42 parts or one atom of the carbonate, and 27 parts or three atoms of water. The native carbonate of magnesia, according to the analysis of Dr. Henry and Stromeyer, is similar in composition to the preci- pitated carbonate. Bicarbonate of Magnesia, is prepared by dissolving the car- bonate in water, charged with carbonic acid. It does not crys- tallize. When exposed to the air, a portion of the acid escapes, and the neutral carbonate is precipitated. 256 MAGNESIUM. Sesqui-carbonate of Magnesia, is insoluble in water. It is noticed by Gay-Lussac, but has not been particularly described. Carbonate of Magnesia and Potassa, may be formed by mix- ing bicarbonate of potassa in excess, with muriate of magnesia. No precipitate appears, but in a few days, the salt arranges itself in crystalline groups, on the sides ofthe vessel. Borate of Magnesia may be formed artificially. It occurs, native, in a mineral called boracite, hitherto only found in the duchy of Lunenburgh. Its primitive form is the cube, but the edges and angles are generally re-placed by secondary planes, and four of the angles are always observed to present a greater number of facets than the other four; these crystals become electric by heat, the most complex angles being rendered posi- tive, and the simplest negative. It sometimes contains lime. Phosphate of Ammonia and Magnesia.—The simple phosphate of magnesia, which is prepared by mixing a solution of the sul- phate pf magnesia with phosphate of soda, is of little interest; but the double phosphate is of importance as constituting a dis- tinct species of urinary concretion. It is easily procured by ad- ding corbonate of ammonia and afterwards phosphate of soda to a solution of the sulphate of magnesia, when the double phos- phate subsides in the form of minute crystalline grains. This salt is insoluble in pure water; but is dissolved by most acids, even by the acetic, and is precipitated unchanged when the so- lution is neutralized by ammonia. The composition of this salt has not been satisfactorily deter- mined, on exposure to heat it emits water and ammonia, and a compound of phosphoric acid and magnesia is left, which is in- soluble in water, but is dissolved by strong acids. When strongly heated it undergoes fusion, and yields a white enamel. Sulphate of Magnesia.—This sulphate generally known by the name of Epsom salt, is frequently contained in mineral springs. It may be made directly, by neutralizing dilute sulphuric acid with carbonate of magnesia; but it is procured for the purposes* of commerce by the action of dilute sulphuric acid on magnesian limestone, the native carbonate of lime and magnesia. Sulphate of magnesia has a saline, bitter, and nauseous taste. It crystallizes readily in small quadrangular prisms, which efflo- resce slightly in a dry air. It is obtained also in larger crystals, which are irregular six sided prisms, terminated by six sided sum- mits. Its primary form is a right rhombic prism, the angles of which are 90° 30' and 89° 30'.—Its crystals are soluble in an equal weight of water at 60°, and in three-fourths of their weight of boiling water. They undergo the watery fusion when heated ; and the anhydrous salt is deprived of a portion of its acid at a white heat. The crystals are composed, according to M. Gay- Lussac, of 60 parts or one equivalent ofthe dry sulphate, and 63 parts or seven equivalents of water. MAGNESIUM. 257 On mixing solutions of sulphate of magnesia and sulphate of potassa in atomic proportion, and evaporating, a double salt is formed, which consists of one equivalent of each ofthe salts and six equivalents of water. The crystals are prismatic, but of a complicated nature, and are connected with an oblique rhombic prism. A similar double salt, isormorphous with the preceding, is formed by spontaneous evaporation from the mixed solutions of sulphate of ammonia and sulphate of magnesia. The crystals contain one equivalent of each of the two salts, and eight equiva- lents of water. Sulphate of Ammonia and Magnesia crystallizes in octahe- drons, and consists of 68 sulphate of magnesia, -f 32 sulphate of ammonia. Sulphite of Magnesia is prepared by passing sulphurous acid through water containing diffused magnesia. It forms tetrahe- dral crystals soluble in 20 parts of water at 60°. Hyposulphite of Magnesia may be formed by boiling flowers of sulphur in solution of sulphite of magnesia, it is bitter, very so- luble, but not deliquescent. Being more soluble in hot than in cold water, it readily crystallizes as its solution cools. It burns with a blue flame, and by a sufficient continuance ofthe heat the whole of the acid is expelled. Arseniate of Magnesia may be obtained by mixing the alka- line arseniates with nitrate of magnesia. CHAPTER IV. We have here arranged all the metallic bodies, which, by com- bining with oxygen, produce an acid reaction on vegetable colours, that is, they change the blues and purples red, or they possess some other acid property. It will be recollected that tel- lurium, arsenic, and tin, also possess acid properties; but as they unite with hydrogen, as well as oxygen, their proper place is in our second chapter. The metals to be noticed in this place, are nine in number, antimonium, chromium, manganesium, molybde- num, tungstenum, columbium, titanium, uranium, and gold. Some of these substances, by uniting ,to oxygen, act the part both of acids and alkalies; thus we have the antimoniate of po- tassa, in which the acid powers of the compound are exhibited; and the sulphate of antimony in which its alkaline functions may be observed; but, for the most part, the acid character of the compounds are predominant. Kk ( 258 ) SECTION I. Antimony, or Antimonium. Antimony sometimes occurs native ; but its only ore which is abundant, and from which the antimony of commerce is derived, is the sulphuret. This sulphuret was long regarded as the metal itself, and was called antimony, or crude antimony; while the pure metal was termed the regulus of antimony. Metallic antimony may be obtained either by heating the na- tive sulphuret in a covered crucible with half its weight of iron filings; or by mixing it with two-thirds of its weight of cream of tartar and one-third x>f nitre, and throwing the mixture, in small successive portions, into a red-hot crucible. By the first process the sulphur unites with iron, and in the second it is expelled in the form of sulphurous acid; while the fused antimony, which in both cases collects at the bottom of the crucible, may be drawn off and received in moulds. The antimony, thus obtained, is not absolutely pure ; and therefore, for chemical purposes, should be procured by heating the oxide with an equal weight of cream of tartar. Antimony is a brittle metal, of a white colour running into bluish-gray, and is possessed of considerable lustre. Its density is about 6.7. At 810° F. it fuses; and when slowly cooled, sometimes crystallizes in octahedral or dodecahedral crystals. Its structure is highly lamellated. It has the character of being a volatile metal; but Thenard found that it bears an intense white heat without subliming, provided atmospheric air be per- fectly excluded, and no gaseous matters, such as carbonic acid or watery vapour, be disengaged during the process. Its surface tarnishes by exposure to the atmosphere; and by the continued action of air and moisture, a dark matter is formed, which Berze- lius regards as a definite compound. It appears, however, to be merely a mixture of the real protoxide and metallic antimony. Heated to a white or even full red beat in a covered crucible, and then suddenly exposed to the air, it inflames, and burns with a white light. During the combustion a white vapour rises, which condenses on cool surfaces, frequently in the form of small shining needles of silvery whiteness. These crystals were formerly called argen- tine flowers of antimony, and in chemical works are generally described as the deutoxide of antimony; but according to Berze- lius they are a protoxide. The chemists who have paid most attention to the oxides of antimony are Th6nard, Proust, Berzelius, and Thomson. The former maintained the existence of six, the second of two, the third of four, and the last of three oxides of antimony. The ANTIMONY. 259 opinion of Dr. Thomson is now admitted by most chemists; and there is reason to believe -that the proportions which he has assigned to these oxides are very near the truth. Antimony. Oxygen. Protoxide . 44, or one equivalent, 8, = 52 Deutoxide .44, . . . 12, = 56 Peroxide .44, . . . 16, _= 60 Protoxide.—When the muriate of the protoxide of antimony, made by boiling the sulphuret in muriatic acid, is poured into water, a white curdy precipitate, formerly called powder of Alga- roth, subsides, which is a submuriate of the protoxide. On di- gesting this salt in a solution of carbonate of potassa, and then edulcorating it with water, the protoxide is obtained in a state of purity. It may also be procured directly, by adding the carbo- nate of potassa or soda to a solution of tartar emetic. It is also generated during the combustion of metallic antimony; but as thus formed, perhaps it is not quite pure. Protoxide of antimony, when prepared in the moist way, is a white powder with a somewhat dirty appearance. When heated it acquires a yellow tint, and at a dull red-heat in close vessels it is fused, yielding a yellow fluid, which becomes an opaque grayish crystalline mass on cooling. It is very volatile, and if protected from atmospheric air may be sublimed completely without change. When heated in open vessels it absorbs oxy- gen ; and when the temperature is suddenly raised, and the oxide is porous, it takes fire, and burns. In both cases the deutoxide is generated. It is the only oxide of antimony which forms regu- lar salts with acids, and is the base of the medicinal preparation tartar emetic, the tartrate of antimony and potassa. Most of its salts, however, are either insoluble in water, or, like the muriate of antimony, are decomposed by it, owing to the affinity of that fluid for the acid being greater than that ofthe acid for the oxide of antimony. This oxide is therefore a feeble base ; and, indeed, possesses the property of uniting with alkalies. To the foregoing remark, however, the tartrate of antimony and potassa is an ex- ception ; for it dissolves readily in water without change. By excess of tartaric or muriatic acid, the insoluble salts of antimony may be rendered soluble in water. The presence of antimony in solution is easily detected by sulphuretted hydrogen. This gas occasions an orange-coloured precipitate, the hydrated protosulphuret of antimony, which is so- luble in pure potassa, and is dissolved with disengagement of sul- phuretted hydrogen gas by hot muriatic acid, forming a solution from which the white submuriate is precipitated by water.* * Pbr an account of the means of detecting antimony in mixed fluids, for the purpose of judicial inquiry, the reader may consult an essay on that subject in the Medical and Surgical Journal for 1827. 260 ANTIMONY. Deutoxide.—When metallic antimony is digested in strong ni- tric acid, the metal is oxidized at the expense ofthe acid, and a white hydrate of the peroxide is formed ; and on exposing this substance to a red heat, it gives out water and oxygen gas, and is converted into the deutoxide. It is also generated when the protoxide is exposed to heat in open vessels. Thus, on heating sulphuret of antimony with free exposure to the air, sulphurous acid and protoxide of antimony are generated ; but on continuing the roasting until all the sulphur is burned, the protoxide gradu- ally absorbs oxygen and passes into the deutoxide. Hence this oxide is formed in the process of preparing the pulvis antimo- nialis of the pharmacopoeia. The deutoxide of antimony is white, infusible, and fixed in the fire, two characters by which it is readily distinguighed from the protoxide. It is insoluble in water, and likewise in acids after being heated to redness. It combines with alkalies, and for this reason it has been called antimonious acid, and its salts antimo- nites, by Berzelius. The antimonious acid is precipitated from these salts by acids as a hydrate, which reddens litmus paper, and is dissolved by muriatic and tartaric acids, though without ap- pearing to form with them definite compounds. The peroxide of antimony, or antimonic acid, is obtained as a white hydrate, either by digesting the metal in strong nitric acid, or by dissolving it in nitro-muriatic acid, concentrating by heat to expel excess of acid, and throwing the solution into water. When recently precipitated it reddens litmus paper, and may be dissolved in water, by means of muriatic or tartaric acids. It does not enter into definite combination with acids, but with al- kalies forms salts, which are called antimoniates. When the hy- draled peroxide is exposed to a temperature of 500° or 600° F. the water is evolved, and the pure peroxide of a yellow colour re- mains. In this state it resists the action of muriatic acid. When exposed to a red heat, it parts with oxygen, and is converted into the deutoxide. Phosphuret of Antimony, is formed by heating together equal parts of the oxide of antimony, phosphoric acid, and charcoal. It is white and brittle. Sulphurets of Antimony.—The native sulphuret of antimony is of a lead-gray colour, and though generally compact, sometimes occurs in acicular crystals, or in rhombic prisms. When heated in close vessels, it enters into fusion without undergoing any other change. Boiled in hot muriatic acid, it is dissolved with disengagement of sulphuretted hydrogen. The experiments of Berzelius, Dr. Davy, and Thomson, leave no doubt of its being analogous in composition to the protoxide of antimony, that is, consisting of one equivalent of each of its elements. It may be formed artificially by fusing together antimony and sulphur, or by transmitting a current of sulphuretted hydrogen gas through ANTIMONY. 261 a solution of tartar emetic. The orange precipitate, which sub- sides in the last mentioned process, is commonly regarded as the hydrosulphuret of the oxide of antimony. In Dr. Turner's opinion it is a hydrated sulphuret of the metal; for when well washed and treated by sulphuric acid it does not yield a trace of sul- phuretted hydrogen. When sulphuret of antimony is boiled in a solution of potassa, a liquid is obtained, from which, as it cools, an orange-coloured matter, called Kermes mineral, is deposited; and on subsequent- ly neutralizing the cold solution with an acid, an additional quan- tity of a similar substance, the golden sulphuret of the pharmaco- poeia, subsides. Both these compounds, thus procured, are essen- tially the same as the hydrated sulphuret above described. The action ofthe alkali on the sulphuret of antimony admits of a two- fold explanation. It is possible that the latter may be dissolved directly by the former, and that it is again deposited when the alkali is neutralized. It is more probable, however, that the ele- ments of water and the sulphuret of antimony react on one another, forming sulphuretted hydrogen and protoxide of anti- mony ; and that the liquid contains a double salt, composed of one equivalent of potassa, one equivalent ofthe protoxide of an- timony, and one equivalent of sulphuretted hydrogen. On neu- tralizing the potassa with an acrd, sulphuretted hydrogen and the protoxide are set at liberty, and by mutual re-action of their elements are reconverted into water and protosulphuret of anti- mony. The sesqui-sulphuret is formed, according to M. Rose, by trans- mitting sulphuretted hydrogen gas through a solution ofthe deu- toxide of antimony in dilute muriatic acid. M. Rose formed the bisulphuret, consisting of one equivalent of antimony and two equivalents of sulphur, by the action of sul- phuretted hydrogen on a solution of the peroxide. The golden sulphuret prepared by boiling sulphuret of antimony and sulphur in a solution of potassa, a process, however, which is not now adopted, is a bisulphuret. M. Rose has likewise demonstrated that the red antimony of Mineralogists (rothspiesglanzerz) is a compound of one equiva- lent ofthe protoxide combined with two equivalents ofthe pro- tosulphuret of antimony. The pharmaceutic preparations known by the terms of glass, liver, and crocus of antimony, are of a simi- lar nature, though less definite in composition, owing to the mode by which they are prepared. They are made by roasting the na- tive sulphuret, so as to form sulphurous acid and oxide of anti- mony, and then vitrefying the oxide together with undecomposed ore, by means of a strong heat. The product will of course differ according as more or lessof the sulphuret escapes oxidation during the process. 262 ANTIMONY. Salts. Antimoniate of Ammonia, is formed by digesting the acid in ammonia, on evaporation a biantimoniate of ammonia is obtained in the form of a white powder. Antimoniate of Potassa dissolves in hot water, and this solu- tion produces precipitates of insoluble antimoniates, in several other metallic solutions. Our knowledge of these combinations is very imperfect. Nitrite of Antimony.—When the protoxide is digested in dilute nitric acid, a difficultly soluble salt is produced, which separates in white scaly crystals, these appear to be the hypo- nitrite of antimony. Phosphate of Antimony has not been formed; but the phos- phate of lime and antimony is the preparation called James1 powder, or pulvis antimonialis. This is formed by heating strongly, in an open vessel, one part of sulphuret of antimony with two parts of hartshorn shavings. This heat drives off the sulphur from the sulphuret, and the animal matter from the shavings. The antimony is then converted into the deutoxide, by absorbing oxygen from the air, and thus unites to the phos- phate of lime of the hartshorn. Sulphate of Antimony.—When sulphuric acid is boiled on finely powdered antimony, the metal is oxidated, and the sul- phate and sub-sulphate of antimony are the results. In both these salts, the antimony is in the state of the protoxide. SECTION II. Chromium. Chromium was discovered in the year 1797 by Vauquelin in a beautiful red mineral, the native chromate of lead. It has since been detected in the mineral called chromate of iron, a compound ofthe oxides of chromium and iron, which occurs abundantly in several parts ofthe continent, in America, and at Unst in Shet- land. Chromium derives its name from X^i**, colour, indicative of its remarkable tendency to form coloured compounds. Chromium, which has hitherto been procured in very small quantity, owing to its powerful attraction for oxygen, may be obtained by exposing the oxide of chromium, mixed with char- coal, to the most intense heat of a smith's forge. Its colour is white with a shade of yellow, and distinct metallic lustre. It is a brittle metal, very infusible, and with difficulty attacked by acids, even by the nitro-muriatic. Its specific gravity has been stated at 5.9 ; but Dr. Thomson found it a little above 5. When fused with nitre it is oxidized, and converted into chromic acid. CHROMIUM. . 263 Chromium unites with oxygen in two proportions, forming the green oxide, and chromic acid. Dr. Thomson some years ago ascertained that the combining proportion of chromic acid is 52 ; and according to the results of an elaborate investigation, pub- lished in the Philosophical Transactions for 1827, the oxide and acid are thus constituted :— Chromium. Oxygen. Green oxide 32 or one equivalent 8 or 1 equivalent. Chromic acid 32 - - - 20 or 2£ equivalents. Protoxide.—This oxide is easily prepared by dissolving chro- mate of potassa in water, and mixing it with a solution of pro- tonitrate of mercury, when an orange-coloured precipitate, the chromate ofthe protoxide of mercury, subsides. On heating this salt to redness in an earthen crucible, the mercury is dissipated in vapour, and the chromic acid is resolved into oxygen and protoxide of chromium. Protoxide of chromium is of a green colour, exceedingly in- fusible, and suffers no change by heat. It is 'insoluble in water, and after being strongly heated, resists the action of the most powerful acids. Deflagrated with nitre, it is oxidized to its maxi- mum, and is thus reconverted into chromic acid. Fused with borax or vitreous substances, it communicates to them a beauti- ful green colour, a property which affords an excellent test of its presence, and renders it exceedingly useful in the arts. The emerald owes its colour to the presence of this oxide. Protoxide of chromium is a salifiable base, and its salts, which have a green colour, may be easily prepared in the following manner. To a boiling solution of chromate of potash in water, equal measures of strong muriatic acid and alcohol are added in successive small portions, until the red tint of the chromic acid disappears entirely, and the liquid acquires a pure green colour. On pouring an excess of pure ammonia into this solution, a pale green bulky precipitate is formed, which consists of one equiva- lent of the protoxide, and 26 equivalents of water. The hydrate is readily dissolved by acids. Chromic Add.—This acid is prepared by digesting chromate of baryta in a quantity of dilute sulphuric acid, exactly sufficient for combining with the baryta. The sulphate of baryta subsides, and a solution of chromic acid is obtained. Another method has been lately proposed by M. Arnold Maus, which consists in de- composing a hot concentrated solution of bichromate of potash by silicated hydro-fluoric acid. The chromic acid, after being separated from the sparingly soluble hydro-fluate of silica and potash, is evaporated to dryness in a platinum capsule, and then re-dissolved in the smallest possible quantity of water. By this means, the last portions of the double salt are rendered insolu- 264 CHROMIUM. ble, and the pure chromic acid is then separated by decantation. The acid must not be filtered in this concentrated state, as it then corrodes paper like sulphuric acid, and is converted into chro- mate of the green oxide of chromium. When it is wished to prepare a large quantity of chromic acid by this process, porce- lain vessels may be safely employed in the first part of the ope- ration, provided care is taken to add a quantity of silicated hydro-fluoric acid not quite sufficient for precipitating the whole ofthe potash. Chromic acid has a dark ruby-red colour, and forms irregular crystals when its solution is concentrated. It is very soluble in water, has a sour taste, and possesses all the properties of an acid. It is converted into the green oxide, with evolution of oxygen, by exposure to a strong heat. It yields a muriate ofthe protoxide when boiled with muriatic acid and alcohol, and the direct solar rays have a similar effect when muriatic acid is pre- sent. With sulphurous acid it forms a sulphate of the protoxide. Chromic acid is characterized by its colour, and by forming coloured salts with alkaline bases. The most important of these salts is the chromate of lead, which is found native in small quantity, and is easily prepared by mixing chromate of potassa with a soluble salt of lead. It is of a rich yellow colour, and is employed in the arts of painting and dyeing, to great extent. When sulphurous acid gas is transmitted into a solution of chromate or bichromate of potash, a brown precipitate subsides, which was long regarded as a distinct oxide of chromium ; but Dr. Thomson, in the essay above cited, has proved that it is the green oxide combined with a little chromic acid. The acid may in a great measure be washed away by means of water, and by ammonia it is entirely removed. The best mode of separating it, is to dissolve the brown matter with muriatic acid, and then pre- cipitate the green oxide by ammonia. Salts. Chromates of Potassa.—The chromate of potassa, from which all the compounds of chromium are directly or indirectly pre- pared, is made by heating to redness the native oxide of chro- mium and iron, commonly called chromate of iron, with an equal weight of the nitrate of potassa, when the chromic acid is gene- rated, and unites with the alkali of the nitre. After digesting the united mass in water until the chromate is dissolved, the solution is neutralized by nitric acid, and concentrated by eva- poration, in order that the nitrate of potassa may crystallize. The residual liquid is then set aside to evaporate spontaneously, and the chromate is gradually deposited in small prismatic crys- tals of a lemon-yellow colour. The chromate of potassa has a cool, bitter, and disagreeable CHROMIUM. 265 taste. It is soluble to great extent in boiling water, and in twice its weight of that liquid at 60° Fahr. It is insoluble in alcohol. It has an alkaline re-action, but it is neutral in composition, con- sisting of 52 parts or one atom of chromic acid, and 48 parts or one atom of potassa. Its crystals are anhydrous. The Bichromate of Potassa, which is made in large quantity at Glasgow for dyeing, is prepared by acidulating the neutral chromate with sulphuric acid, and allowing the solution to crys- tallize by spontaneous evaporation. When slowly formed it is deposited in four-sided tabular crystals, which have an exceed- ingly rich red colour, are anhydrous, and consist of one atom of the alkali, and two atoms of chromic acid. They are soluble in about ten times their weight of water at 60° F., and the solution reddens litmus paper. The chromates of ammonia, soda, lime, and magnesia, are soluble and crystallizable, and of an orange colour. The chro- mates of baryta and strontia are difficultly soluble, and may be formed by adding chromate of potassa, or soda, to their soluble saline compounds. The insoluble metallic chromates may be formed in the same way. Chromates. The salts of chromic acid are mostly either of a yellow or red colour, the latter tint predominating whenever the acid is in excess. The chromates of the common metals are decomposed by a strong red heat, by which the acid is resolved into a green oxide of chromium and oxygen gas; but the chromates of the fixed alkalies sustain a very high temperature without decompo- sition. They are all decomposed, without exception, by the united agency of heat and combustible matter. The chromates are in general sufficiently distinguished by their colour. They may be known, chemically, by the following character:—On boiling a chromate in muriatic acid mixed with alcohol, the chromic acid is at first set free, and is then decom- posed, a green muriate ofthe oxide of chromium being generated. The only native chromate hitherto discovered is the red chro- mate of lead from Siberia, in the examination of which, Vauque- lin made the discovery of chromium. The salts formed by the acids, with chromium as the base, have been but slightly examined. Those, however, which have receiv- ed the greatest attention, are the nitrate and sulphate. L I { 266 ) SECTION III. Manganese. Manganese, which was discovered in the year 1774 by Gahn and Scheele, is a hard brittle metal, of a grayish-white colour, and granular texture. Its specific gravity is 6.85. * When pure it is not attracted by the magnet. It is exceedingly infusible, requiring a heat of 160° Wedgwood for fusion. It soon tarnishes on exposure to the air, and absorbs oxygen with rapidity when heated to redness in open vessels. It is said to decompose water at common temperatures with disengagement of hydrogen gas, though the process is exceedingly slow ; but at a red heat decom- position is rapid, and protoxide of manganese is generated. The decomposition of water is likewise occasioned by dilute muriatic or sulphuric acid, and the muriate or sulphate of the protoxide of manganese is the product. Manganese, owing doubtless to its powerful affinity for oxygen, has never been found in an uncombined state in the earth; but the peroxide of manganese occurs abundantly. This metal re- tains its oxygen with such force that its oxides require a stronger heat for reduction than potassa or soda. The method by which Gahn succeeded in procuring metallic manganese, was by expos- ing the peroxide, surrounded with charcoal, to the most intense heat of a smith's forge ; and this process has been successfully re- peated by others. Oxides of Manganese. Different opinions have prevailed concerning the number ofthe oxides of manganese; nor do chemists, even at present, seem quite decided upon the subject. The existence, however, of four distinct compounds, containing manganese and oxygen, may be regarded as certain. One of these, called the red oxide, is ob- viously composed of two of the others; so that the number of the real oxides of manganese does not exceed three. Their composition has been particularly investigated by Dr. Thomson, M. Arfwedson, M. Berthier, and very lately by Dr. Turner. According, to these chemists, the composition of these oxides may be thus stated :— Managanese. Oxygen, Protoxide . 28, or one equivalent. 8, or one equivalent. Deutoxide . 28 12, or U equivalent. Peroxide .28 . . . . 16, or 2 equivalents. Peroxide.—This is the well-known ore commonly called from MANGANESE. 267 its colour the black oxide of manganese, the nature of which was ascertained in 1774 by Scheele. It generally occurs massive, of an earthy appearance, and mixed with other substances, such as siliceous and aluminous earths, oxide of iron, and carbonate of lime. It is sometimes found, on the contrary, in the form of minute prisms grouped together, and radiating from a common centre. This j. oxide may be made artificially by exposing the nitrate of manganese to a commencing red heat, until the whole of the nitric acid is expelled; but we cannot succeed in pro- curing it quite pure by this process, because the heat required to drive off the last traces of acid, likewise expels some oxygen from the peroxide. Peroxide of manganese undergoes no change on exposure to the air. It is insoluble in water, and does not unite either with acids or alkalies. When boiled with sulphuric acid, it yields oxygen gas, and a sulphate of the protoxide is formed. With muriatic acid, a muriate of the protoxide is generated, and chlo- rine is evolved. The solution, in both cases, is of a deep red co- lour, provided any undissolved oxide is present; but if separated from the undissolved portions, it is readily rendered colourless by heat. The action of sulphuric acid in the cold is exceedingly tardy and feeble, a minute quantity of oxygen gas is slowly dis- engaged, and the acid acquires an amethyst-red tint. On expo- sure to a red heat, it is converted, with evolution of oxygen gas, into the deutoxide of manganese. Peroxide of manganese is employed in the arts, in the manu- facture of glass, and in preparing chlorine for bleaching. In the laboratory it is used for procuring chlorine and oxygen gases, and in the preparation ofthe salts of manganese. Deutoxide.—This oxide occurs nearly pure in nature, and as a hydrate it is found abundantly, often in large prismatic crystals, at Jhlefeld in the Hartz. It may be formed artificially by expos- ing peroxide of manganese for a considerable time to a moderate red heat, and therefore is the chief residue of the usual process for procuring a supply of oxygen gas ; but it is difficult so to regulate the degree and duration of the heat, that the resulting oxide shall be quite pure. The colour of the deutoxide of manganese varies with the source from which it is derived. That which is procured by means of heat from the native peroxide or hydrated deutoxide, has a brown tint; but when prepared from nitrate of manganese, it is nearly as black as the peroxide, and the native deutoxide is of the same colour. With sulphuric and muriatic acids it gives rise to the same phenomenon as the peroxide, but of course yields a smaller proportional quantity of oxygen and chlorine gases. It is more easily attacked than the peroxide by cold sulphuric acid With strong nitric acid it yields a soluble proto-nitrate and the peroxide, as observed by Berthier; and when boiled with dilute 268 MANGANESE. sulphuric acid, it undergoes a similar change. From the pro* portion of oxygen and manganese in this oxide, it may be regard- ed as a compound of 44 parts or one equivalent of the peroxide, and 36 parts or one equivalent ofthe protoxide of manganese. Protoxide.—By this term is meant that oxide of manganese which is a strong salifiable base, is contained in all-, the ordinary salts of this metal, and which appears to be its lowest degree of oxidation. This oxide may be formed, as was shown by Berthier, by exposing the peroxide, deutoxide, or red oxide of manganese to the combined agency of charcoal and a white heat; and Dr. Forchhammer, has described an elegant mode of preparation, by exposing either of the oxides of manganese contained in a tube of glass, porcelain, or iron, to a current of hydrogen gas at an ele- vated temperature. The best material for this purpose is the red oxide prepared from nitrate of manganese ; for some ofthe oxides, especially the peroxide, are fully reduced to the state of protoxide by hydrogen with difficulty. The reduction commences at a low red heat; but to decompose all the red oxide, a full red heat is required. The same compound is formed by the action of hy- drogen gas at an intense white heat. Protoxide of manganese, when pure, is of a pretty light green colour, very near the mountain-green. According to Forchham- mer, it attracts oxygen rapidly from the air; but in Dr. Turner's experiments it was permanent, undergoing no change either in weight or appearance during the space of nineteen days. At 600° F. it is oxidized with considerable rapidity, and at a low red heat is converted in an instant into the red oxide. According to Forchhammer and Arfwedson, it takes fire when thus heated ; but this was not observed by Dr. Turner. It unites readily with acids without effervescence, producing the same salts as when the same acids act on carbonate of manganese. When it comes in contact with concentrated sulphuric acid, intense heat is instantly evolved ; and the same phenomenon is produced, though in a less degree, by strong muriatic acid. The resulting salt is the same as when these acids are heated with either of the other oxides of manganese. If quite pure, the protoxide should readily and com- pletely dissolve in cold dilute sulphuric acid, and yield a colour- less solution. In order to prepare a pure salt of manganese from the common peroxide of commerce, the following processes should be em- ployed. The impure deutoxide left in the process for procuring oxygen gas from the peroxide by means of heat, is mixed with a sixth of its weight of charcoal in powder, and exposed to a white heat for half an hour in a covered crucible. The protoxide thus formed is to be dissolved in muriatic acid, the solution evaporated to dryness, and the residue kept for a quarter of an hour in per- fect fusion ; being protected as much as possible from the air. By this means the chlorides of iron, calcium, and other metals MANGANESE. 269 are decomposed. The fused chloride of manganese is then poured out on a clean sandstone, dissolved in water, and the solution separated from insoluble matters by filtration. If free from iron, it will give a white precipitate with ferrocyanate of potassa, with- out any appearance of green or blue, and a flesh-coloured pre- cipitate wkl^^lrosulphuret of ammonia. The absence of lime may be pfo^ewor traces of it separated, by oxalate of potassa. The manganese is then thrown down as a white carbonate by the bicarbonate$F potash or soda; and from this salt, after being well washed, all the other salts of manganese may be prepared. The salts of manganese are in general colourless if quite pure; but more frequently they have a shade of pink, owing to the pre- sence of a little red oxide. The protoxide is precipitated from their solutions, as the white hydrate by ammonia, or the pure fixed alkalies;' as the white carbonate of manganese by alkaline car- bonates and bicarbonates ; as the white ferrocyanate of man- ganese by ferrocyanate of potassa, a character by which the ab- sence of iron may be demonstrated. These white precipitates, with the exception of that obtained by means of a bicarbonate, very soon become brown from the absorption of oxygen. None of the salts of manganese which contain a strong acid, such as the nitric, muriatic, or sulphuric acid, are precipitated by sul- phuretted hydrogen. With an alkaline hydrosulphuret, on the contrary, a flesh-coloured precipitate is formed, which is either a hydrosulphuret of the protoxide, or a hydrated protosulphuret of metallic manganese. When heated in close vessels, it yields a dark coloured sulphuret, and water is evolved. Red oxide.—The substance called red oxide of manganese, the Oxidum Manganoso-Manganicum of Arfwedson, occurs as a natural production, and may be formed artificially by exposing the peroxide or deutoxide to a white heat either in close or open vessels. It is also produced by absorption crfVpxygen from the atmosphere when the protoxide is precipitatealfrom its salts by pure alkalies, or when the anhydrous protoxfcre or carbonate is heated to redness. It is very permanent in the air, not passing to a higher stage of oxidation at any temperature. Its colour, when rubbed to the same degree of fineness, is brownish red when cold, and nearly black while warm. Fused with borax or glass, it com- municates a beautiful violet tint, a character by which manga- nese may be easily detected before the blow-pipe ; and it is the cause ofthe rich colour of the amethyst. It is acted on by strong sulphuric and muriatic acids, with the aid of heat, in the same manner as the peroxide and deutoxide, but of course yields pro- portionally a smaller quantity of oxygen and chlorine gases. By cold concentrated sulphuric acid it is dissolved in small quanti- ty, without appreciable disengagement of oxygen gas, and the solution is promoted by a slight increase of temperature. The liquid has an amethyst tint, which disappears when heat is ap- 270 MANGANESE. plied, or by the action of deoxidizing substances, such as proto- muriate of tin, or nitrous, sulphurous, and phosphorous acids, pro- tosulphate of manganese being generated. The pink colour which the salts of manganese generally possess, is owing to the presence of a small quantity of red oxide. By strong nitric acid, or when boiled with dilute sulphuric acid, it undergoes the same kind of change as the deutoxide. *\l * The red oxide of manganese contains more oxygert^than the protoxide and less than the deutoxide. Its elemenw are*£n such proportion, that it may be regarded as a compound either of Deutoxide 80 or two equiv. ) C Peroxide 44 or one equiv. Protoxide 36 or one equiv. ) ( Protoxide 72 or two equiv. 116 116 It contains 27.586 per cent of oxygen, and loses 6.896 per cent of oxygen when converted into the green oxide. It has been inferred from some experiments of Berzelius and John, that there are two other oxides of manganese, which con- tain less oxygen than the green or protoxide. We have no proof, however, ofthe existence of such compounds. Manganese is one of those metals which is capable of forming an acid with oxygen. When the peroxide of manganese is mixed with an equal weight of nitre or carbonate of potash, and the mixture is exposed to a red heat, a green-coloured fused mass is formed, which has been long known under the name of mineral chameleon. On putting this substance into water, a green solu- tion is obtained, the colour of which soon passes into blue, pur- ple, and red ; and ultimately, a brown flocculent matter, the red oxide of manganese, subsides, and the liquid becomes colourless. These changes take place more rapidly by dilution, or by employ- ing hot water. We are indebted to MM. Chevillot and Edwards for a consistent expanation of these phenomena. They demon- strated that the aKxide of manganese, when fused with potassa, absorbs oxygen ffdm the atmosphere, and is thereby converted into an acid the manganesic, which unites with the alkali. They attributed the different changes of colour above mentioned to the combination of this acid with different proportions of potassa. By evaporating the red solution rapidly, they succeeded in obtain- ing a manganesiate of potassa in the form of small prismatic crystals of a purple colour. This salt yields oxygen to combus- tible substances with great facility, and detonates powerfully with phosphorus. It is decomposed when in solution by very slight causes, being converted into the red oxide of manganese. The subsequent researches of Dr. Forchhammer render it pro- bable that the green and red colours are produced by two dis- tinct acids, the manganeseous and manganesic, the former giving rise to the green, and the latter to the red tint. He succeeded in forming a solution of manganesic acid in the following man- MANGANESE. 271 ner : A mixture of the nitrate of baryta was heated with peroxide of manganese, by which means the manganesite of baryta was generated ; and to this salt, after having been well washed with water, a quantity of dilute sulphuric acid was added, precisely sufficient for combining with its base. The manganeseous acid, at the momenj^f being set free, resolved itself into the deutoxide of manganese and manganesic acid, and the latter, dissolving in the water, formed a beautiful red solution. Dr. Forchhammer infers from his analysis of these compounds, that the mangane- seous acid contains three, and the manganesic four atoms of oxygen united with one atom of manganese. Phosphuret of Manganese may be formed by dropping phosphorus upon red hot manganese ; it is of a white colour, brittle, granu- lated, disposed to crystallize, not altered by exposure to the air, and more fusible than manganese ; when heated, the phosphorus burns and the metal is oxidized. The Protosulphuret of Manganese may be procured by igniting the sulphate with one-sixth of its weight of charcoal in powder.— It is also formed by the action of sulphuretted hydrogen on the protosulphate at a red heat. It occurs native in Cornwall and at Nagyag in Transylvania. It dissolves completely in dilute sulphuric or muriatic acid, with disengagement of very pure sul- phuretted hydrogen. Carburet of Manganese occurs occasionally, in small cavities, in the mass of cast iron. It is known by the name of keesh ; it is composed of thin scales, having the lustre and appearance of steel, but very brittle. Salts. Nitrate of Manganese.—By dissolving carb^ete of manganese in nitric acid, and evaporating cautiously, flvi^rate of man- ganese is obtained in needle-form crystals; iMKory bitter, very soluble in water, and deliquescent. This salw^curs in nature, muted with other salts. % ttyrbonate of Manganese is easily obtained, by pouring car- bonate of potassa into a solution of sulphate or nitrate of man- ganese ; a white powder precipitates, which, on drying, acquires a slight shade of yellow. It occurs native in Transylvania, and many other places, in rhomboidal crystals, which have always a rosy tinge, and frequently a pearly lustre. It almost always con- tains a small quantity of carbonate of lime, or carbonate of iron, and sometimes a little silex. Silicate of Manganese.—The mineral distinguished by the name of foliated red manganese ore, appears to be in reality a silicate of manganese nearly pure. It has a rose red or flesh- red colour, a foliated fracture, a slight degree of translucency, and is hard enough to scratch glass. Its specific gravity is 3.5. 272 MOLYBDENUM. Phosphate of Manganese may be obtained in the form of a precipitate, by mixing an alkaline phosphate with a solution of manganese in sulphuric or nitric acid. Sulphate of Manganese.—Sulphuric acid combines with all the oxides of manganese. The sulphate ofthe protoxide has a styptic bitter taste, and crystallizes in transparent rhomlioidal prisms. The sulphate of the deutoxide has been but li!tl^'examined; the sulphate of the peroxide, is of a red colour, and has an acid re-action. Arseniate of Manganese occurs in crystals, and is formed by adding arsenic acid to the protoxide of manganese. SECTION IV. Molybdenum. When the native sulphuret of molybdenum, in fine powder, is digested in nitro-muriatic acid until the ore is completely decom- posed^Tind the residue is briskly heated, in order to expel sulphu- ric acid, molybdic acid remains in the form of a white heavy powder. From this acid metallic molybdenum may be obtained, by exposing it with charcoal to the strongest heat of a smith's forge ; or by conducting over it a current of hydrogen gas while strongly heated in a tube of porcelain. Molybdenum is a brittle metal, very infusible, and of a white colour. It has hitherto been procured in small quantities only, and its properties are known imperfectly. When heated in open vessels it absorbs oxygen, and is converted into molybdic acid. It has three degrees of oxidation, forming two oxides and one acid. The molyJ^k: acid, according to Bucholz, is composed of 48 parts of vqg>m Bnum, and 24 parts of oxygen ; and conse- quently, on theBBosition that this acid contains three atoms of oxygen, 48 is theHTomic weight of the metal itself. Molybdic acid Is a white powder, of specific gravity 3.4.^git has a sharp metallic taste, reddens litmus paper, and forms^Jhlts with alkaline bases. It is very sparingly soluble in water ; but the molybdates of potassa, soda, and ammonia, dissolve in that fluid, and the molybdic acid is precipitated from the solutions by any of the strong acids. Berzelius has lately described the two oxides of molybdenum. The protoxide is black, and consists of one atom of oxygen and one atom of molybdenum. The deutoxide is brown, and contains twice as much oxygen as the protoxide. They both form salts with acids. Berzelius states that the blue molybdous acid of Bucholz, is a bimolybdate ofthe deutoxide of molybdenum. Phosphuret of Molybdenum is a compound which has received but little examination. MOLYBDENUM. 273 The native Sulphuret of Molybdenum according to the analy- sis of Bucholz, is composed of 48 parts or one atom of molybde- num, and 32 parts or two atoms of sulphur. Berzelius has lately discovered another sulphuret, of a ruby-red colour, transparent, and crystallized. It is proportional to the molybdic acid ; that is, it contains three atoms of sulphur to one atom ofthe metal. Salts. Molybdate of Ammonia is not crystallizable, and when heated to redness the ammonia is driven off, and the acid converted into oxide of molybdenum. Molybdate of Potassa is formed by digesting the acid in po- tassa. The solution yields small rhomboidal crystals by evapo- ration, and affords a precipitate of molybdic acid to nitric and sulphuric acids. Molybdate of Soda is more soluble than the last salt, and fur- nishes permanent and transparent crystals. In obtaining both these salts, a deposit of a yellowish powder ensues, which is pro- bably a bi-molybdate of potassa and of soda. SECTION V. Tungsten, or Tungstenum. Tungsten may be procured in the metallic state by exposing tungstic acid to the action of charcoal' or dry hydrogen gas at a red heat; but, though the reduction is easily effected, an ex- ceedingly intense temperature is required for fusing the metal. Tungsten has a grayish white colour, and cxjasiderable lustre. It is brittle, nearly as hard as steel, and lefsmsible than man- ganese. Its specific gravity is near 17.4. ^HpP heated to red- ness in the open air it takes fire, and is convpted into tungstic acjd ; and it undergoes the same change by the action of nitric acid* Digested with a concentrated solution of pure potassa, it is dissolved with disengagement of hydrogen gas, and tungstate of potassa is generated. Chemists are acquainted with two compounds of this metal and oxygen, namely, the dark brown oxide, and the yellow acid of tungsten; and according to the analyses of Berzelius, the oxygen of the former is to that of the latter in the ratio of two to three. It is hence inferred, that the real protoxide of tungsten is yet unknown, and that tungstic acid contains three atoms of oxygen to one atom of the metal. Now,, Bucholz ascertained that this acid consists of 96 parts of tungsten and 24 parts of oxygen, and consequently 96 is the atomic weight of tungsten, and 120 the equivalent of its acid. The brown oxide is composed of 96 parts M m 274 TUNGSTEN. or one equivalent of metal, and 16 parts or two equivalents of oxygen. A convenient method of preparing tungstic acid is by digest- ing the native tungstate of lime, very finely levigated, in nitric acid; by which means the nitrate of lime is formed, and the tungstic acid separated in the form of a yellow powder. Long digestion is required before all the lime is removed; but the process is facilitated by acting upon the mineral alternately by nitric acid and ammonia. The tungstic acid is dissolved readily by that alkali, and may be obtained in a separate state by heat- ing the tungstate of ammonia to redness. Tungstic acid may also be prepared by the action of muriatic acid on Wolfram, the native tungstate of iron and manganese. It is also obtained by heating the brown oxide to redness in open vessels. Tungstic acid is of a yellow colour, is insoluble in water, and has no action on litmus paper. With alkaline bases it forms salts called tungstates, which are decomposed by the stronger acids, the tungstic acid in general falling combined with the acid by which it is precipitated. When strongly heated in open ves- sels, it acquires a green colour, and becomes blue when exposed to the action of hydrogen gas at a temperature of 500° or 600° F. The blue compound, according to Berzelius, is a tungstate of the oxide of tungsten; and the green colour is probably pro- duced by an admixture of this compound with the yellow acid. The oxide of tungsten is formed by the action of hydrogen gas on tungstic acid at a low red heat; but the best mode of procur- ing it, both pure and in quantity, is that recommended by Wohler. This process consists in mixing Wolfram in fine powder with twice its weight of carbonate of potassa, and fusing the mixture in a platinum crucible. The resulting tungstate of potassa is dis- solved in hot water, mixed with about half its weight of muriate of ammonia in sowRion, evaporated to dryness and exposed in a hessian cruciblefflffa red heat. The mass is well washed with boiling water, ancRhe insoluble matter digested in dilute potassa to remove any tungstic acid. The residue is oxide of tungsten. It appears that in this process the tungstate of potassa and muriate of ammonia mutually decompose each other, so that the dry mass consists of chloride of potassium and tungstate of ammonia. The elements of the latter re-act on each other at a red heat, giving rise to water, nitrogen gas, and oxide of tungsten ; and this com- pound is protected from oxidation by the fused chloride of potas- sium with which it is enveloped. This oxide is also formed by putting tungstic acid in contact with zinc in dilute muriatic acid. The tungstic acid first becomes blue, and then assumes a copper colour; but the oxide in this state can with difficulty be preserved, as by exposure to the air, and even under the surface of water, it absorbs oxygen, and is reconverted into tungstic acid. TUNGSTEN. 275 Oxide of tungsten, when prepared by means of hydrogen gas, has a brown colour, and when polished acquires the colour of copper; but when procured by Wohler's process, it is nearly black. It does not unite, so far as is known, with acids; and when heated to near redness, it takes fire and yields tungstic acid. Sulphuret of Tungsten may be formed by heating together, tungstic acid and sulphuret of mercury, the mercury is driven off, and a blackish-gray compound remains which is a bi-sulphuret of tungsten. Salts. Tungstate of Ammonia is procured in crystalline scales, of a metallic taste, by digesting the acid in ammonia or its carbonate. Tungstate of Potassa is uncrystallizable and deliquescent. The acids occasion a precipitate, in its solution, which are compounds of tungstic acid, potassa, and the acid used as a pre- cipitant. Tungstate of Soda crystallizes in hexahedral tables, soluble in four parts of cold, and two of boiling water, and of an acrid taste. Sulphuric, nitric, and muriatic acids occasion precipitates, as in the tungstate of potassa. The Tungstates of Baryta, Strontia, and Lime, are insoluble white compounds. Tungstate of Magnesia crystallizes in pearly scales. The acids produce precipitates of triple compounds in its solution. SECTION VI. Columbium. * This metal was discovered in 1801 by Mr. Hatchett, who de- tected it in a black mineral belonging to the British Museum, supposed to have come from the United States, and from this cir- cumstance he applied to it the name of Columbium. About two years after, M. Ekeberg, a Swedish chemist, extracted the same substance from tantalite and yttro-tantalite; and, on the suppo- sition of its being different from columbium, described it under the name of tantalum. The identity of these metals, however, was established in the year 1809 by Dr. Wollaston. Columbic acid is with difficulty reduced to the metallic state by the action of heat and charcoal; but Berzelius succeeded in obtaining this metal by the same process which he employed in the preparation of zirconion and silicion, namely, by heating po- tassium with the double fluoride of potassium and columbium. On washing the reduced mass with hot water, in order to remove 276 COLUMBIUM. the fluoride of potassium, columbium is left in the form of a black powder. In this state it does not conduct electricity; but, in a denser state, it is a perfect conductor. By pressure it acquires metallic lustre, and has an iron-gray colour. It is not fusible at the temperature at which glass is fused. When heated in the open air, it takes fire considerably below the temperature of igni- tion, and glows with a vivid light, yielding columbic acid. It is scarcely at all acted on by the sulphuric, muriatic, or nitro-muri- atic acid; whereas it is dissolved with heat and disengagement of hydrogen gas by hydro-fluoric acid, and strll more easily by a mixture of nitric and hydro-fluoric acids. It is also converted into columbic acid by fusion with hydrate of potassa, the hydro- gen gas of the water being evolved. Columbium unites with oxygen in two proportions, giving rise to an oxide and an acid. The oxygen in these compounds is in the ratio of 2 to 3, and the experiments of Berzelius lead to the inference that the oxide is formed of 185 parts or one equivalent of columbium, united with 16 parts or two equivalents of oxygen; and the acid of one equivalent ofthe metal to three of oxygen. But the combining proportion of the acid is not known with such certainty as altogether to establish the accuracy of this opinion. The Oxide of Columbium is generated by placing columbic acid in a crucible lined with charcoal, luting carefully to exclude atmospheric air, and exposing it for an hour and a half to intense heat. The acid, when in direct contact with charcoal, is en- tirely reduced; but the film of metal is very thin. The in- terior portions are pure oxide of a dark gray colour, very hard and coherent. When reduced to powder, its colour is dark brown. It is not attacked by any acid, even by nitro-hydrofluo- ric acid; but it is converted into columbic acid either by fusion with hydrate of potassa, or deflagration with nitre. When heated to low redness, iMakes fire, and glows, yielding a light gray powder ; but in this way it is never completely oxidized. Ber- zelius states that tnis oxide, in union with protoxide of iron and a little protoxide of manganese, occurs at Kimito in Finland, and may be distinguished from the other ores of columbium by yield- ing a chesnut-brown powder. Columbium exists in most of its ores as an acid, united either with the oxides of iron and manganese, as in tantalite, or with the earth yttria, as in the yttro-tantalite. This acid is obtained by fusing its ore with three or four times its weight of carbonate of potassa, when a soluble columbate of that alkali results, from which columbic acid is precipitated as a white hydrate by acids. Berzelius also prepares it by fusion with bisulphate of potassa. The hydrated columbic acid is tasteless, and insoluble in water; but when placed on moistened litmus paper, it communicates a red tinge. It is dissolved by the sulphuric, muriatic, and some vegetable acids; but it does not diminish their acidity, or appear COLUMBIUM. 277 to form definite compounds with them. With alkalies it unites readily ; and though it does not neutralize their properties com- pletely, crystallized salts may be obtained by evaporation. When the hydrated acid is heated to redness, water is expelled, and the anhydrous columbic acid remains. In this state it is attacked by alkalies only. Sulphuret of Columbium.—This compound, first prepared by Rose, is generated with the phenomena of combustion, when columbium is heated to commencing redness in the vapour of sulphur; or by transmitting the vapour of sulphuret of carbon over columbic acid in a porcelain tube at a white heat, carbonic oxide being also evolved. Salts. Columbate of Potassa, as appears from Mr. Hatchett's experi- ments, forms white glittering scales like boracic acid; acids preci- pitate the columbic acid from its solution; columbate of soda was also discovered by Mr. Hatchett. An infusion of galls gives an orange-coloured precipitate with the columbate of potassa. SECTION VII. Titanium. Titanium was first recognized as a new substance by Mr. Gre- gor, of Cornwall, and its existence was afterwards established by Klaproth. But the properties of the metal were not ascertained in a satisfactory manner, until the year 1822, when Dr. Wollaston was led to examine some minute crystals which were found in a slag at the bottom of a smelting furnace, at the great iron works at Merthyr Tydvil, in Wales, and were presented to him by Mr. Buckland. These crystals, which have since been found at other iron works, are of a cubic form, and in colour and lustre are like burnished copper. They conduct electricity, and are attracted slightly by the magnet, a property which seems owing to the presence of a minute quantity of iron. Their specific gravity is 5.3; and their hardness is so great, that they scratch a polished surface of rock crystal. They are exceedingly infusible; but when exposed to the united action of heat and air, their surface becomes covered with a purple-coloured film, which is an oxide. They resist the action of the nitric and nitro-muriatic acids, but are completely oxidized by being strongly heated with nitre. They are then converted into a white substance, which possesses all the properties of the peroxide of titanium. By this character, they are proved to be metallic titanium. Oxides of Titanium.—This metal has probably two degrees of 278 TITANIUM. oxidation. The protoxide is of a purple colour, and is supposed to exist pure in the mineral called Anatase ; but its composition and chemical properties are unknown. The peroxide exists in a nearly pure state in the titanite or rutile. The menaccanite, in which titanium was originally discovered by Mr. Gregor, is a compound of the oxides of titanium, iron, and manganese. This oxide is best prepared from rutile ; the process is rather complex, owing to the difficulty of separating it from iron. The oxide of titanium, when pure, is quite white. It is ex- ceedingly infusible and difficult of reduction ; and after being once ignited, ceases to be soluble in acids. M. Rose has ob- served that, like silica, it possesses weak acid properties. Thus he finds that it unites readily with alkalies, and he denies its power of acting as an alkaline base. On this account, he pro- poses for it the name of titanic acid. If previously ignited with carbonate of potassa, the oxide of titanium is soluble in dilute muriatic acid ; but it is retained in solution by so feeble an attraction, that it is precipitated merely by boiling. It is likewise thrown down by the pure and carbo- nated alkalies, both fixed and volatile. A solution of gall-nuts causes an orange-red colour, which is very characteristic of the presence of titanium. When a rod of zinc is suspended in the solution, a purple-coloured powder, probably the protoxide, is precipitated, which is gradually re-converted into the peroxide. The atomic weight of titanium, as deduced by Dr. Thomson, from experiments made by M. Rose, and by himself, is 24. Ti- tanic acid is inferred, from the same data, to be composed of 24 parts, or one atom of titanium, and 16 parts or two atoms of oxygen. Phosphuret of Titanium has not been particularly examined. Sulphuret of Titanium, is of a deep green colour ; the slightest friction with a hard body gives it a metallic lustre like that of brass. Salts. Titanate of Potassa, appears to be the only salt of the titanic acid which has been examined. Nitrate of Titanium crystallizes in hexagonal tables; it is white, acid, and easily decomposed by heat. The other salts of titanium are not of sufficient interest to require particular de- scription. Alloys.—Dr. Wollaston attempted to form alloys of titanium with tin and several other metals, but without success. Solutions of titanium are colourless, but afford white precipitates with po- tassa and soda. Hydrosulphate of ammonia occasions a greenish deposit. ( 279 ) SECTION VIII. Uranium. Uranium was discovered in 1789, by Klaproth, in a mineral of Saxony, called from its black colour pitchblende, which consists of the protoxide of uranium and oxide of iron. From this ore, the uranium may be conveniently extracted by the following process : After heating the mineral to redness, and reducing it to fine powder, it is digested in pure nitric acid, diluted with three or four parts of water, taking the precaution to employ a larger quantity of the mineral than the nitric acid present can dissolve. By this mode of operating, the protoxide is converted into the peroxide of uranium, which unites with the nitric acid, almost to the total exclusion of the iron. A current of sulphu- retted hydrogen is then transmitted through the solution, in order to separate lead and copper, the sulphurets of which are always mixed with pitchblende. The solution is boiled, to expel the free sulphuretted hydrogen, and after being concentrated by eva- poration, is set aside to crystallize. The properties of metallic uranium are as yet known imper- fectly. It was prepared by Arfwedson, by conducting hydrogen gas over the protoxide of uranium heated in a glass tube. The substance obtained by this process was crystalline, of a metallic lustre, and of a reddish-brown colour. It suffered no change on exposure to the air at common temperatures ; but when heated in open vessels absorbed oxygen, and was re-converted into the protoxide. From its lustre, it was inferred to be metallic uranium. Chemists are acquainted with two compounds of uranium and oxygen, the composition of which has been minutely studied by Arfwedson and Thomson. According to the chemist last men- tioned, whose experiments are the most recent, the weight of an atom of uranium is 208, and its oxides are composed of Uranium. Oxygen. Protoxide . 208 . 8 = 216 Peroxide* . 208 . 16 = 224 According to the analyses of Arfwedson, 216 is the atomic weight of uranium, and the oxygen in its two oxides is in the ratio of 1 to 1.5, and Berzelius, from the composition of three salts of uranium, has arrived .at a similar conclusion. The Protoxide of Uranium is of a very dark green colour, and is obtained by decomposing the nitrate of the peroxide by heat. It is exceedingly infusible, and bears any temperature hitherto tried without change. It unites with acids, forming salts of a green colour. It is readily oxidized by nitric acid, and yields a 280 URANIUM. yellow solution which is a nitrate of the peroxide. The pro- toxide is employed in the arts, for giving a black colour to porcelain. The Peroxide of Uranium is of a yellow or orange colour, and most of its salts have a similar tint. It not only combines with acids, but likewise unites with alkaline bases, a property which was first noticed by Arfwedson. It is precipitated from acids as a yellow hydrate by pure alkalies, fixed or volatile ; but retains a portion of these bases in combination. It is thrown down as a carbonate by the carbonate of soda or ammonia, and is re-_iis- solved by an excess of the precipitant, a circumstance which affords an easy method of separating uranium from iron. It is not precipitated by sulphuretted hydrogen. With ferrocyanate of potassa it gives a brownish-red precipitate, not unlike the fer- rocyanate ofthe peroxide of copper. The peroxide of uranium is decomposed by a strong heat, and converted into the protoxide. From its affinity for alkalies, it is difficult to obtain it in a state of perfect purity. It is employed in the arts for giving an orange colour to porcelain. Sulphuret of Uranium exists native. Salts. The salts of the uranic acid have not received much examina- tion. Arfwedson employed the uraniate of lead, in ascertaining ihe composition ofthe oxides of uranium. Nitrate of Uranium, is formed in the manner we have above stated; it crystallizes in flattened four sided prisms of a beautiful lemon colour. Some other salts of this metal with the nitric acid, seem also to have been formed. Phosphate and Sesqui-phosphate of Uranium, occur in the native compounds of uranium, such as the green and yellow uran-mica. Protcffsulphate of Uranium, was found native by Dr. John, in beautiful emerald green crystals. Other salts of this base and the sulphuric acid, have also been observed. The tendency of uranium to form sesqui salts and double salts, is remarkable; thus we have a potassa persulpliate, and an am- monia persulphate of uranium. The salts of uranium have generally a yellow colour, and an astringent metallic taste. Potassa forms in their solutions a yel- low precipitate. (281 ) SECTION IX. Gold, or Aurum. Gold has been known and prized from the earliest ages of the world. Pure gold seems to have been brought from Ophir, even be- fore the days of Job. Few metals combine so many valuable properties, and it was probably adopted, soon after its discovery, as a medium of exchange for other property. It has hitherto been found only in the metallic state, either pure or in combination with other metals. It occurs massive, capillary, in grains, and crystallized in octahedrons and cubes, or their allied forms. It is sometimes found in primary mountains; but more frequently in alluvial depositions, especially among sand in the beds of rivers, having been washed by water out of disintegrated rocks in which it originally existed. Gold is the only metal which has a yellow colour, a character by which it is distinguished from all other simple metallic bodies. It is capable of receiving a high lustre by polishing, but is infe- rior in brilliancy to steel, silver, and mercury. In ductility and malleability, it exceeds all other metals; but it is surpassed by several in tenacity. Its density is 19.3. When pure, it is ex- ceedingly soft and flexible. It fuses at 32° of Wedgwood's py- rometer. Gold may be exposed for ages to air and moisture without change, nor is it oxidized by being kept in a state of fusion in open vessels. When intensely ignited by means of electricity or the oxy-hydrogen blow-pipe, it burns with a greenish-blue flame, and is dissipated in the form of a purple powder, which is sup- posed to be an oxide. Gold is not oxidized or dissolved by any ofthe pure acids ; for it may be boiled even in nitric acid without undergoing any change. Its only solvents are chlorine and nitro-muriflpc acid ; and it appears from the observations of Sir H. Davy, that chlorine is the agent in both cases, since the nitro-muriatic acid does not dissolve gold, except when it gives rise to the formation of chlo- rine. It is to be inferred, therefore, that the chlorine unites di- rectly with the gold. Whether the resulting solution is really a chloride of the metal, or a muriate of its oxide, generated by the decomposition of water, is uncertain ; but from some recent ob- servations of M. Pelletier, which will be mentioned immediately, the former opinion appears to be the more probable. There is no inconvenience, however, in regarding it as a muriate, be- cause re-agents act upon it as if it were such. The most convenient method of forming a solution of gold, is to digest fragments of the metal in a mixture, composed of two measures of muriatic and one of nitric acid, until the acid is Nn 282 GOLD. saturated. The orange-coloured solution is then evaporated to dryness by a regulated heat, in order to expel the free acid with- out decomposing the residual chloride of gold. On adding water, the chloride is dissolved, forming a neutral solution of a reddish-brown colour. Oxides of Gold.—The chemical history of the oxides of gold is as yet very imperfect. Berzelius is of opinion that there are three oxides. His protoxide is obtained by decomposing the protochloride of gold by a solution of pure potassa, and is of a dark green colour. The deutoxide or purple oxide is the product of the combustion of gold. The composition of these oxides has not yet been satisfactorily determined, and the very existence of the first, though probable, may be questioned. The only well- known oxide is that which is supposed to exist in the solution of gold combined with muriatic acid. It may be prepared by mixing with a concentrated neutral solution of gold, a quantity of pure potassa exactly sufficient for combining with the muriatic acid. A reddish-yellow coloured precipitate, the hydrous peroxide, subsides, which is rendered anhydrous by boiling, and assumes a brownish-black colour. The best method of forming it, is by digesting the muriate with pure magnesia, washing the precipi- tate with water, and removing the excess of magnesia by dilute nitric acid. The peroxide of gold is yellow in the state of hydrate, and nearly black when pure, is insoluble in water, and is completely decomposed by solar light or a red heat. Muriatic acid dissolves it readily, yielding the common gold solution. As chemists are but imperfectly acquainted with the number and composition ofthe oxides of gold, it is at present impossible to determine the atomic weight of this metal in a satisfactory manner. M. Javal has recently analyzed the oxide of gold, and finds that the proportion stated by Berzelius is very near the truth. If we adopt th^numbers given by this chemist, and regard the peroxide as containing three atoms of oxygen, 200 will be the atomic weight of gold, and 224 the equivalent of its oxide. Phosphuret of Gold, is obtained by heating gold leaf with phos- phorus in a tube, deprived of air. It is a gray substance of a metallic lustre, and consists probably of 1 atom of gold 4-11 of phosphorus. Sulphuret of Gold.—On transmitting a current of sulphuretted hydrogen gas through a solution of gold, a black precipitate is formed, which is a sulphuret. It is resolved by a red heat into gold and sulphur, and appears, from the analysis of Oberkampf, to to be composed of 200 parts or one atom of gold, and 48 parts or three atoms of sulphur. The compounds of gold with the other non-metallic bodies have been little examined. GOLD. 283 Salts. Nitrate of Gold.—This, according to Brande, is a yellow styptic deliquescent salt; but later researches seem to prove that gold forms no definite compound with any acid which contains oxygen. The oxide may indeed be dissolved by both the nitric and sul- phuric acids, but their affinity for it is so slight, that the oxide is precipitated in the state of a hydroxide on the addition of water. Aurate of Potassa.—The oxide of gold combines with alka- line bases, such as potassa and baryta, and form regular salts; this circumstance induced M. Pelletier to deny that the peroxide is a salifiable base, and to contend that the muriatic solution of gold is in reality a chloride ofthe metal. On this supposition he proposes the term auric acid for the peroxide of gold, and to its compounds with alkalies he gives the denomination aurates. If a considerable excess of potassa be mixed with the chloride of gold, the supernatant liquid acquires a light greenish yellow colour, and a blackish sediment is formed in which not more than TV ofthe gold is found that was held in solution. The re- maining t9q, united with oxygen have combined with potassa, which acts the part of a base, while the oxide of gold serves as a salifying principle. This compound is the aurate of potassa. Aurate of Baryta.—Baryta produces the same effects on the chloride of gold as potassa, but seems to have a stronger affinity for auric acid. Aurate of Ammonia.—The peroxide of gold is thrown down of a yellow colour by ammonia, and the precipitate is an aurate of that alkali. It is a highly detonating compound analogous to fulminating silver. Alloys of Gold.—The presence of other metals in gold has a remarkable effect in impairing its malleability and ductility. The metals which possess this property in the greatest degree, are bismuth, lead, antimony, and arsenic. Thus, when gold is alloyed with 1-1920th part of its weight of lead, its malleability is surprisingly diminished. A very small proportion of copper has an influence over the colour of gold, communicating to it a red tint, which becomes deeper as the quantity of copper in- creases. Pure gold, being too soft for coinage, and many pur- poses in the arts, is always alloyed either with copper or an alloy of copper and silver, which increases the hardness of the gold without materially affecting its colour or tenacity. Gold coins contain about l-12th of copper. Gold unites with remarkable facility with mercury, forming a white-coloured compound. An amalgam composed of one part of gold to eight of mercury is employed in gilding brass. The brass, after being rubbed with the nitrate of mercury, in order to- 284 GOLD. give it a thin film of quicksilver, is covered with the amalgam of gold, and then exposed to heat for the purpose of expelling the mercury. CHAPTER V. In our third chapter we noticed the metals, which, by com- bining with oxygen, produce alkalies; in our fourth, the metals which produce acids; and here we shall arrange the metals which produce oxides only; these oxides have no acid or alkaline re- action on vegetable colours, an inertness, no doubt, owing to their insolubility. The metals we are now to mention are twenty in number, viz: Lead Iridium Iron Osmium Copper Pluranium Mercury Zinc Cerium Cadmium Platinum Bismuth Cobalt Silver Nickel Aluminum Palladium Glucinum Rhodium Yttrium These metals, added to the list of elementary inflammable bodies already described, constitute the whole of the simple electro-positive substances known. SECTION I. Lead, or Plumbum. Lead appears to have been very early known. It is mentioned several times by Moses. The ancients seem to have considered it as nearly allied to tin. Native lead is an exceedingly rare production; but in combi- nation, especially with sulphur, it occurs in large quantity. All the metallic lead of commerce is extracted from the native sul- phuret, the galena of mineralogists. Lead has a bluish-gray colour, and when recently cut, a strong metallic lustre ; but it soon tarnishes by exposure to the air. Its density is 11.358. It is soft, flexible, and inelastic. It is both malleable and ductile, possessing the former property in particu- LEAD. 285 lar to a considerable extent. In tenacity, it is inferior to all duc- tile metals. It fuses at about 612° F., and when slowly cooled forms octahedral crystals. It may be heated to whiteness in close vessels without subliming. Most of the compounds of lead are poisonous. Lead absorbs oxygen quickly at high temperatures. When fused in open vessels, a gray film is formed upon its surface, which is a mixture of metallic lead and protoxide; and when strongly heated, it is dissipated in fumes of the yellow oxide of lead. In pure water it is oxidized with considerable rapidity, yielding minute shining, brilliantly white, crystalline scales of carbonate of lead, the oxygen and carbonic acid being derived from the atmosphere. The presence of saline matter in water retards the oxidation of the lead; and some salts, even in exceed- ingly minute quantity, prevent it altogether. Many kinds of spring water, owing to the salts which they contain, do not cor- rode lead; and hence, though intended for drinking, may be safely collected in leaden cisterns. Of this, the water of Edin- burgh is a remarkable instance. Dr. Christison is at present occupied with an experimental inquiry on this subject, and has already collected a variety of interesting facts. Lead is not attacked by the muriatic or the vegetable acids, though their presence, at least in some instances, accelerates the absorption of oxygen from the atmosphere in the same manner as with copper. Cold sulphuric acid does not act upon it; but when boiled in that liquid, the lead is slowly oxidized at the ex- pense of the acid. The only proper solvent for lead is the nitric acid. This re-agent oxidizes it rapidly, and forms with its oxide a salt which crystallizes in opaque octahedrons by evaporation. Oxides of Lead.—Lead has three degrees of oxidation, and the composition of its oxides, as determined with great care by Ber- zelius, is as follows :— Lead. Oxygen. Protoxide . 104 . 8 . = 112 Deutoxide . 104 . 12 . = 116 Peroxide . 104 . 16 . =120 Protoxide.—This oxide is prepared on a large scale by col- lecting the gray film which forms on the surface of melted lead, and exposing it to heat and air until it acquires a uniform yel- low colour. In this state it is the massicot of commerce; and when partially fused by heat, the term litharge is applied to it. As thus procured it is always mixed with the deutoxide. It may be obtained pure by heating the carbonate or nitrate to low red- ness in a vessel from which atmospheric air is excluded. The protoxide of lead has a yellow colour, is insoluble in water, fuses at red heat, and in close vessels is fixed and un- 286 LEAD. changeable in the fire. Heated with combustible matters it parts with oxygen, and is reduced. From its insolubility it does not change the vegetable colours under common circumstances; but when rendered soluble by a small quantity of acetic acid, it has a distinct alkaline re-action. It unites with acids, and is the base of all the salts of lead. Most of its salts are of a white colour. The protoxide of lead is precipitated from its solutions by pure alkalies as a white hydrate, which is re-dissolved by potassa in excess; as a white carbonate, which is the well-known pigment white lead, by alkaline carbonates; as a white sulphate by solu- ble sulphates; as a dark brown sulphuret by sulphuretted hy- drogen ; and as the yellow iodide of lead by hydriodic acid or hydriodate of potassa. M. Orifilahas proved experimentally that the sulphate of lead, owing to its insolubility, is not poisonous , and therefore the sul- phate of magnesia, or any soluble sulphate, renders the active salts of lead inert. The best method of detecting the presence of lead in wine, or other suspected mixed fluids, is by means of sulphuretted hydro- gen. The sulphuret of lead, after being collected on a filter and washed, is to be digested in nitric acid diluted with twice its weight of water, until the dark colour of the sulphuret disappears. The solution ofthe nitrate of lead should then be brought to per- fect dryness on a watch glass, in order to expel the excess of nitric acid, and the residue re-disolved in a small quantity of cold water. On dropping a particle ofthe hydriodate of potassa into a portion of this liquid, the yellow iodide of lead will instantly ap- pear. The protoxide of lead unites readily with earthy substances, form- ing with them a transparent colourless glass. Owing to this pro- perty it is much employed for glazing earthen ware and porcelain. It enters in large quantity into the composition of flint glass, which it renders more fusible, transparent, and uniform. Lead is separated from its salts in the metallic state by iron or zinc. The best way of demonstrating this fact is by dissolv- ing one part of the acetate of lead in sixteen of water, and sus- pending a piece of zinc in the solution by means of a thread. The lead is deposited upon the zinc in a peculiar arborescent form, giving rise to the appearance called arbor saturni. This is a convenient method of obtaining very pure metallic lead. Deutoxide.—The deutoxide of lead is the minium or red lead of commerce, which is employed as a pigment, and in the manu- facture of flint glass. It is formed by heating litharge in open vessels while a current of air is made to play upon its surface. This oxide does not unite with acids. When heated to redness it gives off pure oxygen gas, and is re-converted into the pro- toxide. When digested in nitric acid it is resolved into the pro- LEAD. 287 toxide of lead, the former of which unites with the acid, while the latter remains as an insoluble powder. Peroxide.—This oxide may be obtained by the action of nitric acid on minium, as just mentioned ; but the most convenient me- thod of preparing it is by transmitting a current of chlorine gas through a solution ofthe acetate of lead. In this process water is decomposed ;—its hydrogen uniting with chlorine, and its oxy- gen with the protoxide of lead, gives rise to muriatic acid and the peroxide of lead The peroxide of lead is of a puce colour, and does not unite with acids. It is resolved by a red heat into the protoxide and oxygen gas. Phosphuret of Lead, may be formed by dropping phosphorus into melted lead. It is of a silver white colour, with a shade of blue, but it soon tarnishes when exposed to the air. Sulphuret of Lead, may be formed artificially by fusion, its lustre and colour much resemble pure lead, but it is brittle. It consists of 104 lead + 16 sulphur. Native Sulphuret, or Galena, is the principle source from whence the vast quantity of lead, which is employed in the arts is derived. It occurs massive and crystallized, particularly in limestone rocks; its primitive form is the cube, of which there are several modifications, and among them the octahedron. It often contains traces of silver, and sometimes in such quantity as to render it worth separating, which is effected by exposing the roasted sulphuret to the action of heat and air, in shallow earthen dishes, the lead becomes oxidized and converted into litharge, while the silver is left pure, in consequence of its power of resisting the influence of heat and air. This process is called cupellation; the litharge is afterwards reduced by fusion with charcoal. The reduction of galena, upon a large scale, is a very simple process. The picked ore, after having been broken and washed, is roasted in a reverberatory fire, the temperature being such as to soften but not to fuse it; during this operation it is raked till the fumes of the sulphur are dissipated, when it is brought into perfect fusion, the lead sinks to the bottom, and is run out into oblong moulds called pigs; the scoria are again melted and furnish a portion of a less pure metal. Galena is found in great abundance in the state of Missouri. Salts. Nitrate of Lead.—This salt is formed by digesting litharge in dilute nitric acid. It crystallizes readily in octahedrons, which are almost always opaque. These crystals are anhydrous. This salt has an acid re-action, but is neutral in composition, con- 288 LEAD. sisting of 54 parts or one atom of acid, and 112 or one atom of the protoxide of lead. A dinitrate of lead, composed of one atom of acid to two atoms of the protoxide, was formed by Berzelius by adding to a solution ofthe neutral nitrate, a quantity of pure ammonia insufficient for separating the whole of the acid. If an additional quantity of the ammonia be added, a | nitrate is formed ; with an excess of ammonia, a - nitrate is formed which is not altered by any ad- ditional quantity of the ammonia. Supposing nitrogen to be a simple substance, the oxygen ofthe acid in the respective salts will be to that ofthe base, as 5, <2\, If and £ to 1—these numbers are not simple multiples of each other; but if we suppose ni- trogen to be an oxide, then the oxygen of the acid in the differ- ent salts will be to that in the base, as 5, 3, 2, 1 to 1, hence Ber- zelius infers that nitrogen is composed of oxygen and a base which he terms ammonium. Hyponitrite of Lead crystallizes in octahedrons of a yellow colour, and very soluble ; other salts of this acid with lead exist. Carbonate of Lead.—This salt, which is the white lead or ceruse of painters, occurs native, but may be obtained by double decompostiion. It is prepared for the purposes of commerce by exposing coils of thin sheet lead to the vapours of vinegar, when, by the united action of the oxygen of the atmosphere and the acid fumes, the lead is both oxidized and converted into a carbo- nate. / Borate of Lead is precipitated in the form of a white powder, when borate of soda is mixed with nitrate of lead. Phosphate of Lead is formed by mixing solutions of nitrate of lead and phosphate of soda. It is of a yellowish white colour, insoluble in water, soluble in alkaline solutions, and in nitric acid. It is decomposed by sulphuric acid. It fuses before the blow-pipe, and crystallizes on cooling ; it consists of 112 oxide of lead and one atom of phosphoric acid. Phosphite of Lead and Hypophosphite of Lead are unimpor- tant compounds. Sulphate of Lead.—When metallic lead is boiled in concentra- ted sulphuric acid, sulphurous acid is evolved, and a white sul- phate of lead is formed. It is so nearly insoluble, that it may be formed by adding dilute sulphuric acid or an alkaline sulphate, to a solution of nitrate of lead ; after having been dried at a tem- perature of 400° it may be heated to redness in a platinum cruci- ble without losing weight. Heated on charcoal by the blow-pipe it is decomposed and reduced ; it consists of one atom of acid and one of the base. Sulphate of lead is insoluble in alcohol and in nitric acid, it is sparingly soluble in dilute sulphuric acid, and separates from it in small prismatic crystals. Sulphite of Lead may be obtained by digesting the yellow LEAD. 289 oxide of lead in sulphurous acid; it is white, insoluble, and taste- less, and consists of one atom of each of its components. Hyposulphite of Lead is precipitated in the form of a white powder, nearly insoluble in water, by adding a solution of nitrate lead to hyposulphite of potassa. Arseniate of Lead.—Arsenic acid attacks lead in a digesting heat, communicates a portion of its oxygen, and converts it into an arseniate in the state of an insoluble white powder. Chromate of Lead.—This salt may be formed by mixing to- gether the solutions of nitrate of lead, and an alkaline chromate; it precipitates in the state of a red powder. It occurs native in crystals of a fine orange-colour, it is a very rare mineral, hitherto only found in the Uralian mountains in Siberia. A Dicromate of Lead, composed of one atom of chromic acid, and two atoms ofthe protoxide of lead, may be formed by boiling carbonate of lead with an excess of chromate of potassa. It is of a beautiful red colour, and has been recommended by Mr. Badams as a pigment. Molybdate of Lead may be formed by adding molybdic acid to the nitrate of lead. It occurs native, principally in crystals of different shades of yellow. The Antimoniate, antimonite, and tungstate of Lead, are unim- portant salts, the uraniate we have already mentioned. Alloys.—Common pewter consists of about 80 parts of tin, and 20 of lead. Equal parts of these metals constitute an alloy, which is more fusible than either separately, and is the plumb- ers solder. Printers types are made of an alloy of three parts of lead, to one of antimony. The alloy of lead and arsenic is brittle, dark coloured, and composed of plates; common shot is an alloy of arsenic and lead. Tests.—All the solutions of lead are decomposed by sulphu- retted hydrogen, and by alkaline hydrosulphates. Hence, these compounds are excellent tests of the presence of lead in wine, or any other liquor, discovering it by a dark coloured precipitate. The hydrosulphate of ammonia, is the most convenient one for this purpose. Lead is separated from its salts in the metallic state by iron or zinc. The best way of demonstrating this fact is by dissolving one part ofthe acetate of lead in sixteen of water, and suspend- ing a piece of zinc in the solution by means of a thread. The lead is deposited upon the zinc in a peculiar arborescent form, giving rise to the appearance called arbor saturni. This is a convenient method of obtaining very pure metallic lead. Oo ( -J-Hi ) SECTION II. Iron, or Ferrum. As iron is the most common, we had almost said, it is there- fore the most useful of all the metals. No one, who reflects on the universal and abundant diffusion of this substance, through- out the earth, can disregard so strong an indication of the good- ness of the Great Author of Nature. It has been known from time immemorial; it is mentioned frequently in the Pentateuch by Moses, and occasionally in the poems of Homer. The pro- gress of the arts and sciences may be said to be owing, in a great measure, to the applications of iron ; indeed, there is scarcely a branch of human industry, which does not derive some advantage from this metal. Though iron was thus early known, from the difficulty of working it, it seems to have been but little used ; so high a value was set upon it, as late as the Trojan war, that Achilles proposed a ball of iron as one of the prizes, during the games which he celebrated in honour of Patroclus. In the time of the Alchemists, iron was called Mars, and, until lately, many of its medicinal preparations were familiarly known by titles de- rived from that term. Iron has a peculiar gray colour, and strong metallic lustre, which is susceptible of being heightened by polishing. In duc- tility and malleability, it is inferior to several metals, but exceeds them all in tenacity. At common temperatures, it is very hard and unyielding, and its hardness may be increased by being heated and then suddenly cooled; but it is at the same time rendered brittle. When heated to redness, it is remarkably soft and pliable, so that it may be beaten into any form, or be in- timately incorporated or welded with another piece of red-hot iron by hammering. Its texture is fibrous, and its specific gravity 7.78. In its pure state it is exceedingly infusible, requiring for fusion a temperature of 158° of Wedgwood's pyrometer. It is attracted by the magnet, and may itself be rendered permanently magnetic by several processes; a property of great interest and importance, and which is possessed by no other metal, excepting cobalt and nickel. The occurrence of pure native iron is very rare, and most of the specimens said to be such, have, not been well attested. It has been found filling a vein in a mass of mica slate by Major Burrall, on Canaan Mountain, in the state of Connecticut. The iron of meteoric origin is impure ; for all the masses hitherto examined contain nickel and cobalt. Metallic iron is easily pro- cured by heating the native oxide with charcoal; but when thus obtained it is never quite free from carbonaceous matter. The only method of preparing iron absolutely pure, is by passing dry IRON. 291 hydrogen gas over the pure oxide heated to redness in a tube of porcelain. ' Iron has a strong affinity for oxygen. In a perfectly dry at- mosphere, it undergoes hardly any change; but when moisture is likewise present, it oxidizes or rusts in the course of a few days. Heated to redness in the open air, it absorbs oxygen rapidly, and is converted into black scales, called the black oxide of iron ; and in an atmosphere of oxygen gas it burns with vivid scintillations. It decomposes the vapour of water, by unit- ing with its oxygen, at all temperatures, from a dull red to a white heat; a singular fact when it is considered, that at the very same temperatures the oxides of iron arc reduced to the metallic state by hydrogen gas. Oxides of Iron. Iron combines with oxygen in two proportions only, forming the blue or protoxide, and the red or peroxide of iron. Both these compounds arc capable of yielding regular crystallizable salts with acids. Protoxide.—This oxide is the base of the native carbonate of iron, and of the green vitriol of commerce. Its existence was inferred some years ago by Gay-Lussac ; but Stromeyer first ob- tained it in an insulated form by transmitting dry hydrogen gas over the peroxide of iron at a very low temperature. The protoxide of iron has a dark blue colour, and when melted with vitreous substances communicates to them a tint of blue. It is attracted by the magnet, though less powerfully than metal- lic iron. It is exceedingly combustible; for when fully exposed to air at common temperatures, it suddenly takes fire and burns vividly, being re-converted into the peroxide. Its salts, parti- cularly when in solution, absorb oxygen from the atmosphere with such rapidity that they may even be employed in eudio- metry. This protoxide is always formed with evolution of hydro- gen gas when metallic iron is put into dilute sulphuric or muriatic acid ; and its composition may be determined by collecting and measuring the gas which is disengaged. According to Gay- Lussac it is composed of 8 parts of oxygen, and 28.3 parts of iron; but Dr. Thomson infers from an analysis of the protosul- phate of iron, that the quantity of iron united with 8 parts of oxygen is 28 precisely. The atomic weight of the protoxide is therefore 36. The protoxide of iron is precipitated as a white hydrate by pure alkalies ; as a white carbonate, by alkaline carbonates ; and as a white ferrocyanate, by ferrocyanate of potassa. The two former precipitates become first green and then red, and the latter green and blue by exposure to the air. The solution of gall-nuts produces no change of colour. Sulphuretted hydrogen 292 IRON. does not act if the protoxide is united with any of the stronger acids; but the alkaline hydrosulphurets cause a black precipitate, the protosulphuret of iron. Peroxide.—The red or peroxide is a natural product, known to mineralogists under the name of red hematite. It sometimes occurs massive, at other times fibrous, and occasionally in the form of beautiful rhomboidal crystals. It may be made chemi- cally by dissolving iron in nitro-muriatic acid, and adding an alkali. The hydrate of the red oxide of a brownish red colour subsides, which is identical in composition with the mineral called brown hematite, and consists of 40 parts or one equivalent of the peroxide, and 9 parts or one equivalent of water. The peroxide of iron is not attracted by the magnet. Fused with vitreous substances it communicates to them a red or yellow colour. It combines with most of the acids, forming salts, the greater number of which are red. Its presence may be detected by very decisive tests. The pure alkalies, fixed or volatile, pre- cipitate it as the hydrate. The alkaline carbonates have a similar effect, for the peroxide of iron does not form a permanent salt with carbonic acid. With ferrocyanate of potassa it forms Prussian blue, the ferrocyanate of the peroxide of iron. The sulphocyanate of potassa causes a deep blood-red, and infusion of gall-nuts, a black colour. Sulphuretted hydrogen converts the peroxide into the protoxide of iron, and deposition of sulphur takes place at the same time. These re-agents, and especially the ferrocyanate and sulphocyanate of potassa, afford an unerring test ofthe presence of minute quantities ofthe peroxide of iron. On this account it is customary, in testing for iron, to convert it into the peroxide, which is easily effected by boiling the solution with a small quantity of nitric acid. The researches of several chemists, such as Gay-Lussac, Ber- zelius, Bucholz, and Thomson, leave no doubt that the oxygen contained in the blue and red oxides of iron is in the ratio of one to one and a half. Consequently, the peroxide consists of 28 parts or one equivalent of iron, and 12 parts or an equivalent and a half of oxygen. Black oxide.—This substance, long supposed to be the pro- toxide of iron, contains more oxygen than the blue, and less than the red oxide. It cannot be regarded as a definite compound of iron and oxygen; but is composed of the two real oxides united in a proportion which is by no means constant. It occurs native, frequently crystallized in the form of a regular octahedron, which is not only attracted by the magnet, but is itself sometimes mag- netic. It is always formed when iron is heated to redness in the open air; and is likewise generated by the contact of watery vapour with iron at elevated temperatures. The composition of the product, however, varies with the duration ofthe process and the temperature which is employed. Thus, according to Buc- IRON. 293 holz, Berzelius, and Thomson, 100 parts of iron, when oxidized by steam, unite with nearly 30 of oxygen ; whereas, in a similar experiment performed by Gay-Lussac, 37.8.parts of oxygen were absorbed. The oxide of Gay-Lussac may be regarded as a com- pound of one equivalent ofthe protoxide and two equivalents of the peroxide ; and Berzelius is of opinion that the composition of magnetic iron ore is similar. M. Mosander states, that on heating a bar of iron in the open air, the outer layer ofthe scales contains a greater quantity of peroxide than the inner layer. The former consists of one equivalent of peroxide to two of the pro- toxide, and in the latter are contained one equivalent of peroxide to three equivalents of protoxide. The inner layer seems uni- form in composition ; but the outer is variable, its more exposed parts being richer in oxygen. The nature of the black oxide is further elucidated by the action of acids. On digesting the black oxide in sulphuric acid, an olive-coloured solution is formed, containing two salts, sul- phate of the peroxide and protoxide, which may be separated from e.ach other by means of alcohol. These mixed salts give green precipitates with alkalies, and a very deep blue ink with an infusion of gall-nuts. The black oxide of iron is the cause of the dull green colour of bottle glass. Carburets of Iron.—Carbon and iron unite in very various proportions ; but there are four compounds which are distinct from one another, namely, cast or pig iron, steel, cast steel, and graphite or plumbago. The native oxides of iron, which commonly contain argilaceous and siliceous substances, are reduced to the metallic state by the action of coke or charcoal and lime, at a high temperature. The oxygen of the oxide of iron unites with one portion of carbon, and the metal with another, yielding carbonic acid and carburet of iron ; while the earthy substances, together with a little oxide of iron, enter into combination, forming a vitreous substance called slag, which rises to the surface. The fused carburet is then drawn oft' by an aperture at the bottom ofthe furnace, and received in hollows or moulds, made with sand. In this state, it is neither ductile nor malleable, but very brittle; and fuses with such facility at a red heat that it cannot bo welded. It is highly crystalline, and its texture is granular. It contains about l-43d of its weight of carbon, together with small quantities of manga- nese, calcium, silicon, and probably aluminum; and besides these substances, which are chemically combined with the iron, particles of charcoal, earthy matters, and unreduced ore, are frequently inclosed within it. Cast iron is converted into malleable iron, by exposure in a reverberatory furnace to the combined action of air and intense heat. During this process, all the decomposed ore is reduced, earthy matters rise to the surface as slag, and the carbon is oxi- 294 IRON. dized. As the purity of the iron increases, its fusibility diminishes, until at length, though the temperature remains the same, the iron becomes solid. It is then subjected, while still hot, to the operation of rolling or hammering, by which its particles are ap- proximated. The metal, thus procured, is no longer a carburet, but is the purest iron of commerce. It is not, however, abso- lutely pure; for Berzelius has detected in it about one-half per cent, of carbon, and it likewise appears to contain silicon. Steel is made by exposing bars of the purest malleable iron, surrounded with charcoal in powder, to a long-continued red heat. During this process, the iron unites with about 1-150th of its weight of carbon, and acquires new properties. In ducti- lity and malleability it is far inferior to iron; but exceeds it greatly in hardness, sonorousness, and elasticity. Its texture is more compact than that of iron, and is susceptible of a far higher polish. It bears a strong red heat without entering into fusion, and may be welded with iron. When combined with an addi- tional quantity of carbon, it forms cast steel. In this state it is harder and more elastic, has a closer texture, and receives a higher polish than common steel. It is so fusible, however, that it cannot be welded. Steel differs chemically from cast iron, in being composed of purer iron, and in containing a smaller proportion of carbon. It is readily distinguished from malleable iron by the action of an acid. When a drop of dilute muriatic acid is placed on steel, a black spot appears, in consequence of a portion of iron being dissolved, while the charcoal is left. Graphite, more commonly known under the name of plumbago, or black lead, is a native carburet of iron, which contains 95 per cent, of carbon. It is unchangeable in the air, and, like pure charcoal, is attacked with difficulty by chemical substances. It has an iron-gray colour, metallic lustre, and granular texture. Its chief use is in making pencils and crucibles, and in burnish- ing iron to protect it from rust. Borruret of Iron, formed by fusing a mixture of iron filings and boracic acid, in a covered crucible, is a ductile mass, of a silver white colour. Silicuret of Iron, is of a silver white colour and ductile. Phosphuret of Iron.—This compound may be formed by heat- ing the phosphate of iron with charcoal. It is sometimes con- tained in metallic iron, to the properties of which it is exceed- ingly injurious, by causing it to be brittle at common tempe- ratures. Sulphurets of Iron.—There are two compounds of iron and sulphur, both of which are natural products. The protosulphuret is the magnetic iron pyrites of mineralogists. It is a brittle yel- low substance, of a metallic lustre, and is feebly attracted by the maguet. By exposure to air and moisture, it is gradually con- IRON. 295 verted into the protosulphate of iron. It may be made artificially by igniting the protosulphate of iron with charcoal; or still more conveniently, by heating a mixture of iron filings and sul- phur. It is dissolved completely and readily by dilute sulphuric or muriatic acid, with disengagement of sulphuretted hydrogen. It is composed of one atom of iron and one atom of sulphur. The bisulphuret, which contains two atoms of sulphur, is the common iron pyrites. When heated to redness, it loses half its sulphur, and is converted into the protosulphuret. It is insoluble in sulphuric and muriatic acid. Selenuret of Iron is an unimportant compound. Salts. Nitrate of Iron.—Nitric acid dissolves the protoxide and pe- roxide of iron, and produces a green protonitrate and a red per- nitrate. Nitric acid, diluted with a very little water, acts violently on iron and peroxidizes it, a vast quantity of gas being at the same time generated, which consists of a mixture of nitrous and nitric oxides; and a solution is formed of a reddish-brown colour, con- taining pernitrate of iron, and affording a brown precipitate to the alkalies. If the nitric acid be considerably diluted, the action is slow, and very little gas escapes ; the solution acquires an olive-brown colour from the nitric oxide which it contains, but when exposed to the air it becomes pale gteen, in consequence of the escape of that gas. The alkalies produce a green precipitate in this solu- tion ; it cannot be obtained in crystals by the usual process, and passes into penitrate by exposure to the air. Carbonate of Iron.—Carbonic acid does not form a definite compound with the peroxide of iron, but with the protoxide it constitutes a salt, which is an abundant natural production, oc- curring sometimes massive, and at other times crystallized in rhomboids or in hexagonal prisms. This protocarbonate of iron is contained also in most of the chalybeate mineral waters, being held in solution by free carbonic acid ; and it may be formed by mixing an alkaline carbonate with the protosulphate of iron. When prepared by precipitation, it attracts oxygen rapidly from the atmosphere, and the protoxide of iron, passing into the state of peroxide, parts with carbonic acid. For this reason, the car- bonate of iron ofthe pharmacopoeia is of a red colour, and con- sists chiefly of the peroxide. Borate of Iron.—When liquid borate of soda is poured into a solution of sulphate of iron, a pale yellow powder immediately precipitates, which is the borate of iron. This salt is insoluble in water. Before the blow-pipe, it melts readily into a globule of glass. 296 IRON. Phosphates of Iron.—The protophosphate is of a pale blue co- lour, the perphospate is white. They are both insoluble. Native phosphate of iron occurs in the form of a blue earthy powder, and also in prismatic crystals ; the former has sometimes impro- perly been termed native Prussian blue; it has been found in allu- vial soil. The latter occurs with iron pyrites in Cornwall. Sulphate of Iron.—The sulphate of the protoxide of iron, com- monly called green vitriol, is formed by the action of dilute sul- phuric acid on metallic iron, or by exposing the protosulphuret of iron in fragments to the combined agency of air and moisture. This salt has a strong, styptic, inky taste. Though neutral in composition, being composed of one atom of each element, it red- dens the vegetable blue colours. It is soluble in two parts of cold, and in three-fourths of its weight of boiling water. It oc- curs in transparent pale green-coloured rhombic crystals, which consist, according to Berzelius, of 76 parts or one atom of the protosulphate, and 63 parts or seven atoms of water. In the anhy- drous state, it is of a dirty white colour. It is this salt which is em- ployed in the manufacture of the fuming sulphuric acid. The protosulphate of iron absorbs oxygen from the air, especi- ally when in solution, by which an insoluble sub-sulphate of the peroxide of iron is generated, consisting, according to Berzelius, of one atom of sulphuric acid, and four atoms ofthe peroxide. When a solution of the protosulphate of iron is boiled with a little nitric acid, until the liquid acquires a red colour, and is then evaporated to dryness by a moderate heat, a salt remains, the greater part of which is soluble both in alcohol and in water, and which attracts moisture from the atmosphere. The analysis of Berzelius has proved it to be a compound of 40 parts or one atom of the peroxide of iron, and 60 parts or an atom and a half of sulphuric acid. It is, therefore, a sesqui-sulphate of the peroxide of iron. Protosulphate of iron forms double salts with sulphate of potas- sa and sulphate of ammonia, the former of which contains six, and the latter eight equivalents of water. They are isomorphous with the analogous double sulphates of magnesia. By mixing sulphate of potassa with persulphate of iron, and allowing the solution to crystallize by spontaneous evaporation, crystals are obtained similar to common alum in form, colour, taste, and composition. In this double salt the sulphate of alu- mina is replaced by persulphate of iron, with which it is isomor- phous. A similar double salt may be made with a mixture of sulphate of ammonia and persulphate of iron. Sulphite of Iron.—This salt can only be formed by dissolving recently precipitated protoxide of iron in sulphurous acid. It is insoluble in alchol, and when exposed to the air, is converted into sulphate of iron. IRON. 297 Hyposulphite of Iron is crystallizable; the crystals dissolved in water and exposed to the air, are gradually converted into sulphate of iron. Arseniate of Iron.—This salt may be formed by pouring arse- niate of ammonia into sulphate of iron. The salt precipitates in the state of a powder, insoluble in water. It exists native crys- tallized in cubes, which, in some instances, have their alternate angles truncated. Their colour is usually dark green, and their specific gravity is 3. This native salt usually contains a little copper. Per-arseniate of Iron, may be formed by boiling the arseniate of iron in nitric acid. The native arseniate is sometimes found converted into this salt, in consequence ofthe absorption of oxy- gen from the air ; it has then a brownish-red colour. Antimoniate of Iron.—Antimoniate of potassa precipitates iron perfectly white, and the antimoniate of iron preserves its white colour, as long as it is under water, but when dried in the open air, it becomes gray; when heated, it gives out water and be- comes red. Chromate of Iron, has been found native in small crystalline grains of an octahedral form. It commonly occurs massive of a black colour, with a slight metallic lustre, and hard enough to cut glass. It has been found in Siberia, France, and in this country, and has become useful in the arts as a source of some fine pigments. It is not a pure chromate. Molybdate of Iron.—The alkaline molybdates precipitate iron brown from its solution in acids. Ferrocyanic Acid. The ferrocyanic acid has, within these few years, been the subject of able researches by Mr. Porrett, Berzelius, and M. Robi- quet. Mr. Porrett recommends two methods for obtaining the ferrocyanic acid, by one of which it is procured in crystals, and by the other in a state of solution. The first process consists in dissolving 58 grains of crystallized tartaric acid in alcohol, and mixing the liquid with 50 grains of the ferrocyanate of potassa dissolved in the smallest possible quantity of hot water. The bitartrate of potassa is precipitated, and the clear solution, on being allowed to evaporate spontaneously, gradually deposits ferrocyanic acid in the form of small cubic crystals of a yellow colour. In the second process, the ferrocyanate of baryta, dis- solved in water, is mixed with a quantity of sulphuric acid, which is precisely sufficient for combining with the baryta. The insolu- ble sulphate of baryta subsides, and the ferrocyanic acid remains in solution. According to Mr. Porrett, every ten grains of the ferrocyanate of baryta require so much liquid sulphuric acid as is equivalent to 2.53 grains of real acid. PP 298 IRON. The ferrocyanic acid is neither volatile, nor poisonous in small quantities, and has no odour. It is gradually decomposed by exposure to the light, forming hydrocyanic acid and Prussian blue; but it is far less liable to spontaneous decomposition than the hydrocyanic acid. It differs also from this acid by possessing the properties of acidity in a much greater degree. Thus it reddens litmus paper permanently, neutralizesalkalies, and separates the carbonic and acetic acids from their combinations. It even de- composes some salts of the more powerful acids. The peroxide of iron, for example, unites with the ferrocyanic in preference to the sulphuric acid, unless the latter is concentrated. Different opinions have prevailed as to the nature of ferrocyanic acid. Berzelius maintains that it is a super-hydrocyanate of the protoxide of iron; but M. Robiquet has shown by arguments which appear to us unanswerable, that this supposition is incon- sistent with the phenomena. The view which is now commonly taken of the composition of this acid, was suggested by an ex- periment made by Mr. Porrett. On exposing the ferrocyanate of soda to the agency of galvanism, the soda was observed to collect at the negative pole, while oxide of iron, together with the ele- ments of hydrocyanic acid, appeared at the opposite end of the battery. From this he inferred, that the iron does not act the part of an alkali in the salt, for on that supposition it should have accompanied the soda, but that it enters into the constitution of the acid itself. Mr. Porrett at first considered the iron to be in the state of an oxide ; but he concludes, from subsequent re- searches, that the ferrocyanic acid contains no oxygen, and that its sole elements are carbon, hydrogen, nitrogen, and metallic iron. To the acid thus constituted, he proposes the name of ferruretted chyazic acid; but the term ferro-cyanic acid, intro- duced by the French chemists, is more generally employed. This view has the merit of accounting for the fact, that iron, though contained in ferrocyanic acid and all its salts, cannot be detected in them by the usual tests of iron. For the liquid tests are fitted only for detecting the oxide of iron as existing in a salt, and therefore cannot be expected to indicate the presence of metallic iron while forming one ofthe elements of an acid. We may now also understand how it happens that the ferrocyanic should actually contain the elements of hydrocyanic acid, and yet differ from it totally in its properties. According to the experiments of Mr. Porrett, the ferrocyanic acid is composed of one atom of iron, one atom of hydrocyanic * acid, and two atoms of carbon. M. Robiquet states, however, that its elements are in such proportion as to form cyanide of iron, and hydrocyanic acid; and the result of his researches, to- gether with the analysis of Berzelius, appears to justify the con- clusion that the ferrocyanic acid is composed of IRON. 299 Hydrogen ... 2 atoms. Iron .... I atom. Cyanogen ... 3 atoms. or of Hydrocyanic acid . . 2 atoms. Cyanide of Iron . . 1 atom. The ferrocyanic acid is, therefore, analogous to several acids, such as the muriatic, hydriodic, and hydrosulphuric acids, all of which contain hydrogen as an essential element, and which, for this reason, are termed hydracids. Under this point of view, the ferrocyanic acid may be regarded as a compound of a certain radical and hydrogen. This radical, which has not been obtain- ed in an insulated state, is composed of Cyanogen . 3 atoms.) ,. C Cyanogen . 2 atoms. Iron . . 1 atom. ) F (. Cyanide of iron 1 atom. and the acid itself consists of one atom of the radical and two atoms of hydrogen. The salts of ferrocyanic acid were once called triple prussi- ates, on the supposition that they are composed of prussic or hy- drocyanic acid, in combination with the oxide of iron and some other alkaline base. They are now termed ferrocyanates. The beautiful dye, Prussian blue, is a ferrocyanate ofthe peroxide of iron. It is always formed when ferrocyanic acid or its salts are mixed in solution with a per-salt of iron ; and for this reason the per-salts of iron, provided no free alkali is present, afford a cer- tain and an extremely delicate test of the presence of ferrocyanic acid. Ferrocyanate of Ammonia forms hexangular crystals of a light lemon colour, is very soluble in water, and deliquesces when exposed to the air. Ferrocyanates. The neutral ferrocyanates, so far as is known, appear to be formed in the same manner as the salts ofthe hydracids in gene- ral ; namely, the hydrogen of the acid is in exact proportion for forming water with the oxygen of the salifiable base with which it is united. Thus, the ferrocyanate of potassa is composed of one equivalent of ferrocyanic acid, which contains two atoms of hydrogen, and two atoms of potassa. With the alkalies and alkaline earths this acid forms soluble compounds; but it precipitates nearly all the salts ofthe common metals, giving rise either to the ferrocyanate of an oxide or the ferrocyanide of a metal. Ferrocyanate of Potassa.—This salt, sometimes called triple prussiate of potash, is prepared by digesting pure ferrocyanate of the peroxide of iron in potassa until the alkali is neutralized, by 300 IRON. which means the peroxide of iron is set free, and a yellow liquid is formed, which yields crystals of the ferrocyanate of potassa by evaporation. This salt is made on a large scale in the arts by igniting dried blood or other animal matters, such as hoofs and horns, with potassa and iron. By the mutual re-action of these substances at a high temperature, the ferrocyanide of potassium, consisting of one atom ofthe radical of ferrocyanic acid, and two atoms of potassium, is generated. Such at least is inferred to be the product; for on digesting the residue in water, a solution ofthe ferrocyanate of potassa is obtained. The ferrocyanate of potassa is a perfectly neutral salt, which is soluble in less than its own weight of water, and forms large transparent, lamellated crystals of a lemon-yellow colour. It is inodorous, has a slightly bitter taste, but quite different from that of hydrocyanic acid, and is permanent in the air. When heated to 212° F. or even below that temperature, each atom ofthe salt parts with two atoms of water, leaving one atom of the ferrocya- nide of potassium. The water, indeed, is disengaged with such facility, that Berzelius regards the crystals as consisting of the ferrocyanide of potassium combined with two atoms of water of crystallization. On heating the dry compound to full redness in close vessels, decomposition takes place, nitrogen gas is disen- gaged, and cyanide of potassium mixed with carburet of iron remains in the retort. The ferrocyanate of potassa is employed in the preparation of several compounds of cyanogen, and as a re-agent for detecting the presence of iron and other substances. Ferrocyanate of Soda crystallizes in four sided prisms. They are transparent, have a bitter taste, and are soluble both in water and in alcohol. The Ferrocyanate of Baryta, is prepared by digesting purified Prussian blue with a solution of pure baryta. It is soluble in water, and forms yellow crystals by evaporation. It is used in the formation of ferrocyanic acid. The Ferrocyanates of Strontia, Lime, and Magnesia, may be prepared by boiling those substances with Prussian blue. The Ferrocyanate ofthe Peroxide of Iron, which is formed by mixing the ferrocyanate of potassa with a per-salt of iron in slight excess, and washing the precipitate with water, is characterized by an intensely deep blue colour, and is the basis of the beauti- ful pigment called Prussian blue. It is insipid and inodorous, in- soluble in water, and is not decomposed by dilute muriatic or Sulphuric acids. Concentrated muriatic acid, by the aid of heat, separates the acid, and strong sulphuric acid renders it white__a change, the nature of which has not been explained. The alka- lies and alkaline earths decompose it readily, uniting with the ferrocyanic acid and separating the peroxide of iron. The per- oxide of mercury, as already mentioned, effects the complete de- IRON. 301 composition of the salt, forming the cyanide of mercury. Very complicated changes are produced by an elevated temperature. On heating the ferrocyanate to redness in a close vessel, a consi- derable quantity of water and carbonate of ammonia, together with a small portion of hydrocyanate of ammonia, are generat- ed ; while a carburet of iron remains in the retort—phenomena which, in conjunction with the facts above stated, leave no doubt of this compound containing ferrocyanic acid and the peroxide of iron. The precise proportion of its constituents has not been satisfactorily determined ; but it most probably consists of one atom ofthe peroxide, and an atom and a half of the acid. Prussian blue, the discovery of which was made in 1710, has been studied by several chemists, especially by Proust, and by Berzelius, Porrett, and Robiquet, to whom we referred while de- scribing the ferrocyanic acid. The colouring matter of this pigment is ferrocyanate of the peroxide of iron, which is mixed with alumina and peroxide of iron, together with the sub-sul- phates of one or both of those bases. It is prepared by heating to redness dried blood, or other animal matters, with an equal weight of pearlash, until the mixture has acquired a pasty con- sistence. The residue, which consists chiefly of cyanide of po- tassium and carbonate of potassa, is dissolved in water, and after being filtered, is mixed with a solution of two parts of alum and one part of the protosulphate of iron. A dirty greenish precipi- tate ensues, which absorbs oxygen from the atmosphere, and passes through different shades of green and blue, until at length it acquires the proper colour ofthe pigment. The chemical changes which take place in this process are of a complicated nature. The precipitate, which is at first thrown down, is occasioned by the potassa, and consists chiefly of alumi- na and the protoxide of iron. The ferrocyanic acid is generated by the protoxide re-acting upon some ofthe hydrocyanic acid, so as to form water and cyanide of iron, which then unites with undecomposed hydrocyanic acid. The ferrocyanic acid, thus produced, combines with oxide of iron ; and when the latter has attained its maximum of oxidation, the compound acquires its characteristic blue tint. Dr. Thomson, knowing the protoxide to be necessary to the success of the operation, concludes that this oxide enters into the composition of the Prussian blue ; but here this chemist is certainly in error. The only use of the protoxide of iron is to convert the hydrocyanic into ferro- cyanic acid; a purpose for which its presence is essential, because the peroxide of iron does not produce this effect, or at least in a very slow and imperfect manner. For the other metallic ferrocyanates, see the table at the end ofthe volume. Alloys of Iron.—The only alloy of consequence is tin-plate, which is made by dipping perfectly clean iron plates into melted 302 IRON. tin, the surface of which is prevented from absorbing the oxygen ofthe air by melted tallow. When tin plate is washed over with a weak acid, the crystalline texture of the tin becomes beautifully evident, forming an appearance which has been called moire metalique. Alloys of Steel.—Messrs. Stodart and Faraday have succeeded in making some very important alloys of steel and other metals. Their experiments induced them to believe that the celebrated Indian steel, called wootz, is an alloy of steel with small quanti- ties of silicon and aluminum ; and they succeeded in preparing St similar compound, possessed of all the properties of wootz. Tests.—The salts of iron are mostly soluble in water, and the solution is reddish-brown, or becomes so by exposure to air. It affords a blue precipitate with ferrocyanate of potassa, and a black precipitate with hydrosulphate of ammonia. Infusion of gall-nuts produces a black or purple precipitate. SECTION III. Copper, or Cuprum. Copper was perhaps the first metal used by mankind. It was known before the Noachean deluge, and was first wrought into instruments by Tubalcain, in the seventh generation from Adam. Anciently, copper was employed for all the purposes for which we now use iron. Arms and tools for husbandry and the mechanic arts, were all made of copper, for many ages. The name copper, or rather cuprum, is derived from the island Cy- prus, where copper was first wrought to a considerable extent by the Greeks. Native copper is by no means uncommon. It occurs in large amorphous masses in some parts of the United States, and is sometimes found in octahedral crystals, or in forms allied to the octahedron. The metallic copper of commerce is extracted chiefly from the native sulphuret. Copper is distinguished from all other metals, titanium excep- ted, by having a red colour. It receives a considerable lustre by polishing. Its density is 8.78, and is increased by hammering. It is both ductile and malleable, and in tenacity is inferior only to iron. It is hard and elastic, and consequently sonorous. In fusibility it stands between silver and gold. Copper undergoes little change in a perfectly dry atmosphere, but is rusted in a short time by exposure to air and moisture, being converted into a green substance, the carbonate of the pe- roxide of copper. At a red heat, it absorbs oxygen, and is con- verted into the peroxide, which appears in the form of black scales. It is attacked with difficulty by muriatic and sulphuric COPPER. 303 acids, and not at all by the vegetable acids, if atmospheric air be excluded; but if air has free access, the metal absorbs oxygen with rapidity, the attraction of the acid for the oxide of copper co-operating with that ofthe copper for oxygen. Nitric acid acts with violence on copper, forming a nitrate ofthe peroxide. Oxides of Copper.—The oxides of this metal have been stu- died by Proust, Chenevix, Dr. Davy, and Berzelius, and especial- ly by the former. Frora the labours of these chemists, it appears that there are but two oxides of copper, and that they are thus constituted : Copfier Oxygen Protoxide - 64 - 8 = 72 Peroxide - 64 - 16 = 80 Consequently, if the first be regarded as a compound of one equivalent of each element, 64 is the atomic weight of copper. The red or protoxide occurs native in the form of octahedral crystals, and is found of peculiar beauty in the mines of Cornwall. It may be prepared artificially by mixing 64 parts of metallic copper in a state of fine division with 80 parts of the peroxide, and heating the mixture to redness in a close vessel ; or by boil- ing a solution ofthe acetate of copper with sugar, when the per- oxide is partially deoxidized, and subsides as a red powder. The protoxide of copper combines with the muriatic, sulphuric, and probably with several other acids, forming salts, most of which are colourless, and from which the protoxide is precipita- ted as an orange-coloured hydrate by alkalies. They attract oxygen rapidly from the atmosphere, by which they are converted into per-salts. The protomuriate is easily formed by putting a solution of the per-muriate with free muriatic acid and copper filings into a well-closed glass phial. The protoxide of copper is soluble in ammonia, and the solution is quite colourless. It be- comes blue, however, with surprising rapidity by free exposure to air, owing to the formation of the peroxide. The peroxide of copper, the copper black of mineralogists, is sometimes found native, being formed by the spontaneous oxida- tion of other ores of copper. It may be prepared artificially by calcining metallic copper, by precipitation from the per-salts of copper by means of pure potassa, and by heating the nitrate of copper to redness. The peroxide of copper varies in colour from a dark brown to a bluish-black, according to the mode of formation. It undergoes no change by heat alone, but is readily reduced to the metallic state by heat and combustible matter. It is insoluble in water, and does not affect the vegetable blue colours. It combines with nearly all the acids, and most of its salts have a green or blue tint. It is soluble likewise in ammonia, forming with it a deep blue solution, a property by which the peroxide of copper is distinguished from all other substances. 304 COPPER. The peroxide of copper is precipitated by pure potassa as a blue hydrate, which is rendered black by boiling, the hydrate being decomposed at that temperature. Pure ammonia at first throws down a greenish-blue insoluble sulphate, which is re-dis- solved by the precipitant in excess, and forms the deep blue ammo- niacal sulphate of copper. Alkaline carbonates cause a bluish- green precipitate, the carbonate of copper, which is re-dissolved by an excess of carbonate of ammonia. It is precipitated as a dark brown bi-sulphuret by sulpbtrretted hydrogen, and as a red- dish-brown ferrocyanate by the ferrocyanate of potassa. The oxide of copper is thrown down of a yellowish-white colour by albumen, and M. Orfila has proved that this compound is inert, so that albumen is an antidote to poisoning by copper. Copper is separated in the metallic state by a rod of iron or zinc. The copper thus obtained, after being washed with a di- lute solution of muriatic acid, is chemically pure. The best mode of detecting copper, when supposed to be pre- sent in mixed fluids, is by sulphuretted hydrogen. The sulphu- ret, after being collected, should be placed on a piece of porce- lain, and digested in a few drops of nitric acid. A sulphate of copper is formed, which, when evaporated to dryness, strikes the characteristic deep blue on the addition of ammonia. The red oxide of copper is by some chemists supposed to be a suboxide or a compound of two atoms of copper and one atom of oxygen; while the elements ofthe black oxide are thought to be in the ratio of one atom of each. According to this view the atomic weight of copper is 32, or half that above stated. This opinion, which is adopted by Dr. Thomson, is certainly supported by the tendency ofthe red oxide to absorb oxygen and pass into the state of black oxide ; and other arguments may be adduced in its favour. But, nevertheless, as the red oxide is unquestiona- bly a definite compound, capable of uniting with acids, and pro- portional to several other compounds, such as the protosulphuret and protochloride of copper, it appears more consistent to consider it as the real protoxide, composed of one atom of each of its elements. Phosphuret of Copper, made by dropping phosphorus on red hot copper wire, is a brittle, gray compound, more fusible than copper. Sulphurets of Copper.—The protosulphuret of copper, the cop- per glance of mineralogists is formed artificially by heating cop- per filings with a third of its weight of sulphur. The combina- tion is attended with such free disengagement of caloric, that the mass becomes vividly luminous. According to the analysis of Berzelius, it is composed of 64 parts or one atom of copper, and 16 parts or one atom of sulphur. The bisulphuret is a constituent of copper pyrites, in which mineral it is combined with the sulphuret of iron. It may be COPPER. 305 formed artificially by the action of sulphuretted hydrogen on a per-salt of copper. When exposed to a red heat in a close ves- sel, it loses half its sulphur, and is converted into the proto- sulphuret. The compounds of copper with the other non-metallic bodies are of minor interest, and have hitherto been but little studied. Ammoniuret of Copper.—If peroxide of copper be digested in ammonia it is dissolved, forming a bright blue solution, which, by careful evaporation, affords fine blue crystals; a mixture of lime, sal ammoniac, and water, placed in a copper vessel, or mixed with oxide of copper, also affords a fine blue liquor, in conse- quence of the action of the ammonia on the oxide of copper. This solution is the aqua sapphirina, of old pharmacy. The compound has sometimes been called ammoniuret of copper, a name now given to the sulphate of copper and ammonia. The protoxide of copper also dissolves in ammonia, but the solution is colourless; if it be exposed to the air, it becomes blue. This may be well shown by filling a tall glass with liquid ammo nia and adding a few drops of protomuriate of copper; the liquid presently acquires a blue colour upon the surface, but remains for some time colourless below. Into a half ounce phial, filled with a solution of ammonia, drop a few pieces of metallic copper: if the bottle be left un- stopped, a beautiful blue liquid will be obtained ; if the phial be stopped this colour in a short time will disappear, and re- appear, on again admitting the air. In this manner a blue and colourless liquid can be alternately produced as we withdraw or replace the stopper. In this experiment the peroxide, when excluded from the air, is converted into a protoxide by the action ofthe metallic copper, which again becomes the peroxide by the action of the atmosphere, as already mentioned. Salts. Nitrate of Copper.—Nitric acid, diluted with three parts of water, rapidly peroxidizes copper, evolving nitric oxide and form- ing a bright blue solution, which affords deliquescent prismatic crystals on evaporation, of a fine blue colour, and very caustic. It consists of 80 per oxide + 108 acid, but the crystals contain a considerable portion of water, which causes them to liquefy at a temperature below 212°. At a higher temperature, they lose water and acid, and according to Proust, become a sub-pernitrate, which is insoluble in water, and entirely decomposed at a red heat. There appears to be no protonitrate of copper; for pro- toxide of copper, digested in very dilute nitric acid, is resolved into peroxide which dissolves, and into metallic copper. Potassa forms, in this solution, a bulky blue precipitate of hydrated per- 306 COPPER. oxide of copper, which, when boiled in potassa or soda, becomes black from the loss of its combined water. When crystals of nitrate of copper are coarsely powdered, sprinkled with a little water, and quickly rolled up in a sheet of tin foil, there is great heat produced, nitrous gas is rapidly evolv- ed, and the metal often takes fire. If ammonia be added to solu- tion of nitrate of copper, it occasions a precipitate of the hy- drated peroxide, but if it be added in excess, the precipitate is re-dissolved, and an ammonia-nitrate of copper is produced. Carbonate of Copper.—The beautiful green mineral, called Malachite, is a carbonate of the peroxide of copper; and a similar compound may be formed from the persulphate by dou- ble decomposition, or by exposing metallic copper to air, and moisture. According to the analysis of malachite by Mr. Phillips, this mineral is composed of 80 parts or one atom ofthe peroxide of copper, one atom of carbonic acid, and one atom of water. The blue pigment called verditer, said to be prepared by de- composing the nitrite of copper by chalk, is an impure car- bonate. Borate of Copper.—Solution of borax poured into sulphate of copper, produces a bulky pale green, precipitate of borate of copper. Silicate of Copper.—The mineral, called by the Germans eme- rald copper ore, and by the French dioptase, is a hydrous tri- silicate of copper, if we consider the analysis of it by Lowitz as correct. Phosphate of Copper.—Phosphoric acid unites with peroxide of copper, in two proportions. If solutions of phosphate of soda and sulphate of copper be mingled together, a bluish green pre- cipitate is formed, consisting of one proportional peroxide of cop- per, two of phosphoric acid, and one of water; it is therefore a bi- phosphate. The phosphate has not yet been formed artificially, but has been found native of an emerald green colour. Sulphates of Copper.—The sulphate of the protoxide of copper has not been obtained in a separate state. The sulphate of the peroxide of copper, the blue vitriol employed by surgeons as an escharotic and astringent, may be prepared for chemical pur- poses by dissolving the peroxide of copper in dilute sulphuric acid ; but it is procured for sale by roasting the native sulphuret, so as to bring both its elements to a maximum of oxidation. This salt forms regular crystals of a blue colour, reddens litmus paper, and is soluble in about four of cold, and in two parts of boiling water. According to the researches of Proust, Thomson, anti Berzelius, it is composed of 80 parts or one atom ofthe peroxide of copper, 80 parts or two atoms of acid, and 90 parts or ten atoms of water. It is, therefore, strictly, a bisulphate. When pure potassa is added to a solution of the bisulphate of copper in a quantity which is insufficient for separating the whole COPPER. 307 of the acid, a pale bluish-green precipitate, the sub-sulphate, is thrown down, which is composed of one atom of acid, and one atom of the peroxide. The sulphate of copper and ammonia is generated by drop- ping pure ammonia into a solution of the bisulphate, until the sub-salt at first thrown down is nearly all dissolved. It forms a dark blue solution, from which, when concentrated, crystals are deposited by the addition of alcohol. It may be formed also by rubbing briskly in a mortar two parts of the crystallized bisul- phate of copper with three parts of carbonate of ammonia, until the mixture acquires a uniform deep blue colour. Carbonic acid gas is disengaged with effervescence during the operation, and the mass becomes moist, owing to the water of the blue vitriol being set free. This compound, which is the ammoniuret of copper of some pharmacopoeias, contains sulphuric acid, peroxide of copper, and ammonia; but its precise nature has not been determined in a satisfactory manner. It parts gradually with ammonia by ex- posure to the air. Sulphate of Copper and Potassa, formed by digesting peroxide of copper in bi-sulphate of potassa; crystallizes in rhomboids of a pale blue colour. Sulphite of Copper, may be obtained by passing a current of sulphurous acid gas, (which has been first passed through a small quantity of water in order to deprive it of sulphuric acid) into a vessel, containing water and peroxide of copper, a green liquid is formed which contains sulphite of copper, with a larga excess of acid; and sulphite of copper in very small red crystals, re- mains at the bottom ofthe vessel. When sulphite of potassa is added to nitrate of copper a pre- cipitate falls, which assumes the form of red and yellow crystals. The former are sulphite of copper, the latter sulphite of potassa and copper. Hyposulphite of Copper, formed by mixing hyposulphite of potassa with sulphate of copper, is colourless, of an intensely sweet taste; and provided the air be excluded, it is not turned blue by ammonia, which seems to show that the metal is in the state of a protoxide. Arseniate of Copper.—When arsenic acid is digested on cop- per, the metal is oxidized and dissolved, and a bluish white pow- der is formed, which consists of the arseniate of copper. This salt occurs native, in five varieties, differing from each other in the proportions of oxide, acid, and water which they contain. Their colour varies from a deep blue to green, and even to brown, yellow, and black. Arsenite of Copper, usually distinguished by the name of Scheele's green, may be formed by dissolving two parts of sul- phate of copper in 44 parts of water, and likewise two parts of 308 COPPER. the potassa of commerce and nearly one part of arsenious acid pulverised, in 44 parts of water, by the assistance of heat, the solution of copper is gradually added while hot to the arsenite of potassa, and the whole is often stirred during the mixture. The mixture on standing gradually deposits the arsenite of copper in the form of a fine green powder, it is to be washed well with water and then dried. The antimoniate, antimonite, chromate, molybdate, and tungstate of copper, are unimportant compounds. Alloys.—Many ofthe alloys of copper are highly important. Arsenuret of Copper.—An alloy of copper, with a tenth part of arsenic, is so very similar in appearance to silver, that it has been substituted for it. The whiteness of this alloy affords a rough mode of testing for arsenic ; for if arsenious acid and char- coal be heated between two plates of copper, a white stain afterwards appears upon its surface, owing to the formation of an arsenuret of copper. Stannuret of Copper.—Copper forms with tin several valuable alloys, which are characterized by their sonorousness. Bronze is an alloy of copper, with about eight or ten per cent, of tin, together with small quantities of other metals which are not essential to the compound. The armour of the Trojans was of tin and copper or bronze, and many of the old coins now found at Tenedos, are perhaps the very same bronze which once pro- tected the heroes of Homer. Cannons are cast with an alloy of a similar kind. The best bell-metal is composed of 80 parts of copper and 20 of tin ;—the Indian gong, celebrated for the richness of its tones, contains copper and tin in this proportion. Lead and antimony, though in small quantity, have a remarkable effect in diminishing the elasticity and sonorousness of the compound. The speculum- metal, with which mirrors for telescopes are made, consists of about two parts of copper and one of tin. The whiteness ofthe alloy is improved by the addition of a little arsenic. The art of tinning copper consists in covering that metal with a thin layer of tin, in order to protect its surface from rusting. For this purpose, pieces of tin are placed upon a well-polished sheet of copper which is heated sufficiently for fusing the tin. As soon as the tin liquefies, it is rubbed over the whole sheet of copper, and if the process is skilfully conducted, adheres uni- formly to its surface. The oxidation of the tin, a circumstance which would entirely prevent the success of the operation, is avoided by employing fragments of resin or muriate of ammonia, and regulating the temperature with great care. The two metals do not actually combine with one another; but the adhesion is certainly owing to their mutual affinity.—Mr. Dalton appears to have ascertained that in all the alloys of copper, which are characterized by useful properties, the ingredients unite in de- MERCURY. 309 finite proportions; if this should prove to be the case, the manu- facture of these valuable alloys will be vastly improved. Tests.—The cupreous salts are nearly all soluble in water, and of a blue or green colour. Ammonia produces a compound of a very deep blue, when added in excess to these solutions; hydro- sulphate of ammonia forms a black precipitate; and a plate of iron plunged into a liquid salt of copper precipitates metallic copper. Ferrocyanate of potassa produces a brown cloud in solutions containing the peroxide of copper. SECTION IV. Mercury, or Mercurium. Mercury, or quicksilver, is found in the native state ; but it occurs more commonly in combination with sulphur as cinnabar. From this ore the mercury of commerce may be extracted by heating it with lime or iron filings, by which means the mercury is volatilized, and the sulphur retained. As prepared on a large scale, it is usually mixed in small quantity with other metals, from which it may be purified by cautious distillation. Mercury is distinguished from all other metals by being fluid at common temperatures. It has a tin-white colour and strong metallic lustre. It becomes solid at a temperature which is 39 or 40 degrees below Zero of Fahr., and in congealing, evinces a strong tendency to crystallize in octahedrons. It contracts great- ly at the moment of congelation ; for while its density at 47° F. is 13.545, the specific gravity of frozen mercury is 15.612. When solid it is malleable, and may be cut with a knife. At 660° F., or near that degree, it enters into ebullition, and condenses again on cool surfaces into metallic globules. Mercury, if quite pure, is not tarnished in the cold by exposure to air and moisture ; but if it contain other metals, the amalgam of those metals oxidizes readily, and collects as a film upon its surface. Mercury is said to be oxidized by long agitation in a bottle half full of air, and the oxide so formed was called by Boerhaave Ethiops per se ; but it is very probable that the oxida- tion of mercury observed under these circumstances was solely owing to the presence of other metals. When mercury is ex- posed to air or oxygen gas, while in the form of vapour, it slowly absorbs oxygen, and is converted into the peroxide of mercury. The only acids that act on mercury are the sulphuric and nitric acids. The former has no action whatever in the cold; but on the application of heat, the mercury is oxidized at the expense of the acid, pure sulphurous acid gas is disengaged, and a sulphate of mercury is generated. Nitric acid acts energetically upon 310 MERCURY. mercury, both with and without the aid of heat, oxidizing and dissolving it with evolution ofthe deutoxide of nitrogen. Oxides of Mercury. Mercury is susceptible of two stages of oxidation, and both its oxides are capable of forming salts with acids. It appears from the researches of Donovan and Sefstrom, whose results are con- firmed by the experiments of Dr. Thomson, that these oxides are formed in the following proportions :— Mercury. Oxygen. Protoxide . 200 . 8 = 20S Peroxide • 200 . 16 = 216 Protoxide.—The protoxide of mercury, which is a black pow- der, insoluble in water, is best prepared by mixing calomel brisk- ly in a mortar with pure potassa in excess, so as to effect its decomposition as rapidly as possible. The protoxide is then to be washed with cold water, and dried spontaneously in a dark place. These precautions are rendered necessary by the ten- dency of the protoxide to resolve itself into the peroxide and metallic mercury, a change which is easily effected by heat, by the direct solar rays, and even by day-light. It is on this account very difficult to procure the protoxide of mercury in a state of absolute purity. This oxide is precipitated from its salts, of which the nitrate is the most interesting, as the black protoxide by pure alkalies; as a white carbonate, which soon becomes dark from the loss of carbonic acid, by alkaline carbonates; as calomel by muriatic acid or any soluble muriate; and as the black protosulphuret by sulphuretted hydrogen. Of these tests, the action of muriatic acid is the most characteristic. The oxide is reduced to the me- tallic state by copper, phosphorous acid, or protomuriate of tin. Peroxide.—This oxide may be formed either by the combined agency of heat and air, as already mentioned^ or by dissolving mercury in nitric acid, and exposing the nitrate so formed to a temperature just sufficient for expelling the whole of the nitric acid. It is commonly known by the name of red predpitate. The peroxide of mercury, thus prepared, is commonly in the form of shining crystalline scales of a red colour. It is soluble to a small extent in water, forming a solution which has an acrid metallic taste, and communicates a green colour to the blue infu- sion of violets. When heated to redness, it is converted into metallic mercury and oxygen. Long exposure to light has a similar effect. Some ofthe neutral salts of this oxide, such as the nitrate and sulphate, are converted by water, especially at a boiling tempera- MERCURY. 311 ture, into insoluble yellow sub-salts, and into soluble colourless per-salts. The oxide is separated from all acids as a red, or, when hydratic, as a yellow precipitate, by the pure and carbo- nated fixed alkalies. Ammonia and its carbonate cause a white precipitate, which is a double salt, consisting of one atom of the acid, one atom ofthe peroxide, and one atom of ammonia. Sul- phuretted hydrogen, phosphorous acid, and protomuriate of tin, reduce the peroxide into the protoxide; and when added in lar- ger quantity the first throws down a black sulphuret, and the two latter metallic mercury. The oxide is readily reduced by inser- tion of a rod of copper. Cyanide of Mercury.—This compound is best prepared by boiling, in any convenient quantity of water, eight parts of finely levigated ferrocyanate of the peroxide of iron, quite pure and well dried on a sand bath, with eleven parts of the peroxide of mercury in powder, until the blue colour of the ferrocyanate entirely disappears. A colourless solution is formed, which, when filtered and concentrated by evaporation, yields crystals of the cyanide of mercury in the form of quadrangular prisms. In this process, the oxygen ofthe oxide of mercury unites with the iron and hydrogen of the ferrocyanic acid; while the metallic mercury enters into combination with the cyanogen. The brown insoluble matter is peroxide of iron. Pure ferrocyanate of iron is easily procured by digesting the common Prussian blue of commerce with muriatic acid, diluted with ten parts of water, so as to remove the subsulphate of iron and alumina which it com- monly contains, and then edulcorating the insoluble ferrocyanate till the free acid is removed. The cyanide of mercury, when pure, is colourless and ino- dorous, has a very disagreeable metallic taste, and is highly poisonous. It does not affect the colour of litmus or turmeric paper. When strongly heated it is converted into cyanogen and metallic mercury. It is more soluble in hot than in cold water, and dissolves in that liquid without change. The solution has not the characteristic odour of the salts of hydrocyanic acid, nor do alkalies throw down the oxide of mercury. It is composed of 200 parts or one atom of mercury, and 52 parts or two atoms of cyanogen. Phosphuret of Mercury, may be formed by heating phosphorus with oxide of mercury. It is a sectile solid, of a bluish black colour. Sulphurets of Mercury.—The protosulphuret of mercury may be prepared by transmitting a current of sulphuretted hydro- gen gas through a dilute solution of the protonitrate of mercury, or through water in which calomel is suspended. It is a black- coloured substance, convertible into the sulphate of mercury by digestion in strong nitric acid. When exposed to heat it is resolved into the bisulphuret and metallic mercury. It is com- 312 MERCURY. posed of 200 parts or one atom of mercury, and 16 parts or one atom of sulphur. The bisulphuret is formed by fusing sulphur with about six times its weight of mercury, and subliming in close vessels. When procured by this process it has a red colour, and is known by the name offactitious cinnabar. Its tint is greatly improved by being reduced to powder, in which state it forms the beautiful pigment vermilion. It may be obtained in the moist way by pouring a solution of corrosive sublimate into an excess of hy- drosulphuret of ammonia. A black precipitate subsides, which acquires the usual red colour of cinnabar when sublimed. Cin- nabar, as already mentioned, occurs native. When equal parts of sulphur and mercury are triturated to- gether until metallic globules cease to be visible, the dark co- loured mass, called Elhiops mineral, results, which Mr. Brande has proved to be a mixture of sulphur and the bisulphuret of mercury. Cinnabar is not attacked by alkalies, or any simple acid ; but is dissolved by the nitro-muriatic acid, with formation of sulphu- ric acid and the oxide of mercury. M. Guibourt has shown that it is composed of one atom of mercury and two atoms of sulphur. Salts. Nitrates of Mercury.—The protonitrate is conveniently formed by digesting mercury in nitric acid, diluted with three or four parts of water, until the acid is saturated, and then allowing the solution to evaporate spontaneously in an open vessel. The so- lution always contains, at first, some nitrate of the peroxide, but if metallic mercury is left in the liquid, a pure protonitrate is gradually deposited. The composition of this salt has not been determined in a satisfactory manner. It dissolves completely in water, slightly acidulated with nitric acid, but in pure water, a small quantity of a yellow sub-salt is generated. When mercury is heated in an excess of strong nitric acid, it is dissolved with brisk effervescence, owing to the escape of the deutoxide of nitrogen, and transparent prismatic crystals of the pernitrate are deposited as the solution cools. When this salt is put into hot water, a yellow insoluble sub-salt is generated. The former salt is composed, according to Dr. Thomson, of one atom of acid to one atom of the peroxide ; and M. Grouvelle states the latter to consist of one atom of acid to two atoms of the peroxide. Carbonates of Mercury.—Alkaline carbonates produce buff- coloured precipitates in solutions of both oxides of mercury. These are probably the protocarbonate and the percarbonate of mercury. MERCURY. 313 Borate of Mercury, obtained by adding borate of soda to ni- trate of mercury, is a yellow insoluble powder. Phosphates of Mercury.—When phosphate of soda is added either to nitrate or pernitrate of mercury, a white precipitate is formed. There is, probably, a protophosphate and a perphos- phate. The latter is soluble in excess of acid. Sulphates of Mercury.—When two parts of mercury are gently heated in three parts of strong sulphuric acid, so as to cause a slow effervescence, a sulphate ofthe protoxide of mercury is ge- nerated. But if a strong heat is employed in such a manner as to excite brisk effervescence, and the mixture is brought to dry- ness, a pure sulphate of the peroxide results. The former is composed of one atom of sulphuric acid and one atom of the protoxide ; and the latter of two atoms of acid and one atom of the peroxide. When this bisulphate, which is the salt employed in making corrosive sublimate, is thrown into hot water, decom- position ensues, and a yellow sub-salt, formerly called turpeth mineral, subsides. This salt is composed of one atom of the acid and one atom of the peroxide. The hot water retains some of the sulphate in solution, together with free sulphuric acid. Arseniates of Mercury.—Arsenic acid occasions a pale yellow precipitate in asolution of protonitrate of mercury, and a yellowish- white precipitate in a solution of the pernitrate. Arsenious acid produces white precipitates in both solutions. The chromate, molybdate, and tungstate of mercury, are not important salts. Amalgams.—Quicksilver unites with potassium when agitated in a glass tube with that metal, forming a solid amalgam. When the amalgam is put into water, the potassium is gradually oxi- dized, hydrogen gas is disengaged, and the mercury resumes its liquid form. A similar compound may be obtained with sodium. These amalgams may also be procured by placing the negative wire in contact with a globule of mercury, during the process of decomposing potassa and soda by galvanism. A solid amalgam of tin is employed in making looking-glasses ; and an amalgam made of one part of lead, one of tin, two of bismuth, and four parts of mercury, is used for silvering the inside of hollow glass globes. This amalgam is solid at common tem- peratures ; but is fused by a slight degree of heat. The amalgam of zinc and tin, used for promoting the action of the electrical machine, is made by fusing one part of zinc with one of tin, and then agitating the liquid mass with two parts of mercury placed in a wooden box. Mercury evinces little dispo- sition to unite with iron, and, on this account, it is usually pre- served in iron bottles. Tests.—The soluble salts of mercury furnish whitish precipi- tates with ferrocyanate of potassa, and black with sulphuretted R"r 214 CERIUM, hydrogen. A plate of copper immersed in their solutions, occa- sions the separation of metallic mercury. SECTION V. Cerium. Cerium was discovered in 1803 by MM. Hisinger and Berze- lius, in a rare Swedish mineral known by the name of cerite, and its existence was recognised about the same time by Klaproth. Dr. Thomson has since found it to the extent of thirty-four per cent, in a mineral from Greenland, called Allanite, in honour of Mr. Allan, who first distinguished it as a distinct species. The properties of cerium are in a great measure unknown. It appears from the experiments of Vauquelin, who obtained it in minute buttons not larger than the head of a pin, that it is a white brittle metal, which resists the action of nitric, but is dis- solved by nitro-muriatic acid. According to an experiment made by Mr. Children, metallic cerium is volatile in very intense degrees of heat. Oxides of Cerium.—Cerium unites with oxygen in two pro- portions, and the composition of the resulting oxides has been particularly studied by M. Hisinger. Dr. Thomson has likewise made experiments on the subject, and infers from data furnished partly by himself and partly by M. Hisinger, that 50 is the atomic weight of cerium, and that its oxides are thus constituted— Cerium. Oxygen. Protoxide - 50 - 8 = 58 Deutoxide 50 - 12 = 62 The protoxide of cerium is a white powder, which is insoluble in water, and forms salts with acids, all of which, if soluble, have an acid re-action. Exposed to the air at common temperatures it suffers no change ; but if heated in open vessels, it absorbs oxygen and is converted into the peroxide. It is precipitated from its salts as a white hydrate by pure alkalies ; as a white carbonate by alkaline carbonates, but is re-dissolved by the pre- cipitant in excess ; and as a white oxalate by the oxalate of am- monia. The peroxide of cerium is of a fawn-red colour. It is dissolved by several of the acids, but is a weaker base than the protoxide. Digested in muriatic acid, chlorine is disengaged and a proto- muriate results. The most convenient method of extracting pure oxide of cerium from cerite, is by the process of Laugier. After reducing the cerite to powder, it is dissolved in nitro-muriatic acid, and CERIUM. 215 the solution is evaporated to perfect dryness. The soluble parts are then re-dissolved by water, and an excess of ammonia is added. The precipitate thus formed, consisting ofthe oxides of iron and cerium, is well washed and afterwards digested in a solution of oxalic acid, which dissolves the iron, and forms an insoluble oxalate with the cerium. By heating this oxalate to redness in an open fire, the acid is decomposed, and the peroxide of cerium is obtained in a pure state. Carburet of Cerium is a heavy blackish powder, which, when heated in the air, burns vividly into oxide of cerium without any apparent change of weight. Sulphuret of Cerium is a red powder, formed by passing the vapour of the sulphuret of carbon over cerium at a red heat. Salts. Nitrate of Cerium.—Nitric acid unites with both oxides of cerium, but most readily with the protoxide with which it forms a sweetish uncrystallizable liquid. Carbonate of Cerium is precipitated from the above solution in the form of a white silver powder, by the carbonate of potassa. Sulphates of Cerium.—The sulphate of the protoxide is a white crystalline solid of a saccharine taste; that ofthe peroxide occurs in yellow crystals. The salts of cerium are either white or yellow, and both may be known by their having a sweetish acid taste. SECTION VI. Platinum. This valuable metal occurs in the metallic state, associated or combined with various other metals, such as copper, iron, lead, gold, silver, palladium, rhodium, osmium, and iridium. It has hitherto been found chiefly in Brazil, Peru, and other parts of South America, in the form of rounded or flattened grains, of a metallic lustre and white colour, mixed with sand and other allu-' vial depositions. Within these two years, however, M. Boussin- gault has discovered it in a syenitic rock in the province of Antio- quia in North America, where it occurs in veins associated with gold. Rich mines of gold and platinum have also been recently discovered in the Uralian mountains. Pure platinum has a white colour, very much like silver, but of inferior lustre. It is the heaviest of known metals, its density being about 21.5. Its malleability is considerable, though far less than that of gold and silver. It may be drawn into wires, the diameter of which does not exceed the 2000th part of an inch. 316 PLATINUM. It is a soft metal, and, like iron, admits of being welded at a high temperature. Dr. Wollaston has observed that it is a less perfect conductor of caloric than most other metals. Platinum undergoes no change from the combined agency of air and moisture; and it may be exposed to the strongest heat of a smith's forge without suffering either oxidation or fusion. On heating a small wire of it by means of galvanism or the oxy- hydrogen blow-pipe, it is fused, and afterwards burns with the emission of sparks. The late Mr. Smithson Tennant showed that it is oxidized when ignited with nitre; and a similar effect is oc- casioned by pure potassa and lithia. Platinum is not attacked by any of the pure acids. Its only solvents are chlorine and nitro-muriatic acid, which act upon it with greater difficulty than on gold. The resulting orange-red coloured liquid, from which the excess of acid should be expelled by cautious evaporation, may be regarded as containing either the chloride of platinum, or the muriate of its oxide. Oxides of Platinum—According to Berzelius there are two ox- ides of platinum, the oxygen of which is in the ratio of 1 to 2. The protoxide is prepared by the action of potassa on the pro- tochloride of platinum. It is of a black colour, is reduced by a red heat, and is composed of 96.5 parts of platinum, and 8 parts of oxygen. Now, Dr. Thomson infers froro his researches, that 96 is the atomic weight of platinum, from which it is probable that the two oxides of Berzelius are thus constituted :— Platinum. Oxygen. Protoxide .96 . . .8 Peroxide .96 . . .16 The peroxide has not hitherto been obtained in a perfectly pure state. Berzelius supposes it to exist in the muriate of plati- num combined with muriatic acid; and Dr. Thomson states that it is contained in the sulphate of platinum. Another oxide was described by Mr. E. Davy. It is of a gray colour, and is prepared by heating fulminating platinum with ni- trous acid. It appears from his analysis to be composed of 96 parts or one atom of platinum, and 12 parts or an atom and a half of oxygen. Mr. Cooper has likewise described an oxide of platinum ; but its existence as a definite compound, distinct from those above described, has not been satisfactorily demonstrated. Sulphuret of Platinum.—When sulphuretted hydrogen gas is transmitted through a solution ofthe muriate of platinum, a black precipitate is thrown down, which Vauquelin regards a hydrosul- phuret ofthe oxide of platinum. It absorbs oxygen from the air while in a moist state, giving rise to the formation of sulphuric acid. Its composition has not been determined with accuracy. A black sulphuret of platinum was procured by Mr. E. Davy PLATINUM. 317 by heating the metal with sulphur; and Vauquelin obtained a similar compound by igniting the yellow muriate of platinum and ammonia with twice its weight of sulphur. According to the analysis of these chemists, it contains about 16 per cent, of sulphur. The hydrosulphuret of platinum is converted by the action of nitric acid into a sulphate which possesses remarkable properties. On boiling it in strong alcohol, a black powder is precipitated, which consists, according to Mr. E. Davy, of 96 per cent, of pla- tinum, together with a little oxygen, nitrous acid, and carbon, the last of which is supposed to be accidental. When this powder is placed on bibulous paper moistened with alcohol, a strong action, accompanied with a hissing noise, ensues, and the powder be- comes red-hot, and continues so until the alcohol is consumed. The substance which remains is pure platinum. Fulminating platinum may be prepared by the action of am- monia in slight excess on a solution ofthe sulphate of platinum. It is analogous to the detonating compounds which ammonia forms with the oxides of gold and silver. Alloys. An alloy of platinum with ten parts of arsenic is fusible at a heat a little above redness, and may therefore be cast in moulds. On exposing the alloy to a gradually increasing temperature in open vessels, the arsenic is oxidized and expelled, and the platinum recovers its purity and infusibility. The alloy of steel with 100th part of platinum, though less hard than that with silver, possesses a greater degree of toughness, and is therefore highly valuable when tenacity as well as hardness is required. If a piece of lead foil, and another of platinum foil of equal dimensions, be rolled up together, and the flame of a candle be cautiously directed by a blow-pipe towards the edges ofthe roll, at about read heat, the two metals will combine with a sort of explosive force, scattering their melted particles, and emitting light and heat in a surprising manner. A small bit of tin, zinc, or antimony, may be substituted for the lead, and similar results will obtain. From the quantity of platinum lately found in Russia, and its intrinsic value, the emperor has ordered coins to be struck from this metal. A few platinum coins were formerly in circulation in Russia, but they were all bought up for the cabinets of the curious. ( 318 ) SECTION VI. Cobalt, or Cobaltum. This metal is met with in the earth chiefly in combination with arsenic, constituting an ore from which all the cobalt of com- merce is derived. It is a constant ingredient of meteoric iron; at least Professor Stromeyer, who has analysed several varieties, states, that in every one he has detected the presence of cobalt. When the native arseniuret of cobalt is broken into small pieces, and exposed in a reverberatory furnace to the united ac- tion of heat and air, its elements are oxidized, most of the arseni- ous acid is expelled in the form of vapour, and# an impure oxide of cobalt, called zaffre, remains. On heating this substance with a mixture of sand and potassa, a beautiful blue-coloured glass is obtained, which, when reduced to powder, is known by the name of smalt. Metallic cobalt may be obtained by dissolving zaffre in muria- tic acid, and transmitting through the solution a current of sul- phuretted hydrogen gas until the arsenious acid is completely se- parated in the form of sulphuret of arsenic. The filtered liquid is then boiled with a little nitric acid, in order to convert the protoxide into the peroxide of iron, and an excess of the carbo- nate of potassa is added. The precipitate, consisting of the pe- roxide of iron and carbonate of cobalt, after being well washed with water, is digested in a solution of oxalic acid, which dissolves the iron and leaves the cobalt in the form of an insoluble oxalate. On heating the oxalate of cobalt in a retort from which the at- mospheric air is excluded, a large quantity of carbonic acid is evolved, and a black powder, a metallic cobalt, is left. The pure metal is easily procured also by passing a current of dry hydrogen gas over the oxide of cobalt heated to redness in a tube of porcelain. Cobalt is a brittle metal, of a reddish-gray colour, and weak metallic lustre. Its density is 8.538. It fuses at about 130° of Wedgwood, and when slowly cooled it crystallizes. It is at- tracted by the magnet, and is susceptible of being rendered per- manently magnetic. It undergoes little change in the air, but absorbs oxygen when heated in open vessels. It is attacked with difficulty by sulphuric or muriatic acid, but is readily oxidized by means of nitric acid. Oxides of Cobalt.—Chemists are acquainted with two oxides of cobalt. According to the experiments of Rothoff, the protoxide is composed of 29.5 parts of cobalt and 8 parts of oxygen, so that the atomic weight of cobalt is 29.5. Dr. Thomson, on the con- COBALT. 319 trary, infers from his analysis of the sulphate of cobalt, that 26 is the equivalent of this metal. From this discordance it is clear that the atomic weight of cobalt is not yet known with certainty. According to Rothoff, the oxygen contained in the two oxides is as 1 to 1.5. The protoxide is of an ash-gray colour, and is the basis of the salts of cobalt, most of which are of a pink hue. When heated to redness in open vessels it absorbs oxygen, and is converted into the peroxide. It may be prepared by decomposing the car- bonate of cobalt by heat in a vessel from which the atmospheric air is excluded. It is easily recognised by giving a blue tint to borax when melted with it; and is employed in the arts, in the form of smalt, for communicating a similar colour to glass, earthenware, and porcelain. The protoxide of cobalt is precipitated from its salts by pure potassa as a blue hydrate, which absorbs oxygen from the air, and gradually becomes black. Pure ammonia, likewise, causes a blue precipitate, which is re-dissolved by the alkali if in excess. Sulphuretted hydrogen produces no change, unless the solution is quite neutral, or the oxide is combined with a weak acid. Al- kaline hydrosulphurets always precipitate it as the black sulphu- ret of cobalt. The peroxide of cobalt is of a black colour, and is easily form- ed from the protoxide in the way already mentioned. It does not unite with acids. When strongly heated in close vessels, it gives off oxygen, and is converted into the protoxide. Phosphuret of Cobalt is a white brittle compound. Sulphuret of Cobalt, is formed by heating the oxide with sul- phur. It is of a yellowish-white colour. Salts. Nitrate of Cobalt, crystallizes in small prisms of a red-colour. They are deliquescent in the air, and decomposable by heat, leaving a deep red powder. Carbonate of Cobalt.—Solutions of cobalt are precipitated by carbonated alkalies, at first of a peach-blossom colour and after- wards of a lilac hue. Borate of Cobalt.—Solutions of borax produce a pink precipi- tate in a solution of muriate of cobalt. Phosphate of Cobalt may be formed by decomposing the ni- trate of cobalt with phosphate of soda. It is insoluble, of a lilac colour, and if mixed with eight parts of gelatinous alumina, and heated, it produces a beautiful blue, which may sometimes be em- ployed by painters as a substitute for ultra-marine. Sulphate of Cobalt.—Sulphuric acid does not attack cobalt unless when concentrated and heated, nor does it readily dis- solve the oxide. They may, however, be brought to combine by 320 NICKEL. dissolving the newly precipitated protoxide in sulphuric acid, di- luted with its bulk of water. Small red prismatic crystals are obtained, composed of one proportion of oxide, one of acid, and seven of water ; when dried at a temperature of 500° the crystals fall into a blue powder, which in a bright heat fuses and gives out sulphuric acid, leaving a black oxide. The blue powder is the anhydrous sulphate of cobalt, perfectly soluble in water, and forming a pink solution ; it is slightly deliquescent and becomes lilac coloured by exposure to air. Sulphate of cobalt forms triple compounds with potassa, and with ammonia. If it contain nickel the crystals are of a greenish tinge, but pink when the cobalt is pure. Arseniate of Cobalt.—Arsenic acid does not precipitate cobalt from its solution in acids, but the alkaline arseniates occasion a precipitate of a fine red colour, which is arseniate of cobalt. This salt is found native ; sometimes in the state of a fine red efflorescence, and sometimes crystallized in small four sided prisms or tables. SECTION VIII. Nickel, or Nickelum. Nickel is a constituent of meteoric iron. It occurs likewise in the copper-coloured mineral of Westphalia, termed copper-nickel, a native arseniuret of nickel, which, in addition to its chief con- stituents, contains sulphur, iron, cobalt, and copper. The pre- parations of nickel may either be made from this mineral or from the artificial arseniuret called speiss, a metallurgic production obtained in forming smalt from the roasted ores of cobalt. Vari- ous processes have been devised for procuring a pure salt of nickel, but the following appears as simple and perhaps as successful as any. After reducing speiss to fine powder, it is digested in sulphuric acid, to which a fourth part of nitric acid is added ; and when the solution is saturated with nickel, it is set aside for several hours in order that arsenious acid may sepa- rate, and then filtered. The clear liquid is subsequently mixed with a solution of sulphate of potassa, and set aside to crystallize spontaneously; when a double salt, the sulphate of nickel and potassa, is deposited. Dr. Thomson, who proposed this process, states that the crystals thus obtained are quite free from arsenic and iron, and contain no impurities except copper and cobalt. The former is easily precipitated as sulphuret by a current of sulphuretted hydrogen gas, a little free sulphuric acid being pre- viously added; and at the same time any traces of arsenic, if present, would likewise subside as orpiment. The filtered liquid is then heated to expel free sulphuretted hydrogen, and the oxides NICKEL. 321 of nickel and cobalt precipitated by carbonate of potassa. The separation of these oxides may then be effected by the method suggested by M. Berthier. The mixed hydrates, after being well washed, are suspended in water through which chlorine is transmitted to saturation. All the cobalt, and generally some nickel, is converted into peroxide and thus rendered insoluble ; while the greater part of the nickel is dissolved in the form of muriate, and may be removed from the insoluble peroxides by filtration. Metallic nickel, which may be prepared either by heating the oxalate in close vessels, or by the combined action of heat and charcoal or hydrogen on the oxide of nickel, is of a white colour, intermediate between that of tin and silver. It has a strong metallic lustre, and is both ductile and malleable. It is attracted by the magnet, and like iron and cobalt may be rendered mag- netic. Its specific gravity after fusion is about 8.279, and is in- creased to near 9.0 by hammering. Nickel is exceedingly infusible, even more so than pure iron. It suffers no change at common temperatures by exposure to air and moisture; but it absorbs oxygen at a red heat, though not rapidly, and is partially oxidized, The muriatic and sulphuric acids act upon it with difficulty. By the nitric acid it is readily oxidized, and forms a nitrate ofthe protoxide of nickel. Nickel is susceptible of two stages of oxidation. According to the experiments of Berzelius, Berthier, and Thomson, the com- bining proportion of nickel is 26, and that of its protoxide 34. The protoxide may hence be regarded as a compound of one equivalent of each element. The peroxide of nickel has been less fully examined than the protoxide ; but from some experi- ments of Rothoff, it appears to consist of 26 parts or one equi- valent of nickel, and 12 parts or one equivalent and a half of oxygen. The protoxide of nickel may be formed by heating the car- bonate, oxalate, or nitrate to redness in an open vessel, and is then of an ash-gray colour ; but after being heated to whiteness, its colour is a dull olive-green. It is not attracted by the mag- net. It is a strong alkaline base, and nearly all its salts have a green tint. It is precipitated as a hydrate of a pale green colour by the pure alkalies, but is re-dissolved by ammonia in excess; as a pale green carbonate by alkaline carbonates, but is dissolved by an excess of the carbonate of ammonia; and as a black sul- phuret by alkaline hydrosulphurets. Sulphuretted hydrogen oc- casions no precipitate, unless the solution is quite neutral, or ihe oxide combined with a weak acid. The peroxide of nickel is of a black colour, and is formed by transmitting chlorine gas through water in which the hydrate of the protoxide is suspended. The peroxide of nickel does not unite with acids, is decomposed by a red heat, and with hot S s 322 NICKEL. muriatic acid forms a protomuriate with disengagement of chlo- rine gas. Sulphuret of Nickel.—Nickel may be combined directly with sulphur by fusion, and forms a gray compound of a metallic lustre. Salts. Nitrate of Nickel is a green deliquescent salt, difficultly crys- tallizable in rhomboids. Carbonate of Nickel is precipitated in the form of a green pow- der, when carbonate of potassa is added to sulphate of nickel. Borate of Nickel is a pale green insoluble compound. Phosphate of Nickel being nearly insoluble, is precipitated upon adding phosphate of soda to a solution of nickel. It is of a pale green colour. Sulphate of Nickel is formed by digesting the oxide in dilute sulphuric acid, a bright green solution is formed, which affords quadrangular prismatic crystals soluble in about three parts of water at 60°, and which effloresce by exposure. Their taste is sweet and astringent; the crystals contain one atom of acid, one of oxide, and seven of water. Ammonia sulphate of Nickel is formed by evaporating a mixed solution of ammonia and sulphate of nickel; it forms four sided prismatic crystals. Potassa sulphate of Nickel is obtained by adding potassa to sulphate of nickel (not in excess) filtering and evaporating. It forms green rhomboidal crystals. Sulphate of Nickel and Iron is formed by dissolving the mixed protoxides in sulphuric acid. It is a green efflorescent salt, in tabular crystals. Arseniate of Nickel has an apple green colour; when heated in a glass tube it loses its colour with its water, and becomes hya- cinth coloured and transparent. When heated to redness, it becomes bright yellow and remains unaltered. Alloys of Nickel—That with iron forms the principal metallic ingredient in those lapideous masses which in different countries have fallen upon our globe, and which have been termed cerolites or meteoric stones. In meteoric iron the proportion of nickel varies considerably. In a specimen from the arctic region, Mr. Brande found 3.2 per cent. In that from Siberia, Mr. Children found nearly 10 per cent. The analysis may be performed by solution in nitro-muriatic acid ; the iron is thrown down by excess of ammonia in the state of peroxide, of which 100 grains indicate 70 of metallic iron; it is separated by filtration, washed, and dried, and on evaporating the filtrated liquor, and heating its dry residue red hot, the oxide of nickel is obtained, which should be re-dis- solved in nitric acid, and precipitated by pure potassa, the mix- PALLADIUM. 323 ture being boiled for a few seconds. 100 grains of this oxide of nickel are equal to 79 of metallic nickel. Meteoric iron has been imitated by fusing iron with nickel. The alloy of 90 parts of iron with 10 of nickel, is of a whitish yel- low cast, and not so malleable as pure iron. The alloy with 3 per cent, of nickel is perfectly malleable, and whiter than iron. These alloys are less disposed to rust than pure iron, but nickel alloyed with steel increases the tendency to rust; with copper nickel forms a hard white alloy. Tests.—The ferrocyanate of potassa produces a pale gray, or greenish white precipitate in all the solutions of nickel. SECTION IX. Palladium, Rhodium, Osmium, Iridium, and Pluranium. The five metals to be described in this section are all con- tained in the ore of platinum, and have hitherto been procured in very small quantity. When the ore is digested in nitro-mu- riatic acid, the platinum, together with palladium, rhodium, iron, copper, and lead, is dissolved; while a black powder is left con- sisting of osmium, iridium, and pluranium. Palladium. This metal was discovered in 1803 by Dr. Wollaston. On adding cyanide of mercury dissolved in water to a neutral solu- tion of the ore of platinum, either before or after the separation of that metal by muriate of ammonia, a yellowish-white flocculent precipitate is gradually deposited, which is a cyanide of palla- dium. When this compound is heated to redness, the cyanogen is expelled, and pure palladium remains. Palladium resembles platinum in colour and lustre. It is both malleable and ductile, and considerably harder than platinum. Its specific gravity varies from 11.3 to 11.8. In fusibility it is intermediate between gold and platinum, and it is dissipated in sparks when intensely heated by the oxy-hydrogen blow-pipe. Palladium is oxidized and dissolved by nitric acid, and even the sulphuric and muriatic acids act upon it by the aid of heat; but its proper solvent is the nitro-muriatic acid. Its oxide forms beautiful red-coloured salts, from which metallic palladium is precipitated by the protosulphate of iron and by all the metals described in the foregoing sections, excepting gold and plati- num. The oxide of palladium is precipitated by pure potassa, as an orange-coloured hydrate, which becomes black when dried, and is decomposed by a red heat. It consists, according to Berzelius, 324 RHODIUM. of nearly 56 parts of palladium and 8 parts of oxygen; so that 56 is most probably the atomic weight of the metal itself, and 64 the equivalent of its oxide. Rhodium. This metal was discovered by Dr. Wollaston at the time he was occupied with the discovery of palladium. On immersing a thin plate of clean iron into the solution from which palladium and the greater part of the platinum have been precipitated, the rhodium, together with small quantities of platinum, copper, and lead, is thrown down in the metallic state; and on digesting the precipitate in dilute nitric acid, the two last metals are removed. The rhodium and platinum are thus dissolved by means of nitro- muriatic acid, and the solution, after being mixed with some muriate of soda, is evaporated to dryness. Two double salts re- sult, the muriate of platinum and soda, and the muriate of rhodium and soda, the former of which is soluble and the latter insoluble in alcohol, and may therefore be separated from one another by that menstruum. The salt of rhodium is then dissolved in water, and the pure rhodium precipitated by the insertion of a rod of zinc. Rhodium, thus procured, is in the form of a black powder, which requires the strongest heat that can be produced in a wind furnace for fusion, and when fused has a white colour and me- tallic lustre. It is brittle, and its specific gravity is about 11. It is not attacked by any of the acids when in its pure state; but if alloyed with other metals, such as copper or lead, it is oxidized and dissolved by the nitro-muriatic acid, a circumstance which accounts for its presence in the solution of crude platinum. It is oxidized also by being ignited with nitre. Most of its salts are either red or yellow, and the muriate is of a rose-red colour, from which it has received the name of rhodium from poSov a rose. The number deduced by Dr. Thomson as the atomic weight of rhodium is 44 ; and its oxides, according to the same chemist, are thus constituted:— Rhodium. Oxygen. Protoxide - 44 8 Peroxide - 44 16 The protoxide is black, and the peroxide, which is the base of the salts of rhodium, is of a yellow colour. Berzelius, whose re- sults do not accord with those of Dr. Thomson, has described a brown oxide ; but it is as yet undetermined whether it is a dis- tinct oxide or a mixture of the two others. OSMIUM AND IRIDIUM. 325 Osmium and Iridium. These metals were discovered by the late Mr. Tennant in the year 1803, and the discovery of iridium was made about the same time by M. Descotils in France. The black powder mentioned at the beginning of this section is a compound of iridium and osmium, an alloy which Dr. Wollaston has detected in the form of flat white grains among fragments of crude platinum. From this alloy, which is quite insoluble in nitro-muriatic acid, Mr. Tennant prepared iridium and osmium in the following manner. The black powder mixed with soda was heated to redness in a silver crucible, and the residue, after removing the alkali by means of water, was digested in muriatic acid. In this way two solutions, one alkaline and the other acid, were procured, the former of a deep orange-colour, containing the oxide of osmium united with soda, and the latter, the muriate of iridium. From the refractory nature of this alloy, it is necessary to ignite with successive portions of soda before the whole of any given quanti- ty of the black powder is oxidized. Osmium.—On neutralizing the alkaline liquid just described, and heating it in a retort, the oxide of osmium, which is both volatile and soluble in water, passes over into the recipient, and is there dissolved in'the fluid that accompanies it. The aqueous solution is colourless, and emits a pungent peculiar odour, some- what like that of chlorine, a property which suggested the name of osmium from oafiyj odour. The oxide of osmium has not been procured free from water, nor has its composition been deter- mined. The infusion of gall-nuts is a delicate test of its pre- sence, striking a purple colour which afterwards acquires a deep blue tint. The oxide of osmium is precipitated in the metallic state by nearly all the metals, excepting gold and platinum. On agitating it with mercury an amalgam is formed, which, when heated in close vessels, yields pure osmium, capable of supporting a white heat without being volatilized or fused. If ignited in open ves- sels, it is oxidized and is then dissipated in vapour. After ex- posure to heat it resists the action of all the acids. Iridium.—The solution of the oxide of iridium in muriatic acid, when first prepared, is of a blue colour; but it afterwards becomes of an olive-green hue, and subsequently acquires a deep red tint. This diversity of colour, which gave origin to the name of iridium, is attributed to the metal passing through different stages of oxidation, an opinion which is probable, though by no means established. Chemists, indeed, are as yet ignorant both of the number and composition ofthe oxides of iridium. The muriate of iridium, when deprived of its excess of acid by heat, may be procured in crystals of a deep brown colour by evaporation. This salt is characterized by forming with water a 326 PLURANIUM. red solution, which is rendered colourless by the pure alkalies or alkaline earths, by sulphuretted hydrogen, infusion of gall-nuts, or by the ferrocyanate of potassa. It is decomposed by nearly all the metals excepting gold and platinum, the iridium being thrown down in the metallic state. Iridium may likewise be procured from the muriate by exposing that salt to a red heat. Iridium is the most infusible metal known ; but Mr. Children, by means of his large galvanic battery, succeeded in fusing it into a globule of a brilliant metallic lustre and white colour. Its specific gravity in this state is 18.68. It is attacked with great difficulty by nitro-muriatic acid; but is oxidized when heated with nitre. Pluranium. This metal was first noticed by M. Osann, in 1828. The native platinum of Russia, is operated upon in the first place for osmium, and after this is separated, the residual liquid is suffered to rest for about 24 hours, when long prismatic and brilliant crystals, of a light rose colour, appear; these, upon heated charcoal, are reduced to a metallic form, of a gray colour. The crystals are the oxide of pluranium, and Berzelius, who examined them, says " they can not be confounded with any other known body." Sulphuret of Pluranium, is a transparent yellowish substance when first formed; but it soon assumes an opaque gray colour and metallic lustre. SECTION X. Zinc, or Zincum. The zinc of commerce, sometimes called spelter, is obtained either from calamine, the native carbonate of zinc, or from the native sulphuret, the blende of mineralogists. It is procured from the former by heat and carbonaceous matters ; and from the latter by a similar process after the ore has been previously oxidized by roasting, that is, by exposure to the air at a low red heat. When first extracted from its ores it is never quite pure; but contains charcoal, sulphur, and several metals in small quantity. It may be freed from these impurities by distillation,—by expos- ing it to a white heat in an earthen retort, to which a receiver full of water is adapted. Zinc has a strong metallic lustre, and a bluish-white colour. Its texture is lamellated, and its density about 7. It is a hard metal, being acted on by the file with difficulty. At low or high degrees of heat it is brittle ; but at temperatures between 210° and 300° F., it is both malleable and ductile. It fuses at 680 F., ZINC. 327 and when slowly cooled assumes regular forms. Exposed in close vessels to a white heat, it sublimes unchanged. Zinc undergoes little change by the action of air and moisture. When fused in open vessels, it absorbs oxygen, and forms the white oxide, called flowers of zinc. Heated to full redness in a covered crucible, it bursts into flame as soon as the cover is re- moved, and burns with a brilliant white light. The combustion ensues with such violence, that the oxide, as it is formed, is me- chanically carried up into the air. Zinc is readily oxidized by dilute sulphuric or muriatic acid, and the hydrogen which is evolved contains a small quantity of metallic zinc in combination. Oxide of Zinc.—Chemists are acquainted with one compound only of zinc and oxygen, and this oxide is formed under all the circumstances just mentioned. At common temperatures it is white ; but when heated to low redness, it assumes a yellow co- lour, which gradually disappears on cooling. It is quite fixed in the fire. It is insoluble in water, and therefore does not affect the blue colour of plants ; but it is a strong salifiable base, form- ing regular salts with acids, most of which are colourless. It combines also with some of the alkalies. According to Thomson, it is composed of Zinc . 34 one atom. Oxygen . 8 one atom. Liquid ammonia readily dissolves oxides of zinc, and even acts upon the metal. The concentrated solution of the oxide furnishes feathery crystals, it is decomposed by the acids, and the immer- sion of a plate of copper causes a precipitation of the zinc, the ammonia acquiring at the same time a blue colour. Phosphuret of Zinc, is of a whitish colour, and a metallic lustre not unlike lead. It has some malleability, exhales a phosphoric smell, and at a high temperature burns like common zinc. The native Sulphuret of Zinc, or blende, is frequently found in dodecahedral crystals, or in forms allied to the dodecahedron. Its structure is lamellated, its lustre adamantine, and its colour variable, being sometimes yellow, red, brown, or black. It may be made artificially, by heating to redness a mixture of oxide of zinc and sulphur, by decomposing the sulphate of zinc by char- coal, or by drying the white precipitate obtained on adding the hydrosulphuret of ammonia to a salt of zinc. The sulphuret of zinc is composed of one atom of each of its constituents, and is dissolved with disengagement of sulphuretted hydrogen by dilute sulphuric acid. Salts. Nitrate of Zinc.—Nitric acid, moderately strong, acts on zinc with great violence. The solution, by evaporation, crystallizes in four-sided prisms, and affords a deliquescent salt, copiously soluble in water and alcohol. 328 ZINC. Carbonate of Zinc, occurs native, forming one of the varieties of the mineral called calamine. It may be formed by adding carbonate of potassa to sulphate of zinc. It is white, and taste- less. The primitive form of calamine, which occurs both crys- tallized and massive, is an obtuse rhomboid. It is often found investing carbonate of lime which has sometimes been decom- posed, and the calamine remains in pseudo-crystals. A variety of calamine containing siliceous earth, is known by the name of electric calamine, from its property of becoming electrical when gently heated. Borate of Zinc, is an insoluble white powder. Phosphate of Zinc, is not crystallizable. It may be obtained by dissolving zinc in phosphoric acid, and evaporating to dryness. A phosphate of zinc is also precipitated, upon the addition of phosphate of soda to sulphate of zinc. It is probable that there is a phosphate and a biphosphate of zinc. Sulphate of Zinc.—The sulphate of zinc, frequently called white vitriol, is the residue of the process for forming hydrogen gas by the action of dilute sulphuric acid on metallic zinc, but is made, for the purposes of commerce, by roasting the native sul- phuret of zinc in a reverberatory furnace. It crystallizes by spontaneous evaporation into transparent four-sided prisms, which dissolve in two parts and a half of cold, and are still more solu- ble in boiling water. It has a strong styptic taste. It reddens vegetable blue colours, though in composition it is a strictly neutral salt, consisting of one atom of each of its elements. The crystals are composed of 82 parts or one atom of the anhydrous sulphate, and 63 parts or seven atoms of water. Native sulphate of zinc is found in places where the sulphuret of zinc occurs; it is probably the result of the decomposition of that ore. Sulphite of Zinc, is formed by dissolving the oxide in sulphu- rous acid; the solution yields crystals of sulphite of zinc, the crystals have a less acrid, but more styptic taste than the hypo- sulphite, are less soluble in water, and more easily crystallized. They are insoluble in alcohol. Hyposulphite of Zinc, maybe formed by digesting metallic zinc in sulphurous acid, sulphuretted hydrogen is disengaged, and by gentle evaporation, crystals are obtained, which are to be digested in alcohol; this liquid dissolves the hyposulphite, and affords it in prismatic crystals. Arseniate of Zinc is a white powder, insoluble in water. Antimoniate, Molybdate, Chromate, and l\ngstate of Zinc, do not require a particular description. Alloys.—With potassium and sodium, zinc forms brittle alloys, decomposable by exposure to air and water. With iron, it forms a white, and somewhat malleable alloy. If plates of hot iron be dipped into melted zinc, they acquire the appearance of tin plate. ZINC. 329 Copper and zinc unite in several proportions, forming alloys of great importance in the arts. The best brass consists of four parts of copper to one of zinc ; and when the latter is in a greater proportion, compounds are generated which are called Tombac, Dutch-gold, and Pinchbeck. The while copper ofthe Chinese is composed, according to the analysis of Dr. Fife, of 40.4 parts of copper, 25.4 of zinc, 31.6 of nickel, and 2.6 of iron. Tests.—The presence of zinc is easily recognised by the fol- lowing characters:—The oxide is precipitated from its solutions as a white hydrate by pure potassa or ammonia', and as carbonate, by carbonate of ammonia, but is completely re-dissolved by an excess of the precipitant. The fixed alkaline carbonates pre- cipitate it permanently as the carbonate of zinc. Hydrosulphuret of ammonia causes a white precipitate, which is either a hydro- sulphuret of the oxide of zinc, or a hydrated sulphuret of the metal. Sulphuretted hydrogen acts in a similar manner, if the solution is quite neutral; but it has no effect if an excess of any strong acid is present. SECTION XL Cadmium. Cadmium was discovered in 1817 by Stromeyer in an oxide of zinc, which had been prepared for medical purposes ; and he has since found it in several ofthe ores of that metal, especially in a radiated blende from Bohemia, which contains about five per cent. of cadmium. The late Dr. Clarke detected its existence in some of the zinc ores of Derbyshire, and in the common zinc of com- merce. Mr. Herapath has found it in considerable quantity in the zinc works near Bristol. During the reduction of calamine by coal, the cadmium, which is very volatile, flies off in vapour mixed with soot and some oxide of zinc, and collects in the roof ofthe vault, just above the tube leading from the crucible. Some portions of this substance yielded from twelve to twenty per cent. of cadmium. The process by which Stromeyer separates cadmium from zinc or other metals is the following: The ore of cadmium is dissolv- ed in dilute sulphuric or muriatic acid, and after adding a portion of free acid, a current of sulphuretted hydrogen gas is transmitted through the liquid, by means of which the cadmium is precipitat- ed as^ sulphuret, while the zinc continues in solution. The sul- phuret of cadmium is then decomposed by nitric acid, and solu- tion evaporated to dryness. The dry nitrate of cadmium is dis- solved in water, and an excess of carbonate of ammonia is added. The white carbonate of cadmium subsides, which, when heated to redness, yields a pure oxide. By mixing this oxide with char- Tt 330 CADMIUM. coal, and exposing the mixture to a red heat, metallic cadmium sublimes. A very elegant process for separating zinc from cadmium was proposed by Dr. Wollaston". The solution of the mixed metals is put into a platinum capsule, and a piece of metallic zinc is placed in it. If cadmium is present, it is reduced, and adheres so tenaciously to the capsule, that it may be washed with water with- out danger of being lost. It may then be dissolved either by nitric or dilute muriatic acid. Cadmium, in colour and lustre, has a strong resemblance to tin, but is somewhat harder and more tenacious. It is very ductile and malleable. Its specific gravity is 8.604 before being ham- mered, and 8.694 afterwards. It melts at about the same tempera- ture as tin, and is nearly as volatile as mercury, condensing like it into globules which have a metallic lustre. Its vapour has no odour. When heated in the open air, it absorbs oxygen, and is con-. verted into an oxide. Cadmium is readily oxidized and dissolv- ed by nitric acid, which is its proper solvent. Sulphuric and muriatic acids act upon it less easily, and the oxygen is then de- rived from water. Cadmium combines with oxygen, so far as is yet known, in one proportion only; and this oxide is conveniently procured in a separate state by igniting the carbonate. It has an orange co- lour, and is fixed in the fire. It is insoluble in water, and does not change the colour of violets; but it is a powerful salifiable base, forming neutral salts with acids. This oxide, according to the analysis of Stromeyer, is composed of 56 parts of cadmium and 8 parts of oxygen. It is, of course, regarded as a compound of one atom of each element, and consequently 56 is the atomic weight of cadmium. The oxide of cadmium is precipitated as a white hydrate by pure ammonia, but is re-dissolved by excess of the alkali. It is precipitated permanently by pure potassa as a hydrate, and by all the alkaline carbonates as carbonate of cadmium. Phosphuret of Cadmium, has a gray colour and a feeble metal- lic lustre. The Sulphuret of Cadmium, which occurs native in some kinds of zinc blende, is easily procured by the action of sulphuret- ted hydrogen on a salt of cadmium. It has a yellowish orange colour, and is distinguished from the sulphuret of arsenic by being i insoluble in pure potassa, and by sustaining a white heat with- out subliming. It is composed of 56 parts or one atom of cad- mium, and 16 parts or one atom of sulphur. CADMIUM. 331 Salts. Nitrate of Cadmium, crystallizes in prisms, or needles, which are deliquescent. Carbonate of Cadmium, is pulverulent and insoluble in water, and readily decomposible by heat. Phosphate of Cadmium., is pulverulent and insoluble. Sulphate of Cadmium, crystallizes in large rectangular prisms, resembling sulphate of zinc, which are very soluble in water. They effloresce in the air, and, at a gentle heat, lose their water of crystallization. Alloys.—The alloys of cadmium are not important. SECTION XII. Bismuth, or Bismuthum. Bismuth is found in the earth, both native and in combination with other substances, such as sulphur, oxygen, and arsenic. That which is employed in the arts is derived chiefly from native bis- muth, and commonly contains small quantities of sulphur, iron, and copper. It may be obtained pure for chemical purposes by heating the oxide or subnitrate to redness, along with charcoal. Bismuth has a reddish-white colour and considerable lustre. Its structure is highly lamellated, and, when slowly cooled, it crys- tallizes in octahedrons. Its density is about 10. It is brittle when cold, but may be hammered into plates while warm. At 476° F. it fuses, and sublimes in close vessels at about 30° Wedgwood. It is a less perfect conductor of caloric than most others metals. Bismuth undergoes little change by exposure to air at common temperatures. When fused in open vessels, its surface becomes covered with a gray film, which is a mixture of metallic bismuth with the oxide of the metal. Heated to its subliming point, it burns with a bluish-white flame, and emits copious fumes ofthe oxide of bismuth. The metal it attacked with difficulty by muriatic or sulphuric acid, but it is readily oxidized and dissolv- ed by nitric acid Oxide of Bismuth.—This metal unites with oxygen in one pro- portion only, formingayellow-colouredoxide, which may be easily procured by heating the subnitrate to redness. At a full red heat it is fused, and yields a transparent yellow glass. At a still higher temperature it is sublimed. It unites with acids, and most of its salts are white. According to the experiments of Dr. J. Davy, it is composed of 72 parts of bismuth, and 8 parts of oxygen, and 332 BISMUTH. therefore 72 is the atomic weight of bismuth, and 80 the equiva- lent of its oxide. Sulphuret of Bismuth.—This sulphuret is found native, and may be formed artificially by fusing bismuth with sulphur. It is of a lead-gray colour, and metallic lustre. The experiments of Drs. Davy, Thomson, and Lagerhielm leave no doubt of its being composed of one atom of bismuth and one atom of sulphur. The dark brown precipitate, caused by the action of sulphuretted hy- drogen on the salts of bismuth, is probably a protosulphuret. Salts. Nitrate of Bismuth.—Nitric acid dissolves bismuth with great rapidity. The solution is crystallizable in small four sided prisms. When the nitrate of bismuth, either in solution or in crystals, is put into water, a copious precipitate, the subnitrate, of a beauti- fully white colour subsides, which was formerly called the magis- tery of bismuth. From its whiteness, it is sometimes employed as a paint for improving the complexion ; but it is an inconvenient pigment, owing to the facility with which it is blackened by sul- phuretted hydrogen. If the nitrate with which it is made con- tains no excess of acid, and a large quantity of water is employed, the whole of the bismuth is separated as subnitrate. By this character bismuth may be both distinguished and separated from other metals. Sulphate of Bismuth, is a white compound insoluble in, but decomposed by, water, which converts it into a sub-sulphate and a super-sulphate. The sub-sulphate described by Berzelius con- sists of three atoms of oxide and one of acid. The carbonate, borate, arseniate, and molybdate of bismuth do not require a special notice. Alloys.—Bismuth forms alloys, some of which are remarkable for their fusibility. With gold, platinum, and silver, it forms brit- tle compounds. A compound of eight parts of bismuth, five of lead, and three of tin, liquefies at 212°; it is called Sir I. Newton's fusible metal; the addition of one part of quicksilver renders it yet more fusible. Bismuth enters into the composition of soft solders. These alloys are mostly white, brittle, and easily oxidat- ed. Bismuth has the singular property of depriving gold of its ductility. This effect is produced by merely keeping gold in fusion near melted bismuth. ( 333 ) SECTION XIII. Silver, or Argentum. Silver is one ofthe ancient metals, and perhaps exceeds them all in beauty. The alchemists compared it to the moon, and called it Luna, or Diana. This metal frequently occurs native in silver mines, both massive and in octahedral or cubic crystals. It is also found in combination with lead, gold, antimony, copper, and arsenic, and with sulphur. The silver mines of Peru and Mexico are the most valuable. Pure silver may be obtained for chemical purposes by placing a clean piece of copper in a solution of the nitrate of silver, washing the precipitated metal with pure water, and then digest- ing it in ammonia, in order to remove any adhering copper. It may also be prepared from the chloride of silver, either by ex- posing that compound, mixed with a pure or carbonated alkali, to a strong heat in a black-lead crucible, or by conducting over it a current of hydrogen gas when heated to redness in a tube of porcelain. Silver has the clearest white colour of all the metals, and is susceptible of receiving a lustre surpassed only by polished steel. In malleability and ductility, it is inferior only to gold, and its tenacity is considerable. It is very soft when pure, so that it may be cut with a knife. Its density after being hammered is 10.51. At 20° or 22° of Wedgwood's pyrometer it fuses. Pure silver does not rust by exposure to air and moisture, nor is it oxidized by fusion in open vessels. It appears, indeed, that a film of oxide is formed when melted silver is exposed to a cur- rent of air or oxygen gas; but it spontaneously parts with the oxygen as it becomes solid. When silver, in the form of leaves or fine wire, is intensely heated fey means of electricity, galvan- ism, or the oxy-hydrogen blow-pipe, it burns with vivid scintilla- tions of a greenish white colour. The only pure acids that act on silver are the sulphuric and nitric acids, by both of which it is oxidized, forming with the first a sulphate, and with the second a nitrate of silver. Oxide of Silver.—The oxide of silver is best procured by mix- ing a solution of pure baryta with nitrate of silver dissolved in water. This oxide is of a brown colour, is insoluble in water, and is completely reduced by a red heat. According to Sir H. Davy, it is composed of 110 parts of silver and eight parts of oxygen, and, therefore, regarding it as the real protoxide, 110 is the atomic weight of silver. The oxide of silver is separated from its solutions in nitric acid, by pure alkalies and alkaline earths, as the brown oxide, which is re-dissolved by ammonia in excess; by alkaline carbonates as 334 SILVER. a white carbonate, which is soluble in an excess of the carbonate of ammonia; as a dark brown sulphuret by sulphuretted hydro- gen ; and as a white curdy chloride of silver, which is turned violet by light, and is very soluble in ammonia, by muriatic acid or any soluble muriate. By the last character, silver may be both distinguished and separated from other metallic bodies. Silver is precipitated in the metallic state by most other metals. When mercury is employed for this purpose, the silver assumes a beautiful arborescent appearance, called arbor Diance. A very good proportion for the experiment is twenty grains of lunar caustic to six drachms or an ounce of water. The silver thus deposited always contains mercury. When the oxide of silver, recently precipitated by baryta or lime water, and separated from adhering moisture by bibulous paper, is left in contact for ten or twelve hours with a strong so- lution of ammonia, the greater part of it is dissolved ; but a black powder remains, which detonates violently from heat or percussion. This substance, which was discovered by Berthollet, appears to be a compound of ammonia and oxide of silver; for the products of its detonation are metallic silver, water, and nitrogen gas. It should be made in very small quantity at a time, and dried spontaneously in the air. From some late ex- periments, this compound appears to be an ammonuret of silver, and not an ammonuretted oxide. On exposing a solution of the oxide of silver in ammonia to the air, its surface becomes covered with a pellicle, which Mr. Faraday considers to be an oxide containing less oxygen than that just described. This opinion he has made highly probable ; but further experiments are requisite before the existence of this oxide can be regarded as certain. Cyanide of Silver is formed by mixing hydrocyanic acid with nitrate of silver. It is a white curdy substance, similar in ap- pearance to the chloride of sil«er, insoluble in water and nitric acid, and soluble in a solution of ammonia. It is decomposed by muriatic acid with formation of hydrocyanic acid and chloride of silver. Phosphuret of Silver is a white colour, and appears granulated, or as if it were crystallized. It breaks under the hammer, but may be cut with a knife. It is composed of 4 parts of silver and 1 of phosphorus. Sulphuret of Silver.—Silver has a strong affinity for sulphur. This metal tarnishes rapidly when exposed to an atmosphere, con- taining sulphuretted hydrogen gas, owing to the formation of a sulphuret. On transmitting a current of sulphuretted hydrogen through a solution of lunar caustic, a dark brown precipitate subsides, which is a sulphuret of silver. The silver glance of mineralogists is a similar compound, and the same sulphuret may SILVER. 335 be prepared by heating thin plates of silver with alternate layers of sulphur. The sulphuret of silver, according to the experiments of Berze- lius, is a compound of 110 parts or one atom of silver, and 16 parts or one atom of sulphur. Salts. Nitrate of Silver.—Silver is readily oxidized and dissolved by nitric acid diluted with two or three times its weight of water, forming a solution which yields transparent tabular crystals by evaporation. These crystals, which are anhydrous, undergo the igneous fusion when heated, and assume a crystalline texture in cooling. At a red heat it is completely decomposed, and metal- lic silver remains. When liquefied by heat, and received in small circular moulds, it forms the lapis infernalis or lunar caus- tic, employed by surgeons as a cautery. The nitric acid appears to be the agent which destroys the animal texture, and the black stain is owing to the separation of the oxide of silver. It is sometimes employed for giving a black colour to the hair, and is the basis ofthe indelible ink for marking linen. The nitrate of silver deliquesces on exposure to the air. It is soluble in its own weight of cold, and in half its weight of hot water. It dissolves also in four times its weight of alcohol. The aqueous solution undergoes little change if preserved in glass vessels; but when paper moistened with it is exposed to light, especially to sun-shine, a black stain is produced, owing to the decomposition ofthe salt, and reduction of the oxide to the me- tallic state. This solution is employed by chemists as a test of the presence of chlorine and muriatic acid. The nitrate of silver, even after fusion, reddens vegetable colouring matters; but it is neutral in composition, consisting of one atom of acid and one atom of the oxide. Carbonate of Silver is precipitated in the form of white insolu- ble powder by adding carbonate of potassa to nitrate of silver. It blackens by exposure to light. It consists of one atom of the oxide, and 1 of acid. Borate of Silver is thrown down from the nitrate of silver in the form of white powder, by adding a solution of borate of soda. Phosphate of Silver is a compound of some importance from its use in preparing chloric acid. To obtain it, crystals of nitrate of silver may be dissolved in pure water, and a solution of phos- phate of soda be added; the neutrality ofthe nitrate of silver is destroyed, and though the phosphate contains an excess of alkali, the resulting liquor is acid. The precipitate is of a yellow colour; when washed and dried, it is fusible at a red heat without any further loss of weight. Sulphate, Sulphite, and Hyposulphite of Silver have been 336 SILVER. formed. The sulphate is made by boiling the acid upon the metal. The hyposulphite of potassa and silver has also been I produced; it is in the form of gray pearly scales of a sweetish taste. Arseniate, Arsenite, Chromate, and Molybdate, are unimportant compounds; the chromate is distinguished by its beautiful crim- son colour, and is made by adding the chromate of potash to the nitrate of silver. Alloys of Silver.—Silver is capable of uniting with most other metals, and suffers greatly in malleability and ductility by their presence. It may contain a large quantity of copper without losing its white colour. The standard silver for coinage contains about •£ part of copper, which increases its hardness, and thus renders it more fit for coins and many other purposes. Silver combines with steel, forming an alloy, which, although it contains only T^7 of its weight of silver, is superior to the best cast sfeel in hardness, and is admirably adapted to the formation of cutting instruments. The amalgam of silver is a mineral production. The process of separating silver from its ores by amalgamation, practised on a large scale at Freyberg, in Germany, is founded on the affinity of mercury for silver. On exposing the amalgam to heat, the quicksilver is volatilized, and pure silver remains. Tests.—The soluble salts of silver are recognised b.y furnishing a white precipitate with muriatic acid, which blackens by expo- sure to light, and which is readily soluble in ammonia, and by affording metallic silver upon the immersion of a plate of copper. The salts insoluble in water are soluble in liquid ammonia, and, when heated on charcoal before the blow-pipe, they afford a globule of silver. SECTION XIV. Aluminum. That alumina is an oxidized body, was proved by Sir H. Davy, who found that potassa is generated when the vapour of potas- sium is brought into contact with pure alumina heated to white- ness ; and it was inferred, chiefly by analogical reasoning, to be a metallic oxide. The propriety of this inference has been demon- strated by M. Wohler, who has lately procured aluminum, the metallic base of alumina, in a pure state. The preparation of this metal depends on the property which potassium possesses, of decomposing the chloride of aluminum. Decomposition is effected by aid of a moderate increase of tem- perature ; but the action is so violent, and accompanied with such intense disengagement of heat and light, that the process cannot ALUMINUM. 337 be safely conducted in glass vessels. Dr. Wohler succeeded in effecting the decomposition in a platinum crucible, retaining the cover in its place by a piece of wire. The heat developed during the action was so great, that the crucible, though but gently heated externally, suddenly became red hot. The platinum is scarcely attacked during the process; but to prevent the possi- bility of error from this source, the decomposition was effected in a crucible of porcelain. The potassium employed for the pur- pose should be quite free from carbon, and the quantity operated on at one time not exceed the size of ten peas. The heat was applied by means of a spirit lamp, and continued until the action was completed. The proportion of the materials requires to be carefully adjusted; for the potassium should be in such quantity as to prevent any chloride of aluminum from subliming during the process, but not so much as to yield an alkaline solution when the product is put into water. The matter contained in the crucible at the close ofthe operation is in general completely fused, and of a dark gray Colour. When quite cold, the crucible is put into a large glass full of water, in which the saline matter is dissolved, with slight disengagement of hydrogen of an offen- sive odour; and a gray powder separates, which, on close inspec- tion, especially in sunshine, is found to consist solely of minute scales of metal. After being well washed with cold water, it is pure aluminum. The solution is neutral, and contains a quantity of alumina, owing to a combination being formed between chlo- ride of aluminum and chloride of potassium during the action. Aluminum, as thus formed, is a gray powder, very similar to that of platinum. It is generally in small scales or spangles of a metallic lustre; and sometimes small, slightly coherent, spongy masses are observed, which in some places have the lustre and white colour of tin. The same appearance is rendered perfectly distinct by pressure on steel, or in an agate mortar; so that the lustre of aluminum is decidedly metallic. In its fused state it is a conductor of electricity, though it does not possess this property when in the form of powder. This remark, of a metal conducting the electric fluid in one state and not in another, is very instruc- tive ; and Dr. Wohler observed an instance of the same kind in iron, which in a state of fine powder is a non-conductor of elec- tricity. Aluminum requires for fusion a temperature higher than that at which cast iron is liquefied. When heated to redness in the open air, it takes fire and burns with vivid light, yielding alu- minous earth of a white colour, and of considerable hardness. Sprinkled in powder in the flame of a candle, brilliant sparks are emitted, like those given off during the combustion of iron in oxygen gas. When heated to redness in a vessel of pure oxygen gas, it burns with an exceedingly vivid light, and emission of intense heat. The resulting alumina is partially vitrified, of a U u 338 ALUMINUM. yellowish colour, and equal in hardness to the native crystallized aluminous earth, the corundum. Heated to near redness in an atmosphere of chlorine, it takes fire, and chloride of aluminum is sublimed. Aluminum is not oxidized by water at common temperatures, nor is its lustre tarnished by lying in water during its evapora- tion. On heating the water to near its boiling point, oxidation of the metal commences, with feeble disengagement of hydrogen gas, the evolution of which continues even long after cooling, but at length wholly ceases. The oxidation, however, is very slight; and even after continued ebullition, the smallest particles of aluminum appear to have suffered scarcely any change. Aluminum is not attacked by concentrated sulphuric or nitric acid at common temperatures. In the former, with the aid of heat, it is rapidly dissolved with disengagement of sulphurous acid gas. In dilute muriatic and sulphuric acid it is dissolved with evolution of hydrogen gas. It is easily and completely dis- solved even by a dilute solution of pptassa, hydrogen gas being evolved at the same time. Ammonia produces a similar effect, and renders soluble a large quantity of alumina. The hydrogen gas which makes its appearance is of course derived from water, the oxygen of which combines with aluminum. Alumina is one of the most abundant productions of nature. It is found in every region of the globe, and in rocks of all ages, being a constituent of the oldest primary mountains, of the secondary strata, and of the most recent alluvial depositions. The different kinds of clay of which bricks, pipes, and earthen- ware are made, consists of hydrate of alumina in a greater or less degree of purity. Though this earth commonly appears in rude amorphous masses, it is sometimes found beautifully crys- tallized. The ruby and the sapphire, two of the most beautiful gems of which we are acquainted, are composed almost solely of alumina. Pure alumina is prepared from alum, the sulphate of alumina and potassa. This salt, as purchased in the shops, is frequently contaminated with oxide of iron, and consequently unfit for many chemical purposes ; but it may be separated from this impurity by repeated crystallization. The absence of iron is proved by the alum being soluble without residue in a solution of pure po- tassa ; whereas when oxide of iron is present, it is either left uh- dissolved in the first instance, or deposited after a few hours in yellowish.brown flocks. Any quantity of purified alum is dis- solved in four or five times its weight of boiling water, a slight excess of carbonate of potassa added, and after digesting for a few minutes the bulky hydrate of alumina is collected on a filter, and well washed with hot water. It is necessary in this opera- tion to digest and employ an excess of alkali; since otherwise the precipitate would retain some sulphuric acid in the form of ALUMINUM. 339 a sub-sulphate. But the alumina, as thus prepared, is not yet quite pure; for it retains some ofthe alkali with such force, that it cannot be separated by the acfion of water. For this reason the precipitate must be re-dissolved in dilute muriatic acid, and thrown down by means of pure ammonia or its carbonate. This precipitate, after being well washed and exposed to a white heat, yields pure anhydrous alumina. Ammonia cannot be employed for precipitating aluminous earth directly from alum, because the sulphate of alumina is completely decomposed by this alkali. An easier process, proposed by Gay-Lussac, is to expose the sulphate of alumina and ammonia to a strong heat, so as to expel the ammonia and sulphuric acid. Alumina has neither taste nor smell, and is quite insoluble in water. It is very infusible, though less so than lime or magne- sia. It has a powerful affinity for water, attracting moisture from the atmosphere with avidity ; and, for a like reason, it ad- heres tenaciously to the tongue when applied to it. Mixed with a due proportion of water, it yields a soft cohesive mass, suscep- tible of being moulded into regular forms, a property upon which depends its employment in the art of pottery. When once mois- tened, it cannot be rendered anhydrous, except by exposure to a full white heat; and in proportion as it parts with water, its vo- lume diminishes. Alumina most probably forms several different hydrates with water. Dr. Thomson has described two different compounds of this kind. One is the bi-hydrate, composed of one equivalent of alumina to two of water ; and it is procured by exposing, for the space of two months, alumina, precipitated by means of an alkali, to a dry air, the temperature of which does not exceed 60° F. The other compound is a protohydrate, obtained by drying the bi-hydrate at a temperature of 100° F. by which means half of its water is expelled. Alumina, owing to its insolubility, does not affect the blue co- lour of plants. It appears to possess the properties both of an acid and of an alkali;—of an acid, by uniting with alkaline bases, such as potassa, lime, and baryta ;—of-an alkali, by forming salts with acids. In neither case, however, are its soluble compounds neutral with respect to test paper. Chemists are not agreed as to the combining proportion of alu- mina ; but Dr. Thomson, after comparing the results of a consi- derable number of analyses, has fixed upon 18 as its equivalent. T!;o composition of alumina is still more uncertain, for as yet no direct experiment has been made on the subject. Dr. Thomson considers it a compound of one proportional of aluminum and one of oxygen, and on this supposition 10 is the equivalent of the former; but Berzelius believes its constitution to be ana: ^ji us to that of the peroxide of iron, and .. strong argument may L adduced in favour of this view. 340 ALUMINUM. Alumina is easily recognised by the following characters : ,1. It is separated from acids, as a hydrate, by all the alkaline carbo- nates, and by pure ammonia.. 2. It is precipitated by pure po- tassa or soda, but the precipitate is completely re-dissolved by an excess ofthe alkali. Phosphuret of Aluminum.—When aluminum is heated to red- ness in contact with the vapour of phosphorus, it takes fire, and emits a brilliant light. The product is described by Dr. Wohler, as a blackish gray pulverulent mass, which, by friction, acquires a dark gray metallic lustre, and in the air smells instantly of phosphuretted hydrogen. By the action of water, alumina and phosphuretted hydrogen gas are generated, but the latter is not spontaneously explosive. The effervescence is less rapid than with the sulphuret, but is increased by heat. Sulphuret of Aluminum.—Sulphur may be distilled from alumi- num without combining with it; but if a piece of sulphur be dropped on aluminum, when strongly incandescent, so that it may be enveloped in an atmosphere ofthe vapour of sulphur, the union is effected with vivid emission of light. The resulting sulphuret is a partially vitrified, semi-metallic mass, which ac- quires an iron-black metallic lustre when burnished. On expo- sure to the air, it emits a strong odour of sulphuretted hydrogen, swells up gradually, and falls into a gray powder, sulphuretted hydrogen gas and alumina being obviously generated at the ex- pense ofthe watery vapour floating in the atmosphere. Applied to the tongue, it excites a pricking warm taste of sulphuretted hydrogen. When throw.n into pure water, sulphuretted hydrogen gas is rapidly disengaged, and gray alumina deposited. Dr. Wohler finds that sulphuret of aluminum cannot be gene- rated by the action of hydrogen gas on sulphate of alumina at a red heat; for in that case all the acid is expelled, without the aluminous earth being reduced. Selenuret of Aluminum.—This compound is formed, with dis- engagement of heat and light, by heating to redness a mixture of selenium and aluminum. The product is black, pulverulent, and assumes a dark metallic lustre when rubbed. In the air it emits a strong odour of selenuretted hydrogen; and this gas is rapidly disengaged by the action of water, and which is speedily reddened by the separation of selenium. Telluriet of Aluminum.—When a mixture of aluminum and tellurium are heated to redness, they unite with such violence that the whole mass is projected from the vessel as if shot from a gun. This inconvenience may be prevented by adding the tel- lurium in mass. It is similar in its properties to the last com- pound. Arsenuret of Aluminum, is readily made with powdered arsenic and aluminum; the combination takes place with less heat and light than in the preceding compounds. ALUMINUM, 341 Salts. Nitrate of Alumina, crystallizes in thin ductile plates. The crystals are extremely soluble and deliquescent. Sulphate of Alumina.—The pure sulphate of alumina is a compound of little interest; but with the sulphate of potassa, it forms an interesting double salt, the weH-known alum of com- merce. Alum has a sweetish astringent taste. It is soluble in five parts of water at 60° F., and in little more than its own weight of boiling water. The solution reddens litmus paper : but it is doubtful whether this is owing to an excess of acid, or to the weak affinity existing between alumina and sulphuric acid. It crystal- lizes readily in octahedrons, or in segments of an octahedron, and the crystals contain almost 50 per cent, of water of crystal- lization. On being exposed to heat, they froth up remarkably, and part with all the water, forming anhydrous alum, the alumen ustum of the pharmacopoeia. At a full red heat, the alumina is deprived of its acid. There is some doubt as to the real composition of alum. Ac- cording to Thomson, it is composed of Sulphate of alumina, 174 3 atoms. Sulphate of potassa, 88 1 atom. Water, 225 25 atoms. Mr. Phillips, on the contrary, regards it as a compound of two atoms ofthe sulphate of alumina, one atom ofthe bi-sulphate of potassa, and 22 atoms of water. The sulphate of alumina forms with the sulphate of ammonia, and with the sulphate of soda, double salts, which are very ana- logous to common alum. SECTION XV. Gludnum. Glucinum was first satisfactorily ascertained by Dr. F. Wohler, near the close of the year 1828; till then glueina, a substance first discovered by Vauquelin in the beryl and emerald, was only supposed from analogy to be the oxide of a metal called gluci- num. Dr. Wohler reduced glueina to its metallic state by the action of potassium, on the chloride of glucinum in the manner described in the last section for obtaining aluminum. The com- pound thus produced was thrown into a large quantity of water; the chloride of potassium was soon found in solution, and the glucinum precipitated in the form of a dark gray powder, which is to be washed and dried. Pure glucinum is a deep gray-coloured 342 GLUCINUM. powder, which, upon rubbing or burnishing, exhibits a dull me- tallic lustre; it is exceedingly difficult of fusion, and does not oxi- date either in the air or water. At a high temperature it burns brilliantly, both in oxygen gas and in the air, and is converted into glueina. Glueina is a white powder, which has neither taste nor odour, and is quite insoluble in water. Its specific gravity is 3. Vege- table colours are not affected by it. The salts which it forms with acids, have a sweetish taste, a circumstance which distin- guishes glueina from other earths, and from which its name is de- rived. According to the analysis of Thomson and Berzelius, 26 is the atomic weight of glueina. Glueina may be known chemically by the following characters: 1. Pure potassa or soda precipitates glueina from its salts, but an excess of the alkali re-dissolves it. 2. It is precipitated perma- nently by pure ammonia as the hydrate, and by fixed alkaline carbonates, as the carbonate of glueina. 3. It is dissolved com- pletely by a cold solution of carbonate of ammonia, and is preci- pitated from it by boiling. By means of this property, glueina may be both distinguished and separated from alumina. Phosphuret of Glucinum is a gray substance, easily formed by burning glucinum in the vapour of phosphorus. It decomposes water Hke the phosphuret of lime. Sulphuret of Glucinum is a compound possessing but little in- terest. Selenuret of Glucinum is produced with a great disengagement of caloric when selenium and glucinum are melted together. Its fracture is crystalline. Telluret and arsenuret of Glucinum, have also been formed. SECTION XVI. Yttrium. Though the experiments of Sir H. Davy in 1807, rendered it highly probable that the metals called glucinum and yttrium ex- isted, these facts were never clearly and satisfactorily demon- strated till the experiments of Dr. F. Wohler in 1828. He ob- tained yttrum in the same manner as aluminum and glucinum, by exposing its chloride to the action of potassium. Yttrium appears in small shining metallic scales, something like particles of iron, and are readily distinguished from glucinum by their superior lustre. At ordinary temperatures yttrium does not unite with the oxygen ofthe air, and it remains unaltered in wa- ter, but when subjected to red heat, it burns with great brillian- cy, both in the air and in oxygen gas, and is converted into yttria. YTTRIUM. 343 Yttria was first discovered in 1794, by Professor Gadolin, in a mineral found at Ytterby in Sweden, from which it received the name of Yttria. Yttria resembles alumina and glueina in its chemical properties; but is distinguished from both by being insoluble in a-solution of pure potassa. Its atomic weight, as deduced by Dr. Thomson from the analyses of Berzelius, is 42. The combinations of yttrium with phosphorus, sulphur, and selenium, are analagous to the similar combinations of glucinum, which we have just described. The substance called thorina, supposed by Berzelius to be a distinct earth, has recently been recognised by that chemist as the phosphate of yttria. On the Analogies between Elementary substances ; and some speculations respecting their nature. The elementary substances most analogous to each other are certainly to be found amongst the metals; some of these are so similar, that it requires refined observation, and sometimes ex- periment, to distinguish them. There is likewise a chain of gra- dations of resemblance which may be traced throughout the whole series of metallic bodies, at the same time that certain similar and characteristic properties are found to belong to metals in other respects most unlike each other. Silver and palladium, antimony and tellurium, agree in a great number of qualities. Potassium and platinum, if we except their lustre, colour, and power of conducting electricity, are bodies extremely dissimilar; yet, by arranging the metals in the order of their natural resemblances, these two substances may be made parts of one chain of natural bodies: potassium, sodium, and barium are very like each other; barium approaches to man- ganesum, zinc, iron, tin, and antimony. Platinum is analogous to gold, silver, and palladium; and palladium is connected by distinct analogies with tin, zinc, iron, and manganesum. Arse- nic and chromium, though amongst the most dissimilar of the metals in other respects, agree in the property of forming acid matter by combination with oxygen. Amongst the inflammable bodies not metallic there are analo- gies, but not a similar series. Sulphur and phosphorus agree in many respects; carbon, boron, silicon, and zerconion, are like- wise analogous, and are connected by distinct relations with the metallic substances. Nitrogen agrees with the other combusti- ble bodies that have been named in forming an acid by saturation with oxygen. 344 ANALOGIES, &c. As far as our knowledge ofthe nature of compound bodies has extended, analogy of properties is connected with analogy of composition ; if one of the inflammable solids or metals is proved to be a compound, there would be strong evidence for supposing that the others were likewise compounded. It has been already mentioned that sulphur and phosphorus, when Voltaic electrical sparks are taken in them in a state of fusion, afford hydrogen gas. Sir H. Davy, found likewise, that when an alloy of tellurium and potassium was acted upon by melted sulphur, telluretted, and sul- phuretted hydrogen, equal to at least 80 times the volume of the sulphur, were disengaged. He made many experiments of this kind with similar results, the sulphur being recently sublimed in nitrogen gas, and moisture being excluded with the greatest care. In the experiments of Voltaic electrization, it might be supposed that the hydrogen being only in very small quantity might be- long to an accidental admixture in the sulphur and the phospho- rus; but the proportion is too large in the experiments on the action of tellurium, potassium, and sulphur, to allow of a similar inference, and it seems more probable that it arises either from the decomposition of the sulphur, or of the metals, or all of these bodies. We know nothing of the true elements belonging to nature ; but as far as we can reason from the relations of the properties of matter, hydrogen is the substance which approaches nearest to what the elements may be supposed to be. It has energetic powers of combination, its parts are highly repulsive as to each other, and attractive of the particles of other matter; it enters into combination in a quantity very much smaller than any other substance, and in this respect it is approached by no known body. After hydrogen, oxygen partakes most of the elementary cha- racter ; it has perhaps a greater energy of attraction, and next to hydrogen is the body that enters into combination in the small- est proportion. We have already hinted that all inflammable matters may be similarly constituted, and may contain hydrogen. And on this supposition they may be conceived to owe their powers of com- bining with oxygen, to the attractive energy of the combined hydrogen. On the most probable view of the nature of the amalgam from ammonia, it must be supposed to be composed of hydrogen, ni- trogen, and quicksilver ; and it may be regarded as a kind of type of the composition of the metals ; and by supposing them and the inflammable bodies different combinations of hydrogen with another principle as yet unknown in the separate form, all the phenomena may be easily accounted for, and will be found in harmony with the theory of definite proportions. The probabilities that the metals and inflammable solids may ANALOGIES, &c. 345 be constituted by different and various proportions of hydrogen and an unknown basis, are strengthened by the fact, that the metals in which hydrogen is supposed to be attracted by the largest quantity of other matter are the least disposed to com- bine with oxygen ; and those that are supposed to contain the largest quantity of hydrogen to the smallest quantity of other matter, are the most combustible, and likewise those supposed to contain the largest and consequently the least attracted quantity of hydrogen, have the lowest specific gravity. When the analogy of the oxides to many of the hydrates, is considered, bodies so much alike, that, till lately, they have been confounded together; the view that the inflammable bodies con- tain hydrogen becomes still more likely. Water cannot be separated from the hydrates of potassa or soda by heat; and the hydrate of lime is extremely analogous to the pure earth ; and supposing the oxides to be compounds of unknown bases and water, it might be expected that the water would adhere to them with great energy, and would only be separated in consequence ofthe bases entering into a new combination. When a globule of mercury under water is subjected to galva- nic action, oxygen appears to combine with the metal, and yet no hydrogen is evolved. Sir H. Davy made a number of experi- ments on this subject, and ascertained that, in this process, an oxide is formed, without any apparent compensation in the pro- duction of inflammable matter; nor was he able to detect any combination into which the hydrogen could have entered; so that these experiments, as they now stand, would induce the be- lief that water is the ponderable basis of both oxygen and hydro- gen, and that these two forms of matter owe their peculiar pro- perties, either to the agency of imponderable substances, or to peculiar arrangements of the particles of the same matter; but such a formidable conclusion as this must not be hastily adopted ; for, in all other cases, oxygen and hydrogen appear as perfectly inconvertible substances, and in no other instance can one be procured from water without the correspondent quantity of the other, or without some product in which the other may be sup- posed to enter. There is no improbability in the supposition that the same ponderable matter in different electrical states, or in different arrangements, may constitute substances chemically different: there are parallel cases in the different states in which bodies are found, connected with their different relations to temperature. Thus steam, ice. and water, are the same ponderable matter; and certain quantities of ice and steam mixed together produce ice- cold water. Even if it should be ultimately found that oxygen and hydrogen are the same matter in different states of electricity, or that two or three elements in different proportions constitute all bodies, the great doctrines of chemistry, the theory of definite X x 346 ANALOGIES, &c. proportions, and the specific attractions of bodies must remain immutable; the causes of the difference of form of the bodies supposed to be elementary, if such a step were made, must be ascertained, and the only change in the science would be, that those substances, now considered as primary elements, must be considered as secondary; but the numbers representing them would be the same, and they would probably be all found to be produced by the additions of multiples of some simple numbers. That the forms of natural bodies may depend upon different arrangements ofthe same particles of matter, has been a favourite hypothesis advanced in the earliest era of physical research, and often supported by the reasonings of the ablest philosophers. This sublime chemical speculation, sanctioned by the authority of Hooke, Newton, and Boscovich, must not be confounded with the ideas advanced by the alchemists concerning the converti- bility of the elements into each other. The possible transmuta- tion of metals has generally been reasoned upon, not as a philoso- phical research, but as an empirical process. Those who have asserted the actual production of the precious metals from other elements, or their decomposition, or who have defended the chimera of the philosopher's stone, have been either impostors, or men deluded by impostors. In this age of rational inquiry, it will be useless to decry the practices of the adepts, or to caution the public against confounding the hypothetical views respecting the elements founded upon distinct analogies, with the dreams of alchemical visionaries, most of whom, as an author ofthe last century justly observed, professed an art without principles, the beginning of which was deceit, the progress delusion, and the end poverty. DIVISION II. We are now to examine the nature and properties of Chlorine, and its combinations with the substances described jn our first division. In noticing the properties of chlorine we shall first examine its relations to oxygen, and then its union with the sim- ple electro-positive elements in the order in which we have pla- ced them. Though Chlorine agrees with oxygen in being an electro-negative substance, it is to be recollected that this is only a relative character; that is, it exerts an electro-positive energy with regard to oxygen, but it sustains an opposite state in relation to all other substances. As we have already noticed the chemical history of all the electro-positive bodies under separate heads, it will be unneces- sary to divide this part of our work into chapters and sections. Chlorine. The discovery of Chlorine was made in 1770 by Scheele, while investigating the nature of manganese, and he described it under the name of dephlogisticated marine add. The French chemists called it oxygenized muriatic acid, a term which was afterwards contracted to oxymuriatic acid, from an opinion proposed by Berthollet that it is a compound of muriatic acid and oxygen. In 1809 Gay-Lussac and Thenard published an abstract of some experiments upon the subject, which subsequently appeared at length in their Recherches Physico-Chimiques, wherein they state that oxymuriatic acid may be regarded as a simple body, though they gave the preference to the doctrine advanced by Berthollet. Sir H. Davy engaged in the inquiry about the same time, and, after having exposed oxymuriatic acid to the most powerful de- composing agents which chemists possess, without being able to effect its decomposition, he communicated to the Royal Society a paper in which he denied its compound nature, and maintained that, according to the true logic of chemistry, it is entitled to rank with simple bodies. This view, which is commonly termed the new theory of chlorine, though strongly objected to at the time it was first proposed, is now almost universally received by chemists. Chlorine gas is obtained by the action of muriatic acid on the peroxide of manganese. The most convenient method of pre- paring it is by mixing concentrated muriatic acid, contained in a glass flask, with half its weight of finely powdered peroxide of manganese. An effervesence, owing to the escape of chlorine, takes place even in the cold; but the gas is evolved much more 348 CHLORINE. freely by the application of a moderate heat. It should be col- lected in inverted glass bottles filled with warm water ; and when the water is wholly displaced by the gas, the bottles should be closed with a well-ground glass stopper. Before explaining the theory of this process, it may be premised that muriatic acid consists of 36 parts or one atom of chlorine, and one part or one atom of hydrogen. The peroxide of manganese, as already men- tioned is composed of 28 or one atom of manganese, and 16 or two atoms of oxygen. When these compounds act on one ano- ther, one atom of each is decomposed. The peroxide of manga- nese gives one atom of oxygen to the hydrogen of the muriatic acid, in consequence of which one atom of water is generated, and one atom of chlorine disengaged; while the protoxide of manganese unites with an atom of undecomposed muriatic acid, and forms an atom ofthe muriate of the protoxide of manganese. Consequently, for every 44 grains of the peroxide of manganese, 74 (37x2) grains of muriatic acid disappear; and 36 chlorine, 9 water, and 73 protomuriate of manganese, are the products of the decomposition. The affinities which determine these changes are the attraction of oxygen for hydrogen, and of the protoxide of manganese for muriatic acid. When it is an object to prepare chlorine at the cheapest rate, as for the purposes of manufacture, the preceding process is mo- dified in the following manner: Three parts of sea-salt are inti- mately mixed with one of the peroxide of manganese, and to this mixture two parts of sulphuric acid, diluted with an equal weight of water, are then added. By the action of sulphuric acid on sea-salt, muriatic acid is disengaged, which re-acts as in the former case, upon the peroxide of manganese; so that, instead of adding muriatic acid directly to the manganese, the materials for forming it are employed. Chlorine, from ^wgoj, green, is a yellowish-green coloured gas, which has an astringent taste, and a disagreeable odour. It is one of the most suffocating of the gases, exciting spasms and great irritation of the glottis, even when considerably diluted with air. When strongly and suddenly compressed, it emits both heat and light, a character which it possesses in common with oxygen gas. According to Sir H. Davy, 100 cubic inches of it at 60° F., and when the barometer stands at 30 inches, weigh between 76 and 77 grains. Thomson states its weight at 76.25 grains, and his result agrees very nearly with that of Gay- Lussac and Thenard. Adopting this estimate, its specific gravity is 2.5. Under the pressure of about four atmospheres, it is a limpid liquid of a bright yellow colour, which does not freeze at the temperature of zero, and which assumes the gaseous form with the appearance of ebullition when the pressure is removed. Cold recently boiled water, at the common pressure, absorbs twice its volume of chlorine, and yields it again when heated. CHLORINE. 349 The solution, which is made by passing a current of chlorine gas through cold water, has the colour, taste, and most of the other properties of the gas itself. When moist chlorine gas is exposed to a cold of 32° F., yellow crystals are formed, which consist of water and chlorine in definite proportions. They are composed, according to Mr. Faraday, of 36 or one atom of chlorine to 90 or ten atoms of water. Chlorine experiences no chemical change from the action of the imponderables. Thus it is not affected chemically by intense heat, by strong shocks of electricity, or by a powerful galvanic battery. Sir H. Davy exposed it also to the action of charcoal, heated to whiteness by galvanic electricity, without separating oxygen from it, or in any way affecting its nature. Light does not act on dry chlorine ; but if water be present, the chlorine decomposes that liquid, unites with the hydrogen to form muriatic acid, and oxygen gas is set at liberty. This change takes place quickly in sunshine, more slowly in diffused daylight, and not at all when the light is wholly excluded. Hence the necessity of keeping moist chlorine gas, or its solution, in a dark place, if it is wished to preserve it for any time. Chlorine is a supporter of combustion. If a lighted taper be plunged into chlorine gas, it burns with a small red flame, and emits a large quantity of smoke. Phosphorus takes fire in it spontaneously, and burns with a pale white light. Several of the metals, such as tin, copper, arsenic, antimony, and zinc when introduced into chlorine in the state of powder or in fine leaves, are suddenly inflamed. In all these cases the combustible sub- stances unite with chlorine. Chlorine has a very powerful attraction for hydrogen; and many of the chemical phenomena to which chlorine gives rise, are owing to this property. A striking example is its power of de- composing water by the action of light, or at red heat; and most compound substances, of which hydrogen is an element, are de- prived of that principle, and therefore decomposed in like man- ner. For the same reason, when chlorine, water, and some other body, which has a strong affinity for oxygen, are presented to one another, the water is resolved into its elements, the hydrogen attaches itself to the chlorine, and the oxygen to the other body. Hence it happens that chlorine is indirectly one of the most powerful oxidizing agents which we possess. When any compound of chlorine and an inflammable is expos- ed to the influence of galvanism, the inflammable body goes over to the negative, and the chlorine to the positive pole ofthe battery. This establishes a close analogy between oxygen and chlorine, both of them being supporters of combustion, and both negative electrics. Chlorine, though formerly called an acid, possesses no acid pro- perties. It has not a sour taste, does not redden the blue colour 350 CHLORINE, of plants, and shows little disposition to unite with alkalies. Its strong affinity for the metals is sufficient to prove that it is not an acid ; for chemists are not acquainted with any instance of direct combination between an acid and a metal. The mutual action of chlorine and the pure alkalies leads to complicated changes. If chlorine gas is passed into a solution of potassa till all alkaline re-action ceases, a liquid is obtained which has the odour of a solution of chlorine in water. But on applying heat, the chlorine disappears entirely, and the solution is found to contain two neutral salts, the chlorate and muriate of potassa. The production of the two acids is owing to the decom- position of water, the elements of which unite with separate por- tions of chlorine, and form the chloric and muriatic acids. The affinities which give rise to this change, are the attraction of chlorine for hydrogen, of chlorine for oxygen, and ofthe two re- sulting acids for the alkali. One ofthe most important properties of chlorine is its.bleach- ing power. All animal and vegetable colours are speedily remov- ed by chlorine; and when the colour is once discharged, it can never be restored. Chlorine cannot bleach unless water is pre- sent, thus, dry litmus paper suffers no change in dry chlorine; but when water is admitted, the colour speedily disappears. It is well known also, that muriatic acid is always generated when chlorine bleaches. From these facts it is inferred that water is decomposed during the process; that its hydrogen unites with chlorine ; and that the decomposition of the colouring matter is occasioned by the oxygen which is liberated. The bleaching property of the deutoxide of hydrogen, of which oxygen is cer- tainly the decolourizing principle, leaves little doubt of the accu- racy of the foregoing explanation. Chlorine is useful, likewise, for the purposes of fumigation. The experience of Guyton-Morveau is sufficient evidence of its power in destroying the volatile principles given off by putrefy- ing animal matter; and it probably acts in a similar way on con- tagious effluvia. Chlorine is in general easily recognised by its colour and odour. Chemically it may be detected by its bleaching property, added to the circumstance that a solution of the nitrate of silver occasions in it a dense white precipitate (a compound of chlorine and metallic silver), which becomes dark on exposure to light, is insoluble in acids, and dissolves completely in pure ammonia. The compounds of chlorine, which are not acid, are termed chlorides or chlorurets. The former expression is. the more ap- propriate, from the analogy between chlorine and oxygen. CHLORINE. 351 Chlorine and Oxygen. Chlorine unites with oxygen in four different proportions. The leading character of these compounds is derived from the circum- stance that chlorine and oxygen, the attraction of which for most elementary substances is so energetic, have but a feeble affinity for one another. These principles, consequently, are never met with in nature in a state of combination. Indeed, they cannot be made to combine directly ; and when they do unite, very slight causes effect their separation. Notwithstanding this, their union is always regulated by the law of definite proportions, as appears from the following tabular view of the constitution of the compounds to which they give rise. Chlorine. Oxygen. Protoxide of Chlorine 36 . . 8 Peroxide of Chlorine 36 . .32 Chloric acid . 36 . . 40 Perchloric acid 36 . -56 Protoxide of Chlorine.—This gas was discovered in 1811, by Sir H. Davy, and was described by him under the name of Euchlorine. It is made by the action of muriatic acid (which is a compound of chlorine and hydrogen), on the chlorate of potassa; and its production is explicable on the fact, that muriatic and chloric acids mutually decompose each other. When muriatic acid and chlorate of potassa are mixed together, a part of the muriatic acid unites with the potassa of the salt, and thus sets chloric acid free, which instantly re-acts on the free muriatic acid. The result of the re-action depends on the manner in which the operation is conducted. If the chlorate of potassa is mixed with an excess of concentrated muriatic acid, the chloric acid undergoes complete decomposition. For one atom of the chloric, five atoms of muriatic acid are decomposed: the five atoms of oxygen contained in the former unite with the hydrogen of the latter, producing five atoms of water; while the chlorine of both acids is disengaged. If, on the contrary, the salt is in excess, and the muriatic acid diluted, the chloric acid is deprived of a part of its oxygen only; and the products are water, pro- toxide of chlorine, and chlorine, the two latter escaping in the gaseous form. From the proportion of these gases, it is probable that for each atom ofthe chloric, three of muriatic acid must be decomposed; and that by the re-action of their elements, they yield three atoms of water, two of pure chlorine, and two ofthe protoxide of chlorine. The best proportion of the ingredients for forming this com- pound is two parts of the chlorate of potassa, one of strong mu- riatic acid, and one of water. Effervescence ensues on the appli- 352 CHLORINE. cation of a gentle heat, and the gases should be collected over mercury. The chlorine combines with the mercury, and the pro- toxide of chlorine is left. The protoxide of chlorine has a yellowish-green colour similar to that of chlorine, but considerably more brilliant, which induced Sir H. Davy to give it the name of euchlorine. Its odour is like that of burned sugar. Water dissolves eight or ten times its volume of the gas, and acquires a colour approaching to orange. It bleaches vegetable substances, but gives the blue colours a tint of red before destroying them. It does not unite with alkalies, and therefore is not an acid. The protoxide of chlorine is explosive in a high degree. The heat of the hand, or the pressure occasioned in transferring it from one vessel to another, sometimes causes an explosion. This effect is also occasioned by phosphorus, which bursts into flame at the moment of immersion. All burning bodies, by their heat, occasion an explosion, and then burn vividly in the decomposed gas. With hydrogen it forms a mixture which explodes by flame or the electric spark, with production of water and muriatic acid. The best proportion is 50 measures of the protoxide of chlorine to 80 of hydrogen. The protoxide of chlorine is easily analyzed by heating a known quantity of it in a strong tube over mercury. An explo- sion takes place ; and 50 of the gas expand to 60 measures, 20 of which are oxygen, and 40 chlorine. The specific gravity of a gas so constituted must be 2.444, and its composition by weight is, chlorine 36 + oxygen 8. The weight of its atom is consequent- ly 44. Peroxide of Chlorine.—The peroxide of chlorine was disco- vered in 1815 by Sir H. Davy, and soon after by Count Stadion of Vienna. It is formed by the action of sulphuric acid on the chlorate of potassa. A quantity of this salt, not exceeding 50 or 60 grains, is reduced to powder, and made into a paste by the addition of strong sulphuric acid. The mixture, which acquires a deep yellow colour, is placed in a glass retort, and is heated by warm water, the temperature of which is kept under 212° F. A bright yellowish-green gas, of a still richer colour than the protoxide of chlorine, is disengaged, which has an aromatic odour without any smell of chlorine, is absorbed rapidly by water, to which it communicates its tint, and has no sensible action on mercury. This gas is the peroxide of chlorine.- The chemical changes which take place in the process are explained in the following manner : The sulphuric acid decom- poses some of the chlorate of potassa, and sets chloric acid at liberty. The chloric acid, at the moment of separation, resolves itself into peroxide of chlorine and oxygen; the last of which, instead of escaping as free oxygen gas, goes over to the acid of some undecomposed chlorate of potassa, and converts it into per- CHLORINE. 353 chloric acid. The whole products are bisulphate and perchlorate of potassa, and peroxide of chlorine. It is most probable, from the data contained in the preceding table, that every three atoms of chloric acid yield one atom ofthe perchloric acid, and two atoms ofthe peroxide of chlorine. The peroxide of chlorine does not unite with alkalies. It de- stroys most vegetable blue colours without previously reddening them. Phosphorus takes fire when introduced into it, and occa- sions an explosion. It explodes violently when heated to a tem- perature of 212° F., emits a strong light, and undergoes a greater expansion than the protoxide of chlorine. Forty measures of the gas occupy the space of 60 measures after the explosion; and of these, 20 are chlorine and 40 oxygen. The peroxide is there- fore composed of 36, or one atom of chlorine united with 32 or four atoms of oxygen. Its specific gravity must be 2.361. Chloric acid.—When to a dilute solution of the chlorate of baryta a quantity of weak sulphuric acid, exactly sufficient for combining with the baryta, is added, the insoluble sulphate of baryta subsides, and pure chloric acid remains in the liquid. This acid, the existence of which was originally observed by Mr. Chenevix, was first obtained in a separate state by Gay-Lussac. Chloric acid reddens vegetable blue colours, has a sour taste, and forms neutral salts, called chlorates, (formerly hyperoxymuri- ales) with alkaline bases. It possesses no bleaching properties, a circumstance by which it is distinguished from chlorine. It gives no precipitate in a solution of nitrate of silver, and hence cannot be mistaken for muriatic acid. Its solution may be con- centrated by a gentle heat till it acquires an oily consistence with- out decomposition; but at a higher temperature, the acid in part is volatilized unchanged, while another portion is converted into chlorine and oxygen. It is easily decomposed by deoxidizing agents. Sulphurous acid, for instance, deprives it of oxygen, with formation of sulphuric acid and evolution of chlorine. By the action of sulphuretted hydrogen, water is generated, while sulphur and chlorine are set free. Chloric acid is readily known by forming a salt with potassa, which crystallizes in tables, and has a pearly lustre, which defla- grates like nitre when thrown on burning charcoal, and yields the peroxide of chlorine by the action of concentrated sulphuric acid. The chlorate of potassa, like most of the chlorates, gives off pure oxygen when heated to redness, and leaves a residue of the chloride of potassium. This was the mode by which Gay- Lussac ascertained the composition of chloric acid, as stated in the table. Perchloric acid.—The saline matter which remains in the re- tort after forming the peroxide of chlorine, is a mixture ofthe perchlorate and bisulphate of potassa, and by washing it with cold water, the bisulphate is dissolved, and the perchlorate is left. Vy 354 CHLORINE. The perchloric acid may be prepared from this salt by mixing it in a retort with half its weight of sulphuric acid, diluted with one-third of water, and applying heat to the mixture. At the temperature of about 284° F. white vapours rise, which condense as a colourless liquid in the receiver. This is a solution ofthe perchloric acid. The properties of the perchloric acid have hitherto been little examined. Count Stadion, its discoverer, found it to be a com- pound of one atom, or 36 of chlorine, to 56 or seven atoms of oxygen; and his analysis has been confirmed by Gay-Lussac. Chlorine and-Nitrogen. The mutual affinity of chlorine and nitrogen is very slight; they do not combine at all if presented to each other in their gas- eous form; and when combined, they are easily separated. The chloride of nitrogen is formed by the action of chlorine on some salt of ammonia. Its formation is owing to the decomposition of ammonia by chlorine. The hydrogen ofthe ammonia unites with chlorine, and forms muriatic acid ; while the nitrogen ofthe ammonia, being presented in its nascent state to chlorine, dis- solved in the solution, enters into combination with it. A convenient method of preparing the chloride of nitrogen is the following : An ounce of muriate of ammonia is dissolved in twelve or sixteen ounces of hot water; and when the solution has cooled to the temperature of 90° F., a glass bottle, with a wide mouth, full of chlorine, is inverted in it. The solu- tion gradually absorbs the chlorine, and acquires a yellow co- lour; and in about twenty minutes, or half an hour, minute glo- bules of a yellow fluid are seen floating like oil upon its surface, which, after acquiring the size of a small pea, sink to the bottom ofthe liquid. The drops ofthe chloride of nitrogen, as they de- scend, should be collected in a small saucer of lead, placed for that purpose under the mouth ofthe bottle. The chloride of nitrogen, discovered in 1811 by M. Dulong, is one ofthe most explosive compounds yet known, having been the cause of serious accidents both to its discoverer and to Sir H. Davy. Its specific gravity is 1.653. It does not congeal by the intense cold produced by a mixture of snow and salt. It may be distilled at 160° F.; but at a temperature between 200° and 212° F. it explodes. It appears from the investigation of Messrs. Porrett, Wilson, and Kirk, that mere contact with some substances of a combustible nature cause detonation even at common tempera- tures. This property belongs particularly to the oils, both vola- tile and fixed. The products of the explosion are chlorine and nitrogen. Sir H. Davy analyzed the chloride of nitrogen by means of mer- cury, which unites with the chlorine, and liberates the nitrogen. CHLORINE. 355 He inferred from his analysis that its elements are united in the proportion of four measures of chlorine to one of nitrogen; and it hence follows that, by weight, it consists of Chlorine - 144 - - or four atoms Nitrogen - 14 - - or one atom Chlorine and Hydrogen. Muriatic or Hydrochloric acid gas may be conveniently pre- pared by putting an ounce of strong muriatic acid into a glass flask, and heating it by means of a lamp till the liquid boils. Pure muriatic acid gas is freely evolved, and may be collected over mercury. Another method of preparing it is by the action of concentrated sulphuric acid on an equal weight of sea-salt. A brisk effervescence ensues at the moment of making the mixture, and on the application of heat a large quantity of muriatic acid gas is disengaged. In the first process, muriatic acid, previously dissolved in water, is simply expelled from the solution by an in- creased temperature. The explanation of the second process is rather more complicated. Sea-salt was formerly supposed to be a compound of muriatic acid and soda ; and on this supposition, the soda was believed merely to quit the muriatic and unite with the sulphuric acid. But, sea-salt in its dry state consists, not of muriatic acid and soda, but of chlorine and sodium. The pro- portions of its constituents are Chlorine 36-1 atom, Sodium 24-1 atom. When sulphuric acid is added to it, one atom of water is resolved into its elements ; the hydrogen unites with chlorine, forming muriatic acid, which escapes in the form of gas ; while soda is generated by the combination ofthe oxygen with sodium, which combines with the sulphuric acid, and forms sulphate of soda. The water contained in the liquid sulphuric acid is therefore es- sential to the success of the operation. The affinities which de- termine the change are the attraction of chlorine for hydrogen, of sodium for oxygen, and of soda for sulphuric acid. Muriatic acid may be generated by the direct union of its ele- ments. When equal measures of chlorine and hydrogen are mixed together, and an electric spark is passed through the mix- ture, instantaneous combination takes place, heat and light are emitted, and muriatic acid is generated. A similar effect is pro- duced by flame, by a red-hot body, and by spongy platinum. Light also causes them to unite. A mixture of the two gases may be preserved without change in a dark place ; but if exposed to the diffused light of day, a gradual combination ensues, and is completed in the course of 24 hours. The direct solar rays produce, like flame or electricity, a sudden inflammation of the whole mixture, accompanied with an explosion ; and the vivid 356 CHLORINE. light emitted by charcoal intensely heated by galvanic electricity, acts in a similar manner. Hydrogen and chlorine unite in equal volumes, and muriatic acid, which is the sole and constant product, occupies the same space as the gases from which it is formed. From these facts the composition of muriatic acid is easily inferred. For, as Grains. 50 cubic inches of chlorine weigh - - 38.125 and 50 . hydrogen - - 1.059 100 cubic inches of muriatic acid gas must weigh 39.184 Its specific gravity, therefore, is 1.2847. By weight it con- sists of Chlorine - 38.125 - 36 Hydrogen - 1.059 - 1 Since chlorine and hydrogen unite in one proportion only, chemists regard muriatic acid as a compound of one atom of each of its elements, a conclusion which is fully justified by the pro- portions in which chlorine and hydrogen unite with other bodies. Hence, 36 is the weight of one atom of chlorine, and 37 of mu- riatic acid. Muriatic acid is a colourless gas, of a pungent odour, and acid taste. Under a pressure of 40 atmospheres, and at the tempera- ture of 50° F. it is liquid. It is quite irrespirable, exciting vio- lent spasm ofthe glottis; but when diluted with air, it is far less irritating than chlorine. All burning bodies are extinguished by it, and the gas itself does not take fire on the approach of flame. Muriatic acid gas is not ehemically changed by mere heat. It is readily decomposed by galvanism, hydrogen appearing at the negative, and chlorine at the positive pole. It is also decom- posed by ordinary electricity. The decomposition, however, is incomplete ; for though one electric spark resolves a portion of the gas into its elements, the next shock in a great measure ef- fects their re-union. It is not affected by oxygen under common circumstances; but if a mixture of oxygen and muriatic acid gases is electrified, the oxygen unites with the hydrogen ofthe muriatic acid to form water, and chlorine is set at liberty. One of the most striking properties of muriatic acid gas is its powerful attraction for water. A dense white cloud appears whenever muriatic acid escapes into the air, owing to a combina- tion which takes place between the acid and watery vapour. When a piece of ice is put into a jar full of the gas confined over mercury, the ice liquefies on the instant, and the whole ofthe gas disappears in the course of a few seconds. On opening a long wide jar of muriatic acid gas under water, the absorption ofthe CHLORINE. 357 gas takes place so instantaneously, that the water is forced up into the jar with the same violence as into a vacuum. A concentrated solution of muriatic acid gas in water has long been known under the names of spirit of salt, and of marine or muriatic add. It is made by passing a current of gas into water as long as any of it is absorbed. A considerable increase of tem- perature takes place during the absorption, and therefore the apparatus should be kept cool by ice. Sir H. Davy states, that water, at the temperature of 40° F., absorbs 480 times its volume of the gas, and that the solution has a density of 1.2109. Dr. Thomson finds that one cubic inch of water, at 69° F., absorbs 418 cubic inches of gas, and occupies the space of 1.34 cubic inch. The solution has a density of 1.1958, and one cubic inch of it contains 311.04 cubic inches of muriatic acid gas. The quantity of real acid contained in solutions of different densities may be determined by ascertaining the quantity of pure marble dissolved by a given weight of each. Every 50 grains of mar- ble correspond to 37 of real acid. The following table from Thomson's "Principles of Chemistry," is constructed by this rule. The first and second columns show the atomic constitution of each acid. Table exhibiting the specific gravity of Muriatic Acid of deter- minate strengths. Atoms of Atoms of Real acid in J00 Sfiecijic Acid. water. ofthe liquid. gravity. 6 40.659 1.203 7 37.000 1.179 8 33.945 1.162 9 31.346 1.149 10 29.134 1.139 11 27.206 1.1285 12 25.517 1.1197 13 24.026 1.1127 14 . 22.700 1.1060 15 21.512 1.1008 16 20.442 1.0960 17 19.474 1.0902 18 18.590 1.0860 19 17.790 1.0820 20 17.051 1.0780 All the pharmacopoeias give directions for forming muriatic acid. The proportions generally recommended are equal weights of sea-salt, water, and sulphuric acid, more acid being purposely employed than is sufficient to form a neutral sulphate with the soda, so that the more perfect decomposition of the sea-salt may be insured. The acid, to prevent too violent an effervescence at first, is mixed wjth one-third of the water, and when the mixture 358 CHLORINE. has cooled, it is poured upon the salt previously introduced into a glass retort. The distillation is continued to dryness ; and the gas, as it escapes, is conducted into the remainder of the water. The theory of the process has already been explained. The re- sidue is a mixture ofthe sulphate and bi-sulphate of soda. The specific gravity of muriatic acid obtained by this process, is 1.170. The common muriatic acid of commerce has a yellow colour, and is always impure. The usual impurities are nitric acid, sul- phuric acid, and oxide of iron. The presence of nitric acid may be inferred if the muriatic acid has the property of dissolving gold leaf. Iron may be detected by the ferrocyanate of potassa, and the sulphuric acid by muriate of baryta, the suspected mu- riatic acid being previously diluted with three or four parts of water. To provide against the presence of nitric acid, the sea- salt is first ignited, to decompose any nitre which it may con- tain. The other impurities may be avoided by employing a Woulfe's Apparatus. A few drachms of water are put into the first bottle, to retain the muriate of iron and sulphuric acid, which pass over, and the muriatic acid gas is condensed in the second. Pure concentrated muriatic acid is a colourless liquid, which emits white vapours when exposed to the air, is intensely sour, reddens litmus paper strongly, and unites with alkalies. It com- bines with water in every proportion, and causes an increase of temperature when mixed with it, though in a much less degree than sulphuric acid. It freezes at 60° F.; and boils at 110° F., or a little higher, giving off pure muriatic acid gas in large quantity. ,• Muriatic acid is decomposed by substances which yield oxygen readily. Thus several peroxides, such as those of manganese, cobalt, and lead, effect its decomposition. The action of nitric acid is illustrative ofthe same circumstance. A mixture of nitric and muriatic acids, in the proportion of one measure of the former to two ofthe latter, has long been known under the name of Aqua regia as a solvent for gfold and platinum. When these acids are mixed together, the solution instantly becomes yellow; and on heating the mixture, pure chlorine is evolved, and the colour of the solution deepens. On continuing the heat, chlo- rine and nitrous acid vapours are disengaged. At length, the evolution of chlorine ceases, and the residual liquid is found to be a solution of muriatic and nitrous acids, which is incapable of dissolving gold. The explanation of these facts is, that nitric and muriatic acids decompose one another, giving rise to the production of water and nitrous acid, and the separation of chlorine; while muriatic and nitrous acids may be heated toge- ther without mutual decomposition. It is hence inferred, that CHLORINE. 359 the power of nitro-muriatic acid in dissolving gold, is owing to the chlorine which is liberated. Muriatic acid is distinguished by its odour, volatility, and strong acid properties. With nitrate of silver, it yields the same precipitate as chlorine; but no chloric acid is generated, be- cause the oxygen of the oxide of silver unites with the hydrogen of the muriatic acid, and the chlorine, in consequence, is entirely precipitated. Notwithstanding nitrate of silver yields the same precipitate with chlorine and muriatic acid, there is no difficulty in distinguishing between them ; for the bleaching property of the former is a sure ground of distinction. Chlorine and Carbon. Perchloride of Carbon.—For the knowledge of the compounds of chlorine and carbon, chemists are indebted to the ingenuity of Mr. Faraday. When olefiant gas is mixed with chlorine, combination takes place between them, and an oily-like liquid is generated, which consists of chlorine, carbon, and hydrogen. On exposing this liquid in a vessel full of-chlorine gas to the direct solar rays, the chlorine acts upon, and decomposes the liquid, muriatic acid is set free, and the carbon, at the moment of sepa- ration, unites with chlorine. The Perchloride of Carbon, as this compound is named by Mr. Faraday, is solid at common temperatures, has an aromatic odour approaching to that of camphor, is a non-conductor of electricity, and reflects light very powerfully. Its specific gravity is exactly double that of water. It fuses at 320° F., and after fusion it is colourless and very transparent. It boils at 360° F., and maybe distilled without change, assuming a crystalline arrangement as it condenses. It is sparingly soluble in water, but dissolves in alcohol and ether, especially by the aid of heat. It is soluble also in fixedftnd volatile oils. The perchloride of carbon burns with a red light when held in the flame of a spirit-lamp, giving out acid vapours and smoke; but the combustion ceases as soon as it is withdrawn. It burns vividly in oxygen gas. Alkalies do not act upon it; nor is it changed by the stronger acids, such as the muriatic, nitric, or sulphuric acids, even with the aid of heat. When transmitted along with hydrogen through a red-hot tube, charcoal is separat- ed, and muriatic acid gas is evolved. On passing its vapour over the peroxides of metals, such as those of mercury and copper, heated to redness, a chloride of the metal and carbonic acid are generated. Protoxides, under the same treatment, yield carbonic oxide gas and a metallic chloride. Most of the metals decom- pose it also at the temperature of ignition, uniting with the chlo- rine, and causing a deposition of charcoal. From the proportions of chlorine and olefiant gas employed in 360 CHLORINE. forming the perchloride of carbon, and from its analysis, made by passing it over the peroxide of copper at the temperature of ignition, Mr. Faraday infers that this compound consists of Chlorine . 108 . . or three atoms. Carbon . 12 . . or two atoms. Protochloride of Carbon.—When the vapour of the perchlo- ride of carbon is passed through a red-hot glass or porcelain tube, containing fragments of rock crystal to increase the extent of heated surface, a partial decomposition takes place; chlorine gas escapes, and a fluid passes over, which Mr. Faraday calls the protochloride of carbon. The protochloride of carbon is a limpid colourless fluid, which does not congeal at zero of Fahrenheit, and at 160° or 170° F. is converted into vapour. It may be distilled repeatedly without change ; but when exposed to a red heat, some of it is resolved into its elements. Its specific gravity is 1.5526. In its chemi- cal relations, it is very analogous to the perchloride of carbon. Mr. Faraday analyzed it by passing its vapour over ignited peroxide of copper, and infers from the products of its decompo- sition—carbonic acid and chloride of copper—that it is com- posed of Chlorine . 36 . . or one atom. Carbon . 6 . . or one atom. A third compound of chlorine and carbon was brought from Sweden by M. Julin, and is said to have been formed during the distillation of nitric acid from crude nitre, and sulphate of iron. It occurs in small, soft, adhesive fibres of a white colour, which have a peculiar odour, somewhat resembling spermaceti. It fuses on the application of heat, and boils at a temperature be- tween 350° and 450° F. At 250° F. it sublimes slowly, and con- denses again in the form of long needles. It i|§insoluble in water, acids, and alkalies ; but is dissolved by hot oil of turpen- tine or by alcohol, and forms acicular crystals as the solution cools. It burns with a red flame, emitting much smoke, and fumes of muriatic acid gas. The nature of this substance is shown by the following circum- stances. When its vapour is exposed to a red heat, an evolution of chlorine gas ensues, and charcoal is deposited. A similar deposition of charcoal is produced by heating it with phosphorus, iron, or tin, and a chloride is formed at the same time. Potas- sium burns vividly in its vapour, with formation of the chloride of potassium, and separation of charcoal. On detonating a mix- ture of its vapour with oxygen gas over mercury, a chloride of that metal and carbonic acid are generated. From these facts, the greater part of which were ascertained by Messrs. Phillips and Faraday, it follows that the substance brought from Sweden by CHLORINE. 361 M. Julin is a compound of chlorine and carbon; and the same able chemists conclude from their analysis that its elements are united in the proportion of Chlorine . 36, or one atom Carbon . 12, or two atoms. Chlorocarbonic Acid Gas. This compound was discovered in 1812 by Dr. John Davy, who described it under the name of phosgene gas. It is made by ex- posing a mixture of equal measures of dry chlorine and carbonic oxide gases to sunshine, when a rapid but silent combination en- sues, and they contract to one half their volume. The diffused day-light also effects their union slowly ; but they do not com- bine at all when the mixture is wholly excluded from the light. Chlorocarbonic acid gas is colourless, has a strong odour, and reddens dry litmus paper. It combines with four times its volume of ammoniacal gas, forming a white solid salt; so that is pos- sesses the characteristic property of acids. It is decomposed by contact with water. One atom of each compound undergoes decomposition; and as the hydrogen of the water unites with chlorine, and its oxygen with carbonic oxide, the products are carbonic and muriatic acids. When tin is heated in chlorocar- bonic acid gas, the chloride of tin is generated, and carbonic oxide gas is set free, which occupies exactly the same space as the chlorocarbonic acid which was employed. A similar change occurs when it is heated in contact with antimony, zinc, or ar- senic. As chlorocarbonic acid gas contains its own volume of both its constituents, it follows that 100 cubic inches of that gas, at the standard, temperature, and pressure, must weigh 105.9 grains; namely, 76.25 of chlorine added to 29.65 of carbonic oxide. Its specific gravity is therefore 3.4721 ; and it is composed, atomi- cally, of Chlorine 36 . or one atom. Carbonic oxide 14 . or one atom. Chlorine and Cyanogen. Cyanide' of Chlorine.—The existence of this compound was first noticed by Berthollet, who named it oxy-prussic acid, on the supposition of its containing prussic acid and oxygen; and it was afterwards described by Gay-Lussac, in his essay on cyano- gen, under the appellation of chloro-cyanic acid. It was pro- cured by this chemist by transmitting chlorine gas into an aque- ous solution of hydrocyanic acid until the liquid acquired bleach- ing properties, removing the excess of chlorine by agitation with mercury, and then heating the mixture, so as to expel the gaseous Z z 362 CHLORINE. cyanide of chlorine. The chemical changes which take place during this process are complicated. At first the elements of hydrocyanic acid unite with separate portions of chlorine, and give rise to muriatic acid and cyanide of chlorine; and when heat is applied, the elements of the cyanide and water re-act on each other, in consequence of which muriatic acid, ammonia, and carbonic acid are generated. Owing to this circumstance, the cyanide of chlorine was always mixed with carbonic acid, and its properties imperfectly understood. During the course of the last year M. Serullas succeeded in procuring this compound in a pure state, by exposing cyanide of mercury, in powder and moistened with water, to the action of chlorine gas contained in a well stopped phial. The vessel is kept in a dark place; and after ten or twelve hours the colour of the chloride is no longer perceptible, bichloride of mercury is found at the bottom of the phial, and its space is filled with the vapour of cyanide of chlorine. The bottle is then cooled down to zero by freezing mixtures of snow and salt, at which tempera- ture the cyanide of chlorine is solid. Some chloride of calcium is then introduced, the stopper re-placed, and the bottle kept in a moderately warm situation, in order that the moisture within may be completely absorbed. The cyanide of chlorine is then again solidified by cold, the phial completely filled with dry and cold mercury, and a bent tube adapted to its aperture by means of a cork. The solid cyanide of chlorine, which remains ad- hering to the inner surface of the phial, is converted into gas by gentle heat, and passing along the tube, is collected over mer- cury. Exposure to the direct solar rays interfere with the suc- cess of this process. Muriate of ammonia, together with a little carbonic acid, is then generated, and a yellow liquid collects, which appears to be a mixture of chloride of carbon and chloride of nitrogen. The cyanide of chlorine is solid at zero of Fahrenheit'^ ther- mometer, and in congealing crystallizes in very long slender needles. At temperatures between 5° F. 10.5° it is liquid, and also 68° under a pressure of four atmospheres; but at the com- mon pressure, and when the thermometer is above 10.5° or 11° F. it is a colourless gas. In the liquid state it is as limpid and colourless as water. It has a very offensive odour, irritates the eyes, is corrosive to the skin, and highly injurious to animal life. The cyanide of chlorine is very soluble in water, and alcohol. The former under the common pressure, and at 68° F. dissolves twenty-five times its volume. Alcohol takes up 100 times its volume, and the absorption is effected almost with the same velo- city as that of ammoniacal gas by water. These solutions are quite neutral with respect to litmus and turmeric paper, and may be kept without apparent change. The gas may even be separated CHLORINE. 363 without decomposition by boiling. The cyanide of chlorine, accordingly, does not possess the character of an acid. The changes induced by the action of alkalies do not appear to be very clearly understood. M. Serullas agrees with Gay- Lussac in stating, that if to a solution ofthe cyanide of chlorine a pure alkali is added, and then an acid, effervescence ensues from the escape of carbonic acid gas. Ammonia, and probably muriatic and hydrocyanic acid, is also generated. The statement of Gay-Lussac relative to the composition of cyanide of chlorine is confirmed by the analysis of M. Serullas. According to these chemists, it is composed of equal measures of chlorine and cyanogen gases, united without any condensa- tion; and, by weight, of 36 parts or one equivalent of chlorine, and 26 parts or one equivalent of cyanogen. Its equivalent is therefore 62, and its specific gravity, in the gaseous state, 2.1527. Hydrocarburet of Chlorine.—Chlorine acts powerfully on ole- fiant gas. When these gases are mixed together in the propor- tion of two measures ofthe former to one ofthe latter, they form a mixture which takes fire on the approach of flame, and which burns rapidly with formation of muriatic acid gas, and deposition of a large quantity of charcoal. But if the gases are allowed to remain at rest after being mixed together, a very different action ensues. The chlorine, instead of decomposing the olefiant gas, enters into direct combination with it, and a yellow liquid like oil is generated. This substance is sometimes called chloric ether; but the term hydrocarburet of chlorine, as indicative of its composition, is more appropriate. The hydrocarburet of chlorine was discovered by the Dutch chemists. To obtain it in a pure and dry state, it should be well washed with water, and then distilled from the chloride of cal- cium. As thus purified, it is a colourless volatile liquid, of a peculiar sweetish taste and ethereal odour. Its specific gravity at 45° F. is 1.2201. It boils at 152° F., and may be distilled without change. It suffers complete decomposition when its vapour is passed through a red-hot porcelain tube, being resolved into charcoal, light carburetted hydrogen, and muriatic acid §as- The composition of the hydrocarburet of chlorine is readily in- ferred from the fact, that in whatever proportions olefiant gas and chlorine may be mixed together, they always unite in equal volumes. Consequently, they combine by weight according to the ratio of their densities, so that the hydrocarburet of chlorine consists of Chlorine . 2.5 . 36 one atom. Olefiant gas , 0.9722 14 one atom. 3.4722 T>0 364 CHLORINE. and its atomic weight is 50. This estimate is confirmed by the analysis of Robiquet and Colin. The hydrocarburet of chlorine forms a very dense vapour, its specfic gravity, according to Gay-Lussac, being 3.4434. This is so near the united densities of chlorine and olefiant gas, as to leave no doubt that the vapour contains its own volume of each of its constituents. Dr. Henry has demonstrated that light is not essential to the action of chlorine on olefiant gas. On this he has founded an ingenious and perfectly efficacious method of separating olefiant gas from light carburetted hydrogen and carbonic oxide gases, neither of which is acted on by chlorine unless light is present. Chloride of Boron, is a gaseous substance, made by passing dry chlorine over an incandescent mixture of charcoal and bo- racic acid. It must be collected over mercury. Chloride of Silicon, is formed by heating silicon in chlorine; it is a yellow volatile liquid, of a very penetrating odour, resem- bling that of cyanogen. Chlorine and Phosphorus. Chloride of Phosphorus.—There are two definite compounds of chlorine and phosphorus. When phosphorus is introduced into a jar of dry chlorine, it inflames, and a white matter collects on the inside ofthe vessel, which is the perchloride of phosphorus. It is very volatile, a temperature much below 212° F. being suf- ficient to convert it into vapour. Under pressure it may be fused, and yields transparent prismatic crystals in cooling. Water, and the perchloride ^of phosphorus mutually decom- pose each other; and the sole products are muriatic and phos- phoric acids. The nature of the change will be apparent, as soon as the composition of the perchloride is known. Sir H. Davy finds that one grain of phosphorus unites with six of chlo- rine, when it is burned in that gas ; and hence it follows that the perchloride consists of Chlorine . 72, or two atoms. Phosphorus . 12, or one atom. Consequently, for every atom of the perchloride of phosphorus, two atoms of water suffer decomposition. The two atoms of hy- drogen unite with the two atoms of chlorine, and form two atoms of muriatic acid; while the two atoms of oxygen combine with the one atom of phosphorus, and convert it into phosphoric acid. The Protochloride of Phosphorus may be made either by heat- ing the perchloride with phosphorus, or by passing the vapour of phosphorus over corrosive sublimate, contained in a glass tube. It is a clear liquid like water, which is composed, according to Sir H. Davy, of thirty-six parts, or one atom of chlorine, and twelve parts, or one atom of phosphorus. Its specific gravity is CHLORINE. 365 1.45. It emits acid fumes when exposed to the air, owing to the decomposition of watery vapour; but when pure, it does not redden dry litmus paper. On mixing it with water, mutual de- composition ensues, heat is evolved, and a solution of muriatic and phosphoric acids is obtained. In this case, one atom of water is decomposed for each atom of the protochloride. Chlorine and Sulphur. The Chloride of Sulphur was discovered in 1804, by Dr. Thom- son, and was afterwards examined by Berthollet. It is most conveniently prepared by passing a current of chlorine gas over flowers of sulphur, gently heated. Direct combination takes place, and the product is obtained under the form of a liquid which appears red by reflected, and yellowish-green by trans- mitted, light. Its density is 1.6. It is volatile below 200° F. and condenses again without change in cooling. It emits acrid fumes when exposed to the air, which irritate the eyes powerfully, and have an odour somewhat resembling sea-weed, but much stronger. Dry litmus paper is not reddened by it, nor does it unite with alkalies. It acts with energy on water ;—mutual de- composition ensues, the water becomes cloudy from deposition of sulphur, and a solution is obtained, in which muriatic, sul- phurous, and sulphuric acids may be detected. Similar pheno- mena ensue when it is mixed with alcohol or ether. Sir H. Davy concludes from his experiments, that the chloride of sulphur is composed of thirty parts of sulphur, and 68.4 of chlorine. This proportion leaves little doubt of its being a com- pound of 36, or one atom of chlorine, and of 16, or one atom of sulphur. Chloride of Selenium.—Selenium absorbs chlorine gas, be- comes hot, and forms a brown liquid, which, by an additional quantity of chlorine, is converted into a white solid mass. This is stated by Berzelius to be a compound of muriatic and selenic acids, but it is probably composed of chloride of selenium and the latter acid. Chloride of Tellurium, a white semi-transparent compound, which is decomposed when added to water. It consists, accord- ing to Sir H. Davy, of 100 tellurium -f 90.5 chlorine. Chloride of Arsenic.—When arsenic in powder is thrown into ajar full of dry chlorine gas, it takes fire, and a chloride of arse- nic is generated ; the same compound may be formed by dis- tilling a mixture of six parts of corrosive sublimate with one of arsenic. It is a colourless volatile liquid, which fumes strongly on exposure to the air, hence called fuming liquor of arsenic, and is resolved by water into muriatic and arsenious acids. Ac- cording to Dr. J. Davy, it is composed of 60.48 parts of chlorine 366 CHLORINE. and 39.52 of arsenic, a proportion which does not correspond with the laws of combination, and, therefore, is doubtless inexact. The following process has been lately proposed by M. Dumas. Into a tubulated retort is introduced a mixture of arsenious acid, with ten times its weight of concentrated sulphuric acid ; and after raising its temperature to near 212°, fragments of sea-salt are thrown in by the tubular. If the salt is added in successive small portions, scarcely any muriatic acid gas is evolved, and the pure chloride may be collected in cooled vessels. Towards the end of the process, a little water frequently passes over with the chloride, but this hydrated portion does not mix with the anhy- drous chloride, but swims on its surface. The hydrate may be decomposed, and a pure chloride obtained, by distilling the mixture from a sufficient quantity of concentrated sulphuric acid. M. Dumas considers this compound a proto-chloride of arsenic, so that it is probably different from that obtained by means of corrosive sublimate. Metallic Chlorides. Chlorine has a powerful affinity for metallic substances. It combines readily with most metals at common temperatures, and the action is in many instances so violent as to be accompanied with the evolution of light. For example, when powdered zinc, arsenic, or antimony, is thrown into a jar of chlorine gas, the metal is instantly inflamed. The attraction of chlorine for metals even surpasses that of oxygen. Thus, when chlorine is brought into contact at a red heat with pure lime, magnesia, baryta, strontia, potassa, or soda, oxygen is emitted, and a chloride of the metal is generated, the elements of which are so strongly united, that no temperature hitherto tried can separate them. All other metallic oxides are, with few exceptions, acted on in the same manner by chlorine, and, in some cases, the change takes place below ignition. All the metallic chlorides are solid at the common temperature except the bichlorides of tin and of arsenic, which are liquid. They are fusible by heat, assume a crystalline texture in cooling, and, under favourable circumstances, crystallize with regularity. Several of them, such as the chlorides of tin, arsenic, antimony, and mercury, are volatile, and may be sublimed without change. They are for the most part colourless, do not possess the metallic lustre, and have the aspect of salt. Two of the chlorides are insoluble in water, namely, the chloride of silver, and the pro- tochloride of mercury : all the others are more or less soluble in that fluid. Two only of the metallic chlorides, those namely of gold and platinum, are decomposable by heat. All the chlorides of the common metals are decomposed at a red heat by hydrogen gas, CHLORINE. 367 muriatic acid being disengaged while the metal is set free. Pure charcoal does not effect their decomposition; but if moisture be present at the same time, muriatic and carbonic acid gases are formed, and the metal remains. They resist the action of anhydrous sulphuric acid ; but all the chlorides, excepting those of silver and mercury, are readily decomposed by hydrated sulphuric acid, with disengagement of muriatic acid gas. The change is accompanied with the decom- position of water, the hydrogen of which combines with chlorine, and its oxygen with the metal. All chlorides, when in solution, may be recognised by their yielding with nitrate of silver a white precipitate, which is chloride of silver. Metallic chlorides may, in most cases, be formed by direct ac- tion of chlorine on the pure metals. They are also frequently procured by evaporating a solution of the muriate of a metallic oxide to dryness, and applying heat so long as any water is expell- ed. Metallic chlorides are often deposited from such solutions by crystallization. Chlorine manifests a feeble affinity for metallic oxides. No combination of the kind can occur at a red heat, and no chloride of a metallic oxide can be heated to redness without decom- position. Such compounds can only be formed at low tempera- tures ; and they are possessed of little permanency. It is well known that chlorine may combine, under favourable circum- stances, with the alkalies and alkaline earths ; and Mr. Grouvelle has succeeded in making it unite with magnesia, and the oxides of zinc, copper, and iron. Of these chlorides, that of potassa may be taken as an example. If chlorine is conducted into a dilute and cold solution of pure potassa, the chloride of that alkali will be produced; but the affinity which gives rise to its formation is not sufficient for rendering it permanent. It is destroyed by most substances that act on either of its constituents. Thus,':the addi- tion of an acid has this effect by combining with the alkali, and hence the carbonic acid of the air tends to decompose it. Ani- mal or vegetable colouring matters are fatal to it, by giving chlorine an opportunity to exert its bleaching power; and, in- deed, the colour is removed by the chloride of potassa as readily as by a solution of chlorine in pure water. It is also destroyed by the action of heat; nor can its solution be concentrated with- out decomposition; for, in either case, the muriatic and chloric acids are generated. Chlorides of Tin.—Tin unites in two proportions with chlo- rine, and the researches of Dr. Davy leave no doubt of these com- pounds being analogous in composition to the oxide of tin. The protochloride, which consists of one atom of tin and one atom of chlorine, may be made either by evaporating the muriate of the protoxide to dryness and fusing the residue in a close vessel, or by heating an amalgam of tin with calomel. It is a 368 CHLORINE. gray solid substance, of a resinous lustre, which fuses at a heat below redness, and when heated in chlorine gas is converted into the bichloride. The bichloride, composed of one atom of tin and two atoms of chlorine, may be prepared either by heating metallic tin or the protochloride in an atmosphere of chlorine, or by distilling a mixture of eight parts of tin in powder with twenty-four of cor- rosive sublimate. It is a colourless volatile liquid, which emits copious white fumes, when exposed to the atmosphere. It has very strong attraction for water, and is converted by that fluid into the permuriate. It was formerly called the fuming liquor of Libavius. Chloride of Potassium.—Potassium takes fire spontaneously in an atmosphere of chlorine, and burns with greater brilliancy than in oxygen gas. This chloride is also generated when potassium is heated in muriatic acid gas, hydrogen being evolved at the same time. It is the residue of the decomposition of the chlorate of potassa by heat; and it is obtained in the form of colourless cubic crystals, when a solution of the muriate of potassa evapo- rates spontaneously. The chloride of potassium has a saline and rather bitter taste. It requires three parts of water at 60° F. for solution, and is rather more soluble in hot water. Its solution contains the muriate of potassa. It is composed of 36 parts or one atom of chlorine, and 40 parts or one atom of potassium. Chloride of Sodium.—This compound may be formed directly by burning sodium in chlorine, or by heating it in muriatic acid gas. It is deposited in crystals, when a solution of muriate of soda is evaporated; for this salt, like muriate of potassa, exists only while in solution, and is converted into a chloride during the act of crystallizing. Hence, sea water, the chief ingredient of which is muriate of soda, yields chloride of sodium by evapora- tion ; and from this source is derived most of the different kinds of common salt, such as fishery salt, stoved salt, and bay salt, sub- stances essentially the same, and between which the sole differ- ence depends on the mode of preparation. Chloride of sodium is known likewise as a natural product, under the name of rock or mineral salt. The common varieties of salt, of which rock and bay salt are the purest, always contain small quantities of sulphate of mag- nesia and lime, and muriate of magnesia. These earths may be precipitated as carbonates, by boiling a solution of salt for a few minutes with a slight excess of carbonate of soda, filtering the liquid, and neutralizing with muriatic acid. On evaporating this solution rapidly, chloride of sodium crystallizes in holiow four-sid- ed pyramids; but it occurs in regular cubic crystals, when the solution is allowed to evaporate spontaneously. These crystals contain no water of crystallization, but decrepitate remarkably CHLORINE. 369 when heated, owing to the expansion of water mechanically con- fined within them. Pure chloride of sodium has an agreeably saline taste. It fuses at a red heat, and becomes a transparent brittle mass on cooling. It deliquesces slightly in a moist atmosphere, but un- dergoes no change when the air is dry. In pure alcohol it is insoluble. It requires twice and a half its weight of water at 60° F. for solution, and its solubility is not increased by heat. Like the soluble chlorides in general, it passes into a muriate while in the act of dissolving. Sulphuric acid decomposes it with evolution of muriatic acid gas, and formation of sulphate of soda. In composition it is analogous to the chloride of potas- sium, consisting of one equivalent of chlorine, and one of sodium. The uses of chloride of sodium are well known. Besides its employment in seasoning food, and in preserving meat from pu- trefaction, a property which it possesses in a high degree, it is used for various purposes in the arts, especially in the formation of muriatic acid and chloride of lime. Chloride of Soda.—This compound has lately acquired the attention of scientific men under the name of Labarraque's dis- infecting soda liquid, which was announced by M. Labarraque as a compound of chlorine and soda, analogous to the well known bleaching powder, chloride of lime. The nature of this liquid has been since investigated by Mr. Phillips and Mr. Faraday, especially by the latter; and it appears from the experiments of this chemist, that while chloride of soda is the active ingredient, its properties are considerably modified by the presence of car- bonate of soda. Pure chloride of soda is easily prepared, by transmitting to saturation a current of chlorine gas into a cold and rather dilute solution of caustic soda. Common carbonate of soda may be substituted for the pure alkali; but considerable excess of chlo- rine must then be employed in order to displace the whole of the carbonic acid. It may also be formed easily, cheaply, and of uniform strength, by decomposing chloride of lime with car- bonate of soda, as proposed by M. Payen. However prepared, its properties are the same. As its constituents are retained in combination by a feeble affinity, the compound is easily destroy- ed. It emits an odour of chlorine, and possesses the bleaching properties of that substance in a very high degree. When kept in open vessels, it is slowly decomposed by the carbonic acid of the atmosphere with evolution of chlorine; and the change is more rapid in air charged with putrid effluvia, because the car- bonic acid produced during putrefaction promotes the decompo- sition of the chloride. On this, as was proved by M. Gaultier de Claubry, depends the efficacy of an alkaline chloride in puri- fying air loaded with putrescent exhalations. When the solu- tion is heated to the boiling point, or concentrated by means of 3 A 370 CHLORINE. heat, the chloride undergoes a change previously explained, and is converted into chlorate and muriate of soda. Chloride of soda may be employed in bleaching, and for. all purposes to which chlorine gas or its solution was formerly ap- plied. It is now much used in removing the offensive odour arising from drains, sewers, or all kinds of animal matter in a sfate of putrefaction. Bodies disinterred for the purpose of ju- dicial inquiry, or parts of the body advanced in putrefaction, may by its means be rendered fit for examination : and it is em- ployed in surgical practice for destroying the fetor of malignant ulcers. Clothes worn by persons during pestilential diseases are disinfected by being washed with this compound. It is also used in fumigating the chambers of the sick; for the disengagement of chlorine is so gradual, that it does not prove injurious or an- noying to the patient. In all these instances chlorine appears actually to decompose noxious exhalations by uniting with the elements of which they consist, and especially with hydrogen. In preparing the disinfecting liquid of Labarraque, it is neces- sary to be exact in the proportion of the ingredients employed. The quantity used by Mr. Faraday, founded on the directions of Labarraque, are the following : He dissolved 2800 grains of crys- tallized carbonate of soda in 1.28 pints of water, and through the solution, contained in a Woulfe's apparatus, was transmitted the chlorine evolved from a mixture of 967 grains of sea-salt and 750 grains of peroxide of manganese, when acted on by 960 grains of sulphuric acid, diluted with 750 grains of water. In order to re- move any accompanying muriatic acid gas, the chlorine before reaching the soda was conducted through pure water, by which means nearly a third part was dissolved, but the remaining two- thirds were fully sufficient for the purpose. The gas was readily absorbed by the solution, and from the beginning to the end of the process, not a particle of carbonic acid gas was evolved; whereas, by employing an excess of chlorine, the carbonic acid may be entirely expelled. The solution thus prepared has all the characters of Labar- raque's soda liquid. Its colour is a pale yellow, and it has but a slight odour of chlorine. Its taste is at first sharp, saline, and scarcely at all alkaline; but it produces a persisting biting effect upon the tongue. It first reddens and then destroys the colour of turmeric paper. When boiled it does not give out chlorine, nor is its bleaching power perceptibly impaired ; and if carefully evaporated, it yields a mass of damp crystals, which, when re- dissolved, bleach almost as powerfully as the original liquid. When rapidly evaporated to dryness, the residue contains scarcely any chlorate of soda or chloride of sodium; but it has neverthe- less lost more than half of its bleaching power, and therefore chlorine must have been evolved during the evaporation. The solution deteriorates gradually by keeping, chloric acid and CHLORINE. 371 chloride of sodium being generated. When allowed to evapo- rate spontaneously, chldrine gas is gradually evolved, and crys- tals of carbonate of soda remain. In some respects the nature of this liquid is still obscure; but, from the preceding facts, drawn from the experiment of Faraday, two points seem to be established. First, that the liquid contains chlorine, carbonic acid, and soda. Secondly, that the chlorine is not simply combined either with water or soda ; for by boiling, the gas is neither expelled as it would be from an aqueous solu- tion, nor does the liquid yield chloric acid and chloride of sodi- um as when pure chloride of soda is heated. It may perhaps be regarded as a compound of chloride of sodium and bi-carbonate of soda. Its production may be conceived by supposing, that when chlorine is introduced in due quantity into a solution of carbonate of soda, it combines with half of the alkali, while the remainder with all the carbonic acid constitutes bicarbonate of soda. Should this salt unite, though by a feeble affinity, with chloride of soda, both may thence derive a degree of perma- nence, which neither singly possesses. During spontaneous evaporation, the tendency of the common carbonate to crystal- lize may occasion its re-production, arid the disengagement of chlorine. These remarks, however, are merely speculative. Chloride of Lithium is obtained by evaporating the muriate to dryness, and fusing it; it is a semi-transparent substance. It evidently differs from the chlorides of potassium and sodium, in being extremely deliquescent; in being soluble in alcohol; in being decomposed when strongly heated in the open air, when it loses chlorine, absorbs oxygen, and becomes highly alkaline ; in being very difficultly crystallizable ; and in tinging the flame of alcohol of a red colour. Chloride of Barium.—This compound is generated when chlo- rine gas is conducted over baryta at a red heat, and oxygen gas is disengaged. It may also be formed by heating to redness the crystallized muriate of baryta. It consists of one atom of each of its constituents. It requires five times its weight of water at 60° F. for solution, and is much more soluble in boiling water. The Chloride of Strontium is formed under precisely the same circumstances as the chloride of barium, and its composition is analogous. It is exceedingly soluble in boiling water, and re- quires twice its weight of water at 60° F. for solution. It is readily soluble in alcohol. Chloride of Calcium.—The chloride of calcium is formed in the same manner as the chloride of strontium. In decomposing the muriate of lime by heat, a little muriatic acid is sometimes expelled as well as water. The chloride of calcium is soluble in alcohol, and deliquesces rapidly on exposure to the atmosphere. On account of its strong affinity for water, it is much employed to deprive gases and other substances of their moisture. For a 372 CHLORINE. like reason, it may be used for forming frigorific mixtures with snow ; but for this purpose the crystallized muriate of lime, which contains six atoms of water of crystallization is far preferable. The chloride of calcium contains one atom of each of its ele- ments. Chloride of Lime.—This compound commonly called oxymu- riate of lime, or bleaching powder, is prepared by exposing thin strata of recently slaked lime in fine powder to an* atmosphere of chlorine. The gas is absorbed in large quantity, and combines directly with the lime. The chloride of lime is a dry white powder, which smells faintly of chlorine, and has a strong taste. It dissolves partially in wa- ter, and the solution possesses powerful bleaching properties, and contains both chlorine and lime ; while the undissolved por- tion is hydrate of lime, retaining a small quantity of chlorine. The aqueous solution, when exposed to the atmosphere, is gra- dually decomposed ; chlorine is set free, and carbonate of lime is generated. On boiling the liquid, muriatic, and perhaps chloric acids are formed ; and by long keeping, the dry chloride appears to undergo a similar change, at least muriatic acid is produced in large quantity. The chloride of lime is also decomposed by a strong heat. At first, chlorine is evolved ; but pure oxygen is afterwards disengaged, and chloride of calcium remains in the retort. The composition of the chloride of lime was first carefully in- vestigated by Mr. Dalton, and it has since been analyzed by Dr. Thomson, M. Welter, and Dr. Ure. The three first mentioned che- mists infer from their researches that the bleaching powder is a hydrated sub-chloride or di-chloride of lime, in which 36 parts or one atom of chlorine are united with 56 parts or two atoms of lime. They are also of opinion that, on mixing the sub-chloride with water, a real chloride is dissolved, and one atom of lime is separated. Dr. Ure, on the contrary, denies that the bleaching powder is a sub-chloride ; and maintains, according to the result of his own analysis, that the elements of this compound do not constitute a regular atomic combination. He found that the quantity of chlorine absorbed by hydrate of lime is variable, de- pending not only on the pressure and degree of exposure, but on the quantity of water which is present. The following is the result of his analysis of three specimens, No. 1 being good commercial bleaching powder, No. 2 made by himself with pure proto-hydrate of lime, and No. 3 prepared by himself with lime containing more water than in No. 2. No. 1. No. 2. No. 3. Chlorine 23 - 40.32 - 39.5 Lime 46 - 45.40 - 39.9 Water 31 - 14.28 - 20.6 100 100 100 CHLORINE. 373 The e xperiments of Dr. Ure appear to have been made with great care, and his results to be entitled to equal if not greater confidence than those of the other chemists. Upon the whole it is probable, that common commercial bleaching powder con- sists of chloride of lime, a compound of 36 parts or one equiva- lent of chlorine, and 28 parts or one equivalentof lime ; and that this, the essential ingredient, is mixed with variable quantities of hydrate of lime. Several methods have been proposed for estimating the value of different specimens of the chloride of lime. Perhaps the most convenient for the artist is that of Welter, which consists in as- certaining the power ofthe bleaching liquid to deprive a solution of indigo of known strength of its colour. For analytical pur- poses, the best method is to decompose the chloride of lime, con- fined in a glass tube over mercury, by means of muriatic acid. The muriate of lime is generated, and the chlorine being set free, its quantity may easily be measured. Chloride of Magnesium is formed by decomposing the muriate of magnesia by heat; but it is apt to lose a portion of muriatic acid during the process. It is very deliquescent, and is soluble in alcohol. It is composed of one atom of chlorine, and one atom of magnesium. Chlorides of Antimony.—When antimony in powder is thrown into a jar of chlorine gas, combustion ensues, and the protochlo- ride of antimony is generated. The same compound may be formed by distilling a mixture of antimony with about twice and half its weight of corrosive sublimate, when the volatile chloride of antimony passes over into the recipient, and metallic mercury remains in the retort. At common temperatures it is a soft solid, thence called butter of antimony, which is liquefied by gentle heat, and crystallizes on cooling. It deliquesces on exposure to the air; and when mixed with water, is converted into muriatic acid, and the protoxide of antimony. If a large quantity of water is employed, the whole of the oxide subsides as the sub- muriate. The bichloride is generated by passing dry chlorine gas over heated metallic antimony. It is a transparent volatile liquid, which emits fumes on exposure to the air. Mixed with water, it is converted into muriatic acid, and the hydrated peroxide which subsides. It contains twice as much chlorine as the protochlo- ride, or is composed of one atom of antimony, and two atoms of chlorine. Dr. Thomson, in his " First Principles," has described another chloride of antimony, composed of one atom of chlorine and two atoms ofthe metal. It is, therefore, a dichloride. Chloride of Chromium is formed by the action of fuming sul- phuric acid on a mixture of chromate of lead and chloride of sodium. It is a red coloured gas which may be collected in glass 374 CHLORINE. vessels over mercury. It is decomposed instantly by water, and yields a solution of muriatic and chromic acids. It may be re- garded as a compound of muriatic and chromic acids, or of chlorine and chromium. Chloride of Molybdenum.—Berzelius has succeeded in form- ing three chlorides of molybdenum, the composition of which is analogous to the compounds of this metal with oxygen. Chloride of Manganese.—This compound is best prepared by evaporating a solution of muriate of manganese to dryness by a gentle heat, and heating the residue to redness in a glass tube, while a current of muriatic acid gas is transmitted through it. The heat of a spirit-lamp is sufficient for the purpose. It fuses readily at a red heat, and forms a pink-coloured lamellated mass on cooling. It is deliquescent, and of course very soluble in water, being converted by that fluid, with evolution of caloric, into muriate of manganese. It is composed of 28 parts or one equivalent of manganese, and 36 parts or one equivalent of chlorine. A new chloride of manganese, remarkable for its volatility, has lately been described by M. Dumas. It is readily formed by putting a solution of manganesic into strong sulphuric acid, and then adding fused sea-salt. The muriatic and manganesic acids mutually decompose each other; water and perchloride of man- ganese are generated, and the latter escapes in the form of vapour. The best mode of preparation is to form the common green mineral chameleon, and convert it into red by means of sulphuric acid. The solution, when evaporated, leaves a residue of sulphate and manganesiate of potash. This mixture, treated by strong sulphuric acid, yields a solution of manganesic acid, into which are added small fragments of sea-salt, as long as coloured vapour continues to be evolved. The new chloride, when first formed, appears as a vapour of a copper or greenish colour; but on traversing a glass tube cooled to 5° or —4° F., it is condensed into a greenish brown coloured liquid. When generated in a capacious tube, its vapour gradu- ally displaces the air, and soon fills the tube. If it is then poured into a large flask, the sides of which are moist, the colour ofthe vapour changes instantly on coming into contact with the mois- ture, a dense smoke of a pretty rose tint appears, and muriatic and manganesic acids are generated. From this it is manifest, that the new chloride is proportional to manganesic acid; that is, when its chlorine unites with hydrogen, the oxygen required to constitute water with that hydrogen exactly suffices for form- ing manganesic acid with the manganese. It is hence supposed to consist of 28 parts or one equivalent of manganese, and 144 art s or four equivalents of chlorine. Chloride of Columbium.—When columbium is heated in chlorine gas, it takes fire and burns actively, yielding a yellow CHLORINE. 375 vapour, which condenses in the cold parts of the apparatus in the form of a white powder, with a tint of yellow. Its texture is not in 'the least crystalline. By contact with water, it is con- verted, with a hissing noise and increase of temperature, into columbic and muriatic acids. Chlorides of Tungsten.—According to Wohler, tungsten and chlorine unite in three proportions. The perchloride is gene- rated by heating the oxide of tungsten in chlorine gas. The action is attended with the appearance of combustion, dense fumes arise, and a thick sublimate is obtained in the form of white scales, like native boracic acid. It is volatile at a low temperature, without previous fusion. It is converted by the action of water into tungstic and muriatic acids, and must there- fore, in composition, be proportional to tungstic acid; that is, it consists of 96 parts or one equivalent of tungsten, and 108 parts or three equivalents of chlorine. When metallic tungsten is heated in chlorine gas, it takes fire, and yields the deutochloride. The compound appears in the form of delicate fine needles, of a deep red colour, resem- bling wool, but more frequently as a deep red fused mass, which has the brilliant fracture of cinnabar. When heated, it fuses, boils, and yields a red vapour. By water, it is changed into muriatic acid and oxide of tungsten. It is entirely dissolved by a solution of pure potassa, with disengagement of hydrogen gas, yielding muriate and tungstate of potassa. A similar change is produced by ammonia, except that some oxide of tungsten is left undissolved. Another chloride has been described by Wohler. It is formed at the same time as the first; and though it is converted into muriatic and tungstic acids by the action of water, and would thus seem identical with the perchloride in the proportion of its elements, its other properties are nevertheless different. It is the most beautiful of all these compounds, existing in long transparent crystals, of a fine red colour. It is very fusible and volatile, and its vapour is red like that of nitrous acid. The dif- ference between this compound and the chloride first described, has not yet been discovered. Chloride of Titanium.—This substance was first prepared in the year 1824, by Mr. George, of Leeds, by transmitting dry chlorine gas over metallic titanium at a red heat. At common temperatures, it is a transparent colourless fluid, of considerable specific gravity, boils violently at a temperature a little above 212° F., and condenses again without change. In open vessels it is attacked by the moisture of the atmosphere, and emits dense white fumes of pungent odour, similar to that of chlorine, but not so offensive. On adding a few drops of water to a few drops of the liquid, a very rapid, almost explosive, disengagement of chlorine gas ensues, attended with considerable increase^>f tem- 376 CHLORINE. perature; and if the water is not in excess, a solid residue is obtained. This substance is deliquescent, soluble in water; and its solution possesses all the characters of muriate of titanium. The composition of this chloride has not been satisfactorily established ; but it contains more chlorine than is capable of uniting with the hydrogen derived from water, wjien the oxygen of that fluid converts titanium into the peroxide. Chlorides of Gold.—On concentrating the solution of gold to a sufficient extent by evaporation, the perchloride may be obtain- ed in red prismatic crystals, which become brown when brought to perfect dryness. It deliquesces on exposure to the air, and is dissolved readily by water without residue. At a temperature far below that of redness, it is converted, with evolution of two-thirds of its chlorine, into the yellow insoluble protochloride, from which the chloride is entirely expelled by a red heat. This pro- tochloride is converted, by being boiled in water, into the soluble perchloride and metallic gold. The composition of the chlorides of gold was investigted by Berzelius and Pelletier; but the results of their analyses are so very discordant, that no satisfactory conclusion can be drawn from them. The solution of gold is decomposed by substances which have a strong affinity for oxygen. On adding to it the protosulphate of iron dissolved in water, the iron is oxidized to a maximum, and a copious brown precipitate subsides, which is metallic gold in a state of very minute division.—This precipitate, when duly wash- ed with dilute muriatic acid, in order to separate adhering iron, is gold in a state of perfect purity. A similar reduction is effected by most of the metals, and by sulphurous and phosphorous acids. When a piece of charcoal is immersed in the solution of gold, and exposed to the direct solar rays, its surface acquires a coating of metallic gold ; and ribands may be gilded by moistening them with a dilute solution of gold, and exposing them to a current of hydrogen or phosphuretted hydrogen gas. When a strong aque- ous solution of gold is shaken in a phial with an equal volume of pure ether, two fluids result, the lighter of which is an ethereal solution of gold. From this liquid flakes of metal are deposited on standing, especially by exposure to light and substances mois- tened with it receive a coating of metallic gold. When the protomuriate of tin is added to a dilute aqueous so- lution of gold, a purple coloured precipitate, called the purple of Cassius, is thrown down, which is the substance employed in painting on porcelain for giving a pink colour. It appears to be a compound ofthe protoxide of tin and the purple oxide of gold, in which the former is supposed to act as an acid. Chloride of Lead.—This compound, sometimes called horn lead, or plumbum corneum, is slowly formed by the action of CHLORINE. 377 chlorine gas on thin plates of lead, and may be obtained more easily by adding muriatic acid or a solution of sea-salt to the acetate or nitrate of lead, dissolved in water. This chloride dissolves to a considerable extent in hot water, especially when acidulated with muriatic acid. In solution, it is most probably a muriate of the oxide of lead; but in cooling, the chloride sepa- rates in the form of small acicular crystals, of a white colour. It fuses at a temperature below redness, and forms, as it cools, a semi-transparent horny mass. It bears a full red heat in close vessels, without, subliming. According to the analysis of Dr. Davy, it is composed of one atom of lead, and one atom of chlorine. The pigment called mineral or patent yellow, is a compound of the chloride and protoxide of lead. It is prepared for the purposes of the arts, by the action of moistened sea-salt on litharge, by which means a portion ofthe protoxide is converted into chloride of lead, and then fusing the mixture. Soda is set free during this process, and is converted into a carbonate by absorbing carbonic acid from the atmosphere. Chlorides of Iron.—Chlorine unites in two proportions with iron, forming compounds which were described in 1812, by Dr. John Davy. The protochloride is made by evaporating a solu- tion of the protomuriate to dryness, and heating it to redness in a glass tube, from which the air is excluded. The resulting chloride has a gray colour, a lamellated texture, and metallic lustre. It is composed of one atom of each element, and is con- verted by water into the protomuriate of iron. The perchloride is formed by burning iron wire in an atmos- phere of chlorine. It is of a bright yellowish-brown colour, crys- tallizes in small iridescent plates, and is volatile at a temperature a little above 212° F. It consists of one atom of iron and an atom and a half of chlorine, and forms with water a red-coloured solution, which is the permuriate of iron. Chlorides of Copper.—-The chlorides of copper have been minutely studied by Proust and Dr. Davy. From the able re- searches of these chemists, and especially of the latter, there is no doubt that the two chlorides are proportional to the two oxides of copper, or that they are composed of Co/ifier. Chloride. Protochloride 64 . 36 Perchloride . 64 . 72 When copper filings are introduced into an atmosphere of chlorine gas, the metal takes fire spontaneously, and both the chlorides are generated. 3 B 378 CHLORINE. The protochloride may be conveniently prepared by heating copper filings with twice their weight of corrosive sublimate. In this way it was originally made by Mr. Boyle, who termed it resin of copper, from its resemblance to common resin. Proust pro- cured it by the action of the protomuriate of tin on the permu- riate of copper; and also by decomposing the permuriate by heat. He gave it the name of white muriate of copper. The protochloride of copper is fusible at a heat just below red- ness, and bears a red heat, in close vessels without subliming. It is insoluble in water, but dissolves in muriatic acid, and is pre- cipitated unchanged by water as a white powder. Its colour varies with the mode of preparation, being white, yellow, or dark brown. The perchloride is best formed by exposing the permuriate of copper to a temperature not exceeding 400° F. It is a pulveru- lent substance, of a yellow colour, deliquesces on exposure to the air, and is re-converted by water into the permuriate. It parts with half its chlorine when strongly heated, and the protochloride of copper is generated. Chlorides of Mercury.—Mercury unites with chlorine in two proportions; and the researches of Sir H. Davy and Mr. Chene- vix, leave no doubt that these compounds are analagous in com- position to the oxides of mercury, that is, are composed of Mercury. Chlorine. Protochloride . 200 36 = 236 Bichloride . 200 72 = 272 Bichloride.—When mercury is heated in chlorine gas, it takes fire, and burns with a pale red flame, forming the well-known medicinal preparation and virulent poison, corrosive sublimate, or bichloride of mercury. It is prepared for medical purposes by subliming a mixture ofthe bisulphate ofthe peroxide of mer- cury, with the chloride of sodium or sea-salt. The exact quan- tities required for mutual decomposition, are 296 parts, or one atom of the bisulphate, to 120 parts, or two atoms of the chlo- ride. Thus, One atom ofthe bisulphate Two atoms ofthe chloride of mercury, consists of of sodium, consists of Sulphuric acid . 80 or two atoms. 72 or two atoms of chlorine Peroxide of mercury 216 or one atom. 48 or two atoms of sodium 296 120 and the products are, CHLORINE. 379 One atom ofthe bichloride of Two atoms ofthe sulphate mercury, consisting of of soda, consisting of Mercury . 200 or one atom. Sulphuric acid 80 or two atoms. Chlorine . 72 or two atoms. Soda - 64 or two atoms. 272 144 The bichloride of mercury, when obtained by sublimation, is a semi-transparent colourless substance, of a crystalline texture. It has an acrid burning taste, and leaves a nauseous metallic flavour on the tongue. Its specific gravity is 5.2. It sublimes at a red heat without change. It requires twenty times its weight of cold, and only twice its weight of boiling water for solution, and is deposited from the latter, as it cools, in the form of prismatic crystals. Strong alcohol and ether dissolve it in the same pro- portion as boiling water; and it is soluble in half its weight of concentrated muriatic acid at the temperature of 70° F. With the muriates of ammonia, potassa, soda, and several other bases, it enters into combination, forming double salts, which are more soluble than the chloride itself. The bichloride of mercury is probably converted at the moment of being dissolved into a muriate of the peroxide; at least this view may safely be admitted, since alkalies and other re-agents act upon it precisely in the same manner as on other per-salts of mercury. Its aqueous solution is gradually decomposed by light, calomel being deposited. The presence of mercury in a fluid supposed to contain corro- sive sublimate may be detected by concentrating and digesting it with an excess of pure potassa. The oxide of mercury, which subsides, is then sublimed in a small glass tube by means of a spirit-lamp, and obtained in the form of metallic globules. Dr. Christison supposes that this and other processes recommended by medical jurists for the detection of corrosive sublimate in mixed fluids, are not altogether satisfactory. He is at present engaged in an inquiry on the subject, and will soon make known the result of his researches. A very elegant method of detecting the presence of mercury is to place a drop ofthe suspected liquid on polished gold, and to touch the moistened surface with a piece of iron wire or the point of a pen-knife, when the part touched instantly becomes white, owing to the formation of an amalgam of gold. This pro- cess was originally suggested by Mr. Sylvester, and has since been simplefied by Dr. Paris. Many animal and vegetable solutions convert the bichloride of mercury into calomel, a portion of muriatic acid being set free at the same time. Some substances effect this change slowly, while others, and especially albumen, produce it in an instant. Thus, when a solution of corrosive sublimate is mixed with, albu- men, a white flocculent precipitate subsides, which M. Orfila has 380 CHLORINE. shown to be a compound of calomel and albumen, and which he has proved experimentally to be inert. Consequently, a solution ofthe white of eggs is an antidote to poisoning by corrosive sub- limate. Protochloride.—The protochloride of mercury, or calomel, is always generated when chlorine comes in contact with mercury at common temperatures. It may be made by precipitation, by mixing muriatic acid or any soluble muriate with a solution of the protonitrate of mercury. It is more commonly prepared by sublimation. This is conveniently done by mixing 272 parts or one atom of the bichloride with 200 parts or one atom of mer- cury, until the metallic globules entirely disappear, and then subliming. When first prepared, it is always mixed with some corrosive sublimate, and therefore it should be reduced to pow- der and well washed before being employed for chemical or medical purposes. The protochloride of mercury is a rare mineral production, called horn quicksilver, which occurs crystallized in quadrangu- lar prisms, terminated by pyramids. When obtained by sublima- tion it is in semi-transparent crystalline cakes ; but as formed by precipitation, it is a white powder. Its density is 7.2. It is distinguished from the bichloride by not being poisonous, by having no taste, and by being exceedingly insoluble in water. Acids have little effect upon it; but pure alkalies decompose it, separating the black protoxide of mercury and uniting with muriatic acid,—products which necessarily imply the decomposi- tion of water. When calomel is boiled in a solution of the muriate of ammonia, it is converted into corrosive sublimate and metallic mercury. Muriate of soda has a similar effect, though in a less degree. Chloride of Cerium, is made by passing chlorine over sulphuret of cerium, at a red heat; it is a white fusible compound. Chlorides of Platinum.—The perchloride is procured by eva- porating the muriate of platinum to dryness, at a gentle heat. It is deliquescent, and is soluble both in water, alcohol, and ether. The ethereal solution is decomposed by the agency of light, metallic platinum being deposited. It is probable from the analysis of the double chloride of potassium and platinum by Thomson and Berzelius, that the perchloride of platinum is com- posed of 96 parts or one atom of metal, to 72 parts or two atoms of chlorine ; but this inference requires confirmation. When the perchloride is strongly heated, it parts with some of its chlorine, and is converted into a protochloride, which is re- solved by a red heat into platinum and chlorine. Platinum is distinguished from all other substances by the fol- lowing circumstances. When pure potassa or a salt of potassa is added to a concentrated solution of platinum, a yellow crystal- CHLORINE. 381 line precipitate subsides, which is very sparingly soluble in wa- ter. When heated to full redness, chlorine gas is disengaged, and the residue consists of metallic platinum and the chloride of potassium. According to the analysis of Thomson, it is com- posed of Bichloride of Platinum . 168 or one atom. Chloride of Potassium . 76 or one atom. Ammonia, or its salts, produce a similar precipitate, which is composed, according to Thomson, of Bichloride of Platinum . 168 or one atom. Muriate of Ammonia . 54 or one atom. When this compound, which is generally called the muriate of platinum and ammonia, is heated to redness, chlorine and mu- riate of ammonia are evolved, and pure platinum remains in the form of a delicate spongy mass, the power of which in kindling an explosive mixture of oxygen and hydrogen gases, has already been mentioned. This salt affords an easy method of procuring platinum in a metallic state, and of separating it from other metals. Soda forms with muriate of platinum a double salt, which is soluble in water and alcohol, and crystallizes in flattened, ob- lique, four-sided prisms, of an orange-red colour. According to Thomson, it is a compound of one atom of the bichloride of platinum, one atom of the chloride of sodium, and eight atoms of water. Chloride of Cobalt.—Cobalt burns when heated in chlorine, and forms a chloride of cobalt, when muriate of cobalt is evapo- rated to dryness and the residuum heated to redness out of the contact of air, a substance of a blue colour and micaceous texture is obtained, which is pure chloride of cobalt. It dissolves per- fectly in water, forming a pink solution. Chlorides of Nickel.—The protochloride of nickel is obtained by evaporating to dryness a solution of nickel in muriatic acid ; it consists of one atom of chlorine and one atom of nickel; when this compound is heated, the bichloride sublimes in light shining yellow crystals, consisting of two atoms of chlorine and one atom of nickel. Chloride of Rhodium and Potassium.—Berzelius has recently examined this double salt, and states its composition as follows : chloride of potassium 41.50, chlorine 29.53, rhodium 28.97. Chloride of Rhodium and Sodium.—This salt is composed of chloride of sodium 45.55, chlorine 27.48, rhodium 26.97. We may here also state, that Berzelius found the hydrated oxide of rhodium to consist of, rhodium 75.9, oxygen 17.5, and water 6.6. Chloride, or Butter of Zinc, was made by Dr. J. Davy, by evaporating the muriate to dryness, and then heating it to red- 382 CHLORINE. ness in a glass tube. It deliquesces on exposure to the air, be- ing reconverted into a muriate. It is composed of one atom of chlorine and one atom of zinc. Chloride of Cadmium may be prepared by decomposing the muriate by heat. Chloride of Bismuth.—When bismuth, in fine powder, is intro- duced into chlorine gas, it takes fire, burns with a pale blue light, and is converted into a chloride, formerly termed butter of bismuth. It may be prepared conveniently by heating two parts of corrosive sublimate with one of bismuth, and afterwards ex- pelling the excess of the former, together with the metallic mer- cury, by heat. The chloride of bismuth is of a grayish-white colour, opaque, and of a granular texture. It fuses at a temperature a little above that at which the metal itself is liquefied, and bears a red heat in close vessels without subliming. From the experiments of Drs. Davy and Thomson, it appears to consist of one atom of each of its elements. Chloride of Silver.—This compound, which sometimes occurs native in silver mines, is always generated when silver is heated in chlorine gas, and may be prepared conveniently by mixing muriatic acid, or any soluble muriate, with a solution of the ni- trate of silver. As formed by precipitation, it is quite white; but by exposure to the direct solar rays it becomes violet, and almost black, in the course of a few minutes, and a similar effect is slowly produced by diffused day-light. Muriatic acid is set free during this change, and, according to Berthollet, the dark colour is owing to a separation ofthe oxide of silver. The chloride of silver, sometimes called luna cornea or horn silver, is insoluble in water, and is dissolved very sparingly by the strongest acids; but it is soluble in ammonia. Hyposulphurous acid likewise dissolves it. At a temperature of about 500° F. it fuses, and forms a semi-transparent horny mass, on cooling. It bears any degree of heat, or even the combined action of pure charcoal and heat, without decomposition; but hydrogen gas decomposes it readily with formation of muriatic acid. Accord- ing to the experiments of Berzelius and Thomson, it is composed of 110 parts or one atom of silver, and 36 parts or one atom of chlorine. Chloride of Aluminum is of a pale yellowish green colour; semi-transparent, lamellated, and distinctly* crystalline. In the air it fumes, evolves the odour of muriatic acid, and rapidly deli- quesces. Chloride of Glucinum.—When glucinum is heated in chlorine, it burns with great splendor, and sublimes in the form of a crys- talline chloride. It was from this substance that Wohler first obtained the base of glueina. The chloride he used was first CHLORINE. 383 formed by Mr. H. Rose in the following manner: the glueina obtained from the beryl was first dissolved in the carbonate of ammonia; this then being intimately mixed with charcoal is to be heated to redness in a tube, and a current of dry chlorine made to pass over it. The chloride of glucinum sublimed, in the form of white shining needles. Chloride of Yttrium may be formed by the same process as that of glucinum. Salts. Chlorate of Ammonia is formed by saturating chloric acid with carbonate of ammonia. It forms very soluble acicular crystals of a sharp taste, which detonate when thrown upon hot coals. Chlorates. The salts of chloric acid are very analogous to the nitrates. As the chlorates of the alkalies, alkaline earths, and most of the common metals, are composed of one atom of chloric acid and one atom of a protoxide, it follows that the oxygen of the latter is to that of the former in the ratio of 1 to 5. The chlorates are decomposed by a red heat, nearly all of them being converted into metallic chlorides, with evolution of pure oxygen gas. They deflagrate with inflammable substances with greater violence than the nitrates, yielding oxygen with such facility that an explo- sion is produced by slight causes. All the chlorates hitherto examined are soluble in water, ex- cepting the proto-chlorate of mercury, which is of sparing solu- bility. These salts are distinguished by the action of strong muriatic and sulphuric acids, the former of which occasions the disengagement of chlorine, and the protoxide of chlorine, and the latter ofthe peroxide of chlorine. None of the chlorates are found native. The only ones that are of much importance are the chlorates of potassa and baryta. Chlorate of Potassa.—This salt, formerly called oxymuriate or hyper oxy-muriate of potassa, is colourless, and crystallizes in four and six-sided scales of a pearly lustre. It is soluble in six- teen times its weight of water at 60° F. and in two and a half of boiling water. It is quite anhydrous, and when exposed to a temperature of 400° or 500° F. undergoes the igneous fusion. On increasing the heat almost to redness, effervescence ensues, and pure oxygen gas is disengaged, for which purpose it is some- times employed. The chlorate of potassa is made by transmitting chlorine gas through a concentrated solution of pure potassa, until the alkali is completely neutralized. The solution which, after being boiled 384 CHLORINE. for a few minutes, contains nothing but the muriate and chlorate of potassa, is gently evaporated till a pellicle forms upon its sur- face, and is then allowed to cool. The greater part ofthe chlo- rate crystallizes, while the muriate remains in solution. The crystals, after being washed with cold water, may be purified by a second crystallization. A mixture of sulphur with three times its weight of chlorate of potassa explodes when struck between two hard surfaces. With charcoal, and the sulphurets of arsenic and antimony, this salt forms similar explosive mixtures; and with phosphorus it deto- nates violently by percussion. The mixture employed in the percussion locks for guns consists of sulphur and the chlorate of potassa. Chlorate of Soda may be obtained by saturating chloric acid with soda. Its crystals resemble those of chlorate of potassa, its taste is also nearly similar. The Chlorate of Baryta is of interest, as being the compound employed in the formation of chloric acid. The readiest mode of preparing this salt is by the process of Mr. Wheeler. On di- gesting for a few minutes a concentrated solution ofthe chlorate of potassa with a slight excess of silicated fluoric acid, the al- kali is precipitated in the form of an insoluble double fluate of silica and potassa, while the chloric acid remains in solution. The liquid after filtration is neutralized by carbonate of baryta, which likewise throws down the excess of fluoric acid and silica. The silicated fluoric acid employed in the process is made by conducting fluosilicic acid gas into water. Chlorate of Strontia may be obtained by the direct action of chloric acid on carbonate of strontia. It is a deliquescent salt, having an astringent taste. It detonates when thrown upon red hot coals with a beautiful purple light. Chlorate of Lime is a very soluble deliquescent salt of a sharp bitterish taste; it is most easily produced by dissolving carbo- nate of lime in chloric acid; exposed to heat oxygen is evolved, and a chloride is formed. Chlorate of Magnesia.—This salt may be prepared in the same way as chlorate of lime, which it resembles in most of its properties. Chlorate of Lead.—This salt may be formed by dissolving litharge in fine powder in chloric acid. The solution has a very sweet and astringent taste. When left to spontaneous evapo- ration, it deposits brilliant crystalline plates. Chlorate of Copper.—Peroxide of copper dissolves readily in chloric acid. It is not possible to neutralize the acid by this oxide. This salt does not crystallize readily. Its colour is green ; on burning coals it fuses slightly, and gives out a green light. Paper dipped into the solution of this salt burns with a fine green flame. CHLORINE. 385 Protochlorate of Mercury.—Chloric acid readily dissolves protoxide of mercury ; as the saturation goes on, the protochlorate precipitates in the form of yellowish grains. When heated it detonates, oxygen gas is given out, and corrosive sublimate formed. Perchlorate of Mercury may be formed by dissolving peroxide of mercury in chloric acid. It crystallizes in needles, is soluble in water, and has a strong taste like that of corrosive sublimate. It always contains an excess of acid ; when heated in a glass tube it gives out large quantites of oxygen. Chlorate of Zinc.—This salt has a very astringent taste; it crys- tallizes in low octahedrons. Its solution in water does not pre- cipitate nitrate of silver. Chlorate of Silver is formed by digesting oxide of silver in chlo- ric acid; it forms small rhombic crystals. When this salt is exposed to a moderate heat, it melts, oxygen is given out, and chloride of silver remains behind. When mixed with half its weight of sul- phur and struck slightly, it detonates with prodigous violence. Muriate of Ammonia.—This salt, the sal-ammonic of com- merce, was formerly imported from Egypt, where it is procured by sublimation from the soot of camel's dung; but it is now manufactured in Europe by several processes. The most usual method is to decompose sulphate of ammonia by the muriate, either of soda, or of magnesia. Double decomposition ensues, giving rise in both cases to muriate of ammonia, and to the sul- phate of soda, when the muriate of that base is used, or to the sulphate of magnesia when the muriate of magnesia is employed The sal-ammoniac is afterwards obtained in a pure state by sub- limation. The sulphate of ammonia may be conveniently pro- cured for this purpose, either by lixiviating the soot of coal, which contains that salt in considerable quantity ; or by digest- ing the impure carbonate of ammonia, procured by exposing bones and other animal matters to a red heat with gypsum, so as to form an insoluble carbonate of lime, and a soluble sulphate of ammonia. The muriate of ammonia has a pungent saline taste, and is soluble in three parts of water at 60° F., causing a considerable reduction of temperature during the solution. Boiling water dissolves about an equal weight, and the solution deposits crystals in cooling. At a temperature below redness, it sublimes without fusing or undergoing any change in composition, and condenses on cool surfaces as an anhydrous salt, which attracts humidity in a moist atmosphere, but if pure is not deliquescent. When muriatic acid gas is mixed with an equal volume of ammonia, both gases disappear entirely, and pure muriate of ammonia results. It hence follows, that this salt is composed, by weight, of 37 parts or one atom of muriatic acid, and 17 parts or one atom of ammonia. 3C 386 CHLORINE. Muriates, or Hydrochlorates. Most of the salts of muriatic acid are soluble in water, and some of them exist only in a state of solution. They are distinguished from other salts by forming the white insoluble chloride of silver when mixed with the nitrate of that base, and by being decomposed with disengagement of muriatic acid fumes by strong sulphuric acid. The decomposition of the muriates, owing to the volatile nature of their acid, is effected by the phos- phoric and arsenic acids at the temperature of ebullition. Muriate of Tellurium, is a colourless, acrid, and difficultly crys- tallizable salt. Muriate of Arsenic, a very acrid liquid, which does not crys- tallize. Muriates of Tin.—The protomuriate may be obtained by boil- ing one part of tin, with two of muriatic acid, in a tubulated retort. The solution has always an excess of acid, is perfectly colourless, and contains the metal at the minimum of oxidation It has a tendency to acquire a further proportion of oxygen, and should, therefore, be carefully preserved from contact with the air. It has the property of reducing to a minimum of oxidation, those compounds of iron in which the metal is fully oxidized; for example, it reduces the red sulphate to the green ; it is a test also of gold and platinum, and blackens the solutions of corrosive sublimate; with hydrosulphurets it gives a black precipitate. With solution of gold it produces a purple precipitate used in painting porcelain, and known under the name of Purple of Cassius. The permuriate of tin, forms acicular crystals in the upper parts of the phials, containing the bichloride imperfectly secured from air. Nitromuriate of Tin is employed by dyers to heighten the co- lours of cochineal, gum lac, and some other red tinctures, from crimson to a bright scarlet, in the dying of woollens. Muriate of Potassa and Soda.—These salts exist only in a state of solution, and are frequently contained in mineral springs. The muriate of soda, as already mentioned in the section on so- dium, is the chief constituent of sea water. Muriate of Lithia forms small regular cubes, very similar to common salt in their taste. They deliquesce very speedily when exposed to the air. Muriate of Baryta.—This compound is best formed by dissolv- ing the carbonate of baryta, either native or artificial, in muriatic acid diluted with three parts of water. It may also be formed by the action of muriatic acid on the hydro-sulphuret of baryta or by heating sulphate of baryta with an equal weight of muriate of lime until fusion takes place, and then dissolving the muriate of baryta, which is generated, and separating it by means of a filter from the sulphate of lime. CHLORINE. 387 The muriate of baryta crystallizes readily in quadrangular ta- bles, when its solution is gently evaporated. The crystals, accord- ing to Thomson, consist of 115 parts or one atom of the muriate of baryta, and nine parts or one atom of water. On heating the crystals to redness, two atoms of water are expelled, and 106 parts or one atom ofthe chloride of barium are left. The crys- tals, therefore, may be regarded as the chloride of barium with two atoms of water of crystallization, or as the muriate of baryta with one atom of water. The crystallized muriate of baryta is insoluble in pure alcohol. It requires about two and a half times its weight of water at 60° F. for solution, and is much more soluble in boiling water. The crystals are permanent in the air. This salt is much employed as a re-agent in chemistry. Muriate of Strontia is made in the same manner as the muriate of baryta, from which it is distinguished by forming pris- matic crystals, by its solubility in alcohol, and by imparting a red tint to flame. The crystals consist of one atom of the muriate of strontia, and eight atoms of water ; and when heated to red- ness, nine atoms of water are expelled, and one atom of the chloride of strontium remains. The crystallized muriate attracts humidity from a moist atmos- phere, but, if pure, it is permanent in a dry air. The crystals are exceedingly soluble in boiling water, and require for solution about twice their weight of water at 60° F. Muriate of Lime is formed by neutralizing muriatic acid with pure marble.. This salt is very soluble, both in water and alco- hol, and deliquesces with rapidity even in a dry atmosphere. It crystallizes, though with considerable difficulty, in prisms, which consist, according to Thomson, of one atom of the muriate of lime, and six atoms of water. When heated, seven atoms of wa- ter are expelled, and chloride of calcium remains. The crystallized muriate is the compound which produces such an intense degree of cold when mixed with snow. It is prepared for this purpose by evaporating the solution until a drop of it, on falling upon a cold saucer, becomes solid. Muriate of Magnesia exists in many mineral springs, and is contained abundantly in sea-water. When the muriate of soda is separated from sea-water by crystallization, an uncrystallizable liquid called bittern, is left, which consists chiefly ofthe muriate of magnesia, and is much employed in the manufacture of sal- ammoniac for decomposing the sulphate of ammonia. Muriate of magnesia has a bitter taste, is highly soluble in al- cohol and water, and deliquesces with rapidity in the open air. When heated to redness, it loses a portion of its acid as well as water. Muriate of Antimony.—The muriate of the protoxide is a very caustic, colourless liquid, possessing acid properties. The mu- 388 CHLORINE. riate of the deutoxide is yellow, very acid, and does not crys- tallize. Muriate of Chromium is green, and very soluble in water. Muriate of Molydenum has not been particularly described. Muriate of Manganese may be formed by heating excess of the black oxide with muriate of ammonia, in a crucible, dissolving the mass and filtering Muriate of Titanium is of a yellowish white colour, it reddens turnsole, and does not crystallize. Muriate of Uranium is of a yellowish green colour, very solu- ble in water, very deliquescent; and does not crystallize. Muriate of Lead exists only in the liquid state; it is formed by dissolving the chloride in wafer. Muriate of Iron.—When iron is dissolved in dilute muriatic acid, a muriate of the protoxide is generated, which yields pale green coloured crystals when the solution is concentrated by evapora- tion. This salt is much more soluble in hot than in cold water, and is not deliquescent. It absorbs oxygen with rapidity from the air, forming an insoluble muriate of the peroxide. When boiled with a little nitric acid, a soluble muriate of the peroxide is ge- nerated, which is of a red colour, crystallizes with difficulty, de- liquesces on exposure to the air, and is dissolved by alcohol. It is composed of one atom of the peroxide, and an atom and a half of muriatic acid, being a sesqui-muriate. The black oxide is also dissolved by muriatic acid, forming a dark coloured solution, which may be regarded as a mixture of the muriates ofthe peroxide and protoxide of iron. Muriates of Copper.—If metallic copper be digested in mu- riatic acid with the peroxide, an olive coloured solution of pro- tomuriate of copper is formed, which strongly attracts oxygen, and which, when concentrated, deposits small gray crystals. Muriatic acid readily dissolves the peroxide of copper, forming a brown or grass-coloured solution, according to its state of dilu- tion. This is a permuriate of copper. If plates of copper be exposed to the joint action of air and the fumes of muriatic acid, they become incrusted with a green powder, which is readily soluble in muriatic acid, and which is the subpermuriate. Native Submuriate of Copper, is found in Peru and Chili, sometimes in the form of green sand, sometimes massive and crystalline. The submuriate of copper is formed by the destructive action of sea water upon the copper sheathing of ships ; the oxygen ne- cessary to the formation of the muriate being derived from the air. Now, as copper can only act upon sea water when in a po- sitive state, if this electrical condition be reversed, by bringing some metal of more energetic electrical power in contact with it, the action ofthe sea water will cease. This led Sir H. Davy to a discovery which promises to be important, viz.: that exten- CHLORINE. 389 sive surfaces of copper may be protected from the corroding effects of sea water, by placing small plates of iron in contact with the sheathing of a ship. It has been found that the cover- ing of vessels so protected, is uninjured, even by long voyages in tropical climates. This discovery has been applied by Dr. Bostock, to the protection of utensils employed for culinary purposes. Muriate of Cerium.—Muriatic acid dissolves the red oxide of cerium, and the solution crystallizes confusedly. The salt is deliquescent, soluble in water and alcohol ; when the solutionis concentrated, it burns with a yellow sparkling flame. Of the nature of Chlorine. The change of opinion which has gradually taken place among chemists concerning the nature of chlorine, is a remarkable fact in the history ofthe science. The hypothesis of Berthollet, un- founded as it is, prevailed at one time universally. It explained phenomena so satisfactorily, and in a manner so consistent with the received chemical doctrines, that for some years no one thought of calling its correctness into question. A singular re- verse, however, has taken place. Though it has not hitherto been rigidly demonstrated to be erroneous, it has within a short period been generally abandoned, even by persons who, from having adopted it in early life, were prejudiced in its favour. The reason of this will appear on comparing the two theories, and ex- amining the evidence in favour of each. I. Chlorine, according to the new theory, is maintained to be a simple body, because like oxygen, hydrogen, and other analo- gous substances, it cannot be resolved into more simple parts. It does not indeed follow that a body is simple, because it has not hitherto been decomposed; but as chemists have no other mode of estimating the elementary nature of bodies, they must neces- sarily adopt this one, or have none at all. Muriatic acid, according to the same doctrine, is considered to be a compound of chlorine and hydrogen. For when it is exposed to the agency of galvan- ism, it is resolved into these substances; and by mixing the two gases in due proportion, and passing an electric spark through the mixture, muriatic acid gas is the product. Chemists have no other kind of proof of the composition of water, of potassa, or of any other compound. II. Very different is the evidence in support of the theory of Berthollet. According to that view, muriatic acid gas is com- posed of absolute muriatic acid, and water or its elements; chlorine consists of absolute muriatic acid and oxygen ; and absolute mu- riatic acid is a compound of a certain unknown base and oxygen gas. Now all these propositions are gratuitous. For, in the first place, muriatic acid gas has not been proved to contain water. 390 CHLORINE. Secondly, the assertion that chlorine contains oxygen is opposed to direct experiment, the most powerful deoxidizing agents having been unable to deprive that gas of a particle of oxygen. Thirdly, the existence of such a substance as absolute muriatic acid is wholly without proof, and therefore its supposed base is also imaginary. But this is not the only weak point of the doctrine. Since chlorine is admitted by this theory to contain oxygen, it was ne- cessary to explain how it happens that no oxygen can be sepa- rated from it. Thus, on exposing chlorine to a powerful gal- vanic battery, oxygen does not appear at the positive pole, as occurs when other oxydized bodies are subjected to its action ; nor is carbonic acid or carbonic oxide evolved, when chlorine is conducted over ignited charcoal. To account for the oxygen not appearing under these circumstances, it was assumed that absolute muriatic acid is unable to exist in an uncombined state, and therefore cannot be separated from one substance except by uniting with another. This supposition was thought to be sup- ported by the analogy of certain compounds, such as the nitric and oxalic acids, to the existence of which, unless combined with another body, water seems to be essential. It will be found, however, on close examination, that these instances are not ap- plicable to the case of chlorine and muriatic acid. For though the nitric and oxalic acids have not hitherto been obtained free from water, this obviously arises from the tendency of their ele- ments to obey other affinities, and to arrange themselves in a new order. Admitting the various assumptions which have been stated, most of the phenomena receive as consistent an explanation by the old as by the new theory. Thus when muriatic acid gas is resolved by galvanism into chlorine and hydrogen, it may be supposed that the absolute muriatic acid attaches itself to the oxygen of the water, and forms chlorine, while the hydrogen of the water is attracted to the opposite pole of the battery. When chlorine and hydrogen enter into combination, the oxygen ofthe former may be said to unite with the latter, and that muriatic acid gas is generated by the water, so formed, combining with the absolute muriatic acid ofthe chlorine. The evolution of chlorine, which ensues on mixing muriatic acid and the peroxide of man- ganese, is explained on the supposition that absolute muriatic acid unites directly with the oxygen of the black oxide of man- ganese. It will not be difficult, after these observations, to account for the preference shown to the new theory. In an exact science, such as chemistry, every step of which is required to be matter of demonstration, there is no room to hesitate between two modes of reasoning, one of which is hypothetical, and the other founded on experiment. Nor is there, in the present instance, tempta- CHLORINE. 391 tion to deviate from the strict logic of the science, for there is not a single phenomenon which may not be fully explained on the new theory, in a manner quite consistent with the laws of chemical action in general. It was supposed, that the sudden decomposition of water, occasioned by the action of that liquid on the compounds of chlorine with many simple substances, con- stituted a real objection to the doctrine; but new facts have deprived this argument of-all its force. While nothing there- fore can be gained, much may be lost by adopting the doc- trine of Berthollet. If chlorine is regarded as a compound body, the same opinion, though in direct opposition to the result of observation, ought to be extended to iodine ; and as other analo- gous substances may hereafter be discovered, in regard to which a similar hypothesis will apply, it is obvious that this view, if proper in one case, may legitimately be extended toothers. One encroachment on the method of strict induction would conse- quently open the way to another, and thus the genius of the science would eventually be destroyed. An able attempt was made some years ago by the late Dr. Murray, to demonstrate the presence of water or of its elements as a constituent part of muriatic acid gas, and thus to establish the old theory to the subversion of the new. But Dr. Murray did not succeed in establishing his point; and his arguments, though exceedingly plausible and ingenious, were fully answered by Sir Humphrey and Dr. John Davy. The history ofthe only ex- periment which strictly bears upon the question,—that, namely, in which muriatic acid and ammonical gases were mixed together, —amounts very nearly to a demonstration of the absence of com- bined water in muriatic acid gas. The quantity of water which did make its appearance during the experiment, was so very small in comparison to what ought to have appeared on Dr. Murray's supposition, as to leave little doubt that its origin was acci- dental. DIVISION III. Oxygen, our first electro-negative element, is known to us only in the state of gas; chlorine, under great compression, appears as a liquid, but Iodine, which we are now to consider, is a solid at ordinary temperatures. The discovery of this remarkable substance will always be regarded as an important era in the history of chemistry. The necessity of abandoning Levoisier's hypothesis of oxygenation was then found to be absolute, and the sound and comprehensive doctrines of Sir H. Davy, on che- mical theory, first promulgated in his masterly researches on chlorine, were afterwards almost universally embraced. Iodine. Iodine was first discovered in 1812, by M. Courtois, a manu- facturer of saltpetre at Paris. In preparing carbonate of soda from the ashes of sea-weeds, he observed that the residual liquor corroded metallic vessels powerfully; and in investigating the cause of the corrosion, he noticed that sulphuric acid threw down a dark coloured matter, which was converted by the appli- cation of heat into a beautiful violet vapour. Struck with its appearance, he gave some of the substance to M. Clement, who recognised it as a new body, and in 1813, described some of its leading properties in the Royal Institute of France. Its real na- ture was soon after determined by Gay-Lussac and Sir H. Davy, each of whom proved that it is a simple non-metallic substance, exceedingly analogous to chlorine. Iodine, at common temperatures, is a soft friable opaque solid, of a bluish-black colour, and metallic lustre. It occurs, usually, in crystalline scales, having the appearance of micaceous iron ore ; but it sometimes crystallizes in large rhomboidal plates, the primitive form of which is an octahedron. Its specific gravity, according to Gay-Lussac, is 4.948; but Thomson found it only 3.0844. At 225° F. it fuses, and enters into ebullition at 347 F°.; but when moisture is present, it sublimes rapidly even below the degree of boiling water, and suffers a gradual dissipation at low temperatures. Its vapour is of an exceedingly rich violet colour, a character to which it owes the name of Iodine, from ioS^i violet. This vapour is remarkably dense, its specifie gravity be- ing 8.6102. Hence, 100 cubic inches, at the standard tempera- ture and pressure, must weigh 262.612 grains. Thomson infers, partly from the experiments of Gay-Lussac, and partly from his own researches, that the atomic weight of iodine is 124. Iodine is a non-conductor of electricity, and, like oxygen and IODINE. 393 chlorine, is a negative electric. It has a very acrid taste, and its odour is almost exactly similar to that of chlorine, when much diluted with air. It acts energetically on the animal system as an irritant poison, but is employed with advantage in medicine in very small doses. Iodine is very sparingly soluble in water, requiring about 7000 times its weight of that liquid for solution. It communicates, however, even in this minute quantity, a brown tint to the men- struum. Alcohol and ether dissolve it freely, and the solution has a deep reddish brown-colour. Iodine possesses an extensive range of affinity. It destroys vegetable colours, though in a much less degree than chlorine. It manifests little disposition to combine with metallic oxides; but it has a strong attraction for the pure metals, and for most of the simple non-metallic substances. These combinations are termed Iodides or Iodurets. It is not inflammable ; but, under favourable circumstances, may, like chlorine, be made to unite with oxygen. A solution ofthe pure alkalies acts upon it in the same manner as upon chlorine, giving rise to the decomposition of water, and the formation of the iodic and hydriodic acids. Pure iodine is not influenced chemically by the imponderables. Exposure to the direct solar rays, or to strong shocks of electri- city, does not change its nature. It may be passed through red- hot tubes, or over intensely ignited charcoal, without any ap- pearance of decomposition ; nor is it affected by the agency of galvanism. Chemists, indeed, are unable to resolve it into more simple parts, and, consequently, it is regarded as an elementary principle. The violet hue ofthe vapour of iodine, is, for many purposes, a sufficiently sure indication of its presence. A far more deli- cate test, however, was discovered by MM. Collin and Gaultier de Claubry. They found that iodine has the property of uniting with starch, and of forming with it a compound insoluble in wa- ter, which is recognized with certainty by its deep blue colour. This test, according to Professor Stromeyer, is so delicate, that a liquid containing 1—450,000 of its weight of iodine, receives a blue tinge from a solution of starch. Two precautions should be observed to insure success. In the first place, the iodine must be in a free state ; for it is the iodine itself only, and not its compounds, which unite with starch. Secondly, the solution should be quite cold at the time of adding the starch ; for boiling water decomposes the blue compound, and consequently removes its colour. Iodine and Oxygen. Iodous acid.—This name was applied to a compound prepared in 1824 by Professor Sementini of Naples, by the action of iodine 3D 394 IODINE. on chlorate of potassa. Equal parts of the materials are tritura- ted together in a glass or porcelain mortar until they form a very fine pulverulent yellow mass, in which the metallic lustre of the iodine is no longer perceptible. The mixture is then heated in a glass retort; and as soon as the chlorate begins to lose oxygen, iodous acid rises in the form of a dense white va- pour, and condenses in the neck ofthe retort into a yellow liquid, which falls in drops into the receiver. The liquid thus formed is of an oily consistence, and of a pe- culiar disagreeable odour, somewhat resembling euchlorine. It has an acid astringent taste, and leaves a burning sensation on the tongue. It reddens vegetable blue colours permanently, without destroying them. With water and alcohol it forms am- ber-coloured solutions. Its density is greater than that of water. It is rapidly volatilized at 212° F. and evaporates slowly at com- mon temperatures. It is decomposed by sulphur, and phosphorus ; and potassium takes fire as soon as they come in contact with it. After repeating the experiments of Sementini, and examining the product, Dr. Wohler asserts that it does not consist of iodine and oxygen, but chlorine and iodine. Part of the chloric acid, it appears is decomposed; but its elements, uniting.with sepa- rate portions of iodine, yield iodic acid, which remains in the re- tort combined with potassa, and chloride of iodine, similar to that described by Gay-Lussac, which is sublimed. From some other experiments, however, M. Sementinf has almost proved the existence both of iodous acid and an oxide of iodine. He states that on bringing together the vapour of iodine and oxygen gas considerably heated, the violet tint ofthe former disappears, and a yellow matter ofthe consistence of solid oil is generated. This he regards as the oxide of iodine ; and if the supply of oxygen is kept up after its formation, it is converted into iodous acid simi- lar to that above mentioned. From the mode in which the pro- cess is described, there can scarcely be a doubt that some com- pound of iodine and oxygen is thus formed ; but, at the same time, the new compounds have not been examined analytically, nor has the chemical constitution of the substances hitherto pre- pared by M. Sementini been determined with that accuracy re- quired for inspiring confidence in his results. Iodic add was discovered about the same time by Gay-Lussac and Sir H. Davy ; but the latter first succeeded in obtaining it in a perfectly pure state. When iodine is brought into contact with the protoxide of chlorine, an immediate action ensues ; the chlorine of the protoxide unites with one portion of iodine, and its oxygen with another, forming two compounds, a volatile orange-coloured matter, the chloride of iodine, and a white solid substance, which is iodic acid. On applying heat, the former passes off in vapour, and the latter remains. IODINE. 395 This compound which was termed oxiodine by Sir H. Davy, is anhydrous iodic acid. It is a white semi-transparent solid, which has a strong astringent sour taste, but no odour. Its den- sity is considerable, as it sinks rapidly in sulphuric acid. When heated to the temperature of about 500° F. it fuses, and at the same time is resolved into oxygen and iodine. Iodic acid deliquesces in a moist atmosphere, and is very solu- ble in water. The liquid acid thus formed reddens vegetable blue colours, and afterwards destroys them. On evaporating the solution, a thick mass ofthe consistence of paste is left, which is hydrous iodic acid, and from which, by cautious application of heat, the water may be expelled. It acts powerfully on inflamma- ble substances. Wim charcoal, sulphur, sugar, and similar com- bustibles, it forms mixtures which detonate when heated. It enters into combination with metallic oxides, and the resulting salts are called iodates. These compounds, like the chlorates, yield pure oxygen by heat, and deflagrate when thrown on burning char- coal. Iodic acid unites with several of the acids, such as the sulphu- ric, nitric, phosphoric, and boracic acids ; and with the three first it forms crystallizable compounds. It is decomposed by the sulphurous, phosphorous, and hydriodic acids, and by sulphuret- ted hydrogen. Iodine in each case is set at liberty, and may be detected as usual by starch. The muriatic and iodic acids de- compose each other, water and chloroiodic acid being generated. Sir H. Davy analyzed iodic acid by determining the quantity of oxygen which it evolves when decomposed by heat. Gay-Lus- sac effected the same object by heating the iodate of potassa, when pure oxygen was given off, and the iodide of potassium re- mained. From the result of these analyses, it appears that iodic acid is a compound of one atom of iodine and five atoms of oxy- gen ; so that its elements are in the proportion of Iodine - 124, or one atom. Oxygen - 40, or five atoms. And its atomic weight is 164. Iodine and Nitrogen. Iodide of Nitrogen.—From the weak affinity that exists be- tween iodine and nitrogen, these substances cannot be made to unite directly. But when iodine is put into a solution of ammonia, the alkali is decomposed; its elements unite with different por- tions of iodine, and thus cause the formation of hydriolic acid and iodide of nitrogen. The latter subsides in the form of a dark powder, which is characterised, like the chloride of nitrogen, by its explosive property. It detonates violently as soon as it is 396 IODINE. dried, and slight pressure, while moist, produces a similar effect. Heat and light are emitted during the explosion, and iodine and nitrogen are set free. According to the experiments of M. Colin, the iodide of nitrogen consists of one atom of nitrogen to three of iodine. Iodine and Hydrogen. Hydriodic acid Gas.—When a mixture of hydrogen and the vapour of iodine is transmitted through a red-hot porcelain tube, direct combination takes place between them, and a colourless gas, possessed of acid properties, is the product. To this sub- stance the term hydriodic acid gas is applied. This gas may be obtained quite pure by the action of water on the iodide of phosphorus. Any convenient quantity of moistened iodine is put into a small glass retort, and about one-twelfth of its weight of phosphorus is then added. An iodide of phosphorus is formed, which instantly re-acts upon the water. Mutual decom- position ensues ; the oxygen of the water unites with the phos- phorus, and the hydrogen with the iodine, giving rise to the for- mation of phosphoric and hydriodic acids. On the application of a moderate heat, the latter passes over in the form of a colour- less gas. The hydriodic acid gas has a very sour taste, reddens vegetable blue colours without destroying them, and has an odour similar to that of muriatic acid gas. It combines with alkalies, forming salts which are called hydriodates. Like muriatic acid gas it cannot be collected over water; for that liquid dissolves it in large quantity. Hydriodic acid is decomposed by several substances which have a strong affinity for either of its elements. Thus oxygen gas, when heated with it, unites with the hydrogen, and liberates the iodine. Chlorine effects the decomposition instantly ; mu- riatic acid gas is produced, and the iodine appears in the form of vapour. With strong nitrous acid it takes fire, and the vapour of iodine is free. It is also decomposed by mercury. The decom- position begins as soon as the hydriodic acid comes in contact with the mercury, and proceeds steadily, and even quickly if the gas is agitated, till nothing but hydrogen remains. Gay-Lussac ascertained by this method that 100 measures of hydriodic acid gas contain precisely half their volume of hydrogen. This result induced him to suspect that the composition of hydriodic must be analogous to that of muriatic acid gas; that, as 100 measures of the latter contain 50 of hydrogen and 50 of chlorine, 100 measures of the former consist of 50 of hydrogen and 50 of the va- pour of iodine. If this view be correct, then the composition of hydriodic acid gas, by weight, may be determined by calculation. IODINE. 397 For since Grains. 50 cubic inches of the vapour of iodine weigh 131.306. 50 . hydrogen gas . 1.059. 100 of hydriodic acid gas must weigh . 132.365 and its specific gravity will be 4.3398. Now, Gay-Lussac ascer- tained, by weighing the hydriodic acid gas, that its density is 4.443,—a number which corresponds so closely to the pre- ceding, as to leave no doubt that the principle of the calculation is correct. There is good reason to believe, indeed, that the calculated result, if not rigidly exact, is very near the truth; for Gay-Lussac states, that the number determined by him is too high. Since iodine and hydrogen unite in one proportion only, hy- driodic acid is regarded as a compound of one atom of each ele- ment,—an opinion, supported both by the proportions in which iodine combines with other substances, and by the analogy of muriatic acid. The constitution of hydriodic acid may therefore be thus stated: By Volume. By Weight. Iodine 50 124 or one atom. Hydrogen 50 1 or one atom. 100 125 and its combining proportion is 125. When hydriodic acid gas is conducted^into water till that li- quid is fully charged with it, a colourless acid solution is obtain- ed, which emits white fumes on exposure to the air, and has a density of 1.7. It maybe prepared also by passing a current of sulphuretted hydrogen gas through water in which iodine in fine powder is suspended. The iodine, from having a greater affinity than sulphur for hydrogen, decomposes the sulphuretted hydrogen; and hence sulphur is set free, and hydriodic acid is produced. As soon as the iodine has disappeared, the solution is heated for a short time, to expel the excess of sulphuretted hydrogen, and subsequently filtered to separate the free sulphur. The solution of hydriodic acid is readily decomposed. Thus, on exposure during a few hours to the atmosphere, the oxygen of the air forms water with the hydrogen of the acid, and sets iodine free. The solution is found to have acquired a yellow tinge from the presence of uncombined iodine, and a blue co- lour is occasioned by the addition of starch. The nitric and sul- phuric acids likewise decompose it by yielding oxygen, the for- mer being at the same time converted into nitrous, and the latter into sulphurous acid. Chlorine unites directly with the hydrogen of the hydriodic acid, and muriatic acid is formed. The sepa- ration of iodine in all these cases may be proved in the way just 398 IODINE. mentioned. These circumstances afford a sure test of the pre- sence of hydriodic acid, whether free or in combination with al- kalies. All that is necessary, is to mix a cold solution of starch with the liquid, previously concentrated by evaporation if neces- sary, and then to add a few drops of strong sulphuric acid. A blue colour will make its appearance if hydriodic acid is present. Hydriodic acid is frequently met with in nature in combination with potassa or soda. Under this form is occurs in many salt and other mineral springs. It has been detected in the water of the Mediterranean, in the oyster, and some other marine and mollus- cous animals, in sponges, and in most kinds of sea-weed. In some of these productions, such as the Fucus serratus and Fucus di- gitatus, it exists ready formed, and, according to Dr. Fyfe, may be separated by the action of water; but in others it can be de- tected only after incineration. The marine animals and plants doubtless derive the hydriodic acid they contain from the sea. Vauquelin has found it also in the mineral kingdom, in combina- tion with silver. All the iodine of commerce is procured from the impure car- bonate of soda, called kelp, which is prepared in large quantity on the northern shores of Scotland, by incinerating sea-weeds. The kelp is employed by soap-makers for the preparation of car- bonate of soda; and the dark residual liquor, remaining after that salt has crystallized, contains a considerable quantity of hy- driodic acid, combined with soda or potassa. By adding a suffi- cient quantity of sulphuric acid, the hydriodic acid is separated from the alkali, and #then decomposed. The iodine sublimes when the solution is boiled, and may be collected in cool glass receivers. A more convenient process is, to employ a moderate excess of sulphuric acid, and then add some of the peroxide of manganese to the mixture. The oxygen of the manganese de- composes the hydriodic acid, and a protosulphate of manganese is formed. Iodine and Carbon. When the alcoholic solutions of iodine and soda are mixed together, the iodine combines with the sodium, and the oxygen set free unites the hydrogen of the alcohol to form water, whilst the carbon of the alcohol combines with another portion of the iodine, and forms the protoiodide of carbon. When this iodide of carbon is distilled with corrosive sublimate a liquid is obtained, which is the periodide of carbon; the following is the composi- tion of these iodides. Iodine. Carbon. Protoiodide of carbon . 1 atom . 1 atom Periodide ... 3 atoms . 2 atoms IODINE. 399 Iodine and Cyanogen. The Cyanide of Iodine, which was discovered in 1824, by M. Serullas, may be prepared by the following process : two parts of the cyanide of mercury and one of iodine, quite dry, are inti- mately and quickly mixed in a glass mortar, and the mixture is introduced into a phial with a wide mouth. On applying heat, the violet vapours of iodine appear ; but as soon as the cyanide of mercury begins to be decomposed, the vapour of iodine is suc- ceeded by white fumes, which, if received in a cool glass re- ceiver, condense upon its sides into flocks like cotton wool. The cyanide of iodine, when slowly condensed, occurs in very long and exceedingly slender needles, of a white colour. It has a very caustic taste and penetrating odour, and excites a flow of tears. It sinks rapidly in sulphuric acid. It is very volatile, and sustains a temperature much higher than 212° F. without decom- position ; but is decomposed by a red heat. It dissolves in water and alcohol, and forms solutions which do not redden litmus paper. The cyanide of iodine is decomposed by a concentrated solu- tion of potassa with formation of hydriodic and hydrocyanic acids. As these compounds could only have been formed by the decom- position of water, the solution ought also to contain the iodic and cyanic acids; but M. Serullas did not succeed in detecting their presence. The sulphurous acid, when water is present, has a very pow- erful action on the cyanide of iodine. On adding a few drops of this acid, iodine is set free, and hydrocyanic acid is produced; but when more of the sulphurous acid is employed, the iodine disappears, and the solution is found to contain hydriodic acid. These changes are of course accompanied with the formation of sulphuric acid, and the decomposition of water. The cyanide of iodine has not been analyzed with accuracy; but M. Serullas infers, from an approximative analysis, that it is composed of one atom of iodine and one atom of cyanogen. Iodine and Olefiant Gas. Hydrocarburet of Iodine.—This compound was discovered by Mr. Faraday, by exposing olefiant gas and iodine contained in the same vessel, to the direct rays of the sun. It is a solid, white, crystalline body, which has a sweet taste and aromatic odour. It sinks rapidly in strong sulphuric acid. It fuses when heated, and then sublimes without change, condensing into crystals, which are either tabular or prismatic. On exposure to strong heat it is decomposed, and iodine escapes. It burns, if held in the flame of a spirit lamp, with evolution of iodine and some hydriodic acid. It is insoluble both in water and in acid or al- 400 IODINE. kaline solutions. Alcohol and ether dissolve it, and on evapora- ting the solution, it crystallizes. The hydrocarburet of iodine is composed, according to the analysis of Mr. Faraday, of iodine 124 or one atom, and olefiant gas 14 or one atom. M. Serullas has also discovered a compound of olefiant gas and iodine. It has a yellow colour like sulphur, and forms scaly crystals of a pearly lustre. Though it differs from the preceding compound in some of its properties, its composition, according to the analysis of M. Serullas, is precisely analogous. This compound was originally prepared by adding potassium to a solution of iodine in alcohol, but M. Serullas has since made it by mixing a solution of pure potassa in alcohol with an alcoholic solution of iodine. The object of both processes is to present iodine in solution to olefiant gas in a nascent state. It has been stated that, when an alkali, such as potassa, acts on iodine, hy- driodic and iodic acids are generated by the decomposition of water. It has been mentioned, also, that pure alcohol is a com- pound of water and olefiant gas. Now when iodine, potassa, and alcohol are mixed together, the latter is decomposed : the water contributes to the formation of iodic and hydriodic acids; while the olefiant gas, instead of assuming the gaseous form, unites with iodine. Potassium acts still more powerfully, because it is converted into potassa at the expense of the water of the alcohol. Some very recent experiments of Mitscherlich seem to demon- strate that the above compound of Serullas is not a hydriodide of carbon, but only a combination of iodine and carbon formed in the manner we have already described. This removes the diffi- culty of supposing that two hydriodides of carbon could exist of exactly the same composition, but of different properties. Iodide of Phosphorus.—Iodine and phosphorus combine readily in the cold, evolving so much caloric as to kindle the phosphorus, if the experiment is made in the open air; but in close vessels no light appears. The combination takes place in several propor- tions, which have not been determined. Its most interesting property is that of decomposing water, with formation of hydrio- dic and phosphoric acids. Iodide of Sulphur.—This compound is formed by heating gent- ly a mixture of iodine and sulphur. The product has a dark colour and radiated appearance, like antimony. Its elements are easily disunited by heat. Iodide of Arsenic, obtained by heating the metal with excess of iodine, is of a deep red colour and is volatile. Metallic Iodides.—Iodine has a strong attraction for metals; and most of the compounds it forms with them, sustain a red heat in close vessels without decomposition. But in the degree of its affinity for metallic substances it is inferior both to chlorine and oxygen. We have seen that chlorine has a stronger affinity IODINE. 401 for metals than oxygen, since it decomposes nearly all oxides at high temperatures: and it separates iodine also from metals under the same circumstances. If the vapour of iodine is brought into contact with potassa, soda, protoxide of lead, or the oxide of bismuth, heated to redness, oxygen gas is evolved, and an iodide of these metals will be formed. But iodine, so far as is known, cannot separate oxygen from any other metal; nay, all the iodides, except those just mentioned, are decomposed by exposure to oxygen gas at the temperature of ignition. All the iodides are decomposed by chlorine, bromine, and concentrated sulphuric and nitric acids; and the iodine which is set free may be recog- nised either by the colour of its vapour, or by its action on starch. The metallic iodides are generated under circumstances anala- gous to those which we mentioned for procuring the chlorides. When the vapour of iodine is conducted over red-hot lime, baryta, or strontia, oxygen is not disengaged, but an iodide of those oxides, according to Gay-Lussac, is generated. The iodides of these oxides are therefore more permanent than the analogous compounds with chlorine. Iodine does not combine with any other oxide under the same circumstances; and indeed all other such iodides, very few of which exist, are, like the chlorides of oxides, possessed of little permanency, and are decomposed by a red heat. The action of iodine on metallic oxides, when dissolved or suspended in water, is precisely analogous to that of chlorine. On adding iodine to a solution of the pure alkalies or alkaline earths, water is decomposed, and the hydriodic and iodic acids are generated. Iodide of Tin may be formed directly by heating the metal with iodine. It is an orange coloured compound. Iodide of Potassium.—This compound is formed with emis- sion of light, when potassium is heated in contact with iodine. It may likewise be obtained by means of heat from the iodate, and by crystallization from the hydriodate of potassa. It fuses readily when heated, and is volatilized at a temperature below redness. It deliquesces in a moist atmosphere, and is very solu- ble in water. It dissolves also in strong alcohol, and the solu- tion, when gently evaporated, yields small colourless cubic crys- tals of the iodide of potassium. It is composed of one atom of iodine and one atom of potassium. Iodide of Sodium is very analogous to the last compound. Iodide of Barium may be formed by heating baryta in hydrio- dic acid, water and iodide of barium are the results. Iodide of Strontium may be formed in the same manner as iodide of barium. Iodide of Calcium is a white fusible compound. Iodide of Antimony is of dark red colour; acted upon by water, it produces hydriodic acid, and oxide of antimony. 3E 402 IODINE. The Iodide of Lead is easily formed by mixing a solution of hydriodic acid or hydriodate of potassa with the acetate or nitrate of lead dissolved in water. It is of a rich yellow colour. It is dissolved by boiling water, forming a colourless solution, and is deposited on cooling in yellow crystalline scales of a brilliant lustre. It is composed of one atom of iodine and one atom of lead. Iodide of Iron is a brown compound, fusible at a red heat; when acted on by water, it forms a hydriodate of a green colour. Iodide of Copper is precipitated from solutions of the metal by hydriodic acid. It is brown and insoluble. Iodides of Mercury.—The protoiodide is formed by mixing a solution of the protonitrate of mercury with the hydriodate of potassa; and the deutiodide by the action of the same hydriodate on any per-salt of mercury. The former is yellow, and is com- posed of one atom of iodine and one atom of mercury. The other is of an exceedingly rich red colour, and may be used with advantage in painting. It contains twice as much iodine as the yellow iodide. Both these compounds are insoluble in pure water, but are dissolved by a solution ofthe hydriodate of potassa. Iodide of Gold.—When hydriodate of potassa is added to chlo- ride of gold, it produces a copious precipitate of the iodide of gold, which is of a yellowish brown colour, insoluble in water, and easily decomposed by heat. Iodide of Zinc, is a fusible, volatile, and crystalline com- pound, which, when exposed to air, deliquesces into hydriodate of zinc. Iodide of Bismuth, obtained by heating iodine with the metal, is of an orange colour, and insoluble in water Iodide of Silver.—This compound is formed when the hydrio- date of potassa is mixed with a solution of the nitrate of silver. It is of a greenish-yellow colour, is insoluble in water and am- monia, and contains one atom of each of its elements. Iodide of Glucinum, is formed by heating glucinum in the va- pour of iodine. It sublimes in long white needles, which are fusible, and exceedingly volatile ; these dissolve in water, with the production of great heat. Iodide of Yttrium, is analagous to that of glucinum. Iodide of Chlorine, or Chloriodic Acid.—Chlorine is absorbed at common temperatures by dry iodine with evolution of caloric and a solid compound of iodine and chlorine results, which was discovered both by Sir H. Davy and Gay-Lussac. The colour of the product is orange-yellow, when the iodine is fully saturated with chlorine, but is of a reddish-orange if the iodine is in ex- cess. It is converted by heat into an orange-coloured liquid, which yields a vapour of the same tint on an increase of tempe- rature. It deliquesces in the open air, and dissolves freely in water. Its solution is colourless, is very sour to the taste, and IODINE. 403 reddens vegetable blue colours, but afterwards destroys them. From its acid properties, Sir H. Davy gave it the name of chlor- iodic add. Gay-Lussac, on the contrary, calls it chloride of iodine, conceiving that the acidity of its solution arises from the presence of muriatic and iodic acids, which he supposes to be generated by the decomposition of water. The opinion of Sir H. Davy appears to be more probable; for we know that free muriatic and iodic acids mutually decompose each other, and therefore, could hardly be generated by the action of vyater on the compound of iodine and chlorine. The chloriodic acid, however, does not unite with alkaline substances. On mixing it, for example, with baryta, the muriate and iodate of baryta are obtained. From this, it may be inferred, that water and chloriodic acid re-act on each other when an alkali is added to them. Salts. Iodate of Ammonia, forms small indeterminate crystals; when heated, they are decomposed into oxygen, nitrogen, water, and iodine. Iodates. From the close analogy in the composition of chloric and iodic acids, it follows that the general character of the iodates must be similar to that of the chlorates. Thus, in all neutral proto- iodates, the oxygen contained in the oxide and acid is in the ratio of 1 to 5. They form deflagrating mixtures with combusti- ble matters; and on being heated to low redness, oxygen gas is disengaged, and a metallic iodide remains. As the affinity of iodine for metals is less energetic than that of chlorine, many of the iodates part with iodine as well as oxygen, when heated, especially if a high temperature is employed. The iodates are easily recognized by the facility with which their acid is decomposed by deoxidizing agents. Thus, the sul- phurous, phosphorous, muriatic, and hydriodic acids, deprive the iodic acid of its oxygen, and set iodine at liberty. Sulphuretted hydrogen not only decomposes the acid of these salts, but occa- sions the formation of hydriodic acid by yielding hydrogen to the iodine. Hence, an iodate may be converted into a hydrio- date by transmitting a current of sulphuretted hydrogen gas through its solution. None ofthe iodates have been found native. They are all of very sparing solubility, or actually insoluble in water, excepting the iodates ofthe alkalies. Iodate of Potassa.—'This salt is easily procured, by adding iodine to a concentrated hot solution of pure potassa, until the 404 IODINE. alkali is completely neutralized, The liquid which contains the iodate and hydriodate of potassa, is evaporated to dryness by a gentle heat, and the residue, when cold, is treated by strong alcohol. The iodate, which is insoluble in that menstruum is left, while the hydriodate of potassa is dissolved. All the insoluble iodates may be procured from the salt by double decomposition. Thus the iodate of baryta may be formed by mixing the muriate of baryta with a solution of the iodate of potassa. Iodate of Soda ,forms small prismatic tufted crystals, which, when heated, afford oxygen and iodide of sodium. Iodate of Baryta, is a whjte powder, very sparingly soluble in water. Iodate of Strontia, is a very difficultly soluble compound. Iodate of Lime, is difficultly crystallizable in small quadran- gular prisms. Hydriodate of Ammonia, may be formed by mixing equal vo- lumes of hydriodic and ammoniacal gases. It forms very soluble and deliquescent cubic crystals, volatile in close vessels, without decomposition. Hydriodates. Hydriodic acid unites with the alkalies and alkaline earths, with magnesia, and with the oxides of manganese, zinc, and iron. With seVeral ofthe metallic oxides, it does not enter into com- bination. Thus, on mixing the hydriodate of potassa with a salt of mercury or silver, the iodides of those metals are deposited. With the acetate of lead, a yellow compound is thrown down, which is an iodide of lead. The most direct method of forming the hydriodates ofthe al- kalies and alkaline earths, all of which are soluble in water, is by neutralizing those bases with hydriodic acid. The hydrio- dates of iron and zinc may be made by digesting small fragments of those metals with water, in which iodine is suspended. All the hydriodates are decomposed by sulphuric and nitric acids, or by chlorine, the hydriodic acid being deprived of hy- drogen, and the iodine set at liberty. They undergo no change by exposure to the air. The only hydriodates which have hitherto been found native are those of potassa and soda, the sources of which have already been mentioned in the section on iodine. Of these salts, the hydriodate of potassa is the most common. Hydriodate of Potassa.—This salt, which is the only hydrio- date of importance, exists only in solution ; for it is converted in the act of crystallizing into the iodide of potassium. It is ex- ceedingly soluble in boiling water, and requires only two-thirds of its weight of water at 60° F. for solution. It is dissolved freely IODINE. 405 by alcohol ; and when a saturated, hot, alcoholic solution is set aside to cool, the iodide of potassium is deposited in cubic crys- tals. A solution of the hydriodate of potassa is capable of dis- solving a large quantity of iodine, a property which is common to all the hydriodates. The hydriodate of potassa is easily made by neutralizing hy-* driodic acid with pure potassa; but in preparing a considerable quantity of the salt, as for medical use, it is desirable to dispense with the preliminary step of making the acid. With this inten- tion, the following method, proposed by Dr. Turner, may be em- ployed with advantage. The process consists in adding to a hot solution of pure potassa as much iodine as it is capable of dis- solving, by which means a deep brownish-red coloured fluid is formed, consisting of the iodate and hydriodate of potassa, toge- ther with a large excess of free iodine. Through this solution, a current of sulphuretted hydrogen gas is transmitted until the free iodine and iodic acid are converted into hydriodic acid, changes which may be known to be accomplished by the liquid becoming quite limpid and colourless. The solution is then gently heated, in order to expel any excess of sulphuretted hy- drogen, and after being filtered, the pure hydriodic acid is ex- actly neutralized by pure potassa. A still easier process has been proposed, which consists in adding iodine to a solution of hydrosulphate of potassa, or the common hepar-sulphuris of the pharmacopoeia, until the po- tassa is exactly neutralized. The hydriodate is then form- ed at once, without the necessity of a current of sulphuretted hydrogen gas. Hydriodate of Soda.—This salt crystallizes without alteration. The crystals are flat rhomboids, which, uniting together, form larger crystals, somewhat similar to sulphate of soda. They con- tain much water of crystallization, and are deliquescent. Hydriodate of Baryta, crystallizes in fine prisms. It is very soluble in water, and but slightly deliquescent. Hydriodate of Strontia, is analagous to the last compound. Hydriodate of Lime, is crystallizable, very soluble in water, and very deliquescent. Hydriodate of Magnesia, is very deliquescent, and crystallizes with difficulty. DIVISION IV. Bromine. Bromine was discovered by M. Balard, of Montpellier, about two years ago. The name first applied to it by its discoverer was muride; but it has since been changed to brome, a word derived from the Greek p^opos, (graveolentia) signifying a strong or rank odour. This appellation, may, in the English language, be pro- perly converted into that of bromine. Bromine exists in sea water in the form of hydro-bromic acid, combined, in the opinion of M. Balard, with magnesia. It is pre- sent, however, in very small quantity; and even the uncrystalliza- ble residue called bittern, left after the muriate of soda has been separted from sea water by evaporation, contains but little of it. On adding chlorine to this liquid, an orange-yellow tint appears; and on heating the solution to the boiling point, the red vapours of bromine are expelled, which may be condensed by a freezing mixture. A better process for preparing bromine is to transmit a current of chlorine gas through the bittern, and then to agitate a portion of ether with the liquid. The ether dissolves the whole of the bromine, from which it receives a beautiful hyacinth red tint, and, on standing, rises to the surface. When the ethereal solution is agitated with caustic potassa, its colour entirely disap- pears, and, on evaporation, cubic crystals ofthe hydrobromate of potassa are deposited. M. Balard has ascertained that bromine exists in marine plants which grow on the shores of the Mediterranean sea, and has procured it in appreciable quantity from the ashes of the sea- weeds that furnish iodine. He has likewise detected its presence in the ashes of some animals, especially in those of the Janthina violacea, one of the testaceous mollusca. At common temperatures bromine is a liquid, the colour of which is blackish-red when viewed in mass and by reflected light, but appears hyacinth red when a thin stratum is interposed be- tween the light and the observer.' Its odour, which somewhat resembles that of chlorine, is very disagreeable; and its taste powerful. It acts with energy on organic mattery, such as wood or cork, and corrodes the animal texture ; but if applied to the skin for a short time only, it communicates a yellow stain, which is less intense than that produced by iodine, and soon disap- pears. It is highly destructive to animals, one drop of it placed on the beak of a bird having proved fatal. Its specific gravity is about 3. Its volatility is very considerable ; for at common temperatures it emits red-coloured vapours, which are very simi- BROMINE. 407 lar in appearance to those of nitrous acid, and at 116.5° F. it enters into ebullition. It retains its liquid form at the tempera- ture of zero of Fahrenheit's thermometer; at a degree or two below this, it becomes solid, and is then hard and brittle. Bromine is a non-conductor of electricity, and undergoes no chemical change from the agency of the imponderables. It was transmitted through a red-hot glass tube, and exposed to the action of a Voltaic pile, sufficiently powerful for disuniting the elements of water, without evincing the least trace of decom- position. It supports combustion in a very feeble manner:—a lighted taper immersed in the vapour of bromine is soon extin- guished; but before going out, it burns a few seconds with a flame which is green at its base and red at its upper part, as in an atmosphere of chlorine. Bromine is soluble in water, in alcohol, and particularly in ether. It does not redden litmus paper, but bleaches it rapidly like chlorine; and it likewise discharges the blue colour from a solution of indigo. Bromine and Oxygen.—Bromic acid may be procured in a separate state, by decomposing a dilute solution of bromate of baryta with sulphuric acid, so as to precipitate the whole of the baryta. The resulting solution of bromic acid may be concen- trated by slow evaporation until it acquires the consistence of syrup; but on raising the temperature in order to expel all the water, one part ofthe acid is volatalized, and the other resolved, into oxygen and bromine. A similar result took place when the evaporation was conducted in vacuo with sulphuric acid ; and accordingly all attempts to procure anhydrous bromic acid, have hitherto failed. Bromic acid has scarcely any odour, but its taste is very acid, though not at all corrosive. It reddens litmus paper powerfully at first, and soon after destroys its colour. It is not affected by nitric or sulphuric acids, except when the latter is highly con- centrated, in which case bromine is set free; and effervescence, probably owing to the escape of oxygen gas, ensues. From the analysis of bromate of potassa, bromic acid is obviously similar in constitution to iodic, chloric, and nitric acids ; that is, it con- sists of one proportion of bromine, united with five of oxygen. Bromine and Hydrogen.—From the close resemblance between bromine and chlorine, M. Balard was led to examine its rela- tions with hydrogen. No chemical action takes place between the vapour of bromine and hydrogen gas at common temperatures, not even by the agency of the direct solar rays; but on introducing a lighted candle or a piece of red-hot iron into the mixture, com- bination ensues in the vicinity of the heated body, though with- out extending to the whole mixture, and without explosion. The union is readily effected by the action of bromine on some ofthe gaseous compounds of hydrogen. Thus, on mixing the vapour of 408 BROMINE. bromine with hydriodic acid, sulphuretted hydrogen, or phos- phuretted hydrogen gases, decomposition follows, and a colour- less gas, possessed of acid properties, is generated. To this gas the name of hydro-bromic acid is applied. The hydro-bromic acid gas may be conveniently procured for experimental purposes by a process similar to that for forming hydriodic acid. A mix- ture of bromine and phosphorus, slightly moistened, yields, by the aid of gentle heat, a large quantity of pure hydro-bromic acid gas, which may be collected over mercury. The hydro-bromic acid gas is colourless, has an acid taste, and a pungent odour. It irritates the glottis powerfully, so as to ex- cite cough, and when mixed with moist air, yields white vapours, which are denser than those occasioned under the same circum- stances by muriatic acid gas. It undergoes no decomposition when transmitted through a red-hot tube, either alone, or mixed with oxygen. It is not effected by iodine; but chlorine decom- poses it instantly, with the production of muriatic acid gas, and a deposition of bromine. It may be preserved without change over mercury; but potassium and tin decompose it with facility, the first at common temperatures, and the last by the aid of heat. The hydro-bromic acid gas is very soluble in water. The aque- ous solution may be made by treating bromine with sulphuretted hydrogen dissolved in water, or still better, by transmitting a cur- rent of hydro-bromic acid gas through pure water. The liquid becomes hot during the condensation, acquires great density, increases in volume, and emits white fumes when exposed to the air. This acid solution is colourless when pure, but7possesses the property of dissolving a large quantity of bromine, and then re- t ceives the tint of that substance. Chlorine decomposes the solution of hydro-bromic acid in an % instant. Nitric acid likewise acts upon it, though less suddenly, occasioning the disengagement of bromine, and probably the for- mation of water and nitrous acid. The nitro-hydro-bromic acid is analogous to aqua regia, and possesses the property of dissolv- ing gold. The elements of sulphuric and hydro-bromic acids re-act on each other in a slight degree ; and hence, on decomposing the hydro-bromate of potassa by sulphuric acid, the hydro-bromic is generally mixed with a little sulphurous acid gas. The metallic oxides, as might be expected, do not act in an uniform manner on the hydro-bromic acid. The alkalies, earths, the oxides of iron, and the peroxides of copper and mercury, form compounds which may be regarded as hydro-bromates; whereas the oxide of silver, and the protoxide of lead, give rise to double decomposition, in consequence of which water and a metallic bromide result. The composition of hydro-bromic acid gas is easily inferred from the two following facts: 1. On decomposing hydro-bromic BROMINE. 409 acid gas, by potassium, a quantity of hydrogen remains precisely equal to half the volume of the gas employed ; and 2d, when hy- driodic acid gas is decomposed by bromine, the resulting hydro- bromic acid occupies the very same space as the gas which is decomposed. It is hence apparent that the hydro-bromic is ana- logous to hydriodic and muriatic acid gases; or, in other words, that 100 measures of hydro-bromic acid gas contains fifty mea- sures ofthe vapour of bromine, and fifty of hydrogen. By weight it may be regarded as a compound of one proportion of each element. Since bromine decomposes the hydriodic, and chlorine the hy- dro-bromic acid, it is obvious that bromine, in relation to hydro- gen, is intermediate between chlorine and iodine, its affinity for that substance being weaker than the first, and stronger than the second. The affinity of bromine and oxygen for hydrogen ap- pears nearly similar; for while oxygen cannot detach hydrogen from bromine, bromine does not decompose watery vapour. Bromide of Carbon.—To form this substance two parts of bromine are to be added to one part of periodide of carbon ; just enough of solution of alkali is to be added to make the iodine set free, disappear; the liquid bromide of carbon which will ap- pear at the bottom of the solution is to be separated by a funnel or otherwise, (but without washing with water,) and allowed to stand until it has become quite clear, during this time a quantity of iodate of potassa in crystals will rise to the surface, the clear fluid beneath is to be withdrawn and put into a weak solution of potassa for the purpose of decomposing a little protoiodide of carbon formed at the same time, a little bromide is also decom- posed, but that which remains is soon left in a pure state. The bromide of carbon very much resembles the protoiodide of carbon. They are both heavier than water—have the same appearance at first under its surface—the same ethereal and penetrating odour, and sweet taste—are both liquid, and be- come colourless by washing with a solution of potassa for the purpose of removing impurities. Bromine and Cyanogen. The Cyanide of Bromine has been prepared by M. Liebig by a process very similar to that described for procuring the cyanide of iodine. At the bottom of a small tubulated retort, or a rather long tube, are placed two parts of cyanide of mercury slightly moist- ened; and after cooling the apparatus by cold water, or still better by a freezing mixture, a precaution which is indispen- sable in summer, one part of bromine is introduced. Strong re- action instantly ensues, and caloric is so freely evolved, that a considerable quantity of the bromine would be dissipated, un- 3F 410 BROMINE. less the temperature of the retort had been previously reduced. The new products are bromide of mercury and cyanide of bro- mine, the latter of which collects in the upper part of the tube in the form of long needles. After allowing any vapour of bro- mine, which may have risen at the same time, to condense and fall back upon the cyanide of mercury, the cyanide of bromine is expelled by a gentle heat, and collected in a recipient carefully cooled. As thus formed, the cyanide is crystallized, sometimes in small regular colourless and transparent cubes, and sometimes in long and very slender needles. In its physical properties it is so very similar to the cyanide of iodine, that they may easily be mistaken for each other, especially when the crystals of the cyanide of bro- mine possess the acicular form. They agree closely in odour and volatility, but the cyanide of bromine is even more volatile than the cyanide of iodine. It is converted into vapour at 59° F. and crystallizes suddenly on cooling. Its solubility in water and alcohol is likewise greater than that ofthe cyanide of iodine. By a solution of caustic potassa it is converted into the hydrocy- anate and hydrobromate of potassa. Cyanide of bromine is highly deleterious. A grain of it dis- solved in a little water, and introduced into the oesophagus of a rabbit, proved fatal on the instant, acting with the same rapidity as prussic acid. In consequence of the volatility and noxious qualities of this substance, experiments with it should be con- ducted with circumspection. The danger from this cause, to- gether with a deficient supply of bromine, prevented M. Serullas from continuing the investigation of its properties. Hydrocarburet of Bromine may be formed by placing a drop of bromine in olefiant gas; it is colourless, heavier than water, has a penetrating ethereal odour, an exceedingly sweet taste, and is very volatile. It does not become coloured in the air like the hydrocarburet of iodine, and when dropped upon ignited porce- lain it yields white vapours instead of violet; when this substance is cooled to about 22° F. it becomes solid, and then breaks in the manner of camphor. When transmitted through a red-hot tube, it suffers decomposition, charcoal being deposited, and hy- drobromic acid gas evolved. It is therefore very analogous to the hydrocarburet of chlorine. Bromides of Phosphorus.—Phosphorus and bromine made to act on each other in an atmosphere of carbonic acid gas, form two compounds, the deutobromide of phosphorus which sublimes and crystallizes on the upper part ofthe vessel, and the proto- bromide which remains fluid beneath. Bromide of Sulphur, made by adding sublimed sulphur to bro- mine, is a reddish liquid producing fetid white vapours in the air, and producing strong acids with water. It is decomposed by chlorine. BROMINE. 411 Bromide of Arsenic is a perfectly transparent liquid, of a light lemon colour : it crystallizes in long prisms. Metallic Bromides.—The action of bromine on the metals pre- sents the closest resemblance to that which chlorine exerts on the same substances. Antimony and tin take fire by contact with bromine ; and its union with potassium is attended with such intense disengagement of heat as to cause a vivid flash of light, and to burst the vessel in which the experiment is performed. Deutobromide of Tin.—A solid white crystalline compound, readily fusible and volatile, yielding slight vapours in moist air, and dissolving in water to form an acid deutobromate. Perbromide of Iron.—Take a quantity of pure bromine, and put it into a porcelain capsule, containing about twenty times its weight of distilled water, and add gradually, stirring with a brass rod, iron filings until the liquor ceases to emit bubbles; it is then to be gently heated, and when it has acquired a greenish tint, it is to be filtered. The solution contains protobromide of iron, which is precipitated white by potassa, like the protosalts of iron, emitting a very peculiar smell; then evaporates to dryness by exposure to the air. The residual mass is of an orange red colour ; treated with water is does not entirely dissolve, there re- main some portions ofthe peroxide of iron derived from the per- oxidation of a small portion of the iron of the protobromide. When again evaporated, the red matter yields a deposit of a simi- lar red colour, rather more of a brick red, which strongly attracts moisture from the air, and is soluble in alcohol; when treated with sulphuric or muriatic acid, white acid vapours are disen- gaged. It is composed of Iron - 15.27 Bromine - - - 84.73 100 Bromide of Magnesium.—An excess of calcined magnesia is to be added to a solution of protobromide of iron, and slightly boiled. The filtered liquor, when evaporated to dryness, yields crystals, which, when purified by solution, and dried in a stove, are small acicular prisms, very soluble both in water and alcohol, deliquescent, of a bitter sharp taste, and precipitate in a flocculent state by ammonia, and by heat decompose into acid and base. It is composed of Magnesium - - - 7.760 Bromine - - - 92.240 100 Bromide of Calcium.—The bromide of iron is decomposed by hydrate of lime ; the liquor is to be filtered when the precipi- tale becomes brick red. Bromide of calcium is very deliquescent, fuses into a whitish mass, and gives out a peculiar smell which has some resemblance 412 BROMINE. to that of bromine, a small quantity of it appearing to suffer de- composition. This bromide crystallizes in acicular crystals, which are very soluble in water and alcohol; its taste resembles that of chloride of calcium. Sulphuric acid disengages a white vapour of hydrobromio acid, and towards the end, reddish vapours of bromine and sulphurous acid. When analysed by means of neutral oxalate of soda, it yielded such a quantity of oxalate of lime as showed that its composition was Calcium - - - 11.974 Bromine - - - 89.026 100 Bromide of Barium.—Protobromide of iron is to be boiled with an excess of moist carbonate of baryta; when the precipi- tate becomes red, the liquor is to be filtered, evaporated, and cal- cined. The product, re-dissolved in pure water and carefully evaporated, yields white rhombic prismatic crystals, slightly de- liquescent, soluble in water and alcohol, disagreebly bitter in taste, undecomposable by heat, and giving, with sulphuric acid, at first thick white vapours, and then reddish vapours. When treated with sulphuric acid, it yields such a proportion of sul- phate of baryta as indicates its composition to be Barium - - - 31.75 Bromine - 68.31 100.06 The bromide of barium, when dissolved, serves for preparing by double decomposition the bromides of magnesium and zinc, by employing the sulphates of these bases. Bromide of Potassium.—This is prepared by decomposing protobromide of iron with carbonate of potassa; when the satu- ration is perfect, the mixture is to be heated in the air to facili- tate the peroxidation of the iron ; the solution is to be filtered and evaporated, and by one or two crystallizations the pure bro- mide is obtained. This salt crystallizes very well in cubes ; it has a slightly sa- line taste, is slightly alterable by exposure to moisture, is soluble in alcohol, is decomposed by sulphuric acid, like the bromides of calcium and barium, and fuses without decomposing. When de- composed by sulphuric acid and heat, a portion of sulphate of potassa is obtained, which shows it to be composed of Potassium - 26.548 Bromine - 73.452 100 Bromide of Sodium.—Obtained as the last, substituting car- bonate of soda for that of potassa. This bromide crystallizes very well in groups of small acicular crystals, of a whitish colour. BROMINE. 413 It slightly attracts moisture by exposure to the air; its taste is rather alkaline than saline, and it is very soluble in water and al- cohol. It is composed of Sodium - 13.38 Bromine - 86.62 100 Protobromide of Mercury.—Pour a neutral solution of bromide of potassium, calcium, or magnesium, &c, into a very dilute so- lution of protonitrate of mercury ; an abundant flocculent pre- cipitate is formed, which is of a yellowish white colour : when this is carefully washed, and dried in the shade, the residue may be volatilized by a strong heat, and it condenses in the state of an acicular crystalline mass, which is of a yellowish colour while hot, but becomes whiter on cooling. It fuses like the protochlo- ride and perchloride of mercury. Re-agents, such as potassa, soda, and the hydrosulphurets, precipitate this bromide in the state of mercurial protosalts. It is probably composed of Mercury - 57.36 Bromine - 42.64 100 Perbromide of Mercury.—This compound may be prepared directly as proposed by M. Balard, by treating mercury with bro- mine, and subliming, or by decomposing persulphate of mercury with very dry bromide of potassium with the assistance of heat; equal quantities, sublimed with a strong heat, yield a substance which is crystalline on the inner surface, and of a yellowish white colour; it is partly soluble in water, and contains some insoluble protobromide. It may also be prepared by heating equal quantities of bromine and mercury under water. The mix- ture becomes pasty, and by evaporating the fluid, silky needles of perbromide are formed. Or the evaporation may be continued to dryness, and the residue sublimed; when purified by sublima- tion, it has the form of very fine silky needles, which are very soluble, have a. penetrating smell and are very volatile. It is precipitated yellow by potassa, and red by chromate of potassa. It is composed of Mercury - - 59.47 Bromine - - 46.53 100 Bromide of Antimony is colourless, it forms needle-shaped crystals. Bromide of Lead is precipitated from a solution of lead by hy- drobromic acid—fusing by heat—concreting, when cooled, into a yellow mass. Bromide of Gold.—Bromine and its aqueous solution dissolve gold. A yellow bromide is obtained, which stains animal sub- 414 BROMINE. stances of a violet colour; and is decomposed by heat into bro- mine and gold. Bromide of Platinum.—This metal dissolves in bromo-nitric acid, and forms a yellow compound, decomposed by heat, and giving yellow precipitates with salts of potassa and ammonia. Bromide of Bismuth, when in fusion, is of a red-hyacinth colour, becoming gray upon cooling. Bromide of Silver, produced by precipitation from the nitrate, is yellow, when dried in the shade, becoming black when exposed to the sun. It is insoluble in water or nitric acid, and soluble in ammonia. When exposed to heat it fuses, and upon cooling is converted into a reddish yellow hornlike substance. The Bromides of Glucinum and Yttrium are precisely analo- gous to the iodides of those metals. Salts. M. Balard is of opinion, that the soluble metallic bromides are converted, like the similar compounds of chlorine and iodine, into neutral hydro-bromates; and reciprocally, that the hydro- bromates are frequently converted into bromides in passing into the solid state. All the bromides are decomposed by chlorine with evolution of bromine; and the hydro-bromates are not only attacked by chlorine, but by all substances, such as the chloric or nitric acids, which have a strong tendency to deprive other bodies of hydrogen. Bromine acts upon metallic oxides much in the same manner as chlorine. On passing the vapour of bromine over potassa, soda, baryta, or lime, a vivid incandescence ensues, oxygen is disengaged, and a metallic bromide results. Magnesia and zir- conia are not decomposed by this treatment. When bromine acts on the solution of an alkali or alkaline earth, considerably diluted with water, the bromide of an oxide is produced, which possesses bleaching properties, and from which acetic acid causes the disengagement of bromine. But when this substance acts upon a concentrated solution of potassa, or when solid potassa is agitated with the ethereal solution of bromine, two salts are generated, the hydro-bromate and bromate of potassa; and on evaporating the solution the former is obtain- ed in cubic, and the latter in acicular crystals. The bromate of potassa is separated from the hydro-bromate by being very sparingly soluble in cold water. The alkaline earths likewise cause the formation of the two acids, but magnesia does not appear to possess that property. The bromates are analogous to the chlorates and iodates. Thus the bromate of potassa is converted by heat into the bro- mide of potassium, with disengagement of pure oxygen, defla- grates when thrown on burning charcoal, and forms with sulphur BROMINE. 415 a mixture which detonates by percussion. The acid of the bro- mates is decomposed by deoxidizing agents, such as the sulphur- ous acid and sulphuretted hydrogen, in the same manner as the acid of the iodates. The bromates likewise suffer decomposition from the action of hydro-bromic and muriatic acids. The bromate of potassa does not precipitate the salts of lead ; but occasions a white precipitate with the nitrate of silver, and a yellowish-white with the proto-nitrate of mercury; characters which, if correctly observed, distinguish the bromate from the iodate and chlorate of potassa in a very satisfactory manner. Hydro-bromate of Ammonia.—Ammoniacal gas unites with its own volume of hydro-bromic acid gas, forming a white, solid, volatile salt, which is soluble in water, and crystallizes in long prisms by evaporation. The Hydro-bromate of Baryta is very soluble in water, and is also dissolved by alcohol. It forms opaque mammillated crystals, which have no resemblance to the transparent scales ofthe mu- riate of baryta. The Hydro-bromate of Magnesia is deliquescent and uncrys- tallizable. and, like the muriate of that base, is decomposed by an elevated temperature. The salts of hydro-bromic acid have as yet been but partially examined, and the chief facts known respecting them have been mentioned. Chloride of Bromine. Bromine unites with chlorine at common temperatures, form- ing a very volatile liquid of a reddish-yellow colour, penetrating odour, and exceedingly disagreeable taste. It is soluble in wa- ter, and dissolves in that liquid apparently without decomposi- tion ; for the solution bleaches litmus paper without previously reddening it, and has the characteristic odour and colour of the compound. By the action of alkalies it is resolved into muriatic and bromic acids. Iodides of Bromine. Iodine appears to form two compounds with bromine. In certain proportions a solid is obtained, which, when heated, yields reddish-brown vapours, condensing into dendritic crystals. A further addition of bromine converts these crystals into a dark coloured liquid. The latter substance is soluble in water, yielding a bleaching fluid; with alkalies, it yields bromides and iodates. DIVISION V. Fluorine. The substance to which this name is applied has not hitherto been obtained in an insulated form, and therefore the properties which are peculiar to it in that state, are entirely unknown. From the nature of its compounds it appears to belong to the class of negative electrics, and, like oxygen and chlorine, to have a powerful affinity for hydrogen and metallic substances. With hydrogen it constitutes a peculiar and very powerful acid, the hydro-fluoric, the history of which will occupy the greater part of this division. Hydro-fluoric Acid. This acid was first produced in its pure state in the year 1810 by MM. Gay-Lussac and Thenard. It is prepared by acting on th^mineral called fluor-spar, carefully separated from siliceous earth and reduced to fine powder, with twice its weight of con- centrated sulphuric acid. The mixture is made in a leaden retort; and on applying heat, an acid and highly corrosive vapour distils over, which must be collected in a receiver of the same metal surrounded with ice. As the materials swell up consider- ably during the process, owing to a quantity of vapour forcing its way through a viscid mass, the retort should be capacious. At the close of the operation pure hydro-fluoric acid is found in the receiver, and the retort contains dry sulphate of lime. The chemical changes are similar to those which occur in the decom- position of chloride of sodium by sulphuric acid, as before ex- plained. Fluor-spar consists of fluorine and calcium, and when acted on by oil of vitriol, the water of that acid is resolved into its elements ; the hydrogen uniting with fluorine generates hydro- fluoric acid, and the lime, formed by the union of the oxygen of water and calcium, combines with sulphuric acid. If the oil of vitriol is of sufficient strength, all its water is decomposed, and the resulting hydro-fluoric acid is anhydrous. Hydro-fluoric acid, at the temperature of 32° F., is a colourless fluid, and remains in that state at 59°, if preserved in well stopped bottles; but when exposed to the air, it flies off in dense white fumes, which consist ofthe acid vapour combined with the mois- ture of the atmosphere. Its specific gravity is 1.0609; but its density may be increased to 1.25 by gradual additions of water. Its affinity for this liquid far exceeds that of the strongest sul- FLUORINE. 417 phuric acid, and the combination is accompanied with a hissing noise, as when red-hot iron is quenched by immersion in water. The vapour of hydro-fluoric acid is much more pungent than chlorine or any of the irritating gases. Of all known substances, it is the most destructive to animal matter. When a drop ofthe concentrated acid of the size of a pin's head comes in contact with the skin, instantaneous disorganization ensues, and deep ulceration of a malignant character is produced. On this account the greatest care is requisite in the preparation of pure hydro- fluoric acid. This acid, when concentrated, acts energetically on glass. The transparency of the glass is instantly destroyed, caloric is evolved, and the acid boils, and in a short time entirely disap- pears. A colourless gas, commonly known by the name of fluo- silicic acid gas is the sole product. This compound is always formed when hydro-fluoric acid comes in contact with siliceous substances. For this reason it cannot be preserved in glass; but must be prepared and kept in metallic vessels. Those of lead, from their cheapness, are often used; but vessels of silver or pla- tinum are preferable. In consequence of its powerful affinity for siliceous matter, hydro-fluoric acid may be employed for etching on glass; and when used with this intention, it should be diluted with three or four times its weight of water. Hydro-fluoric acid has all the usual characters of a powerful acid. It has a strong sour taste, reddens litmus paper, and with alkaline substances forms salts, which are termed hydro-fluates. All these salts are decomposed by strong sulphuric acid with the aid of heat, and the hydro-fluoric acid while escaping may be detected by its action on glass. Hydro-fluoric acid acts violently on some of the metals, espe- cially on the bases of the alkalies. Thus when potassium is brought in contact with the concentrated acid, an explosion attended with heat and light ensues ; hydrogen gas is disengaged, and a white compound, the fluoride of potassium, is generated. It is a solvent for some elementary principles which resist the action even of nitro-muriatic acid. Thus it dissolves silicon, zirconium, and columbium, with evolution of hydrogen gas; and when mixed with nitric acid, it proves a solvent for silicon which has been condensed by heat, and for titanium. The nitro-hydro- fluoric acid, however, is incapable of dissolving gold and plati- num. Several oxidized bodies, which are not attacked by sul- phuric, nitric, or muriatic acid, are readily dissolved by hydro- fluoric acid. As examples of this fact, several of the weaker acids, such as silica or silicic acid, titanic, columbic, molybdic, and tungstic acids may be enumerated. Chemists are not agreed as to the precise combining propor- tion of fluorine. According to the experiments of Dr. Thomson 18 is the true atomic weight of this substance; but as Berzelius 3 G 418 FLUORINE. has far more practical knowledge of the compounds of fluorine than other chemists, his result is probably nearer the truth. He found that 100 parts of pure fluoride of calcium prepared with the greatest care, yielded with sulphuric acid 175 parts of sulphate of lime. According to these numbers, fluoride of calcium con- sists of 20 parts or one proportion of calcium, and 18.86 parts or one proportion of fluorine, giving 38.86 as an equivalent of the compound ; and as the constitution of hydro-fluoric is analogous to that of muriatic and hydriodic acids, it is composed of 18.86 parts of fluorine and 1 part of hydrogen. A different view of the compounds of fluorine was originally taken by Gay-Lussac and Thenard, and is still held by some chemists. . They adopted the opinion that hydro-fluoric acid is a compound of a certain inflammable principle and oxygen, and applied to it the name of fluoric acid, previously introduced by Scheele. Fluor-spar, on this view, is a fluate of lime, and when this salt is decomposed by oil of vitriol, the fluoric rs merely dis- placed by the sulphuric acid, and the former passes off combined with the water of the latter. What we have described as anhy- drous hydro-fluoric acid is, according to this hypothesis, hydrated fluoric acid ; and when acted on by potassium, this metal is oxi- dized at the expense of the water, and potassa thus generated unites with fluoric acid, forming, not fluoride of potassium, but fluate of potassa. The combining proportion of fluoric acid, as inferred from the analysis of Berzelius, is 10.86; for 38.86 parts or one equivalent of fluor-spar is supposed to contain 28 parts of lime, (20 calcium and 8 oxygen,) thus leaving 10.86 as the equiv- alent ofthe acid. The theory, according to which fluor-spar is a compound of fluorine and calcium, originated as a suggestion with M. Ampere of Paris, and was afterwards supported experimentally by Sir H. Davy. It wds found that pure hydro-fluoric acid evinces no sign of containing either oxygen or water. Charcoal may be intensely heated in the vapour of the acid without the production of car- bonic acid. When hydro-fluoric acid was neutralized with dry ammoniacal gas, a white salt resulted, from which no water could be separated; and on treating this salt with potassium, no evi- dence could be obtained of the presence of oxygen. On exposing the acid to the agency of galvanism, there was a disengagement at the negative pole of a small quantity of gas, which was inferred from its combustibility to be hydrogen; while the platinum wire of the opposite side ofthe battery was rapidfy corroded, and be- came covered with a chocolate-coloured powder. Sir H. Davy explains these phenomena by supposing hydro-fluoric acid to have been resolved into its elements, and that fluorine, at the moment of arriving at the positive side of the battery, entered into combi- nation with the platinum wire which was employed as a con- ductor. Unfortunately, however, he did not succeed in obtaining FLUORINE. 419 fluorine in an insulated state. Indeed, from the noxious vapours that arose during the experiment, it was impossible to watch its progress, and examine the different products with that precision, which is essential to the success of minute chemical inquiries, and which Sir H. Davy has so frequently displayed on other occasions. Though these researches led to no conclusive result, they afforded so strong a presumption in favour of the opinion of Ampere and Davy, that it was adopted by several other chemists. This view has very recently received strong additional support from the experiments of M. Kuhlman. It was found by this chemist that fluor-spar is not in the slightest degree decomposed by the action of anhydrous sulphuric acid, whether at common temperatures or at a red heat. The experiment was made both by transmitting the vapour of anhydrous sulphuric acid over flour-spar heated to redness in a tube of platinum, and by put- ting the mineral into the liquid acid. In neither case did decom- position ensue; but when the former experiment was repeated with the difference of employing concentrated hydrous instead of anhydrous sulphuric acid, evolution of hydro-fluoric acid was produced. M. Kuhlman also transmitted dry muriatic acid gas over fluor-spar at a red heat, when hydro-fluoric acid was dis- engaged, without any evolution of hydrogen, and chloride of calcium remained. We are aware of no satisfactory explanation of these facts, except by regarding fluor-spar as a compound of fluorine and calcium, and hydro-fluoric acid as a compound of fluorine and hydrogen. We shall accordingly adopt this view, and never employ the term fluoric acid except when explaining phenomena according to the theory of Gay-Lussac. Fluo-boric Acid Gas. The chief difficulty in determining the nature of hydro-fluoric acid, arises from the water of the sulphuric acid which is em- ployed in its preparation. To avoid this source of uncertainty, Gay-Lussac and Thenard made a mixture of vitrified boracic acid and fluor-spar, and exposed it in a leaden retort to heat under the expectation that as no water was present, anhydrous fluoric acid would be obtained. In this, however, they were disappoint- ed ; but a new gas came over, to which they applied the term of fluo-boric acid gas. A similar train of reasoning led Sir H. Davy about the same time to the same discovery; though the French chemists had the advantage in priority of publication. Fluo-boric acid gas may be prepared more conveniently by mix- ing one part of vitrified boracic acid, and two of fluor-spar, with twelve parts of strong sulphuric acid, and heating the mixture gently in a glass retort. When thus prepared, however, it con- tains fluo-silicic acid, according to Berzelius, in considerable 420 FLUORINE. quantity; and Dr. Thomson detected in it traces of sulphuric acid. The gas may likewise be formed by the action of hydro- fluoric acid on a solution of boracic acid. In the decomposition of fluor-spar by vitrified boracic acid, the former and part of the latter undergo an interchange of ele- ments. The fluorine uniting with boron gives rise to fluo-boric acid gas; and by the union of calcium and oxygen lime is gene- rated, which combines with boracic acid, and is left in the retort as borate of lime. The fluo-boric acid gas, therefore, is com- posed of boron and fluorine. Those who adopt the theory of Gay- Lussac give a different explanation,' and regard this gas as a com- pound of fluoric and boracic acids. The lime of fluor-spar is supposed to unite with one portion of boracic acid, and fluoric acid at the moment of separation with another, yielding borate of lime and fluo-boric acid gas. Fluo-boric acid gas is colourless, has a penetrating pungent odour, and extinguishes flame on the instant. Its specific gravity, according to Dr. Thomson, is 2.3622. It reddens litmus paper as powerfully as sulphuric acid, and forms salts with alkalies which are called fluo-borates. It has a singularly great affinity for water. When it is mixed with air or any gas which contains watery vapour, a dense white cloud appears, which is a combina- tion of water and fluo-boric acid gas. From this circumstance it affords an exceedingly delicate test of the presence of mois- ture in gases. Fluo-boric acid gas is rapidly absorbed by water. According to Dr. John Davy, water absorbs 700 times its volume. Caloric is evolved during the absorption, and the water acquires an increase of volume. The saturated solution is limpid, fuming, and very caustic. On the application of heat, part of the gas is disengaged; but afterwards the whole solution is distilled. Gay-Lussac and Thenard and Dr. Davy were of opinion that fluo- boric acid gas is dissolved by water without decomposition ; but Berzelius denies the accuracy of their observation. On trans- mitting the gas into water until the liquid acquires a sharply sour taste, but is far from being saturated, a white powder begins to subside, and on cooling a considerable quantity of boracic acid is deposited in crystals. It appears that in a certain state of dilution, part of the fluo-boric acid and water mutually decom- pose each other with formation of boracic and hydro-fluoric acids. The latter unites, according to Berzelius, with undecom- posed fluo-boric acid, forming what he has called the boro-hy- drofluoric acid. On concentrating the liquid by evaporation, the boracic and hydro-fluoric acids decompose each other, and the original compound is re-produced. Fluo-boric acid gas does not act on glass, but attacks animal and vegetable matters with energy, converting them like sul- phuric acid into a carbonaceous substance. This action is most probably owing to its affinity for water. FLUORINE. 421 When potassium is heated in fluo-boric acid gas, the metal takes fire, and a chocolate-coloured solid, wholly devoid of me- tallic lustre, is formed. This substance is a mixture of fluoride of potassium and boron, and by the action of water the former is dissolved, and the boron left in a solid state. The composition of fluo-boric acid gas has not hitherto been determined by direct experiment. Dr. Davy ascertained that it unites with an equal measure of ammoniacal gas, forming a solid salt; and also combines with twice and three times its volume of ammonia, yielding liquid compounds. In the first salt, the rela- tive weights of the constituent gases are in the ratio of their specfiic gravities; and if the compound consists of one proportion of each, it will be thus constituted, Fluo-boric acid gas . 2>3622 . 68.04 one proportional. Ammoniacal gas . 0.5902 . 17 one proportional, and the combining proportion of the acid may be assumed in round numbers to be 68. Now, supposing this acid to be formed of three proportionals of fluorine and one of boron, its equivalent will be 64.58, a number which approximates to the preceding. But this view is quite hypothetical. Dr. Thomson considers 34 as the equivalent of fluo-boric acid gas, and believes it to consist of one proportion of fluorine and two of boron. His opinion, however, is very improbable; for the formation of the gas from a mixture of boracic acid and fluor-spar, according to this sup- position, appears quite inexplicable. These remarks will serve to show that the data for forming an opinion on this subject are uncertain. Fluosilidc Add Gas. This gas is formed whenever hydrofluoric acid comes in con- tact with siliceous earth ; and this is the reason why pure hy- drofluoric acid can be prepared in metallic vessels only, and with fluor-spar that is free from rock crystal. The most conve- nient method of procuring the gas is to mix in a retort one part of pulverized fluor-spar with its own weight of sand or pounded glass, and two parts of strong sulphuric acid. On applying a gentle heat, fluosilicic acid gas is disengaged with effervescence, and may be collected over mercury. The chemical changes attending this process are differently explained, according to the view which is taken concerning the nature ofthe product. In regarding fluor-spar as a compound of fluoric acid and lime, the former at the moment of being set free is thought to unite directly with silica; so that the resulting compound consists of silica and fluoric acid. But for reasons al- ready stated, fluor-spar is here not considered as a fluate of lime; and therefore this view cannot be admitted. It is inferred, on the contrary, that when, by the action of sulphuric acid on fluo- 422 FLUORINE. ride of calcium, hydro-fluoric acid is generated, the elements of this acid re-acton those of silica, and give rise to the production of water and fluosilicic acid gas. This gas is, therefore, a fluoride of silicon ; and though, in compliance with the usage of other chemists, we have retained its ordinary name, its title to be con- sidered an acid is questionable. It may occur to some whether hydro-fluoric acid does not unite directly with silica ; but this idea is inconsistent with the proportion in which the elements of the gas are found to be united. This compound is a colourless gas, which extinguishes flame, destroys animals that are immersed in it, and irritates the respi- ratory organs powerfully. It does not corrode glass vessels, pro- vided they are quite dry. When mixed with atmospheric air it forms a white cloud, owing to the presence of watery vapour. Its specific gravity, according to Thomson, is 3.6111 ; and 100 cubic inches of it, at 60° F. and when the barometer stands at 30 inches, weigh 110.138 grains. Water acts powerfully on fluosilicic acid gas, of which it con- denses, according to Dr. John Davy, 365 times its volume. The gas suffers decomposition at the moment of contact with water, depositing part of its silica in the form of a gelatinous hydrate, which, when well washed, is quite pure. The liquid, which has a sour taste, and reddens litmus paper, contains the whole ofthe hy- dro-fluoric acid, together with two thirds of the silica which was originally present in the gas. By conducting fluo-silicic acid gas into a solution of ammonia, complete decomposition ensues ; hydrofluoric acid unites with the alkali, forming hydro-fluate of ammonia, and all the silica is deposited. On this fact is founded the mode of analyzing fluo-silicic acid gas, adopted by Dr. Davy and Dr. Thomson. According to the results obtained by Thomson, which appear more correct than those of Dr. Davy, this gas is composed of 18.86 parts or one equivalent of fluorine, and 8 parts or one equivalent of silicon. Considered as a com- pound of fluoric acid and silica, it consists of 10.86 parts or one equivalent of fluoric acid, and 16 parts or one equivalent of silica. The solution which is formed by fully saturating water with fluo-silicic acid gas is powerfully acid, and emits fumes on expo- sure to the air. It is commonly known by the name of silicated fluoric acid; but a more appropriate term is silico-hydrofluoric acid. According to the experiments of Berzelius, it appears to be a definite compound of hydro-fluoric acid and silica in the ratio of three equivalents of the former to two of the latter. If evaporated before separation from the silica deposited bv the ac- tion of water on fluo-silicic acid gas, this compound is re-pro- duced. But if the solution is poured off from the silica thus de- posited, and then evaporated, fluo-silicic acid gas is at first evolv- ed and subsequently hydro-fluoric acid and water are expelled. The evaporation of silico-hydrofluoric acid in vacuo is attended FLUORINE. 423 by a similar change, so that this acid cannot be obtained free from water. It does not corrode glass; but when evaporated in glass vessels, the production of free hydrofluoric acid of course gives rise to corrosion. On neutralizing silico-hydrofluoric acid with ammonia, and gently evaporating to dryness, all the silica is rendered insoluble. By exactly neutralizing with carbonate of potassa, nearly all the silica and acid are precipitated in the form of a sparingly solu- ble double hydro-fluate of silica and potassa; and a still more complete precipitation is effected by muriate of baryta in excess, when hydrofluate of silica and baryta is generated. A variety of similar compounds may be obtained either by double decomposi- tion, or by the action of silico-hydrofluoric acid on metallic oxides. Most of these salts are soluble in water, those of potassa, soda, lime, baryta, and yttria, being the only sparingly soluble ones no- ticed by Berzelius. They have in general a sour bitter taste, redden litmus paper, and are decomposed at a high temperature with disengagement of fluo-silicic acid gas. These salts were formerly known by the name of fluo-silicates, in which silica and fluoric acid were thought to act the part of a compound acid ; but Berzelius has shown that this view is inaccurate, and that they may be regarded as double salts, consisting of two propor- tionals of hydro-fluate of silica, and one proportional of a hydro- fluate of some other base. Most ofthe facts contained in the preceding account of silico- hydrofluoric acid are drawn in part from an Essay of Berzelius in the Annals of Philosophy, XXIV. 450. Fluo-chromic Acid Gas.—When a mixture of fluor-spar and chromate of lead is distilled with fuming, or even common sul- phuric acid in a leaden retort, a red-coloured gas is disengaged. This gas acts rapidly upon glass, with deposition of chromic acid and formation of fluo-silicic acid gas. It is absorbed by water, and the solution is found to contain a mixture of fluoric and chromic acids. The watery vapour of the atmosphere ef- fects its decomposition, so that when mixed with air, red fumes appear, owing to the separation of minute crystals of chromic acid. This gas may be regarded as a compound of fluorine and chromium, a view which is rendered very plausible by the cir- cumstance of its being decomposed so readily by moisture. Berzelius has discovered that hydro-fluoric acid is susceptible of forming combinations with titanic, columbic, tungstic, and molybdic acids; that these compound acids dissolved in water, are analogous to liquid fluo-silicic acid; and that the water may be re-placed by other bases, forming distinct genera of salts, called fluo-titanites, fluo-lungstates, &c. Fluoride of Manganese.—A gaseous compound of fluorine and manganese has been lately discovered by M. Dumas and Dr. Wohler. It is best formed by mixing common mineral chame- 424 FLUORINE. leon with half its weight of fluor-spar, and decomposing the mix- ture in a platinum vessel, by fuming sulphuric acid. The fluo- ride is then disengaged in the form of a greenish-yellow gas or vapour, of a more intensely yellow tint than chlorine. When mixed with atmospheric air, it instantly acquires a beautiful purple-red colour; and is freely absorbed by water, yielding a solution of the same red tint. It acts instantly on glass, with formation of fluo-silicic acid gas, a brown matter being at the same time deposited, which becomes of a deep purple-red tint on the addition of water. From the experiments of Dr. Wohler, this yellow gas may be inferred to be a fluoride of manganese; that when mixed with water, both compounds are decomposed, and hydro-fluoric and manganesic acids generated, which are dissolved; that a similar formation of the two acids ensues from the admixture of the yel- low gas with atmospheric air, owing to the moisture contained in the latter; and that by contact with glass, fluo-silicic acid gas is produced, and anhydrous manganesic acid deposited. In con- sequence of its acting so powerfully on glass, its other proper- ties have not been ascertained ; but from those above mentioned, its composition is obviously similar to that of the gaseous chlo- ride of manganese. It hence consists of one equivalent of man- ganese, and four equivalents of fluorine. As fluorine has not hitherto been obtained in a separate state, the nature of its action on the metals is unknown; but the chief difficulty of procuring it in an insulated form, appears to arise from its extremely powerful affinity for metallic substances, in consequence of which, at the moment of becoming free, it attacks the vessels and instruments employed in its preparation. The best mode of preparing the soluble fluorides, such as those of potassa and soda, is by dissolving the carbonate of these alka- lies in hydro-fluoric acid, and evaporating the solution to perfect dryness. The insoluble fluorides are easily formed from the hydro-fluates of potassa and soda by double decomposition. These compounds are, without exception, decomposed by con- centrated sulphuric acid with the aid of heat; and the hydro- fluoric acid, in escaping, may easily be detected by its action on glass. Hydrofluates. Hydro-fluoric acid unites readily with the pure alkalies, yield- ing soluble hydrofluates, which are converted into metallic fluo- rides by .the action of heat. The neutral hydrofluates of the alkalies, those, namely, that contain one equivalent of acid and one equivalent of base, have an alkaline re-action. It may be doubted if this acid can unite at all with the alkaline earths; for it yields with them insoluble compounds, which have all the cha- FLUORINE. 425 racters of metallic fluorides. The same remark applies to the action of hydro-fluoric acid on the earths, with the exception of alumina and zirconia, which form soluble hy/lro-fluates. The salts of hydro-fluoric acid are recognised by forming with muriate of lime, a white gelatinous precipitate, which yields hydro-fluoric acid when heated with concentrated sulphuric acid. It is doubtful if any hydro-fluate exists ready formed in the mineral kingdom. Four minerals may be enumerated as such ; namely, the topaz, or the double hydro-fluate of silica and alu- mina, the hydro-fluate of cerium, double hydro-fluate of cerium and yttria, and cryolite, or the double hydro-fluate of alumina and soda. It is probable, however, that these compounds, like fluor-spar, are metallic fluorides. Hydro fluate of Potassa.—Potassa unites with hydro-fluoric acid in two proportions, forming a hydro-fluate and a bi-hydro- fluate ; the former of which consists of one, and the latter of two, equivalents of acid, united with one equivalent of potassa. The hydro-fluate, which has an alkaline re-action, is best prepared by supersaturating carbonate of potassa with hydro-fluoric acid, evaporating the solution to-dryness, and expelling the excess of acid by heat. The residue has a sharp saline taste; is deli- quescent, and crystallizes with difficulty ; but when evaporated at a temperature between 95° and 104°, it forms cubic crystals. These crystals, like the salt, after being heated, are most proba- bly fluoride of potassium. The bi-hydro-fluate is easily procured by adding to hydro- fluoric acid a quantity of potassa insufficient for neutralizing it completely, and concentrating the solution. By slow evapora- tion, it yields rectangular tables, the/lateral edges of which are bevelled. This salt has an acid re-action, is soluble in water, and decomposed by heat. Hydro-fluate of Soda.—The neutral and acid hydro-fluates, of soda may be formed in the same manner as the preceding salts. The acid hydro-fluate consists of one equivalent of base and two of the acid, possesses a sharp and purely sour taste, is but spa- ringly soluble in cold water, and crystallizes in transparent rhombohedrons. The neutral hydro-fluate is sparingly soluble in water, and its solubility is not increased by elevation of tempe- rature. It is almost completely insoluble in alcohol. It com- monly crystallizes in cubes, like chloride of sodium, but assumes the form of an octahedron when carbonate of soda is present. The neutral and acid hydro-fluates of lithia are sparingly solu- ble in water. The neutral hydro-fluate of ammonia may be prepared by mix- ing in a platinum crucible one part of sal-ammoniac and 2i parts of fluoride of sodium, both in fine powder and quite dry, and ap- plying a gentle heat with a spirit lamp. The hydro-fluate of ammonia sublimes, and condenses in small prisms on the lid of 3H 426 FLUORINE. the crucible, if kept cool, without any admixture of muriate of ammonia. Chloride of sodium is generated at the same time. This salt is permanent in the air, slightly soluble in alcohol, and copiously dissolved by water. It corrodes glass vessels even in its dry state. In solution, it gradually parts with ammonia, and is converted into a deliquescent bi-hydro-fluate. It is doubtful if the alkaline earths combine at all with hydro- fluoric acid. On digesting recently precipitated carbonate of baryta in an excess of this acid, carbonic acid is gradually evolv- ed, and a compound is formed, which appears to be a fluoride of barium. It is very slightly soluble in water and hydro-fluoric acid; but it is dissolved freely by muriatic acid, and ammonia added to the solution causes a precipitate, which is a compound of fluoride and chloride of barium. A similar substance is form- ed on mixing a solution of muriate of baryta with an alkaline hydro-fluate. On digesting newly precipitated carbonate of lime in an ex- cess of hydro-fluoric acid, agranular fluoride of calcium is generat- ed. It is insoluble in water, and hydro-fluoric acid, and is very slightly dissolved by muriatic acid. * It may also be formed by double decomposition ; but it then forms a translucid jelly, which fills up the pores of a filter, and is therefore washed with difficul- ty. This compound appears to be identical with the beautiful mineral commonly known by the name of fluor or Derbyshire spar. This mineral frequently accompanies metallic ores, espe- cially those of lead and tin; and it often occurs crystallized either in cubes or some of its allied forms. The crystals found in the lead mines of Derbyshire are remarkable for the largeness of their size, the regularity of their form, and the variety and beauty of their colours. It is employed in forming vases, as a flux in metallurgic processes, and in the preparation of hydro- fluoric acid. The nature and composition of this substance were considered on a former occasion. For an account of the action of hydro-fluoric acid on other metallic oxides, we may refer to an essay of Berzelius on this subject. Remarks upon the Compounds of Chlorine, Iodine, Bromine, Fluo- rine, Selenium, Sulphur, and Cyanogen, with the metals. Respecting these compounds, there remains one subject, the consideration of which, as applying equally to all, has been pur- posely delayed. The non-metallic ingredient of each of these compounds is the radical of a hydracid, that is, it has the pro- perty of forming with hydrogen an acid, which, like other acids, is unable to unite with metals, but appears to combine readily with many metallic oxides. Owing to this circumstance, a dif- ficulty arises in explaining the action of such substances on THEORETICAL VIEWS. 427 water. Thus, when the chloride of potassium is put into water, it may dissolve without suffering any other chemical change, and the liquid accordingly contain chloride of potassium in solution. But it is also possible that the elements of this compound may re-act on those of water, its potassium uniting with oxygen, and its chlorine with hydrogen; and as the resulting potassa and muriatic acid have a strong affinity for each other, the solution would of course contain muriate of potassa. A similar uncer- tainty attends the action of water on other metallic chlorides, and on the compounds of metals with iodine, bromine, sulphur, and similar substances; so that when the iodide, sulphuret, and cy- anide of potassium are put into water, chemists are in doubt whe- ther they are dissolved as such, or whether they may not be con- verted, by decomposition of water, into the hydriodate, hydrosul- phate, and hydrocyanate of potassa. This question would at once be decided, could it be ascertained whether water is or is not decomposed during the process of solution; but this is the precise point of difficulty, since, from the operation of the laws of chemical union, no disengagement of gas does or can take place by which the occurrence of such a change may be indicat- ed. Chemists, accordingly, being guided by probabilities, are divided in opinion, and we shall therefore give a brief statement of both views, with the arguments in favour of each. According to one view, then, the chloride of potassium and all similar compounds dissolve in water without undergoing any other change, and are deposited in their original state by crys- tallization. When any hydracid, such as muriatic or hydriodic acid, is mixed with potassa or any similar metallic oxide, the acid and salifiable base do not unite, as happens in other cases, but the oxygen ofthe oxide combine with the hydrogen of the acid, and the metal itself with the radical ofthe hydracid. This kind of double decomposition unquestionably takes place in some instances, as when sulphuretted hydrogen acts upon a salt of lead, the insoluble sulphuret of lead being actually precipitated; but it is also try some thought to occur even when the trans- parency of the solution is undisturbed. According to this view muriate of potassa, and the salts ofthe hydracids in general have no existence. When nitrate ofthe oxide of silver is added to a solution of the chloride or cyanide of potassium, metallic silver unites with chlorine or cyanogen, while the oxygen ofthe oxide of silver combines with potassium; so that nitrate of potassa and chloride or cyanide of silver are generated. On adding sulphuric acid to a solution of the chloride of potassium, instantaneous production of muriatic acid and potassa ensues, in consequence of water being decomposed, and yielding its hydrogen to chlo- rine, and its oxygen to potassium; and this explanation is justi- fied by the circumstance, that the same change is admitted to occur when concentrated sulphuric acid is brought into contact 428 THEORETICAL VIEWS. with solid chloride of potassium. It is further believed that the crystallized muriates of lime, baryta, and strontia, which contain water, or its elements, are metallic chlorides combined with wa- ter of crystallization ; and the same view is applied to all analo- gous compounds. According to the other view, chloride of potassium is convert- ed into muriate of potassa in the act of dissolving; and when the solution is evaporated, the elements existing in the salt re- unite at the moment of crystallization, and crystals of the chlo- ride of potassium are deposited. The same explanation applies in all cases, when the salt of a hydracid crystallizes without re- taining the elements of water. Of those compounds, which, in crystallizing, retain water or its elements in combination, two opinions may be formed. Thus crystallized muriate of baryta, which consists of one equivalent of chlorine, one of barium, two of oxygen, and two of hydrogen, may be regarded as a compound either of muriate of baryta, with one equivalent of water of crys- tallization, or of chloride of barium with two equivalents of wa- ter. When exposed to heat, two proportionals of water are ex- pelled, and chloride of barium is left. When nitrate of the oxide of silver is mixed in solution with muriate of potassa, the oxygen of the oxide of silver unites with'*the hydrogen of the muriatic acid; chloride of silver is precipitated, and nitrate of potassa re- mains in the liquid. On adding sulphuric acid to a muriate, mu- riatic acid is simply displaced, as when carbonic acid in marble is separated from lime by the action of nitric acid. On comparing these opinions, it is manifest that both are con- sistent with well known affinities. When, for example, a metallic chloride is dissolved in water, the attraction of chlorine for the metal, and that of oxygen for hydrogen, tends to prevent chemi- cal change ; but the affinities of the metal for oxygen, of chlo- rine for hydrogen, and of muriatic acid for metallic oxides, co- operate in determining the decomposition of water, aW the pro- duction of a muriate. Neither view has materially the advantage in point of simplicity ; for while some phenomena are more sim- ply explained by one mode of reasoning, others are more easily explicable according to the other. It is certainly an objection to the second view, that it supposes the frequent decomposition and re-production of water, without there being any direct proof of its occurrence ; for the solution of chlorides and similar com- pounds often takes place, even without disengagement of caloric. The circumstances which may be mentioned as appearing to in- dicate the decomposition of water, are the following:—1. The solution of some compounds, such as sulphuret and cyanide of potassium, actually emit an odour of sulphuretted hydrogen and hydro-cyanic acid. 2. Other compounds, such as the chlorides of copper, cobalt, and nickel, instantly acquire, when put into water, the colour peculiar to the salts ofthe oxides of those me- THEORETICAL VIEWS. 429 •— •— tals. 3. The solution of protochloride of■♦rQa,*4B5BfKS*j_roto-* sulphate, absorbs oxygerflrom the atiftrjsphej^ jTnd tjys effect could scarcely be expected to occur, unless the protoxide oT«*on were contained in the liquid. 4. In some instances there is direct proof of decomposition of water. Thus, when sulphuret of aluminum is put into that fluid, alumina is generated, and sul- phuretted hydrogen gas disengaged with effervescence. In like manner the chloride and sulphuret of silicon are converted by water into silica and muriatic acid and sulphuretted hydrogen. In these cases, the want of affinity between the new compounds causes their separation, and thus affords direct proof that water is decomposed. But the affinities which produce this change do not appear so likely to be effective, as those which are in opera- tion when the chloride of potassium is put,into water ; especially when it is considered that the attraction of chlorine for hydrogen, and potassium for oxygen, is aided by that of the resulting acid and oxide for each other. 5. The last argument we shall men- tion in favour of this opinion, is founded on the production of the hydro-carburet of iodine by the mutual action of potassa, iodine, and alcohol, as observed by M. Serullas. It has been stated, that when potassa acts on iodine, iodic and hydriodic acids _are generated by decomposition of water, and the solution con- tains the iodate and hydriodate of that alkali. But if the exis- tence ofthe hydriodate of potassa be denied, the only consistent explanation of the phenomena is, that the elements of potassa unite with separate portions of iodine, producing iodic acid, which unites with undecomposed potassa, and iodide of potas- sium. According to this view, water is not decomposed at all; whereas the process of M. Serrulas does not seem explicable ex- cept by the decomposition of water. The first argument is not perhaps to be trusted, because the production of sulphuretted hydrogen and hydrocyanic acid is probably occasioned by the carbonic acid of the atmosphere. The four latter, though not amounting to demonstration, give a high degree of probability to the existence of salts of muriatic and hydriodic acid ; and if this be admitted, the same view may be extended to other hydracids. This opinion, which is preferred by most chemists, except by Berzelius and his pupils, has been adopted in the present work. Considering how much the affinity of metals for oxygen, and of the radicals ofthe hydracids for hy- drogen, differs in force, it is likely that some of the chlorides and similar compounds dissolve without change, while others give rise to decomposition of water. But, as in general, chemists possess no means of determining the nature of the change in particular instances, we have thought it would be most consistent to apply the same view to all, except in some special cases when the contrary has been mentioned. ( 430 ) ^% ^ «■* On ike, Atomic Theory of Mr. Dalton. The brief sketch which has been given ofthe laws of combi- nation in the section on nitrogen, will serve to set the impor- tance of this department of chemical science in its true light. It is founded, as will have been seen, on experiment alone, and the laws which have been stated are the pure expression of fact. It is not necessarily connected with any speculation, and may be kept wholly free from it. It is not uncommon for persons commencing the study of chemistry, to entertain a vague notion that this department of the science comprehends something uncertain and hypothetical in its nature, and to be thus led to form an erroneous idea of its importance. This misapprehension may easily be traced to its source. It was impossible to reflect on the regularity and con- stancy with which bodies obey the laws of combination, without speculating about the cause of that regularity; and consequently, the facts themselves were no sooner noticed, than an attempt was made to explain them. Accordingly, when Mr. Dalton published his discovery of those laws, he at once incorporated the descrip- tion of them with his notion of their physical cause; and even expressed the former in language suggested by the latter. Since that, period, though several British chemists of eminence, and in particular Dr. Wollaston and Sir H. Davy, have recommended and practised an opposite course, both subjects have been but too commonly comprised under the name of atomic theory; and hence it has often happened that beginners have rejected the whole as hypothetical, because they could not satisfactorily dis- tinguish those parts that are founded on fact, from those which are conjectural. All such perplexity would have been avoided, and this department of the science have been far better under- stood, and its value more justly appreciated, had the discussion concerning the atomic constitution of bodies been always kept distinct from what it is intended to explain. When employed in this limited sense, the atomic theory may be discussed in a few words. Two opposite opinions have long existed concerning the ulti- mate elements of matter. It is supposed, according to one party, that every particle of matter, however small, may be divided into smaller portions, provided our instruments and organs were adapted to the operation. Their opponents contend, on the other hand, that matter is composed of certain atoms which are of such a nature as not to admit of division. These opposite opinions have, from time to time, been keenly contested, and With variable success, according to the acuteness and ingenuity of their respective champions. But it was at last perceived that no positive data existed capable of deciding the question, and its ATOMIC THEORY. 431 interest therefore gradually declined. The progress of modern chemistry has revived the general attention to this controversy, by affording a far stronger argument, in favour of the atomic con- stitution of bodies than was ever advanced before, and which is almost irresistible. We have only in fact to assume with Mr. Dalton, that all bodies are composed of ultimate atoms, the weight of which is different in different kinds of matter, and we explain at once the foregoing laws of chemical union. The phe- nomena do not appear explicable on any other supposition. According to the atomic theory, every compound is formed of the atoms of its constituents. An atom of A may unite with 1, 2, 3, or more atoms of B. Thus, supposing water to be com- posed of one atom of hydrogen and one atom of oxygen, the deutoxide of hydrogen will consist of one atom of hydrogen to two atoms of oxygen. If carbonic oxide is formed of one atom ef carbon and one atom of oxygen, carbonic acid will consist of one atom of carbon to two atoms of oxygen. If, in the compounds of nitrogen and oxygen, enumerated at page 111, the first, or pro- toxide is constituted of one atom of nitrogen to one atom of oxy- gen, the four others will be regarded as compounds of one atom of nitrogen to 2, 3, 4, and 5 atoms of oxygen. From these in- stances it will appear, that the law of multiple proportion is a necessary consequence of the atomic theory. There is also no apparent reason why two or more atoms of one substance may not combine with 2, 3, 4, 5, or more atoms of another. Such combinations will account for the complicated proportion noticed in some compounds, especially in many of those belonging to the animal and vegetable kingdoms. In consequence of the very complete explanation which the laws of chemical union receive by means of the atomic theory, it has become customary to employ the term atom in the same sense as combining proportion or equivalent. For example, instead of saying water is composed of one equivalent of oxygen and one equivalent of hydrogen, it is said to consist of one atom of each element. In like manner sulphate of potassa is formed of one equivalent or one atom of sulphuric acid and one atom of potassa, the word, in this case, denoting, as it were, a compound atom, that is, the smallest integral particle of the acid or alkali; such a particle, which does not admit of being divided, except by the separation of its elementary or constituent atoms. The num- bers expressing the proportions in which bodies unite, must like- wise indicate, consistently with this view, the relative weights of atoms; arid accordingly these numbers are often called atomic weights. Thus, as water is composed of eight parts of oxygen and one of hydrogen, it follows, on the supposition of water con- sisting of one atom of each element, that an atom of oxygen must be eight times heavier than an atom of hydrogen. If carbonic oxide is formed of an atom of carbon and an atom of oxygen, the 432 ATOMIC THEORY. relative weights of their atoms are as 6 to 8; and in short the relative weights of all other bodies are expressed by the numbers which denote their combining proportions. Though the phenomena of chemical combination leave little doubt of the atomic constitution of matter, other powerful argu- ments may now be adduced in favour of this theory. Dr. Wol- laston, in his Essay on the Finite Extent of the Atmosphere, has supported this doctrine on a new and independent principle, the particulars of which have been stated in the section on nitrogen. Another argument, which amounts almost to demonstration, is deducible from the peculiar connection noticed by Professor Mitscherlich between the form and composition of certain crys- talline substances. But in adopting the notion that matter is composed of ultimate individual particles, we are by no means satisfied ofthe propriety of expressing the facts of the science in language founded on this theory; because, though the elements of bodies be arranged atomically, we have no certain method of ascertaining, in the present state of chemistry, how many atoms are contained in any compound. This difficulty is particularly felt with respect to those series of compounds in which half a proportion occurs ; for as the idea of half an atom is inconsistent with the atomic theory, such an arrangement of the atoms must be imagined, as shall avoid the occurrence of a fraction. The mode of accomplishing this object may be exemplified in reference to the oxides of lead and iron, the constituents of which were mentioned on a former occasion. The oxides of lead may either be regarded as com- posed, the protoxide of one atom of lead to one atom of oxygen, the deutoxide of two atoms of lead to three atoms of oxygen, and the peroxide of one atom of lead to two atoms of oxygen ; or they may be viewed as compounds, the protoxide of one atom of lead to two atoms of oxygen, the deutoxide of one atom of lead to three atoms of oxygen, and the peroxide of one atom of lead to four atoms of oxygen. In like manner the oxides of iron are either composed, the protoxide of one atom of iron and one atom of oxygen, and the peroxide of two atoms of iron to three atoms of oxygen; or the protoxide of one atom of iron to two atoms of oxygen, and the peroxide of one atom of iron to three atoms of oxygen. The uncertainty attending these atomic speculations cannot be more forcibly evinced than by the fact, that Berzelius, two or. three years ago, regarded all the stronger bases, such as the alkalies, alkaline earths, and the protoxides of several of the common metals, as composed of one atom of metal and two atoms of oxygen; but that he has suddenly abandoned this view, and now believes the very same substances to contain one atom of metal and one atom of oxygen. Such sudden changes cannot take place without producing material confusion; and tend to show that the science is not yet so far advanced as to admit of ATOMIC THEORY. 433 the atomic constitution of bodies being settled on permanent principles. Until the period when this desirable object may be accomplished, it is to be hoped that chemists will persevere in the practice, which is now almost universal, of stating the com- bining proportions of bodies as nearly as possible in the way supplied by analysis, instead of doubling some numbers and halving others to make them conformable to some favourite hy- pothesis of the moment. Mr. Dalton supposes that the atoms of bodies are spherical, and has invented certain symbols to represent the mode in which he conceives they may combine together, as illustrated by the following figures. O Hydrogen. O Oxygen. © Nitrogen. © Carbon. Binary Compounds. O O Water. ' O • Carbonic oxide. Ternary Compounds. O O O Deutoxide of hydrogen. O • O Carbonic acid. &c. &c. &c. All substances containing only two atoms he called binary com- pounds, those composed of three atoms ternary compounds, of four, quaternary, and so on. There are several questions relative to the nature of atoms, most of which will perhaps never be decided. Of this nature are the questions which relate to the actual form, size, and weight of atoms, and to the circumstances in which they mutually differ. All that we know with any certainty is, that their weights do differ, and by exact analysis the relations between them may be determined. It is but justice to the memory of the late Mr. Higgins of Dublin, to state that he first made use ofthe atomic hypothesis in chemical reasonings. In his " Comparative View of the phlo- gistic and anti-phlogistic theories," published in the year 17S9, he observes that " in volatile vitriolic acid, a single ultimate par- ticle of sulphur is intimately united only to a single particle of dephlogisticated air; and that, in perfect vitriolic acid, every single particle of sulphur is united to two of dephlogisticated air, being the quantity necessary to saturation ;" and he reasons in the same way concerning the constitution of water and the compounds of nitrogen and oxygen. These remarks of Mr. Hig- gins do not appear to have had the slightest connection with the o I 434 THEORY OF VOLUMES. subsequent views of Mr. Dalton. When in Europe we had an inter- view with Mr. Dalton on this subject, and are perfectly satisfied that this philosopher had not seen the work of Mr. Higgins till after he had given an account of his own doctrine. The obser- vations of Mr. Higgins, therefore, though highly creditable to his sagacity, do not affect Mr. Dalton's claim to originality. They were made, moreover, in so casual a manner, as not only not to have attracted the notice of his contemporaries, but to prove that Mr. Higgins himself attached no particular interest to them. Mr. Dalton's real merit lies in the discovery of the laws of combi- nation, a discovery which is solely and indisputably his ; but in which he would have been anticipated by Mr. Higgins, had that chemist perceived the importance of his own opinions. On the Theory of Volumes. Soon after the publication of the New System of Chemical Philosophy in 1808, in which work Mr. Dalton explained his views of the atomic constitution of bodies, a paper appeared in the second volume of the Memoires d'Arcueil, by M. Gay-Lussac, on the "Combination of Gaseous Substances with one another." He there proved that gases unite together by volume in very sim- ple and definite proportions. In the combined researches of him- self and M. Humboldt, those gentlemen found that water is com- posed precisely of 100 measures of oxygen and 200 measures of hy- drogen ; and M. Gay-Lussac, being struck by this peculiarly sim- ple proportion, was induced to examine the combinations of other gases with the view of ascertaining if any thing similar occurred in other instances. The first compounds which he examined were those of ammo- niacal gas with muriatic, carbonic, and fluoboric acid gases. 100 volumes of the alkali were found to combine with precisely 100 volumes of muriatic acid gas, and they could be made to unite in no other ratio. With both the other acids, on the contrary, two distinct combinations were possible. These are 100 Fluoboric acid gas, with 100 Ammoniacal gas. 100 do. 200 do. 100 Carbonic acid gas, 100 do. 100 do. 200 do. Various other examples were quoted, both from his own experi- ments and from those of others, all demonstrating the same fact. Thus ammonia was found by M. A. Berthollet to consist of 100 volumes of nitrogen and 300 volumes of hydrogen. 100 volumes of sulphurous acid, and 50 volumes of oxygen, produced sulphuric acid. Carbonic acid is composed of 50 volumes of oxygen and 100 volumes of carbonic oxide. From these and other instances, M. Gay-Lussac established the THEORY OF VOLUMES. 435 fact, that gaseous substances unite in the simple ratio of one, to one, one to two, one to three, &c; and this original observation has been confirmed by such a multiplicity of experiments, that it may be regarded as one of the best established laws in chemis- try. Nor does it apply to the true gases merely, but to vapours likewise. For example, sulphuretted hydrogen, sulphurous acid, and hydriodic acid gases are composed of 100 vol. hydrogen and 100 vol. vapour of sulphur. 100 oxygen 100 . . sulphur. 100 oxygen 100 . . iodine. There are very good grounds to suppose, also, that solid bodies which are fixed in the fire would, when in the form of vapour, be subject to the same law. By a method heretofore explained, we may calculate what the specific gravity of carbon would be if converted into vapour; and 0.4166 is the number so determined^ atmospheric air being unity. Now, if we assume that carbonic acid is formed of 100 volumes of oxygen, and 100 volumes of the vapour of carbon, condensed into the space of 100 volumes, the specific gravity of carbonic acid will be 1.1111 (the sp. gr. of oxygen)+0.4166=1.5277, which is the precise number determin- ed by experiment. Again, it follows from our assumption, that carbonic acid is composed by weight of Oxygen 1.1111 . 16 or 2 proportionals. Carbon 0.4166 . 6 or 1 proportional. and this deduction is confirmed by analysis. If we assume that carbonic oxide is composed of 50 volumes of oxygen and 100 volumes ofthe vapour of carbon, condensed into the space of 100 volumes, then its specific gravity will be 0.5555 (half the sp. gr.of oxygen) +0.4166 = 0.9721; and its composition will be Oxygen 0.5555 . 8 or 1 proportional. Carbon 0.4166 . 6 or 1 proportional. both of which results have been determined by other methods. The compounds of carbon and hydrogen are equally illustra- tive ofthe same point. If light carburetted hydrogen is formed of 200 volumes of hydrogen and 100 volumes of the vapour of carbon, condensed into 100 volumes, its specific gravity should be 0.1388 (twice the sp. gr. of hydrogen) + 0.4166 = 0.5554 ; and its composition by weight will be Hydrogen . 0.1388 . 2 or 2 P. Carbon . 0.4166 . 6 or 1 P. If olefiant gas is composed of 200 volumes of hydrogen and 200 volumes of the vapour of carbon, its specific gravity will be 0.1388 +0.8332 = 9720; and its composition by weight must be Hydrogen . ■ 0.1388 . 2 or 2 P. Carbon . . 0.8332 . 12 or 2 P. both these results have been ascertained by analysis. Another remarkable fact established by M. Gay-Lussac in the 436 THEORY OF VOLUMES. same paper is, that the diminution of bulk which gases frequently suffer in combining, is also in a very simple ratio. Thus, the 4 volumes of which ammonia is constituted, (three volumes of hy- drogen and one of nitrogen) contract to one-half or two volumes when they unite. There is a contraction to two-thirds in the formation of nitrous oxide gas. The same applies to the combi- nation of gases and vapours. There is contraction to a half in the formation of sulphuretted hydrogen ; and to a third in that of sulphurous acid. The instances just quoted relative to the vapour of carbon confirm the same remark. There is a contrac- tion to two-thirds in carbonic oxide ; to a half in carbonic acid; to a third in light carburetted hydrogen ; and to a fourth in ole- fiant gas. The rapid progress which chemistry has made within the last few years is in a great measure attributable to the ardour with which pneumatic chemistry has been cultivated. That very department which at first sight appears so obscure and difficult, has afforded a greater number of leading facts than any other; and the law of Gay-Lussac, by giving an additional degree of precision to such researches, as well as from its own intrinsic value, is one ofthe brightest discoveries that adorn the annals of science. The practice of estimating the quantity in weight of any gas, by measuring its bulk or volume, of itself susceptible of much accuracy, is rendered still more precise and satisfactory by the operation of this law. It will not perhaps be superfluous, therefore, to exemplify the method of reasoning employed in these investigations by a few examples ; which will serve, moreover, as a useful specimen to the beginner of the nature of chemical proof. One essential element in every inquiry of this kind, which is indeed the keystone of the whole, is a knowledge of the specific gravity of the gases. But it is exceedingly difficult to determine the specific gravity of gases with perfect accuracy ; for not only do slight alterations of temperature and pressure during the ex- periment effect the result, but the presence of a little watery vapour, atmospheric air, or other impurity, may cause material error, especially when the gas to be weighed is either very light or very heavy. The specific gravity of important gases has, ac- cordingly, been stated differently by different chemists, and there is none in regard to which more discordant statements of this fact have been made than of hydrogen gas. Fortunately we possess the power of correcting the results, and of estimating their accuracy by means of other data, upon which greater reliance may be placed. According to our best data, the specific gravity of oxygen, hydrogen, and nitrogen gases, air being one, is Oxygen . . . 1.1111 Hydrogen . . . 0.0694 Nitrogen . . . 0.9722 THEORY OF VOLUMES. 437 It has been proved by analysis that 200 volumes of ammoniacal gas are composed of 300 volumes of hydrogen and 100 volumes of nitrogen, a fact from which the specific gravity of that alkali may be calculated. Thus, 0.9722+ (0.0694X3) = 1.1804. 1.1804 —2— =0.2951, the specific gravity which ammoniacal gas should have, did its constituent gases suffer no contraction ; but as they contract to one-half, the real specific gravity is double what it otherwise would be, or is 0.5902. Now, if by weighing a certain quantity of ammoniacal gas, the same number is procured for its specific gravity, it follows that all the elements of the cal- culation must have been correct. Nitric oxide is composed of 100 volumes of nitrogen and 100 volumes of oxygen, united without any contraction, and forming, consequently, 200 volumes ofthe compound. Its specific gravity must, therefore, be the mean of its components, or 1.1111 +0.9722 ------2—W— = L0416. The coincidence of this calculated result with that determined by weighing the gas itself, proves that all the data are true. It is obvious, indeed, that the calcu- lated results, as being free from the unavoidable errors of mani- pulation, must be the most accurate, provided the elements ofthe calculation may be trusted. Dr. Henry has proved by careful analysis that 100 volumes of light carburetted hydrogen gas, a compound of carbon and hy- drogen, require 200 volumes of oxygen for complete combustion; that water and carbonic acid are the sole products; and that the latter amounts precisely to 100 volumes. From these data the pro- portions of its constituents and its specific gravity may be deter- mined. For 100 volumes of carbonic acid contains 100 volumes ofthe vapour of carbon, which must have been present in the carburetted hydrogen, and 100 volumes of oxygen. One half of the oxygen originally employed is thus accounted for ; and the remainder must have combined with hydrogen. But 100 volumes of oxygen require 200 volumes of hydrogen for combination, all of which must likewise have been contained in the carburetted hydrogen. The 100 volumes of light carburetted hydrogen, sub- mitted to analysis, are hence composed of 100 volumes of the vapour of carbon, and 200 volumes of hydrogen. Its specific gravity must therefore be 0.5554; that is, 0.4166 (the sp.gr. of carbon vapour) + 0.1388 or twice the sp. gr. of hydrogen gas. Having ascertained that light carburetted hydrogen gas is composed of two measures of hydrogen to one of the vapour of carbon, it is easy to calculate the proportion of its constituents 438 THEORY OF VOLUMES. in weight. For this purpose we need only multiply the bulk of the gases by their respective specific gravities. Thus 200x 0.0694= 13.88, and 100x0.4166 = 41.66. Hence light carbu- retted hydrogen is composed by weight of Carbon - - 41.66 - 6 Hydrogen - - 13.88 - 2 The theory of volumes has very considerble resemblance to the laws of combination by weight developed by Mr. Dalton; for the multiple proportions are as apparent in the former as in the lat- ter. But there is one remarkable difference between them. The weights ofthe two elements of a compound have no apparent de- pendence on one another. Thus 6 parts of carbon and 8 parts of oxygen constitute carbonic oxide, and 8 parts of oxygen and 14 of nitrogen are contained in nitrous oxide ; but 8 is not a multiple by any whole number of 6, nor 14 of 8. On the other hand, the elements of a compound are always united by volume in the ratio of 1 to 1, 1 to 2, 1 to 3, and so on. This simple ratio is peculiarly interesting, because it appears to indi- cate a close correspondence in the size of the atoms of gaseous bodies. It naturally suggests the idea that this peculiarity may arise from the atoms of elementary principles possessing the same magnitude. On this supposition, equal measures of such sub- stances in the gaseous form, at the same temperature and pres- sure, would probably contain an equal number of atoms ; and the specific gravity of these gases would depend on the relative weights of their atoms. The same numbers which indicate the specific gravity of elementary principles in the gaseous state, would then express the relative weights of their atoms; so that the latter would be ascertained by means of the former, or the atomic weight of a solid or liquid represent*the specific gravity of its vapour. The proportional numbers adopted by Sir H. Davy in his Elements of Chemical Philosophy, and the atomic weights employed by Berzelius in his System of Chemistry, were selected in accordance with this view. Thus water being formed of two measures of hydrogen and one measure of oxygen, is be- lieved by Berzelius to consist of 2 atoms of the former, and 1 atom of the latter; and for a similar reason, he regards the pro- toxide of nitrogen as a compound of 2 atoms of nitrogen and 1 atom of oxygen. The atoms and volumes ofthe four elementary gases, oxygen, chlorine, hydrogen, and nitrogen, are thus made to coincide with each other. This method, though perhaps pre- ferable to any other, has not hitherto been generally followed. Most chemists consider water, protoxide of chlorine, and protox- ide of nitrogen, as containing one atom of each of their elements; and consequently, as these compounds consist of 1 measure of oxygen united with 2 measures ofthe other constituent, the atom of hydrogen, chlorine, and nitrogen is supposed to occupy twice as much space as an atom of oxygen. An atom of oxygen is THEORY OF VOLUMES. 439 therefore represented by half a volume, and an atom ofthe other three gases by a whole volume. Dr. Prout, in an ingenious Essay " On the Relation between the Specific Gravities of Bodies in their Gaseous State and the Weights of their Atoms," published in the 6th volume of the Annals of Philosophy, considers it probable that the same relation which is thought to exist between the atoms and volumes ofthe four elementary gases, may hold equally of the vapours of the other elements. Thus in representing the atom of oxygen by half a volume, he believes the atoms ofthe other elementary prin- ciples, such as iodine, carbon, and sulphur, correspond to a whole volume of their vapour. From this he has deduced a mode of calculating the specific gravity of any vapour from the atomic weight of the body which yields it. The rule consists in multi- plying 0.5555, or half the specific gravity of oxygen gas, by the atomic weight of any element, and dividing the product by the atomic weight of oxygen ; the quotient is the.specific gravity of the vapour. For example, the specific gravity of the vapour of carbon is thus found : As 8:6:: 0.5555 : 0.4166 in which 8 is the atomic weight of oxygen, 6 that of carbon, and 0.4166 the specific gravity of the vapour of carbon. The same relation which exists between the atomic weight of oxygen and half its specific gravity, subsists between the atomic weight of any other element, and the specific gravity of its vapour. Though the accuracy of Dr. Prout's views has not yet been established by experiment, his formula may often be employed with advantage. In the essay above quoted, Dr. Prout has advanced several in- stances, in which the equivalents or atomic weights of bodies appear to be multiples by a whole number of the atomic weight of hydrogen gas ; and he threw out a conjecture that the same relation may perhaps exist in other cases. This subject has since been experimentally investigated by Dr. Thomson, who has declared, after a most elaborate inquiry, the fruits of which are contained in his " First Principles of Chemistry," that the law is of universal application ; that the atomic weights of all the sim- ple substances which he has examined are not only multiples by a whole number of the atomic weight of hydrogen, but, with a few exceptions, of two atoms of hydrogen. But in opposition to this statement, Berzelius insists that the law is inconsistent with the results of his analyses, and that the experiments of Thomson are inaccurate. Considering the direct opposition of evidence, and the authority by which it is supported on both sides, we can- not but infer that the question is just as far from being decided as ever. ( 440 ) On the Theory of Berzelius. It is well known that the celebrated Professor of Stockholm has for many years devoted himself to the study of the laws of definile proportions, and that he has been led to form a peculiar hypothesis, by way of generalizing the facts which his industry had collected. To give a detailed account of his system, does not fall within the plan of this work ; but considering the extra- ordinary number of facts with which this indefatigable chemist has enriched the science, and especially this department, it will be proper to give a short account of his doctrines, offering, at the same time, a few comments upon them. Berzelius mentions in the historical introduction to his treatise on the " Theory of Definite Proportions," that he commenced his researches on the subject in the year 1807 ; and that they originated in the study of the Works of Richter. From Rfchter's explanation of the fact, that when two neutral salts decompose one another, the resulting compounds are likewise neutral, he perceived that one good analysis of a few salts would furnish the means of calculating the composition of all others. He accord- ingly entered upon an inquiry, which was at first limited in its ob- ject ; but as he proceeded, his views enlarged, and advancing from one step to another, he at length set about determining the laws of combination in general. In perusing his account ofthe investigation, we are at a loss whether most to admire the num- ber of exact analyses which he performed, the variety of new facts he determined, his acuteness in detecting sources of error, his ingenuity in devising new analytical processes, or the persevering industry which he displayed in every part of the inquiry. But it is at the same time impossible to suppress regret, that, instead of forming a complex system of his own, he did not adopt the sim- ple views of Mr. Dalton. This he might have done with very great propriety ; since the fundamental laws which he discovered, are, with very little exception, either identical with those pre- viously pointed out by the British Philosopher, or the direct result of their operation. Berzelius assumes, with Mr. Dalton, the existence of ultimate indivisible atoms, to the combination of which with one another the laws of chemical proportion are owing. The first law of Berzelius is the following : " One atom of one element unites with 1, 2, 3, or more atoms of another element." This coincides with the law of Mr: Dalton, and requires no com- ment, further than that it has been amply confirmed by the labours of Berzelius. The second is, that " two atoms of one element combine with three and five atoms of another." These are the two laws which regulate the union of simple or elemen- tary atoms. THEORY OF BERZELIUS. 441 The combination of compound atoms with each other, obeys another law, and is confined within still narrower limits. "Two compounds which contain the same electro-negative body, always combine in such a manner that the electro-negative ele- ment of the one is a multiple by a whole number of the same element of the other." Thus, for instance, if two oxidized bodies unite, the oxygen of one is a multiple by a whole number of the oxygen in the other. Various examples may be given of this. The hydrate of potassa is composed of Potassa 48, the oxygen of which is 8. Water 9, do. 8. In like manner, if two acids or two oxides combine, the same will be observed. In the earthy minerals which often contain several oxides, the same law is found to prevail with great uniformity. The composition of the salts is likewise under its influence. Carbonate of potassa, for example, is composed of Carbonic acid 22, the oxygen of which is 16. Potassa . 48, do. 8. and sulphate of potassa of Sulphuric acid 40, the oxygen of which is 24. Potassa . 48, do. 8. Berzelius has remarked, that the nitrates, phosphates, and ar- seniates, may prove exceptions to the law in some instances. There is also a similar relation in salts which contain water of crystallization, between the oxygen of the base of the salt and that of the water. For instance, crystallized sulphate of soda is composed of Sulphuric acid 40. Soda . 32, the oxygen of which is 8. Water . 90, . do. 80. Double salts are also influenced by the same law. In the tar- trate of potassa and soda, for example, the oxygen ofthe potassa is exactly equal to the oxygen in the soda; and the oxygen in the tartaric acid, which neutralizes the potassa, is equal to that of the soda. But this is not all that Berzelius has remarked with respect to the constitution of the salts. He observes that in each series of salts, the same relation always exists between the oxygen of the acid and of the base. In all the neutral sulphates this ratio is as one to three, as may be seen in the sulphates of soda and po- tassa. In the carbonates, the oxygen ofthe acid is double; and in the bicarbonates quadruple the oxygen of the base. The existence of these remarkable laws was discovered by Berzeliu^ at a very early period of his researches; and he men- tions, that as a subsequent observation, during the course of seve- ral years, has not afforded a single exception to them, he now regards them as universal. He accordingly places unlimited 3K 442 THEORY OF BERZELIUS. confidence in their accuracy, and is in the habit of calculating the composition of bodies on this principle. It will of course be interesting to inquire into the cause of these phenomena; to ascertain if there is any property peculiar to oxygen, or other negative electrics, which may give rise to them. Berzelius himself says that "the cause is involved in such deep obscurity, that it is impossible at the present moment to give a probable guess at it." But so far from being obscure, it is perfectly intelligble, and is precisely what may be anticipated from the present state of chemical knowledge. Most of the salts called neutral sulphates, are composed of one proportion or one atom of sulphuric acid, and one proportion of some pro- toxide. This is the case with all the alkaline and earthy sul- phates, and with several of the common metals, such as lead, zinc, and iron. Now, one proportion of sulphuric acid is com- posed of Sulphur 16—1 proportion. Oxygen 24—3 proportions. and every protoxide of Metal —1 proportion. Oxygen 8—1 proportion. Hence a number of laws may be deduced which must hold in every sulphate of a protoxide. 1. The oxygen of the acid is a multiple of that ofthe base. 2. The acid contains three times as much oxygen as the base. 3. The sulphur ofthe acid is just double the oxygen ofthe base. 4. The acid itself is five times as much as the oxygen of the base. Metallic sulphurets are frequently composed of one propor- tion of each element ; and should oxidation ensue, so that the sulphur is converted into sulphuric acid, and the metal into a protoxide, they will be in the exact proportion for forming a neutral sulphate. Berzelius has proved by analysis, that this happens frequently, and he is disposed to convert it into a gene- ral law. Again, the carbonates are composed of one proportion of car- bonic acid, and one proportion of some protoxide. But one proportion of carbonic acid is composed of Carbon 6, 1 proportion. Oxygen 16, 2 proportions. and every protoxide of Metal — 1 proportion. Oxygen 8, 1 proportion. It is inferred, therefore, that in all the carbonates, the oxygen of the acid is exactly double that of the base; and the same mode of reasoning is applicable to the various genera of salts. These few examples will suffice to show, that what seemed so obscure to Berzelius, is rendered quite obvious by the Daltonian THEORY OF BERZELIUS. 443 method. We perceive, moreover, that no constant ratio can exist between the quantity of oxide and that of the acid or oxy- gen of the acid; and the reason is, because the atomic weights ofthe metals in general are different. But this view ofthe sub- ject answers another useful purpose ; it enables us to see whe- ther the law of Berzelius is or is not universal. The observations made on this subject by Thomson, in his " First Principles of Chemistry," are so much to the point, that we give them in his own words. " Before concluding these general observations," says Dr. Thomson, " I may say a few words on Berzelius' law, that in all salts, the atoms of oxygen in the acid constitute a multiple by a whole number of the atoms of oxygen of the base. This law was founded upon the first set of exact analyses of neutral salts which Berzelius made. Now, as neutral salts in general are combina- tions of an atom of a protoxide with an atom of an acid, it is obvious that the atoms of oxygen in the acid must in all such salts be multiples of the atom of oxygen in the base ; because every whole number is a multiple of unity. Neutral salts, there- fore, are not the kind of salts by means of which the precision of this supposed law can be put to the test. " Even in the subsalts, composed of one atom of acid united to two atoms of base, it is obvious enough that the law will hold whenever the acid combined with the base happens to contain 2 or 4, or any even number of atoms; because all even num- bers are multiples of 2. Now, this is the case with the follow- ing acids: Phosphoric. Nitrous. Antimonic. Citric. Carbonic. Titanic. Manganesic. Saclactic. Boracic. Arsenious. Molybdous. Chromous. Sulphurous. Selenic. Uranic. Consequently, the law must hold good in all combinations of one atom of these acids with two atoms of base." " In the case of all these acids which contain only one atom of oxygen, all the subsalts composed of one atom of the acid united to two atoms of base, the law will also in some sort hold ; for the atoms ofthe oxygen in such acids being one, this number will always be a submultiple of two, the number of atoms of oxy- gen in two atoms of base. This is the case with the following acids: Silicic. Hypo-sulphurous. Phosphorous. Oxide of Tellurium. It is only in the subsalts of acids containing an odd number of atoms of oxygen, that exceptions to the law can exist. It is to them, therefore, that we must have recourse when we wish to de- termine whether this empirical law of Berzelius be founded in nature or not. Now, there are 13 acids, the integrant particles of which contain an odd number of atoms of oxygen. The fol- 444 THEORY OF BERZELIUS. lowing table exhibits the names of these acids, together with the number of atoms of oxygen in each." Atoms of Oxygen. Atoms of Oxygen. " Sulphuric acid - 3 Acetic acid - - - 3 Arsenic - _ - 3 Succinic - - - 3 Chromic - - - 3 Benzoic - - - 3 Molybdic - - 3 Nitric - - - - 5 Tungstic - - 3 Tartaric - - - 5 Oxalic - - 3 Hypo-sulphuric - - 2r Formic - - 3 Dr. Thomson informs us that the number of subsalts he has examined is exceedingly small, because Ids "object was not to investigate the truth of Berzelius' law, but to determine the quan- tity of water of crystallization which the salts contain." He observes, that " it would certainly be a most remarkable circum- stance if two atoms of any protoxide were incapable of combining with one atom of any of the 13 acids in the preceding list." Dr. T. adduces seven instances in which this does happen, three of which are completely in point, being a subsulphate of alumina, a subacetate of lead, and a subacetate of copper; and he is "persuaded that many more will be discovered whenever the attention of chemists is particularly turned to the subsalts." He also mentions other kinds of salts, in regard to which, for equally obvious reasons, the law cannot and does not hold. These extracts will suffice for placing the law of Berzelius in its true light; for showing thnt it is a direct consequence of the general operation of the Laws of Definite Proportion ; and that we must expect to find some exceptions to his law, derived from the very cause which gives rise to it. It is to be hoped that Berzelius will take the remarks of Dr. Thomson into mature con- sideration, by which he will probably perceive that his favourite canon is not so universal as he imagines, and be led to avoid the errors to which, from its indiscriminate employment, both himself and his pupils might otherwise be exposed. That part of the law which applies to the combined water is likewise more than doubtful. When the base contains two equivalents of oxygen and an uneven number of equivalents of water is present, it cannot be correct. When the base contains three equivalents of oxygen, the law would not apply whenever there chanced to be 2, 4, 8, or 10 equivalents of water. When the base has only one equivalent of oxygen, then it must hold for obvious reasons. If the base has an equivalent and a half of oxygen, the law can only be true when 3, 6, 9, or 12 equivalents of water are in combination; with 1, 2, 4, 5, 7, 8, or 10, it must fail. THEORY OF BERZELIUS. 445 An attempt has been made within these few years to determine the atomic constitution of minerals, an inquiry in which Berze- lius has highly distinguished himself. The composition of mine- rals must of course be influenced by the usual laws of combina- tion, though there are sometimes obstacles in the way of discover- ing it. In the compounds made artificially, chemists possess the power of having each constituent perfectly pure; but, unfortu- nately, we cannot always command the same condition with respect to natural productions. The materials of which a mineral is composed, once formed part of some heterogeneous fluid or semifluid mass, and in assuming the solid form are very likely to have enclosed within them some substance which is not, chemi- cally considered, an essential ingredient of the mineral. The result of chemical analysis, accordingly, does not always give us a view ofthe actual constitution of a mineral species; some sub- stances are often detected which are foreign to it, and the chemist must exercise his judgment in determining what is and what is not essential. Now nothing is so well calculated to direct him as a knowledge of the laws of combination ; but as a great dis- cretionary power is in his hands, it is important that his mode of investigation should be the simplest possible, and that his rules should be founded on well-established principles, which involve nothing hypothetical. It is but very lately that due care has been bestowed in selecting sufficiently pure specimens for exam- ination, or in performing the analyses themselves with the pre- cision necessary for determining the chemical constitution of minerals. It were much to be wished, that the first essays in this difficult field should be confined as much as possible to such minerals as contain but few substances, and which occur in dis- tinct transparent crystals. We are indebted to Berzelius for this mode of studying the composition of minerals; and certainly if skill in analytical inves- tigation could encourage any one to make the attempt, none could undertake it with greater chance of success than the inde- fatigable Professor of Stockholm. ( 446 ) On the Chemical Constitution of Isomorphous Salts. In the year 1819, a discovery extremely important both to mi- neralogy and chemistry, was made by Professor Mitscherlich, of Berlin, relative to the connection between the crystalline form and composition of bodies. It appears from his researches, that certain substances are capable of being substituted for each other in combination, without influencing the form of the com- pound. This singular circumstance- has been ably traced by Professor Mitscherlich, in the salts of phosphoric and arsenic acids. Thus the neutral phosphate and biphosphate of soda have exactly the same form as the arseniate and binarseniate of soda. The phosphate and biphosphate of ammonia correspond in like manner to the arseniate and binarseniate of ammonia. The neutral phosphate and arseniate of potassa could not be ob- tained in crystals fit for examination ; but the biphosphate and binarseniate of that alkali have the same form. Each arseniate has a corresponding phosphate, possessed of the same form, and containing the same number of equivalents of acid, alkali, and water. These series of salts, in fact, differ in nothing but in one containing arsenic and the other phosphoric acid. From these and analogous facts, it appears that certain sub- stances, when similarly combined with the same body, are dis- posed to affect the same crystalline form. This discovery has led to the formation of groups, each comprehending substances which crystallize in the same manner, and which are hence said to be isomorphous. The salts of arsenic acid are isomorphous with those of phosphoric acid. The oxide of lead, baryta, and strontia, when combined with the same acid, yield salts which are said by Professor Mitscherlich to be isomorphous. The salts of lime are isomorphous with those of magnesia, protoxides of manganese, iron, cobalt, and nickel, oxide of zinc, and per- oxide of copper. The salts of selenic and sulphuric acids, when similarly united with water and the* same base, assume the same form ; and the salts of the peroxide of iron are isomorphous with those of alumina. The similarity of the chemical constitution of isomorphous bo- dies is peculiarly striking. The first singularity of the kind which merits notice, is the tendency of some isomorphous salts to com- bine with the same quantity of water of crystallization. This is especially remarkable in the salts of arsenic and phosphoric acids. The biphosphate and binarseniate of potassa crystallize with two equivalents of water. The neutral phosphate and arseniate of soda contain twelve and a half equivalents of water; and in the bi- phosphate and binarseniate of soda four equivalents of water are present. The quantity of water contained in the arseniates of ammonia corresponds to that ofthe phosphates of ammonia. In- deed, scarcely any crystallized artificial arseniate is known, to ISOMORPHOUS SALTS, 447 which a corresponding phosphate has not been discovered. If, on the contrary, two isomorphous salts crystallize with different equivalent quantities of water, their forms are found to differ also. The common sulphates of manganese and copper differ in form from the sulphates of iron and zinc ; whereas when their crystals contain the same number of equivalents of water,. their form is identical. Mitscherlich has remarked that isomorphous salts, which, when pure, combine with different proportional quantities of water, are disposed in crystallizing together to unite with the same number of equivalents of water, and assume the same form. The mixed sulphates of iron and copper crystallize together with great facility ; and the'crystals, though containing a considerable quantity of copper, have the same proportional quantity of water and the same form as the pure protosulphate of iron. According to Mitscherlich, the sulphates of zinc and copper, of copper and magnesia, of copper and nickel, of zinc and manganese, and of magnesia and manganese, crystallize together with six equiva- lents of water of crystallization, (the same number he states as in protosulphate of iron) and have the same form as green vitriol, without containing a trace of iron. In these instances the isomorphous salts do not occur in definite proportions; so that though they crystallize together, they do not appear to be che- mically united. The similarity in the chemical constitution of isomorphous sub- stances may be illustrated in a different way. Thus, in isomor- phous salts the proportional quantities of acid and base are the same. A neutral phosphate does not correspond to a binarse- niate, nor a biphosphate to a neutral arseniate. There is in general also an exact similarity in the composition ofthe consti- tuents of isomorphous substances. Thus, all chemists agree that the atomic constitution of arsenic and phosphoric acids is the same ; and the fact is still further evinced by the composition of selenic and sulphuric acids. This singular coincidence led Pro- fessor Mitscherlich to believe, that the form of crystals depends on their atomic constitution. He at first suspected that identity of crystalline form is determined solely by the number of atoms, and the mode in which they are united, quite independently of their nature. Subsequent observation, however, induced him to abandon this view; and his opinion now appears to be, that certain ele- ments, which are themselves isomorphous, when combined in the same manner with the same substance, communicate the same form. Similarly constituted salts of arsenic and phosphoric acids yield crystals of the same figure, because the acids, it is thought, are themselves isomorphous; and as the atomic consti- tution of these acids is similar, each containing the same number of atoms of oxygen united with the same number of atoms ofthe other ingredient, it is inferred that phosphorus is isomorphous with arsenic. In like manner it is believed that selenic acid must be isomorphous with sulphuric acid, and selenium with sul- 448 ISOMORPHOUS SALTS. phur; and the same identity of form is ascribed to all those ox- ides above enumerated, the salts of which are isomorphous. The accuracy of this ingenious view has not yet been put to the test of extensive observation, because the crystalline forms of the sub- stances in question are for the most part unknown. But our knowledge, so far as it goes, is favourable ; for the peroxide of iron and alumina, the salts of which possess the same form, are themselves isomorphous. It may hence be inferred as probable, that isomorphous compounds in general arise from isomorphous elements uniting in the same manner with the same substance. The discovery of Professor Mitscherlich, while it serves as a caution to mineralogists against too implicit reliance on crystallographic character, is in several respects of deep inte- rest to the chemist.—It tends to lay open fields of inquiry which may not otherwise have been thought of, and thus lead to the discovery of new substances.—The tendency of isomorphous bodies to crystallize together accounts for the difficulty of pu- rifying mixtures of isomorphous salts by crystallization.—The same property sets the chemist on his guard against the oc- currence of isomorphous substances in crystallized minerals. The native phosphates, for example, frequently contain arsenic acid, and conversely the native arseniates, phosphoric acid, with- out the form of the crystals being thereby affected in the slight- est degree.—It is likely to afford a useful guide in discovering the atomic constitution of compounds. Thus Berzelius considers peroxide of iron to be composed of two atoms of iron and three atoms of oxygen ; and as it is isomorphous with alumina, the com- position of the latter is by some thought to be analagous. The similarity in the composition of several other isomorphous com- pounds gives considerable weight to the argument; but our knowledge of this subject is as yet too limited to excite much confidence. It is possible that aluminum and iron may them- selves be not isomorphous, but yield isomorphous oxides by uni- ting with oxygen in different proportions.—The phenomena pre- sented by isomorphous bodies afford a powerful argument in fa- vour of the atomic theory. They are intimately connected with the laws of chemical union; and like these laws, admit of a satis- factory explanation only by supposing the constitution of matter to be atomic. In some of the experiments of Professor Mitscherlich, he observed that the bi-phosphate of soda is capable of yielding two distinct kinds of crystals, which, though different in form, in com- position appeared to be identical. The more uncommon of the two forms resembled the binarseniate of soda; but the more usual form is quite dissimilar. He has since discovered, that sul- phur is capable of yielding two distinct kinds of crystals ; and in- fers from his observations that a body, whether simple or com- pound, can assume two different crystalline forms. The cause of this unexpected fact is not yet ascertained. PART IV. ON ORGANIC CHEMISTRY. The department of organic chemistry comprehends the his- tory of those compounds which are solely of animal or vegetable origin, and which are hence called organic substances. These bodies, viewed collectively, form a remarkable contrast with those of the mineral kingdom. Such substances in general are characterized by containing some principle peculiar to each. Thus the presence of nitrogen in the nitric, and of sulphur in the sulphuric acid, establishes a wide distinction between these substances; and although in many instances two or more inor- ganic bodies consist of the same elements, as is exemplified by the compounds of sulphur and oxygen, or of nitrogen and oxy- gen, they are always few in number, and distinguished by a well marked difference in the proportion in which they are united. The products of animal and vegetable life, on the contrary, con- sist essentially of the same elementary principles, the number of which is very limited. They are nearly all composed of carbon, hydrogen, and oxygen, in addition to which some of them con- tain nitrogen. Besides these, portions of phosphorus, sulphur, iron, silica, potassa, lime, and other substances of a like nature, may sometimes be detected; but their quantity is exceedingly minute when compared with the principles above mentioned. In point of composition, therefore, most organic substances differ only in the proportion of their constituents, and on this account may not unfrequently be converted into one another. The constitution of organic bodies is subject to the general laws of chemical union; but chemists are not agreed as to the mode in which they conceive the elements to be combined. Ber- zelius, for instance, is of opinion that the elements of organic substances do not form binary compounds in the same manner as the constituents of inorganic bodies, but are united indiscrimi- nately with one another.—Thus alcohol, which consists of three equivalents of hydrogen, one of oxygen, and two of carbon, is supposed by that chemist to consist of all these six equivalents, combined directly with each other, the oxygen belonging as much to the carbon as to the hydrogen. This opinion, however, is not universally adopted. Gay-Lussac, for instance, regards alcohol as a compound of olefiant gas and water, a view which is not only justified by the number of equivalents contained in that compound, but which harmonizes with the constitution of other 3 L 450 ORGANIC CHEMISTRY. bodies better than that of Berzelius. It may, therefore, be admit- ted as probable, that the elements of organic substances are ar- ranged in a similar manner. Organic substances, owing to the energetic affinities with which their elements are endowed, are very prone to spontaneous decomposition. The prevailing tendency of carbon and hydro- gen is to appropriate to themselves so much oxygen as shall con- vert them into carbonic acid and water; and hence, in whatever manner these three elements may be mutually combined in vege- table substances, they are always disposed to resolve themselves into the compounds just mentioned. If, at the time this change occurs, there is an insufficient supply of oxygen to oxidize the hydrogen and carbon completely, then, in addition to carbonic acid and water, carbonic oxide and carburetted hydrogen gases will probably be generated. One or both of these combustible products must in every case be formed, except when oxygen is freely supplied from extraneous sources; because organic bodies are so constituted that their oxygen is never in sufficient quan- tity for converting the carbon into carbonic acid, and the hydro- gen into water. If substances composed of oxygen, hydrogen, and carbon, are liable to spontaneous decomposition, that tendency becomes much stronger when, in addition to these elements, nitrogen is annexed. Other and powerful affinities are then superadded to those above enumerated, and especially that of hydrogen for ni- trogen. A body which contains these principles is peculiarly liable to change, and the usual products are water, carbonic acid, and ammonia, the two latter, having a strong attraction for each other, being always in combination. Another circumstance which is characteristic of organic pro- ducts is the impracticability of forming them artificially by direct union of their elements. Thus, no chemist has hitherto suc- ceeded in causing oxygen, hydrogen, and carbon to unite directly so as to form gum or sugar. When these principles are made to combine by chemical means, they always give rise to the pro- duction of water and carbonic acid. Animal and vegetable substances are all decomposed by a red heat, and nearly all are partially affected by a temperature far below ignition. When heated in the open air, or with substances which yield oxygen freely, they burn, and are converted into water and carbonic acid; but if exposed to heat in vessels from which atmospheric air is excluded, very complicated products fensue. A compound, consisting of carbon, hydrogen, and oxygen, yields water, carbonic acid, carbonic oxide, carburetted hydrogen of various kinds, and probably pure hydrogen. Besides these pro- ducts, some acetic acid is commonly generated, together with a volatile oil which has a dark colour and burnt odour, and is hence called empyrheumatic oil. An azotized substance, in VEGETABLE CHEMISTRY. 451 addition to these, yields ammonia, cyanogen, and probably free nitrogen. From the foregoing remarks, it appears that organic products are characterized by the following circumstances :—1st, by being composed of the same elements; 2d, by the facility with which they undergo spontaneous decomposition ; 3d, by the impractica- bility of forming them by the direct union of their principles ; and, 4th, by being decomposed at a red heat. CHAPTER I. Vegetable Chemistry. Vegetable substances are nearly all composed of oxygen, hy- drogen, and carbon, and in a few of them nitrogen is likewise present. Every distinct compound which exists ready formed in plants, is called a proximate or immediate principle of vegetables. Thus sugar, starch, and gum, are proximate principles. Opium, though obtained from a plant, is not a proximate principle ; but consists of several proximate principles mixed more or less inti- mately with one another. The proximate principles of vegetables are sometimes distri- buted over the whole plant, while at others they are confined to a particular part. The methods by which they are procured are very variable. Thus gum exudes spontaneously, and the sac- charine juice ofthe maple tree is obtained by incisions made in the bark. In some cases a particular principle is mixed with such a variety of others, that a distinct process is required for its separation. Of such processes consists the proximate analysW of vegetables. Sometimes a substance is separated by mechani- cal means, as in the preparation of starch. On other occasions, advantage is'taken ofthe volatility of a compound, or of its solu- bility in some particular menstruum. Whatever method is em- ployed, it should be of such a nature as to occasion no change in the composition ofthe body to be prepared. The reduction of the proximate principles into their simplest parts, constitutes their ultimate analysis. By this means, chemists ascertain the quantity of oxygen, carbon, and hydrogen, present in any compound. The former method of performing this ope- ration was by destructive distillation; that is, by exposing the compounds to a red heat in close vessels, and collecting all the products. So many different substances, however, are procured in this way, such as water, carbonic acid, carbonic oxide, carbu- retted hydrogen, &c. that it is almost impossible to arrive at a satisfactory conclusion. A more simple and effectual method was proposed by Gay-Lussac and Thenard. The object of their 452 VEGETABLE CHEMISTRY. process, which is applicable to the ultimate analysis of animal, as well as vegetable* substances, is to convert the whole of the carbon into carbonic acid, and the hydrogen into water, by means of some compound which contains oxygen in so loose a state of combination, as to give it up to those elements at a red heat. The agent first employed by these chemists was chlorate of potassa. This substance, however, is liable to the objection that it not only gives oxygen to the substance to be analyzed, but is itself decomposed by heat. On this account it is now very rarely employed in ultimate analysis, the peroxide of copper, likewise proposed by Gay-Lussac and Thenard, having been substituted for it. This oxide, if alone, may be heated to whiteness without parting with oxygen ; whereas it yields oxygen readily to any combustible substance with which it is ignited. It is easy, therefore, by weighing it before and after the analysis, to disco- ver the precise quantity of oxygen which has entered into union with the carbon and hydrogen of the substance submitted to examination. The ultimate analysis of organic bodies is one of the most deli- cate operations with which the analytical chemist can be en- gaged. The chief cause of uncertainty in the process, arises from the presence of moisture, which is retained by some animal and vegetable substances with such force that it can be expelled only by a temperature which endangers the decomposition ofthe compound itself. The best mode of drying organic matters for the purpose, is by confining them with sulphuric acid under the exhausted receiver of an air-pump, and exposing them at the same time to a temperature of 212° F., a method adopted by Ber- zelius, and for which a neat apparatus has been described by Dr. Prout. Another source of difficulty is occasioned by atmospheric air within the apparatus, owing to the presence of which, nitro- gen may be detected in the products, without having been con- tained in the substance analyzed. But though the ultimate analysis of organic substances is diffi- cult in practice, in theory it is exceedingly simple. It consists in mixing three or four grains of the body to be analyzed with about 200 grains of the peroxide of copper, heating the mixture to redness in a glass tube, and collecting the gaseous products in a graduated glass jar over mercury. From the quantity of carbonic acid procured by measure, its weight may readily be inferred ; and from this, the quantity of carbonaceous matter is calculated, by recollecting that every 22 grains of the acid con- tain 16 of oxygen and 6 of carbon. In order to ascertain the quantity of hydrogen, the gaseous products are transmitted through a tube filled with fragments of fused chloride of calcium, which absorbs all the watery vapour; and by its increase in weight, indicates the precise quantity of VEGETABLE CHEMISTRY. 453 that fluid generated. Every nine grains of water thus collected, correspond to one grain of hydrogen and eight of oxygen. If the quantity of oxygen contained in the carbonic acid and water corresponds precisely to that lost by the oxide of copper, it follows that the organic substance itself was free from oxygen. But if, on the other hand, more oxygen exists in the products than was lost by the copper, it is obvious that the difference indicates the amount of oxygen contained in the subject of analysis. Ifnitrogen enters into the constitution ofthe organic substance, it will pass over in the gaseous state, mixed with carbonic acid. Its quantity may be ascertained by removing the carbonic acid by means of a solution of pure potassa. It need scarcely be observed, that if the analysis has been suc- cessfully performed, the weight of the different products, added together, should make up the exact weight of the organic sub- stance employed. In analyzing an animal or vegetable fluid, the foregoing pro- cess will require a slight modification. If the fluid is of a fixed nature, it may be made into a paste with the oxide of copper, and heated in the usual manner. But if it is volatile, a given weight of its vapour is conducted over the peroxide of copper heated to redness in a glass tube. The constitution of vegetable substances is not yet sufficiently known to admit of their being classified in a purely scientific or- der. The chief data hitherto furnished towards forming a sys- tematic arrangement, are derived from a remarkable agreement between the composition and general properties of several vege- table compounds, first noticed by Gay-Lussac and Thenard. From the ultimate analysis of a considerable variety of proximate principles, these chemists draw the three following conclusions : —1st, A vegetable substance is always acid, when it contains more than a sufficient quantity of oxygen for converting all its hydrogen into water; 2dly, It is always resinous, oily, or alcoho- lic, &c. when it contains less than a sufficient quantity of oxygen for combining with the hydrogen; and, 3dly, It is neither acid nor resinous, but in a state analogous to sugar, gum, starch, or the woody fibre, when the oxygen and hydrogen, which it con- tains are in the exact proportion for forming water. These laws, indeed, are not rigidly exact, nor do they include the vegetable products containing nitrogen. We shall arrange the proximate principles of plants in five divisions. The first includes the vegeta- ble acids ; the second the vegetable alkalies ; the third comprises those substances which contain an excess of hydrogen ; the fourth includes those, the oxygen and hydrogen of which are in propor- tion for forming water; and the fifth comprehends those bodies which, so far as is known, do not belong to either of the other divisions. ( 454 ) SECTION I. Vegetable Acids. These acids, like all organic principles, are decomposed by a red heat. They are in general less liable to spontaneous decom- position than other vegetable substances ; a circumstance w,hich probably arises from the large proportion of oxygen which they contain. They are nearly all decomposed by concentrated hot nitric acid, by which they are converted into carbonic acid and water. Acetic Acid. • The acetic acid exists ready formed in the sap of many plants, either free or combined with lime or potassa; it is generated during the destructive distillation of vegetable matter, and is an abundant product of the acetous fermentation. Common vinegar, the acidifying principle of which is acetic acid, is commonly prepared by fermentation from an infusion of malt, on from the same processjtaking place in weak wine or cyder. Vinegar, thus obtained, is a very impure acetic acid, containing the saccharine, mucilaginous, and other matters existing in the fluid from which it is prepared. It is separated from these impurities by distillation. Distilled vinegar was formerly called acetous acid, on the supposition of its differing chemically from strong acetic acid; but it is now admitted that distilled vinegar is real acetic acid merely diluted with water, and commonly con- taining a small portion of empyrheumatic oil, formed during the distillation, and from which it receives a peculiar flavour. It may be rendered stronger by exposure to cold, when a consider- able part of the water is frozen, while the acid remains liquid. The distilled vinegar, which is now generally employed /or chemical purposes, is prepared by the distillation of wood, and is sold under the name of pyroligneous acid. When first made it is very impure, and of a dark colour, holding in solution tar and volatile oil; but it may be purified, at least in part, by digestion with animal charcoal and a second distillation, or by filtration through animal charcoal. It is made in large quantities in Glasgow. Concentrated acetic acid is best obtained by decomposing the acetates either by sulphuric acid, or in some instances by heat. A convenient process is to distil acetate of potassa with half its weight of concentrated sulphuric acid, the recipient being kept cool by the application of ice. The acid is at first contaminated with sulphurous acid; but by mixing it with a little peroxide of manganese, and re-distilling, it is rendered quite pure. A strong VEGETABLE ACIDS. 455 acid may likewise be procured from the bin-acetate of copper by the sole action of heat. The acid when first collected has a greenish tint, owing to the presence of copper, from which it is freed by a second distillation. The density of the product varies from 1.056 to 1.08, the lightest acid being procured towards the end of the process. MM. Derosnes, indeed, have remarked that the liquid which passes over towards the end of the process is lighter than water, and contains very little acetic acid. On neutralizing the latter with pure solid potassa, and distilling by a gentle heat, they procured an ethereal fluid, to which they ap- plied the term of.pyro-acetic §ther. Strong acetic acid is exceedingly pungent, and even raises a blister when kept for some time in contact with the skin. It has a very sour ta«te and an agreeable refreshing odour. Its acidity is well marked, as it reddens litmus paper powerfully, and forms neutral salts with the alkalies. It is exceedingly volatile, rising rapidly in vapour at a moderate temperature without undergoing any change. Its vapour is inflammable, and burns with a white light. In its most concentrated form it is a definite cbmpound of one equivalent of water, and one equivalent of acid ; and in this state it crystallizes when exposed to a low temperature, retain- ing its solidity until the thermometer rises to 50° F. It is decom- posed by being passed through red-hot tubes; but owing to its volatility, a large quantity of it escapes decomposition. Dr. Prout has established the singular fact, relative to the con- stitution of this acid, that its oxygen and hydrogen are in exact proportion to form water, and that it contains 47.05 per cent, of carbon. It may hence be inferred to consist of 24 parts or 4 equivalents of carbon, 24 parts or 3 equivalents of oxygen, and 3 of hydrogen. This would make the combining proportion of acetic acid 51, instead of 50, as stated by Thomson. The only correct mode of estimating the strength of acetic acid is by its neutralizing power. Its specificigravity is no criterion. The acetic is distinguished from all other acids by its flavour, odour, and volatility. Its salts, which are called acetates, are all soluble in hot and most of them in cold water, are destroyed by a high temperature, and are decomposed by sulphuric acid. • The acetate of ammonia is made by neutralizing the common carbonate of ammonia with acetic acid. It crystallizes with diffi- culty in consequence of being deliquescent and highly solu- ble. It has been long used in medicine'as a febrifuge under the name of spirit of Mindererus. Acetate of Potassa.—This salt is made by neutralizing carbonate of potassa with acetic acid, or by decomposing acetate of lime with sulphate of potassa. When cautiously evaporated it forms irregular crystals, which are obtained with difficulty, owing to the deliquescent property of the salt. According to Thomson, the crystals are composed of one equivalent ofithe neutral acetate 456 VEGETABLE ACIDS. of potassa, and two equivalents of water. It is commonly pre- pared for pharmaceutic purposes by evaporating the solution to dryness, and heating the residue so as to cause the igneous fu- sion. On cooling it becomes a white crystalline foliated mass, which is generally alkaline. This salt is highly soluble in water, and requires twice its weight of boiling alcohol for solution. Dr. Thomson procured a bin-acetate by mixing acetic acid and carbonate of potassa in the proportion of two equivalents of the former to one of the latter. On confining the solution along with sulphuric acid under the exhausted receiver of an air-pump, the bin-acetate was deposited in large transparent flat plates. The crystals contain six equivalents of water, and deliquesce ra- pidly on exposure to the air. Acetate of Soda is prepared in large quantity by manufacturers of pyroligneous acid by neutralizing the impure acid, with chalk, and then decomposing the acetate of lime by sulphate of soda. It crystallizes readily by gentle evaporation, and its crystals, which are not deliquescent, are composed of 50 parts or one equivalent of acetic acid, 32 parts or one equivalent of soda, and 54 parts or six equivalents of water. The form of its crystals is very complicated, and derived from an oblique rhombic prism. When heated to 550° F. it is deprived of its water, and under- goes the igneous fusion without parting with any of its acid. At 600° F. decomposition takes place. Acetate of soda is much employed for the preparation of con- centrated acetic acid. The Acetates of Baryta, Strontia, and Lime, are of little im- portance. The former, which is occasionally employed as a re- agent,-crystallizes in irregular six-sided prisms, terminated by di- hedral summits, the primary form of which is a right rhomboi- dal prism. The latter crystallizes in very slender acicular crys- tals of a silky lustre, and is chiefly employed in the preparation of the acetate of soda. Acetate of Alumina is formed by adding acetate of lead to sul- phate of alumina, when the sulphate of lead subsides and the acetate of alumina remains in solution. It is used by Dyers and Calico Printers as a basis or mordaunt. Acetate of Lead.—This salt, long known by the names of sugar of lead (saccharum saturni) and cerussa acetata, is made by dissolving either carbonate of lead or litharge in distilled vine- gar. The solution has a sweet, succeeded by an astringent taste, does not redden litmus paper, and deposits shining acicular crys- tals by evaporation. When more regularly crystallized it occurs in six-sided prismatic crystals, cleavable parallel to the lateral and terminal planes of a right rhombic prism, which may be re- garded as its primary form. The crystals effloresce slowly by exposure to the air, and require about four times their weight of VEGETABLE ACIDS. 457 water at 60° F. for solution. They are composed of 50 parts or one equivalent of the acid, 112 parts or one equivalent ofthe protoxide of lead, and 27 parts or three equivalents of water. The acetate of lead is partially decomposed, with formation of the carbonate of lead, by water which contains carbonic acid, or by exposure to the air; but a slight addition of acetic acid ren- ders the solution quite clear. This salt is much used in the arts, in medical and surgical practice, as a sedative and astringent, and in chemistry as a re- agent. The sub-acetate of lead, commonly called extractum saturni, is prepared by boiling one part of the neutral acetate, and two parts of litharge, deprived of carbonic acid by heat, with 25 parts of water. This salt is less sweet and less soluble in water than the neu- tral acetate, has an alkaline re-action, and crystallizes in white plates by evaporation. It is decomposed by a current of carbo- nic acid, with production of pure carbonate of lead; and forms a turbid solution, owing to the formation of a carbonate, when it is mixed with water in which carbonic acid is present. It appears from the analysis of Berzelius to consist of one equivalent of acid, and three equivalents ofthe oxide of lead, and is therefore a iris-acetate. A di-acetate may likewise be formed by boiling with water a mixture of litharge and acetate of lead in atomic proportion. Acetate of Copper.—The pigment called verdigris, which is an impure acetate ofthe peroxide of copper, may be formed by exposing" metallic copper to the vapour of vinegar, when the me- tal gradually absorbs oxygen from the atmosphere, and then unites with the acid. It is prepared in large quantity in the south of France by covering copper plates with the refuse of the grape after the juice has been extracted for making wine. The saccharine matter contained in the husks furnishes acetic acid by fermentation, and in four or six weeks the plates acquire a coating ofthe acetate. Verdigris is commonly of a pale green, but sometimes of a blue colour. Its essential constituent is an acetate of copper, com- posed of 80 parts or one equivalent of the peroxide of copper, 50 parts or one equivalent of acetic acid, and six equivalents of water. This compound is decomposed by water, and is converted into an insoluble green di-acetate, and into a soluble bin-acetate of copper. The first, as its name implies, consists of one equivalent of acid and two equivalents ofthe oxide. The bin-acetate crys- tallizes readily in-rhombic octahedrons of a green colour, and is soluble in twenty times its weight of cold, and five of boiling wa- ter. It is conveniently prepared by dissolving verdigris in dis- tilled vinegar, and evaporating the solution. The crystals con- sist of one Equivalent of acid and two equivalents of the peroxide 3M 458 VEGETABLE ACIDS. of copper, combined, according to Mr. Phillips, with three, and according to Berzelius and Dr. Ure, with two equivalents of water. Besides these compounds, Berzelius has described three other acetates of copper; but they are of little importance. Acetate of Mercury.—The only interesting compound of mer- cury and acetic acid is the acetate of the protoxide, which is sometimes employed in the practice of medicine. It is prepared by mixing crystallized protonitrate of mercury with neutral ace- tate of potassa in the ratio of one equivalent of each. If both salts are dissolved in a considerable quantity of hot water, the solutions retain their transparency after being mixed; but on cooling, the proto-acetate of mercury is deposited in white scales of a silky lustre. It is easily decomposed; and it should be dried by a very gentle heat, and washed with cold water slightly acidu- lated with acetic acid. Acetate of Zinc.—This salt may be prepared by way of double decomposition by mixing sulphate of zinc with acetate of lead in equivalent proportions. When made in this way it is very apt to retain some sulphate of lead in solution. The best mode of obtaining it quite pure, is by suspending metallic zinc in a dilute solution of the acetate of lead, until all the lead is removed. This is known to be accomplished by the addition of sulphuretted hy- drogen, which then occasions a pure white precipitate. This salt is frequently employed as an astringent collyrium. Oxalic Acid. Oxalic acid exists ready formed in several plants, especially in the rumex acetosa or common sorrel, and in the oxalis acetosella or wood sorrel; but it almost always occurs in combination, either with lime or potassa. These plants contain the binoxalate of potassa; and the oxalate of lime has been found in large quantity by M. Braconnot in several species of lichen. Oxalic acid is easily made artificially by digesting sugar in five or six times its weight of nitric acid, and expelling the excess of that acid by distillation, until a fluid ofthe consistence of syrup remains in the retort. The residue in cooling yields crystals of oxalic acid, the weight of which amounts to rather more than half the quantity of the sugar employed. They should be puri- fied by solution in pure water, and re-crystallization. In this process, changes of a very complicated nature ensue, during which a portion of nitric acid is resolved, chiefly, into oxygen and deutoxide of nitrogen, while the sugar is converted, with formation of carbonic acid and water, into oxalic acid. A small quantity of malic and acetic acids are generated at the same time. As oxalic acid does not contain any hydrogen, and has a smaller proportional quantity of carbon than sugar, there can be VEGETABLE ACIDS. 459 no doubt that the production of this acid essentially depends upon the sugar being deprived of all its hydrogen and a portion of its carbon by oxygen derived from the nitric acid. Many organic substances besides sugar, such as starch, gum, most of the vegetable acids, wool, hair, and silk, are converted into oxalic by the action of nitric acid;—a circumstance which is explicable on the fact that oxalic acid contains more oxygen than every other principle, whether of animal or vegetable origin. Oxalic acid crystallizes in slender, flattened, four and six sided prisms terminated by two-sided summits; but their primary form is an oblique rhombic prism. It has an exceedingly sour taste, reddens litmus paper strongly, and forms neutral salts with alka- lies. The crystals effloresce on exposure to the air, but undergo no other change. They are soluble in twice their weight of cold and in their own weight of boiling water. They are dissolved also by alcohol, though less freely than in water. They contain half their weight of water of crystallization, part of which only, amounting to about 28 per cent, can be expelled by heat without decomposing the acid itself. The atomic weight of oxalic acid, is precisely 36; and the crystals consist of 36 parts or one equivalent of real acid, and 27 parts or three equivalents of water. It differs in composition from all other vegetable acids in containing no hydrogen, the absence of which seems to be fully established by the analyses of Berze- lius, Dr. Prout and Dr. Ure. From the researches of these chemists, oxalic acid is composed of one part of carbon and two parts of oxygen ; and since its equivalent is 36, it must be regarded as a compound of Carbon . 12 or 2 equivalents. Oxygen . 24 or 3 equivalents. 36 . It is therefore intermediate between carbonic oxide and car- bonic acid, and may even be supposed to consist of Carbonic oxide . 14 . or 1 equivalent. Carbonic acid . 22 . or 1 equivalent. 36 Consistently with this view, Dobereiner found that oxalic acid is converted into carbonic acid and carbonic oxide by the action of a very large excess of fuming sulphuric acid. The experiment succeeds even with the common oil of vitriol of commerce. Oxalic acid is one of the most powerful and rapidly fatal poi- sons which we possess; and frequent accidents have occurred from its being sold and taken by mistake for Epsom salts, with the appearance of which its crystals have some resemblance. These substances may be easily distinguished, however, by the strong acidity o oxalic acid, which may be tasted without danger, 460 VEGETABLE ACIDS. while the sulphate of magnesia is quite neutral, and has a bitter saline taste. The experiments of Drs. Christison and Coindet have demonstrated that chalk and magnesia are certain antidotes to poisoning by oxalic acid, in consequence of forming with it insoluble and inert compounds. Oxalic acid is easily distinguished from all other acids by the form of its crystals, and by its solution giving with lime water a white precipitate, which is insoluble in an excess of the acid. The salts of oxalic acid are termed oxalates. Most of these compounds are either insoluble or sparingly soluble in water; but they are all dissolved by the nitric, and also by muriatic acid, except when the latter precipitates the base of the salts. The only oxalates which are remarkable for solubility are those of potassa, soda, lithia, ammonia, alumina, and iron. A soluble oxalate is easily detected by adding to its solution a neutral salt of lime or lead, when a white oxalate of those bases will be thrown down. On digesting the precipitate in a little sulphuric acid, an insoluble sulphate is formed, and the solution yields crystals of oxalic acid on cooling. All insoluble oxalates, the bases of which form insoluble compounds with sulphuric acid, may be decomposed in a similar manner. All other insolu- ble oxalates may be decomposed by potassa, by which means a soluble oxalate is procured. The oxalates, like all salts which contain a vegetable acid, are decomposed by a red heat, a carbonate being left, provided the oxide can retain carbonic acid at the temperature which is em- ployed. As oxalic acid is so highly oxidized, its salts leave no charcoal when heated in close vessels. Several oxalates are reduced to the metallic state, with evolu- tion of pure carbonic acid, when heated to redness in close ves- sels. The peculiar constitution of oxalic acid accounts for this change; for one equivalent ofthe acid, to be converted into car- bonic acid, requires precisely one equivalent of oxygen, which is the exact quantity contained in the oxide of a neutral proto-oxalate. Oxalate of Ammonia, prepared by neutralizing that alkali with oxalic acid, is much used as a re-agent. It is very soluble in hot water, and is deposited in acicular crystals when a saturated hot solution is allowed to cool. The crystals contain two equivalents of water. Dr. Thomson has likewise described a binoxalate of ammonia, which is less soluble than the preceding, and contains three equivalents of water. Oxalates of Potassa.—Oxalic acid forms with potassa three compounds, of which the description was given, and the compo- sition determined, in the year 1808 by Dr. Wollaston. The first is the neutral oxalate which is formed by neutralizing carbonate of potassa with oxalic acid. It crystallizes in oblique quadran- gular prisms, which have a cooling bitter taste, require about twice their weight of water at 60° F. for solution, and contain VEGETABLE ACIDS. 461 36 parts or one equivalent of oxalic acid, 48 parts or one equivalent of potassa, and one equivalent of water. This salt is much employed as a re-agent for detecting lime. The bin- oxalate of potassa is contained in sorrel, and may be pro- cured from that plant by solution and crystallization. It crys- tallizes readily in small rhomboids, which are less soluble in water than the neutral oxalate. It is often sold under the name of essential salt of lemons for removing iron moulds from linen; —an effect which it produces by one equivalent of its acid uniting with the oxide of iron and forming a soluble oxalate. The third salt contains twice as much acid as the preceding compound, and has hence received the name of quadroxalate of potassa. It is the least soluble of these salts, and is formed by digesting the binoxalate in nitric acid, by which it is deprived of one-half of its base. It is composed of four equivalents of acid, one of potassa, and seven of water. Oxalate of Soda, which may be made in the same manner as oxalate of potassa, is very rarely employed, and is of little im- portance. It likewise forms a binoxalate, but no quadroxalate is known. Oxalate of Lime.—This salt, like all the insoluble oxalates, is easily prepared by the way of double decomposition. It is a white finely divided powder, which is remarkable for its extreme insolubility in pure water. On this account a soluble oxalate is an exceedingly delicate test for lime. It is very soluble, how- ever, in muriatic and nitric acids. It is composed of 36 parts or one equivalent of the acid, and 28 parts or one equivalent of lime. It may be exposed to a temperature of 560° F- without decom- position, and is then quite anhydrous. No binoxalate of lime is known. This salt is interesting in a pathological point of view, because it is a frequent ingredient of urinary concretions. It is the basis of what is called the mulberry calculus. Oxalate of Magnesia.—This salt may be prepared by mixing oxalate of ammonia with a hot concentrated solution of sulphate of magnesia. It is a white powder, which is very sparingly solu- ble in water; but, nevertheless, when the sulphate of magnesia is moderately diluted with cold water, the oxalate of ammonia occasions no precipitate. On this fact is founded the best analy- tic process for separating lime from magnesia. Tartaric Acid. This acid exists in the juice of several acidulous fruits, but it is almost always in combination with lime or potassa. It is pre- pared by mixing intimately 198 parts or one equivalent of cream of tartar, in fine powder, with 50 parts or one equivalent of chalk, and throwing the mixture by small portions at a time into ten 462 VEGETABLE ACIDS. times it weight of boiling water. On each addition brisk efferves- cence ensues, owing to the escape of carbonic acid, and one equivalent of the insoluble tartrate of lime subsides; while one equivalent of neutral tartrate of potassa is held in solution. On washing the former with water, and then digesting it, diffused through a moderate portion of water, with one equivalent of sul- phuric acid, the tartaric acid is set free; and after being separated from the sulphate of lime by a filter, may be procured by evapo- ration in prismatic crystals, the primary form of which is a right rhombic prism. Tartaric acid has a sour taste, which is very agreeable when diluted with water. It reddens litmus paper strongly, and forms, with alkalies, neutral salts, to which the name of tartrates is ap- plied. It requires five or six times its weight of water at 60° for solution, and is much more soluble in boiling water. It is dissolved likewise, though less freely, in alcohol. The aqueous solution is gradually decomposed by keeping, and a similar change is experienced under the same circumstances by most of the tartrates. The crystals may be exposed to the air without change. They are converted, into the oxalic by digestion in nitric acid. When heated in close vessels, it fuses, froths up, and is decomposed, yielding, in addition to the usual products of destructive distillation, a distinct acid to which the name of pyro-tartaric acid is applied. A considerable quantity of char- coal remains. The atomic weight of tartaric acid, inferred by Dr. Thomson from the tartrates of potassa and lead, is 66 ; and the crystals, which cannot be deprived of their water by heat without decom- position, consist of 66 parts or one equivalent of acid, and one equivalent of water. According to the analysis of Dr. Prout and Dr. Thomson, which agrees pretty closely with that of Ber- zelius, the acid itself is composed of Carbon . 24 . . or 4 equivalents. Oxygen . 40 . . or 5 equivalents, 'j Hydrogen . 2 . . or 2 equivalents. 66 Tartaric acid is distinguished from other acids by forming a white precipitate, the bitartrate of potassa, when mixed with any ofthe salts of that alkali. This acid, therefore, separates potassa from every other acid. It occasions a white precipitate with lime water, which is very soluble in an excess ofthe acid. Tartaric acid is remarkable for its tendency to form double salts, the properties of which are often more interesting than the simple salts. The most important of these double salts, and the only ones which have been much studied, are the tartrate of po- VEGETABLE ACIDS. 4G3 tassa and soda, and the tartrate of antimony and potassa. The neutral tartrates of the alkalies, of magnesia, and copper, are soluble in water ; but most of the tartrates of the other bases, and especially those of lime, baryta, strontia, and lead, are inso- luble. All these neutral tartrates, however, which are insoluble in pure water, are soluble in an excess of their acid. They are decomposed by digestion in carbonate of potassa, and when an acid is added in excess, the bitartrate of potassa is precipitated. All the insoluble tartrates are easily procured from the neutral tartrate of potassa by way of double decomposition. Tartrates of Potassa.—The neutral tartrate, frequently called soluble tartar, is formed by neutralizing a solution of the bitar- trate with carbonate of potassa ; and it is a product of the opera- tion above described for making tartaric acid. Its primary form is a right rhomboidal prism ; but it often occurs in irregular six sided prisms, with dehedral summits. Its crystals are very solu- ble in water, and attract moisture when exposed to the air. They consist of 114 parts or one equivalent ofthe neutral tartrate, and two of water. They are rendered quite anhydrous by a tempe- rature not exceeding 248° Fahr. Of the bitartrate, an impure form, commonly known by the name of tartar, is found encrusted on the sides and bottom of wine casks, a source from which all the tartar of commerce is derived. This salt exists in the juice of the grape, and, owing to its insolubility in alcohol, is gradually deposited during the vinous fermentation. In its crude state, it is coloured by the wine from which it was procured; but when purified, it is quite white, and in this state constitutes the cream of tartar of the shops. The bitartrate of potassa is very sparingly soluble in water, requiring sixty parts of cold, and fourteen of boiling water, for solution, and is deposited from the latter on cooling in small crystalline grains. Its crystals are commonly irregular six sided prisms, terminated at each extremity by six surfaces ; and its primary form is either a right rectangular, or a right rhombic prism. It has a sour taste, and distinct acid re-action. It con- sists of one equivalent of potassa, and two of the acid, united, according to Berzelius with one, and according to Dr. Thomson, with two equivalents of water. Assuming the latter to be cor- rect, the atomic weight of the bitartrate is 198. Its water of crystallization cannot be expelled without decomposing the salt itself. The bitartrate of potassa is employed in the formation of tar- taric acid and all the tartrates. It is likewise used in preparing pure carbonate of potassa. When exposed to a strong heat, it yields an acrid empyrheumatic oil, some pyro-tartaric acid, toge- ther with water, carburetted hydrogen, carbonic oxide, and car- bonic acid gases, the last of which combines with the potassa. 464 VEGETABLE ACIDS. The fixed products are carbonate of potassa and charcoal, which may be separated from each other by solution and filtration. When deflagrated with half its weight of nitre, by which part of the charcoal is consumed, it forms black-flux; and when an equal weight of nitre is used, so as to oxidize all the free carbon of the tartaric acid, a pure carbonate of potassa, called white- flux, is procured. Tartrate of Potassa and Soda.—This double salt, which has been long employed in medicine under the name of seignette or rochelle salt, is prepared by neutralizing bitartrate of potassa with carbonate of soda. By evaporation, it yields prismatic crystals, the sides of which often amount to ten or twelve in number; but the primary form, as obtained by cleavage, is a right rhombic prism. The crystals are soluble in five parts of cold, and in a less quantity of boiling water, and are composed of 114 parts, or one equivalent of tartrate of potassa, 98 parts or one equivalent of tartrate of soda, and eight equivalents of water. Tartrate of Soda is of little importance. It is frequently made extemporaneously by dissolving equal weights of tartaric acid and bicarbonate of soda in separate portions of water, and then mixing the solutions. A very agreeable effervescing draught is procured in this way. Soda is better adapted for this purpose than potas- sa, because the former has little or no tendency to form an inso- luble bitartrate. Tartrate of Antimony and Potassa.-—This compound, long celebrated as a medicinal preparation under the name of tartar emetic, is made by boiling protoxide of antimony with a solution of bitartrate of potassa. The oxide of antimony is furnished for this purpose in various ways. Sometimes the glass or crocus of that metal is employed. The Edinburgh college prepared an oxide by deflagrating sulphuret of antimony with an equal weight of nitre ; and the college of Dublin employ the submuriate. Mr. Phillips recommends that 100 parts of metallic antimony in fine powder should be boiled to dryness in an iron vessel with 200 parts of sulphuric acid, and that the residual sub-sulphate be boiled with an equal weight of cream of tartar. The solution of the double salt, however made, should be concentrated by evaporation, and allowed to cool in order that crystals may form. The tartrate of antimony and potassa commonly crystallizes in tetrahedrons, which are often transparent when first formed, but become white and opaque by exposure to the air. It has a styptic metallic taste, reddens litmus paper slightly, and is solu- ble in fifteen parts of water at 60°, and in three of boiling water. Its aqueous solution, like that of all the tartrates, under- goes spontaneous decomposition by keeping; and, therefore, if kept in the liquid form, alcohol should be added in order to pre- VEGETABLE ACIDS. 465 serve it. According to the analysis of Dr. Thomson, it is com- posed of Tartaric acid - (66 X 2) - 132 or 2 equivalents. Protoxide of Antimony (52 X 3) - 156 or 3 equivalents. Potassa - - - 48 or 1 equivalent. Water - - - 18 or 2 equivalents. 354 With this result the analysis of Mr. Phillips accords, except that he found three instead of two equivalents of water. Tartar emetic is decomposed by many re-agents. Thus al- kaline substances, from their superior attraction for tartaric acid, separate the oxide of antimony. The pure alkalies, indeed, and especially potassa and soda, precipitate it imperfectly, owing to their tendency to unite with, and dissolve the oxide; but the al- kaline carbonates throw down the oxide much more completely. Lime water occasions a white precipitate, which is a mixture of oxide or tartrate of antimony and tartrate of lime. The stronger acids, such as the sulphuric, nitric, and muriatic, cause a white precipitate, consisting of bitartrate of potassa and a sub-salt of antimony. Decomposition is likewise effected by several metallic salts, the bases of which yield insoluble compounds with tartaric acid. Sulphuretted hydrogen throws down the orange sulphuret of antimony. It is precipitated by many vegetable substances, especially by an infusion of gall-nuts, and other similar astringent solutions, with which it forms a dirty white precipitate, which is regarded as a compound of tannin and oxide of antimony. This combination is inert, and therefore a decoction of cinchona bark is recommended as an antidote to tartar emetic. Citric Acid. This acid is contained in many of the acidulous fruits, but exists in large quantity in the juice of the lime and lemon, from which it is procured by a process very similar to that described for preparing tartaric acid. To any quantity of lime or lemon juice, finely powdered chalk is added as long as effervescence ensues ; and the insoluble citrate of lime, after being well washed with water, is decomposed by digestion in dilute sulphuric acid. The insoluble sulphate of lime is separated by a filter, and the citric acid obtained in crystals by evaporation. They are ren- dered quite pure by being dissolved in water and re-crystallized. The proportions required in this process are 86 parts or one equivalent of dry citrate of lime, and 49 parts or one equivalent of strong sulphuric acid, which should be diluted with about ten parts of water. Citric acid crystallizes in rhomboidal prisms terminated by four plain surfaces. The crystals are large and transparent, undergo 3N 466 VEGETABLE ACIDS. no.change in the air, and if kept dry may be preserved for any length of time without decomposition. They have an intensely sour taste, redden litmus paper, and neutralize alkalies. Then* flavour when diluted is very agreeable. They are soluble in an equal weight of cold and in half their weight of boiling water, and are also dissolved by alcohol. The aqueous solution is gra- dually decomposed by keeping. It is converted into oxalic by the action of nitric acid. Exposed to heat, the crystals undergo the watery fusion, and the acid itself is decomposed before all its water of crystallization is expelled. Besides the usual products of the decomposition of vegetable matter, a peculiar acid sub- limes, to which the name of pyro dlric acid is applied. The atomic weight of citric acid, as deduced from the compo- sition of citrate of lead by Berzelius, is 58 ; and the crystals consist of 58 parts or one equivalent ofthe acid, and 18 parts or two equivalents of water. According to the analysis of the same chemist, this acid is inferred to consist of Carbon . 24 or 4 equivalents. Oxygen . 32 or 4 equivalents. Hydrogen . 2 . or 2 equivalents. 58 The analysis of Gay-Lussac and Thenard, of Dr. Prout and Dr. Ure, would lead to a different statement; but the foregoing agrees better with the atomic weight ofthe acid. Citric acid is characterized by its flavour, by the shape of its crystals, and by forming an insoluble salt with lime and a deli- quescent soluble compound with potassa. It does not render lime water turbid, unless the latter is in excess, and fully satu- rated with lime in the cold. Citric acid is chiefly employed as a substitute for lemon juice. On some occasions, as in making effervescing draughts or acidu- lous drinks, tartaric acid may be used with equal advantage. The salts of citric acid are of little importance. The citrates of potassa, soda, ammonia, magnesia, and iron, are soluble in watOT. The first is often made extemporaneously as an effer- vescing draught. The citrates of lime, baryta,'and strontia, lead, mercury, and silver, are very sparingly soluble. All of them are dissolved by an excess of their own acids, and are de- composed by sulphuric acid. Malic Acid. This acid is contained in most of the acidulous fruits, being frequently associated with the tartaric and citric acids. Grapes, currants, gooseberries, and oranges, contain it. Vauquelin found it in the tamarind mixed with tartaric and citric acids, and in the house leek, (sempervivum tectorum,) combined with lime. It is VEGETABLE ACIDS. 467 contained in considerable quantity in apples, a circumstance to which it owes its name. It is almost the sole acidifying princi- ple of the berries of the service tree (sorbus aucuparia,) in which it was detected by Mr. Donovan, and described by him under the name of sorbic add; but it was afterwards identified with the malic acid by Braconnot and Houton-Labillardiere. Malic acid may be formed by digesting sugar with three times its weight of nitric acid ; but the best mode of procuring it is from the berries of the service tree. The juice of the unripe berries is diluted with three or four parts of water, filtered and heated ; and while boiling, a solution of acetate of lead is added as long as any turbidity appears. The colouring matter of the berry is thus precipitated, while malate of lead remains in solu- tion. The liquid, while at a boiling temperature, is then filtered. At first a small quantity of dark coloured salt subsides; but on decanting the hot solution into another vessel, the malate of lead is gradually deposited, in cooling, in groups of brilliant white crystals. This process—a modification ofthe common one—has lately been recommended by Wohler. The malate of lead is then decomposed by a quantity of dilute sulphuric acid, insuffi- cient for combining with all the oxide of lead ; by which means a solution is procured containing malic acid together with a little lead. The latter is afterwards precipitated by sulphuretted hy- drogen. Malic acid has a very pleasant acid taste. It crystallizes with great difficulty and in an imperfect manner, attracts moisture from the atmosphere, and is very soluble in water and alcohol. Its aqueous solution is gradually decomposed by keeping. Nitric acid converts it into oxalic acid. Heated in close vessels it is decomposed with formation of a new and volatile acid, which has hence received the name of pyro-malic acid. According to a recent analysis of the malates of lime, lead, and copper by Dr. Prout, 100 parts of anhydrous malic acid consist of 40.68 parts of carbon, 54.24 of oxygen, and 5.08 parts of hy- drogen. Most of the salts of malic acid are more or less soluble in water. The malates of soda and potassa are deliquescent and very soluble. Those of lead and lime, the most insoluble of the malates, are sparingly soluble in cold water, but are freely dis- solved by that liquid at a boiling temperature, a circumstance which distinguishes the malic from the oxalic, tartaric, and citric acids. Benzoic Add. Benzoic acid exists in gum benzoin, in storax, in the balsams of Peru and Tolu, and in several other vegetable substances. M. Vogel has detected it in the flowers of the trifolium melilotus 468 VEGETABLE ACIDS. officinalis. It is found in considerable quantity in the urine of the cow and other herbivorous animals, and is perhaps derived from the grasses on which they feed. It has also been detected in the urine of children. This acid is commonly extracted from gum benzoin. One method consists in heating the benzoin in an earthen pot, over which is placed a cone of paper to receive the acid a3 it sub- limes ; but since the product is always impure, owing to the pre- sence of empyreumatic oil, it is better to extract the acid by means of an alkali. The usual process consists in boiling finely powdered gum benzoin in a large quantity of water along with lime or carbonate of potassa, by which means a benzoate is formed. To the solution, after being filtered and concentrated by evaporation, muriatic acid is added, which unites with the base, and throws down the benzoic acid. It is then dried by a gentle heat, and purified by sublimation. Benzoic acid has a sweet and aromatic, rather than a sour taste; but it reddens litmus paper, and neutralizes alkalies. It fuses readily by heat, and at a temperature a little above its point of fusion, it is converted into vapour, emitting a peculiar, fragrant, and highly characteristic odour, and condensing on cool surfaces without change. When strongly heated, it takes fire, and burns with a clear yellow flame. It undergoes no change by exposure to the air, and is not decomposed by the action even of nitric acid. It requires about 24 parts of boiling water for solution, and nearly the whole of it is deposited on cooling in the form of minute acicular crystals of a silky lustre. It is very soluble in alcohol, especially by the aid of heat. Benzoic acid is easily distinguished by its odour and volatility. Its salts are all decomposed by muriatic acid, with deposition of benzoic acid if the solution is moderately concentrated. The atomic weight of benzoic acid, is 120. The ultimate analysis of this acid by Berzelius, together with the number representing the weight of its combining proportion, appears to justify the opinion that it is composed of Carbon - 90 - or 15 equivalents. Oxygen - 24 - or 3 equivalents. Hydrogen - 6 - or 6 equivalents. 120 According to the analysis of Dr. Ure, it contains 13, instead of 15 equivalents of carbon. Most of the benzoates are soluble in water. Those of lead, mercury, and peroxide of iron are the most insoluble. The ben- zoate of soda and ammonia are sometimes employed for separating iron from manganese. If the solution is quite neutral, the perox- ide of iron is completely precipitated, while the manganese re- mains in solution. VEGETABLET ACIDS. 469 Gallic Acid. This acid was discovered by Scheele in 1786, and exists ready formed in the bark of many trees, and in gall-nuts. It is always associated with tannin, a substance to which it is allied in a man- ner hitherto unexplained. Several processes have been described for the preparation of gallic acid; but the most economical appears to be that of Scheele as modified by M. Braconnot. Any quantity of gall-nuts, reduced to powder, is infused for a few days in four times its weight of water ; and the infusion, after being strained through linen, is kept for two months in a moderately warm atmosphere. During this period, the surface ofthe liquid becomes mouldy, the tannin ofthe gall-nuts disappears more or less completely, and a yellowish crystalline matter is deposited. On evaporating the solution to the consistence of syrup, and allowing it to cool, an additional quantity of the same substance subsides. The gallic acid, thus procured, is impure, owing to the presence of colour- ing matter and a peculiar acid, to which M. Braconnot has ap- plied the name of ellagic acid. The gallic acid is separated from the latter by boiling water, in which the ellagic acid is inso- luble; and it is rendered white by digestion with animal charcoal deprived of its phosphate of lime by muriatic acid. When the colourless solution is concentrated by evaporation, the gallic acid is deposited in small white acicular crystals of a silky lustre. Some crystals prepared by Mr. Phillips, and examined by Mr. Brooke, were in the form of an oblique rhombic prism. Gallic acid has a weak sour taste, accompanied with a slight sensation of astringency. It reddens litmus paper, and efferves- ces with alkaline carbonates. It is soluble in twenty-four parts of cold and in three of boiling water ; and it is likewise dissolved by alcohol. The aqueous solution becomes mouldy by keeping. Nitric acid converts it into oxalic acid. When strongly heated in the open air, it takes fire. At a high temperature, in close ves- sels, it is in part decomposed, and in part sublimes, apparently without change. The composition and atomic weight of gallic acid has not been determined in a satisfactory manner. From an analysis of the gallate of lead by Berzelius, the equivalent ofthe acid is probably about 63 or 64; and, according to the same chemist, it is composed of Carbon - - 56.64 Oxygen - - 38.36^ Hydrogen - - 5.0(T With lime water gallic acid yields a brownish-green precipi- tate, which is re-dissolved by an excess ofthe solution, and ac- quires a reddish tint. It is distinguished from tannin by causing 470 VEGETABLE ACIDS. no precipitate in a solution of gelatine. With a salt of iron it forms a dark blue coloured compound, which is the basis of ink. The finest colour is procured when the peroxide and protoxide of iron are mixed together. This character distinguishes gallic acid from every other substance excepting tannin. The salts of gallic acid, called gallates, have been imperfectly examined. The gallates of potassa, soda, and ammonia, are solu- ble in water; but most ofthe other gallates are of sparing solu- bility. On this account many of the metallic solutions are preci- pitated by gallic acid. Sucdnic Acid. This acid is procured by heating powdered amber in a retort by a regulated temperature, when the succinic acid passes over and condenses in the receiver. It is at present uncertain whe- ther it exists ready formed in amber, or is a product of the des- tructive distillation. As first obtained, it has a yellow colour and peculiar odour, owing to the presence of some empyreuma- tic oil; but it is rendered quite pure and white by being dissolv- ed in nitric acid, and then evaporated to dryness. The oil is decomposed, and the succinic acid left unchanged. Succinic acid has a sour taste, and reddens litmus paper. It is soluble both in water and alcohol, and crystallizes by evapo- ration in anhydrous prisms. When briskly heated, it fuses, un- dergoes decomposition, and in part sublimes, emitting a peculiar and very characteristic odour. The salts of succinic acid have been little examined. The succinates of the alkalies are soluble in water. That of ammonia is frequently employed for separating iron from manganese, the succinate ofthe peroxide of iron being quite insoluble in water, provided the solutions are neutral. The succinate of manganese, on the contrary, is soluble. The atomic weight of succinic acid, deduced from the com- position of the succinate of iron and of lead by Thomson and Berzelius, is 50; and according to the analysis of the succinate of lead by Berzelius, this acid is inferred to consist of Carbon . 24 . or 4 equivalents. Oxygen . 24 . or 3 equivalents. Hydrogen . 2 . or 2 equivalents. 50 From this it appears that succinic is identical with the acetic acid, both in the proportion of its constituents and the number of its equivalent. If this is true, and there seems to be no good rea- son to doubt the accuracy of the data, the sole difference between these acids consists in the manner in which their elements are VEGETABLE ACIDS. 471 combined, a circumstance which is very favourable to the opinion already mentioned relative to the constitution of organic sub- stances in general. Camphoric Acid.—This compound has not hitherto been found in any plant, and is procured only by digesting camphor for a considerable time in a large excess of nitric acid. It is sparingly soluble in water. Its taste is rather bitter, and its odour somewhat similar to that of saffron. It reddens litmus paper, and combines with alkalies, forming salts which are called cam- phorates. This acid has not been applied to any useful purpose. The Mucic or Saccholactic Acid was discovered by Scheele in 1780. It is obtained by the action of nitric acid on certain sub- stances, such as gum, manna, and the sugar of milk. The rea- diest and cheapest mode of forming it is by digesting gum with three times its weight of nitric acid. On applying heat efferves- cence ensues, and three acids—the oxalic, malic, and saccho- lactic, are the products. The latter, from its insolubility, sub- sides as a white powder, and may be separated from the others by washing with cold water. In this state Dr. Prout says it is very impure. To purify it he digests with a slight excess of am- monia, and dissolves the resulting salts in boiling water. It is filtered while hot. and the solution evaporated slowly almost to dryness. The saccholactate of ammonia is thus obtained in crys- tals, which are to be washed with cold distilled water, until they become quite white. They are then dissolved in boiling water. and the saturated hot solution dropped into cold dilute nitric acid. The saccholactic is a weak acid, which is insoluble in alcohol, and requires sixty times its weight of boiling water for solution. When heated in a retort it is decomposed ; and in addition to the usual products, yields a volatile white substance, to which the name of pyro-mudc acid has been applied. According to the analysis of Dr. Prout, saccholactic acid is composed of 33 parts of carbon, 61.5 of oxygen, and 4.9 of hydrogen. Moroxylic Add.—This compound, which was discovered by Klaproth, is found in combination with lime on the bark ofthe morus alba or white mulberry, and has hence received the ap- pellation of moric or moroxylic acid. It is obtained by decom- posing the moroxylate of lime by acetate of lead, and then sepa- rating the lead from the moroxylate of that base by means of sulphuric acid. The Hydrocyanic or Prussic Acid, which is not an unfrequent production of plants, has already been described. The Sorbic, as already mentioned, has been shown to be the malic acid. Rhuemic Acid.—This name was applied to the acid principle contained in the stem ofthe garden rhubarb; but M. Lassaigne has shown it to be the oxalic acid. 472 VEGETABLE ACIDS. Boletic acid was discovered by M. Braconnot, in the juice of the Boletus pseudo-igniarius. It is a compound of no impor- tance. Igasuric Acid.—M. Pelletier and Caventou have proposed this name for the acid which occurs in combination with strychnia in the nux vomica and St. Ignatius's bean ; but its existence, as dif- ferent from all other known acids, is doubtful. Mellitic Acid.—This acid is contained in the rare substance called honey-stone, which is occasionally met with at Thuringia in Germany. The honey-stone, according to Klaproth, is a mel- litate of alumina, and on boiling it in a large quantity of water, the acid is dissolved, and the alumina subsides. On concentra- ting the solution, the mellitic acid is deposited in minute acicu- lar crystals. From its rarity it has been little studied, and is of little importance. Suberic Acid is procured by the action of nitric acid on cork. Its acid properties are feeble. It is very soluble in boiling water, and the greater part of it is deposited from the solution in cooling in the form of a white powder. Its salts, which have been little examined, are known by the name of suberates. Zumic Acid.—This compound, procured by Braconnot from several vegetable substances which had undergone the acetous fermentation, appears, from the observations of Vogel, to be the lactic acid. Kinic Acid.—This acid exists in the cinchona bark in combi- nation with lime. On evaporating an infusion of bark to the consistence of an extract, and treating the residue with alcohol, a viscid matter remains, consisting of the kinate of lime and mu- cilagineous matters. On dissolving it in water, and allowing the concentrated solution to evaporate spontaneously in a warm place the kinate crystallizes in rhombic prisms with dihedral summits. From a solution of this salt, Vauquelin precipitated the lime by means of oxalic acid, and thus obtained kinic acid in a pure state. Kinic acid has an acid taste, and reddens vegetable blue co- lours. It is very soluble in water, and crystallizes with diffi- culty. It forms soluble compounds with the alkalies and alka- line earths, and is not precipitated by a salt of mercury, lead, or silver. Meconic Acid, which is combined with morphia in opium, will be most conveniently described in the following section. Peciic Acid.—See Vegetable Jelly. Carbazotic Acid.—Th\s name has been applied by M. Liebig to a peculiar acid, formed by the action of nitric acid on indigo. It is made by dissolving small fragments of the best indigo in eight or ten times their weight of moderately strong nitric acid, and boiling the solution as long as nitrous acid fumes are evolv- ed. On cooling, a large quantity of semi-transparent yellow VEGETABLE ACIDS. 473 crystals will be formed ; and, on evaporating the residual liquid, and adding cold water, an additional quantity ofthe acid is pro- cured. To render the new acid quite pure, it should be dis- solved in hot water, and neutralized by carbonate of potassa. As the liquid cools, the cnrbazotate of potassa crystallizes, and may be purified by repeated crystallization. The acid may be preci- pitated from this salt by sulphuric acid. Carbuzotic acid is sparingly soluble in cold water; but is dis- solved much more freely by the aid of heat, and on cooling, yields brilliant crystalline plates of a yellow colour. Ether and alcohol dissolve it readily. It is fused and volatilized by heat, without decomposition ; but when suddenly exposed to a strong heat, it inflames without explosion, and burns with a yellow flame, with a residue of charcoal. Its solution has a bright yel- low colour, reddens litmus paper, is extremely bitter, acts like a strong acid on metallic oxides, and yields crystallizable salts. It is composed of carbon, nitrogen, and oxygen, in the proportion of 15 equivalents of the first, 3 of the second, and 15 of the third substance. The bitter principle of Welter, formed by the action of nitric acid on silk, is also carbazotic acid. SECTION II. Vegetable Alkalies. Under this title are comprehended those proximate vegetable principles which are possessed of alkaline properties. The hon- our of discovering the existence of this class of bodies is due to Sertuerner, a German apothecary, who published an account of morphia so long ago as the year 1S03 ; but the subject excited no notice until the publication of his second essay in 1816. The chemists who have since cultivated this department with most success are M. Robiquet, and MM. Pelletier and Caventou. All the vegetable alkalies, according to the researches of Pel- letier and Dumas, consist of carbon, hydrogen, oxygen, and ni- trogen. They are decomposed with facility by nitric acid and by heat, and ammonia is always one of the products of the de- structive distillation. They never exist in an insulated state in the plants which contain them ; but are apparently in every case combined with an acid, with which they form a salt more or less soluble in water. These alkalies are, for the most part, very in- soluble in water, and of sparing solubility in cold alcohol; but they are all readily dissolved by that fluid at a boiling tempera- ture, being deposited from the solution, commonly in the form of crystals, on cooling. Most of the salts are far more soluble in 3 O 474 VEGETABLE ALKALIES. water than the alkalies themselves, and several of them are re- markable for their solubility. As the vegetable alkalies agree in several of their leading che- mical properties, the mode of preparing one of them admits of being applied, with slight variation, to all. The general outline ofthe method is as follows :—The substance containing the alka- line principle is digested, or more commonly macerated, in a large quantity of water, which dissolves the salt, the base of which is the vegetable alkali. On adding some more powerful salifiable base, such as potassa or ammonia, or boiling the solu- tion for a few minutes with lime, or pure magnesia, the vegetable alkali is separated from its acid, and being in that state insoluble in water, may be collected on a filter and washed. As thus pro- cured, however, it is impure, retaining some of the other princi- ples, such as the oleaginous, resinous, or colouring matters with which it is associated in the plant. To purify it from these sub- stances, it should be mixed with a little animal charcoal, and dissolved in boiling alcohol. The alcoholic solution, which is to be filtered while hot, yields the pure alkali, either on cooling or by evaporation ; and if not quite colourless, it should again be subjected to the action of alcohol and animal charcoal. In or- der to avoid the necessity of employing a large quantity of alco- hol, the following modification of the process may be adopted. The vegetable alkali, after being precipitated and collected on a filter, is made to unite with some acid, such as the acetic, sul- phuric, or muriatic, and the solution boiled with animal charcoal until the colouring matter is removed. The alkali is then preci- pitated by ammonia or some other salifiable base. Morphia. Opium contains a great diversity of different principles, among which the following may in particular be enumerated : morphia, meconic acid, narcotine, gummy, resinous, and extractive co- louring matters, lignin, fixed oil, and a small quantity of caout- chouc. On infusing opium in water, several of these principles are dissolved, and especially the meconate of morphia, together with narcotine, which is likewise rendered soluble by an acid. One of the best processes for preparing pure morphia is that recommended by M. Robiquet. The concentrated infusion of a pound of opium is boiled for a quarter of an hour with about 150 grains of pure magnesia, and the grayish crystalline precipitate, which consists of the meconate of magnesia, morphia, narcotine, colouring matter, and the excess of magnesia, is collected on a filter and edulcorated with cold water. This powder is then di- gested at a temperature of 120° or 130° F. in dilute alcohol, which removes the narcotine and the greater part of the colour- ing matter. The morphia is then taken up by concentrated VEGETABLE ALKALIES. 475 boiling alcohol, and is deposited in crystals on cooling. Dr. Christison, by this process, procured three drachms and a half of morphia from a half a pound of a very pure specimen ofthe best Turkey opium. Dr. Thomson proposes to precipitate the morphia by ammonia, and to purify it by solution in acetic acid and digestion with ani- mal charcoal. The animal charcoal should be deprived of phos- phate of lime by muriatic acid before being used. Pure morphia crystallizes readily when its alcoholic solution is evaporated, and yields colourless crystals of a brilliant lustre. They mostly occur in irregular six-sided prisms with dihedral summits; but their primary form is a right rhombic prism, of which the lateral planes only appear in the crystals. It is al- most wholly insoluble in cold, and to very small extent in hot wa- ter. It is soluble in strong alcohol, especially by the aid of heat. In its pure state it has scarcely any taste ; but when ren- dered soluble by combining with an acid, or by solution in alco- hol, it is intensely bitter. It has an alkaline re-action, and com- bines with acids, forming neutral salts, which are far more solu- ble in water than morphia itself, and for the most part are capable of crystallizing. Strong nitric acid decomposes morphia, forming a red solution, which by the continued action of the acid acquires a yellow co- lour, and is ultimately converted into oxalic acid. This circum- stance was first noticed by Pelletier and Caventou ; but it is not peculiar to morphia, since nitric acid has a similar effect on strychnia. Morphia is the narcotic principle of opium. When pure, owing to its insolubility, it is almost inert; for M. Orfila gave twelve grains of it to a dog without its being followed by any sensible effect. In a state of solution, on the contrary, it acts on the animal system with great energy, Sertuerner having noti- ced alarming symptoms from so small a quantity as half a grain. From this it appears to follow that the effects of an overdose of a salt of morphia may be prevented by giving a di\ute solution of ammonia, or an alkaline carbonate, so as to precipitate the vege- table alkali. When carefully administered morphia may be em- ployed very advantageously in the practice of medicine ; since, according to Magendie, it produces the soothing effects of opium, without causing the feverish excitement, heat, and headach, which so frequently accompany the employment of that drug. The best mode of exhibiting it is in the form of acetate of morphia, a salt which is very soluble in water, and crystallizes in diver- gent prisms by evaporation. The basis of Battley's sedative li- quor is supposed to be acetate of morphia. This compound, from being inodorous, and therefore less easily detected than opium, has been employed for criminal purposes, and M. Las- saigne has described the following method for discovering its 476 VEGETABLE ALKALIES. presence. The suspected solution is evapoarted by a tempera- ture of 212°, and the residue treated with alcohol, by which the acetate of morphia, together with osmazome and some salts, is dissolved. The alcohol is next evaporated, and water added to separate some fatty matter. The aqueous solution is then set aside for spontaneous evaporation, during which the acetate of morphia, if present, crystallizes in divergent prisms of a yellow- ish colour. The salt is recognized by its bitter taste, by yielding a precipitate with ammonia, by the disengagement of acetic acid on the addition of concentrated sulphuric acid, and by the orange red colour developed by nitric acid. The composition of morphia, as will appear from the following numbers, has been stated differently by different chemists. The specimen analyized by Dr. Thomson must surely have been im- pure. Pelletier and Dumas. Bussy. Brande. Thomson. Carbon - 72.02 69.0 72.0 44.71 Oxygen - 14.84 20.0 17.0 49.69 Hydrogen 7.61 6.5 5.5 5.59 Nitrogen 5.53 4.5 5.5 0.00 100 100 100 100 Meconic Acid, from M^xav, papaver.—This acid was procured by M. Robiquet from the magnesian precipitate above mentioned, after the morphia had been separated from it. The meconate of magnesia is dissolved in dilute sulphuric acid, and muriate of baryta is then added, which throws down the sulphate and meco- nate of that base. By acting on this precipitate with dilute sul- phuric acid, the meconic acid is set free, and crystallizes when its solution is evaporated. As it retains colouring matter very obstinately, it should be purified by sublimation. Meconic acid may easily be prepared, as recommended by Dr. Hare, by pre- cipitating the acid from an aqueous infusion of opium with ace- tate of lead, and decomposing the insoluble meconate of lead, while diffused through water, by a current of sulphuretted hydro- gen gas. The filtered solution yields crystals of meconic acid by evaporation. Meconic acid has a sour, followed by a bitter taste, reddens litmus paper, and is very soluble both in water and alcohol. It is characterized by giving a red colour to a salt of the peroxide of iron, and communicates an emerald green tint to sulphate of copper. It exefts no action on the animal system. Its presence even in a dilute solution of opium may be detected by acetate of lead. The insoluble meconate of lead, which subsides, is decom- posed by sulphuric acid ; and on adding a per-salt of iron, the red colour caused by the free meconic acid make its appearance. VEGETABLE ALKALIES. 477 Narcotine.—This substance, though not regarded as a vege- table alkali, may be conveniently noticed in connection with morphia. It was particularly described in 1803 by Derosne, and was long known by the name of the salt of Derosne. Sertuerner supposed it to be the meconate of morphia; but M. Robiquet proved that it is an independent principle, and applied to it the name of narcotine. It is easily prepared by evaporating an aqueous infusion of opium to the consistence of an extract, and digesting it in sulphuric ether. This solvent, which does not act on the meconate of morphia, takes up all the narcotine, and de- posits it in acicular crystals by evaporation; and the extract of opium, thus deprived of narcotine, may be advantageously em- ployed in medical practice. Morphia may be purified from nar- cotine in the same manner. Pure narcotine is insoluble in cold, and very slightly soluble in hot water. It dissolves in oil, ether, and alcohol, the latter, though diluted, acting as a solvent for it by the aid of heat. It does not possess alkaline properties, though it is rendered soluble in water by means of an acid. Its presence in an aqueous solu- tion of opium seems owing to a free acid, which M. Robiquet imagines to be different from the meconic. Like the vegetable alkalies, nitrogen enters into its constitution. The unpleasant stimulating properties of opium are attributed by Magendie to the presence of narcotine, the ill effects of which, according to the experiments of the same physiologist, are in a great degree counteracted by acetic acid. These results render it probable that the superiority assigned to the black drop over the common tincture of opium is owing to the vegetable acids which enter into its composition. Cinchonia and Quina. The existence of a distinct vegetable principle in cinchona bark was inferred by Dr. Duncan, junior, in the year 1803, who ascribed to it the febrifuge virtues ofthe plant, and proposed for it the name of cinchonin. Dr. Gomez, of Lisbon, whose atten- tion was directed to the subject by the researches of Dr. Duncan, succeeded in procuring cinchonin in a separate state; but its alkaline nature was first discovered in 1820 by MM. Pelletierand Caventou. It has been fully established by the labours of those chemists that the febrifuge property of bark is possessed by two alkalies, the cinchonia or cinchonin of Dr. Duncan, and quina, both of which are combined with kinic acid. These principles, though very analogous, are distinctly different, standing in the same relation to each other as potassa and soda. The former exists in the Cinchona condaminea, or pale bark; the latter is present in the C. cordifolia, or yellow bark; and they are both contained in the C. oblongifolia, or red bark. They were pro- 478 VEGETABLE ALKALIES. cured by Pelletier and Caventou by a process similar to that of M. Robiquet for preparing morphia; and slight modifications of the method have been proposed by M. Badollier and M. Voreton. From one pound of yellow bark M. Voreton procured 80 grains of quina, which is nearly 1.4 per cent. Pure cinchonia is white and crystalline, requires 2500 times its weight of boiling water for solution, and is insoluble in cold water. Its proper menstruum is boiling alcohol ; but it is dis- solved in small quantity by oils and ether. Its taste is bitter, though slow in being perceived, on account of its insolubility; but when the alkali is dissolved by alcohol or an acid, the bit- terness is very powerful, and accompanied by the flavour of cin- chona bark. Its alkaline properties are exceedingly well mark- ed, since it neutralizes the strongest acids. The sulphate, mu- riate, nitrate, and acetate of cinchona are soluble in water, and the sulphate crystallizes in very short six-sided prisms derived from an oblique rhomboidal prism. It commonly occurs in twin crystals. The neutral tartrate, oxalate, and gallate of cinchonia, are insoluble in cold, but may be dissolved by hot water, or by alcohol. Quina, which was discovered by Pelletier and Caventou, does not crystallize like cinchonia when precipitated from its solu- tions, but it has a white, porous, and rather flocculent aspect. It is very soluble in alcohol, forming a solution which is intensely bitter, and possesses a distinct alkaline re-action.—Ether like- wise dissolves it, but it is almost insoluble in water. Its febri- fuge virtues are more powerful than those of cinchonia, and it is now extensively employed in the practice of medicine. It is commonly exhibited in the form of the sulphate, a salt of such activity that three grains have been known to cure an intermittent fever. This salt, which consists of 90 parts of the alkali and 10 of the acid, crystallizes in delicate white needles, having the ap- pearance of amianthus. It is less soluble in water than the sul- phate of cinchonia, but is very bitter. It dissolves readily in strong alcohol by the aid of heat, a character which affords a useful test of its purity. The analyses of different chemists, relative to the composition of cinchona and quina, do not correspond better than those of morphia, as appears by the following results :— Pelletier and Dumas. Brande. f Cinchonia. Carbon . 76.97 Oxygen . 7.97 Hydrogen 6.22 Nitrogen . 9.02 Quina. 74.14 6.77 8.80 10.76 r Cinchonia. 79.30 0.00 7.17 13.72 Quina. 73.80 5.55 7.65 13.00 100.1S 100.47 100.19 100.00 VEGETABLE ALKALIES. 479 The neutral gallate, tartrate, and oxalate of quina, like the analogous salts of cinchonia, are insoluble in cold water. From the new facts which have been ascertained relative to the constitution of bark, the action of chemical tests on a decoc- tion of this substance is now explicable. According to the analy- sis of Pelletier and Caventou, the different kinds of Peruvian bark, besides the kinate of cinchonia or quina, contain the fol- lowing substances:—a greenish fatty matter; a red insoluble matter; a red soluble principle, which is a variety of tannin; a yellow colouring matter; kinate of lime; gum, starch, and lig- nin. It is hence apparent that a decoction of bark, owing to the tannin which it contains, may precipitate a solution of tartar emetic, of gelatine, or a salt of iron, without containing a trace ofthe vegetable alkali, and consequently without possessing any febrifuge virtues. An infusion of gall-nuts, on the contrary, causes a precipitate only by its gallic acid uniting with cinchonia or quina, and there- fore affords a test for distinguishing a good from an inert variety of bark. Strychnia.—Brucia. Strychnia.—Strychnia was discovered in 1818 by Pelletier and Caventou, in the fruit of the Strychnos ignatia and Strychnos nux vomica, and has since been extracted by the same chemists from the Upas. The most economical process for preparing this alkali is that recommended by M. Corriol. It consists in treating nux vomica with successive portions of cold water, evaporating this solution to the consistence of syrup, and precipitating the gum, which is present, by alcohol. The alcoholic solution is then evaporated to the consistence of an extract by the heat of a water-bath. The extract, which consists almost entirely of the igasurate of strychnia, is dissolved by cold water, and by this means deprived of a little fatty matter, which had originally been dissolved, pro- bably through the medium of the gum. The solution is next heated, and the strychnia precipitated by a slight excess of lime water, and then dissolved by boiling alcohol. On evaporating the spirit, the alkali is obtained pure, except in containing a little brucia and colouring matter, both of which are effectually re- moved by maceration in dilute alcohol. Strychnia is very soluble in boiling alcohol, and is procured in minute four-sided prisms by allowing the solution to evaporate spontaneously. It is almost insoluble in water, requiring more than 6000 parts of cold and 2500 of boiling water for solution; but, notwithstanding its sparing solubility, it excites an in- supportable bitterness in the mouth.—Water containing only l-600,000th of its weight of strychnia has a bitter taste. It has 480 VEGETABLE ALKALIES. a distinct alkaline re-action, and neutralizes acids, forming salts, most of which are soluble in water. It is united in the nux vomica and St. Ignatius's bean with igasuric acid. By the action of strong nitric acid it yields a red colour; but it appears proba- ble, from some recent observations of Pelletier and Caventou, that the red tint is owing to the presence of some impurity. Strychnia is one of the most virulent poisons hitherto disco- vered, and is the poisonous principle of the substance in which it is contained. Its energy is so great, that half a grain blown into the throat of a rabbit occasioned death in the course of five minutes. Its operation is always accompanied with symptoms of locked jaw and other tetanic affections. Strychnia, according to the analysis of Pelletier and Dumas, is composed of 78.22 of carbon, 6.38 of oxygen, 6.54 of hydrogen, and 8.92 of nitrogen. Brucia.—This alkali was discovered in the Brucea antidy- senterica by Pelletier and Caventou soon after their discovery of strychnia ; and it likewise exists in small quantity in the St. Igna- tius's bean and nux vomica. In its bitter taste and poisonous qualities, it is very similar to strychnia, but is twelve or sixteen times less energetic than that alkali. It is soluble both in hot and cold alcohol, especially in the former; and it crystallizes when its solution is evaporated. Even dilute alcohol by aid of heat dissolves it, and on this property is founded the method of separating it from strychnia. It is more soluble in water than most ofthe other vegetable alkalies, requiring only 850 times its weight of cold, and 500 of boiling water for solution. It is com- posed of 75.04 of carbon, 11.21 of oxygen, 6.52 of hydrogen, and 7.22 of nitrogen. Veratria, Emeliaf Picrotoxia, Solania, Delphia, fyc. Veratria.—The medicinal properties ofthe seeds of the Vera- trum sabadilla, and the root of the Veratrum album or white hellebore, and Colchicum autumnale or meadow saffron, are owing to the peculiar alkaline principle veratria, which was dis- covered by Pelletier and Caventou in 1819, and may be extracted by the usual process. This alkali, which appears to exist in those plants in combination with gallic acid, is white and pul- verulent, inodorous, and of an acrid taste. It requires 1000 times its weight of boiling, and still more of cold water for solution. It is very soluble in alcohol, and may also be dissolved, though less readily, by means of ether. It has an alkaline re-action, and neutralizes acids; but it is a weaker base than morphia, quina, or strychnia. It acts with singular energy on the mem- brane of the nose, exciting violent sneezings though in very minute quantity. When taken internally in very small doses, it produces excessive irritation of the mucous coat of the stomach VEGETABLE ALKALIES. 481 and intestines ; and a few grains were found to be fatal to the lower animals. Veratria, according to the analyses of Pelletier and Dumas, consists of 66.75 of carbon, 19.6 of oxygen, 8.54 of hydrogen, and 5.04 of nitrogen. Emetia.—Ipecacuanha consists of an oily matter, gum, starch, lignin, and a peculiar principle, which was discovered in 1817 by M. Pelletier, and to which he has applied the name of emetine. This substance, of which ipecacuanha contains 16 per cent, ap- pears to be the sole cause of the emetic properties of that root, and is procured by a process similar to that for preparing the other vegetable alkalies. Emetia is a white pulverulent substance, of a rather bitter and disagreeable taste, sparingly soluble in cold but more freely in hot water, and insoluble in ether. It is readily dissolved by al- cohol. At 122° it fuses. It has a distinct alkaline re-action, and neutralizes acids; but its salts are little disposed to crystal- lize. According to Pelletier and Dumas, it consists of carbon 64.57, oxygen 22.95, hydrogen 7.77, and nitrogen, 4. Picrotoxia.—The bitter poisonous principle of the Cocculus indicus was discovered in 1819 by M. Boullay, who gave it the name of picrotoxine. Its claim to the title of a vegetable alkali, among which class of bodies it was placed by its discoverer, has been called in question by M. Casaseca, from whose remarks it seems that picrotoxia has no alkaline re-action, and does not neutralize acidity. It combines, however, with acids, and with the acetic and nitric acids forms crystallizable compounds. It appears also, that the menispermic acid, supposed by M. Boullay to be united in the cocculus indicus with picrotoxia, is merely a mixture of sulphuric and malic acids. Corydalin.—This alkali, discovered by Dr. Wackenroder, is contained in the root of the fumitory, (not the common fumitory, fumaria officinalis, but,) fumaria cava, and corydalis berosa of Decandolle. It exists in the plant as a soluble malate, and is precipitated from its aqueous solution in the usual manner, and purified by alcohol. It is soluble in alcohol, and the hot saturated solution in cool- ing yields colourless prismatic crystals of a line in length. By spontaneous evaporation fine laminae are formed. It is likewise soluble in ether, but very sparingly in water. It is insipid and inodorous ; but when dissolved by acids or alcohol it is very bit- ter. Its solution has an alkaline re-action, and it neutralizes acids. Cold dilute nitric acid dissolves it and yields a colourless solu- tion ; but when heated it acquires a red tint, and becomes blood- red when concentrated. Its salts are precipitated by potassa, pure or carbonated, and by infusion of gall-nuts. The precipi- tate is white when the solution is dilute, and grayish-yellow if concentrated. 3P 482 VEGETABLE ALKALIES. Solania.—The active principle of the Solanum dulcamara, or woody nightshade, was procured in a pure state by Desfosses. This compound has distinct alkaline properties, and is combined in the plant with malic acid. Cynopia.—Professor Ficinus of Dresden has discovered a new alkali in the JEthusa Cynapium, or lesser hemlock, to which he has given the name of Cynopia. It is crystallizable, and soluble in water and alcohol, but not in ether. The crystals are in the form of a rhombic prism, which is also that of the crystals of the sulphate. Delphia.—This substance was discovered in the Delphinium staphysagria, or stavesacre, by MM. Feneuille and Lassaigne. It possesses the general characters ofthe vegetable alkalies. Althea was announced by M. Bacon of Caen as a new vegeta- ble alkali, said to be procured from the root of the marsh-mallow. (Althea Officinalis.) According to M. Plisson, this alkali has no existence, and what was thought to be supermalate of althea is asparagin. Besides the vegetable alkalies, already described, it has been rendered highly probable, chiefly by the researches of M. Brandes, that several other plants, such as the Atropa belladonna, Conium maculatum, Hyoscyamus niger, Datura stramonium, and Digitalis, owe their activity to the presence of an alkali. SECTION III. Substances which, in relation to Oxygen, contain an excess of Hydrogen. Oils. Oils are characterized by a peculiar unctuous feel, by inflam- mability, and by insolubility in water. They are divided into the fixed and volatile oils, the former of which are comparatively fixed in the fire, and therefore give a permanently greasy stain to paper; while the latter, owing to their volatility, produce a stain which disappears by gentle heat. Fixed Oils.—The fixed oils are usually contained in the seeds of plants, for example in the almond, linseed, rapeseed, and pop- py seed ; but olive oil is extracted from the pulp which surrounds the stone. They are procured by bruising the seed, and subject- ing the pulpy matter to pressure in hempen bags, a gentle heat being generally employed at the same time to render the oil more limpid. Fixed oil, the palm oil excepted, are fluid at common tempera- tures, are nearly inodorous, and have little taste. They are light- er than water, their density in general varying from 0.9 to 0.96. OILS, 483 They are commonly of a yellow colour, but may be rendered nearly or quite colourless by the action of animal charcoal. At or near the temperature of 600° F. they begin to boil, but suffer partial decomposition at the same time, an inflammable vapour being disengaged even below 500°. When heated to redness in close vessels a large quantity of the combustible compounds of carbon and hydrogen are formed! together with the other pro- ducts ofthe destructive distillation of vegetable substances ; and in the open air they burn with a clear white light, and formation of water and carbonic acid. They may hence be employed for the purposes of artificial illumination, as well in lamps, as for the manufacture of gas. Fixed oils undergo considerable change by exposure to the air. The rancidity which then takes place is occasioned by the mucilaginous matters which they contain becoming acid. From the operation of the same cause, they gradually lose their limpidity, and some of them, which are hence called drying oils, become so dry that they no longer feel unctuous to the touch nor give a stain to paper. This property, for which linseed oil is remarkable, may be communicated quickly by heating the oil in an open vessel. The drying oils are employed for making oil paint, and mixed with lamp-black constitute printer's ink. Dur- ing the process of drying, oxygen is absorbed in considerable quantity. The absorption of oxygen by fixed, and especially by drying oils, is under some circumstances so abundant and rapid, and accompanied with such free disengagement of caloric, that light porous combustible materials, such as lamp-black, hemp, or cot- ton-wool, may be kindled by it. Substances of this kind, mois- tened with linseed oil, have been known to take fire during the space of 24 hours, a circumstance which has repeatedly been the cause of extensive fires in warehouses and in cotton manu- factories. Fixed oils do not unite with water, but they may be per- manently suspended in that fluid by means of mucilage or sugar, so as to constitute an emulsion. They are for the most part very sparingly soluble in alcohol and ether. Strong sulphuric acid thickens the fixed oils, and forms with them a tenacious matter like soap; and they are likewise rendered thick and viscid by the action of chlorine. Concentrated nitric acid acts upon them with great energy, giving rise in some instance to the production of flame. Fixed oils unite with the common metallic oxides. Of these compounds, the most interesting is that with the oxide of lead. When linseed oil is heated with a small quantity of litharge a liquid results which is powerfully drying, and is employed as oil varnish. Olive oil, combined with half its weight of litharge, forms the common diachylon plaster. 484 OILS. The fixed oils are readily attacked by alkalies. With ammonia, oil forms a soapy liquid to which the name of volatile liniment is applied. The fixed alkalies, boiled with oil or fat, give rise to the soap employed for washing, the soft inferior kind being made with potassa, and the hard with soda. The chemical nature of soap has of late years been elucidated by the labours of M. Chevreul. This chemist has found that fixed oils and fats are not pure proximate principles, but consist of two substances, one of which is solid at common temperatures, while the other is fluid. To the former he has applied the name of stearine, from ansae; suet, and to the latter elaine, from zxaiov oil. Stearine is the chief in- gredient of suet, butter, and lard, and is the cause of their solidity; whereas oils contain a greater proportional quantity of elaine, and are consequently fluid. These principles may be separated from one another by exposing fixed oil to a low temperature, and pressing it, when congealed, between folds of bibulous paper. The stearine is thus obtained in a separate form ; and by pressing the bibulous paper under water, an oily matter is procured, which is elaine in a state of purity. This principle is peculiarly fitted for greasing the wheels of watches, or other delicate machinery, since it does not thicken or become rancid by exposure to the air, and requires a cold of about 20° F. for congelation. In the formation of soap the stearine and elaine disappear entirely, being converted by a change in the arrangement of their elements into three compounds, to which M. Chevreul has applied the names of margaric and oleic acids, and glycerine. The two acids enter into combination with the alkali employed, and the resulting com- pound is soap. A similar change appears to be effected by the action not only ofthe alkaline earths, but of several ofthe other metallic oxides. Soap is decomposed by acids, and by earthy and most metallic salts. On mixing muriate of lime with a solution of soap, a mu- riate of the alkali is produced, and the lime forms an insoluble compound with the margaric and oleic acids. A similar change ensues when a salt of lead is employed. According to the analysis of Gay-Lussac and Thenard, 100 parts of olive oil consists of carbon 77.213, oxygen 9.427, and hydrogen 13.36. From these proportions it is inferred that olive oil contains ten equivalents of carbon, one of oxygen, and eleven of hydrogen. Volatile oil—Aromatic plants owe their flavour to the presence of a volatile or essential oil, which may be obtained by distilla- tion, water being put into the still along with the plant, in order to prevent the latter from being, burned. The oil and water pass over into the recipient, and the oil collects at the bottom or the surface ofthe water according to its density. Essential oils have a penetrating odour and acrid taste, which are often pleasant when sufficiently diluted. They are soluble OILS. 485 in alcohol, though in different proportions. They are not ap- preciably dissolved by water ; but that fluid acquires the odour of the oil with which it is distilled. With the fixed oils they unite in every proportion, and are sometimes adulterated with them, an imposition easily detected by the mixed oil causing on paper a greasy stain, which is not removed by heat. Volatile oils burn in the open air with a clear white light, and the sole products ofthe combustion are water and carbonic acid. On exposure to the atmosphere, they gradually absorb a large quantity of oxygen, in consequence of which they become thick, and are at length converted into a substance resembling resin. This change is rendered more rapid by the agency of light. Of the acids, the action of strong nitric acid on volatile oils is the most energetic, being often attended with vivid combustion, an effect which is rendered more certain by previously adding to the nitric a few drops of sulphuric acid. Volatile oils do not unite readily with metallic oxides, and are attacked with difficulty even by the alkalies. The substance called Starkey's soap is made by triturating oil of turpentine with an alkali. Volatile oils dissolve sulphur in large quantity, forming a deep brown coloured liquid, called balsam of sulphur. The so- lution is best made by boiling flowers of sulphur in spirit of tur- pentine. Phosphorus may likewise be dissolved by the same menstruum. The most interesting of the essential oils are those of turpen- tine, caraway, cloves, peppermint, nutmeg, anise, lavender, cin- namon, citron, and chamomile. Of these, the most important is the first, which is much employed in the preparation of varnishes, and for some medical and chemical purposes. It is procured by distilling common turpentine; and when purified by a second distillation, it is spirit or essence of turpentine. Common oil of turpentine is inferred by Dr. Ure to consist of 14 equivalents of carbon, 1 of oxygen, and 10 of hydrogen. Ac- cording to M. Houton Labillardiere, the purified oil contains no oxygen, but is composed of carbon and hydrogen in such pro- portions, that one volume of its vapour contains 4 volumes of olefiant gas, and two volumes ofthe vapour of carbon. Camphor.—This inflammable substance, which in several re- spects is closely allied to the essential oils, exists ready formed in the laurus camphora of Japan, and is obtained from its trunk, root, and branches, by sublimation. Camphor has a bitterish, aromatic, pungent taste, accompanied with a sense of coolness. It is unctuous to the touch, and brit- tle ; but it possesses a degree of toughness which prevents it from being pulverized with facility. It is easily reduced to pow- der by trituration with a few drops of alcohol. Its specific gra- vity is 0.988. It is exceedingly volatile, being gradually dissi- 486 oms. pated in vapour if kept in open vessels. At 288° F. it enters into fusion, and boils at 400° F. Camphor is insoluble in water; but when triturated with su- gar, and then mixed with that fluid, a portion is dissolved suffi- cient for communicating its flavour. It is dissolved freely by alcohol, and is thrown down by the addition of water. It is likewise soluble in the fixed and volatile oils, and in strong acetic acid. Sulphuric acid decomposes camphor, converting it into a substance like artificial tannin. With the nitric it yields cam- phoric acid. Camphor, according to the analysis of Dr. Ure, appears to con- sist often equivalents of carbon, one equivalent of oxygen, and nine equivalents of hydrogen. On transmitting a current of dry muriatic acid gas through the purified oil of turpentine, surrounded by a mixture of snow and salt, a quantity of gas is absorbed equal to one-third of the weight of the oil; and a white crystalline substance, very simi- lar to camphor, is generated. This matter was discovered by Kind, and has since been studied by Trommsdorf, Gehlen, and Th6nard. The last chemist maintains that this peculiar substance is a compound of turpentine and muriatic acid, a view which is supported by the researches of M. Houton Labillardiere. Coumarin.—This name was first applied to the odoriferous principle ofthe Tonka bean, by M. Guibourt, and has since been adopted by MM. Boullay and Boutron-Charlard. It is derived from the term Coumarouna odorata, given by Stublet to the plant which yields the bean. Coumarin is white, of a hot pungent taste, and distinct aroma- tic odour. It crystallizes sometimes in square needles, and at other, times in short prisms. It is moderately hard, fracture clean, lustre considerable, and density greater than that of water. It fuses at a moderate temperature into a transparent fluid, which yields an opaque crystalline mass on cooling. Heated in close vessels, it is sublimed without change. It is sparingly soluble in water; but is readily dissolved by ether and alcohol, and the so- lutions crystallize by spontaneous evaporation. It is very solu- ble in fixed and volatile oils. M. Vogel mistook coumarin for benzoic acid ; but MM. Boul- lay and Boutron-Charlard maintain, that it has neither an acid nor alkaline re-action, and that it is a peculiar independent prin- ciple, nearly allied to the essential oils. These chemists did not find any benzoic acid in the Tonka bean, and consider coumarin as the sole cause of its odour. Resins. Resins are the inspissated juices of plants, and commonly oc- cur either pure or in combination with an essential oil. They RESINS. 487 are solid at common temperatures, brittle, inodorous, and insipid. They are non-conductors of electricity, and when rubbed be- come negatively electric. They are generally of a yellow colour, and semi-transparent. Resins are fused by the application of heat, and by a still higher temperature are decomposed. In close vessels they yield empyreumatic oil, and a large quantity of carburetted hydrogen, a small residue of charcoal remaining. In the open air they burn with a yellow flame and much smoke, being resolved into carbonic acid and water. Resins are dissolved by alcohol, ether, and the essential oils, and the alcoholic and ethereal solutions are precipitated by wa- ter, a fluid in which they are quite soluble. Their best solvent is pure potassa and soda, and they are also soluble in the alka- line carbonates by the aid of heat. The product is in each case a soapy compound, which is decomposed by an acid. Concentrated sulphuric acid dissolves resins; but the acid and the resin mutually decompose each other, with disengagement of sulphurous acid, and deposition of charcoal. Nitric acid acts upon them with violence, converting them into a species of tan- nin, which was discovered by Mr. Hatchett. No oxalic acid is formed during the action. The uses of resin are various. Melted with wax and oil, resins constitute ointments and plasters. Combined with oil or alcohol, they form different kinds of oil and spirit varnish. Sealing-wax is composed of lac, Venice turpentine, and common resin. The composition is coloured black by means of lamp-black, or red by cinnabar or red lead. Lamp-black is the soot of imperfectly burned resin. Of the different resins the most important are common resin, copal, lac, sandarach, mastich, elemi, and dragon's blood. The first is procured by heating turpentine, which consists of oil of turpentine and resin, so as to expel the volatile oil. The com- mon turpentine, obtained by incisions made in the trunk of the Scotch fir tree, (Pinus sylvestris) is employed for this purpose ; but the other kinds of turpentine, such as the Venice turpentine, that from the larch, (Pinus larix.) the Canadian turpentine from the Pinus balsamea, or the Strasburgh turpentine from the Pinus picea, yield resin by a similar treatment. When turpentine is extracted from the wood ofthe fir tree by heat, partial decomposition ensues, and a dark substance, con- sisting of resin, empyreumatic oil, and acetate acid is the product. This constitutes tar; and when inspissated by boiling, it forms pitch. Common resin fuses at 276° F. is completely liquid at 306°, and at about 316° bubbles of gaseous matter escape, giving rise to the appearance of ebullition. At a red heat it is entirely decomposed, yielding a large quantity of combustible gas, which is employed for the purpose of artificial illumination. 488 RESINS. Thomson. Ure. 63.15 75.00 25.26 12.50 11.59 12.50 Considerable uncertainty prevails as to the composition of com- mon resin, as will appear by the following statement:— Gay-Lussac and Thenard. Carbon, 75.944 Oxygen, 13.337 Hydrogen, 10.719 100 100 100 Amber.—This substance is found chiefly on the coast of Prus- sia, Livonia, Pomerania, and Denmark, occurring sometimes on the shore, and sometimes in beds of bituminous wood. It is un- doubtedly of vegetable origin, and has the general properties of a resin; but it differs from the resinous substances in yielding succinic acid, when heated in close vessels. Balsams.—The balsams are native compounds of resin and benzoic acid, and issue from incisions made in the trees, which contain them, in the same manner as turpentine from the fir. Some of them such as storax and benzoin, are solid; while others, of which the balsams of Tolu and Peru are examples, are viscid fluids. Gum Resins.—The substance to which this name is applied are the concrete juices of certain plants, and consist of resin, es- sential oil, gum, and extractive vegetable matter. The two for- mer principles are soluble in alcohol, and the two latter in water. Their proper solvent, therefore, is proof spirit. Under the class of gum resins are comprehended several valuable medicines, such as aloes, ammoniacum, assafoetida, euphorbium, galbanum, gam- boge, myrrh, scammony, and guaiacum. Caoutchouc, commonly called elastic gum, or Indian rubber, is the concrete juice of the Hcevea caoutchouc and Iatropa elas- tica, natives of South America, and of the Ficus Indica and Ar- tocarpus integrifolia, which grow in the East Indies. It is a soft yielding solid, of a whitish colour when not blackened by smoke, possesses considerable tenacity, and is particularly remarkable for its elasticity. It is inflammable, and burns with a bright flame. When cautiously heated, it fuses without decomposition. It is insoluble in water and alcohol; but it dissolves, though with some difficulty, in pure ether. It is very sparingly dissolved by the alkalies, but its elasticity is destroyed by their action. By the sulphuric and nitric acids it is decomposed, the former caus- ing deposition of charcoal, and the latter formation of oxalic acid. Caoutchouc is soluble in the essential oils, in petroleum, and in cajeput oil; and may be procured by evaporation from the two latter without loss of its elasticity. The purified naphtha from coal tar dissolves it readily, and as the solvent is cheap, and the properties of the caoutchouc are unaltered by the process, the WAX. 489 solution may be conveniently employed for forming elastic tubes, or other apparatus of a similar kind. The composition of caoutchouc has not been determined in a satisfactory manner. According to the analysis of Dr. Ure, 100 parts of it consist of carbon 90, oxygen 0.88, and hydrogen 9.12. But caoutchouc yields ammonia when heated in close vessels, and therefore must contain nitrogen as one of its constituents, a principle which was not detected Dr. Ure. Wax.—This substance, which partakes of the nature of a fixed oil, is an abundant vegetable production, entering into the com- position of the pollen of flowers, covering the envelope of the plumb and other fruit, especially the berries of the Myrica ceri- fera, and in many instances forming a kind of varnish to the sur- face of leaves. From this circumstance it was long supposed that wax is solely of vegetable origin, and that the wax of the honey-comb is derived from flowers only; but it appears from the observations of Huber that it must likewise be regarded as an animal product, since he found bees to deposit wax though fed on nothing but sugar. Common wax is always more or less coloured, and has a dis- tinct peculiar odour, of both which it may be deprived by expo- sure in thin slices to light, air, and moisture, or more speedily by the action of chlorine. At ordinary temperatures it is solid, and somewhat brittle; but it may easily be cut with a knife, and the fresh surface presents a characteristic appearance, to which the name of waxy lustre is applied. Its specific gravity is 0.96. At about 150° F. it enters into fusion, and boils at a high tem- perature. Heated to redness in close vessels it suffers complete decomposition, yielding products very similar to those which are procured under the same circumstances from oil. As it burns with a clear white light it is employed for forming candles. Wax is insoluble in water, and is only sparingly dissolved by boiling alcohol or ether, from which the greater part is deposited on cooling. It is readily attacked by the fixed alkalies, being converted into a soap which is soluble in hot water. It unites by the aid of heat in every proportion with the fixed and volatile oils, and with resin. With different quantities of oil it consti- tutes the simple liniment, ointment, and cerate, of the pharma- copoeia. Wax, according to the observations of Dr. John, consists of two different principles, one of which is soluble and the other insol- uble in alcohol. To the former he has given the name of cerin, and to the latter of myricin. From the ultimate analysis of Dr. Ure, whose result corresponds closely with that of Gay-Lussac and Thenard, 100 parts of wax are composed of carbon 80.4, oxygen 8.3, and hydrogen 11.3; from which it is probable that it consists of 13 equivalents of the first element, 1 equivalent of the second, and eleven equivalents of the third. 3 a 490 ALCOHOL. Alcohol. Alcohol is the intoxicating ingredient of all spiritous and vi- nous liquors. It does not exist ready formed in plants, but is a product of the vinous fermentation, the theory of which will be Stated in a subsequent section. Common alcohol, or spirit of wine, is prepared by distilling whiskey or some ardent spirit, and the rectified spirit of wine is procured by a second distillation. The first has a specific grav- ity of about 0.867, and the last of 0.835 or 0.84. In this state it contains a quantity of water, from which it may be freed by the action of substances which have a strong affinity for that liquid. Thus, when carbonate of potassa, heated to about 300° F. is mixed with spirit of wine, the alkali unites with the water forming a dense solution, which, on standing, separates from the alcohol, so that the latter may be removed by decantation. To the alcohol, thus deprived of part of its water, fresh portions ofthe dry car- bonate are successively added, until it falls through the spirit without being moistened. Other substances, which have a power- ful attraction for water, may be substituted for carbonate of potassa. Gay-Lussac recommends the use of pure lime or baryta; and dry alumina may also be employed with advantage. A very convenient process is to mix the alcohol with chloride of calcium in powder, or with quicklime, and draw off the stronger portions by distillation, Another process which has been recommended for depriving alcohol of water is to put it into the bladder of an ox, and suspend it over a sand bath. The water gradually passes through the coats ofthe bladder, while the pure alcohol is retain- ed ; but though this method answers well for strengthening weak spirit, its power of purifying strong alcohol is very questionable. The strongest alcohol which can be procured by any of these processes has a specific gravity of 0.796 at 60° F. This is called absolute alcohol, on the supposition of its being quite free from water. An elegant and easy process for procuring absolute alcohol has lately been proposed by Mr. Graham. A large shallow basin is covered to a small depth with quicklime in coarse powder, and a smaller one containing three or four ounces of commercial alcohol is supported just above it. The whole is placed upon the plate of an air pump, covered by a low receiver, and the air withdrawn until the alcohol evinces signs of ebullition. Of the mingled vapour9 of water and alcohol which fill the receiver, the former alone is absorbed by the quicklime, while the latter is unaffected. Now it is found that water cannot remain in alcohol, unless cover- ed by an atmosphere of its own vapour; and consequently the water continues to evaporate without interruption, while the eva- poration of the alcohol is entirely arrested by the pressure of the ALCOHOL. 491 vapour of alcohol on its surface. Common alcohol is in this way entirely deprived of water in the course of about five days. The temperature should be preserved as uniform as possible during the process. Sulphuric acid cannot be substituted for quicklime, since both vapours are absorbed by this liquid. Alcohol is a colourless elastic fluid, of a penetrating odour, and burning taste. It is highly volatile, boiling, when its density is 0.820, at the temperature of 176° F. The specific gravity of its vapour, according to Gay-Lussac, is 1.613. Like volatile liquids in general, it produces a considerable degree of cold dur- ing evaporation. It has hitherto retained its fluidity under every degree of cold to which it has been exposed. Mr. Hutton, in- deed, announced in the 34th volume of Nicholson's Journal, that he had succeeded in freezing alcohol; but the fact itself is regarded as doubtful, since no description of the method has hitherto been published. In the experiments of Mr. Walker, alcohol was found to retain its fluidity at—91° F. Alcohol is highly inflammable, and burns with a lambent yel- lowish-blue flame. Its colour varies considerably with thestrength of the alcohol, the blue tint predominating when it is strong; and the yellow when it is diluted. Its combustion is not attended with the least degree of smoke, and the sole products are water and carbonic acid. When transmitted through a redhot tube of por- celain, it is resolved into carburetted hydrogen, carbonic oxide, and water, and the tube is lined with a small quantity of charcoal. Alcohol unites with water in every proportion. The act of combining is usually attended with diminution of volume, so that a mixture of 50 measures of alcohol and 50 of water occupies less than 100 measures. Owing to this circumstance, the action is accompanied with increase of temperature. Since the density of the mixture increases as the water predominates, the strength of the spirit may be estimated by its specific gravity. Equal weights of absolute alcohol and water constitute proof spirit, the density of which is 0.917 ; but the proof spirit employed for tinc- tures has a specific gravity of 0.930, or 0.935. Ofthe salifiable bases, alcohol can alone dissolve potassa, soda, lithia, ammonia, and the vegetable alkalies. None of the earths, or other metallic oxides, are dissolved by it. Most ofthe acids attack it by the aid of heat, giving rise to a class of bodies to which the name of ether is applied. All the salts which are either insoluble, or sparingly soluble in water, are insoluble in alcohol. The efflorescent salts are, likewise, for the most part insoluble in this menstruum ; but, on the contrary, it is capable of dissolving all the deliquescent salts, except the carbonate of potassa. Many ofthe vegetable principles, such as sugar, man- na, camphor, resins, balsams, and the essential oils, are soluble in alcohol. The solubility of certain substances in alcohol appears owing 492 ALCOHOL. to the formation of definite compounds, which are soluble in that liquid. This has been proved ofthe chlorides of calcium, man- ganese, and zinc, and of the nitrates of lime and magnesia, by Mr. Graham. It appears from his experiments that all these bodies unite with alcohol in definite proportion, and yield crystalline compounds which are deliquescent and soluble both in water and alcohol. From their analogy to hydrates, Mr. Graham has applied to them the name of alcoates. These are formed by dis- solving the substances in absolute alcohol by means of heat, when on cooling a group of crystals more or less irregular is de- posited. The salt and alcohol employed for the purpose should be quite anhydrous ; for the crystallization is prevented by a very small quantity of water. Estimating the combining proportion of alcohol at 23, the alcoate of chloride of calcium is composed of one equivalent of chloride of calcium, and three equivalents and a half of alcohol. Nitrate of magnesia crystallizes with nine equivalents of alcohol ; nitrate of lime with two and a half equi- valents ; proto-chloride of manganese with three equivalents ; and chloride of zinc with half an equivalent of alcohol. The constitution of alcohol has been ably investigated by M. Saussure, jun. According to his analysis, which was made by transmitting the vapour of absolute alcohol through a red-hot porcelain tube, and examining the products, this fluid is composed of carbon 51.98, oxygen 34.32, and hydrogen 13.70. From these data, alcohol is inferred to consist of Carbon, - 12 2 equivalents - 52.17 Oxygen, - 8 1 equivalent - 34.79 Hydrogen, - 3 3 equivalents - 13.04 23 100.00 These numbers, it is obvious, are in such proportion that alco- hol may be regarded as a compound of 14 parts or one equiva- lent of olefiant gas, and 9 parts or one equivalent of water. Hence the equivalent of alcohol is 23. Knowing the composition of alcohol by weight, it is easy to calculate the proportion of its constituents by measure. For this purpose it is only necessary to divide 14 by 0.972, (the sp. gr. of olefiant gas,) and 9 by 0.625, (the sp. gr. of aqueous vapour ;) and as the quotients are very nearly equal, it follows that alcohol must consist of equal measures of aqueous vapour and olefiant gas. It is inferred, also, that these two gaseous bodies, in uniting to form the vapour of alcohol, occupy half the space which they possessed separately ; because the density ofthe vapour of alco- hol, as calculated on this supposition, (0.9722+0.625=1.5972) corresponds closely with 1.613, the number which was ascer- tained experimentally by Gay-Lussac. Considerable uncertainty prevailed a few years ago as to the state in which alcohol exists in wine. Some chemists were of ALCOHOL. 493 opinion that it is generated by the heat employed in the distilla- tion ; while others thought that the alcohol is merely separated during the process. This question was finally determined by Mr. Brande, who demonstrated that the alcohol exists ready formed in wine, by separating that principle without the aid of heat. His method consists in precipitating the acid and extractive co- louring matters ofthe wine by the sub-acetate of lead, and then depriving the alcohol of water by dry carbonate of potassa, in the way already mentioned. The pure alcohol, which rises to the surface, is then measured by means of a narrow graduated glass tube. The same fact has since been established by the ex- periments of Gay-Lussac, who procured alcohol from wine by dis- tilling it in vacuo at the temperature of 60° F. He also succeed- ed in separating the alcohol by the method of Mr. Brande ; but he suggests the employment of litharge in fine powder, instead of the sub-acetate of lead, for precipitating the colouring matter. The preceding researches of Mr. Brande led him to examine the quantity of alcohol contained in spirituous and fermented liquors. According to his experiments, brandy, rum, gin, and whis- key, contain from 51 to 54 per cent, of alcohol, of specific gravity 0.825. The stronger wines, such as Lissa, Raisin wine, Marsala, Port, Madeira, Sherry, Teneriffe, Constantia, Malaga, Bucellas, Calcavella, and Vidonia, contain from between 18 or 19 to 25 per cent, of alcohol. In Claret, Burgundy, Sauterne, Hock, Cham- pagne, Hermitage, and Gooseberry wine, the quantity is from 12 to 17 per cent. In cyder, perry, ale, and porter, the quantity varies from 4 to near 10 per cent. In all spirits, such as brandy or whiskey, the alcohol is simply combined with water; whereas in wine it is in combination with mucilaginous, saccharine, and other vegetable principles, a condition which tends to diminish the ac- tion of the alcohol upon the system. This may, perhaps, account for the fact that brandy, which contains little more than twice as much real alcohol as good port wine, has an intoxicating power which is considerably more than double. Ether. The name ether was formerly employed to designate the vola- tile inflammable liquid which is formed by heating a mixture of alcohol and sulphuric acid; but the same term has since been extended to several other compounds produced by the action of acids on alcohol, and which, from their volatility and inflamma- bility, were supposed to be identical or nearly so with sulphuric ether. It appears, however, from the researches of several che- mists, but especially of M. Thenard, that ethers, though analo- gous in their leading properties, frequently differ both in compo- sition and in their mode of formation. Sulphuric Ether.—In forming this compound, strong sulphuric 494 ETHER. acid is gently poured upon an equal weight of rectified spirit of wine contained in a thin glass retort, and after mixing the fluids together by agitation, which occasions a free disengagement of caloric, the mixture is heated as rapidly as possible until ebulli- tion commences. At the beginning of the process nothing but alcohol passes over; but as soon as the liquid boils, ether is gene- rated, and condenses in the recipient which is purposely kept cool by the application of ice or moist cloths. When a quantity of ether is collected, equal in general to about half of the alcohol employed, white fumes begin to appear in the retort. At this period, the process should be discontinued, or the receiver changed ; for although ether does not cease to be generated, its quantity is less considerable, and several other products make their appearance. Thus on continuing the operation, sulphurous acid is disengaged, and a yellowish liquid, commonly called ethereal oil, or oil of wine, passes over into the receiver. If the heat be still continued, a large quantity of olefiant gas is disen- gaged, and all the phenomena ensue which were mentioned in the description of that compound. Ether, thus formed, is always mixed with alcohol, and generally with some sulphurous acid. To separate these impurities the ether should be agitated with a strong solution of potassa, which neutralizes the acid, while the water unites with the alcohol. The ether is then distilled by a very gentle heat, and may be rendered still stronger by distillation from the chloride of cal- cium. To comprehend the theory of the formation of ether, it is neces- sary to compare the composition of this substance with that of alcohol. Ether was analyzed by M. Saussure in the same manner as alcohol; and from the data furnished by his analysis, corrected by Gay-Lussac, ether is inferred to consist of 28 parts or two equivalents of olefiant gas, and 9 parts or one equivalent of wa- ter. But alcohol is composed of one equivalent of olefiant gas, and one equivalent of water; so that, if from two equivalents of alcohol one of water be withdrawn, the remaining elements are in exact proportion for constituting ether. This is the precise mode in which sulphuric acid is supposed to operate in generating ether, an effect which it is well calculated to produce, owing to its strong affinity for moisture. This view was first proposed by Fourcroy and Vauquelin, and accounts for the phenomena in a very satisfactory manner. These chemists, it is true, erred in thinking that the sulphuric acid occasions no other change ; since subsequent observation has proved that the sulpho-vinic acid, to the constitution of which sulphuric acid is essential, is formed even at the very commencement ofthe process. Notwithstand- ing this error, however, the production of ether may be justly ascribed to the sulphuric acid abstracting water or its elements from the alcohol, an opinion which is supported by various cir- ETHER. 495 cumstances. Thus it accounts for the disengagement of sulphur- ous acid and olefiant gas towards the middle and close of the process ; for since the elements ofthe alcohol alone contribute to the formation of ether, while all the sulphuric acid remains in the retort, and most of it in a free state, it is apparent that the rela- tive quantities of alcohol and acid must be continually changing during the operation, until at length the latter predominates so greatly as to be able to deprive the former of all its water, and thus give rise to the disengagement of olefiant gas. Accordingly it is well known, that if fresh alcohol be added as soon as the production of pure ether ceases, an additional quantity of that substance will be produced. It follows, also, from the same doc- trine, that the power ofthe same portion of acid in forming ether must be limited, because it gradually becomes so diluted with water that it is at last unable to disunite the elements of the alcohol. Consistently with the same view, it is found that ether, precisely analogous to that from sulphuric acid, may be prepared by digesting alcohol with other acids which have a strong affinity for water, as for example with phosphoric, arsenic, and fluoboric acids. The production of a peculiar acid in the preceding process was first noticed by M. Dabit, about the year 1800. This sub- stance, to which the name of sulpho-vinic acid is applied, has since been examined by Sertuerner, Vogel, and Gay-Lussac, and the two last mentioned philosophers regarded it as a compound of hyposulphuric acid and a peculiar vegetable matter. Mr. Hennel, however, has lately given a different, and to all appear- ance, a more correct view of its nature. According to this che- mist, sulpho-vinic acid and the oil of wine are both composed of sulphuric acid and carburet of hydrogen. The oil of wine, which has no acid re-action when pure, consists of 2 equivalents of sulphuric acid, 8 of carbon, and 8 of hydrogen. When heated, it parts with half of its carbon and hydrogen, and sulpho-vinic acid remains, consisting of 2 equivalents of sulphuric acid, 4 of carbon, and 4 of hydrogen. The oil of wine is a perfectly neu- tral compound, in which the carburet of hydrogen acts the part of an alkali in neutralizing sulphuric acid. In sulpho-vinic acid half the sulphuric acid appears to be neutralized by carburet of hydrogen. Sulphuric ether is a colourless fluid, of a hot pungent taste, and fragrant odour. Its specific gravity in its purest form is about 0.700, or according to Lovitz 0.632 ; but that of the shops is 0.74, or even lower, owing to the presence of alcohol. Its volatility is exceedingly great:—Under the atmospheric pressure, ether of density 0.720 boils at 96° or 98° F., and at about —40° F. in a vacuum. Its evaporation, from the rapidity with which it takes place, occasions intense cold, sufficient under favourable 496 ETHER. circumstances for freezing mercury. Its vapour has a density of 2.586. At 46 degrees below zero of Fahr. it is congealed. Ether combines with alcohol in every proportion, but is very sparingly soluble in water. When agitated with that fluid, the greater part separates on standing, a small quantity being retain- ed, which imparts an ethereal odour to the water. The ether so washed is very pure, because the water retains the alcohol with which it is mixed. Ether is highly inflammable, burning with a blue flame, and formation of water and carbonic acid. With oxygen gas its va- pour forms a mixture which explodes violently on the approach of flame, or by the electric spark. On being transmitted through a red-hot porcelain tube it undergoes decomposition, and yields the same products as alcohol. When a coil of platinum wire is heated to redness, and then suspended above the surface of ether contained in an open ves- sel, the wire instantly begins to glow, and continues in that state until all the ether is consumed. During this slow combustion, pungent acrid fumes are emitted, which, if received in a sepa- rate vessel, condense into a colourless liquid, possessed of acid properties. Mr. Daniell, who prepared a large quantity of it, was at first inclined to regard it as a new acid, and described it under the name of lampic acid; but he has since ascertained that its acidity is owing to the acetic acid, which is combined with some compound of carbon and hydrogen, different both from ether and alcohol. If ether is exposed to light in a vessel partially filled, and which is frequently opened, it gradually absorbs oxygen, and a portion of the acetic acid is generated. This change was first noticed by M. Planche, and has been confirmed by Gay-Lussac. The composition of ether by volume may be inferred in the same manner as in the case of alcohol; (page 492) namely, by dividing 28 by 0.972, and 9 by 0.625. Ether is thus found to consist of two measures of olefiant gas and one measure of watery vapour; and supposing these three measures, in combining, to contract to one-third of their volume, the specific gravity ofthe vapour of ether will be 0.972 x 2 + 0.625 =: 2.569. Now this is so near 2.586, the specific gravity which Gay-Lussac found by ac- ' tual trial, that the preceding supposition may fairly be admitted. The solvent properties of ether are less extensive than those of alcohol. It dissolves the essential oils and resins, and some of the vegetable alkalies are soluble in it. It unites also with ammonia ; but the fixed alkalies are insoluble in this menstruum. Nitrous Ether.—This compound is prepared by distilling a mixture of concentrated nitric acid with an equal weight of alcohol; but as the re-action is apt to be exceedingly violent. the process should be conducted with extreme care. The safest method is to add the acid to the alcohol by small quantities at a ETHER. 497 time, allowing the mixture to cool after each addition before more acid is added. The distillation is then conducted at a very gen- tle temperature, and the ether collected in a Woulfe's apparatus. The theory of the process is in some respects obscure ; but as the formation of ether is attended with the disengagement of the protoxide and deutoxide of nitrogen, together with free nitrogen and carbonic acid, it follows that the alcohol and acid mutually decompose each other. M. Thenard inferred from his experi- ments, that ether is a compound of alcohol and nitrous acid ; and, consequently, that the essential change during its formation consists in the conversion of nitric into nitrous acid, at the ex- pense of one part ofthe alcohol, while the remainder of that fluid combines with the nitrous acid. Consistently with this view, nitrous ether may be made directly by the action of anhydrous nitrous acid on pure alcohol. In an essay lately published by MM. Dumas and Boullay, a different opinion has been suggested. According to a careful analysis of nitrous ether, they find it to consist of 4 equivalents of carbon, 5 of hydrogen, 1 of nitrogen, and 4 of oxygen. These elements are in proportion to constitute 2 equivalents of olefiant gas, 1 of water, and 1 of hyponitrous acid. The nitrous agrees with sulphuric ether in its leading proper- ties; but it is still more volatile. When recently distilled from quicklime by a gentle heat, it is quite neutral; but it soon be- comes acid by keeping. The products of. its spontaneous de- composition are alcohol, nitrous acid, and a little acetic acid. A similar change is instantly effected by mixing the ether with water, or distilling it at a high temperature. It is also decom- posed by potassa, and, on evaporation, crystals of the nitrite or hyponitrite of that alkali are deposited. Acetic Ether.—This ether is analogous in composition to the preceding, and is formed by distilling acetic acid with an equal weight of alcohol. When set on fire, it burns with disengage- ment of acetic acid; and when mixed with a strong solution of potassa, and subjected to distillation, pure alcohol passes over, and acetate of potassa remains in the retort. It is hence in- ferred by Thenard to consist of acetic acid and alcohol. When pure it is quite neutral. According to Thenard, the acetic is the only vegetable acid which forms ether by being heated alone with alcohol. Ether may also be generated by treating the tartaric, oxalic, malic citric, or benzoic acid, with a mixture of alcohol and sulphuric acid, and Thenard regards these ethers as compounds of a ve- getable acid with alcohol. But MM. Dumas and Boullay, in the essay above referred to, declare that the elements of all these ethers are in such proportion as to constitute one equivalent of acid, one of water, and two of olefiant gas. They believe them, as also nitrous acid, to be hydrated salts, in which carburet of 3 R 498 BITUMEN. hydrogen acts the part of an alkali. This view is certainly sup- ported by the observations of Mr. Hennel relative to the oil of wine, and by the constitution of muriatic ether. The employ- ment of sulphuric acid in their formation is likewise favourable to this opinion. The alcohol obtained by distillation with po- tassa, is supposed by Dumas and Boullay to be generated dur- ing the process. Muriatic ether.—This compound, which is prepared by distil- ling a mixture of concentrated muriatic acid and pure alcohol, was supposed by Thenard to be analogous in composition to nitrous ether. It appears, however, from the experiments of MM. Robiquet and Colin, that it consists of muriatic acid and the ele- ments of olefiant gas, and is therefore quite free from oxygen. It does not affect the colour of litmus paper, volatilzes still more rapidly than sulphuric ether, and is highly inflammable. Its combustion is attended with the disengagement of a large quantity of muriatic acid gas. Hydriodic ether, first prepared by Gay-Lussac, appears to be similar in composition to muriatic ether. Bituminous Substances. Under this title are included several inflammable substances which, though of vegetable origin, are found in the earth, or issue from its surface. They may be conveniently arranged under the two heads of bitumen and pit-coal. The first comprehends naphtha, petroleum, mineral tar, mineral pitch, asphalturn, and retinasphaltum, of which the three first mentioned are liquid, and the others solid. The second comprises brown coal, the different varieties of common or black coal, and glance coal. Bitumen—Naphtha is a volatile limpid liquid, of a strong peculiar odour, and light yellow colour. Its specific gravity, when highly rectified, is 0.758. It is very inflammable, and burns with a white flame mixed with much smoke. At 186° F. it enters into ebullition, and its vapour has a density of 2.833. It retains its liquid form at zero of Fahrenheit. It is insoluble in water, and very soluble in alcohol; but it unites in every propor- tion with sulphuric ether, petroleum, and oils. It appears, from the observations of Saussure, to undergo no change by keeping, even in contact with air. Naphtha contains no oxygen, and is hence employed for pro- tecting the more oxidable metals, such as potassium and sodium from oxidation. According to the analysis of Saussure, it is composed of carbon and hydrogen in the proportion of six equi- valents of the former to five of the latter. Dr. Thomson states the composition of naphtha-from coal tar, which seems identical with mineral naphtha, to consist of six equivalents of carbon and six of hydrogen. COAL. 499 Naphtha occur* in some parts of Italy, and on the banks of the Caspian Sea. It may be procured also by distillation from petroleum. Petroleum is much less limpid than naphtha, has a reddish- brown colour, and is unctuous to the touch. It is found in several parts of Britain and the Continent of Europe, in the West Indies, in Persia, and in the United States. It occurs particu- larly in coal districts. The mineral tar is very similar to petro- leum, but is more viscid and of a deeper colour. Both these spe- cies become thick by exposure to the atmosphere, and, in the opinion of Mr. Hatchett, pass into solid bitumen. Asphaltum is a solid brittle bitumen, of a black colour, vitre- ous lustre, and conchoidal fracture. It melts easily, and is very inflammable. It emits a bituminous odour when rubbed, and by distillation yields a fluid like naphtha. It is soluble in about five times its weight of naphtha, and the solution forms a good varnish. It is rather denser than water. Asphaltum is found on the surface and on the banks of the Dead Sea, and occurs in large quantity in Barbadoes and Trini- dad. It was employed by the ancients in building, and is said to have been used by the Egyptians in embalming. Mineral Pitch or Maltha is likewise a solid bitumen, but is much softer than asphaltum. The elastic bitumen, or mineral caoutchouc, is a rare variety of mineral pitch, found only in the Odin mine, near Castleton in Derbyshire. Retinasphaltum is a peculiar bituminous substance, found as- sociated with the brown coal of Bovey in Devonshire, and .des- cribed by Mr. Hatchett. It consists partly of bitumen, and partly of resin, a composition which led Mr. Hatchett to the opinion that bitumens are chiefly formed from the resinous principle of plants. Pit Coal.—Brown coal is characterized by burning with a peculiar bituminous odour, like that of peat. It is sometimes earthy, but the fibrous structure of the wood from which it is derived is generally more or less distinct, and hence this variety is called bituminous wood. Pitch coal or jet, which is employed for forming ear-rings and other trinkets, is intermediate between brown and black coal, but is perhaps more closely allied to the former than the latter. Brown coal is found at Bovey in Devonshire, (Bovey coal,) in Iceland, where it is called surturbrand, and in several parts ofthe continent, especially at the Meissner in Hessia, in Saxony, Prus- sia,- and Styria. Ofthe btack or common coal, there are several varieties, which differ from each other, not only in the quantity of foreign matters, such as the sulphuret of iron and earthy substances which they contain, but also in the proportion of what may be regarded as essential constituents. Thus some kinds of coal consist almost 500 COAL. entirely of carbonaceous matters, and therefore form little flame in burning; while others, of which the cannel coal is an exam- ple, yield a large quantity of inflammable gases by heat, and consequently burn with a large flame. Dr. Thomson has arranged the different kinds of coal which are met with in Britain into four subdivisions. The first is caking coal, because its particles are softened by heat and adhere together, forming a compact mass. The coal found at Newcastle, around Manchester, and in many other parts of England, is of this kind. The second is termed splint coal, from the splintery appearance of its fracture. The cherry coal occurs in Staffordshire, and in the neighbourhood of Glasgow. Its structure is slaty, and it is more easily broken than the splint coal, which is much, harder. It easily takes fire and is consum- ed rapidly, burning with a clear yellow flame. The fourth kind is the cannel coal, which is found of peculiar purity at Wigan in Lancashire. In Scotland it is known by the name parrot coal. From the brilliancy of the light which it emits while burning, it is sometimes used as a substitute for candles, a practice which is said to have led to the name of cannel coal. It has a very com- pact structure, does not soil the fingers when handled, and admits of being polished. Snuff-boxes and other ornaments are made with this coal; and it is peculiarly well fitted for forming coal gas. According to the experiments of Dr. Thomson, these varieties of coal are thus constituted : Caking Coal. Splint Coal. Cherry Coal, Cannel Coal. Carbon, 75.28 75.00 74.45 64.72 Hydrogen, 4.18 6.25 12.40 21.56 Nitrogen, 15.96 6.25 10.22 13.72 Oxygen, 4.58 12.50 2.93 0.00 100.00 100.00 100.00 100.00 Judging from the quantity of oxidized products (water, carbonic acid, and carbonic oxide,) which are procured during the distil- lation of coal, Dr. Henry infers that coal contains more oxygen than was found by Thomson. This opinion is supported by the analysis of Dr. Ure, who found 26.6 per cent, of oxygen in splint, and 21.9 in cannel coal. When coal is heated to redness in close vessels, a great quantity of volatile matter is dissipated, and a carbonaceous residue, called coke, remains in the retort. The volatile substances are coal tar, acetic acid, water, sulphu- retted hydrogen, and hydrosulphuret and carbonate of ammonia, together with the several gases formerly enumerated. The greater part of these substances are real products, that is, are generated during the distillation. The bituminous matters pro- bably exist ready formed in coal; but Thomson is of opinion that SUGAR. 501 these are also products, and that coals are atomic compounds of carbon, hydrogen, nitrogen, and oxygen. Glance coal.—Glance coal, or anthracite, differs from common coal, which it frequently accompanies, in containing no bitumi- nous substances, and in not yielding inflammable gases by distil- lation. Its sole combustible ingredient is carbon, and conse- quently it burns without flame. It commonly occurs in the immediate vicinity of basalt, under circumstances which lead to the suspicion that it is coal from which the volatile ingredients have been expelled by subterranean heat. At the Meissner, in Hessia, it is found between a bed of brown coal and basalt. The Kilkenny coal appears to be a variety of Glance Coal. SECTION IV. Substances, the Oxygen and Hydrogen of which are in exact proportion for forming Water. Sugar. Sugar is an abundant vegetable product, existing in a great many ripe fruits, though few of them contain it in sufficient quan- tity for being collected. The juice which flows from incisions made in the trunk of the American mapl6 tree, is so powerfully saccharine that is often applied to useful purposes. Sugar was prepared in France and Germany during the late war from the beet-root; and this manufacture is at present carried on in France on a scale of considerable magnitude. Proust extracted it in Spain from grapes. But nearly all the sugar at present used in Europe is obtained from the sugar-cane, (Arundo saccha- rifera) which contains it in greater quantity than any other plant. The process, as practised in the West India Islands, consists in evaporating the juice of the ripe cane by a moderate and cau- tious ebullition, until it has attained a proper degree of consis- tence for crystallizing. During this operation lime water is added, partly for the purpose of neutralizing free acid, and partly to facilitate the separation of extractive and other vegetable mat- ters, which unite with the lime and rise as a scum to the surface. When the syrup is sufficiently concentrated, it is drawn off into shallow wooden coolers, where it becomes a soft solid composed of loose crystalline grains. It is then put into barrels with holes in the bottom, through which a black ropy juice, called molasses or treacle, gradually drops, leaving the crystallized sugar com- paratively white and dry. In this state it constitutes the raw or muscovado sugar. Raw sugar is further purified by boiling a solution of it with 502 SUGAR. white of eggs, or the serum of bullock's blood, lime water being generally employed at the same time. When properly concen- trated the clarified juice is received in conical earthen vessels, the apex of which is undermost, in order that the fluid parts may col- lect there, and be afterwards drawn off by the removal of a plug. In this state it is loaf or refined sugar. In the process of refining sugar, it is important to concentrate the syrup at a low tempera- ture ; and on this account a very great improvement was intro- duced some years ago by conducting the evaporation in vacuo. Pure sugar is solid, white., inodorous, and of a very agreeable taste. It is hard and brittle, and when two pieces are rubbed against each other in the dark, phosphorescence is observed. It crystallizes in the form of four or six-sided prisms bevelled at the extremities. The crystals are best made by fixing threads in syrup, which is allowed to evaporate spontaneously in a warm room; and the crystallization is promoted by adding spirit of wine. In this state it is known by the name of sugarcandy. Sugar undergoes no change on exposure to the air; for the deliquescent property of raw sugar is owing to impurities. It is soluble in an equal weight of cold, and to almost any extent in hot water. It is soluble in about four times its weight of boil- ing alcohol, and the saturated solution, by cooling and sponta- neous evaporation, deposits large crystals. When the aqueous solution of sugar is mixed with yeast, it undergoes the vinous fermentation, the theory of which will be explained in a subse- quent section. Sugar unites with the alkalies and alkaline earths, forming compounds in which the taste ofthe sugar is greatly injured ; but it may be obtained again unchanged by neutralizing with sulphu- ric acid, and dissolving the sugar in alcohol. When boiled with the oxide of lead, it forms an insoluble compound, which con- sists of 58.26 parts of the oxide of lead, and 41.74 parts of sugar ; but it is not precipitated by the acetate or subacetate of lead. Sulphuric acid decomposes sugar with deposition of charcoal ; and nitric acid causes the production of oxalic acid, as already described in a former section. The vegetable acids diminish the tendency of sugar to crystallize. Sugar is very easily affected by heat, acquiring a dark colour and burned flavour. At a high temperature it yields the usual products of the destructive distillation of vegetable matter, to- gether with a considerable quantity of pyromucic acid. The analyses of sugar by different chemists are considerably discordant. This is accounted for, not only by errors of manipu- lation, and impurity in the materials, but in part arises, accord- ing to Dr.-Prout, from difference in composition. He states that pure cane sugar, as exemplified in sugarcandy and the best loaf sugar, well dried at 212° F. consists of 42.85 parts of carbon, and 57.15 of oxygen and hydrogen in the proportion for forming wa- SUGAR. 503 ter; while sugar from honey contains only 36.36 per cent, of carbon. He considers the sugar from starch, diabetic urine, and grapes, to be nearly the same as that from honey. The sugar from the maple tree and beet root corresponds with that from the cane ; but the quantity of carbon in these kinds of sugar appears to vary from 40 to 42.85 per cent. The atomic constitution of sugar is unknown ; but from the former analysis of Dr. Prout, it is thought that its elements are in the ratio of 6 parts or one equivalent of carbon to 9 parts or one equivalent of water, or by volume of one measure ofthe vapour of carbon to one measure of aqueous vapour. This estimate is admitted by most chemists. Molasses.—The saccharine principle of treacle has been sup- posed to be different from the crystallizable sugar ; but it more probably consists of common sugar, which is prevented from crystallizing by the presence of foreign substances, such as saline, acid, and other vegetable matters. Sugar of Grapes.—The sugar procured from the grape has the essential properties of common sugar. Its taste, however, is not so sweet as common sugar, and, according to Saussure and Prout, it differs slightly in composition, containing a smaller quantity of carbon. The saccharine principle of the acidulous fruits has not been particularly examined. It is obtained with difficulty in a pure state, owing to the presence of vegetable acids, which pre- vent it from crystallizing. A saccharine substance similar to that from grapes may be procured from several vegetable principles, such as starch and the ligneous fibre, by the action of sulphuric acid. Honey.—According to Proust, honey consists of two kinds of saccharine matter, one of which crystallizes readily and is analo- gous to common sugar, while the other is uncrystallizable. They may be separated by mixing honey with alcohol, and pressing the solution through a piece of linen. The liquid sugar is re- moved, and the crystallizable portion is left in a solid state. Be- sides sugar it contains mucilaginous, colouring, and odoriferous matter, and probably a vegetable acid. Diluted with water, honey is susceptible of the vinous fermentation without the ad- dition of yeast. The natural history of honey is as yet imperfect. It is uncer- tain whether honey is merely collected by the bee from the necta- ries of flowers, and then deposited in the hive unchanged, or whether the saccharine matter of the flower does not undergo some change in the body ofthe animal. Manna.—This saccharine matter is a concrete juice of several species of ash, and is procured in particular from the Fraxinus ornus. The sweetness of manna is owing, not to sugar, but to a distinct principle called mannite, which is mixed with a pecu- liar vegetable extractive matter. Manna is soluble both in wa- ter and boiling alcohol, and the latter on cooling, deposits pure 504 STARCH. mannite in the form of minute acicular crystals, which are often arranged in concentrical groups. Mannite differs from sugar, in not fermenting when mixed with water and yeast. According to Dr. Prout, it contains 38.7 per cent, of carbon, and 61.3 of oxy- gen and hydrogen in the proportion to form water. Starch or Fecula.—Amidine. Starch exists abundantly in the vegetable kingdom, being one ofthe chief ingredients of most varieties of grain, of some roots, such as the potato, and ofthe kernels of leguminous plants. It is easily procured by letting a small current of water fall upon the dough of wheat flour inclosed in a piece of linen, and sub- jecting it at the same time to pressure between the fingers, until the liquid passes off quite clear. The gluten ofthe flour is left in a pure state, the saccharine and mucilaginous matters are dis- solved, and the starch is washed away mechanically, being de- posited from the water on standing in the form of a white powder. An analogous process is practised on a large scale in the pre- paration of the starch of commerce ; and very pure starch may also be obtained in a similar manner from the potato. Starch is insipid and inodorous, of a white colour, and insol- uble in alcohol, ether, and cold water. It does not crystallize; but is commonly found in the shops in six-sided columns of con- siderable regularity, a form occasioned by the contraction which it suffers in drying. Boiling water acts upon it readily, convert- ing it into a tenacious bulky jelly, which is employed for stiffen- ing linen. In a large quantity of hot water, it is dissolved com- pletely, and is not deposited on cooling. The aqueous solution is precipitated by sub-acetate of lead; but the best test of starch, by which it is distinguished from all other substances, is iodine. This principle forms a blue compound with starch, whether in a solid state, or when dissolved in cold water. Starch unites with the alkalies, forming a compound which is soluble in water, and from which the starch is thrown down by acids. Strong sulphuric acid decomposes it. Nitric acid in the cold dissolves starch; but converts it by the aid of heat into the oxalic and malic acids. The effects of heat on starch are peculiar, and have lately been examined by M. Caventou. On exposing dry starch to a tempe- rature a little above 212° F. it acquires a slightly red tint, emits an odour of baked bread, and is rendered soluble in cold water. Starch suffers a similar modification by the action of hot water. Gelatinous starch is generally supposed to be a hydrate of starch ; but M. Caventou maintains that the jelly cannot by any method be restored to its original state. He regards this modified starch as identical with the substance described by Saussure under the name of amidine. Saussure thought it was generated by expos- STARCH. 505 ing a paste made with starch and water, for a long time to the air; but according to Caventou, the amadine was formed by the action of the hot water on starch in making the paste. Its es- sential character is to yield a blue colour with iodine, and to be soluble in cold water. When the solution is gently evaporated to dryness, it yields a transparent mass like horn, which retains its solubility in cold water. When starch is exposed to a still higher temperature than is sufficient for converting it into ami- dine, a more complete change is effected. It now dissolves with much greater facility in cold water, and gives a purple colour to iodine. A similar effect is produced by long continued boiling. To torefied starch, that is, starch modified by heat, whether in the dry way or by boiling water, the term amidine may be applied. The starch from wheat, according to the analysis of Gay-Lus- sac and Thenard, is composed, in 100 parts, of carbon 43.55, oxy- gen 49.68, and hydrogen 6.77; and this result agrees with the analysis of potato starch made by Berzelius. The results of Prout and Marcet correspond closely with the foregoing. The proportion of the constituents of starch is therefore very analo- gous to that of sugar, a circumstance which will account for the conversion of the former into the latter. This change is effect- ed in seeds at the period of germination, and is particularly ex- emplified in the process of malting barley, during which the starch of that grain is converted into sugar. Proust finds that barley contains a peculiar principle which he calls hordein, and which he conceived to be converted in malting partly into starch and partly into sugar. A similar conversion of starch into sugar appears in some instances to be the effect of frost, as in the po- tato, apple, and parsnip. If starch is boiled for a considerable time in water acidulated with l-12th of its weight of sulphuric acid, it is wholly converted into a saccharine matter similar to that of the grape. This fact was first observed by Kirchoff, and has since been particularly examined by Vogel, De la Rive, and Saussure. It has been es- tablished by Saussure that the oxygen of the air exerts no in- fluence over the process, that no gas is disengaged, that the quantity of acid suffers no diminution, and that 100 parts of starch yield 110.14 of sugar. By careful analysis, he found that the only difference in the composition ofthe starch and sugar is, that the latter contains more of the elements of water than the former. He hence inferred that the starch is converted into su- gar by its elements combining with a certain quantity of oxygen and hydrogen in the proportion to form water; and that the acid acts only by increasing the fluidity of the mass. Saussure also found that a large quantity of saccharine matter is produced, when gelatinous starch or amidine is kept for a long time either with or without the access of air. 3'S 506 GUM. The recent researches of M. Caventou, already referred to, have thrown considerable light on the chemical nature of several of the amylaceous principles of commerce. The Indian arrow root, which is prepared from the root of the Maranta arundina- cea, has all the characters of pure starch. Sago, obtained from the pith of an East Indian palm tree, (Cycas circinalis) and ta- pioca, from the root of the Iatropha Manihot, are chemically the same substance. They both exist in the plants from which they are extracted in the form of starch; but as heal is employed in their preparation, the starch is more or less completely convert- ed into amidine. It hence follows that pure potato starch may be used instead of arrow root, and that the same material, modi- fied by heat, would afford a good substitute for sago and tapioca. Salep^ which is obtained from the Orchis mascula, consists almost entirely of the substance called bassorin, together with a small quantity of gum and starch. Gum. Gum is a common proximate principle of vegetables, and is not confined to any particular part of plants. The purest va- riety is the gum arabic, the concrete juice of several species of the Mimosa or Acacia, natives of Africa and Arabia. Gum arabic occurs in small rounded, transparent, friable grains, commonly of a pale yellow colour, inodorous, and nearly tasteless. It softens when put into water, and then dissolves, forming a viscid solution called mucilage. It is insoluble in alco- hol and ether, and the former precipitates gum from its solution in water, in the form of opaque white flakes. It is soluble both in alkaline solutions and in lime water, and is precipitated un- changed by acids. The dilute acids dissolve, and the concen- trated acids decompose gum. Sulphuric acid causes the forma- tion of water and acetic acid, and deposition of charcoal. Di- gested with strong nitric acid, it yields saccholactic acid, a property which forms a good character for gum. The malic and oxalic acids are generated at the same time. The aqueous solution of gum may be preserved a considerable time without alteration ; but at length it becomes sour, and ex- hales an odour of acetic acid ; a change which takes place with- out exposure to the air, and must, therefore, be owing to a new arrangement of its own elements. Gum is precipitated from its solution in water by several me- tallic salts, and especially by the sub-acetate of lead, which occa- sions a curdy precipitate, consisting of 38.25 parts of the oxide of lead, and 61.75 parts of gum. When gum is heated to redness in close vessels, it yields, in addition to the usual products, a'small quantity of ammonia, which is probably derived from some impurity, ft affords a large LIGNIN. 507 residue of ash, when burned, which amounts to three per cent., and consists chiefly of the carbonate, together with some phos- phate of lime, and a little iron. From the analysis of Gay-Lussac and Thenard, it appears that 100 parts of gum arabic consist of carbon 42.23, oxygen 50.84, and hydrogen 6.93. This result corresponds very closely with that of Berzelius. Besides gum arabic there are several well-marked kinds of this principle, especially the gum tragacanth, cherry tree gum, and the mucilage from linseed. All these varieties, though distin- guishable from one another by some peculiarity, have the com- mon character of yielding the saccholactic by the action of nitric acid. The substance called vegetable jelly, such as is derived from the currant, appears to be mucilage, or some modification of gum combined with vegetable acid. A substance very analogous to vegetable jelly, if not identical with it, has been described by M. Braconnot as a distinct acid, under the name of pectic acid, (from itrixnig, coagulum) indicative of its tendency to gelatinize. M. Braconnot believes it to be present in all plants ; but extracts it chiefly from the carrot. The original account of its properties appears to have been exagge- rated, and its claim to be regarded as an independent proximate principle has not yet been clearly established. Lignin. Lignin, or woody fibre, constitutes the fibrous structure of ve- getable substances, and is the most abundant principle in plants. The different kinds of wood contain about 96 per cent, of lignin. It is prepared by digesting the sawings of any kind of wood suc- cessively in alcohol, water, and dilute muriatic acid, until all the substances soluble in these menstrua are removed. Lignin has neither taste nor odour, undergoes no change by keeping, and is insoluble in alcohol, water, and the dilute acids. By digestion in a concentrated solution of pure potassa, it is con- verted, according to M. Braconnot, into a substance similar to ulmin. Mixed mith strong sulphuric acid, it suffers decomposi- tion, and is changed into a matter resembling gum ; and on boil- ing the liquid for some time, the mucilage disappears, and a sac- charine principle like the sugar of grapes is generated. M. Braconnot finds that several other substances which consist chiefly of woody fibre, such as straw, bark, or linen, yield sugar by a similar treatment. Digested in nitric acid, lignin is convert- ed into the oxalic', malic, and acetic acids. When the woody fibre is heated in close vessels, it yields a large quantity of impure acetic acid, (pyroligneous acid) and charcoal of great purity remains in the retort. During this pro- cess, a peculiar spirituous liquid is formed, which was discovered » 503 LIGNIN. in 1812, by Mr. P. Taylor, and has been examined by MM. Ma- caire and Marcet, who proposed for it the name of pyroxylic spirit. This liquid is similar to alcohol in several of its proper- ties, but differs from it essentially in not yielding ether by the action of sulphuric acid. It has a strong, pungent, ethereal odour, with a flavour like the oil of peppermint. It boils at 150° F. and its density is 0.828. It burns with a blue flame, and with- out residue. The pyro-acetic spirit, obtained by Mr. Chenevix, by distilling the acetates of manganese, zinc, and lead, differs from the pyroxylic spirit, not only in composition, but in burning with a yellow flame, and in being miscible in all proportions, with the oil of turpentine. Pyroxylic spirit, according to the analysis of Macaire and Marcet, consists of carbon, oxygen, and hydrogen, very nearly in the proportion of 6 equivalents of the first, 4 of the second, and 7 of the third ; and the pyro-acetic spirit, of 4 equivalents of carbon, 2 of oxygen, and 3 of hydro- gen. The pyro-acetic spirit appears very similar, if not identical with the pyro-acetic ether of Derosne; and, like the pyroxylic spirit, differs essentially from alcohol in not yielding ether by the action of sulphuric acid. The ligneous fibre was found by Gay-Lussac and Thenard to consist of carbon 51.43, oxygen 42.73, and hydrogen 5.82. Ac- cording to Dr. Prout, it contains 50 per cent, of carbon. SECTION V. Substances which, so far as is known, do not belong to either of the preceding sections. Colouring Matter. Infinite diversity exists in the colour of vegetable substances ; but the prevailing tints are red, yellow, blue, and green, or mix- tures of these colours. The colouring matter rarely or never occurs in an insulated state, but is always attached to some other proximate principle, such as mucilaginous, extractive, farinace- ous, or resinous substances, by which some of its properties, and in particular that of solubility, is greatly influenced. Nearly all kinds of vegetable colouring matter are decomposed by the com- bined agency ofthe sun's rays and a moist atmosphere ; and they are all, without exception, destroyed by chlorine. Heat, like- wise, has a similar effect, even without being very intense ; for a temperature between 300° or 400° F. aided by moist air, destroys the colouring ingredient. Acids and alkalies commonly change the tint of vegetable colours, entering into combination with them, so as to form new compounds. COLOURING MATTERS. 509 Several ofthe metallic oxides, and especially alumina and the oxides of iron and tin, form with colouring matter insoluble com- pounds, to which the name of lakes is applied. Lakes are com- monly obtained by mixing alum, or the muriate of the peroxide of tin, with a coloured solution, and then by means of an alkali pre- cipitating the oxide which unites with the colour at the moment of separation. On this property are founded many ofthe processes in dyeing and calico printing. The art of the dyer consists in giving an uniform and permanent colour to cloth. This is some- times effected merely by immersing the cloth in the coloured solu- tion ; whereas in other instances the affinity between the colour and the fibre ofthe cloth is so slight, that it only receives a stain which is removed by washing with water. In this case some third substance is requisite, which has an affinity both for the cloth and colouring matter, and which, by combining at the same time with each, may cause the dye to be permanent. A substance of this kind was formerly oalled a mordaunt, but the term basis, intro- duced by the late Mr. Henry of Manchester, is now more general- ly employed. The most important bases, and indeed the only ones in common use, are alumina, oxide of iron, and oxide of tin. The two former are exhibited in combination either with the sulphuric or acetic acid, and the latter most commonly as the muriate. Those colouring substances that adhere to the cloth without a basis are called substantive colours, and those which require a basis, adjective colours. Various as are the tints observable in dyed stuffs, they may all be produced by the four simple ones, blue, red, yellow, and black ; and hence it will be convenient to treat of colouring mat- ters in that^order. Blue dyes.—Indigo is the chief substance employed for giving the blue dye. The best indigo is obtained from an American and Asiatic plant the Indigofera, but an inferior sort has also been prepared from the Isatis tinctoria or woad, a native of Eu- rope. The plant is cut a short time before its flowering, and is put into large vats covered with water, when fermentation spon- taneously ensues, during which the indigo subsides in the form of a pulverulent pulpy matter. Its colour is at first green ; but by exposure to the air it absorbs oxygen and becomes blue. Indigo is a light brittle substance, of a deep blue colour, and without either taste or odour. At 550° F. it sublimes, forming a violet vapour with a tint of red, and condensing into long flat acicu- lar crystals, which appear red by reflected, and blue by transmit- ted light. The process of subliming indigo is one of considera- ble delicacy, owing to the circumstance that the temperature at which it sublimes is very near that at which it is decomposed. Sublimation, however, affords the best method of procuring in- digo in a state of perfect purity, and minute directions have been given by Mr. Crum for conducting it with success. 510 COLOURING MATTERS. Indigo in its dry state may be preserved without change; but when kept under water it is gradually decomposed. It is quite insoluble in water and alcohol, and is attacked by the alkalies in a partial manner. Its only proper solvent is concentrated sul- phuric acid. When indigo is put into this acid, a yellow solu- tion is at first formed, which, after a few hours, acquires a deep blue colour. If the indigo is pure, sulphurous acid is not gene- rated, nor is the acid decomposed; but the indigo undergoes a change, for it is rendered soluble in water. To the indigo thus modified Mr. Crum has applied the name of cerulin, and he regards it as a compound of one equivalent of indigo, and four of water. This solution, properly diluted with water, is employ- ed by dyers for forming what is called the Saxon blue. Mr. Crum has also described another compound of indigo and water, under the name of Phenecin, from $oivt| purple, because it acquires a purple colour on the addition of a salt. It appears to consist of one equivalent of indigo, and two of water. When indigo, suspended in water, is brought into contact with certain deoxidizing agents, it is deprived of oxygen, becomes green, and is rendered soluble in water, and still more so in the alkalies. This effect is produced, for example, by sulphuretted hydrogen, by the hydrosulphuret of ammonia, by the protoxide of iron precipitated by lime or potassa, or by a solution of the sulphuret of arsenic in potassa. On dipping cloth into a solution of deoxidized indigo, it receives a green tint, which becomes blue by exposure to the air. This is the usual method of dyeing blue by means of indigo, a colour which adheres permanently to cloth without the intervention of a basis. From the analytical researches of Mr. Crum, it appears that indigo is composed of nitrogen, oxygen, hydrogen,*and carbon, in the proportion of 1 equivalent of the first element, 2 ofthe second, 4 of the third, and 16 of the fourth. This would make its atomic weight 130. Red dyes.—The chief substances which are employed for giv- ing the red dye are cochineal, archil, madder, Brazil wood, log- wood, and safflower, all of which are adjective colours. The cochineal is obtained from an insect which feeds upon the leaves of several species of the cactus, and which is supposed to derive this colouring matter from its food. It is very soluble in water, and is fixed on cloth by means of alumina or the oxide of tin. Its natural colour is crimson ; but when the bitartrate of potassa is added to the solution, it yields a rich scarlet dye. The beau- tiful pigment called carmine is a lake made of cochineal and alumina, or the oxide of tin. The dye called archil is obtained from a peculiar kind of lichen, (Lichen roccella,) which grows chiefly in the Canary Islands, and is employed by the Dutch in forming the blue pigment called litmus or turnsol. The colouring ingredient of litmus is a com- COLOURING MATTERS. 511 pound of the red colouring matter of the lichen and an alkali; and hence, on the-addition of an acid, the colouring matter is set free, and the red tint ofthe plant is restored. Litmus is not only used as a dye, but is employed by chemists for detecting the pre- sence of a free acid. The colouring principle of logwood has been procured in a separate state by M. Chevreul, who has applied to it the name of hematin. It is obtained in crystals by digesting the aqueous extract of logwood in alcohol, and allowing the alcoholic solu- tion to evaporate spontaneously. The safflower is the dried flowers of the carthamus tinctorius, which is cultivated in Egypt, Spain, and in some parts of the Le- vant. The pigment called rouge is prepared from this dye. Madder is the root of the rubia tinctorum. Yellow dyes.—The chief yellow dyes are the quercitron bark, turmeric, wild American hiccory, fustic, and saffron. They are all adjective colours. The quercitron bark, which is one of the most important of the yellow dyes, was introduced into notice by Dr. Bancroft. With a basis of alumina, the decoction of this bark gives a bright yellow dye. With the oxide of tin it com- municates a variety of tints, which may be made to vary from a pale lemon colour to deep orange. With the oxide of iron it gives a drab colour. Turmeric is the root of the Curcuma longa, a native of the East Indies. Paper stained with a decoction of this substance constitutes the turmeric or curcuma paper employed by chemists as a test of free alkali; by the action of which it receives a brown stain. The colouring ingredient of saffron (Crocus sativus) is soluble in water and alcohol, has a bright yellow colour, is rendered blue and then lilac by sulphuric acid, artti receives a'green tint on the addition of nitric acid. From the great diversity of colours which it is capable of assuming under different circumstances, MM. Bouillon Lagrange and Vogel have proposed for it the name of Polychroite. Black dyes.—The black dye is made of the same ingredients as writing ink, and therefore consists essentially of a compound of the oxide .$f iron with gallic acid and tannin. From the addi- tion of logwood and acetate of copper, the black receives a shade of blue. By the dexterous combination ofthe four leading colours, blue, red, yellow, and black, all other shades of colour may be pro- cured. Thus green is communicated by forming a blue ground with indigo, and then adding a yellow by means of quercitron bark. The reader who is desirous of studying the details of dyerng and calico printing, a subject which does not fall withinJthe plan of this work, may consult Berthollet's Elements de VArt de la 512 TANNIN. Teinture; the treatise of Dr. Bancroft on Permanent Colours ; a paper by Mr. Henry in the third volume of the Manchester Me- moirs ; and the Essay of Thenard and Roard in the 74th volume of the Annates de Chimie. Tannin. Tannin exists in large quantity in the excrescences of several species of the oak, called gall-nuts ; in the bark of most trees; in some inspissated juices, such as kino and catechu; in the leaves of the tea-plant, sumach, whortleberry, (uva ursi,) and in all astringent plants, being the chief cause of the astringency of vegetable matter. It is frequently associated with gallic acid, as for example in gall-nuts, most kinds of bark, and in tea; but in kino, catechu and cinchona bark, no gallic acid is present. In some instances tannin appears to be converted into gallic acid. Thus on exposing an infusion of gall-nuts for some time to the air, nearly all the tannin disappears, and a quantity of gallic acid is found in the liquid much greater than what it had origi- nally contained. Several processes have been recommended for the preparation of tannin; but it is doubtful if it has ever, by these methods, been obtained in a pure state. Owing to this circumstance, the nature and composition of tannin is involved in obscurity. Proust proposes to prepare tannin by pouring muriate of tin into a con- centrated solution of Aleppo galls, until the yellowish precipitate, which at first falls, ceases to appear. The precipitate is washed with a small quantity of cold water, and then dissolved in warm water, through which a current of sulphuretted hydrogen gas is transmitted, in order to precipitate the tin. From the clear liquid, after being filtered, the tannin, mixed with a little gallic acid and extractive matter is procured by gentle evaporation. Tannin, in its dry state, is a brown friable substance, of a re- sinous fracture, insoluble in pure alcohol, but soluble in water. The aqueous solution has a deep brown colour, and is said not to become mouldy by keeping. It has a strong attraction both for acids and alkalies, forming compounds which are, for the most part, of sparing solubility in water. Thus the sulphuric, muriatic, and most other acids, added to a solution of gall-nuts, cause a precipitate, which is tannin combined with a portion of acid. The alkaline bases have a similar effect. Tannin is precipitated, for example, by the carbonates of potassa and ammonia, by the alkaline earths, by alumina, and many of the oxides ofthe com- mon metals. Nitric acid and chlorine decompose tannin, pro- ducing a change, the nature of which is not well understood. The most characteristic property of tannin is its action on a salt of iron and a solution of gelatine. With the peroxide of iron, or still better with the protoxide and peroxide mixed, tannin TANNIN. forms a black coloured compound, which, together with the gal- late of iron, constitute the basis of writing ink and the black dyes. Mixed with a solution of gelatine, a yellowish flocculent precipitate subsides, which is insoluble in water, resists putrefac- tion powerfully, and on drying becomes hard and tough. This substance, to which the name of tanno-gelatine has been applied, is the essential basis of leather, being always formed when skins are macerated in an infusion of bark. The composition of tanno- gelatine is not always uniform, having been found by Dr. Duncan, jun. and Dr. Bostock, to vary with the proportions employed. If the gelatine is added in slight excess only, the resulting com- pound consists, according to Sir II. Davy, of 54 parts of gelatine and 46 of tannin ; so that the quantity of tannin contained in any fluid may in this way be determined with tolerable precision. Tanno-gelatine is soluble to a considerable extent in an excess of gelatine. From an analysis ofthe compound of tannin and oxide of lead, Berzelius states that 100 parts of tannin are composed of carbon, 50.55, oxygen 45, and hydrogen, 4.45. Little reliance, however, can be placed on this result, because we are quite uncertain as to the purity of the tannin, which was combined with the lead. From the experiments of Sir H. Davy, it appears that the inner cortical layers of barks are the richest in tannin. The quantity is greatest in the beginning of spring, at the time the buds begin to open, and smallest during winter. Of all the varieties of bark which he examined, that of the oak contains the greatest quan- tity of tannin. Artificial Tannin.—This interesting substance was discovered some time ago by Mr. Hatchett, who gave a full description of it in the Philosophical Transactions for 1805 and 1806. The best method of preparing it is by the action of nitric acid on charcoal. For this purpose, 100 grains of charcoal in fine pow- der are digested in nitric acid, of density 1.4, diluted with two ounces of water. The mixture is exposed to a gentle heat, which is to be continued until all the charcoal is dissolved. The red- dish-brown solution is then evaporated to dryness, in order to expel the pure acid, the temperature being carefully regulated towards the close of the process, so that the product may not be decomposed. , Artificial tannin is a brown fusible substance, of a resinous fracture, and astringent taste. It is soluble even in cold water and in alcohol. It reddens litmus paper, probably from adhering nitric acid. With a salt of iron and solution of gelatine, it acts precisely in the same manner as natural tannin. It differs, how- ever, from that substance in not being decomposed by the action of strong nitric acid. Artificial tannin may be prepared in several ways. Thus it is generated by the action of nitric acid, both on animal or vegeta- 3 T 514 GLUTEN. ble charcoal, and on pit-coal, asphaltum, jet, indigo, common resin, and several resinous substances. It is also procured by treating common resin, elemi, assafoetida, camphor, balsams, &c. first with sulphuric acid, and then with alcohol. Gluten.—Yeast.—Vegetable Albumen. Gluten is procured by the process which was described for preparing starch from wheat flour. It has a gray colour and fibrous structure, accompanied with a high degree of viscidity and elasticity. It has scarcely any taste, and is insoluble in water, alcohol, and ether ; but Dr. Bostock found that a small portion is taken up by long digestion in water. Both the acids and alkalies dissolve gluten. The acid solution is precipitated by an alkali, and reciprocally the alkaline solution by an acid, the gluten in each case having lost its elasticity. When gluten is kept in a warm moist situation, it ferments, and an acid is formed ; but in a few days, putrefaction ensues, and an offensive odour, like that of putrefying animal matter, is emitted. According to Proust, who has made these spontaneous changes a particular object of study, the process is divisible into two distinct periods. In the first, carbonic acid and pure hy- drogen gases are evolved ; and in the second, besides the acetic and phosphoric acids and ammonia, two new compounds are ge- nerated, for which he proposes the names of caseic acid and caseous oxide. These are the same principles which are gene- rated during the fermentation ofthe curd of milk, and their real nature will be considered in the section on milk. It is appa- rent, from these circumstances, that gluten contains nitrogen as one of its elements, and that it approaches closely to the na- ture of animal substances. It has hence been called a vegeto- animal principle. If gluten is dried by a gentle heat, it contracts in volume, be- comes hard and brittle, and may in this state be preserved with- out change. Exposed to a strong heat, it yields, in addition to the usual inflammable gases, a thick fetid oil, and carbonate of ammonia. Gluten is present in most kinds of grain, such as wheat, bar- ley, rye, oats, peas, and beans j but the first contains it in by far the largest proportion. This is the reason that wheaten bread is more nutritious than that made with other kinds of flour; for of all vegetable substances gluten appears to be the most nutri- tive. It is to the presence of gluten that wheat flour owes its property of forming a tenacious paste with water. To the same cause is owing the formation of light spongy bread, the carbonic acid which is disengaged during the fermentation of dough, be- ing detained by the viscid gluten, distends the whole mass, and thus produces the rising of the dough. From the experiments GLUTEN. 515 of Sir H. Davy, it appears that good wheat flour contains from 19 to 24 per cent, of gluten. The wheat grown in the south of Eu- rope is richer in gluten than that of colder climates. M. Taddey, an Italian chemist, has succeeded in obtaining two distinct principles from gluten, to one of which he has ap- plied the name of gliadine, from yTua, gluten, and to the other that of zymomt, from £V«j, a ferment. To obtain these principles, the gluten is boiled with succes- sive portions of alcohol, until the spirit ceases to be rendered milky by the addition of water. By this process, the gliadine, which is soluble in alcohol, is dissolved, and may be procured by evaporating the alcoholic solution; while the zymome, which is insoluble in that menstruum, is left in a pure state. Gliadine is a brittle, slightly transparent substance, of a yellow colour, and a sweetish balsamic taste. Its smell, in the cold, is like that of the honeycomb ; but, when heated, it emits an odour similar to that of boiled apples. It is soluble to a considerable extent in boiling alcohol, and is in part deposited in cooling. The alcoholic solution is rendered milky by water, and the glia- dine is precipitated in white flakes by alkaline carbonates. It is insoluble in water, but is dissolved by acids and alkalies. When heated in the open air, it takes fire, and burns with a bright flame. Zymome is a hard tough substance, but does not possess the viscidity of gluten. It is insoluble in water and alcohol ; but it is dissolved in vinegar and the mineral acids by the aid of heat, and forms a soap with pure potassa. Under favourable circum- stances it putrefies, without previously fermenting like gluten ; and when heated, it emits an odour like-that of burning hair. It produces various kinds of fermentation, according to the nature ofthe substance with which it comes in contact. M. Taddey has discovered a very delicate test ofthe presence of zymome. On mixing the powder of guaiacum with zymome, a beautiful blue colour instantly appears, and the same phenomenon ensues, though less rapidly, when it is kneaded with gluten or the flour of good wheat moistened with water. With bad flour, the "-luten of which has suffered spontaneous decomposition, the blue&tint is scarcely visible. The intensity of the colour, indeed, is entirely dependent on the relative quantity of zymome con- tained in the flour; and since the quantity of zymome is propor- tional to the quantity of gluten, the proportion ofthe latter, and, therefore, the quality of the flour, may be estimated approximate- ly by the action of guaiacum. The nature of the change which gives rise to the blue colour has not been explained ; but oxygen gas is obviously essential to it, since the phenomenon does not take place at all when at- mospheric air is excluded. 516 YEAST. Yeast.—This substance is always generated during the vinous fermentation of vegetable juices and decoctions, rising to the surface in the form of a frothy, flocculent, somewhat viscid mat- ter, the nature and composition of which are unknown. It is in- soluble in water and alcohol, and in a warm moist atmosphere gradually putrefies, a sufficient proof that ammonia is one of its elements. Submitted to a moderate heat, it becomes dry and hard, and may, in this state, be preserved without change. Heat- ed to redness in close vessels, it yields products similar to those procured under the same circumstances from gluten. To this substance, indeed, yeast is supposed by some chemists to be very closely allied. The most remarkable property of yeast is that of exciting fer- mentation. By exposure for a few minutes to the heat of boiling water, it loses this property, but after some time again acquires it. Nothing conclusive is known concerning either the nature of these changes, or the mode in which yeast operates in establish- ing the fermentative process. Vegetable Albumen.—Some vegetables contain a substance coagulable by heat, and which is very analogous to animal albu- men or curd. It was found in the bitter almond by Vogel, in the sweet almond by M. Boullay, and probably exists in most of the emulsive seeds. Asparagin, Bassorin, Caffein, Cathartin, Fungin, Suberin, (Jlmin, Lupulin, Inulin, Medullin, Pollenin, Piperin, Olivile, Sarcocoll, Extractive Matter, Bitter Principle, &rc. Asparagin.—This principle was discovered by MM. Vauquelin and Robiquet, in the juice ofthe asparagus, from which it is de- posited in crystals by evaporation. The form of its crystals is a rectangular octahedron, six sided prism, or right rhombic prism. Its taste is cool and slightly nauseous, it is soluble in water, and has neither an acid nor alkaline re-action. Bassorin was first noticed in gum Bassora by Vauquelin. Ac- cording to Gehlen and Bucholz, it is contained together with common gum, in the gum tragacanth ; and John found it in the gum ofthe cherry tree. Salep, from the experiments of Caven- tou, appears to consist almost totally of Bassorin. Bassorin is characterized by forming with cold water a bulky jelly which is insoluble in that menstruum, as well as in alcohol and ether. Boiling water does not dissolve it except by long continued ebullition, when the bassorin at length disappears, and is converted into a substance similar to gum arabic. Caffein was discovered in coffee by M. Robiquet in the year 3 821, and was soon after obtained from the same source by Pel- letier and Caventou, without a knowledge of the discovery of Robiquet. It is a white crystalline volatile matter, which is so- GLUTEN. 517 iuble in boiling water and alcohol, and is deposited on cooling in the form of silky filaments like amianthus. M. Pelletier, con- trary to the opinion of M. Robiquet, at first regarded it as an al- kaline base ; but he now admits that it does not affect the vege- table blue colours, nor combine with acids. Hitherto the properties of Caffein have not been fully de- scribed. From the analysis of Pelletier and Dumas, 100 parts of it consist of carbon 46.51, nitrogen 21.54, hydrogen 4.81, and oxygen 27.14. Though it contains more nitrogen than most animal substances, it does not, under any circumstances, undergo the putrefactive fermentation. Cathartin.—This name has been applied by MM. Lassaigne and Feneulle to the active principle of senna. Fungin.—This name is applied by M. Braconnot to the fleshy substance of the mushroom, and is procured in a pure state by digestion in hot water, to which a little alkali is added. Fungin is nutritious in a high degree, and in composition is very analo- gous to animal substances. Like flesh, it yields nitrogen gas when digested in dilute nitric acid. Suberin.—This name has been applied by M. Chevreul to the cellular tissue of the common cork, the outer bark of the cork- oak, (quercus suber,) after the astringent, oily, resinous, and other soluble matters have been removed by the action of water and alcohol. Suberin differs from all other vegetable principles by yielding the suberic when treated by nitric acid. Ulmin, discovered by Klaproth, is a substance which exudes spontaneously from the elm, oak, chesnut, and other trees ; and, according to Berzelius, is a constituent of most kinds of bark. It may be prepared by acting upon elm-bark by hot alcohol, and cold water, and then digesting the residue in water which con- tains an alkaline carbonate in solution. On neutralizing the alkali with an acid, the ulmin is precipitated. Ulmin is a dark brown, nearly black substance, is insipid and inodorous, and is very sparingly soluble in water and alcohol. It dissolves freely, on the contrary, in the solution of an alkaline carbonate, and is thrown down by an acid. Lupulin is the name applied by Dr. Ives to the active princi- ple of the hop, but which has not yet been obtained in a state of purity. Inulin is a white powder like starch, which is spontaneously deposited from a decoction ofthe roots ofthe Inula helenium or Elecampane. This substance is insoluble in cold, and soluble in hot water, and is deposited from the latter as it cools, a charac- ter which distinguishes it from starch. With iodine it forms a greenish-yellow compound of a perishable nature. Its solution is somewhat mucilaginous ; but inulin is distinguished from gum by insolubility in cold water, and in not yielding the saccholac- tic when digested in nitric acid. 518 GLUTEN. Medullin.—This name was applied by Dr. John to the pith ofthe sun-flower, but its existence as an independent principle is some- what dubious. The term pollenin has been given by the same chemist to the pollen of tulips. Piperin is the name which is applied to a white crystalline sub- stance extracted from black pepper. It is tasteless, and is quite free from pungency, the stimulating property of the pepper being found to reside in a fixed oil. Olivile.—When the gum of the olive tree is dissolved in alco- hol, and the solution is allowed to evaporate spontaneously, a peculiar substance, apparently different from the other proximate principles hitherto examined, is deposited either in flattened needles, or as a brilliant amylaceous powder. To this M. Pel- letier, its discoverer, has given the name of Olivile. Sarcocoll is the concrete juice ofthe Pencea sarcocalla, a plant which grows in the northern parts of Africa. It is imported in the form of small grains of a yellowish or reddish colour like gum arabic, to which its properties are similar. It has a sweet- ish taste, dissolves in the mouth like gum, and forms a mucilage with water. It is distinguished from gum, however, by its solu- bility in alcohol, and by its aqueous solution being precipitated by tannin. Dr. Thomson considers it closely allied to the sac- charine matter of liquorice. Rhubarbarin is the name employed by Pfaff to designate the principle in which the purgative property ofthe rhubarb resides. M. Nani of Milan regards the active principle of this plant as a vegetable alkali; but he has not given any proof of its alkaline nature. Colocyntin.—This name is applied by Vauquelin to a bitter resinous matter extracted from colocynth, and to which he as- cribes the properties of this substance. Bitter Principle.—This name was formerly applied to a sub- stance supposed to be common to bitter plants, and to be the cause of their peculiar taste. The recent discoveries in vege- table chemistry, however, have shown that it can no longer be regarded as an uniform unvarying principle. The bitterness of the nux vomica, for example, is owing to strychnia, that of opium to morphia, that of cinchona bark to cinchonia and quina, &.c. The cause ofthe bitter taste in the root of the squill is different from that of the hop or of gentian. The term bitter principle, when applied to any one principle common to bitter plants, con- veys an erroneous idea, and should therefore be abandoned. Extractive Matter.—This expression, if applied to one deter- minate principle supposed to be the same in different plants, is not less vague than the foregoing. It is indeed true that most plants yield to water a substance which differs from gum, sugar, or any proximate principle of vegetables, which therefore con- stitutes a part of what is called an extract in pharmacy, and \\hich, CHANGES OF VEGETABLE MATTER. for want of a more precise term, may be expressed by the name of extractive. It must be remembered, however, that this matter is always mixed with other proximate principles, and that there is no proof whatever of its being identical in different plants. The solution of saffron in hot water, said to afford pure extract- ive matter by evaporation, contains the colouring matter of the plant, together with all the other vegetable principles of saffron, which happen to be soluble in the menstruum employed. SECTION VI. On the spontaneous changes of vegetable matter. Vegetable substances, for reasons already explained in the re- marks introductory to the study of organic chemistry, are very liable to spontaneous decomposition. So long, indeed, as they remain in connection with the living plant by which they were produced, the tendency of their elements to form new combina- tions is controlled; but as soon as the vital principle is extinct, of whose agency no satisfactory explanation can at present be af- forded, they become subject to the unrestrained influence of chemical affinity. To the spontaneous changes which they then experience from the operation of this power, the term fermenta- tion is applied. As might be expected from the difference in the constitution of different vegetable compounds, they are not all equally prone to fermentation; nor is the nature of the change the same in all. Thus alcohol, oxalic, acetic, and benzoic acids, probably the vegetable alkalies, and pure naptha, may be kept for years with- out change, and some of them appear unalterable; while others, such as gluten, sugar, starch, and mucilaginous substances, are very liable to decomposition. In like manner, the spontaneous change sometimes terminates in the formation of sugar, at another time in that of alcohol, at a third in that of acetic acid, and at a fourth in the total dissolution ofthe substance. This has led to the di- vision ofthe fermentative processes into four distinct kinds, namely the saccharine, the vinous, the acetous, and the putrefactive fer- mentation. Saccharine Fermentation. The only substance known to be subject to the first kind of fermentation is starch. When gelatinous starch, or amidine, is kept in a moist state for a considerable length of time, a change gradually ensues, and a quantity of sugar, equal to about half the weight of the starch employed, is generated. Exposure to 520 VINOUS FERMENTATIONS. the atmosphere is not necessary to this change, but the quan- tity of sugar is increased by the access of air. The germination of seeds, as exemplified in the malting of barley, is likewise an instance of the saccharine fermentation; but as it differs in some respects from the process above men- tioned, being probably modified by the vitality of the germ, it may with greater propriety be discussed in the following section. The ripening of fruit has also been regarded as an example of the saccharine fermentation, especially since some fruits, such as the pear and apple, if gathered before their maturity become sweeter by keeping. We cannot, however, adopt this opinion. The process of ripening appears to consist in the conversion, not of starch, but of acid into sugar. Such at least is the view dedu-i cible from the experiments of Proust, who examined the unripe grape in its different stages towards maturity. He found that the green fruit contains a large quantity of free acid, chiefly the citric, which gradually disappears as the grape ripens, while its place is occupied by sugar. It is hence probable that the ele- ments of the acid itself, as the result of a vital process, are made to enter into a new arrangement, by which sugar is generated. The formation of an acid may be regarded as one step towards the production of saccharine matter, a view which will account for the strong acidity of many fruits, such as the gooseberry and currant, just before they begin to ripen. Vinous Fermentations. The conditions which are required for establishing the vinous fermentation are four in number, namely, the presence of sugar, water, yeast, or some ferment, and a certain temperature. The best mode of studying this process, so as to observe the pheno- mena, and determine the nature of the change, is to place five parts of sugar, with about twenty of water, in a glass flask furnish- ed with a bent tube, the extremity of which opens under an in- verted jar full of water or mercury; and after adding a little yeast, to expose the mixture to a temperature of about 60° or 70° Fahr. In a short time bubbles of gas begin to collect in the vicinity of yeast, and the liquid is soon put into brisk motion, in consequence of the formation and disengagement of a large quan- tity of gaseous matter; the solution becomes turbid, its tempera- ture rises, and froth collects upon its surface. After continuing for a few days, the evolution of gas begins to abate, and at length ceases altogether; the impurities gradually subside, and leave the liquor clear and transparent. The only appreciable changes which are found to have oc- curred during the process, are the disappearance of the sugar, and the formation of alcohol, which remains in the flask, and of carbonic acid gas which is collected in the pneumatic apparatus. VINOUS FERMENTATIONS. 521 A small portion of yeast is indeed decomposed ; but the quantity is so minute that it may without inconvenience be left out of con- sideration. The yeast indeed appears to operate only in excit- ing the fermentation, without further contributing to the products. The atmospheric air, it is obvious, has no share in the phenomena, since it may be altogether excluded without affecting the result. The theory of the process is founded on the fact that the sugar, which disappears, is almost precisely equal to the united weights of the alcohol and carbonic acid; and hence the former is sup- posed to be resolved into the two latter. The mode in which this change is conceived to take place has been ably explained by Gay-Lussac, an explanation which will easily be understood by comparing the composition of sugar with that of alcohol. The elements of sugar, which consists of carbon, hydrogen, and oxy- gen, in the ratio of one equivalent of each, are multiplied by three, in order to equalize the quantity of hydrogen contained in the two compounds. By weight. By volume. Sugar. Alcohol. Sugar. Alcohol. Carbon, 18 or 3 equiv. 12 or 2 equiv. Vapour of Carbon, 3 2 Hydrogen, 3 or 3 equiv. 3 or 3 equiv. Hydrogen, - 3 3 Oxygen, 24 or 3 equiv. 8 or 1 equiv. Oxygen, * £ 45 23 Now, on inspecting this table, and remembering that carbonic acid consists of one equivalent of carbon, or one volume of its vapour, and two equivalents or one volume of oxygen, it will be apparent that the elements of sugar are in such proportion as to form one equivalent of alcohol, or one volume of its vapour, and one equivalent or one volume of carbonic acid. Therefore forty- five parts of sugar are capable of furnishing twenty-three of alco- hol and twenty-two parts of carbonic acid. It admits of doubt whether any substance besides sugar is ca- pable of undergoing the vinous fermentation. The only other principle which is supposed to possess this property is starch, and this opinion chiefly rests on the two following facts : First, it ,is well known that potatoes, which contain but little sugar, yield a large quantity of alcohol by fermentation, during which the starch disappears. And, secondly, M. Clement procured the same quantity of alcohol from equal weights of malted and un- malted barley. Nothing conclusive can be inferred, however, from these data ; for, from the facility with which starch is con- verted into sugar, it is probable that the saccharine may precede the vinous fermentation. Though a solution of pure sugar is not susceptible ofthe vi- nous fermentation without being mixed with yeast, or some such ferment, yet the saccharine juices of plants do not require the addition of that substance, or in other words, they contain some 3 U 522 VINOUS FERMENTATION. principle which, like yeast, excites the fermentative process. Thus, must or the juice of the grape ferments spontaneously ; but Gay-Lussac has observed that these juices cannot begin to fer- ment unless they are exposed to the air. By heating must to 212° F. and then corking it carefully, the juice may be preserved without change ; but if it be exposed to the air for a few seconds only, it absorbs oxygen, and fermentation takes place. From this it would appear that the must contains a principle which is convertible into yeast, or at least acquires the characteristic pro- perty of that substance, by absorbing oxygen. It appears from the experiments of M. Colin, that various sub- stances are capable of acting as a ferment. This property is pos- sessed by gluten, as well as both its .principles, gliadine and zy- mome, caseous matter, albumen, fibrin,gelatine, blood, and urine. In general, they act most efficaciously after the commencement of putrefaction ; and indeed exposure to oxygen gas seems equally necessary for enabling these substances to act as ferments, as to the principle contained in the juice of fruit. The various kinds of stimulating fluids, prepared by means of the vinous fermentation, are divisible into wines which are formed from the juices of saccharine fruits, and the various kinds of ale and beer produced from a decoction ofthe nutritive grains previously malted. The juice of the grape is superior, for the purpose of making wine, to that of all other fruits, not merely ih containing a larger proportion of saccharine matter, since this deficiency may be sup- plied artificially, but in the nature of its acid. The chief or only acidulous principle ofthe mature grape, ripened in a warm cli- mate, such as Spain, Portugal, or Madeira, is the, bitartrate of po- tassa. As this salt is insoluble in alcohol, the greater part of it is deposited during the vinous fermentation; and an addi- tional quantity subsides, constituting the crust, during the pro- gress of wine towards its point of highest perfection. The juices of other fruits, on the contrary, such as the gooseberry or currant, contain the malic and citric acids, which are soluble both in water and alcohol, and of which therefore they can never be deprived. Consequently, these wines are only rendered palatable by the presence of free sugar, which conceals the taste of the acid ; and hence it is necessary to arrest the progress of the fer- mentation long before the whole ofthe saccharine matter is con- sumed. For the same reason, these wines do not admit of being long kept; for as soon as the free sugar is converted into alco- hol by the slow fermentative process, which may be retarded by the addition of brandy, but cannot be prevented, the wine acquires a strong sour taste. Ale and beer differ from wines in containing a large quantity of mucilaginous and extractive matters derived from the malt with which they are made. From the presence of these sub- ACETOUS FERMENTATION. 523 stances they always contain a free acid, and are greatly disposed to pass into the acetous fermentation. The sour taste is con- cealed partly by free sugar, and partly by the bitter flavour of the hop, the presence of which diminishes the tendency to the formation of an acid. The fermentative process which takes place in dough mixed with yeast, and on which depends the formation of good bread, has been supposed to be of a peculiar kind, and is sometimes de- signated by the name of panary fermentation. The late inge- nious researches of Dr. Colquhoun, however, leave little or no doubt that the phenomena are to be ascribed to the saccharine matter of the flour undergoing the vinous fermentation, by which it is resolved into alcohol and carbonic acid. Indeed Mr. Gra- ham has actually procured alcohol by distillation from fermented dough. Acetous Fermentation. When any liquid which has undergone the vinous fermenta- tion, or even pure alcohol diluted with water, is mixed with yeast, and exposed in a warm place to the open air, an intestine movement speedily commences, heat is developed, the fluid be- comes turbid from the deposition of a peculiar filamentous mat- ter, oxygen is absorbed from the atmosphere, and carbonic acid is disengaged. These changes, after continuing a certain time, cease spontaneously ; the liquor becomes clear, and instead of alcohol, it is now found to contain acetic acid. This process is called the acetous fermentation. The vinous may easily be made to terminate in the acetous fermentation; nay, the transition takes place so easily, that in many instances, in which it is important to prevent it, this is with difficulty effected. It is the uniform result if the ferment- ing liquid be exposed to a warm temperature and to the open air ; and the means by which it is avoided is by excluding the atmos- phere, or by exposure to cold. For the acetous fermentation, a certain degree of warmth is indispensable. It takes place tardily below 60° F.; at 50° it is very sluggish; and at 32°, or not quite so low, it is wholly ar- rested. It proceeds with vigour, on the contrary, when the ther- mometer ranges between 60° and 80°, and is even promoted by a temperature somewhat higher. The presence of water is like- wise essential ; and a portion of yeast, or some analogous sub- stance, by which the process may be established, must also be present. The information contained in chemical works relative to the substances susceptible of the acetous fermentation is somewhat confused, a circumstance which appears to have arisen from phenomena of a totally different nature, being included under 524 ACETOUS FERMENTATION. the same name. It seems necessary to distinguish between the mere formation of acetic acid, and the acetous fermentation. Several, or perhaps most vegetable substances yield acetic acid when they undergo spontaneous decomposition. Mucilaginous substances in particular, though excluded from the air, gradually become sour ; and, consistently with this fact, inferior kinds of ale and beer are known to acquire acidity in a short time, even when confined in well-corked bottles. In like manner, a solu- tion of sugar, mixed with water, in which the gluten of wheat has fermented, and kept in close vessels, was found by Fourcroy and Vauquelin to yield acetic acid. All these processes, how- ever, appear essentially different from the proper acetous fer- mentation above described, being unattended with visible move- ment in the liquid, with absorption of oxygen, or disengagement of carbonic acid. The acetous fermentation, in this limited sense, consists in the conversion of alcohol into acetic acid. That this change does really take place is inferred, not only from the disappearance of alcohol and the simultaneous production of acetic acid, but also from the quantity of the latter being precisely proportional to that of the former. The nature of the chemical action, how- ever, is at present exceedingly obscure. Indeed the only pro- bable explanation which has been offered is the following : Since alcohol contains a greater proportional quantity of carbon and hydrogen than acetic acid, it has been supposed that the oxygen of the atmosphere, the presence of which is indispensable, ab- stracts so much of those elements, by giving rise to the forma- tion of carbonic acid and water, as to leave the remaining car- bon, hydrogen, and oxygen of the alcohol in the precise ratio for forming acetic acid. The experiments of Saussure, however, are incompatible with this view. According to his researches, the quantity of carbonic acid generated during the acetous fer- mentation, is precisely equal in volume to the oxygen which is absorbed ; and hence it is inferred, that this gas unites exclu- sively with the carbon of the alcohol. This result is different from what might have been anticipated, and requires confir- mation. The acetous fermentation is conducted on a large scale for yield- ing the common vinegar of commerce. In France it is prepared by exposing weak wines to the air during warm weather ; and in this country it is made from cyder. The vinegar thus obtained always contains a large quantity of mucilaginous and other vegeta- ble matters, the presence of which renders it liable to several ulterior changes. PUTREFACTIVE FERMENTATION. 525 Putrefactive Fermentation. By this term is implied a process which is not attended with the phenomena of the saccharine, vinous, or acetous fermentation, but during which the vegetable matter is completely decompos- ed. All proximate principles are not equally liable to this kind of dissolution. Those in which charcoal and hydrogen prevail, such as the oils, resins, and alcohol, do not undergo the putrefac- tive fermentation; nor do acids, which contain a considerable ex- cess of oxygen, manifest a tendency to suffer this change. Those substances alone are disposed to putrefy, the oxygen and hydrogen of which are in proportion to form water; and such, in particu- lar, as contain nitrogen. Among these, however, a singular dif- ference is observable. Caffein evinces no tendency to spontane- ous decomposition; while gluten, which certainly must contain a less proportional quantity of nitrogen, putrefies with great faci- lity. It is difficult to assign the precise cause of this difference; but it most probably depends partly upon the mode in which the ultimate elements of bodies are arranged, and partly on their cohesive power;—those substances, the texture of which is the most loose and soft, being, ccderis paribus, the most liable to spontaneous decomposition. The conditions which are required for enabling the putre- factive process to take place, are moisture, air, and a certain temperature. The presence of a certain degree of moisture is absolutely necessary; and hence vegetable substances, which are disposed to putrefy under favourable circumstances, may be preserved for an indefinite period if carefully dried, and protected from humi- dity. Water acts apparently by softening the texture, and thus counteracting the agency of cohesion ; and a part of the effect may also be owing to its affinity for some of the products ofthe putrefaction. It is not likely that this liquid is actually decom- posed, since water appears to be an uniform product. The air cannot be regarded as absolutely necessary, since putrefaction is found to be produced by the concurrence of the two other conditions only; but the process is without doubt materially promoted by free exposure to the atmosphere. Its operation is of course attributable to the oxygen combining with the carbon and hydrogen of the decaying substance. The temperature most favourable to the putrefactive process is between 60° and 100°. Fahr. A strong heat is unfavourable, by expelling moisture ; and a cold of 32° F. at which water congeals, arrests its progress altogether. The mode in which caloric acts is the same as in all similar cases, namely, by tending to separate elements from one another which are already combined. 526 PUTREFACTIVE FERMENTATION. The products of the putrefactive fermentation may be divided into the solid, liquid, and gaseous. The liquid are chiefly water, together with a little acetic acid, and probably oil. The gaseous products are light carburetted hydrogen, carbonic acid, and, when nitrogen is present, ammonia. Pure hydrogen, and probably nitrogen, are sometimes disengaged. Thus hydrogen and car- bonic acid, according to Proust, are evolved from putrefying gluten ; and Saussure obtained the same gases from the putre- faction of wood in close vessels. Under ordinary circumstances, however, the chief gaseous product of decaying plants is light carburetted hydrogen, which is generated in great quantity at the bottom of stagnant pools during summer and autumn. (Page 155.) Another elastic principle, supposed to arise from putrefy- ing vegetable remains, is the noxious miasm of marshes. The origin of these miasms, however, is exceedingly obscure. Every attempt to obtain them in an insulated state has hitherto proved abortive ; and, therefore, if they are really a distinct species of matter, they must be regarded, like the effluvia of contagious fevers, as of too subtile a nature for being subjected to chemical analysis. When the decay of leaves or other parts of plants has proceed- ed so far that all trace of organization is effaced, a dark pulveru- lent substance remains, consisting of charcoal combined with a little oxygen and hydrogen. This compound is vegetable mould, which, when mixed with a proper quantity of earth, constitutes the soil necessary to the growth of plants. Saussure, in his ex- cellent Recherches Chimiques sur la Vegetation, has described vegetable mould as a substance of uniform composition; and on heating it to redness in close vessels, he procured carburetted hydrogen and carbonic acid gases, water holding the acetate or carbonate of ammonia in solution, a minute quantity of empyreu- matic oil, and a large residue of charcoal mixed with saline and earthy ingredients. On exposing vegetable mould to the action of light, air, and moisture, a chemical change ensues, the effect of which is to render a portion of it soluble in water, and thus applicable to the nutrition and growth of plants. SECTION VII. On the Chemical Phenomena of Germination and Vegetation. Germination. Germination is the process by which a new plant originates from seed. A seed consists essentially of two parts, the Germ ofthe future plant, endowed with a principle of vitality, and the GERMINATION. 527 Cotyledons or Seed-lobes, (a a) both of which a are enveloped in a common covering of cuticle. /W^7\ In the germ, two parts the radicle (b) and plu- /MlkS) mula, (c) may be distinguished, the former of tglW/ which is destined to descend into the earth an^\^^E\ constitute the root, the latter to rise into the air ^wyB) and form the stem of the plant. The office of fa the seed-lobes is to afford nourishment to the young plant until its organization is so far advanced, that it may draw materials for its growth from extraneous sources. For this reason seeds are composed of highly nutritious ingredients. The chief con- stituent of most of them is starch, in addition to which they fre- quently contain gluten, gum, vegetable albumen or curd, and sugar. The conditions necessary to germination are three-fold ; name- ly, moisture, a certain temperature, and the presence of oxygen gas, The necessity of moisture to this process has been proved by extensive observation. It is well known that the concurrence of other conditions cannot enable seeds to germinate provided they are kept quite dry. A certain degree of warmth is not less essential than moisture. Germination cannot take place at 32° F.; and a strong heat, such as that of boiling water, prevents it altogether by depriving the germ of the vital principle. The most favourable temperature ranges from 60° to 80°, the precise degree varying with the na- ture of the plant, a circumstance that accounts for the difference in the season of the year at which different seeds begin to ger- minate. u That the presence of air is necessary to germination was de- monstrated by several philosophers, such as Ray, Boyle, Mus- chenbroeck and Boerhaave, before the chemical nature of the at- mosphere was discovered; and Scheele, soon after the discovery of oxygen, proved that beans do not germinate without exposure to that gas. Achard afterwards demonstrated the same fact with respect to seeds in general, and his experiments have been fully confirmed by subsequent observers. It has even been shown by Humboldt, that a dilute solution of chlorine, owing to the ten- dency of that gas" to "decompose water arid set^qxygeri at liberty, promotes the germination of seeds. These circumstances ac- count for the fact that seeds, when buried deep in the earth, are unable to germinate. It is remarkable that the influence of light, which is so favou- rable to all the subsequent stages of vegetation, is injurious to * the process of germination. Ingenhousz and Sennebier have proved that a seed germinates more rapidly in the shade than in light, and in diffused day-light quicker than when exposed to the direct solar rays. From the preceding remarks it is apparent that when a seed is 528 GERMINATION. placed an inch or two under the surface of the ground in spring, and is loosely covered with earth, it is in a state every way con- ducive to germination. The ground is warmed by absorbing the solar rays, and is moistened by occasional showers; the earth at the same time protects the seed from light, but by its porosity gives free access to the air. The operation of malting barley, in which the grain is made to germinate by exposure to warmth, air, and humidity, affords the best means of studying the phenomena of germination. In this process, water is absorbed, the cotyledon swells and ruptures its cuticle, and soon after the radicle and plumula are protruded. A number of vessels make their appearance in the cotydelon. The reader will have a pretty distinct notion of their distribution by inspect- ing the annexed figure. On examining the grain at this period, it is found to have undergone an essential change in the proportion of its ingredi- ents, as appears from the result of Proust's com- parative analysis of malted and unmalted barley. In 100 parts of Barley In 100 parts of Malt. Resin, ---1 - - - - 1 Gum, ---4 - - - -15 Sugar, - - - 5 - - - -15 Gluten, - - - 3 - - - - 1 Starch, 32 - - - - 56 Hordein, 55 - - - -12 It is hence apparent that in germination the hordein is con- verted into starch, gum, and sugar ; so that from an insoluble ma- terial, which could not in that state be applied to the uses ofthe young plant, two soluble and highly nutritive principles result, which, by being dissolved in water, are readily absorbed by the radicle. The chemical changes which take place in germination have been ably investigated by Saussure. The leading facts which he determined are the following :—that oxygen gas is consumed, that carbonic acid is evolved, and that the volume of the latter is precisely equal to that of the former. Now since carbonic acid gas contains its own volume of oxygen, it follows that this gas must have united exclusively with carbon. It is likewise ob- vious that the grain must weigh less after than before germina- tion, provided it is brought to the same state of dryness in both instances. Saussure indeed found that the loss is greater than can be accounted for by the carbon of the carbonic acid which is evolved, and hence he concluded that a portion of water, ge- nerated at the expense of the grain itself, is dissipated in drying. According to Proust, the diminution in weight is about a third ; but Thomson affirms that in 50 processes, conducted on a ON THE GROWTH OF PLANTS. 529 large scale under his inspection, the average loss did not exceed one-fifth. On the Growth of Plants. While a plant differs from an animal in exhibiting no signs of perception or voluntary motion, and in possessing no stomach to serve as a receptacle for its food, there exists between them a close analogy both of parts and functions, which, though not dis- cerned at first, becomes striking on a near examination. The stem and branches act as a frame work or skeleton for the sup- port and protection ofthe parts necessary to the life ofthe indi- vidual. The root serves the purpose of a stomach by imbibing nutritious juices from the soil, and thus supplying the plant with materials for its growth. The sap or circulating fluid, composed of water holding in solution saline, extractive, mucilaginous, saccharine, and other soluble substances, rises upwards through the wood in a distinct system of tubes called the common vessels, which correspond in their office to the lacteals and pulmonary arteries of animals, and are distributed in minute ramifications over the surface ofthe leaves. In its passage through this organ, which may be termed the lungs of a plant, the sap is fully exposed to the agency of light and air, experiences a change by which it is more completely adapted to the wants of the vegetable economy, and then descends through the inner layer of the bark in another system of tubes called the proper vessels, yielding in its course all the juices and principles peculiar to the plant. The chemical changes which take place during the circulation of the sap are in general of such a complicated nature, and so much under the control ofthe vital principle, as to elude the sa- gacity of the chemist. One part of the subject, however, namely, the reciprocal agency of the atmosphere and growing vegetables on each other, falls within the reach of chemical inquiry, and has accordingly been investigated by several philosophers. For the leading facts relative to what is called the respiration of plants, or the chemical changes which the leaves of growing vegetables produce on the atmosphere, we are indebted to Priest- ley and Ingenhousz, the former of whom discovered that plants ab- sorb carbonic acid from the air under certain circumstances, and emit oxygen in return; and the latter ascertained that this change occurs only during exposure to the direct rays of the sun. When a healthy plant, the roots of which are supplied with proper nour- ishment, is exposed to the direct solar beams in a given quantity of atmospheric air, the carbonic acid after a certain interval is re- moved, and an equal volume of oxygen is substituted for it. If a fresh portion of carbonic acid is supplied, the same result will ensue. In like manner, Sennebier and Woodhouse observed, that when the leaves of a plant are immersed in water, and ex- 3 X 530 ON THE GROWTH OF PLANTS. posed to the rays of the sun, oxygen gas is disengaged. That the evolution of oxygen in this experiment is accompanied with a proportional absorption of carbonic acid, is proved by employ- ing water deprived of carbonic acid by boiling, in which case no oxygen is procured. Such are the changes induced by plants when exposed to sun- shine; but in the dark an opposite effect ensues. Carbonic acid gas is not absorbed under these circumstances, nor is oxygen gas evolved; but, on the contrary, oxygen disappears, and car- bonic acid gas is disengaged. In the dark, therefore, vegetables deteriorate rather than purify the air, producing the same effect on it as the respiration of animals. From several of the preceding facts, it is supposed that the oxygen emitted by plants while under the influence of light is derived from the carbonic acid which they absorb, and that the carbon of that gas is applied to the purposes of nutrition. Con- sistently with this view it has been observed that plants do not thrive when kept in an atmosphere of pure oxygen; and it was found by Dr. Percival and Mr. Henry, that the presence of a little carbonic acid is even favourable to their growth. Saus- sure, who examined this subject minutely, ascertained that plants grow better in an atmosphere which contains about one-twelfth of carbonic acid, than in common air, provided they are exposed to sunshine. But if that gas be present in a greater proportion, its influence is prejudicial:—in an atmosphere consisting of one- half of its volume of carbonic acid, the plants perished in seven days; and they did not vegetate at all when that gas was in the proportion of two-thirds. In the shade, the presence of carbonic acid is always detrimental. He likewise observed that the pre- sence of oxygen is necessary, in order that a plant should derive benefit from admixture with carbonic acid. Saussure is of opinion that plants derive a large quantity of their caroon from the carbonic acid of the atmosphere, an opin- ion which receives great weight from the two following compara- tive experiments. On causing a plant to vegetate in pure water, supplied with common air and exposed to light, the carbon of the plant increased in quantity; but when supplied with common air, in a dark situation, it even lost a portion ofthe carbon which it had previously possessed. Light is necessary to the colour of plants. The experiments of Sennebier and Mr. Gough have shown that the green colour of the leaves is not developed, except when they are in a situa- tion to absorb oxygen and give out carbonic acid. Though the experiments of different philosophers agree as to the influence of vegetation on the air in sunshine and during the night, considerable uncertainty prevails both as to the phenome- na occasioned from diffused daylight, and concerning the total effect produced by plants on the constitution of the atmosphere. ON THE GROWTH OF PLANTS. 531 Priestley found that air, vitiated by combustion or the respiration of animals, and left in contact for several days and nights with a sprig of mint, was gradually restored to its original purity; and hence he inferred that the oxygen gas consumed during these and various other processes is restored to the mass of the atmosphere by the agency of growing vegetables. This doctrine receives confirmation from the researches of In- genhousz and Saussure, who were led to adopt the opinion that the quantity of oxygen gas evolved from plants by day, exceeds that of carbonic acid emitted during the night. The conclusions of Mr. Ellis, on the contrary, are precisely the reverse. From an ex- tensive series of experiments, contrived with much sagacity, Mr. Ellis inferred that growing plants give out oxygen only in direct sunshine, while at all other times they absorb it; that when ex- posed to the ordinary vicissitudes of sunshine and shade, light and darkness, they form more carbonic acid in the period of a day and night, than they destroy ; and, consequently, that the general effect of vegetation on the atmosphere is the same as that produced by animals. This question has been ably discussed by Sir H. Davy, in his elements of Agricultural Chemistry. Sir H. Davy is of opinion that the experiments of Mr. Ellis cannot be regarded as decisive, having been conducted under circumstances unfavourable to accuracy of result. He considers the original experiments of Priestley as unexceptionable, and adduces others made by him- self in support ofthe same doctrine. On the Food of Plants. The chief source from which plants derive the materials for their growth is the soil. However various the composition ofthe soil, it consists essentially of two parts, so far as its solid consti- tuents are concerned. One is a certain quantity of earthy mat- ters, such as siliceous earth, clay, lime, and sometimes magnesia ; and the other is formed from the remains of animal and vegeta- ble substances, which, when mixed with the former, constitute common mould. A mixture of this kind, moistened by rain, af- fords the proper nourishment of plants. The water, percolating through the mould, dissolves the soluble salts with which it comes in contact, together with the gaseous, extractive, and other mat- ters which are formed during the decomposition of the animal and vegetable remains. In this state it is readily absorbed by the roots, and conveyed as sap to the leaves, where it undergoes a process of assimilation. But though this is the natural process by which plants obtain the greater part of their nourishment, and without which they do not arrive at perfect maturity, they may live, grow, and even in- crease in weight, when wholly deprived of nutrition from this 532 ON THE FOOD OF PLANTS. source. Thus in the experiment of Saussure, already described, sprigs of peppermint were found to vegetate in distilled water ; and it is well known that many plants grow when merely sus- pended in the air. In the hot-houses of the botanical garden of Edinburgh, for example, there are two plants, species of the fig-tree, iheficus australis and ficus elastica, the latter of which has been suspended for four, and the former for nearly ten years, during which time they have continued to send out shoots and leaves. Before scientific men had learned to appreciate the influence of atmospheric air on vegetation, the increase of carbonaceous matter, which occurs in some of these instances, was supposed to be derived from water, an opinion naturally suggested by the important offices performed by this fluid in the vegetable economy. Without water, plants speedily wither and die. It gives the soft parts that degree of succulence necessary for the performance of their functions ; it affords two elements, oxygen and hydrogen, which, either as water, or under some other form, are contained in all vegetable products ;—and, lastly> the roots absorb from the soil those substances only, which are dissolved or suspended in water. So carefully, indeed, has nature provided against the chance of deficient moisture, that the leaves are endowed with a property both of absorbing aqueous vapour directly from the atmosphere, and of lowering their temperature during the night by radiation, so as to cause a deposition of dew upon their sur- face, in consequence of which, during the dryest seasons and in the warmest climates, they frequently continue to convey this fluid to the plant, when it can no longer be obtained in sufficient quantity from the soil. But necessary as is this fluid to vegeta- ble life, it cannot yield to plants a principle which it does not possess. The carbonaceous matter which accumulates in plants, under the circumstances above mentioned, may, with every ap- pearance of justice, be referred to the atmosphere ; since we know that carbonic acid exists there, and that growing vegeta- bles have the property of taking carbon from that gas. When plants are incinerated, their ashes are found to contain saline and earthy matters, the elements of which, if not the compounds themselves, are supposed to be derived from the soil. Such, at least, is the view deducible from the researches of Saussure, and which might have been anticipated by reasoning on chemical principles. The experiments ofM. Schrader, how- ever, lead to a different conclusion. He sowed several kinds of grain, such as barley, wheat, rye, and oats, in pure flowers of sul- phur, and supplied the shoots as they grew, with nothing but air, light, and distilled water. On incinerating the plants, thus treat- ed, they yielded a greater quantity of saline and earthy matters than were originally present in the seeds. ANIMAL CHEMISTRY. 533 These results, supposing them accurate, may be accounted for in two ways. It may be supposed, in the first place, that the foreign matters were introduced accidentally from extraneous sources, as by fine particles of dust floating in the atmosphere ; or, secondly, it may be conceived, that they were derived from the sulphur, air, and water, with which the plants were supplied. If the latter opinion be adopted, we must infer either that the vital principle, which certainly controls chemical affinity in a surprising manner, and directs this power in the production of new compounds from elementary bodies, may likewise convert one element into another; or that some of the substances, sup- posed by chemists to be simple, such as oxygen and hydrogen, are compounds, not of two, but of a variety of different princi- ples. As these conjectures are without foundation, and are ut- terly at variance with the facts and principles ofthe science, we do not hesitate in adopting the more probable opinion, that the experiments of M. Schrader were influenced by some source of error which escaped detection. CHAPTER II. ANIMAL CHEMISTRY. All distinct compounds, which are derived from the bodies of animals, are called proximate animal principles. Th'ey are dis- tinguished from inorganic matter by the characters stated in the introduction to inorganic chemistry. The circumstances which serve to distinguish them from vegetable matter are, the presence of nitrogen, their strong tendency to putrefy, and the highly of- fensive products to which their spontaneous decomposition gives rise. It should be remembered, however, that nitrogen is like- wise a constituent of many vegetable substances ; though few of these, the vegeto-animal principles excepted, are prone to suffer the putrefactive fermentation. It is likewise remarkable that some compounds of animal origin, such as cholesterine and the oils, do not contain nitrogen as one of their elements, and are not disposed to putrefy. The essential constituents of animal compounds are carbon, hydrogen, oxygen, and nitrogen, besides which, some of them contain phosphorus, sulphur, iron, and earthy and saline matters in small quantity. Owing to the presence of sulphur and phos- phorus, the process of putrefaction, which will be particularly described hereafter, is frequently attended with the disengage- ment of sulphuretted and phosphuretted hydrogen gases. When heated in close vessels, they yield water, carbonic oxide, carbu- retted hydrogen, probably free nitrogen and hydrogen, the car- 534 FIBRIN. bonate and hydrocyanate of ammonia, and a peculiarly fetid thick oil. The carbonaceous matter left in the retort is less easily burned, and is more effectual as a decolorizing agent, than charcoal derived from vegetable matter. The principle of the method of analyzing animal substances has already been mentioned. In describing the proximate animal principles, the number of which is far less considerable than the vegetable compounds, we shall adopt the arrangement suggested by Gay-Lussac and The- nard in their Recherches Physico-Chimiques, and followed by Thenard in his System of Chemistry. The animal compounds are accordingly arranged in three sections. The first contains sub- stances which are neither acid nor oleaginous; the second com- prehends the vegetable acids ; and the third includes the animal fats. Several of the principles belonging to the first division, such as fibrin, albumen, gelatine, caseous matter, and urea, were shown by Gay-Lussac and Thenard to have several points of simi- larity in their composition. They all contain, for example, a large quantity of carbon, and their hydrogen is in such propor- tion as to convert all their oxygen into water, and their nitrogen into ammonia. No general laws have been established relative to the constitution of the compounds comprised in the other sections. SECTION I. Substances which are neither Add nor Oleaginous. Fibrin. Fibrin enters largely into the composition of the blood, and is the basis ofthe muscles; it may be regarded, therefore, as one of the most abundant of the animal principles. It is most conve- niently procured by stirring recently drawn blood with a stick during its coagulation, and then washing the adhering fibres with water until they are perfectly white. It may also be ob- tained by removing the soluble parts from lean beef, cut into small slices, by digestion in several successive portions of water. Fibrin is solid, white, insipid, and inodorous. When moist it is somewhat elastic, but on drying it becomes hard, brittle, and semi-transparent. In a moist warm situation it readily putrefies. It is insoluble in water at common temperatures, and is dissolved in very minute quantity by the continued action of boiling water. Alcohol, of specific gravity 0.81, converts it into a fatty adipoci- rous matter, which is soluble in alcohol and ether, but is preci- pitated by water. The action of acids on fibrin has been particularly described FIBRIN. 535 by Berzelius. Digested in concentrated acetic acid, fibrin swells and becomes a bulky tremulous jelly, which dissolves complete- ly, with disengagement of a little nitrogen, in a considerable quantity of hot water. By the action of nitric acid, of specific gravity 1.25, aided by heat on fibrin, a yellow solution is formed, with disengagement of a large quantity of nearly pure nitrogen, in which Berzelius could not detect the least trace of the deutoxide of nitrogen. After digestion for twenty-four hours a pale yellow pulverulent substance is deposited, which Fourcroy and Vauquelin described as a new acid under the name of yellow acid. According to Ber- zelius, however, it is a compound of modified fibrin and nitric acid, together with some malic and nitrous acids. It likewise contains some fatty matter, which may be removed by alcohol. The origin ofthe nitrogen which is disengaged in the beginning ofthe process, is somewhat obscure. From the total absence of the deutoxide of nitrogen, it is probable that in the early stages very little, if any, of the nitric acid is decomposed, and that the nitrogen gas is solely or chiefly derived from the fibrin. Dilute muriatic acid hardens without dissolving fibrin, and the strong acid decomposes it. The action of sulphuric acid, accord- ing to M. Braconnot, is very peculiar. When fibrin is mixed with its own weight of concentrated sulphuric acid, a perfect so- lution ensues without change of colour, or disengagement of sul- phurous acid. On diluting with water, boiling for nine hours, and separating the acid by means of chalk, the filtered solution was found to contain a peculiar white matter, to which M. Bra- connot has applied the name of leucine. Digested in strong sul- phuric acid, a dark reddish-brown, nearly black solution, is formed, and the fibrin is carbonized and decomposed. Fibrin is dissolved by pure potassa, and is thrown down when the solution is neutralized. The fibrin thus precipitated, how- ever, is partially changed, since it is no longer soluble in acetic acid. It is soluble likewise in ammonia. According to the analysis of Gay-Lussac and Thenard, 100 parts of fibrin are composed of carbon, 53.36, hydrogen 7.021, oxygen 19.685, and nitrogen 19.934. From these numbers fibrin may be regarded as an atomic compound of 18 equivalents of carbon, 14 of hydrogen, five of oxygen, and three of nitrogen. Albumen. Albumen enters largely into the composition both of animal fluids and solids. Dissolved in water it forms an essential consti- tuent ofthe serum ofthe blood, the liquor ofthe serous cavities, and the fluid of dropsy; and in a solid state it is contained in several of the textures ofthe body, such as the cellular mem- 536 ALBUMEN. brane, the skin, glands, and vessels. From this it appears that albumen exists under two forms, liquid and-solid. Liquid albumen is best procured from the white of eggs, which consists almost solely of this principle, united with water and free soda, and mixed with a small quantity of saline matter. In this state it is a thick glairy fluid, insipid, inodorous, and easily miscible with cold water, in a sufficient quantity of which it is completely dissolved. When exposed in thin layers to a current of air it dries, and becomes a solid and transparent substance, which retains its solubility in water, and may be preserved for any length of time without change. Kept in its fluid condition it readily putrefies. From the free soda which they contain, albu- minous liquids have always an alkaline re-action, Liquid albumen is coagulated by heat, alcohol, and the stronger acids. Undiluted albumen is coagulated by a tempera- ture of 163°, and when diluted with water at 212° F. Water, which contains only l-1000th of its weight of albumen, is render- ed opaque by boiling. On this property is founded the method of clarifying by means of albuminous solutions; for the albumen being coagulated by heat, entangles in its substance all the foreign particles which are not actually dissolved, and carries them with it to the surface of the liquid. The character of being coagulated by hot water distinguishes albumen from all other animal fluids. The acids differ in their action on albumen. The sulphuric, muriatic, and nitric acids coagulate it; and in each case, accord- ing to Thenard, some of the acid is retained by the albumen. Phosphoric acid, recently ignited, likewise coagulates albumen; but on keeping the acid dissolved in water its power of produc- ing coagulation gradually declines, and after a few days ceases altogether. The solution of albumen is not precipitated at all by acetic acid. By maceration in dilute nitric acid for a month, it is converted, according to Mr. Hatchett, into a substance solu- ble in hot water and possessed ofthe leading properties of gela- tine. Digested in strong sulphuric acid, the coagulum is dissolv- ed, and a dark solution is formed similar to that produced by the same acid on fibrin; but if the heat be applied very cautiously, the liquid assumes a beautiful red colour. This property was discovered some years ago by Dr. Hope, who observes that the experiment does not always succeed, the result being influenced by very slight causes. Albumen is precipitated by several re-agents, especially by metallic salts. This effect is produced by muriate of tin, sub- acetate of lead, muriate of gold and solution of tannin. Corrosive sublimate is a very delicate test of the presence of albumen, causing a milkiness when the albumen is diluted with 2000 parts of water. The nature of the precipitate has already been ex- plained. The ferrocyanate of potassa is equally if not still more ALBUMEN. 537 delicate, provided a little acetic acid is previously added to neu- tralize the free soda. When an albuminous liquid is exposed to the agency of gal- vanism, pure soda makes its appearance at the negative wire, and the albumen coagulates around that which in connection with the positive pole ofthe battery. Mr. Brande, who first observed this phenomenon, ascribes it to the separation of free soda, upon which he supposes the solubility of albumen in water to depend ; but M. Lassaigne attributes it to the decomposition of muriate of soda, the acid of which coagulates the albumen. However this may be, galvanism is one of the most elegant and delicate tests of the presence of albumen in animal fluids which we possess. Chemists are not agreed as to the cause of the coagulation of albumen. When it is coagulated by different chemical agents, such as tannin and metallic salts, the albumen is thrown down in consequence of forming an insoluble compound with the sub- stance employed; and perhaps this is also the mode by which acids coagulate it. With respect to the agency of heat, alcohol; and probably of acids, a different view must be adopted. The explanation usually given is that proposed by Dr. Thomson, who ascribes the solubility of albumen to the presence of free soda, and its coagulation to the removal of the alkali. To this hy- pothesis Dr. Bostock objects, and with every appearance of jus- tice, that albuminous liquids do not contain a sufficient quantity of free alkali for the purpose. Dr. Turner supposes that albumen combines directly with water at the moment of being secreted, at a time when its particles are in a state of minute division ; but as its affinity for that liquid is very feeble, the compound is de- composed by slight causes, and for the same reason the albumen becomes quite insoluble, as soon as it is rendered solid by coagu- lation. Silica affords an instance of a similar phenomenon. Albumen coagulates without appearing to undergo any change of composition, but it is quite insoluble in water, and is less lia- ble to putrefy than in its liquid state. It is dissolved by alkalies with disengagement of ammonia, and is precipitated from its so- lution by acids. In the coagulated state it bears a very close re- semblance to fibrin, and is with difficulty distinguished from it. Alcohol, ether, acids, and alkalies, according to Berzelius, act upon each in the same manner. He observes, however, that acetic acid and ammonia dissolve fibrin more easily than coagu- lated albumen. According to Thenard they are readily distin- guished by means of the deutoxide of hydrogen, from which fibrin causes evolution of oxygen, while albumen has no action upon it. Albumen has been analyzed by Gay-Lussac and Thenard, and Dr. Prout, with the following results :— 3 Y 538 GELATINE. Dr. Prout. ,-----^----v 50, 15 equivalents. 7.78, 14 equivalents. 26.67, 6 equivalents. 15.55, 2 equivalents. 100.000 100.00 Gelatine. Gelatine exists abundantly in many of the solid parts of the body, especially in the skin, cartilages, tendons, membranes, and bones. According to Berzelius, it is not contained in any ofthe healthy animal fluids; and Dr. Bostock, with respect to the blood, has demonstrated the accuracy of this statement. Gelatine is distinguished from all animal principles by its ready solubility in boiling water, and by the solution forming a bulky, semi-transparent, tremulous jelly as it cools. Its tendency to gelatinize is such, that one part of gelatine, dissolved in 100 parts of water, becomes solid in cooling. This jelly is a hydrate of gelatine, and contains so much water, that it readily liquefies when warmed. On expelling the water by a gentle heat, a brit- tle mass is left, which retains its solubility in hot water, and may be preserved for any length of time without change. Jelly, on the contrary, soon becomes acid by keeping, and then putrefies. The common gelatine of commerce is the well-known cement called glue, which is prepared by boiling cuttings of parchment, or the skins, ears, and hoofs of animals, and evaporating the solution. Isinglass, which is the purest variety of gelatine, is prepared from the sounds offish ofthe genus acipenser, especially from the sturgeon. The animal jelly of the confectioners is made from the feet of calves, the tendinous and ligamentous part of which yield a large quantity of gelatine. Gelatine is insoluble in alcohol, but is dissolved readily by most ofthe diluted acids, which form an excellent solvent for it. Mixed with twice its weight of concentrated sulphuric acid, it dissolves without being charred; and on diluting the solution with water, boiling for several hours, separating the acid by means of chalk, and evaporating the filtered liquid, a peculiar saccharine principle is deposited in crystals. This substance has a sweet taste, somewhat like that of the sugar of grapes, is solu- ble in water, though less so than common sugar, and is insoluble in alcohol. When heated to redness, it yields ammonia as one ofthe products, a circumstance which shows that it contains ni- trogen. Mixed with yeast, its solution does not undergo the vi- nous fermentation ; and it combines directly with the nitric acid. It is hence apparent that, though possessed of a sweet taste, it Carbon, Hydrogen, Oxygen, Nitrogen, Gay-Lussac 52.883, 17 7.540, 13 23.872, 6 15.705, 2 Thdnard. equivalents. equivalents. equivalents. equivalents. UREA. 539 differs entirely from sugar. This substance was discovered by M. Braconnot. Gelatine is dissolved by the liquid alkalies, and the solution is not precipitated by acids. Gelatine manifests little tendency to unite with metallic ox- ides. Corrosive sublimate and subacetate of lead do not occa- sion any precipitate in a solution of gelatine, and the salts of tin and silver affect it very slightly. The best precipitant for it is tannin. By means of an infusion of gall-nuts, Dr. Bostock detected the presence of gelatine when mixed with 5000 times its weight of water; and its quantity may even be estimated approximately by this re-agent. But since other animal substances, as for example albumen, are precipitated by tannin, it cannot berelied on as a test of gelatine. The best character for this substance is that of solubility in hot water, and of forming a jelly as it cools. According to the analysis of gelatine by Gay-Lussac and The- nard, 100 parts of this substance consist of carbon 47.881, hy- drogen 7.914, oxygen 27.207, and nitrogen 16.998.—From these numbers it appears that its composition, as to the relative quan- tity of its elements, is identical with that of albumen as deter- mined by Dr. Prout. Urea. Pure Urea is procured by evaporating fresh urine to the con- sistence of a syrup, and then gradually adding to it, when quite cold, pure concentrated nitric acid, till the whole becomes a dark coloured crystallized mass, which is to be slightly washed with cold water, and then dried by pressure between folds of bibulous paper. To the nitrate of urea, thus procured, a pretty strong solu- tion of carbonate of potassa or soda is added, until the acid is neu- tralized ; and the solution is afterwards concentrated by evapora- tion, and set aside, in order that the nitre may separate in crys- tals. The residual liquid, which is an impure solution of urea, is made up into a thin paste with animal charcoal, and is allowed to remain in that state for a few hours. The paste is then mixed with cold water, which takes up the urea, while the colouring matter is retained by the charcoal; and the colourless solution is evaporated to dryness at a low temperature. The residue is then boiled in pure alcohol, by which the urea is dissolved, and from which it is deposited in crystals on cooling. Dr. Prout, to whom we are indebted for the foregoing process for preparing pure urea, has given the following account of its properties. Its crystals are transparent and colourless, of a slight pearly lustre, and have commonly the form of a four-sided prism. It leaves a sensation of coldness on the tongue like nitre. Its smell is faint and peculiar, but not urinous. Its specific gravity is 540 UREA. about 1.35. It does not affect the colour of litmus or turmeric paper. In a moist atmosphere it deliquesces slightly; but other- wise undergoes no change on exposure to the air. Exposed to a strong heat, it melts, and is partly decomposed, and partly sub- limes, apparently without change. The chief product of the de- composition, besides inflammable gas of a very fetid odour, benzoic acid, and charcoal, is carbonate of ammonia. Water at 60° dissolves more than its own weight of urea, and boiling water takes up an unlimited quantity. It requires for solution about five times its weight of alcohol of specific gravity 0.816 at 60° F., and rather less than its own weight at a boiling temperature. The aqueous solution of pure urea may be exposed to the atmosphere for several months, or be heated to the boil- ing point, without change ; but, on the contrary, if the other con- stituents ofthe urine are present, it putrefies with rapidity, and is decomposed by a temperature of 212° F. being almost entirely resolved into carbonate of ammonia by continued ebullition. The pure fixed alkalies and alkaline earths decompose urea, especially by the aid of heat, carbonate of ammonia being the chief product. Though urea has not any distinct alkaline properties, it unites with the nitric and oxalic acids, forming sparingly soluble com- pounds, which crystallize in scales of a pearly lustre. This pro- perty affords an excellent test of the presence of urea. Both compounds have an acid re-action, and the nitrate consists of 54 parts or one equivalent of nitric acid, and 60 parts or two equi- valents of urea. The constituents of urea, according to the analysis of Dr. Prout, are in the proportion of one equivalent of carbon, two of hydrogen, one of oxygen, and one of nitrogen. Its atomic weight, therefore, is 30. A singular instance of the artificial production of urea has been lately noticed by Wohler. It is formed by the action of ammo- nia on cyanogen ; but the best mode of preparing it is by decom- posing cyanate of silver with muriate of ammonia, or acting on cyanate of lead with ammonia. In the last case, oxide of lead is set free, and the only other product appears in colourless, trans- parent, four sided, rectangular crystals. These crystals, judging by the mode of preparation, must be cyanate of ammonia. But yet no ammonia is evolved from them by the action of potassa; the stronger acids do not, as with other cyanates, cause an evolu- tion of carbonic and cyanic acids; nor do they yield precipitates with salts of lead and silver. In fact, though procured by the mutual action of cyanic acid and ammonia, the characters above mentioned do not indicate the presence of either ; but, on the con- trary, the crystals agree with urea obtained from urine in compo- sition and all their chemical properties. The cyanic acid above referred to is that discovered by Wohler. SUGAR OF MILK. 541 Sugar of Milk and Sugar of Diabetes. Sugar of Milk.—The saccharine principle of milk is obtained from whey by evaporating that liquid to the consistence of syrup, and allowing it to cool. It is afterwards purified by means of albumen and a second crystallization. The sugar of milk has a sweet taste, though less so than the sugar of the cane, from which it differs essentially in several other respects. Thus it requires seven parts of cold and four of boil- ing water for solution, and is insoluble in alcohol. It is not sus- ceptible of undergoing the vinous fermentation; and when di- gested with nitric acid it yields the saccholactic acid, a property first noticed by Scheele, and which distinguishes the saccharine principle of milk from every other species of sugar. Like starch, it is convertible into real sugar by being boiled in water acidu- lated with sulphuric acid. The sugar of milk contains no nitrogen, and, according to the analysis of Gay-Lussac and Th6nard, is very analogous to com- mon sugar in the proportion of its elements. Sugar of Diabetes.—In the disease called Diabetes, the urine contains a peculiar saccharine matter, which, when properly pu- rified, appears identical both in properties and composition to ve- getable sugar, approaching nearer to the sugar of grapes than that from the sugar cane. This kind of sugar is obtained in an irregularly crystalline mass by evaporating diabetic urine to the consistence of syrup, and keeping it in a warm place for several days. It is purified by washing the mass with alcohol either cold or at most gently heat- ed, till that liquid comes off colourless, and then dissolving it in hot alcohol. By repeated crystallization it is thus rendered quite pure. Two other principles yet remain to be considered, namely, the colouring principle of the blood, and caseous matter; but these will be more conveniently studied in subsequent sections. SECTION II. Animal Adds. In animal bodies several acids are found, such as the sulphuric, muriatic, phosphoric, acetic, &c. which belong equally to the mineral or vegetable kingdom, and which have consequently been described in other parts of the work. In this section are included those acids only which are believed to be peculiar to animal bodies. 542 ANIMAL ACIDS. Uric, Purpuric, Rosacic, Formic, and Lactic Acids, fyc. Uric or Lithic acid.—This acid is a common constituent of of urinary and gouty concretions, and is always present in healthy urine, combined with ammonia or some other alkali. The urine of birds of prey, such as the eagle, and of the Boa Constrictor and other serpents, consists almost solely of urate of ammonia, from which pure uric acid may be procured by a very simple process. For this purpose the solid urine of the Boa Constrictor is reduced to a fine powder, and digested in a solution of pure potassa, in which it is readily dissolved with disengagement of ammonia. The urate of potassa is then decomposed by adding the acetic, muriatic, or sulphuric acid in slight excess, when the uric acid is thrown down, and after being washed, is collected on a filter. On its first separation from the alkali it is in the form of a gelatinous hydrate, but in a short time this compound is de- composed spontaneously, and the uric acid subsides in small crystals. Pure uric acid is white, tasteless, and inodorous. It is insoluble in alcohol, and is dissolved very sparingly by cold or hot water, requiring about 10,000 times its weight of that fluid at 60° F. for solution. It reddens litmus paper, and unites with alkalies, forming salts which are called urates or lithates. The uric acid does not effervesce with alkaline carbonates; but Dr. Thomson affirms that when boiled for some time with carbonate of soda, the whole of the carbonic acid is expelled. A current of car- bonic acid, on the contrary, throws down the uric acid when dis- solved by potassa. This acid undergoes no change by exposure to the air. Of the acids none exert any peculiar action on the uric, except- ing the nitric acid. When a few drops of nitric acid, slightly diluted, are mixed on a watch glass with uric acid, and the liquid is evaporated to dryness, a beautiful purple colour comes into view, the tint of which is improved by the addition of water. This character affords an unequivocal test of the presence of uric acid. The nature of the change will be considered imme- diately. Uric acid is decomposed by chlorine. On transmitting that gas through water in which uric acid is suspended, the latter dis- appears, and the liquid is found to contain the oxalic and malic acids, and muriate of ammonia. Uric acid has been repeatedly analyzed by Dr. Prout, and its constituents, according to his latest analysis, are in the follow- ing proportions :— ANIMAL ACIDS. 543 Carbon, . 36 . or 6 equivalents. Hydrogen, . 2 . . 2 Oxygen, . 24 . 3 Nitrogen, . 28 . . 2 90 The crystallized acid, as analyzed by Prout, is supposed by most chemists to be anhydrous; but Dr. Thomson maintains that on exposing 90 parts of it to a temperature of 400° F. it loses 18 parts, or two equivalents of water, and that the residue is the real anhydrous uric acid, composed of six equivalents of carbon, one of oxygen, and two of nitrogen. On this view the atomic weight of uric acid is 72, a number which Dr. Thomson has deduced from his analysis ofthe urate of soda. The salts of uric acid have been described by Dr. Henry. The only ones of importance are the urates of ammonia, potassa, and soda. The urate of ammonia is soluble to a considerable extent in boiling, but more sparingly in cold water. The urates of soda and potassa, if neutral, are of very sparing solubility; but an excess of either alkali takes up a large quantity of the acid. The former was found by Dr. Wollaston to be the chief consti- tuent of gouty concretions. Pyro-uric acid.—When uric acid is exposed to heat in a retort, the carbonate and hydrocyanate of ammonia are formed, toge- ther with a peculiar volatile acid, called pyro-uric acid, which was formerly described by Dr. Henry, and has recently been particularly studied by MM. Chevallier and Lassaigne. This acid sublimes without change, and condenses on cool surfaces in the form of white acicular crystals. It is soluble in boiling alcohol, and requires forty times its weight of water for solution. It is not decomposed by digestion in nitric acid, a cha- racter by which it is distinguished from uric acid. Purpuric acid.—This compound was first recognised as a dis- tinct acid by Dr. Prout. Though colourless itself, it has a re- markable tendency to form red or purple coloured salts with alkaline bases, a character by which it is distinguished from all other substances, and to which it owes the name of purpuric acid, suggested by Dr. Wollaston. Thus the purple residue above mentioned, as indicative ofthe presence of uric acid, is the pur- purate of ammonia, which is always generated when the uric is decomposed by nitric acid. This compound is prepared by digesting pure uric acid, ex- tracted from the urine of the Boa Constrictor, in dilute nitric acid, when the former is dissolved with effervescence. The so- lution is then neutralized by ammonia, and concentrated by eva- poration, during the course of which purple coloured crystals of the purpurate of ammonia are deposited. The purpurate of am- 544 ANIMAL ACIDS. monia is then decomposed by digestion with pure potassa, and the liquid is gradually poured into dilute sulphuric acid. The purpuric acid is thus disengaged, and being insoluble in water, subsides to the bottom in the form of a white, or yellowish-white powder, according to its degree of purity. Considerable uncertainty prevails as to the nature of purpuric acid. Vauquelin, for example, denies that its salts have a purple colour, but attributes that tint to the presence of some impurity. M. Lassaigne is likewise inclined to the same opinion. The com- position of the acid is a point equally unsettled ; for Dr. Prout has expressed a doubt of the accuracy of the analysis which he formerly published. The name of erythric acid (from sevOeaiveiv, to redden,) was ap- plied by Brugnatelli to a substance which he procured by the action ofthe nitric on uric acid. It obviously contains purpuric acid, and Dr. Prout thinks it probable that it is a super-salt, con- sisting of purpuric and nitric acids, and ammonia. Rosacic add.—This name was applied by Proust to a peculiar acid supposed to exist in the red matter, commonly called by medical practitioners the lateritious sediment, which is deposited from the urine in some stages of fever. From the experiments of Vogel it appears to be uric acid, either combined with an alkali, or modified by the presence of animal matter. Dr. Prout is of opinion that it contains some purpurate of ammonia ; and, as he has detected the presence of nitric acid in the urine from which such sediments were deposited, he thinks it probable that the purpurate may be generated by the re-action of the uric and ni- tric acids on each other in the urinary passages. Formic acid.—The acid extracted from ants was for some time suspected, chiefly on the authority of Fourcroy and Vau- quelin, to be a mixture of the acetic and malic acids; but the experiments of Suersen, Gehlen, Berzelius, and Dobereiner, ap- pear to leave no doubt of its being a distinct compound. In volatility and odour it does, indeed, resemble the acetic acid; but in composition it is entirely different. According to the analysis of the formate of lead by Berzelius, the atomic weight of formic acid is inferred to be 37 ; and it is composed of carbon 12 parts or two equivalents, hydrogen one or one equivalent, and 24 parts or three equivalents of oxygen. It hence differs from oxalic acid only in containing one equivalent of hydrogen. Ac- cording to Dobereiner, it is resolved into carbonic oxide and wa- ter by the action of strong sulphuric acid. The same ingenious chemist has succeeded in preparing formic acid artificially, by applying a gentle heat to a mixture of tartaric acid, water, and peroxide of manganese. The tartaric acid is converted into water, carbonic acid, and formic acid. Lactic acid.—The existence of this acid, though described by Berzelius, and found by him in sour milk and in many animal ANIMAL ACIDS. 545 fluids, was never demonstrated in a satisfactory manner. Ber- zelius himself now admits it to be acetic acid disguised by ani- mal matter, an opinion which is confirmed by Tiedemann and Gmelin, in their experimental essay on digestion. The Amniotic is a weak acid which was discovered by Buniva and Vauquelin, in the liquor of the amnios of the cow, from which it is deposited, by gentle evaporation, in the form of white acicular crystals. It is very sparingly soluble in water, but yields with the alkalies soluble compounds, which are decomposed by most of the acids. Several other animal acids, such as the stearic, oleic, marga- ric, and others, should also be mentioned here; but as they are closely allied to the fatty principles from which they are deriv- ed, they will be more conveniently described in the following section. SECTION III. Oleaginous Substances. Animal Oils and Fats. The fatty principles derived from the bodies of animals are very analogous in composition and properties to the vegetable fixed oils ; and in Britain, where the latter are comparatively ex- pensive, the former are employed, both for the purposes of giving light, and for the manufacture of soap. Their ultimate elements are carbon, hydrogen, and oxygen; and most of them, like the fixed oils, consist of stearine and elaine. From a curious experiment of Berard, it appears that a sub- stance very analogous to fat may be made artificially. On mix- ing together one measure of carbonic acid, ten measures of car- buretted hydrogen, and twenty of hydrogen, and transmitting the mixture through a red-hot tube, several white crystals were ob- tained, which were insoluble in water, soluble in alcohol, and fusible by heat into an oily fluid. Dobereiner prepared an analogous substance from a mixture of coal gas and aqueous vapour. Train Oil.—Train oil is obtained by means of heat from the blubber of the whale, and is employed extensively in making oil gas, and for burning in common lamps. It is generally of a red- dish or yellow colour, emits a strong unpleasant odour, and has a considerable degree of viscidity, properties which render it unfit for being burned in argand lamps, and which are owing partly to the heat employed in its extraction, and partly to the presence of impurities. By purification, indeed, it may be ren- 546 ANIMAL OILS AND FATS. dered more limpid, and its odour less offensive; but it is always inferior to spermaceti oil. Spermaceti Oil is obtained from an oj COPPER . Protomuriate Yellow-brown Ditto Pernitrate Grass-green LEAD Nitrate Dingy yellow ANTIMONY Tartrate of antimony and , potassa Straw colour BISMUTH Tartrate of bismuth and . potassa Yellow and copious COBALT . Muriate 0 URANIUM Sulphate Bluish black TITANIUM Acid muriate Brown Ditto Neutral sulphate Blood red CERIUM . Yellowish TELLURIUM . Yellow ARSENIC . White oxide Little change Ditto Arsenic acid 0 MOLYBDENUM . Brown NICKEL . Sulphate Green MERCURY Acid protonitrate Yellow Ditto Acid pernitrate Yellow Ditto Corrosive sublimate 0 OSMIUM . Aqueous solution of oxide Purple becoming blue RHODIUM PALLADIUM . SILVER . Nitrate Curdy and brown after some time GOLD Muriate Deep brown Brownish green PLATINUM Muriate 4 G ( 602 ) The following table shows the colours of the precipitates occasioned by solution of ferrocyanate of potassa, in different metallic solutions : METAL. SOLUTION. PRECIPITATE. MANGANESE Neutral protomuriate White IRON Neutral protosulphate White or pale blue Ditto Permuriate Prussian blue* ZINC Muriate Yellowish white TIN Acid protomuriate White, then yellow and bluish Ditto Acid permuriate Pale yellow CADMIUM Muriate COPPER Protomuriate Lilac Ditto Pernitrate Deep brown LEAD Nitrate White ANTIMONY Tartrate of antimony and potassa 0 BISMUTH . Tartrate of bismuth and potassa 0 COBALT . Muriate Pale green URANIUM . Sulphate Deep brown TITANIUM Acid muriate Deep blue (from acid) Ditto Neutral sulphate Sap green CERIUM . TELLURIUM ARSENIC . White oxide Ditto Arsenic acid NICKEL Sulphate Grey MERCURY . Acid nitrate Greenish white Ditto Acid pernitrate Ditto Ditto Corrosive sublimate White RHODIUM PALLADIUM SILVER Nitrate Cream colour GOLD Muriate 0 PLATINUM Nitrate 1 Yellow * We may here also mention a test for the presence of hydrocyanic acid, originally noticed by Scheele : it is the following. To the liquid supposed to contain hydrocyanic acid, add a solution of green vitriol, throw down the pro- toxide of iron by a slight excess of pure potassa, and after exposure to the air for four or five minutes, acidulate with muriatic or sulphuric acid, so as to re- dissolve the precipitate. Prussian blue will then make its appearance if prussic acid had been originally present. As hydrocyanic acid is sometimes administered with criminal designs, the chemist may be called on to search for its presence in the stomach after death. This subject has been investigated experimentally by MM. Leuvet and Las- saigne, and the process they have recommended is the following. The sto- mach or other substances to be examined are cut into small fragments, and in- troduced into a retort along with water ; the mixture being slightly acidulated with sulphuric acid. The distillation is then conducted at a temperature of 212° F., the volatile products collected in a receiver surrounded with ice, and the presence of hydrocyanic acid in the distilled matter, tested by the method above mentioned. These gentlemen found, that prussic acid may be thus de- tected two or three days after death ; but not after a longer period. The dis- appearance of the acid appears owing partly to its volatility, and partly to the facility with which it undergoes spontaneous decomposition. ( 603 ) TABLE, Showing the Proportions in Volumes of several Compounds whose Elements are gaseous. Name. Proportions in -volumes. Resulting Volumes. Air, atmospheric -Alcohol, vapour -Ammonia -Aqueous vapour (steam) Carbonic oxide gas i acid do. j Do. do. -1 Carbureted hydrogen gas Carbonate sub- of ammonia, -j bi- of do. sesqui-of do. Chlorine, protoxide of, gas -peroxide of, do. Chloric acid vapour ether do. -Chlorocarbonic acid gas Chlorocyanic acid vapour Cyanogen gas Ether, muriatic, vapour sulphuric do. Fluoborateof ammonia sub- of do. -Hydriodic acid gas Hydrocyanic acid vapour -Iodic acid -Muriatic acid gas -Muriate of ammonia -Nitric acid vapour Nitrous acid do, -Hyponitrous do. -Nitrous gas- - -oxide gas -Olefiant gas - - - -Phosphureted hydrogen gas -Biphosphureted do. Sulphureted hydrogen gas -Sulphurous acid do. Sulphuric acid vapour -Sulphuret of carbon vapour - 4 Nitrogen -f-1 oxygen -1 Olefiant gas 4- 1 aq. vapour 3 Hydrogen -{-1 nitrogen 2 Hydrogen 4-1 oxygen 1 Vapour of carbon 4* 4 oxygen 1 Ditto -4- 1 do. 1 Carbonic oxide -f- 4 oxygen 2 Hydrogen -f-1 carbon -1 Carbonic acid -J- 2 ammonia. 1 Ditto-4-1 do. -1 Ditto 4- 14 do. -1 Oxygen-{-2 chlorine -2 Ditto + 1 do. -14Ditto-f-ldo. -1 Olefiant gas -f-1 chlorine -1 Carbonic oxide -f-1 do. 1 Cyanogen -f-1 chlorine 1 Nitrogen -j- 2 carbon -1 Muriatic acid gas -f- 2 alcoh. 2 Olefiant gas -j- 1 aq. vapour 1 Fluoboric acid + 1 ammon. 1 Ditto+ 2 do. -1 Hydrogen -4- 1 iodine -1 Cyanogen -f-1 hydrogen -14 Oxygen -{-1 iodine -1 Hydrogen + 1 chlorine 1 Muriatic acid -f- 1 ammonia 1 Nitrogen + 24 oxygen 1 Ditto 2 do. -1 Ditto + 14 do. - - -1 Ditto 4-1 do. lDitto-|-4do. 2 Carbon 4- 2 hydrogen 2 Hydrogen -{-1 phosphuret -1 Ditto 4- 1 do. 1 Sulphur -|- 1 hydrogen 1 Ditto -f- 1 oxygen 2 Sulphurous* acid + 1 oxygen 1 Carbon + 2 sulphur - 5 1 2 2 1 1 1 1 solid ditto ditto 24' 2 1 1 . 2 1 2 1 solid ditto 2 2 2 solid 2 2 ( 604 ) TABLE of Chemical Equivalents, Atomic Heights, or Propor- tional Numbers, Hydrogen being taken as Unity. From the full account already given of the Laws of Combina- tion and ofthe Atomic Theory, it will be superfluous to describe the uses ofthe following table. The only explanation required on this subject, relates to the ingenious contrivance of Dr.'Wol- laston, called the Scale of Chemical Equivalents. This useful in- strument is a table of atomic weights, comprehending all those substances which are most frequently employed by chemists in the laboratory; and it only differs from other tabular arrange- ments of the same kind, in the numbers being attached to a sliding rule, which is divided according to the principle of that of Gun- ter. From the mathematical construction of the scale, it not only serves the same purpose as other tables of atomic weights, but in many instances supersedes the necessity of calculation. Thus, by inspecting the common table of atomic weights, we learn that 88 parts or one equivalent of sulphate of potassa, contain 40 parts of sulphuric acid and 48 of potassa; but recourse must be had to calculation, when it is wished to determine the quantity of acid or alkali in any other quantity of the salt. This knowledge, on the contrary, is obtained directly by means of the scale of chemical equivalents. For example, on pushing up the slide un- til 100 marked upon it is in a line with the name sulphate of po- tassa on the fixed part of the scale, the numbers opposite to the terms sulphuric acid and potassa, will give the precise quanti- ty of each contained in 100 parts ofthe compound. In the fol- lowing table the equivalents of phosphorus and its compounds, and those of a few other substances are given in the precise num- bers derived from the most recent and accurate analyses j they will be found to differ in some instances from those given in the body of the work. d acetic, 50 c. 1. w.* 59 arsenic, (a. 38 -f- o. 20 b.) .12 b.) 58 arsenious, (a 38 4-0 50 benzoic, 120 boracic, (b. 8 + o. 16 24 c. 2 w. 42 bromic, (b. 75 -\- o. 40) 115 carbonic, (c. 6 4" °- 16) ■ 22 chloric, (chl. 36 4" o. 40) 76 chloriodic, (chl. 72-f-iod. 124)196 chloro-carbonic, (chl. 36 -f" carb. o. 14) 50 Acid, chlorocyanic (chl. 36 -f- cyan. 26; 62 chromic, (chr. 28 4~ o. 24) 52 citric, 58 c. 2 w. 76 columbic, 152 fluoboric, 68 ? hydro-fluoric, 19.86 formic, 37 fluosilicic, 26.86? gallic ? 62 hydriodic, iod. 124+hyd. 1) 125 hydrobom. (b. 75 -f h. 1) 76? * C means crystallized, w, water ; and the numeral before w, expresses the number of equivalents of water which the crystals contain. CHEMICAL EQUIVALENTS. 605 Acid, hydrocyanic, (cyan. 26 4" hyd. 1) 27 hyposulphurous, (s. 32 4" o. 8) 40 hyposulphuric, (s. 32 4" o. 40) 72 iodic, (iod. 124 4. o. 40) 164 malic, 70 manganeseous? 52 manganesic? 60 molybdouSj 64 molybdic, 72 muriatic,(chl. 36 4- hyd. 1) 37 nitric, dry (nit. 14 + o. 40) 54 -----liquid (sp. gr. 1. 5) 2 w. 72 nitrous (nit. 14 4- o. 32) 46 oxalic, 36 c. 4. w. 72 perchloric, (chl. 36 4- o. 56) 92 phosphorous, (p. 15.71 4" 12) 27.71 phosphoric, (p. 15,71 4* 20; 35.71 saccholactic, 104 selenious, (sel. 40 + o. 16) 56 selenic, (s. 40 4~ o. 24) 64 succinic, 50 sulphuric, dry (s. 16-f-o. 24) 40 liquid, sp. gr. 1.4838, 1 w. 49 sulphurous, (s. 16 4- o. 16) 32 tartaric, 66 c. 1 w. 75 titanic, 48 tungstic, (t. 96 -f o. 24) 120 uric, 72 Alcohol, (ole. gas 14 4- a9r vap. 9) 23 alum, anhydrous, 262 4-c. 25 w. 487 Alumina, 18 sulphate, 58- Aluminum, 10 Ammonia, (nit. 14 4- hyd. 3) 17 Antimony, 44 chloride, (ant, 44 4- chl. 34) 80 iodide, (ant. 44 -f- iod. 124) 168 oxide, (ant. 44 -+- o. 8) 52 deutoxide, 56 peroxide, 60 sulphuret, 60 Arsenic, 38 sulphuret, (realgar) 54 ♦sesquisulphuret (orpi- ment) 62 persulphuret, 78 Barium, 70 chloride (b. 70 4- chl. 36) 106 iodide, (b. 70 4- iod. 124) 194 Barium, oxide, (baryta) 78 peroxide? 86 phosphuret, 85.71 sulphuret, 86 Bismuth, 72 chloride, (b. 72 4-chl. 36) 108 Bismuth, oxide, 80 iodide, (b. 72 + iod. 124) 196 phosphuret, (b. 72+p 15.71)87.71 sulphuret, (b. 72 4" s. 16) 88 Boron, 8 Bromine, 75} Cadmium, 56 chloride, (cad. 56 4- chl. 36) 92 oxide, 64 iodide, 144 phosphuret, 71.71 sulphuret, 72 Calcium, 20 chloride, (cal. 20-f- chl. 36) 56 iodide, 144 oxide, (lime) 28 phosphuret, 35.71 sulphuret, 36 Carbon, 6 bisulphuret, (c. 6+s. 32) 38 chloride, - 42 perchloride, 120 ■ oxide, 14 phosphuret, 21.71 Cerium, 50 oxide, 58 peroxide, 62 Chlorine, 36 hydrocarburet, (chl. 36 4- ole£ gas 14) 50 oxide, (chl. 36 + o. 8) 44 peroxide, 68 Chromium, 32 oxide, 40 Cobalt, 26 chloride, (cob. 26 4- chl. 36) 62 iodide, 150 oxide, 34 peroxide, 38 phosphuret, 41.71 sulphuret, 42 Columbium, 144 Copper, 64 chloride, (cop. 64 4- chl. 36) 100 bi-chloride, (c. 64 4~ chl. 72) 136 iodide, (c. 64 4-iod. 124) 188 oxide, (c. 64 4- o. 8) 72 peroxide, (c. 64+ 0. 16) 80 phosphuret, 79.71 sulphuret, 80 bisulphuret, 96 Copper, (Thomson) 32 Cyanogen, (carb. 12 4- nit. 14) 26 Cyanuret of sulphur, (cy. -f- 26 s. 32) 58 * 1 Proportion of arsenic, and 14 sulphur. 606 CHEMICAL EQUIVALENTS. Ether, (olef. gas 28 4- wat vap. 9) 37 Fluorine, 18.86 Glucinium, 18 Glueina, 26 Gold, 200 chloride, (g. 200 4- chl. 36) 236 bichloride, (g. 200 4- chl. 72) 272 iodide, (g. 200 4-iod. 124 324 oxide, (g. 200 4- o. 8) 208 peroxide, (g. 200 + o. 24) 224 sulphuret, (g. 200 4- s. 48) 248 Hydrogen, 1 arseniuretted, (a. 38 4- h. 1) 39 carburetted. (c. 6 4- h. 2) 8 olefiant gas, (c. 12 4~ h. 2) 14 seleniuretted, (s. 40 4" h. 1) 41 sulphuretted, (s. 16 4- h. 1) 17 bisulphuretted, (s. 32 4- h. 1) 33 Iodine, 124 Iridium, 30 Iron, 28 chloride, (I. 28 + chl. 36) 64 perchloride, (I. 28 + chl. 54) 82 iodide, (1. 28 4- iod. 124) 152 oxide, (I. 28 4- o. 8) 36 peroxide, (I. 28 4- o. 12) 40 sulphuret, (I. 28 4- s. 16) 44 bisulphuret, (I. 28 4- s. 32) 60 Lead, 104 chloride, (1. 104 4- chl. 36) 140 oxide, (1. 104 4-O. 8) 112 deutoxide, (1. 104 4-O. 12) 116 peroxide, (1. 104 4- 0. 16) 120 phosphuret, (1. 1044-p. 15.71 119.71 sulphuret, (1. 104 + s. 16) 120 Lithium, 10 chloride, (1. 10 4- ch. 36) 46 iodide, 134 oxide, (lithia) 18 sulphuret, 26 Magnesium, 12 chloride, (tn. 12 4- chl. 36) 48 oxide, 20 sulphuret, 28 Manganese, 28 chloride, (m. 28 4~ chl. 36) 64 perchloride, (m. 28 4/- chl. 144) 172 oxide, (m. 28 4- o. 8) 36 deutoxide, (m. 28 -\- o. 12) 40 peroxide, (m. 28 4-o. 16) 44 sulphuret, 44 Mercury, 200 chloride, (calomel) m. 200 4- chl. 36) 236 bichloride, (corrosive subl.) 272 iodide, (m. 200 4- iod. 124) 324 biniodide, (m. 200 4- iod. 244) 448 Mercury, oxide, (m. 200 4-0. 8) 208 peroxide, (m. 200 4- o. 16) 216 sulphuret, 216 bisulphuret, 232 Molybdenum, 48 oxide, (m 48 4-0. 8) 56 deutoxide, (m. 48 4-0. 16) 64 Molybdic acid, (m. 48 -f <>• 24) 72 Nickel, 26 chloride, (m. 26 4- chl. 36) 62 iodide, 150 oxide, (n. 26 4-0. 8) 34 peroxide, (n. 26 4- h, 12) 38 phosphuret 41.71 sulphuret, 42 Nitrogen, 14 bicarburet, (cvanogen) 26 chloride, (n. 14 4- chl. 144) 158 iodide, (n. 14 4- iod. 372) 386 oxide, (n. 14 4-0.8) 22 deutoxide, 30 Oxygen, 8 Palladium, 50 oxide, 64 Phosphorus, 15.71 chloride, 51.71 bichloride, 87.71 carburet, 21.71 sulphuret, 31.71 Platinum, 96 chloride, 132 bichloride, 168 oxide, 104 deutoxide, 112 sulphuret, 112 bisulphuret, 128 Potassium, 40 chloride, 76 iodide, 164 oxide, (potassa) 48 peroxide, (p. 40 4~ °> 24) 64 phosphuret, 55.71 sulphuret, 56 Rhodium, 44 oxide, 52 peroxide, 60 Selenium, 40 Silica, 16 Silicon, 8 Silver, 110 chloride, 146 iodide, 234 oxide, 118 phosphuret, 125.71 sulphuret, 126 Sodium, 24 chloride, 60 iodide, 148 oxide, (soda) 32 peroxide, (s. 244-0. 12) 36 phosphuret, 39.71 sulphuret, 40 CHEMICAL EQUIVALENTS. 607 Strontium, 44 chloride, 80 9 iodide, 140 oxide, (strontia) 52 phosphuret, 59.71 sulphuret, 60 Sulphur, 16 chloride, 52 iodide, 140 phosphuret, 31.71 Sulphuretted hydrogen, 17 Bisulphuretted hydrogen, 33 Tellurium, (Berzelius) 32 chloride, 68 oxide, 40 Tin, 58 chloride, 94 bichloride, 130 oxide, 66 deutoxide, 74 phosphuret, 73.71 sulphuret, 74 bisulphuret, 90 Titanium, 32 oxide, 40 Titanic acid, 48 Tungsten, 96 oxide, (brown,) (t. 96 4- 0. 16) 112 Tungstic acid, (t. 96 4- o. 24) 120 Uranium, 208 oxide, 216 peroxide, 224 Water, 9 Yttrium, 34 Oxide, (Yttria) 42 Zinc, 34 chloride, 70 oxide, 42 phosphuret, 49.71 sulphuret, 50 Zirconion, • 40 Zirconia, 48 Salts. Acetate of alumina, (Ac. 50 4- Al. 18) 68 c. 1 w. 77 ammonia, (Ac. 504- Am« 170 67 c. 7 w. 130 baryta, (Ac. 50 4- B. 78)] ■ 128 c. 3 w. 155 cadmium, (c. 2 w.) 132 copper per-oxide, (Ac. 50 4- C.80) 130 c. 6 w. com. verdigris, 184 binacetate, 180 c. 3 w. distilled verdigris, 207 subacetate, (Ac. 50 + C. 160) 210 lead, 162 c. 3 w. 189 lime, 78 magnesia, 70 Acetate,mercury,(protox.) c. 4w. 294 potassa, 98 silver, 168 strontia, c. 1 w. Ill zinc, 92 o» 7 w. 155 Arseniate of lead, (A 58 4- L. 112) 170 lime, 86 magnesia, 78 potassa, 106 Binarseniate of potassa, c. w. 170 Arseniate of soda, 90 Binarseniate of soda, c. w. 157 Arseniate of strontia, 110 silver, 176 Arsenite of lime, 78 potassa, 98 Arsenite of soda, 82 silver, 168 Carbonate of ammonia, 39 Susquicarbonate of ammonia, (Carb. a. 33 4- A. 17 4- w. 9.) 59 Bicarbonate of do. 1 w. 70 Carbonate of baryta, 100 copper, 102 iron, (protoxide) 58 lead, 134 lime, 50 magnesia, 42 manganese, 58 potassa, 70 Bicarbonate of potassa, 92 c. 1. w. 101 Carbonate of soda, 54 c. 10 w. 144 Bicarbonate of soda, c. 1 w. 85 Carbonate of strontia, 74 zinc, 64 Chlorate of baryta, 154 lead, 188 mercury, 284 potassa, 124 Chromate of baryta, 130 lead, 164 mercury, 260 potassa, 100 Bichromate of potassa, 152 Muriate of ammonia, 54 baryta, c. 1 w. 124 lime, c. 6 w. 119 magnesia, 57 strontia, c. 8 w. 161 Nitrate of ammonia, 71 baryta, 132 bismuth, c, 3 w. 161 lead, 166 lime, 82 magnesia, 74 mercury protoxide, c. 2 w. 280 potassa, 102 silver, 172 608 CHEMICAL EQUIVALENTS. Nitrate of soda, 86 Bisulphate of copper, 160 strontia, 106 c. 10 w. (blue vitriol) 250 Oxalate of ammonia, 53 Sulphate of iron, (protoxide) I6 139 c. 2w. 71 c. 7 w. (green vitriol) baryta, 114 lead, 152 Binoxalate of baryta, • 150 lime, 68 Oxalate of cobalt, 70 c. 2 w. 86 lime, 64 lithia, c. 1 w. 67 nickel, 70 magnesia, c. 7 w. 123 potassa, 84 mercury, (S. a. 404/ perox. c. 1 w. 93 216) 256 Binoxalate of potassa, 120 Bisulphate of mercury, (per- c. 2 w. 138 oxide) 296 Quadroxalate of potassa, 192 potassa 88 c 7 w. 255 Bisulphate of potassa, c. 2 w. 146 Oxalate of strontia, 88 Sulphate of soda, 72 Binoxalate of strontia, 124 c. 10 w. 162 Phosphate of ammonia, c. 2 w. 70.71 strontia, 92 baryta, 113.71 zinc, 82 lead, 147.71 c. 7 w. 145 lime, 63.71 Sulphate of alumina and potassa, 262 magnesia, 55.71 c. 25 w. (alum) 487 soda, 67.71 Nitrate of lead, 178 c. 12£w. 180.21 lime, 94 Sulphate of alumina, 58 potassa, 88 ammonia, c. 1 w. 66 Bitartrate of potassa, 180 baryta, 118 c. 2 w. (cream of tartar) 198 Sulphate of copper, (S. a. 40 Tartrate of antimony and po- 4- perox. 80) 120 tassa, c. 3 w. (tartar emetic) 363 INDEX. A Acetates, 455 Acidifying principles, 137 Acids, definition of, 137 acetic & acetous,454 vegetable, 454 animal, 541 amniotic, 545 antimonic and anti- monious, 260 arsenic, 208 arsenious, 205 auric, 283 benzoic, 467 boletic, 472 boracic, 168 bromic, 407 butyric, capric, ca- proic, 548 camphoric, 471 carbazotic, 472 carbonic, 146 caseic, 514 chloric, 353 chloriodic, 402 chloro-cyanic, 361 . chloro-carbonic, 361 chloro-chromic, 373 cholesteric, 549 chromic, 263 citric, 465 columbic, 276 cyanic, 150 ellagic, 469 erythric, 544 ferro-cyanic, 297 fluoboric, 419 fluo-chromic, 423 fluoric, 418 fluo-silicic, 421 formic, 547 fulminic, 151 gallic, 469 hircic, 548 hydriodic, 396 hydro-bromic, 407 hydro-chloric, 355 hydro-cyanic, 152 hydro-fluoric, 416 hydro-selenic, 201 hydro-xanthic, 193 hypo-nitrous, 116 hypophosphorus, 176 hypo-sulphuric, 188 hypo-sulphurous,187 igasuric, 472 iodic, 394 Acids, iodous, 393 kinic, 472 lactic, 544 lampic, 496 lithic, 542 malic, 466 manganesic, and manganeseous,270 margaric, 484 8c 546 meconic, 476 mellitic, 472 molybdic and molyb- dous, 272 moroxylicr 471 mucic, 471 muriatic, 355 nitric, 119 nitro-muriatic, 358 nitrous, 116 oelic, 484 and 547 oxalic, 458 oxymuriatic, 347 perchloric, 353 phocenic, 548 phosphatic, 177 phosphoric, 177 phosphorous, 176 prussic, 152 purpuric, 543 pyro-citric, 466 pyroligneous, 454 pyromalic, 467 pyromucic, 471 pyro-tartaric, 462 pyro-uric, 543 rheumic, 471 rosacic, 544 saccholactic, 471 sebacic, 547 selenic, 199 selenious, 199 selenio-cyanic, 202 silicic, 172 silico-fluoric, 421 sorbic, 471 stearic, 547 suberic, 472 succinic, 470 sulpho-naphthalic, 163 sulphuric, 185 sulphurous, 183 sulphuretted chya- zic, 193 sulpho-cyanic, 193 sulpho-vinic, 495 tartaric, 461 Acids, titanic, 278 tungstic, 274 uric, 542 zumic, 472 Adipocire, 549 Affinity, chemical, 27 of aggregation, 14 elective simple, 29 elective double, 29 disposing, 127 Alabaster, 253 Albumen, 535 vegetable, 516 incipient, 569 Alcoates, 492 Alcohol, 490 Algaroth, powder of, 259 Alkali, volatile, 130 Alkalies, definition of, 138 native vegetable, 473 decomposition of, by galvanism, 226 Alloys, 224 Althea, 482 Alum, 341 Alumina, 338 acetate of, 456 nitrate, 341 sulphates, 341 Aluminum, 336 arsenuret, 340 chloride, 382 oxide, 337 phosphuret, 340 selenuret, 340 sulphuret, 340 telluriet, 340 Amalgams, 224 Amber, and its acid, 487 Ambergris, and ambre- ine, 550 Ammonia, 130 acetate of, 455 antimoniate, 262 arseniate, 213 arsenite, 213 aurate, 283 borate, 170 carbonates, 165 chlorate, 383 cyanate, 167 ferrocyanate, 299 hydriodate, 404 hydrobromate, 415 hydrocyanate, 167 hydrofluate, 425 hydrosulphate, 196 610 INDEX. Ammonia, hypophos- phate, 180 hypophosphite, 180 iodate, 403 molybdate, 273 muriate, 385 nitrate, 135 oxalate, 460 phosphate, 180 phosphite, 180 purpuriate, 343 sulphate, 195 sulphite, 195 sulphocyanate, 197 tellurate, 204 tungstate, 275 Amnios, liquor of, 573 Amidine, 504 Analogies between ele- mentary substan- ces, 343 Analysis defined, 11 Analysis, proximate and ultimate of organ- ic substances, 451 of minerals, 591 of gases, 588 of mineral waters,596 Animal chemistry, 533 proximate princi- ples, 533 substances, analysis of, 452 heat, 561 fluids, 563 Antimony, 258 alloy of, 289 bromide, 413 chlorides, 373 hydrosulphate, 261 hyponitrite, 262 iodide, 401 muriate, 387 oxides, 259 phosphate, 262 sulphates, 262 tartrate, 464 Anthracite, 501 Aqua regia, 358 Arbor Dianx, 334 Saturni, 289 Archil, 510 Argentine flowers of an- timony, 258 Arrow root, 506 Arseniates, 213 Arsenical solution, 235 Arsenic, 204 alloys of, 308 bromide, 411 chloride, 365 iodide, 400 muriate, 386 oxide, 205 phosphuret, 209 Arsenic, sulphuret, 209 Arsenites, 214 Asparagin, 516 Asphaltum, 499 Atmospheric air, 107 analysis of, 108 weight of, 107 Atomic theory, Dalton's view of, 430 Berzelius's view of, 440 Attraction, chemical, 27 cohesive, 14 terrestrial or gravi- ty, 12 Aurum, musivum, 224 Azotic gas. See nitrogen. B Balloons, 123 Balsams, 487 Barilla, 238 Barium, 242 chloride of, 371 iodide, 401 oxides, 243 phosphuret, 245 sulphuret, 245 Baryta, 243 acetate of, 456 arseniate, 247 aurate, 283 borate, 246 carbonate, 245 chlorate, 384 ferrocyanate, 300 hydrobromate, 415 hydriodate, 405 hydrosulphate, 246 hypophosphite, 246 hyposulphite, 246 iodate, 404 muriate, 386 nitrate, 245 phosphate, 246 phosphite, 246 seleniate, 247 silicate, 246 sulphate, 246 sulphite, 246 Barley, malting of, 528 Barometer, correc- tion of for the ef- fects of heat, 43 Basis, in dyeing, what, 509 Bassorin, 516 Battley's sedative liquor, 475 Bell metal, 308 Benzoates, 468 Bile 8c biliary calculi, 560 Bismuth, 331 alloys of, 332 Bismuth, bromide, 414 chloride, 382 iodide, 402 nitrate, 332 oxides, 331 sulphate 332 sulphuret, 332 Bitter principle, 518 Bituminous substances, 498 Black drop, 477 Black lead, 294 Bleaching, 350 Bleaching powder, 372 Blende, 326 Blood,551 Blow-pipe, with oxygen and hydrogen, 125 with oxygen gas, 125 Blue, Prussian, 300 Saxon, 510 Boiling point of liquids,61 Bones, 584 Borates, 170 Borax, 239 Boracite, 239 Boron, 168 chloride of, 364 sulphuret, 194 Brain, analysis of the 586 Brass, 329 " Bromates, 414 Bromine, 406 chloride of, 415 cyanide, 409 hydrocarburet, 410 iodides, 415 Bronze, 308 Brucia, 480 Butyrine, 548 Butter, 570 ------of antimony, 373 ------of zine, 381 C. Cadmium, 329- alloys of, 331 carbonate, 331 chloride, 382 nitrate, 331 oxide, 330 phosphate, 331 phosphuret, 330 sulphate, 331 sulphuret, 330 Caffein, 516 Calcium, 249 bromide of, 411 chloride, 371 fluoride, 426 iodide, 401 oxides, 250 phosphuret, 251 sulphuret, 251 Calcination, 220 INDEX, 611 Calculi, urinary, 580 biliary, 568 Calomel, 380 Caloric, 32 communication of, 34 radiation of, 37 effects of, 41 expansion produced by, in solids, 42 in liquids, 42 in gases, 45 specific, 51, 52 capacities of bodies lor, 51 of fluidity, 54 sensible and insensi- ble, 52 latent, 52 sources of, 32 quantity of, in bo- dies, 59 Calx, 220 Camphor, 485 Camphorates, 471 Cannon metal, 308 Canton's phosphorus, 73 Caoutchouc, 488 Carbon, 142 bromide of, 409 chlorides, 359 iodide, 398 oxide, 145 phosphuret, 180 sulphuret, 192 Carbonates, general pro- perties of, 166 Carbonic oxide, 145 Carbo-sulphurets, 193 Carburetted hydrogen, 155 Carmine, 510 Cartilage, 585 Caseous matter, 570 Caseous oxide, 514 Cassius, purple powder of, 376 Cathartin, 517 Cerate, 489 Cerin, 489 Ceriam, 314 carbonate of, 315 carburet, 315 chloride, 380 muriate, 389, nitrate, 315 oxides, 314 sulphates, 305 sulphuret, 315 Cerulin, 510 Ceruse, 288 Cetine, 549 Chalk, 252 Chameleon mineral, 270 Charcoal, 142 Charcoal, animal, or ivory black, 142 Cheese, 570 Chemical affinity or at- traction, 27 action, changes which accompany it, 27 Chemistry, object of, 9 organic, 499 Classification of chemical substances, 100 Chlorates, general cha- racters of, 383 Chlorides, metallic, 366 Chlorine, 347 cyanide of, 361 hydrocarburet, 363 nature of, 389 oxides, 351 Cholesterine, 549 Chromium, 262 chloride, 373 muriate, 388 oxide, 263 Chromates, 265 Cinchonia, 477 Chyle, 569 Cinnabar, 312 Citrates, 466 Coke, 500 Coal, 499 Cobalt, 318 arseniate of, 320 borate, 319 carbonate, 319 chloride, 381 nitrate, 319 oxides, 318 phosphate, 319 phosphuret, 319 . sulphate, 319 sulphuret, 319 Cochineal, 510 Cold, artificial methods of producing, 56 Colocyntin, 518 Colouring matter, 508 Colours, adjective and substantive, 509 Columbium, and its acid, 275 sulphuret of, 277 Combination defined, 27 laws of, 111 and 133 Combining proportions defined,133 Combustion, 104 theories of, 104 spontaneous, 483 Composition of bodies, how determined, 11 Conductors of caloric, 34 Congelation, 54 . Copal, 487 Coppernickel, 320 Copper, 302 acetates of, 457 alloys, 308 ammoniuret, 305 arseniate, 307 arsenite, 307 borate, 306 carbonate, 306 chlorate, 384 chloride, 377 hyposulphite, 307 iodide, 402 muriates, 388 nitrate, 305 oxides, 303 phosphate, 306 phosphuret, 304 silicate, 306 sulphate, 306 sulphite, 307 tests, 309 Cork, 517 Corrosive sublimate, 378 Corydalin, 481 Coumarin, 486 Cream of tartar, 464 Crocus of antimony, 261 Cryophorus, 65 Crystallization, 15 water of, 140 Curcuma paper, 511 Cuticle, 585 Cyanides, 149 Cyanogen, 149 Cynopia, 482 D. Decomposition, simple, 28; double, 29 Decrepitation, 140 Deflagration, 220 Deliquescence, 139 Delphia, 482 Derosne. salt of, 477 Destructive distillation, 451 Detonating powders, 384 Diamond, 144 Dutch gold, 329 Dyes, 509 E. Ebullition, 60 Efflorescence, 140 Egg shells, 585 Eggs, 572 Elaine, 484 8c 546 Electricity, 74 Electrical machine, 79 Electro-magnetism, 98 Electro-negative, and electro-positive bo- dies, 78 Electro-chemical the- ory, 90 612 INDEX. Electrometer, 82 Elements, what, 11 Emetia, 481 Emetic, tartar, 464 Epsom salts, 256 Equivalent, chemical, what, 133 Erythrogen, 568 Essential salt of lemons, 460 Ether, 493 acetic, muriatic, hy- driodic, 497 8c 498 chloric, 363 nitrous, 496 pyro-acetic, 455 sulphuric, 493 Ethiops mineral, 312 per se, 309 Euchlorine, 351 Eudiometer, 109 Hope's, 589 Volta's, 588 Evaporation, 63 cause of, 65 Extractive matter, 518 Eye, humours of, 573 F. Farina, (see Starch ) Fat of animals, 545 Feathers, 545 Fecula, 504 Fermentation, 519 acetous, 523 putrefactive, 525 saccharine, 519 vinous, 520 Ferro-cyanates, 299 Fibrin, 534 Fire-damp of coal mines, 157 Flame, 157 Flesh of animals, 585 Flint, 172 Flowers of sulphur, 182 Fluorine, 416 Fluor spar, 426 Flux, white 8c black, 464 Freezing mixtures,57, 58 in vacuo, Leslie's method, 64 Fulminating gold, 283 mercury, 151 silver, 151 Fulminic acid, 151 Fungjn, 517 Fusion, 54 watery, 140 Fusible metal, 332 Fustic, 511 G. Galena, 287 Gallates, 470 Gall-stones, 568 Galvanic battery or trough, 87 arrangements, 88 Galvanism, 15 effects of, 89 chemical agency of, 89 electrical agency of, 19 connection of with magnetism, 98 theories of its pro- duction, 92 Gases, 67 condensation of, 68 law of expansion of, 45 conducting power of, 37 Gases, mode of drying 67 Gas, from coal and oil, 163 Gastric juice, 567 Gelatine, 538 Germination, 526 Gilding, 283 Glass, 173 of antimony, 261 Glauber's salt, 240 Gliadine, 515 Glucinum, 341 bromide of, 414 chloride, 382 iodide, 402 oxide,. 342 phosphuret, 342 selenuret, 342 sulphuret, 342 Glue, 538 Gluten, 514 Glycerine, 484 and 546 Gold, 281 alloys of, 283 bromide, 413 chlorides, 376 iodide, 402 nitrate, 283 oxides, 282 phosphuret, 282 sulphuret, 282 Golden sulphur of anti- mony, 261 Gong, Indian, 308 Graphite, 294 Gravitation, 12 Gravity, absolute, 12 specific, 12 Gum, 506 elastic, 488 Gum-resins, 488 Gun-powder, 231 Gypsum, 253 H Hematin, 511 Hair, 585 Harrowgate water, 598 Hartshorn, spirit of, 130 Heat, intense, how gene- rated, 125 Hircine, 548 Honey, 503 stone, 472 Hordein, 505 Horn and hoof, 585 Horn-lead, 376 Horn-silver, 382 Hydracids, salts of, 167 Hydrates, nature of, 128 Hydriodates, 404 Hydro, in what manner employed, 128 Hydrocyanates, 153 Hydrofluates, 424 Hydroseleniates, 203 Hydrogen, 123 deutoxide, or perox- ide of, 128 arseniuretted, 209 borruretted, 170 carburetted, 155 and carbon, new compounds of, 160 phosphuretted, 178 potassuretted, 230 seleniuretted, 201 stanuretted, 223 sulphuretted, 189 telluretted, 203 Hydro-sulphurets, orhy^ dro-sulphates, 197 Hygrometer, 66 Ice. See water. Imponderables, 31 Incandescence, 72 Indigo, 509 Ink, 470 Inulin, 517 Iodates, 403 Iodides, metallic, 400 Iodine, 392 chloride, 402 cyanide, 399 hydro-carburet, 399 oxide, 394 Ipecacuanha, emetic principle of, 481 Iridium, and its oxides, 325 muriate of, 325 Iron, 290 . alloys of, 301 antimoniate, 297 arseniates, 297 borate, 295 borruret, 294 bromide, 411 carbonate, 295 INDEX. 613 Iron, carburets, 293 chloride, 377 chromate, 297 ferrocyanate, 300 hyposulphite, 296 iodide, 402 molybdate, 297 muriate, 388 nitrate, 295 oxides, 291 phosphates, 296 phosphuret, 294 silicuret, 294 sulphate, 296 sulphite, 296 sulphuret, 294 tests, 302 Isinglass, 538 Ivory black, 142 Jelly, animal, 538 vegetable, 507 K Kermes, mineral, 261 Kelp, 238 King's yellow, 210 Lakes, 509 Lamp without flame, 496 safety, 157 Lamp black, 487 Lateritious sediment, 580 Lead, 284 acetates of, 456 alloys, 289 arseniate, 289 borate, 288 bromide, 413 carbonate, 288 chlorate, 384 chloride, 376 chromates, 289 hyponitrite, 288 hyposulphite, 289 iodide, 402 molybdate, 289 muriate, 388 nitrate, 287 oxides, 285 phosphate, 288 phosphuret, 287 sulphate, 288 sulphite, 288 sulphuret, 287 tests, 289 Lemons, acid of. See citric acid. Leyden jar, 81 Libavius, fuming liquor of, 368 Ligaments, 585 Light. 68 chemical effects of, 71 heating power of, 70 Light,magnetizingpower of, 71 modes of determin- ing its intensity, 73 Lignin, 507 Lime, 249 acetate of, 456 arseitiate, 253 arsenite, <54 borate, 252 borosilicate, 252 carbonate, 252 chlorate, 384 chloride, 372 hydrate, 250 hydriodate, 405 hydrosulphate, 253 hypophosphite, 253 hyposulphite, 253 iodate, 404 muriate, 387 nitrate, 252 oxalate, 461 phosphate, 252 phosphuret, 251 silicate, 252 sulphate, 253 sulphite, 253 sulphuret, 251 tests, 251 Liniment, 489 volatile, 484 Liquefaction, 53 Litharge, 285 Lithia, 24l carbonate of, 242 muriate, 386 phosphate, 242 sulphate, 242 Lithium, 241 chloride of, 371 oxide, 241 sulphuret, 242 Litmus, 510 paper, 596 Liver of antimony, 261 sulphur, (hepar sul- phuris,) 211 Luna cornea, 382 Lunar caustic, 335 Lupulin, 517 Lymph, 573 M Magistery of bismuth, 332 Magnesia, 254 ammonia, nitrate of 255 ammonia phosphate, 256 ammonia, sulphate, 257 arseniate, 257 borate, 256 Magnesia, carbonate, 255 chlorate, 384 hydriodate, 405 hydrobromate, 415 hyposulphite, 257 muriate, 387 nitrate, 255 oxalate, 461 sulphate, 256 sulphite, 257 tests, 254 tungstate, 275 Magnesium, 254 chloride, 373 oxide, 254 Magnetism, 94 Magnetism, electro, 98 Malachite, 306 Malates, 467 Maltha, 499 Malting, 528 Manganese, 266 arseniate of, 272 carbonate, 271 carburet, 271 fluoride, 423 muriate, 388 nitrate, 271 oxides, 266 phosphate, 272 phosphuret, 271 . silicate, 271 sulphate, 272 sulphuret, 271 Manna and mannite, 503 Marble, 252 Massicot, 285 Medullin, 518 Mercury, 3G9 bromides of, 413 acetate, 458 amalgams, 313 arseniate, 313 borate, 313 carbonate, 312 chlorates, 385 chlorides, 354 cyanide, 311 iodides, 402 nitrates, 312 oxides, 310 phosphates, 313 phosphuret, 311 sulphates, 313 sulphurets, 311 tests, 323 and 379 Metallic combinations, 224 Metals, 215 table of discovery of, 215 specific gravity, 216 fusibility of, 218 614 INDEX. Metals, reduction of, 220 combustibility of, 220 Meteoric stones, 322 Milk, 570 Mindererus's spirit, 455 Mineral chameleon, 270 Mineral waters, analysis of 596 Minium, 286 Molybdenum, 272 chloride of, 374 muriate, 388 oxides, 272 phosphuret, 272 sulphuret, 273 Mordaunt, 509 Morphia, 476 acetate of, 476 Mother of pearl, 585 Mucilage, 506 Mucus, 574 Multiples, law of combi- nation in, 111 Muriates, 386 Muscle, 585 converted into fat, 549 Mushrooms,peculiar sub- stance of, 517 Myrica cerifera, wax from, 489 Myricin, 489 N. Nails of animals, 585 Naphtha, 498 from coal tar, 163 , Naphthaline, 163 Narcotine, 477 Neutralization, 32. Nickel, 320 alloys of, 322 arseniate, 322 borate, 322 carbonate, 322 chlorides, 381 nitrate, 322 oxides, 321 phosphate, 322 sulphate, 322 sulphuret, 322 tests, 323 Nitrates, general cha- racter of, 142 Nitre, 231 Nitric oxide, 113 Nitrogen gas, 106 carburet of, 149 chloride, 354 iodide, 395 oxides, 112 Nitrous gas, 113 oxide, 112 Nomenclature, 112 and 136 O. Oil, Dippel's animal, 545 of vitriol. See acid sulphuric. gas, 163 Oils, animal, 545 fixed,482 volatile, or essential, 4S4 Olefiant gas, 158 Olive oil, 584 olivile, 518 Opium, active principle of, 477 Organic chemistry, 499 substances, charac- ter of, 499 Orpiment, 210 Osmazome, 585 Osmium 8c its oxide, 325 Oxalates, 460 Oxidation, 102 Oxide, cystic, 583 xanthic, 583 Oxides, what, 102. nomenclature of, 112 Oxygen, 100 Oxy-hydrogen blowpipe, 125 Oxiodine, 395 P. Palladium and its oxide, 323 Pancreatic juice, 564 Paper, preparation of,for tests, 596 Papin's digester, 61 Pearl, 585 Pearlash, 232 Pitchblende, 279 Perspiration, fluid of,576 Petroleum, 499 Pewter, 2b9 Phenecin, 510 Phlogiston, 104 Phosgene gas, 361 Phosphates, general cha- racter of, 180 Phosphorus, 174 bromides of, 410 carburet, 192 chloride, 194 iodide, 400 oxides, 176 sulphuret, 194 Phosphurets metallic, 209 Photometer, 73 Picromel, 567 Picrotoxia, 481 Pinchbeck, 329 Piperin, 518 • Pitch, mineral, 499 Plants, growth of, 529 food of, 531 Plaster of Paris, 253 Platinum, 315 alloys of, 317 bromide, 414 chloride, 380 oxides, 316 sulphuret, 316 Plumbago, 294 Pluranium, 326 Pollenin, 518 Polychroite, 511 Potassa, 228 acetate of, 455 alloys, 235 am mono-sulphate 234 antimoniate, 262 arseniates, 235 arsenite, 235 aurate, 283 borate, 233 carbonates, 232 chlorate, 383 chromates, 264 columbate, 277 cyanate, 233 ferrocyanate, 299 hydrate, 229 hydriodate, 404 hydrocyanate, 233 hydrofluate, 425 hydrosulphate, 234 hyponitrite, 232 hypophosphite, 234 hyposulphite, 234 iodate, 403 ----molybdate, 273 muriate, 386 nitrate, 231 oxalate, 460 phosphate, 233 phosphite, 234 silicate, 233 sulphates, 234 sulphite, 234 sulpho-cyanate, 235 tartarates, 461 tellurate, 235 titan ate, 278 tungstate, 275 Potassium, 226 bromide of, 412 chloride, 368 cyanide, 230 iodide, 401 oxides, 228 phosphuret, 230 sulphuret, 230 selenuret, 231 Precipitate, red, 310 Pressure, influence, of on the bulk of gases, 14 Proportions in which b< - dies combine, 111 INDEX. 615 Proportional numbers de- fined, 133 Prussiates. See hydro- cynates. Prussiate triple. See fer- rocyanates. Pus, 574 Putrefaction, 525 Pyrites, iron, 295 copper, 304 Pyro-acetic andpyroxilic spirit, 508 Pyrometer, 49 Q. Quick lime, 249 Quicksilver, 309 Quinia, 477 sulphate of, 478 R. Rays, luminous, 69 calorific, 70 chemical, 71 Realgar, 210 Red lead, 286 Reduction of metals, 220 Regulus of antimony,258 Rennet, 570 Repulsion opposed to co- hesion, 53 Resins, 486 Resin of copper, 378 Respiration, 556 Retmasphaltum, 499 Rhodium, and its oxides, 324 Rhubarbarin, 518 Rochelle salts, 464 Rouge, 511 Rusting of iron, 291 S. Sago and salep, 506 Sal-ammoniac, 385 Salifiable base, 138 Saliva, 563 Salt, common, 368 of sorrel. See acid oxalic. petre, 231 spirit of. See acid muriatic. Salts, general remarks on,136 isomorphous, chemical constitution of, 416 Sarcocoll,518 Saturated solution, what, 15 Scheele's green, 207 Secreted animalfluids,563 Sealing wax, 487 Seignette, salt of, 464 Selenite, 253 Selenium, 198 chloride of, 365 Selenium, oxide, 253 phosphuret, 202 sulphuret, 202 Serosity and serum, 551 Shells, 585 Silica, 172 Silicates, 172 Silicated alkali, 172 silicon, 171 chloride, 364 oxide, 172 Silver, 333 alloys of, 336 borate, 335 bromide, 414 carbonate, 335 chlorate, 385 chloride, 382 cvanide, 334 iodide, 402 nitrate, 335 oxide, 333 phosphate, 335 phosphuret, 334 sulphuret, 334 tests, 336 Skin, 585 Smalt,'318 Soda, 257 Soap, 484 acetate of, 456 arseniate, 240 arsenite, 240 borates, 239 carbonates, 238 chlorate, 384 chloride, 369 ferrocyanate, 300 hydriodate, 405 hydrofluate,425 hydrosulphate, 240 hyposulphite, 240 iodate, 404 molybdate, 273 muriate, 386 nitrate, 237 oxalate, 461 phosphate, 239 phosphite, 240 silicate, 239 sulphates, 240 sulphite, 240 tartrate, 464 tungstate, 275 Sodium, 236 bromide of, 412 chloride, 368 iodide, 401 oxides, 237 phosphuret, 237 sulphuret, 237 Solania, 482 Solder, 289 Solution, defined, 15 Sorrel, salt of. See ox- alic acid. Spar, Iceland, 252 fluor, 416 heavy,246 Speculum metal, 308 Spectrum, prismatic, 69 Spelter, 326 Spermaceti, 548 Spirit, proof, 491 of wine, 490 Spirit, pyroxylic and pyro-acetic, 508 Starch, 504 Star key's soap, 485 Steam, temperature of, 61 elasticity of,, 62 latent, heat of, 63 Steam engine, principle of, 62 Stearine, 484 Steel, 294 alloys of, 302 Strontia, 247 arseniate, 249 arsenite, 249 borate, 248 carbonate, 248 chlorate. 384 hydriodate, 405 hydrosulphate, 249 hypophosphite, 249 hyposulphite, 249 iodate, 404 muriate, 387 nitrate, 248 phosphate, 249 phosphite, 249 sulphate, 249 sulphite, 249 Strontium, 236 chloride of, 368 iodide, 401 oxides, 247 phosphuret, 248 sulphuret, 248 Strychnia, 479 Suberin, 517 Succinates, 470 Suet, 546 Sugar of lead,456 Sugar, 501 Sugar of milk and Dia- betes, 541 Sulphates, general char- acters of, 195 Sulphites, general char- acters of, 196 Sulphur, 181 balsam of, 485 bromide, 410 carburet, 192 chloride, 365 iodide, 400 phosphuret, 194 616 INDEX. Sulphurets metallic, 210 Surturbrand, 499 Synthesis defined, 11 T. Tallow, 546 Tannin, 512 artificial formation of, 513 Tanno-gelatine, 513 Tantalum, 275 Tapioca, 506 Tar, mineral, 499 Tartar, cream of, 463 soluble, 463 emetic, 464 Tartrates, 462 Teeth, 584 Tellurium, 203 chloride, 365 muriate, 386 nitrate, 204 oxide, 203 sulphate, 204 Temperature, what, 50 Tenacity of different me- tals, 217 Tendons, 585 Thermometer, 46 differential, 47 Formula for convert- ing the expression of one into ano- ther, 49 graduation of, 48 Thorina, 343 Tin, 222 alloys of, 289 and 308 bromide, 411 chloride, 367 iodide, 401 muriate, 386 nitromuriate, 386 oxides, 222 phosphuret, 224 salts, 224 sulphurets, 224 Tincal, 239 Titanium, 277 chloride of, 375 muriate, 388 nitrate, 278 oxide, 277 phosphuret, 278 sulphuret, 278 Tombac, 329 Trona, 238 Trough, galvanic, 86 Trough, hydro-pneuma- tic, fig. 2 mercurial, 130 Tungsten, 273 chloride of^ 375 oxides, 273 sulphuret, 275 Turpeth mineral, 313 Turmeric, a dye, 511 paper, 511 Turnsol, 510 Turpentine, oil of, 485 Type, metal for/289 U Ulmin, 517 Uranium, 279 muriate of, 388 nitrate, 280 oxides, 279 phosphate, 280 sulphate, 280 ' sulphuret, 280 Urea, 539 Urine, 576 V Vacuum, boiling in, 61 Vaporization, 59 cause of, 59 Vapour, dilatation of, 60 density of, 60 elastic force of, 62 latent heat of, 63 Vegetable acids, 454 alkalies, 473 extract, 518 jelly, 507 chemistry, 451 substances, 451 Vegetation, 529 Veratria, 480 Verdigris, 457 Verditer, 306 Vermilion, 312 Vinegar, 504 Vitriol, blue, 306 green, 296 white, 328 oil of, 185 Volta's eudiometer, 588 pile, 85 theory of, 92 Volumes, theory of, 434 W. Water, composition of, 124 properties of, 127 expansion of in freez- ing, 43 latent heat of, 53 Water, boiling and freez- ing point of, 48 rain, snow, spring, well, river, 596, 597 of the Sea and the Dead Sea, 600 Waters, mineral, 596 acidulous, alkaline, chalybeate, sul- phurous and sili- ceous, 597, 600 Waters, saline, 598 Wax, 489 Welding, 290 Wheat flour, 514 Whey, 570 White lead, 286 White copper, 329 Wine, quantity of alco- hol in, 493 oil of, 498 Wires, tenacity of, 217 Woody fibre, 507 Wool, 585 X Xanthogen, 193 Y Yeast, 516 Yellow, mineral or pa- tent, 377 Yellow kings, $10 Yttrium, 342 bromide of, 414 chloride, 383 iodide, 402 oxide, 342 Z Zaffre, 318 Zero-absolute, 59 Zymome, 515 Zinc, acetate of, 458 alloys, 328 arseniate, 328 borate, 328 carbonate, 328 chlorate, 385 chloride, 381 hyposulphite, 328 iodide, 402 oxides, 327 * phosphate, 328 phosphuret, 327 sulphate, 328 sulphite, 328 sulphuret, 327 tests, 329 Zirconion, 173 oxide of, 173 sulphate, 195 THE END. J