*ffr" 4 k M T»-* > X *" \ £ % %, ' *il,v '¥"•■■' . ....■.■■ ,\ . .....» » A' .*'' V~> ttT*- **" 4 I '^#7 ELEMENTS OF ^EXPERIMENTAL CHEMISTRY, BY WILLIAM HENRY, M.D.F.R.S. \ ice-Pres. of the Lit.and Phil. Soc. at Manchester; Mem. of the Roy. Med and Wernerian Societies at Edinburgh ; the Medice-Chirurgical and Ge- ological Societies of London ; the Physical Soc. of Jena; the Nat. Hist. Soc. of Moscow, &c. &c. THE FIRST AMERICAN FROM THE EIGHTH LONDON EDITION, COMPREHENDING ALL THE RECENT* DISCOVERIES. TOGETHER WITH An Account of Dr. Wollaston's Scale of Chemical Equivalents* ALSO, A Substitute for Woulfe's orNooth's Apparatus ; AND A New Theory of Galvanism, BY ROBERT HARE, M.D. Pt-ofesfsor of Chemistry in the Med. Dep. of the University of Pennsylvania. THE WHOLE ILLUSTRATED WITH THIRTEEN PIATT'S VOLUME II. Ami PHILADELPHIA. PVBLISIIED BY ROBERT DESILYER. XV). 110 Walnct-strvft 1819" .%M^'' o ELEMENTS OF EXPERIMENTAL CHEMISTRY. PART I, CHAPTER XV. PHOSPHORUS--PHOSPHORIC ACID—PHOSPHOROUS ACID—PHOSPHATES. SECTION I. Phosphorus. I. PHOSPHORUS is an inflammable substance, and is distinr guished by the following external characters. (a) It has generally a flesh-red colour, but, when carefully puri- fied, may be obtained colourless, and perfectly transparent. Its specific gravity is 1.77. (b) It is so soft that it readily yields to the knife. (c) It melts at about 90° Fahrenheit, and boils at 550°. When melted, it must be covered with water, in order to prevent it from inflaming. (d) In the atmosphere it emits a white smoke, and a peculiar smell; and a faint and beautiful light arises from it; but these ap- pearances do not take place in the air which has been artificially dried. II. Phosphorus is inflamed by the application of a very gentle heat. According to Dr. Higgins, a temperature- of 60° is sufficient to set it on fire, when perfectly dry. It burns when heated to about 148°, with a very brilliant light, a white smoke, and a suffocating smell, and may even be inflamed in an atmosphere rarefied sixty times. 1. It may be set on fire by friction. Rub a very small bit be- tween two pieces of brown paper; the phosphorus will inflame, and will set the paper on fire also. 2. In oxygen gas it burns with a very beautiful light; and also in nitrous oxide, and chlorine gase«. Vol. II.—A 2 PHOSPHORUS. CHAP. -N^ III. Phosphorus is volatile at 550°. Hence it may be raised by distillation; but,- to prevent its taking fire on the application of heat, the retort should previously be filled with azotic or hydrogen gas, and the mouth of the retort be immersed in wates* To accomplish this, the quantity of phosphorus, which it is in- tended to rectify, should first be put into the retort, with a suffi- cient portion of water to cover it. The water must then be made hot enough to melt the phosphorus, which, on cooling, forms a com- pact mass, of the shape of the bottom of the retort. When cold, fill the retort, and its neck also, with water, and invert it in wa- ter. Displace the water by hydrogen gas, forced from a bladder through a bent pipe; keep the finger on the open end of the retort neck; place it in a sand bath; and immerse the mouth of it in wa- ter. Then apply heat very^autiously. A bladder should also be provided, furnished with a stop-cock and brass pipe, and filled with hydrogen sas. During the distillation, the gas, in the retort, is ab- sorbed, ami it is necessary to add more from the bladder, otherwise the water will rush into the retort, and occasion an explosion. By distillation, in this mode, phosphorus is rendered much purer. In the neck of the retort a substance is condensed of a beautiful red or carmine colour, which is a combination of carbon and phosphorus, or a phosphuret of carbon. Thenard observes that phosphorus, however frequently distilled, cannot be freed entire'y from char- coal, a minute quantity of which does not impair its whiteness or transparency. The only information, which we possess, respecting the nature of phosphorus, is derived from the electro-chemical researches of Sir H. Davy. When acted upon by a battery of 500 pairs of plates in the same manner as sulphur, gas was produced in considerable quantities, and the phosphorus became of a deep red-brown colour. The gas proved to be phosphuretted hydrogen, and was equal in bulk to about four times the phosphorus employed. Hence hydro- gen may possibly be one of its components; but no confirmation of the truth of this view is derived from the recent experiments of the same philosopher, which, indeed, are rather contradictory to it. IV. Phosphorus may be oxygenized in various modes.* \ (a) By exposure to atmospheric air. Let a stick of phosphorus be placed in a funnel, the pipe of which terminates in an empty bottle. The phosphorus will be slowly oxygenized, and, after some time, will be changed into an acid, which will fall into the bottle in a liquid state. A large quantity of acid may be obtained, if a number of sticks be thus exposed: and as they would be in danger of taking fire, if heaped together, each stick should be enclosed in a glass tube, of rather larger diameter than itself. These tubes must be disposed round a funnel, the pipe of which terminates in a bottle. The whole should be covered by a bell-shaped receiver, the air of which is to * On the oxides of phosphorus, see Nicholson's Journal, vi. 134. Theiv existence is so doubtful that I have omitted them entirelv. SECT. II. PHOSPHORIC ACID. 3 be frequently changed. The acid thus obtained is a mixture of phosphorous and phosphoric acids, &c. Dulong, indeed, believes it to be a distinct compound, for which he has proposed the name of phosphatic acid.* But this view of its composition is not supported by the recent investigations of Sir H. Davy, who still considers it as a mixture of the two well-known acids of phosphorus. When phosphorus is burnt in highly rarefied air, three products are formed—a red solid comparatively fixed, and requiring a heat above 212° for its fusion—a white and easily volatile substance, which is combustible, soluble in water, and has acid properties—- and a substance, which is strongly acid and not volatile, even at a white heat. The first appears to be a mixture of unburned phos- phorus and phosphorous acid; the second to be phosphorous acid; and the third to be phosphoric acid. (b) Phosphorus inflames vividly in oxygen gas. When burnt iu this manner, every hundred parts of phosphorus according to La- voisier, gain an addition of 154. This result scarcely differs from the original one of Sir H. Davy, who has stated that 100 grains of phosphorus condense 450 cubic inches or 153 grains of oxygen gas; but having lately examined the subject anew, with e\ery attention to the accuracy of his results, and with the advantage of improved methods of operating, he finds that taking an average of three ex- periments, 100 grains of phosphorus condense 135 grain.s of oxygen. In this estimate, 100 cubic inches of oxygen gas are assumed to weigh 33.9 grains, the barometer being at 26.8 inches, and Fahren- heit's thermometer at from 46° to 49°. (c) By the nitric acid. If phosphorus be cautiously added, by a little at once, to nitric acid, heated in a retort, the nitric acid is de- composed, and its oxygen, uniting with the phosphorus, constitutes phosphoric acid. A tubulated retort must be used for this purpose; and its neck may terminate in the apparatus already described for procuring nitric acid. By this contrivance a considerable quantity of nitric acid will be saved. The liquid, remaining in the retort, may be heated in an open capsule to a thick consistence, in order to expel the redundant nitric acid. SECTION II. Phosphoric Acid. 1. To prepare this acid, the process b or c, seet. i. may be em- ployed; but the following is the most economical method. On 20 pounds of bone, calcined to whiteness and finely powder- ed, pour 20 quarts of Doiling water, and add eight pounds of sul- phuric acid, diluted with an equal weight of water. Let these ma- terials be well stirred together, and be kept in mixture about 24 * Phil. Mug. xlviii. 2r.3. 4 PHOSPHORIC ACID. CHAP. XV. hours. Let the whole mass be next put into a conical bag of suffi- ciently porous and strong linen, in order to separate the clear li- quor, and let it be washed with water, till the water ceases to have much acidity to the taste. Evaporate the strained liquor in earthen vessels, placed in a sand-heat, and, when reduced to about half its bulk, let it cool. A white sediment will form in considerable quan- tity, which must be allowed to subside; the clear solution must be decanted, and boiled to dryness in a glass vessel. A white mass will remain, which is the dry phosphoric acid. This may be fused in a crucible, and poured out in a clean copper dish. A transparent glass is obtained, which is the phosphoric acid in a glacial state; not, however, perfectly pure, but containing sulphate and phosphate of lime.—According to Fourcroy and Vauquelin, it is, in fact, a su- per-phosphate of lime, containing, in 100 parts, only 30 of unoom- bined phosphoric acid, and 70 of neutral phosphate of lime. The glacial acid, however, may be prepared from perfectly pure phos- phoric acid, which has been made by acting on phosphorus with ni- tric acid. It is remarkable that, according to the experiments of Berthier, it contains at least one-fourth its weight of water, a pro- portion which could scarcely be. expected in so hard a substarifce. To procure the phosphoric acid in quantity, and at the same time perfectly pure, the oxygenation of phosphorus by nitric acid is the most eligible process (c, of the preceding article). The acid may be evaporated to dryness in a glass capsule; and the dry mass, when fused, affords glacial phosphoric acid. II. The phosphoric acid has the following properties: (a) When pure it dissolves readily in water. That obtained im- mediately from bones is rendered insoluble by the admixture of earthy salts. But the glacial acid prepared with nitric acid is readily soluble. (6) It is not volatile, nor capable of being decomposed by heat only, nor does it emit any smell when heated. (c) It is composed, according to the experiments of Rose on the combustion of phosphorus in oxygen gas, (the correctness of which is admitted by Dr. Wollaston, in his table of equivalents,) of Phosphorus.....46.72 . . . 100. Oxygen......63.28 . . . 114.6 100. Dulong investigated the composition of phosphoric acid, by find- ing how Much chlorine is absorbed by phosphorus previously com- bined with a base. He then deduced the oxygen, from the quantity known to be the equivalent of the chlorine, which had disappeared. In this way, he intimates the composition of phosphoric to be Phosphorus.....44.48 . . . 100. Oxygen......55.52 . . ,' 124.8 100. 5F.CT. II. PHOSPHORIC ACID. 5 Berzelius, by a still more complicated process, obtained results, the average of which gives 100 phosphorus to 127.5 oxygen.* But if 235 parts of phosphoric acid, as appears from the recent experiments of Sir H. Davy, consist of 100 phosphorus, and 135 oxygen, 100 grains must contain Phosphorus......42.55 Oxygen.......57.45 100. This would very nearly agree with the notion, that phosphoric acid is constituted of one atom of phosphorus, weighing 11.1, and two atoms of oxygen = 15, and the weight of the atom of phospho- ric acid will, therefore, be 26.1, or in round numbers 26. (tf) When distilled in an earthern retort with powdered char- coal, phosphoric acid is clecomposed; its oxygen, uniting with the carbon, forms carbonic acid, and the phosphorus rises in a separate state. This is the usual and best mode of obtaining phosphorus. The phosphoric acid of bones may either be employed for this purpose in the state of gla^s, finely powdered, and mixed with its weight of pulverized charcoal; or to the evaporated acid, when ac- quiring a thick consistence, powdered charcoal may be added, in sufficient quantity, to give it solidity. In the latter mode, however, the materials are apt to swell, and to boil over. The mixture of acid and charcoal is to be put in a stone-ware retort, coated with Willis's lute, the neck of which is lengthened out by a tin pipe. The open end of the pipe is to be immersed in a vessel of water. The heat is to be slowly raised, and at length made very intense. An enormous quantity of gas escapes, which takes fire on coming into contact with the atmosphere; and the phosphorus distils over in drops, which congeal in the water. As it is apt also to condense in, and to stop up, the neck of the retort and tin pipe, it must be occasionally melted out of these, by a shovel full of hot cinders, held under them. The process is rather a difficult one; and though it is proper that the student should perform it, in order to complete a course of experiments, it will be found more economical to pur- chase the phosphorus which may be required for experiments. Phosphorus may also be procured, by adding to urine a solution of lead in nitric acid, which precipitates a phosphate of lead This, when well washed, dried, and distilled in a stone-ware retort, yields phdsphorust or a solution of phosphate of soda (which may be bought at the druggists), mixed with one of acetite of lead, in the proportion of one part of the former salt to 1 £ of the latter, yields a precipitate of phosphate ot lead, from which phosphorus may be procured by 'distillation with charcoal, but at considerably more expense. * Ann. de Chim. et Phys. ii. 222. i See Crell's Journal, Translation, iii. 3P G PHOSPHATES. CHAP. X\- SECTION III. Phosphates. With alkaline and earthy bases, the phosphoric acid composes a class of salts called Phosphates, which have the following gene- ric characters. 1. When heated with charcoal, they are not decomposed, nor is phosphorus obtained. 2. They melt, before the blow-pipe, into a hard globule, some- times transparent, at others opaque. 3. The earthy phosphates are soluble in nitric, muriatic, and ace- tic acids, without effervescence, and are precipitated from those acids by lime-water and by pure ammonia. 4. They are decomposed, in part, by sulphuric acid, and yield a liquor which, on evaporation and distillation with charcoal, affords phosphorus. The most important combinations of phosphoric acid are those which it forms with soda, ammonia, barytes, and lime. 1. Phosphate of Soda, obtained by saturating carbonate of soda with phosphoric acid, and evaporating the solution, exists, in crys- tals, which have always an excess of alkali. These crystals con- tain 62 per cent, of water, and when calcined by a red heat are converted into a white powder, which consists of Phosphoric acid .... 53.48 ... 100 Soda........46.52 ... 87 100. Hence the crystals are composed of Phosphoric acid .... 20.33 Soda........17.67 Water.......62. 100. 2. Phosphate of Ammonia exists with at least three different proportions of its elements. The neutral phosphate forms regular crystals, which are very soluble. By adding to this either an ex- cess of acid or of base, we obtain distinct salts, which require far- ther investigation. 3. Phosphate of Barytes varies, also, in the proportion of its ele- ments. (a) The neutral phosphate may be obtained by mixing the solu- tions of muriate of barytes and phosphate of soda. It consists of 3r.cr. in. pho.sphatis. 7 s Phosphoric acid .... 31.8 .. . 100.00 Barytes......68.2 . . . 214.46 100. (b) When the neutral phosphate is dissolved in an excess of phosphoric acid, and the solution slowly evaporated, acid crystals are obtained, which, independently of water, contain Phosphoric acid . . ., 47.8 . . . 100.00 Barytes......52.2 . . . 107.11 100. The acid, or bi-phosphate, therefore, contains just half as much barytes as the neutral compound. (c) From the solution of the acid salt, alcohol occasions a bulky precipitate, which, when dried, becomes a light and white powder- It is composed of Phosphoric acid . . . 39.13 . . . 100.0 Barytes......60.87 . . . 155.5 100. Berzelhis proposes to call it the acidulous phosphate of barytes. In this compound the base is united with one and a half as much acid, as exists in the neutral phosphate. Water decomposes it, and changes it into the neutral variety. 4. Phosphate of Lime, (a) When a neutral solution of muriate of lime is mixed with a solution of phosphate of soda, the liquor becomes acid, and a copious precipitate takes place of small opaque' fibrous crystals, which when gently dried contain Phosphoric acid .... 41.9ft. Lime....... . 35.42 Water.......22.68 100. Hence the phosphoric acid and lime are to each other in the fol- lowing proportions: Phosphoric acid . . . 54.19 . . . 100.00 Lime ....... 45.81 . . . 84.53 100. This compound may be considered as the neutral phosphate of lime. 8 PHOSPHunoUS ACID. OH"AP. X\. (I) If solution of muriate of lime be poured into solution of phos- phate of soda, taking care to have a considerable excess of the latter salt, a gelatinous precipitate is formed, which, when dried at a mo- derate heat, contains only 5.7 per cent, of water; and, alter this has been expelled by heat, consists of Phosphoric acid . . . 48.32 ... 100 Lime.......51.68 ... 107 100. Having a greater quantity of base than the former, this com- pound may be termed a sub-phosphate. It is this substance which forms the basis of animal bone. Both the phosphates of lime, which have already been described, arc soluble in an excess of phosphoric acid, and afford a transpa- rent solution, from which pure ammonia precipitates the neutral phosphate. From this solution, Berzelius has not succeeded in ob- taining solid compounds with definite proportions of base and acid. It is probable, however, that at least one such super-phosphate exists, and that the phosphates will be found, in this respect, ana- logous to those salts with excess of acid, which have afforded such striking illustrations of the general law of definite proportions. SECTION IV. Phosphorous Ac id—Phosphites. Phosphorous acid cannot, according to Sir H. Davy, be obtain- ed pure by exposing cylinders of phosphorus to atmospheric air; for, when thus prepared, it always contains phosphoric acid. It can only be procured in a state of purity, first, by subliming phos- phorus through corrosive sublimate; then mixing the product with water and heating it, till it becomes of the consistence of syrup. The liquid obtained is a compound of pure phosphorous acid and water, which becomes solid and crystalline on cooling. It is acid to the taste, reddens vegetable blues, and unites with alkalies. The theory of this process is, that when the compound of phos- phorus and chlorine, formed in the first operation, is brought into contact with water, the water is decomposed; its hydrogen uniting with chlorine composes muriatic acid; and its oxygen combining with phosphorus forms phosphorous acid. From this mixture of acids, heat expels the muriatic. The phosphorous acid exhales a disagreeable fa?tid odour; and yields, when strongly heated, penetrating white vapours. When heated in a glass ball, blown at the end of .a-small tube, a gas is- sues from the orifice of the tube, which inflames on coming in con- tact with the atmosphere. Hence it appears to contain an excess SECT. IV. PHOSPHOROUS ACID* 9 of phosphorus. The residuum in the ball is phosphoric acid. From the experiments of Rose on the phosphoric acid, Gay Lussac infers that, conformably to his own hypothetical views, phosphorous acid must consist of Phosphorus . . . 56.81 . . 100 . . 132 Oxygen .... 43.19 . . 76 . . 100 < 100. These proportions do not differ materially from those stated by Dulong, who makes phosphorous acid to consist of 100 phosphorus -f 74.88 oxygen.* They agree, also, still more nearly, with the fol- lowing statement of Berzelius, according to whom this acid con- sists of Phosphorus . . . 56.524 .... 100.00 Oxygen.....43.476 .... 76.92 100.t Sir H. Davy, however, after a careful investigation of the consti- tution of phosphorous acid, has lately been led to conclude that the oxygen, which it contains, is just one half of that existing in phos- phoric acid; or that, in the former, 100 grains of phosphorus are united with 67.5 of oxygen. Hence 100 grains of phosphorous acid must consist of Phosphorus......59.1 Oxygen ........ 40.9 / 100. And phosphorous acid must be constituted of 1 atom of oxygen, 7.5 + 1 atom of phosphorus 11 j and the weight of its atom will be 18.5. The combinations of phosphorous acid with alkaline and earthy bases are called phosphites. The phosphites differ considerably in their characters from phos- phates. 1. They exhale a smell of phosphorus. 2. When heated, they emit a phosphorescent flame. 3. Distilled in a strong heat, they yield a little phosphorus, and are converted into phosphates, in which the elements are com- pletely neutral.:}: 4. They detonate, when heated with chlorate of potash. 5. They are changed into phosphates by nitric, and by oxymu- riatic acid. • Phil. Mag. xlviii. 273. t Ann- de Chim. et Phys. ii. 227 I Gay Lussac, Ann. de Chim. et Phys, i. 212. Vol . II.—B 10 HYPO-PHOSPHOROUS ACID. CHAP. XV 6. Phosohite of potash is very deliquescent, uncrystallizable, but insoluble in alcohol. Those of soda and ammonia are also very soluble. The former crystallizes in rhomboids approaching to cubes. All the rest are sparingly soluble, but can be obtained in crystals only bv spontaneous evaporation, for they are decomposed by heat, and" salts with excess of base are precipitated, which are absolutely insoluble. There exist, therefore, neutral phosphites, sub-phosphites, and super-phosphites, the exact composition of which remains to be investigated.* SECTION V. Hypo-phosphorous or Per-phosphorous Acid. When phosphuret of barytes> carefully prepared, is made to act on water, two distinct compounds are generated, viz. phosphate of barytes, which, being insoluble, is readily separated by filtration; and a soluble salt of barytes, which passes through the filter. To the latter compound, sulphuric acid is to be added, in quantity just sufficient to separate the barytes. The acid solution which re- mains, when concentrated by evaporation, yields a viscous fluid, strongly acid and uncrystallizable. By a still stronger heat, this substance is decomposed; phosphuretted hydrogen is deve- loped; a little phosphorus is sublimed; and phosphoric acid remains in the retortf The compounds of this new acid, with alkaline and earthy bases, are remarkable for their extreme solubility. Those of barytes and strontites crystallize with great difficulty. The hypo-phosphites of potash, soda, and ammonia, are soluble, in all proportions, in highly rectified alcohol. That of potash is even more deliquescent than muriate of lime. They absorb oxygen slowly from the air, and when heated in a retort give the same products as the acid itself. In order to ascertain the proportions of the elements of this acid, Dulong, its discoverer, converted a known quantity of it into phos- phoric acid by means of chlorine, whence he infers it to consist of Phosphorus .... 72.75. .... 100 Oxygen.....27.25 .... 37.44 100. These results are calculated on the supposition that hypo-phos- phorous or per-phosphorous acid is a binary compound of oxygen and phosphorus; but it is doubtful whether it may not be a triple compound of oxygen, phosphorus, and hydrogen, or a hydracid; in which case its proper appellation would be hydro-phosphorous add. * Dulong, 48 Phil. Mag. 272. •{- Dulong, 48 Phil. Mag. 271. SECT. VI. COMBINATIONS OF PHOSPHORUS. 11 In his able investigation of the compounds of phosphorus, Sir H. Davy admits the existence of the new acid of Dulong, but deduces different proportions of its elements. The oxygen of this acid he infers to be precisely half of that which exists in phosphorous acid; or that 100 of phosphorus are united with 33.825 oxygen. But it has been already shown to be probable that phosphorous acid is composed of an atom of each of its elements; and it may, there- fore, be inferred that hypo-phosphorous acid is constituted of one atom of oxygen weighing 7.5 and two atoms of phosphorus weigh- ing 11 x 2 = 22, and the weight of the compound atom may be represented by 29.5. The following table represents the composition of the three acids of phosphorus: Atoms of Atoms of Weight Phosph. Oxyg. ofatoins. Hypo-phosphorous acid 2 + 1 .. 29.5 Phosphorous acid . . 1 «j- 1 .. 18.5 Phosphoric acid . . . 1 + 2 .. 26. SECTION VL Combinations of Phosphorus with Chlorine. There are two compounds of chlorine and phosphorus. 1. Bi-chloride or Perchloride. When phosphorus is introduced into chlorine gas, it takes fire spontaneously, and burns with a pale flame; and a white solid condenses on the sides of the vessel. In ah experiment of Sir H. Davy, conducted with great care, 4 grains of phosphorus condensed 31.9 cubic inches (barometer 30.1, thermometer 46°) of chlorine gas, equivalent to very nearly 24§ grains, or six times its weight. Therefore 100 grains of phosphorus, to form this compound, condense 600 grains of chlorine; and as 33.5 of chlorine appear, from a variety of facts, to be equivalent to 7.5 of oxygen, the above 600 grains are, by the rule of proportion, the equivalent of 135 of oxygen; and thus is derived a collateral proof that phosphoric acid is constituted of 100 phosphorus -f-135 oxygen by weight. The solid compound of phosphorus and chlorine is volatile at a temperature below 212° Fahrenheit. It acts violently on water, the hydrogen of which forms, with the chlorine, muriatic acid; while the oxygen forms, with the phosphorus, phosphoric acid. 2. Chloride or Proto-chloride. Though this compound may be obtained by heating the perchloride with a due proportion of phos- phorus, yet a better method of preparing it is (as Sir H. Davy re- commends) to pass the vapour of phosphorus over corrosive subli- mate, heated in a glass tube. By this process, we obtain a liquid of the specific gravity 1.45, which does not redden litmus paper, though its fumes produce this effect, in consequence of being ren- 12 COMPOUNDS OF PHOSPHORUS. CHAP. XV. dered acid by contact with the moisture of the air. The acid, which results from its action on water, is the phosphorous, which is best procured by the intervention of this chloride. At the same time muriatic acid is formed, by the union of chlorine with the hydrogen of the water. In this chloride, the chlorine exists in half the quantity which constitutes the perchloride, that is, 100 grains of phosphorus are united with 300 of chlorine. But in phosphorous acid, 100 grains of phosphorus are combined with 67.5 of oxygen, which last num- ber is, therefore, the equivalent of 300 chlorine. Now as 67.5 to 300, so is 7^ to 33.5; indicating that in the chloride of phosphorus its elements are united atom to atom; while in the per-chloride two atoms of chlorine are combined with one of phosphorus. Atoms of Atoms of Weight Fhosph. Chlor. of Atoms, Chloride of phosphorus 1 +1 ..41 Perchloride . . . . 1 -r- 2 .. 74.5 SECTION VII. Compounds of Phosphorus, with Alkalies, Earths, and Combustible Bodies. I. Phosphorus is susceptible of combination with sulphur, and affords a compound, the properties of which vary, according to the proportion of its ingredients. It may be obtained by melting these substances together in a tube, the mouth of which is loosely stopped by paper; or by fusing these two bodies, very cautiously, and in small quantities, at the bottom of a Florence oil flask, nearly filled with water. The process is attended with some danger; and re- quires several precautions, which will be suggested by the essays of Mr. Accum and Dr. Briggs, published in the 6th and 7th volumes of Nicholson's Journal. The compound is much more fusible and combustible, than the separate components. It may be purified by being shaken with a solution of ammonia, and left some hours in it. Its reddish or brown colour is thus removed, and a light yellow compound results, which is semi-transparent, remains fluid even at 20° Fahrenheit, and does not act at all on water at common tem- peratures, nor rapidly even on boiling water. It appears to be con- stituted of 5 sulphur, and 7 phosphorus.* II. Phosphorus combines with the pure fixed alkalies, and with earths, and composes the class of phosphurets. That of lime is the most readily formed, and exhibits, extremely well, the properties of these compounds. It is prepared as follows: Take a glass tube, about 12 inches long, and one-third of an inch diameter, sealed hermetically at one end. Let this tube be coated * Faraday in Journ. of Science, iv. 360. SECT. vn. l'HOSPHURETTED HYDROGEN GAS. IS with clay, except within about half an inch of the sealed end. Put first into it a drachm or two of phosphorus, cut into small pieces, and then fill the tube with small bits of fresh burnt lime, of the size of split peas. Stop the mouth of the tube loosely with a little pa- per, in order to prevent the free access of air.—Next, heat to red- ness that part of the tube which is coated with clay, by means of a chafingdish of red-hot charcoal; and, when the lime may be sup- posed to be ignited, apply heat to the part containing the phospho- rus, so as to sublime it, and to bring the vapour of it into contact with the heated lime. The lime and phosphorus will unite, and will afford a compound of a'reddish-brown colour.—Phosphuret of barytes and of strontites may be prepared in a similar manner. If the carbonate of lime be substituted for pure lime, the carbonic acid is decomposed. Its carbon is set at liberty, and appears in the state of charcoal; while its oxygen unites with the phosphorus; and the phosphoric acid, thus produced, forms phosphate of lime. In this process, discovered by the late Mr. Tennant, carbonic acid is clecomposed by the conspiring affinities of phosphorus for oxygen, and of lime for phosphoric acid, though the former affinity only would be inadequate to produce the effect. The phosphuret of lime has the remarkable property of decom- posing water at the common temperature of the atmosphere; and the water afterwards contains phosphite, or hypo-phosphite, not phosphate, of lime.* Drop a small piece of it into a wine-glass of water, and in a short time bubbles of phosphuretted hydrogen gas will be produced; which, rising to the surface, will take fire, and explode. If the phosphuret of lime be not perfectly fresh, it may be proper to warm the water to which it is added. Into an ale-glass put one part of phosphuret of lime, in pieces about the size of a pea (not in powder), and add to it half a part of chlorate of potash. Fill the glass with water, and put into it a fun- nel, with a long pipe, or narrow glass tube, reaching to the bottom. Through this pour three or four parts of strong sulphuric acid, which will decompose the chlorate; and, the phosphuret also decomposing the water at the same time, flashes a fire dart from the surface of the fluid, and the bottom of the vessel is illuminated by a beautiful green light. (Davy.) Another combination of phosphorus, the properties of which ren- der it a fit subject of amusing experiments, is the phosphuretted hydrogen gas. Art. 3.—Phosphuretted Hydrogen Gas. By heating solid phosphorous acid out of the contact of air, a large quantity of elastic fluid is generated, which may be collected by a proper apparatus, and has singular properties. It has a disagreeable smell, but is not so offensive as bi-phosphu- retted hydrogen. It does not explode spontaneously, but detonates • Gay Lussac, 85 Ann. de Chim, 206, and Ann. de Chim. etPhys. vi. »fc 14 COMPOUNDS OF'PHOSPHORUS. OllAP. X\ ■• violently when heated with oxygen to about 300° Fahrenheit; or when a mixture of the two gases is rarefied by diminished pres- sure.* It explodes in chlorine with a white flame. Water absorbs about one-eighth its volume. Its specific gravity was found by Sir H. Davy to be to that of hydrogen as 12 to I. He gave it the name of hydro-phosphoric gas, but he has since adopted that of phosphuret- ted hydrogen. Potassium doubles its volume, and the residue is pure hydrogen. Sulphur occasions the formation of sulphuretted hydrogen, equal in volume to twice the original gas. Three parts of it in volume con- dense more than five of oxygen; and due in volume absorbs four of chlorine. It appears to be constituted of two atoms of hydrogen and one of phosphorus; and the hydrogen in .it is condensed into half its bulk. In that case the weight of its atom will be 13. Its formation appears to be owing to the decomposition of water, the oxyy the filter, which, when dried, and heated in oxygen gas, 20 FLUORIC ACID. CHAP. XVII. burned and absorbed oxygen. By this combustion, fluoric acid was also generated. Hydro-fluoric Acid. The fluoric acid may be obtained in a liquid state, from fluor spar and twice its weight of strong sulphuric acid, by using a leaden retort and leaden receiver. An ingenious apparatus, invented for this pur- pose by Mr. Knight, is described and figured in the 17th volume of the Philosophical Magazine. The receiver should be surrounded with snow or pounded ice. '. The liquid acid must be preserved in leaden or silver bottles, as it soon corrodes and penetrates glass ones. Its volatility, however, is such that it is extremely difficult to confine it. In this state of watery solution, it readily combines with alkalies, and forms soluble com- pounds. Its combinations with the earths are for the most part highly insoluble. The filiates have no properties that can render them inter- esting to the student, except the use of the alkaline ones as tests, which will be described in a subsequent part of the work. To the liquid solution of fluoric acid, Gay Lussac and Thenard have fiven the name of silici-fluoric acid. Its specific gravity, Sir H. Davy finds to be 1.0609. By adding water, in very small quanti- ties at once, its specific gravity is gradually increased to 1.25, a pro- perty observed in no other liquid. When suddenly mixed with water, it becomes very hot and even boils; it emits dense and noxious va- pours; acts instantly and strongly on glass; and powerfully affects the skin, on which it raises painful pustules, or, if in sufficient quantity, occasions deep and dangerous ulcers.—A small piece of potassium thrown intuit detonates violently. The principal use of hydro-fluoric acid is for destroying the polish of glass; but for this purpose it is adviseable to prepare it in a state of considerable dilution, by receiving the gas into water, contained in a leaden vessel. It may, also, be employed to etch on glass, as copper is engraved by aqua fortis; and it affords an useful means of sepa- rating potash from its acid combinations, since it detaches that alkali in the form of an insoluble compound.* Nature of Fluoric Acid. The experiments of Sir II. Davy, made in 1808, led him to conclude, chiefly from the action of potassium on silicated fluoric gas, that the fluoric acid is a compound of oxygen with a combustible basis. But as all acids, so constituted, are decomposed by galvanic electricity, their • base being determined to the negative, and their oxygen to the posi- tive pole, he has latelyt submitted liquid fluoric acid to this test, after having first ascertained, by the result of its combination with ammo- niacal gas, that, in its strongest form, it contains no water. Consider- able difficulty was experienced in making the necessary exposure of * Wheeler in Journal of Science, &c. iv. 287. t Phil. Trans, 1813, part 2; and 1814, part 1. CHAP. XVII. FLU0B011IC ACID. 21 the liquid to electricity, (partly in consequence of the dangerous fumes which it emitted,) and also in collecting the products. At the negative pole, a gas was evolved, which, from its inflammability, ap- peared to be hydrogen. The platina wire at the positive pole was rapidly corroded, and covered with a chocolate powder, the properties of which seem not to have been examined. When fluate of ammonia was treated with potassium, no evidence was obtained of its containing oxygen. * Charcoal, also, intensely ignited in fluoric acid gas, gave no carbonic acid. The most simple way of explaining the phenomena appears, therefore, to Sir H. Davy, to be by the supposition, that the fluoric acid, like the muriatic, is composed of hydrogen, and a peculiar base, possessing, like oxygen and chlorine, a negative electrical energy, and hence determined to the positive surface. For this base, which, like chlorine, he believes to combine at once with metals, the name of fluorine has been pro- posed. This substance, from its strong affinities and decomposing agencies, has not yet been exhibited in a separate state; nor have any of the attempts to detach it from its combinations by chlorine or oxygen, (on the presumption that the attraction of one of those bodies for the metals might be superior to that of fluorine,) been hitherto successful. The number representing the atom of fluorine, as deduced from the composition of fluor spar, is 17.1; and fluor spar must be composed of 20 calcium and 17.1 fluorine. On the whole, Sir H. Davy is dis- posed to estimate the weight of the atom of fluorine at less than half that of chlorine, and to fix it at 33, which is equivalent, on Mr. Dal- ton's scale, to 16.5 Fluoboric Acid. With the view of obtaining fluoric acid gas perfectly free from Water, both Sir H. Davy and Gay Lussac appear to have had recourse to the same expedient, viz. that of distilling perfectly dry boracic acid with fluate of lime. When these substances were exposed to a strong heat in an iron tube, in the proportion of one part of the former to two of powdered fluor spar, 4t gas was collected in great quantity, which exhibited singular properties, and to which Messrs. Gay Lus- sac and Thenard have given the name of gas fluoborique, or fluoboric acid gas. It may, also, be obtained by distilling in a retort one part of vitreous boracic acid with two of fluor spar and 12 of sulphuric acid. One hundred cubic inches weigh 73.5 grains. This gas, according to the latter chemists, appears to contain no water, and to have so strong an affinity for it as to take it from other gases, which hold water in combination. Hence, when mixed with most of those gases, on which it does not exert a chemical action, such as atmospheric air, it loses its transparency and becomes cloudy. With ammoniacai gas it unites in two proportions. If the alkaline gas be put first into the tube, equal measures combine, together, and the compound is neutral. But if we admit fluoboric gas by bubbles 22 IODINE CHAP. XVIII. to the alkaline gas, we obtain a compound, with an excess of base, consisting of one measure of fluoboric gas to two of ammonia. Fluoboric gas is absorbed copiously by water, which takes up 700 times its bulk, and acquires the specific gravity 1.77. The saturated solution has the causticity and aspect of strong sulphuric acid; re- quires for ebullition a temperature considerably exceeding 212° Fah- renheit; and is condensed again in strife which contain much gas. From analogy, Gay Lussac supposes that nitric and even sulphuric acids would, if they could be obtained free from water, be equally elastic with this. When potassium or sodium was heated in fluoboric gas, Gay Lus- sac and Thenard obtained fluate of potash or soda, and the base of the boracic acid. The liquid acid acts almost as intensely as sulphuric acid on vege- table substances. It blackens paper, and affords a true ether with alcohol. It has no effect in corrodingr glass. From analysis, Gay Lussac and Tnenard, as well as Sir H. Davy, have determined it to be a compound of boracic and fluoric acids, in proportions not yet ascertained. CHAPTER XVIIL IODINE AND ITS COMPOUNDS. IODINE was discovered accidentally, about the beginning of the year 1812, by M. Courtois, a manufacturer of saltpetre at Paris. In the processes for procuring soda from the ashes of sea weeds, he found his metallic vessels much corroded; and in searching for the cause, he made this discovery. Specimens of the new substance were given to MM. Desormes and Clement, who read a short memoir upon it, at a meeting of the Institute of France,*in November, 1813. Its pro- perties and combinations have since been ably investigated by Vau- quelin;* by GayLussac;t by SirH.Davy;J and by Gaultier de Clau- bry and Colin.§ When all the soda has been separated by crystallization from a so- lution of kelp or barilla, or from the ley of ashes of marine plants, that afford the mineral alkali, in order to procure iodine from the resi- duary liquor, concentrated sulphuric acid is to be poured upon it, in a retort furnished with a receiver. The iodine passes into the receiver, under the form of beautiful violet vapours, which are condensed in crystalline plates, having the aspect of plumbago. To purify it from the redundant acid, that comes over with it, the iodine may be re- * 90 Ann. de Chim. 20S. i Phil. Trans. 1814. j- 91 Ann. de Chim. § 90, 91, and 93 Ann. de Chim. CHAP. XVIII. IODINE. 23 distilled from water, containing a very small quantity of potash, and afterwards dried by pressing it between folds of blotting paper.* General Properties.—Iodine is a solid, at the ordinary tempera- ture of the atmosphere. It is often in scales, resembling those of mi- caceous iron ore; sometimes in large and brilliant rhomboidal plates; and occasionally in elongated octohedrons.t Its colour is bluish black; its lustre metallic; it is soft and friable, and may easily be rub- bed to a fine powder. Its taste is very acrid, though it is sparingly soluble in water, which does not take up above one 7000th part of its weight. Its specific gravity, at 60° Fahrenheit, is 4.946. It is a non- conductor of electricity; and possesses, in a high degree, the electri- cal properties of oxygen and chlorine, being determined to the posi- tive pole of a galvanic arrangement. When applied to the skin, it produces a yellow stain, but this disappears as the iodine evaporates. Iodine is fusible at 225° Fahrenheit, and, under the ordinary pres- sure of the atmosphere, is volatilized at a temperature somewhere near 350°, forming a gas 117.71 times denser than hydrogen, or, ac- cording to Sir II. Davy, weighing 95.27 grains for 100 cubic inches. The volatilization of iodine at the heat of boiling water, which hap- pens when it is distilled with that fluid, depends on its affinity for aqueous vapour. The colour of its vapour is a beautiful violet and hence its name (from «»<$iis, violaceus). Action of Oxygen.—Iodine undergoes no change by being heated in contact with oxygen gas, or with hyperoxy-munate of potash. It will appear, however, in the sequel, that, by the intervention of euchlo- rine, it admits of being combined with oxygen, and that it then fur- nishes a peculiar acid with that body. Action of Nitrogen.—'Azotic gas has no action on iodine, but a compound of iodine nitrogen will be described in speaking of the effect of ammonia. Action of Water.—It has no power of decomposing water, even when the mixed vapours of the two substances are passed through a >ed hot tube. Action of Hydrogen.—The affinity of iodine for hydrogen is very strong, and it absorbs that basis from hydrogen gas, and detaches it from several of its combinations, affording, as the result, a distinct and well characterized acid. If iodine be heated in dry hydrogen gas, an expansion of its volume takes place; an acid gas is formed, which is very absorbable by water, and acts so much on mercury that it cannot be preserved long over that metal. A similar gaseous compound is formed, by exposing iodine to sulphuretted hydrogen gas. But it is best prepared, in quantity, by the action of moistened iodine and phosphorus on each other, the phosphorus being in excess, and the mixture distilled in a retort The gas may be received into a vessel filled with common * More minute directions for its preparation are given in the Phil. Mar. xl 57,141, and 209. t Dr. Wollaston has described the form of its crystal in Thomson's Annals. v. 237. See also Journ. of Science, &c. v. 364 24 TODIXE. CHAP. XVIII air, which it expels by its superior gravity. Gay Lussac recommends, instead of a retort, a small bent tube, which, after putting the iodine into it, is to be inverted over mercury; the air, which it contains, is to be expelled by a glass rod, that almost fills its capacity; and the phosphorus is to be brought into contact with the iodine, by intro- ducing it through the mercury. As soon as the contact takes place, the acid gas is disengaged, and may be collected by putting the open end of the tube under a glass jar standing inverted in mercury. No sooner does the gas come into contact with the mercury, than it begins to be decomposed; and if the contact, be prolonged a suffi- cient time, or agitation be used, the decomposition is complete. The iodine unites with the mercury; and there remains a volume of hy- drogen gas, which is exactly one half that of the acid gas. It is decomposed, in a similar manner, by all metals, except gold and platinum. The acid gas is colourless, its taste is very sour, and its smell re- sembles that of muriatic acid gas. Its specific gravity was found by experiment to be 4.443; by calculation it should have been 4.428. The acid gas is rapidly decomposed by being heated in contact with oxygen gas, which detaches the hydrogen. Chlorine also, in- stantly deprives it of hydrogen, and produces muriatic acid gas; and the iodine re-appears in the form of a beautiful violet vapour. When mixed with proto-phosphu retted hydrogen, both gases are condensed into white cubical crystals, which are volatilized at a moderate heat without fusion or decomposition.* It is composed, by weight, accord- ingtoGay Lussac, of 100 iodine and 0.849 hydrogen. For this compound Sir H. Davy has proposed the name of hydroi- onic acid, and Gay Lussac that of hydriodic acid. I prefer the lat- ter; because it is easier, by varying its termination, to express il^, combinations with alkaline and other bases. Hydriodic Acid Gas is plentifully absorbed by water; the solution is fuming, and has the density of 1.7. To prepare this liquid in quan- tity, Gay Lussac rcommends to put powdered iodine into water, and to pass sulphuretted hydrogen gas through the mixture. The hydro- gen unites with the iodine, and the sulphur is precipitated. The liquid maybe concentrated by evaporation. Till it attains the temperature 'of 257°, water only distils; above this point, the acid itself is volati- lized, and remains stationary at 262£°, its density being then 1.7. The liquid acid is slowly decomposed by contact with air; its hy- drogen being attracted by the oxygen of the atmosphere, and a portion of iodine liberated, which gives the liquor a colour of intensity pro- portionate to the quantity of free iodine. Concentrated sulphuric acid, nitric acid, and chlorine, decompose it, and separate iodine. With solutions of lead, it gives a fine orange precipitate; with solution of per-oxide of mercury, a red one; and with silver, a white precipi- tate, Insoluble in ammonia. When submitted to Galvanic electricity, the liquid hydriodic acid is rapidly decomposed; iodine appears at the positive, and hydrogen * 6 Ann. de Chim. et Plws. 305. CHAP. XVIII. IODINE. 25 at the negative pole. It dissolves zinc and iron, with a disengagement of hydrogen gas, which proceeds from the water. It has no action on mercury, though the gas so powerfully affects that metal. It is decom- posed by those oxides, which hold their oxygen loosely, and combine with the rest, forming a genus of neutral salts, called hydriodates. In general, the hydriodates are readily soluble in water. Those of potash and barytes are not decomposed by heat, except oxygen is in contact with them; the salt with base of lime is wholly, and that with base of magnesia partially, decomposed at high ternperatures. Charcoal does not combine with iodine. Sulphur and Iodine unite at a gentle heat, and a black radiated r-ompound is formed, resembling sulphuret of antimony. It is easily decomposed by a degree of heat a little higher than that at which it was formed, and iodine is detached in vapour. Phosphorus and Iodine combine at the temperature of the atmos- phere, according to Sir H. Davy, evolving much heat, but no light; but, according to Thenard, with a disengagement both of light and heat. The result is a phosphuret of iodine, of a reddish brown colour, the solidity, fusibility, and volatility of which vary with the proportions of its ingredients. If both the phosphorus and iodine are dry, no gas is given out during their combination; but, when slightly moistened, hy- driodic acid is formed, by the union of iodine with the hydrogen of the water; a little subphosphuretted hydrogen is produced; and phosphorous acid remains in solution. The hydriodic acid gas is also formed, when the phosphuret of iodine, produced from dry materials, is added to water. Potassium and Iodine.—Potassium burns in the vapour of iodine with a pale blue light, and without the disengagement of any gas. The substance produced is white; fusible at a red heat; and soluble in water. It has a peculiar acrid taste. When acted upon by sulphu- ric acid, iodine is set at liberty. The same compound is obtained, by heating potassium in hydriodic acid gas, which is decomposed, and yields half its volume of hydrogen gas. To this compound Sir H. Davy has given the name of iode of potassium, the term iode being a generic one. for the compounds of iodine with the metals and other combustible bases. Gay Lussac has proposed the name of iodure; but it is more conformable to analogy with the similar compounds of oxy- gen and chlorine to give, to the combinations of iodine with combusti- ble bases, the appellation of iodides. When iodide of potassium, silver, mercury, or lead, is heated in chlorine gas, iodine is expelled, and hence the affinity of chlorine for those metals surpasses that of iodine. Sulphuric acid extricates some iodine, and occasions a production of hydriodic and sulphurous acids. Oxalic, acetic, sulphurous, and phosphoric acid have no action on the iodurets. Iodine and Alkalies.—When iodine in vapour is passed over ignited hydrate of potash, oxygen is disengaged, and a compound is formed, precisely similar to that which results from the combination of iodine and potassium. Hence the affinity of iodine for potassium exceeds that of oxygen; and the same mav be said of several other metals, Vol. II.—D lb IODINE. CHAP. XV1U. though not of all, their oxides being decomposed by iodine. From sub- carbonate of potash, it displaces two volumes of carbonic acid and one of oxygen. When iodine is thrown into a moderately strong solution of potash, rendered perfectly caustic, it is dissolved; and, during its solution, crystals fall down, which may be obtained abundantly, by saturating the liquid with iodine. To obtain these crystals pure, they must be washed with alcohol of a specific gravity, between .860 and .920. They are sparingly soluble in water; have a taste like hyper-oxy muriate of poti^h; deflagrate with charcoal; and when heated give oxygen gas, and iodide of potassium. With sulphuric acid, they afford iodine. oxygen, and sulphate of potash. The liquid, which has ceased to yield these crystals, affords, on evaporation, a salt identical with iodide of potassium. In this case, Sir H. Davy imagines the potash is decomposed; one part of it com- bines with iodine, and the oxygen, thus set at liberty, unites with the other part and with iodine. In his view, therefore, the deflagrating salt is a triple compound of oxygen, iodine, and potassium, and is call- ed an oxyiode; but Gay Lussac supposes that the iodine is oxyge- nated, and forms an acid, which he calls iodic acid; and that this, uniting with potash, composes iodate of potash. By acting with iodine on solution of barytes, a similar compound was formed with that earth, which, when decomposed by sulphuric acid, gave, he sup- poses, a mixture of that acid with iodic^acid. But the product, in this case, Sir H. Davy has since shown, is a compound of sulphuric acid with oxyiodine, which will presently be described. Dry ammoniacal gas js absorbed by iodine without decomposition; the product is at first very viscid, and has a metallic aspect; but by an excess of ammonia, it loses these properties, and becomes of a very deep brownish-red. When iodine is added to liquid ammonia, one part of it unites with the hydrogen of the alkali, and forms hydriodic acid, while another portion of iodine combines with the azote, and falls down in the form of a black powder. This compound of azote and iodine detonates with a very gentle heat, and even with the slight- est touch. Iodine and Chlorine.—Iodine absorbs less than one-third its weight of chlorine, and forms a peculiar acid which may be called chloride, or chloriodic acid, and its compounds chloriodates. According to Gay Lussac, indeed, two compounds result, the one of a fine orange- yellow colour, containing the largest proportion of chlorine, the other orange-red. Both are solid and crystalline; deliquiate when exposed to the air; are fusible into an orange liquid; and give an orange-co- loured gas. The watery solution takes more iodine, and acquires a deep colour; but if agitated with chlorine, it is deprived of colour, and when poured in that state, into solution of potash, the deflagrating salt is precipitated. From liquid ammonia,the colourless liquid precipitates a white detonating compound; but the coloured solution throws down the darker compound, which detonates on the slightest touch, and is. indeed, identical with that procured by the direct action of iodine on ammonia. CHAP. XVIII. IODINE. 27 Chloriodic acid (or chlorurg of iodine, as it called by Gay Lussac) precipitates the salts of iron, lead, tin, and copper; probably in the state of oxyiodes. It has been observed by Gay Lussac, that, in order to convert the whole of a quantity of alkali into the deflagrating salt, without any of the hydriodate, (which oUierwise is produced in greater proportion than the oxyiode), it is necessary, first, to combine the iodine with chlo- rine; and, after dissolving the compound in water, to saturate it with alkali. Iodine and Euchlorine.—When iodine is exposed to euchlorine, Sir H. Davy has discovered,* that there is an immediate action; its colour changes to bright orange; and a liquid is formed. By the ap- plication of a gentle heat, the orange compound of chlorine and iodine is expelled, and a compound of oxvgen and iodine remains. This sub- stance is a white semi-transparent solid; it has no smell, but a strong astringent sour taste. Its specific gravity is such, that it sinks in sul- phuric acid. When decomposed by heat in a pneumatic apparatus, it is resolved into oxygen gas and pure iodine; and it is, therefore, termed by Sir H. Davy, oxyiodine; by Gay Lussac, acide iodique anhydre. Thir- teen grains afforded 9.25 cubical inches of oxygen gas, = 3.14 grains. Hence it is composed of Iodine . . . 75.85 . . . 100. . . . 314.8 Oxygen . . . 24.15 . . . 31.84 . . 100. 100. 131.84 414.8 On the supposition that oxyiodine is composed of five atoms of oxygen and one of iodine, the atom of iodine may be deduced to weigh 117.15, Now it is remarkable, that assuming hydriodic acid to con- sist of one atom of iodine and one of hydrogen, the weight of the atom of iodine is 117.77; for as .849 to 100 (the proportions in which hy- drogen and iodine combine) so is 1 to 117.77. If 10 represent the atom of oxygen, then the atom of iodine will weigh 150.62. Oxyiodine is very soluble in water, and is slightly deliquescent Its solution, called by Gay Lussac acide iodique, first reddens, and then destroys, vegetable blues, and reduces other vegetable colours to a dull yellow. When evaporated sufficiently, it becomes a thick pasty substance, and at length, by a cautiously regulated heat, yields oxyio- dine unaltered. When heated in contact with inflammable bodies, or with the more combustible metals, detonations are produced. Its solution in water rapidly corrodes all the metals, and even acts on gold and platinum, but especially the first. When its solution is poured into solutions of alkalies, or alkaline earths, or when made to act on their carbonates, triple compounds are formed of oxygen, iodine, and the metallic bases, called by Sir H. • Phil. Trans. 1815, part 2. • 28 IODINE. CHAP. XVIII. Davy, oxyoides; and by Gay Lussac, it would appear improperly, io- dates. With solution of ammonia, it composes oxyiode of ammonia; and from the soluble salts of barytes and strontites, it precipitates their respective oxyiodes. Forty-eight grains of oxyiode of potassium, when decomposed by heat, afforded Sir H. Davy 31 cubic inches, •= 10.5 grains of oxygen gas. Oxyiodine enters into combination with all those fluid or solid acids, which it does not decompose. Sulphuric acid, dropped into a satu- rated solution of it in hot water, precipitated a solid, which, on cooling, formed rhomboidal crystals of a pale yellow colour. This compound is fu>ible; and, with a heat properly regulated, maybe sublimed unal- tered. Hydronitric and hydrophosphoric acids afford analogous com- pounds. Oxalic and liquid muriatic acids decompose it. All its acid combinations redden vegetable blues; dissolve gold and platinum; and when added to alkalies or earths, afford common neutral salts, and their respective oxyiodes. In their crystalline state, the com- pounds of oxyiodine and acids are most probably hydrates; the acids carrying with them, into combination, their definite proportion of water. For the watery solution of oxyiodine, Sir H. Davy has proposed the name of oxyiodic acid, and is disposed to regard it as a triple com- pound of iodine, hydrogen, and oxygen; or an oxyiode of hydrogen. Iodine and Metals.—All the metals, with the aid of heat, unite with iodine, and form iodes, iodides, or iodurets, analogous, according to Gay Lussac, to sulphurets. When these compounds are placed in con- tact with water, it is decomposed, and a hydriodate of the respective metal is produced, the water furnishing hydrogen to the iodine and oxygen to the metal. Nature of Iodine.—Iodine, from all that we yet know respecting it, is to be considered as a simple or elementary body, having a very striking analogy with chlorine, which it resembles, Istly, in forming one acid by uniting with hydrogen, and a different acid with oxygen; 2dly, in its effects on vegetable colours; 3dly, in its affording, with the fixed alkalies, salts which nearly approach in characters to chlorates or hyper-oxymuriates; and 4thly, in its electrical habitudes. Its dis- covery, indeed, lends strong support to that theory, which considers chlorine as a simple body, and muriatic acid as a compound of chlo- rine and hydrogen. In the property of forming an acid, whether it be united with hydrogen or with oxygen, iodine bears, also, an analogy to sulphur; and it is remarked by Gay Lussac of the combinations of chlorine, iodine, and sulphur, with the elements of water, that while the acids, which they respectively form with oxygen, have their ele- ments strongly condensed, those formed with hydrogen have their elements very feebly united. Sulphur has the strongest affinity for oxygen, then iodine, and lastly chlorine. But for hydrogen, chlorine has a stronger attraction than iodine,and iodine than sulphur; whence it appears that the affinity of each of those bodies for oxygen is in- versely proportionate to its affinity for hydrogen. The source of iodine in nature has been investigated with much CHAP. XIX. METALS IN* GENERAL. 29 ability by M. Gaultier de Claubry.* His first experiments were di- rected to the analysis of the several varieties of Fucus,the combustion of which furnishes the soda of sea-weeds. Before these vegetables are destroyed by combustion, he ascertained that iodine exists in them in the state of hydriodate of potash; and that calcination only de- stroys the vegetable matters, with which it is combined. As the hy- driodate of potash is a deliquescent salt, it remains in the mother li- quor, after separating the carbonate of soda, and most of the other salts, by crystallization. In the course of these experiments, M. de Claubry found that starch is one of the most delicate tests of the pre- sence of iodine, and if added to any liquid containing it, with a few drops of sulphuric acid, iodine is indicated by a blue colour, of greater or less intensity. In this way, he detected iodine in the decoction of several varieties of Fucus; but he was unable to discover the slight- est trace of it in sea-water. The Fucus Saccharinus yielded it most abundantly; and in order to obtain it by the cheapest and easiest pro- cess, he recommends that we should submit this fucus, dried and re- duced to powder, to distillation with sulphuric acid. CHAPTER XIX. OF THE GENERAL PROPERTIES OF METALS. THFi metals compose a class of bodies, which are not more inter- esting from their application to the common arts of life, than from the facts which they contribute to the general principles of chemical science. Only seven or eight were known to the ancients; but the class has been enlarged, within the last century, by the discovery of more than twenty new ones. In addition to the recently discovered bases of the alkalies and earths, the following appear to have a suffi- cient claim to be considered as distinct metals. 1. Gold. 2. Platinum. 3. Silver. 4. Mercury. 5. Rhodium. 6. Palladium. 7. Iridium. 8. Osmium. 9. Copper. 10. Iron. 11. Nickel. 12. Tin. 13. Lead. 14. Zinc. 15. Bismuth. 16. Antimony. 17. Tellurium. 18. Selenium. 19. Arsenic. 20. Cobalt. 21. Manganese. 22. Chrome. 23. Molybdena. 24. Uranium. 25. Tungsten. 26. Titanium. 27. Columbium. 28. Cerium. * Ann. de Chim. xciii. 75, 113. SO METALS IN GENERAL. CHAP. XIX. Of a class comprehending so many individuals, it is not easy to offer a general description; but it will be found that they are all characterised by one or more of the following properties. 1. With the exception of the newly discovered bases of the alkalies and earths, they are distinguished by a high degree of specific gra- vity; the lightest of the metals (tellurium) being considerably heavier than the most ponderous of the earths. They are, perhaps, the only solid bodies, whose specific gravity is affected by mechanical means; or, in other words, whose particles can be brought permanently into a state of nearer approximation by external pressure. In consequence of this property, several of the metals undergo material changes in their -specific gravity, by the mechanical operations of rolling, ham- mering, &c. It may be questioned, whether the metals are heavier, in consequence of the greater specific gravity of their individual atoms, or from a greater number of atoms being aggregated into a given volume. The former, however, is most probably the case, though it must be acknowledged that their specific gravity is by no means ex- actly proportional to the weight of their atoms. 2. They are opaque, at least in the state in which they generally occur to our observation. Gold, however, beat into leaves 1-280000th of an inch in thickness, transmits a faint greenish light, when held between the eye and the direct light of the sun. 3. They possess various degrees of lustre, and it is of so peculiar a kind, that it has been termed by mineralogists the metallic lustre, and referred to as a known standard in the description of other mine- rals. Some of the metals possess this property in so remarkable a degree, as to be applicable to highly ornamental purposes. Polished steel takes place of all the metals in the perfection of its lustre; but some of the class (as cobalt and nickel) appear to be susceptible of it in only a small degree. 4. The metals are excellent reflectors, not only of light but of calo- ric; and hence they are the best materials for the composition of burning mirrors. From the experiments of Mr. Leslie, they appear to possess this property in the following order, the highest number denoting the greatest reflecting power. Brass............100 Silver............90 Tinfoil...........85 Planished block tin.......80 Steel............70 Lead............60 Tinfoil softened by mercury .... 50 In general, the reflecting power was found, by Mr. Leslie, to be proportionate to the degree of polish, and to be impaired by every thing that diminished this quality. A tin reflector, for example, had its reflecting power diminished nine-tenths by being rubbed with sand paper. 5. Metallic bodies are, of all others, the best conductors of electri- CHAP. XIX. G1 N ERAL PROPERTIES.. .31 city. Their property of electro-motion has already been described, in the chapter on the chemical agencies of electricity and galvanism. 6. They are, also, excellent conductors of caloric. 7. One of the most useful properties of the metals is their mallea- bility, or capacity of being extended by the blows of a hammer. In this quality, gold takes place of all the rest. The gold-leaf, which is sold in books, is so extremely thin, that less than five grains cover a surface of about 272^ square inches; and the thickness of each leaf does not exceed l-282020th part of an inch. All the metals, however, are not malleable. Gold, platinum, silver, palladium, mercury (in its frozen state), copper, iron, lead, tin, zinc, and nickel,* are the only ones to which this property belongs. The rest, on account of their brittleness, were formerly called semi-metals. But since, even in these, a diminishing progression of malleability may be observed, the distinction, though retained in common language, is very properly re- jected from chemical and mineralogical systems. 8. All the metals that have been described as malleable (with the ex- ception, perhaps, of nickel) are also ductile, or may be drawn out into wire. In this respect, also, gold appears to take precedence of the rest, for it may be drawn out into wire not thicker than a human hair. 9. Wires of the same diameter, but of different metals, are found to be capable of sustaining very different weights This arises from their variable tenacity, which is estimated by gradually adding weights till the wire is broken. From the experiments of Guyton Morveau, the following are the utmost weights, which wires of 0.787 of an Eng- lish line in diameter can support without breaking. lbs. dec). avoird. parts. A wire of iron supports 549.250 ---------copper ------- 302.278 ---------platinum-------274.320 --------- silver ------- 187.137 ---------gold ------- 150.753 --------- Zinc ------- 109.540 --------- tin ------- 34.630 ---------. lead ------- 27.62 It The tenacity of tin is greatly inferior to that of gold; and lead has still less tenacity than tin, and even than some sorts of wood. 10. Some of the malleable and ductile metals have, also, a high de- gree of elasticity. This property fits them for being applied to the mechanical purpose of springs. Steel and iron are, in this respect, superior to all other metals. Beside the circumstances of agreement in their physical qualities, which have been enumerated, the metals resemble each other, also, in their chemical properties. Some of these resemblances it may be pro- per to state, for the purpose of avoiding unnecessary repetitions. * Nickel on the authority of Richter f 71 Ann. de Chim. 182. i* METALS IN GENERAL. 0HAP. XI>". The metals, so far as we know at present, are simple or elementary bodies, and may be arranged in the class of simple combustibles. They were formerly, indeed, considered, but on very insufficient evi- dence, as composed of a combustible base, peculiar to each metal, united with a general principle of inflammability, which received the name of phlogiston. When the metals are exposed to a strong heat, the first change which is produced in them is that they melt, or run into fusion. This effect takes place, in the different metals, at very diffe- rent temperatures. Some of them may be made to boil, and are actu- ally converted into vapour, at a heat considerably below redness; while others require a very intense heat for their fusion. By a sufficient elevation of temperature, it is probable, however, that they would all be volatilized; for platinum itself, which does not melt at a less heat than 170° of Wegdwood, has been observed to boil, when placed in the focus of a powerful burning lens.* In some of the metals, no far- ther change is produced by the application of heat with the free access of air; and they return, on cooling, to their former condition. But other metals undergo a very remarkable change. Their cohesion, lustre, malleability, tenacity, and all the properties that have been described as characteristic of them, are destroyed. Though their ab- solute weight is increased, yet they become specifically lighter, and they are distinguished by a new train of properties not observed in the metals themselves. These changes have been very differently explained, at different periods in the history of chemical science. On the theory of phlogis- ton, they were accounted for by assuming that the metal s, during the process of exposure to air at a high temperature, abandon their phlo- giston, which, it was supposed, unites with the air and renders itphlo- gisticated, and consequently unfit for supporting the combustion of other inflammable bodies. The hypothesis, however, could no longer be maintained, when it was proved that the metals, so far from losing weight, become heavier after the operation; and though various at- tempts were made, by modifications of the theory, to accommodate it to this fact, yet none of them can be considered as having been at all successful. The theory, which is now almost universally admitted, as best ex- plaining the phenomena in question, though suggested by the hints fur- nished by preceding discoveries, was first reduced to a systematic and consistent form by Lavoisier. The metals, according to the views of this enlightened philosopher, undergo the changes that have already been described, in consequence of the absorption of oxygen from the air. Hence, while the metallic body becomes heavier, the air, in which the process is performed, should sustain a proportional dimi- nution of weight. That this is the fact, admits of being demonstrated; and still more readily and satisfactorily, if we employ oxygen gas in- stead of common air. A certain quantity of oxygen gas (or the whole indeed, under favourable circumstances) disappears; and the increase of weight in the metal is found, on examination, to be precisely equal * Annales de Chimie, Ixix. 92. 11AP. XIX. OXIDATION OF METALS. • # •>•'" to that of the gas which has been condensed. In some cases, we can even go farther: and separate the oxygen from the metal by the mere application of heat, the oxygen being recovered in the state of gas, and the metal returning to a metallic state. More satisfactory evi- dence than this could scarcely be required of the nature of the change which takes place; and it maybe admitted, therefore, as an establish- ed truth, that metals lose their metallic form, in consequence of their combination with oxygen. The process has been called by Lavoisier oxidation, and the result of it an oxide. For the former term, how- ever, Mr. Chenevix, influenced by reasons which are stated in his work on chemical nomenclature, has proposed to substitute that of oxidizement. In the following pages, I shall employ both these ex- pressions indiscriminately. The phenomena and results of the oxidizement of metals are not the same in all cases, but differ very considerably with respect to dif- ferent metals. 1. Some metals are oxidized by mere exposure to atmospheric air at the ordinary temperature, and even to air which has been deprived of its hygrometric water. Arsenic, manganese, and the new metals discovered by Sir H. Davy, are perhaps the only ones which have been proved to possess this property. Others, it is true, as lead and copper, are changed by the action of the air, but extremely slowly, and not without the conjoined operation of moisture. 2. Other metals undergo this change, but not without a considerable increase of their temperature. Iron, zinc, copper, tin, &c, when heat- ed to redness, lose their metallic lustre, and are slowly converted into variously coloured oxides. In some instances, the process is accom- panied with so abundant an extrication of light and heat, as to exhibit a vivid inflammation. This happens, chiefly, with some of the volatile metals. Arsenic and zinc, for example, when projected into a red-hot crucible, emit a brilliant flame. In other metals, the process is unac- companied by any remarkable phenomena, and is known to have taken place only by its results. To convert the metals into oxides, there is a degree of heat, which is peculiar to each metal, and even to different oxides of the same metal. Mercury, for example, is oxidized, at a degree of heat, which produces no change on iron; and lead at one degree of temperature becomes minium, at another massicot. 3. With the exception of mercury, the met^ which have been called perfect (comprehending, also, gold, platinifni, silver, and palla- dium), are not oxidized, even by the combffed operations of air and of an increased temperature. Gold, silver, and other metals of this kind, may be kept for many days in fusion, without undergoing any change. That they have an affinity, however, for oxygen, and are even capable of taking it from atmospheric air, is proved by the effect of an electrical or galvanic battery. By the former, the wires of the perfect metals are, at the same moment, dispersed into smoke and oxidized; and by transmitting a powerful discharge, through any of the perfect metals beaten into thin leaves, the metal burns with a re- markable degree of splendour. Vol. II.—-E b4 * METALS IN GENERAL. CHAP. XIX. 4. All metals, that are oxidized by atmospherical air, are still more readily oxidized by oxygen gas. In many cases a metal, which un- dergoes this change slowly and invisibly by the action of air, takes fire in oxygen gas, and exhibits a bright inflammation. For example, it has already been shown, that an iron wire may be entirely and vi- vidly consumed in oxygen gas. These are the most simple cases of metallic oxidizement. In or- der that the changes, which have been described, may take place, it is only necessary that there should exist a stronger affinity between oxygen and the metal, than between the oxygen and light (and per- haps the electricity) which constitute the gas. In other cases, the phenomena are more complicated, and the metal acquires oxygen by the decomposition of some other compound. Of these sources of oxy- gen, the most important, if not the only ones, are water, the acids, and other oxides; or compounds containing one or more of these sub- stances. I. Water gives up its oxygen to those metals only which manifest a powerful affinity for that basis, and, generally speaking, to those which are most efficient in decomposing atmospherical air. The newly discovered metals of Sir H. Davy decompose it with a rapi- dity, which amounts to actual inflammation; but, in general, the change is slow at common temperatures. Iron filings, for example, when moistened with water, and confined in an inverted jar over mercury, become very gradually oxidized, and evolve hydrogen gas. But water, brought into contact with red-hot iron, is rapidly decom- posed, and hydrogen gas is disengaged in torrents. Water, it is observed by Gay Lussac, has the power of bringing all metals, on which it is capable of acting alone, to the same degree of oxidation as when assisted by the action of acids, sometimes to a higher degree, but never to an inferior one. Thus water by itself oxidates tin to the maximum, and iron and potassium to the medium; but mingled with acids, it oxidates iron and tin to the minimum. II. All those acids in which oxygen has been proved to exist, and especially those which Dr. Thomson has called supporters of combus- tion, and the neutral salts containing them, are efficient means of ox- idizing the metals. In general, the less strong the affinity of the acid base for oxygen, the more rapidly is the metal oxidized. Those acids, that have not been proved to contain oxygen (except the oxymuria- tic, the presence ofcpxygen in which is still a subject of controversy) are remarkably ineW in their action on metals; and the same inacti- vity belongs to other aftls, in which the oxygen and base are held combined by a powerful affinity. Thus concentrated sulphuric acid, at the temperature of the atmosphere, scarcely attacks any of the metals; because the oxygen and sulphur, of which it consists, forci- bly attract each other. On the other hand, the nitric and nitro-mu- riatic acids, in which there exists a large quantity of loosely com- bined oxygen, readily abandon a part of it, and act on the metals with considerable energy. Even the perfect metals are oxidized by the last acid; and thus we obtain proof that the resistance, which the per- fect metals show to the action of oxygen gas, is not owing to their O-HAP. XIX. OXIDATION OF METALS. 35 want of affinity for that basis, but to the predominance of other op- posing forces. Some of the acids, which do not, in their concentrated state, act upon metals, acquire the power of oxidizing them when diluted with water. This is true of the sulphuric and muriatic acidsv to either of which, when concentrated, we may apply iron or zinc, without any change ensuing. But on adding water, the metal disappears, and hy- drogen gas is abundantly evolved. Now it is a principle, to which no exception has yet been discovered, that a metal cannot, in its perfect- ly metallic state, unite with any acid. In order to be dissolved, it must first be brought into the state of an oxide; and in the case which has been just now stated, no substance, capable of furnishing oxygen, is in contact with the iron except water. As an additional proof that water is, in this instance, the source of the oxygen, it has been ascer- tained that no portion of the acid is decomposed; but that the same quantity of acid exists in combination with oxide of iron, as was ori- ginally submitted to experiment. By measuring the quantity of hydrogen gas, evolved in experiments of this kind, it is not difficult to calculate how much oxygen the metal has acquired; since every 100 cubic inches of hydrogen gas indicate the transference to the metal of about 17 grains of oxygen. Equal weights of different metals evolve different quantities of hydrogen gas, in consequence of their combining with different quantities of oxygen. If one metal, for example, in order to become soluble in sul- phuric acid, require 40 per cent, of its weight of oxygen, and another only 20 per cent., the former will disengage twice as much hydrogen gas as the latter. The same metal, also, in different states, may evolve different quantities of hydrogen. If, for example, the metal be already a little oxidized, it will set at liberty less hydrogen than if it were perfectly metallized. On this principle, the different proportions pf real metal in several varieties of iron and steel have been investigated, the most perfectly metallized iron yielding, of course, the most hydro- gen gas. The phenomena, observed during the solution of a metal, and those attending the solution of its oxide, in the same acid, are essentially different. For the most part, a metal is dissolved with effervescence, an appearance always occasioned by the escape of gas. Iron, it has already been stated, effervesces strongly during its solution in dilute sulphuric acid; but the black oxide of that metal is taken up silently, and without any discharge of gas. III. The metals may be oxidized by the transfer of oxygen from other metallic oxides. Thus, when iron filings are distilled with the red oxide of mercury, the oxygen passes to the iron, and the mercury is revived, or appears in a metallic state. In a similar manner, the oxides held in solution by acids, are decomposed by immersing, in the solution, other metals. When copper, for exam- ple, is immersed in a solution of nitrate of mercury (consisting of oxide of" mercury and nitric acid) the latter metal is deprived of its oxygen by the former, and appears on the surface of the copper in a revived state. The nitrate of copper, which is thus produced, is pre- ,>u METALS IN GENERAL. CHAP. XIX- cipitated by iron, which has a stronger affinity than copper for oxy- gen. A variety of similar examples might be given, in which the pre- cipitating metal takes oxygen from that which is precipitated. In cases of this sort, it must be confessed that the comparative affinities of the acid for the oxides of the two metals have some share in the effect, but much less than the affinities of oxygen separately consi- dered. The precipitated metal, also, is seldom quite pure, but almost always contains a portion of the metal, which has caused the precipi- tation. From an attentive examination of facts of this kind, Lavoisier has deduced the proportion of oxygen necessary to the solution of differ- ent metals, according to this analogy: As the quantity of the precipi- tant is to that of the precipitated metal, so is the quantity of oxy- gen necessary for the solution of the precipitated to that necessary for tJie solution of the precipitant. Thus it has been found by expe- riment that 135 grains of mercury are necessary for the precipitation of 100 grains of silver from the nitric acid. It is evident, then, that 135 grains of mercury require, to become soluble, the same quantity of oxygen as 100 grains of silver; and, therefore, as 100 to 135, so is the quantity necessary to render soluble 100 grains of mercury, to that necessary for the solution of 100 grains of silver. Now eight grains of oxygen are necessary to the solution of 100 grains of mer- cury; and therefore 10.8 grains are required for the solution of 100 grains of silver By an extension of the same experiments to other metals, Lavoisier formed a table of the quantity of oxygen necessary for the solution of all the metals; but I omit giving it in this place, because subsequent discoveries have pointed out in it several inac- curacies. Such are the principal means of effecting the oxidation of metals. Different individuals of the class, it has already been stated, combine with different proportions of oxygen; and it has been conceived by M. Frere de Montizon, that a relation exists between the specific gra- vity of the metals, and the quantity of oxygen, with which they are ca- pable of uniting, the oxygen being either a multiple or submultiple of the density.* Thus the specific gravity of manganese being 7, the oxygen of the protoxide is by experiment 28.1, which is very nearly a multiple of the density by 4. The law, however, cannot be con- sidered as sufficiently established. If it were to hold good univer- sally, it would indicate the existence of a relation between the den- sity of metals and the weight of their atoms. The same metal, it may now be added, is susceptible of different degrees or stages of oxidation. Iron, for example, when united with oxygen in the proportion of 29.5 grains to 100 grains of metal, com- poses a. black oxide; and with 43.5 parts of oxygen to 100 of metal, it constitutes a red oxide. These different oxides of the same metal have not only different colours; but each of them is characterized by a distinct train of chemical properties, and especially by different * Ann. de Chim. et Phys. vii. 7. Thomson's Ann. xii. 8. HAP. XIX. METALLIC SALTS. 37 habitudes with respect to the acids. Thus the black oxide of iron readily unites with muriatic and sulphuric acids; but the red oxide less easily. The salts with base of the first oxide afford a white pre- cipitate with triple prussiate of potash; and none at all with the gallic acid, or with sulphuretted hydrogen. But the salts, in which the iron is at the maximum of oxidation, give a deep-blue compound with the triple prussiate, and a black one with the gallic acid. It is an interesting question, whether the same metal is capable of uniting with oxygen, in all proportions between the maximum and minimum, or whether it does not rather combine with that principle in a few proportions only, between which there are no intermediate compounds. Are there, for example, only two oxides of mercury, the black, consisting of 100 parts of metal united with four of oxygen; and the red, composed of the same quantity of metal and eight parts of oxygen? The determination of this point requires more precise and multiplied appeals to experiment, than have hitherto been made. But in a great variety of cases, where the question has been accurate- ly investigated, different oxides of the same metal do appear to con- tain oxygen, in proportions which are simple multiples of each other; and the fact will probably be established with respect to all other oxides. It is by no means necessary, however, that the possible num- ber of oxides of any one metal should be limited, as Proust has sup- posed, to two; for it is perfectly consistent with the atomic hypothesis that there may be three, four, or even a greater number. It had been long known that of different oxides of the same metal, the one which contains a larger proportion of oxygen is capable of saturating more acid, than the one which contains less. Two of the illustrations, which are given of this principle, are furnished by the muriates of copper and the muriates of mercury. Corrosive muriate of mercury is composed of the red oxide of that metal, united with muriatic acid; and the sub-muriate (calomel) consists of the black oxide, combined with the same acid. Now it is remarkable that, ac- cording to the experiments of Thenard, the oxygen in the red oxide is just double of that in the black; and that the acid in the corrosive muriate is, also, precisely double that in the sub-muriate. Similar facts have been ascertained by Proust, with respect to the two mu- riates of copper, as appears from the following statement. {100 copper. 24.57 oxygen. 83.18 acid. {100 copper. 12.28 oxygen. 41.59 acid. The same law appears, also, from the experiments of Sir H. Davy, to hold good with respect to the oxides of potassium and sodium. To this principle, an important addition has lately been proposed by Gay 38 METALS IX GENERAL. CHAP. XIX- Lussac,' and supported by a variety of illustrations: viz. that the quantity of acid, which different metals require for saturation, is in direct proportion to the quantity of oxygen in their oxides. Let us suppose, for example, that of any two metals, A combines with twice as much oxygen as B; then, a given weight of the oxide of A will neutralize twice as much of any acid as an equal weight of the oxide of B. The solubility of the metallic salts in water, it has been observed by Gay Lussac, bears a proportion to the quantity of oxyen in the oxides; and consequently to the quantity of acid with which that oxide is com- bined. Salts, in which the metal is at the minimum of oxidation, are generally those which are most insoluble. This is the fact with re- spect to the salts of lead, silver, and mercury; for these are metals which, at the minimum of oxidizement, take very little oxygen, and consequently very little acid. Corrosive muriate of mercury, also, which contains the largest proportion of oxygen and acid, is much more soluble than the subinuriate, in which both the oxygen and acid are present in considerable less quantity. An important law has been deduced by Berzeliust from the compa- rison of a great number of facts; viz. that in all neutral salts, the oxy- gen of the acid is a multiplication of that of the base by some entire number. The law, he apprehends, may be expressed more generally in the following terms. When two oxidated substances enter into a neutral combination, the oxygen of that, which, in a galvanic circle, would be attracted to the positive pole, is a multiplication, by an en- tire number, of the oxygen of that, which would be deposited at the negative pole. For example, 279 parts of protoxide of lead contain 19.95 parts of oxygen, and saturate 100 parts of sulphuric acid, which contain 59.85 parts of oxygen. Now the oxygen of the oxide 19.95 X 3 = 59.85, which is precisely the oxygen of the acid. The same coincidence holds good in a variety of other instances. There is a certain state of oxidation, peculiar to the different me- tals, in which they are most readily acted upon by the several acids. Iron and manganese, for example, at the maximum of oxidizement, are altogether'insoluble in nitric acid; but readily dissolve in it, when combined with a smaller proportion of oxygen. Even when once brought into combination with that acid, the oxide, by attracting a further quantity of oxygen from the atmosphere, or from any other source, is separated in the state of an insoluble precipitate. This principle explains the change, which is produced in solutions of iron, by keeping them exposed to air. The oxides of iron and manganese, saturated with oxygen, a/e soluble, however, in the less oxygenated acids; for example, in the sulphurous or nitrous, which first deprive the oxide of part of its oxygen, and then dissolve the less saturated oxide. Beside the class of acids, which are the best solvents of the metals, alkaline solutions act upon metallic substances. The water, which * Mcmoires d'Arcueil, ii. 159; or 37 Phil. M^g- 200 r 79 Ann. de Chim. 127. CHAP. XIX. REVIVAL OF OXIDES. 39 holds the alkali in solution, is decomposed; its hydrogen is disen- gaged, arid its oxygen transferred to the metal; and the oxide, thus produced, is taken up by the alkaline liquor. The oxides ready form- ed, are also, in several cases, dissolved by liquid alkalies. When a pure alkali is added to a metallic solution, the metal is precipitated in the state of an oxide; but the precipitate is seldom quite free from alkali, and the metallic oxide, in a few instances, instead of appearing in a separate form, is dissolved by the alkali. When alkaline carbo- nates are employed instead of pure alkalies, for the precipitation of metallic solutions, the oxide combines with carbonic acid, and appears in the state of a metallic carbonate. The compounds of ammonia with metallic oxides are of more import- ance than those of the other alkalies, and have obtained the generic name of Ammoniurets. They may be formed, either by acting on the me- tals with liquid ammonia, the water in which is decomposed, and fur- nishes a metallic oxide, which unites with the alkali; or they may be produced, by exposing the oxides to ammoniacal gas, at the tempera- ture of the atmosphere. At least fifteen oxides, or rather hydrated oxides may be brought into combination with ammonia, viz. oxides of zinc; deutoxidc of arsenic; both the oxides of copper; oxide, of sil- ver; tritoxide and tetroxide of antimony; oxide of tellurium; prot- oxides of nickel, cobalt, and iron; peroxide of tin; deutoxide of mer- cury; and deutoxides of gold and platinum. The ammoniurets are decomposed by a strong heat; the oxygen of the oxide uniting with the hydrogen of the alkali, and the azote of the latter being sot tree. In some cases, as in that of ammoniuret of gold, this decomposition is attended with a loud explosion. The oxides, existing in metallic solutions, are decomposed by in- flammable substances. Light only is sufficient for the decomposition of some of them. Hydrogen gas-, charcoal, sulphur, phosphorus, and the compounds of hydrogen with the last three bodies, when brought into contact with the solutions of perfect metals at common tempera- tures, attract the oxygen from the metal, and occasion its appearance in a metallic form. In this way, several beautiful appearances may be produced, which will be described in treating of the individual me- tals. The oxides themselves are decomposed when exposed to a strong heat in contact with hydrogen, charcoal, or phosphorus. The two first, or substances containing them, are chiefly employed for the de- composition of those oxides, which occur as natural productions. The oxide, mixed with a portion of inflammable matter, is exposed to an intense heat; and, in order to obtain the metal in a coherent mass, and not in the small grains which would otherwise be formed, some substance is generally added, which is capable of being melted, and of allowing the metal to subside through it. Substances of this kind are called fluxes, and the process is termed the revival or reduction of the metal. If only one oxide had existed of each metal, it would have been easy, by applying the general principles of chemical nomenclature, to 4U metals in general. CHAP. XIX. have distinguished them by names sufficiently expressive of their com- position. But as the metals are susceptible of several stages of oxidize- ment, it is difficult to find terms, which sufficiently express the cha- racteristic distinctions of the several oxides of the same metal. The existence of only two oxides would have greatly simplified their no- menclature; for, in this case, we might have applied the term oxide to the metal fully saturated with oxygen, and of oxidule to the com- pound at an inferior state of oxidizement, as has been done by several of the French chemists. In the present state of the science, however, this nomenclature is inadmissible; and the specific name has been de- rived from some external character, chiefly from that of colour. Thus we have the black and red oxides of iron; and the black and red oxides of mercury. In some instances, the denominations, which have been proposed by Dr. Thomson for the metallic oxides, may be advantage- ously adopted. When there are several oxides of the same metal (supposing that the proportions of oxygen and metal in each are de- finite) he has proposed the terms protoxide, deutoxide, tritoxide, &c. signifying that the metal is in its first, second, or third, stage of oxi- dizement. Or if two oxides only of any metal are known, he suggests the. appellation of protoxide for that at the minimum, and of peroxide for that at the maximum, of oxidation. A similar difficulty has been experienced, also, with respect to the neutral salts with metallic bases; for when different oxides of the same metal combine with a given acid, the resulting salts require to be distinguished by appropriate names. This has sometimes been done by prefixing the word oxygenized (or for brevity oxy-) to the salt containing the most highly oxidized metal; as the muriate and oxy-muriate of mercury. The latter term, however, is improper) because, in strictness, it can only be applied to the compounds of oxy-muriatic acid with different bases; whereas what was meant to be expressed is merely a compound of ordinary muriatic acid, with mer- cury in its higliest state of oxidizement, If the principle, assumed by Gay Lussac, should be confirmed by farther investigation (viz. that the acid in metallic salts is proportional to the oxygen in the oxides,) it will be more easy to derive a specific name from the pro- portion of acid than from that of oxygen. Thus we shall have the muriate and submuriate of mercury. But till greater precision is acquired in our knowledge of this class of bodies, it may be well to continue to derive the specific name of the salt from some obvious qualify; as the green and red sulphates of iron, the white and green muriates of copper, &c. CHAP. XIX. COMPOSITION OF OXIDES. 41 The following Table exhibits, at one view, the composition of most of the metallic oxides. Table showing the Proportions of Oxygen with which the Metals combine. Metals. No. of Oxides. Colour of Oxides. 100 of Metal take Oxygen. 10.01 8.287 ? 16.38 5 Authority. Gold 1 Brownish black Oberkampf. Platinum 1 2 Black Berzelius. Palladium 1 14.209 Ditto. Rhodium 1 2 3. 6.71 ■) 13.42 C 20.13 5 Ditto. Iridium 1 2 Blue Red ::i Tennant. Silver 1 Olive 7.925 Berzelius. Mercury 1 2 Black Red t } Thenard. Copper 1 2 Red Black Black Red 12.5 ^ 25. 5 Proust and Berzelius. Iron 1 2 29.5 I 44.25 5 Berzelius. Tin 1 2 ■ Grey "White 13.5 I 27. 5 7.70 7 11.08 £ 15.60 3 27. unknown Gay Lussac. Lead 1 2 3 Yellow Red Puce Berzelius. Nickel 1 2 Ash grey Black Tupputi. Thenard. Zinc 1 White 24.41 Gay Lussac. Bismuth 1 Yellow 11.28 Lagerhielm. Antimony 1 2 (acid) 3 (acid) Dull white Snow white Yellow 18.60 } 27.90 C 37.20 3 34.93 7 52.4 5 Berzelius. Arsenic 1 (acid) 2 (acid) White Ditto Dr. Thomson. Cobalt 1 2 Blue Black 19.8 •) 33.25 5 Proust. Vol. II.—F 42 METALS IN GENERAL. CHAP. XIX. Metals. No. of Oxides. Colour of Oxides. 100 of Metal take Oxygen. 14.05 28.10 •) 42.16 C 56.21 3 34. 1 50. 3 20.5 Authority. Manganese 1 2 3 4 Green Black Dr. John. Berzelius. Molybdena 1 2 (acid) Blue White Bucholz, Tellurium 1 Yellowish Klaproth. Tungsten 1 2 (acid) Black Yellow 25.' 3 25.' 5 Bucholz. Uranium 1 2 Black Yellow Blue Red White Ditto. Titanium 1 2 3 ':':} Vauquelin. Tantalum •• White Cerium 1 2 White Fawn 17.41 7 26.115 i Hisinger. Many of the metallic oxides have an attraction for water, which they manifest by being soluble in it, or by reducing it to a solid, or gelatinous form. The soluble oxides are potash, soda, barytes, stron- tites, and lime; the deutoxide of arsenic, and the oxide of osmium. There are a few others, which are soluble in a very small degree, no exceeding one-thousandth of the weight of the water, viz. oxide of molybdena, deutoxide of mercury, tritoxide and tetroxide of antimony. The compounds of oxides and water, in which the latter exists in a eondensed state, are termed hydrates, or hydro-oxides, or hydrox- ures. The hydrates of potash, soda, and barytes retain the water which constitutes them such, at the temperature of ignition, and it can only, indeed, be expelled by bodies that have a stronger affinity for the alkali or earth. The hydrates of the remaining earths are decom- posed by the heat of ignition. The hydrated oxides of the common metals are obtained, by adding a solution of pure potash, soda, or am- monia, to the solution of the oxide in sulphuric, muriatic, or nitric acid. The precipitate, washed repeatedly with water, is to be col- lected on a filter; and, if dried, the heat employed must be as gentle as possible; for a slight elevation of temperature is sufficient to ex- pel the whole water, and to leave only an oxide. The hydrated oxides are, for the most part, much more soluble in acids than die oxides. According to Berzelius, they are definite compounds, in such proportions, that the oxygen of the water is equal in weight to that of the oxide. This principle requires, however, to be established by a greater number of facts. CHAP. XIX. METALLIC SULPHURETS. 43 Besides the important class of compounds, which result from the union of metals with oxygen, the metals are capable, also, of entering into combination with hydrogen, sulphur, chlorine, phosphorus, and charcoal. They afford, also, by uniting with each other, an interest- ing class of compounds called metallic alloys. I. The compounds of metals with hydrogen are neither nume-. rous nor of much importance. When water is decomposed by cer- tain metals, at the same time that the oxygen combines w ith one por- tion, the hydrogen, which is disengaged in the state of gas, takes up a minute quantity of metal. This is the case, in a small degree, with iron; still more with zinc; and most remarkably with potassium, ar- senic, tellurium, and selenium, all of which afford compounds, having several remarkable properties. II. The combinations of metallic bodies with sulphur have been divided by Vauquelin* into three classes, viz. 1st, the com- pounds of metals with sulphur, which alone are with propriety called sulphurets; 2dly, the compounds of sulphur with metallic oxides, termed sulphuretted oxides; and 3dly, those of sulphuretted hydro- gen with metallic oxides, which may be called hydro-sulphuretted oxides. 1. All the metals, with the exception of gold, zinc, and tin, are, in their metallic state, susceptible of combination with sulphur. In order to effect their union, it is sufficient that one of the bodies be brought into a fluid state; and as sulphur is readily fusible, a very moderate heat only is required for the purpose. Thus a mixture of 45 parts of iron filings with 15 of sulphur, or of 40 parts of copper filings with 15 of sulphur, when heated in a glass tube, combines, the moment the fusion of the sulphur is accomplished. The phenomena are very re- markable, consisting in a sudden and bright glow, like that of intense ignition. During combination, however dry the materials may have been, it appears from the experiments of Mr. Clayfieldt that a quan- tity of elastic fluid is liberated, amounting to nine or ten times the bulk of the mixture, and consisting of sulphuretted hydrogen and sul- phurous acid. The former, probably, arises from the sulphur, and the latter from the metallic filings, which may have been partially oxidized by the process of washing and drying. In these compounds, the properties of the metals cease to be appa- rent; for the sulphurets are brittle; have colours different from those of the metals; and, when artificially formed, are destitute of lustre. The quantity of sulphur, with which different metals are capable of uniting, varies with each metal. The same metal, also, in some in- stances, is susceptible of combination with different quantities of sul- phur, and of affording compounds, characterized by a distinct train of properties. Thus the compound of 100 parts of iron with 58£ of sul- phur is brittle and of a dark grey colour; has little or no lustre; and is attracted by the magnet But 100 parts of iron with 117 of sul- phur form a yellow compact compound; of sufficient hardness to * Annales de Chimie, xxxvii. 57. f Note to Mr. Davy's paper on alkalies. (Philosophical Transactions, 1808.) 44 METALS in general. OHAP. XI>- strike fire with steel; and having so much lustre, as to have been often mistaken by the ignorant for gold. When different sulphurets of the Same metal exist, the sulphur, in those which contain the larger proportion, is an exact simple multiple of the sulphur in those which contain the less. The following Table exhibits the composition of several of the me- tallic sulphurets. 100 Parts of Unite with Sulphur. Gold Platinum 1st --------2d Palladium Silver Copper Iron 1st . --- 2d . Tin 1st . ---2d . Lead . . Nickel 1st ----- 2d Zinc . . Bismuth . Antimony Arsenic 1st ------ 2d Cobalt . Molybdenum ■V" 24.39 8.287 16.38 14.209 14.9 2.5.6 58.75 117. 27.234 54.5 15.92 51.5 77. 48.84 22.52 37.25 33.3 75. 39.8 67. Authority. Berzelius. Ditto. Ditto. Ditto. Ditto. Ditto. Ditto. Ditto. Dr. John Davy. Ditto. Berzelius. E. Davy. Ditto. * Dr. Thomson. Lagerhielm. Berzelius. Proust. Metallic sulphurets can only be partially decomposed by heat: and though this assertion appears to be contradicted by the effect of roast- ing these compounds; yet it is to be considered that the metals, when heated with the contact of air, absorb oxygen, and thus lose their affi- nity for sulphur. The sulphuret of one metal may, in many instances, be. decomposed by another metal. Thus when sulphuret of mercury is distilled with a proper proportion of iron filings, the sulphur passes to the iron, and the mercury comes over in a metallic state. Concentrated sulphuric acid* with the assistance of heat, acts upon metallic sulphurets, and is converted into sulphurous acid, which, being volatile, escapes. Metals which, in their separate state, were dissolved by dilute sulphuric acid, continue sensible to its action, after being combined with sulphur. When dilute sulphuric acid, however, acts on such compounds, instead of hydrogen gas simply, we obtain sulphuretted hydrogen. It is chiefly the compounds with the mini- mum of sulphur, that produce this effect; for the super-sulphurets, or those containing a farther proportion of sulphur, resist the action of this solvent * Berthollet, Annajes de Chimie, xxv. 256, CHAP. XIX. METALLIC SULrilUUETS. 41* Concentrated muriatic acid has no effect on sulphurets; but the di- luted acid acts like the diluted sulphuric. Nitric acid is decomposed by the metallic sulphurets; nitrous gas is disengaged; and sulphur is precipitated.* In this case, though all nitric acid contains water, yet sulphuretted hydrogen is not formed, because the acid yields its oxygen more easily than water. Sulphurets, composed of metals, which powerfully attract oxygen, and the oxides of which have moreover an affinity for sulphuric acid, absorb oxygen from the atmosphere, and pass to the state of sulphates. In this way most of the sulphate of iron is formed, which occurs in commerce. ^But if the metal has either a strong affinity for sulphur, or a weak one for oxygen, then the conversion into a sulphate does not happen, as in the sulphurets of copper, antimony, and mercury.t The sulphuret of jiron containing a full proportion of sulphur resists, also, the conjoined action of air and moisture. 2. In general, the metals have a stronger affinity than their oxides for sulphur. But there are a few cases, in which certain metals are incapable of combining with sulphur, till they are brought into the state of oxides. These are chiefly zinc, mercury, and manganese, the compounds of which with sulphur may be called sulphuretted oxides.% Other metals, also, are capable of affording similar compounds; but in general their affinity for sulphur diminishes, in proportion to the quantity of oxygen which they hold in combination. These compounds act on acids, somewhat differently from the mere sulphurets. If the metal be only oxidized at its minimum, they yield sulphuretted hydrogen with diluted muriatic and sulphuric acids, and nitrous gas with nitric acid. But in their perfectly oxidized state, they dissolve without effervescence, and the sulphur remains unal- tered. 3. Sulphuretted hydrogen enters into combination with a few of the metals, with mercury and silver for example; but it unites, in ge- neral, more readily and permanently with their oxides. From such compounds, the sulphuretted hydrogen is detached in a gaseous state by some concentrated acids, which seize the metallic oxide. Most of ihe sulphuretted oxides, also, undergo, in process of time, spontaneous decomposition, in consequence of the union of the hydrogen and oxy- gen which they contain, and which, by combination, form water. When this happens, the oxide is partly reduced, and the sulphur unites with the deoxidized metal. Hence the same sulphuretted oxide varies in composition, according to the period which has elapsed since its pre- paration. When we precipitate a metallic solution by sulphuretted hydrogen alone, or by its compounds with alkalies, we obtain either a metallic sulphuret or a hydro-sulphuret.. In the first case, the hydrogen of the sulphuretted hydrogen takes all the oxygen of the oxide; and the sui- * Vauquelin, loc. cit. 65. fvBerthollct, loc. cit. 256. $ Vauquelin asserts, however, (Ann. de Chim. et Phys. v. 6,) that the oxides of manganese and iron are decomposed by sulphur, and that true me' tallic sulphurets are formed. 46 METALS £\ GENERAL. CHAP. XIX. phur forms a true sulphuret with the reduced metal. In the second case, the sulphuretted hydrogen unites directly with the oxide, with- out decomposing it, and its proportion is such that the hydrogen is sufficient to saturate all the oxygen of the oxide. The quantity of hydrogen, then, which is destroyed, or may be destroyed, depends on the state of oxidizement of the metal, and so also does the quantity of sulphur. Now if metals, as appears probable, are susceptible of oxidation in only a few determinate degrees, it follows that by pre- cipitations of this kind, we may obtain metallic sulphurets with fixed proportions, which maybe easily calculated from the known quantity of oxygen in the oxide, and the known composition of sulphuretted hydrogen.* Thus the law of fixed proportions will be extended to the compounds of metals with sulphur; and another step will be made, towards establishing the important general principle in chemical phi- losophy, which has been so ably illustrated, in other cases, by Mr. Dalton. 4. Hydroguretted sulphurets of metals and their oxides may be ob- tained* by precipitating metallic solutions with the hydroguretted sul- phurets of alkalies. In sulphuretted oxides, it has been observed by Berzelius.t the oxygen of the oxide is to the hydrogen of the sulphu- retted hydrogen, precisely in the proportion necessary to constitute water. The oxides of all metals, he adds, which have for oxygen a greater affinity than hydrogen has, may unite with sulphuretted hy- drogen. In the compounds, thus produced, the metal, sulphur, hydro- gen, and oxygen exist in such proportions, that the oxygen is precisely sufficient to change the sulphur into acid, the metal into protoxide, and the hydrogen into water. But if the affinity of the metal for oxygen be inferior to that of hydrogen, the oxide is then reduced, and water and a sulphuret are generated. Thus the alkalies, the earths, and protoxides of zinc and manganese, afford, with sulphuretted hy- drogen, saline combinations; but the oxides of lead and copper are decomposed by it. It had been generally supposed that metals, which have a great affi- nity for oxygen, and which decompose water (as manganese, iron, zinc, uranium, nickel, cobalt, &c.) are not precipitated from their so- lutions, by sulphuretted hydrogen, except with the concurrence of double affinities. Gay Lussac, however, has shown! that the com- pounds of these metals with the weaker acids (as the acetic, tartaric, and oxalic) are decomposed by sulphuretted hydrogen, and produce hydrosulphurets of the respective metals. When a still weaker sol- vent of the metal is employed, the decomposition is more easily effect- ed. Thus the ammoniurets of iron, nickel, &c. are entirely decom- posed by^hat gas; and this furnishes an excellent process for obtain- ing pure hydrosulphurets; for the alkaline hydrosulphurets, commonly employed for this purpose, are almost always contaminated with sul- phur. Those metals, which are not precipitable by sulphuretted hy* drogen, become so, when acetate of potash is added to their solutions. * Gay Lussac, Memoires d'Arcueil, ii. 175 f 79 Ann. de Chim. 129. ■ 80 Ann. de Chim. 205. CHAP. XIX. chloranes or chlorurets. 47 III. All the metals are susceptible of combination with chlorine or oxymuriatic acid. When exposed to the gas in a state of minute division, produced either by filing or beating them into leaves, they combine with it, for the most part, with the appearance of combustion. But silver, lead, nickel, cobalt, and gold, unite with chlorine, without the extrication of heat and light. The results of these combinations are differently explained in the old and the new theory. According to the former, the metal attracts oxygen from oxymuriatic acid gas; and the oxide unites with the mu- riatic acid. According to the new theory, the metal unites directly with chlorine; and the combustion is produced not by oxidation, but merely by the intensity of chemical action. Consistently with the former view, the products of the combustion should be called mu- riates. Conformably with the latter, we may either, with Sir H. Davy, designate them by terminating the Latin name of the metal in ane or anea; or (which I should prefer) we may give them the appellation, chlorides; or, as Gay Lussac has proposed, that of chlorures or chlo- rurets. From the greater number of metallic oxides, chlorine expels the whole of the oxygen and takes its place; and when muriatic acid gas is made to act upon them water appears, and compounds are obtain- ed resembling those formed by the direct union of the metals with chlorine. Chlorine combines with the metals in different proportions, which are expressed in the following Table-of the result of experiments, carefully made by Dr. John Davy. Detl. ' Decl. Metals. Grains. Pts. Grains. Pts. . . 60 + 32.77 . . Chlorine — Cuprane. 67 + 67.20 . . Ditto = Cupranea. Tin ...'.. 55 -f 33.40 . 67.00 . . Ditto . Ditto =i= Stannane. + Stannanea. Iron..... . . 29.5 -f- 33.60 . . Ditto = Ferrane. + 55.50 . . Ditto = Ferranea. Manganese. . . 28.4 -f 33.60 . . Ditto = Manganesane . . 97.2 + 33.80 . . Ditto =s Plumbane. . . 34.5 + 34.40 . . Ditto —: Zincane. . . 21.9 + 33.6 . . Ditto = Arsenicane. Antimony . . . 42.5 -f 34.60 . . Ditto = Antimonane. Bismuth . . . . 67.5 -f 34.20 . . Ditto = Bismuthane. IV. Iodine," when heated with the metals, combines with all of them, and forms a class of compounds called, by Sir H. Davy, iodes, and by Gay Lussac, iodures or iodurets. Supposing iodine in its general habitudes most to resemble sulphur, then the latter term is the most appropriate. But if iodine, as seems probable, has a closer analogy with chlorine, its compounds with metals and other combus- tible bodies, should be called iodides. They are all insoluble, ai d when placed in contact with water decompose it; hydriodic acid and 48 METALS in general. CHAP. XIX. an oxide of the metal are formed; and these last, uniting together, compose a hydriodate. V. Several metals have an affinity for phosphorus, and form a class of compounds called metallic phosphurets. The best method of effecting this combination is to expose the metals to heat, in contact with phosphoric acid and charcoal. The charcoal deprives the phos- phorus of oxygen; and the de-oxygenized phosphorus unites with the metal. Metals, however, that have a strong affinity for oxygen, decompose the phosphoric acid, and unite with its base, without the intervention of charcoal. The metallic phosphurets have not hitherto been applied to any useful purpose; and it is sufficient, therefore, to refer to the description of them by Pelletier,in the first and thirteenth volumes of the Annates de Chimie. VI. The compounds of metals with carbon are called carburets. That of iron and carbon, the properties of which vary according to the proportion of the two ingredients, is the only one of importance. It will be described in its proper place. VII. The metals are, for the most part, capable of uniting with each other. For this purpose, they require to be brought into a state of fusion ; and, even when melted, considerable care is necessary to form a permanent compound. If one metal is considerably heavier than the other, it is apt to sink to the bottom of the fluid mass. Nothing can show-this in a more striking manner, than a fact which has been stated by Mr. Hatchett. He found that when gold, which has been melted with a proportion of copper or other metals, is cast into bars, the moulds for which are placed vertically, the lower part of the bar contains more gold in proportion than the upper part. There are a few of the metals that do not unite by being fused to- gether. This is the case with lead and iron; but even in such cases we are scarcely, perhaps, entitled to deny all affinity; for some of the meteils, which were formerly thought incapable of combination, have been made to combine by circuitous processes. This is the fact with respect to iron and mercury.* In the new nomenclature, the word alloy is retained as a general term for all combinations of metals with each other; and the specific name is derived from that of the metal, which prevails in the com- pound. Thus in the alloy of gold with silver, the gold is to be un- derstood as being in greatest proportion; in the alloy of silver with gold, the silver is the principal ingredient. The compounds of mer- cury with other metals, at a very early period of chemistry, were called amalgams, and as the name does not lead to any erroneous notions, it may still be retained to denote this sort of alloys. The metals in general are capable of uniting with each other in un- limited proportions; but in a few instances, it appears probable, though it is not absolutely proved, that they unite in certain propor- tions only. This proposition has been ably maintained by Berzelius, as well as by Dalton. Potassium, the former observes, gives with mercury two * Aikin, in Philosophical Magazine. ..HAP. XIX. properties of metals. 49 crystallized compounds, one of which contains twice as much potas- sium as the other. The arbor Diance is a definite compound of silver and mercury. When zinc and copper are distilled together, a certain quantity of zinc comes over, but the rest cannot be raised by heat. From a fused mixture of antimony, iron, and copper with much tin, metallic crystals separate on cooling, containing fixed proportions of the component metals. Whenever, indeed, the new compound has an opportunity of separating from the fused mass, it appears to be formed in established proportions. By combination, the metals undergo a considerable change of pro- perties, and acquire new ones, not observable in the separate me- tals. 1. The specific gravity of an alloy is seldom the mean of those of its component parts. Thus an alloy of silver with copper or tin, or one of silver or gold with lead, has a greater than the mean specific gravity. All alloy, also, of silver with mercury, though the former metal is specifically lighter than the latter, possesses so much ac- quired density as to sink in quicksilver. In other cases, on the con- trary, the specific gravity of the compound falls short of the mean of that of its components, or there appears to be a degree of dilatation, as in the alloys of gold with copper, iron, or tin. To estimate ex- actly, however, either the increase or diminution of density, requires an attention to several circumstances.* 2. The ductility and malleability of metals is generally changed by combination; and, for the most part, these qualities are impaired- Even two metals, which separately are both malleable and auctile, are rendered brittle by combination. This is very remarkably the case with an alloy of gold and lead, the latter of which, even in the trivial proportion of half a grain to an ounce of gold, renders the alloy quite destitute of tenacity; and an alloy of platinum, copper, and zinc, though eminently ductile and malleable, is rendered brittle by a quantity of iron not exceeding hatf a grain in four ounces of the alloy.t In such cases, it has been supposed that a true chemical union does not take place, and that the newly added metal is merely mechani- cally interposed between the particles of the other, the cohesion of which it thus impairs. This explanation, however, can scarcely be admitted as satisfactory; and, among other arguments in proof of the existence of chemical union, it may be remarked, that gold is ren- dered brittle by being kept in fusion in the vicinity of melted tin, the vapour of which it seems capable of attracting. 3 The hardness of metals is varied by combination. Gold, by com- bination with a small quantity of copper, and silver by a minute pro- portion of the same metal, acquire such an increase of hardness that these additions are always made to gold or silver which is to be ex- posed to wear. By a small addition of gold, iron is said to gain so much hardness, as to be even superior to steel for the fabrication of cutting instruments. * See Aikin's Dictionary, article Alloy. f Journ. of Science, iii. 119. Vol. II.—G 50 metals in general. OHAP. XIX 4. Change of colour is a common effect of the combination of me- tals. Arsenic, for example, which resembles steel, and copper which has a red colour, afford a compound which has nearly the whiteness of silver. 5. The fusibility of compound metals is different from what might have been inferred from that of their components. Platinum, for ex- ample, is rendered easily fusible by arsenic* and a compound of lead, tin, and bismuth melts at a temperature below that of boiling water, though the most fusible of the three (bismuth) requires for fusion a much higher degree of heat. This is the principle of solders. 6. Metals have their volatility increased by being combined with other metals, which are more volatile than themselves. Gold, sepa- rately, requires an intense heat for its volatilization; but when an amal- gam of gold with mercury is distilled, a quantity of gold passes over with the quicksilver. 7. By chemical union with each other, the metals have their ten- dency to combine with oxygen considerably increased, partly in con- sequence of the diminution of their cohesion, but partly, also, perhaps, in consequence of their forming a galvanic combination. Lead, when amalgamated with mercury, is oxidized by merely shaking the com- pound with water. Lead and tin, melted together, acquire such an increase of affinity for oxygen, that, at the moment of combination, they actually inflame. By the oxidation of either ingredient in any of these alloys, the compound is destroyed. The oxide of lead, for example, separates from mercury in the form of a black powder. Hence, also, a pellicle of oxide is generally observed on the surface of melted solders, which is renewed as soon as it is removed. 8. The solubility of metals in acids is modified by their combination with each other. When gold is alloyed with a small proportion of silver, the latter metal is protected from the action of the nitric acid, and in order to render it soluble in that acid, it is necessary to raise its pro- portion to one-fourth the weight of the alloy, which constitutes the process of quartation. In a similar manner, in order to render tin capable of being entirely dissolved out of an alloy of that metal with antimony, it is necessary that it should constitute 20 parts out of 21 of the alloy; in which case the tin is wholly dissolved by boiling with muriatic acid, and the antimony is left untouched.* From a comparison of the resemblances among metals, both as to physical and chemical properties, several arrangements of them have been formed into smaller classes. Besides the subdivisions, which have been already mentioned, into noble and base metals, and, into entire metals and semi-metals, other classifications have been contrived. Fourcroy has proposed to divide them into five orders. 1. The brit- tle and acidifiable include four species, viz. arsenic, tungsten, molyb- dena, and chrome. 2. The brittle and simply oxidizable are seven (nickel having been transferred by Richter to a different class), viz. titanium, uranium, cobalt, manganese, bismuth, antimony, and telluri- um. 3. The metals, that are oxidizable and imperfectly ductile, are * Chaudet, Ann. de Chim. et Phys. iii. 382. *EeT. u Kioiu. 51 mercury and zinc. 4. The ductile and easily oxidizable are tin, lead, iron, and copper. 5. The very ductile and difficult of oxidizement are silver, gold, palladium, and platinum. A better arrangement, however, appears to me to be that which has been proposed by Dr. Thomson, in the third edition of his System of Chemistry.* He divides the metals into four classes. The first class comprehends the malleable metals, which are fourteen in num- ber, viz. gold, platinum, silver, mercury, palladium, rhodium, iridium, osmium, copper, iron, nickel, tin, lead, and zinc. The second class includes the brittle and easily fused, viz. bismuth, antimony, tellu- rium, selenium, and arsenic. The third class, metals that are brit- tle and difficultly fused. These are cobalt, manganese, chrome, molyb- dena, uranium, and tungsten. The fourth class are called refrac- tory metals; because they have never yet been exhibited in a per- fectly metallic form, but always in combination with more or less oxygen. These are titanium, columbium, and cerium.t In this order. I shall now proceed to describe the individual metals. FIRST CLASS MALLEABLE metals. SECTION I. Gold. To obtain gold in a state of purity, one part by weight may be dis- solved in three of nitro-muriatic acid (composed of one. part by weight nitric, and two muriatic acids). To the clear liquid, a solution of green sulphate of iron must be added. The gold will be precipitated in the state of a fine powder, and, after being washed first with di- luted muriatic acid, and then with distilled water, may be either pre- served for solution in powder, or fused into a mass. * I prefer this arrangement to the one adopted by the same author in the fifth edition of his valuable work, because in the latter, bodies are removed from the class of metals, which are closely allied to them in their external as well as in their chemical characters. Thus arsenic, tellurium, and osmium, are Elaced, along with hydrogen, carbon, &c. among acidifiable bodies. Berzelius as divided the metals into two classes; those that are capable of forming acids, and those that act as bases. This classification, however, is liable to the objection, that tellurium when oxidized (and probably selenium) serves both as an acid and as a base. On the whole, it appears to me, that what may be called a natural arrangement of the metals is, in the present state of our know- ledge, preferable to one founded on their chemical resemblances. f Tantalum has lately been shown by Dr. Wollaston to be identical with columbium. 52 metals. CHAP. XIX. I. The external qualities of gold are the following: 1. It has an orange or reddish yellow colour; and may be brought to assume a degree of lustre inferior only to that of steel, platinum, silver, and mercury. . 2. Its specific gravity varies a little according to the mechanical processes which it has undergone; but it may be stated, on the ave- rage, at 19.3. i-i 3. It exceeds all other metals in ductility and malleability, and may be beaten into leaves l-280000th of an inch in thickness. 4. It is considerably tenacious; for a wire only 78-1000ths of an inch diameter will sustain a weight of 150 lb. II. Gold may be melted by a moderate red-heat; viz. at about 32° of Wedgwood's pyrometer. The intense heat of a glass-house fur- nace has no other effect than to keep it in fusion. And even expo- sure to Mr. Parker's powerful burning lens, for several hours, occa- sioned no loss of weight After fusion, it crystallizes in short quad- rilateral pyramids. III. Pure gold is not oxydized by exposure to heat with the access of air; but it may be brought to the state of a purple oxide by trans- mitting, through gold leaf or wire, either a powerful electrical or gal- vanic discharge. IV. Sulphuric, nitric, and muriatic acids have separately no evident action on gold; but the last mentioned acid, Proust has observed, by long boiling with finely divided gold, dissolves a small portion. V. The proper solvents of gold are the oxy-muriatic and nitro- muriatic acids. Oberkampf * prefers the former, because a purer solu- tion is obtained, and one which can more easily be had free from an excess of acid. Gold leaf, introduced into chlorine gas, takes fire and burns. But if gold leaf be suspended in water, into which chlo- rine gas is passed, it is dissolved, and the solution may be concen- trated by evaporation. To dissolve gold in nitro-muriatic acid, Vauquelint reverses the usual proportipns, and mixes two parts by weight of muriatic acid with one of nitric. Three parts of an aqua regia so composed, are equivalent, he finds, to four made with the common proportions. The solution of gold (in whatever way prepared) has an orange- yellow colour: but this, Oberkampf asserts, is owing to an excess of acid, and it passes to a brownish-red, as soon as the redundant acid is neutralized or expelled by heat. The solution should, therefore, be evaporated to dryness, and the dry mass (care being taken not to heat it too strongly) re-dissolved in water. The solution gives a pur- ple stain to the skin, and is susceptible of crystallization. Muriate of gold, prepared by the solution of the metal either in oxy-muriatic or nitro-muriatic acid, is decomposed by solutions of fixed alkalies, and yields a precipitate, which differs greatly in colour, according to the circumstances of the experiment. If it has a yellow colour and a styptic taste, it is a sub-muriate. To avoid this, it is necessary to use a considerable excess of alkali, and then the preci- * 80 Ann. de Chim. l^O. f 77 Ann. de China. 322. stcr. i. cold. 53 pitate is of a brownish-black colour. It is this which Oberkampf con- siders as the true oxide of gold. It should be dried with extreme care, for too much heat drives off a part of its oxygen. The precipi- tation of gold from its solution by alkalies appears, however, to re- quire farther explanation.* VI. This oxide is decomposed entirely by heat, without passing through any inferior stage of oxidation; oxygen gas comes over; and pure gold remains. The mean of three experiments of Oberkampf shows, that 100 parts of gold combine with 10.01 oxygen; but Ber- zelius states the oxygen at 11.982. It is probable that this compound is the peroxide of gold, and that there is also a protoxide, with half as much oxygen as the former; but its existence has not yet been de- monstrated, and at present we are acquainted with only one oxide of this metal. If no other can be proved to exist, the atom of gold must be estimated to weigh 75, for as 10 to 100, so is 7.5 to 75. VII. It is necessary to observe, that the entire decomposition of muriate of gold is not affected by the alkalies, and that the liquor holds in solution a triple salt of gold, alkali, and muriatic acid. VIII. A solution of pure ammonia separates from the solution by nitro-muriatic acid an oxide of gold, and a portion of ammonia, uniting with the oxide, forms a compound which detonates very loudly in a gentle heat,, and is termed fulminating gold. To obtain this compound, add a solution of ammonia in water, or the pure liquid ammonia, to diluted muriate of gold; a precipitate will appear, which will be re-dissolved if too much alkaji be used. Let the liquor be filtered, and wash the sediment, which remains on the filter, with several portions oi" warm water. Dry it by exposure to the air, without any artificial heat, and preserve it in a bottle, closed, not with a glass stopper, but merely by a cork. A small por- tion of this powder, less than a grain in weight, being placed on the point of a knife, and held over a lamp, detonates violently. The precise temperature which is required is not known, but it appears to exceed 250° Fahrenheit. At the moment of explosion, a transient flash is observed.* The principal force is exerted downwards; and hence two or three grains, exploded on a pretty strong sheet of cop- per, will force a hole through it Neither electricity nor a spark from the flint and steel are sufficient to- occasion its detonation; but the slightest friction explodes it, and serious accidents have happened from this cause. This detonation is explained as follows: Fulminating gold is an oxide of that metal, combined with ammonia. When its temperature is raised, the ammonia is decomposed; the hydrogen of the alkali unites with the oxygen of the oxide, and reduces the gold to a me- tallic state; and nitrogen gas, and probably aqueous vapour, are libe- rated in a highly expanded s*tate. The violent impulse of these aeriform products, on the surrounding atmosphere, appears to be the cause of the loud noise that is occasioned by the explosion of this compound. A similar explanation may be applied to other fulmi- See Thomson's Annals, ix. 29. 54 METALS. CHAP. XIX. nating compounds of metallic oxides with ammonia; such as those of silver and mercury, which will be described hereafter. Fixed alkalies throw down, from nitro-muriate of gold, the yellow oxide already alluded to. IX, The solution of gold is also decomposed by certain combustible bodies, which attract the oxygen from the gold, and restore it to a metallic state. (a) Into a dilute solution of muriate of gold, contained in a glass jar, put a long narrow slip of charcoal, and expose the whole to the direct light of the sun. The gold will be revived, and will appear on the charcoal in a metallic state, exhibiting a very beautiful appear- ance. The same change ensues without light if the solution be ex- posed to a temperature of 212°. (b) Moisten apiece of white taffeta riband, with the dilute solution of gold, and expose it to a current of hydrogen gas from iron filings, and dilute sulphuric acid. The gold will be reduced, and the riband will be gilt with the metal. By means of a camel's hair pencil, the gold may also be so applied as to exhibit regular figures, when reduced. (c) The same experiment may be repeated, substituting phosphu- retted hydrogen for common hydrogen gas. The reader, who wishes for a detail of various experiments of a similar kind, may consult an Essay on Combustion, by Mrs. Fulhame, published by Johnson, Lon- don, 1794; and also Count Rumford's paper, in the Philosophical Transactions, 1798, page 449. X. Gold is precipitated from muriatic acid, in a metallic form, by a solution of green sulphate of iron. This depends on the affinity of the protoxide of iron for a farther quantity of oxygen, which it takes from the oxide of gold. XI. When a sheet of pure tin is immersed in a solution of nitro- muriate of gold, the oxide of gold is precipitated of a purple colour; and, when scraped off and collected, forms the purple powder of Cas- sius, much employed in enamelling. Or the metallic salt, largely di- luted with water, may be put into a glass vessel with a few pieces of grain tin. In a short time, the liquor will become*of the colour of red wine, and a very light flocculent precipitate will begin to precipi- tate, leaving the liquor clear. This, when well washed and dried, has a deep purple colour, and is the precipitate of Cassius. The same precipitate is obtained by mixing a solution of gold with a recently made solution of tin in muriatic acid. The composition and colour of the precipitates of gold, thrown down by muriate of tin at the minimum, have been shown, by Ober- kampf, to be very variable. The colour approaches more to a violet, as the salt of tin bears a larger proportion to that of gold; and the co- lour, communicated by the precipitate to porcelain, has the same varia- ble character. When the muriate of gold is in excess, the precipitate has more of a rose colour. A violet compound was proved on analy- sis to contain 60 per cent, of oxide of tin, and 40 of metallic gold; and one of a fine purple consisted of 20§ oxide of tin and 79£ gold. XII. Gold is precipitated from its solvent by ether, but the oxide of gold is instantly re-dissolved by the ether, and forms the ethereal SECT. fc 'GOLD. 55 solution of gold. This solution is advantageously applied to the gild- ing of steel scissors, lancets, and other instruments, which it protects from rust with a very small expenditure of gold. XIII. When a current of sulphuretted hydrogen gas is passed through a solution of gold, a black precipitate falls down. This is a true sulphuret of gold, which gives up its sulphur on the application of heat. It is composed of Gold .... 80.39 .... 100. Sulphur . . . 19.61 .... 24.39 100. 124.39 The sulphuret, thus prepared, is more uniform in its composition, than that which is precipitated by alkaline hydro-sulphurets; for these contain a variable proportion of sulphur, which is thrown down along with the gold. The sulphuret of gold is soluble in hydro-sulphuret of potash. Li- quid potash takes up a part, and leaves a yellow powder, which is metallic gold. The alkaline hydro-sulphurets do not dissolve gold, however minutely divided, till sulphur is added, when probably a sul- phuret of gold is formed, on which the hydro-sulphuret is capable of acting. XIV. Gold may be combined with phosphorus, either by precipi- tating its solution with sulphuretted hydrogen, or, as Mr. E. Davy discovered, by heating finely divided gold with phosphorus in a tube deprived of air. It has a grey rolour, and a metallic lustre; is de- composed by the heat of a spirit lamp; and contains about 14 per cent, of phosphorus. XV. The methods of purifying gold, by the operations of cupelling and quartation, would lead into too long details. They are very per- spicuously described by La Grange, in the 44th chapter of his Ma- nual; and in Aikin's Chemical Dictionary, article Gold. To the lat- ter Work; to Lewis's Philosophical Commerce of the Arts; and to Mr. Hatchett's paper, in the Philosophical Transactions for 1303,1 refer also for information respecting the alloys of gold with other me- tals. It may be proper, however, to add that gold, which is too soft, in its pure state, for many purposes, has its hardness greatly increased by being melted or alloyed with a small proportion of copper. It is a singular fact, that some kinds of copper, which do not themselyes appear defective in any respect, totally destroy the ductility of gold. This appears to be owing to the contamination of the copper with a very small quantity of lead and antimony, of either of which metals only about l-1920th in weight is sufficient to produce this injurious effect. The degree of purity of gold is expressed by the number of parts of that metal, contained in 24 parts of any mixture. Thus, gold, which,. in 24 such parts (termed carats), contains 22 of the pure metal, is said to be 22 carats fine. Absolutely pure gold, using the same Ian- 56 METALS. ~ CHAP. XIX. guage, is 24 carats fine; and gold alloyed with an equal weight'" another metal, 12 carats fine. SECTION II. Platinum. I. Platinum, in the state in which it reaches this country, is con- taminated by the presence of eight or ten other substances; and, in fact, is merely an ore of platinum. It had been discovered in no other places than Choco and Santa Fe, in South America, until about, two years ago, when Vauquelin detected it in some grey silver ores from Estremadura; and, more lately, it has been brought from St. Do- mingo, and from the gold mines of Brazil. The general aspect of the ore of platinum is that of small grains or scales, of a whiter colour than iron, and extremely heavy. Various processes have been con- trived for its purification;* but the one, which is the most simple and practicable, appears to me to be that of Count Moussin Poushkin, communicated by Mr. Hatchett in the ninth volume of Nicholson's Journal.t It is unnecessary, however, to detail these processes; as the metal may now be had, in a pure state, at a reasonable price; among other places, at Carey's, No. 182, Strand, London. II. Platinum has the/ following properties: 1. It is a white metal, resembling silver in colour, but greatly ex- ceeding it, and indeed all other metals, in specific gravity, which may be stated at 22 or 23; according to Sir II. Davy, at 21.3; and, accord- ing to Marquis Ridolfi, at 22.63. It may be drawn into wire about the 2000th part of an inch in diameter, and beat into very thin plates. 2. It is extremely difficult of fusion. It may be melted, however, by the blow-pipe, with the aid of oxygen gas. A globule, also, weigh- ing 29 grains, boiled violently in the focus of a lens about three feet in diameter;! and Dr. Clark, by means of the blow-pipe with compressed oxygen and hydrogen gases, has melted more than 200 grains of pla- tinum intoasingle brilliant metallic globuie.§ 3. It is not oxidized by the long-continued and concurrent action of heat and air. To obtain its oxides, we must have recourse to a circuitous process. The nitro-muriate of platinum is to be decom- posed by lime water, and the precipitate re-dissolved in nitric acid. This solution being evaporated, and heated so as to drive off the acid, a brown powder remains, which is the oxide of platinum at the maxi- ' * See Aikin's Dictionary, article Platinum. -j- A process for purifying platinum, by the intermediation of zinc, is des- cribed by Descotils in the 64th volume of the finales de Chimie, page 334, or 27 Phil. Mag. 65; and another by the Marquis of Ridolfi in Journal of Sci- ence, &c. i. 259. ? 69 Ann. de Chimie, 93. § Thomson's Annals, ix. 162, and x. 374. /SECT, II. PLATINUM. 57 mum, and which contains in 100 parts 13 of oxygen. This oxide, very carefully heated, passes to a green colour, and loses six parts of oxygen, seven only remaining, combined with 93 of metal. It is proper, however, to state, that Sir H. Davy did not succeed in the -re- petition of these experiments. Berzelius* describes two oxides of platinum. The protoxide is pre- cipitated from the muriate by an excess of potash. Its colour is black, and it consists of Platinum ..... 92.35 .... 100. Oxygen......7.65 .... 8.287 100. 108.287 The peroxide, according to the same chemist, has been obtained only in combination. It is composed of Platinum.....85.93 ... 100. Oxygen ...... 14.07 .... 16.38 100. ' 116.38 The accuracy of this statement of the oxides of platinum has been objected to by Mr. Cooper.t The protoxide of platinum was obtained by him, by pouring a perfectly neutral solution of mercury (probably in nitric acid) into a dilute solution of muriate of platinum in hot water. The precipitate, a mixture of calomel and protoxide of plati- num, after being carefully washed and dried, was exposed to a heat barely sufficient to raise the calomel; after which there remained an intense black powder. By distillation Mr. Cooper ascertained that this powder is composed of 100 parts of platinum -f- 4.517 oxygen. If this be correct, the atom of platinum must weigh 175, for 4.517: 100.:: 7.5: L75. On the other hand, we have the testimony of Vauquelin, that the oxide of platinum, obtained from the sub-muriate by means of soda, contains between 15 and 16 parts in the hundred of oxygen ;J while the grey oxide, which enters into the composition of fulminating pla- tinum, contains, according to Mr. E. Davy, 11.7 of oxygen in 100 of the oxide. These discordant results show that the subject requires farther investigation. 5. Platinum has the property of welding,^ which belongs to no other metal but this and iron. « * 87 Ann. de Chim. p. 126. | Journ. of Science, &c. vol. iii. t Ann. de Chim. et Phys. vol. v. 4 Two pieces of wrought iron, raised to a white heat, become covered with a kind of varnish; and, when brought into contact, may be permanently united by forging. This is called the welding >f iron. Vol. II.—H 5g METALS. CJIAP. XIX. 6. It is not acted on by any other acid than the nitro-muriatic and oxy-muriatic* The former is best adapted to effect this solution. Sixteen parts of the compound acid are to be poured on one of the laminated metal, and exposed to heat in a glass vessel; nitrous gas is disengaged, and a reddish-coloured solution is obtained, which gives a brown stain to the skin. When this solution is evaporated, and heated to whiteness, chlo- rine gas is disengaged, and may be collected in a proper apparatus.- The dry compound, investigated by Mr. E. Davy, gave 18.5 per cent. of chlorine; but this is considered by him only as an approximation. From the experiments of Vauquelin, it seems probable that beside the muriate, there are also two sub-muriates, of platinum.t But the pre- cise nature of these compounds is open to farther investigation. 7. The muriate of platinum may be crystallized by careful evapo- ration. The salt has a very acrid taste, and is deliquescent It is decomposed by heat, chlorine gas is evolved, and an oxide of plati- num remains, which is reduced to a metallic form by ignition with charcoal. 8. The muriate of platinum has the characteristic property of be- ing precipitated by a solution of muriate of ammonia. By this cha- racter, platinum is distinguished from all other metals, and may be separated when mingled with them in solution. The precipitate, thus obtained, is decomposed by a strong heat, and leaves pure pla- tinum. 9. Muriate of platinum is not precipitated by prussiate of potash, nor by sulphate of iron. If any precipitate ensue, it is owing to the contamination with other metals. 10. It is precipitated of a dark green colour by the gallic acid as Kresent in tincture of galls. The precipitate becomes gradually paler y standing.^ 11. When pure potash is poured into the muriatic solution, a pre- cipitate ensues, which is not an oxide of platinum, but a triple com- pound of that oxide with the alkali and acid. With soda, also, it Forms a triple combination, or soda-muriate. This is best obtained, by adding to nitric acid, in a retort, platinum, with twice its weight of muriate of soda, and applying heat till about four-fifths of the fluid have come over. The remaining liquor forms, on cooling, fine pris- matic crystals, sometimes four or five inches long; and either reddish- brown, like titanium; yellow, like amber; or of a beautiful coquelicot colour.§ 12. Muriate of platinum is decomposed by ether, and an etherized solution of platinum is obtained; which may be applied to the same uses as the similar solution of gold. It is decomposed, also, by sul- * Mr. P. Johnson has shown that platinum, by being alloyed with silver and gold, is rendered soluble in nitric acid; (40 Phil. Mag. 1.) and Mr. Cooper has established the same fact respecting the alloy of platinum with zinc and copper. (3 Journ. of Science, p. 119.) f Ann. de Chim. et Phys. v. 274. « * La Grange, ii. 272. ■$> Nicholson's Journal, 8vo. ix. 67. SECT. II. PLATINUM. 59 phuretted hydrogen,* and a black powder is obtained, which becomes reddish-brown with an excess of the precipitant but reassumes its black colour, on exposure to the air. Its composition cannot be investi- gated easily, for the sulphur passes so rapidly to the state of sulphu- ric acid, uk, during the desiccation of the powder, to destroy the pa- per on which it was collected. Vauquelin asserts that it is not a simple sulphuret, but a hydro-sulphuretted oxide of platinum.t The direct combination of platinum and sulphur was found by Mr. E. Davy to give an infusible black powder, containing about 16 per cent. of sulphur.^ Vauquelin formed it by heating 10 parts of the triple muriate of ammonia and platinum with 20 parts oi sulphur, or by a similar treatment of one part of finely divided platinum, with two of sulphur. He agrees with Mr. Davy as to the proportions of its ele- ments. Phosphorus and platinum may be united, either by passing phos- phuretted hydrogen into a solution of the muriate; or, according to Mr. E. Davy, they combine directly in exhausted tubes with vivid ignition. The result is a bluish grey powder, infusible, and contain- ing 17 per cent, of phosphorus. 13. Platinum is acted upon by fusion with nitrate of potash and with nitrate of soda, and also with pure fixed alkalies. The latter property diminishes considerably the utility of platinum as a material for crucibles. 14. The most delicate test of the presence of platinum is muriate of tin. A solution of platinum, so dilute as to be scarcely distinguisha- ble from water, assumes a bright red colour, on the addition of a sin- gle drop of the recent solution of tin. 15. Platinum combines with potassium and sodium, and affords brit- tle compounds. It unites also with most metals.§ In the proportion of only one-sixteenth it renders gold pale; it amalgamates with mer- cury; and diminishes the fusibility of the fusible metals. Its alloys, however, have been but little investigated. 16. A fulminating compound of platinum, analogous in its compo- sition and properties to aurum fulminans, has been prepared by Mr. E. Davy, by precipitating a solution of sulphate of platinum with a slight excess of pure ammonia.|| The precipitate thus obtained was washed, and dried sufficiently to separate it from the filter. It was then put into a Florence flask with a solution of pure potash, and the fluid boiled nearly to dryness. A quantity of water was then added, and the solid matter, after being well washed was dried for several days at the temperature of 212° Fahrenheit. The powder thus prepared has different shades of colour, from a light brown to a dark chocolate, and even almost black. One grain, laid on a thin sheet of copper, and heated to 400° or 420° Fahrenheit produces * Berzelius. f Ann. de Chim. et Phys. v. 263. i See his Memoir on some of the Combinations of Platinum, Phil. Mag. vol. xl. § See Darcet on the Alloys of Platinum with Silver. 89 Ann. de Chim. 135, If Phil. Trans. 1817. * bO , METALS. GHAF. XIX^ a report louder than that of a pistol, and the copper is deeply indent- ed. Like fulminating gold, it is incapable of being exploded by per- cussion. It appears to be a triple compound of oxide of platinum, ammonia, and water. 17. Platinum has been discovered by Dr. Wollaston to be a re- markably slow conductor of caloric. When equal pieces of silver, copper, and platinum, were covered with wax, and heated at one end, the wax was melted 3§ inches on the silver; 2£ on the copper; and 1 inch only on the platinum. Its expansion by heat is considerably less than that of steel; which, between the temperatures of 32° and 212°, is expanded about 12 parts in 10,000, while the expansion of platinum is only about 10. From trials made by Mr. Scott of Dublin, it appears to possess sufficient elasticity to be applicable to the making. of pendulum springs for watches.* SECTION III. Silver. Silver is a metal, which admits of a degree of lustre, inferior only to that of polished steel. Its specific gravity, after being hammered, is 10.51. In malleability, ductility, and tenacity, it exceeds all the metals, except gold, Its fusing point, asdetermined by Dr. Kennedy, is 22° of Wedgwood's pyrometer. By considerably raising this heat, it may be volatilized; and, by slow cooling of the fused mass, it may be made to assume a regular crystallized form. To obtain silver in a state of purity, Mr. Donovan recommends. that 240 grains of standard silver be dissolved in as much pure nitric acid of specific gravity about 1^2, as will be barely necessary for solu- tion. This is to be filtered, and distilled water allowed to run through the filter, until the fluids amount to two ounce measures. A bright plate of copper weighing upwards of 64 grains is to be immersed and frequently agitated in it. When the silver has entirely precipitated, which will very soon happen, the clear supernatant liquor is to be poured off, and the precipitate to be well washed with pure water. The silver is then to be boiled for a few minutes in liquid ammonia. It is then to be well washed with water and dried in a filter; after which, if required, it may be melted in a crucible.t The chemical properties of silver are the following: I. Silver is difficultly oxidized by the concurrence of heat and air. The tarnishing of silver is owing not to its oxidation merely, but to its union with sulphur, as Proust has satisfactorily shown. By transmitting a Galvanic or electric discharge through silver wire, it is oxidized; and by long exposure of silver to heat, witl- * Nicholson's Journal, xxii. 148. t Phil. Magazine, xjvii. 205. SECT. III. SILVER. 61 free access of air, it is at length converted into a*h olive-coloured glass. The oxide of silver may, also, be obtained by decomposing nitrate of silver with solution of barytes; and, after washing the pre- cipitate sufficiently, heating it to dull redness. It has an olive co- lour, and is composed, according to Sir H. Davy, of 100 parts of silver united with 7.3 oxygen, or, according to Dr. Wollaston, 7.4. A larger proportion of oxygen is assigned by Berzelius, viz. Silver .... 92.67 . . . 100. Oxygen .... 7.33 . . . 7.925 100. 107.925 No other oxide of silver has been ascertained to exist; but from the experiments of Mr. Faraday, there seems reason to believe that the pellicle, which forms spontaneously on an ammoniacal solution of oxide of silver exposed to the air, is a protoxide of that metal, in which the oxygen is to the silver as 7.5 to 157.4.* II. Silver is acted on by sulphuric acid, which, when assisted by heat, oxidizes and partly dissolves it The sulphate of silver, how- ever, which is very useful as a test, is better prepared by dissolving in sulphuric acid the carbonate of silver, precipitated from the nitrate by carbonate of soda. It forms small brilliant and needle-shaped crystals, which require for solution a large quantity of water. III. Nitric acid diluted with from two to four parts of water dis»- solves silver with a disengagement of nitrous gas. If the silver be pure, the solution is colourless, otherwise it has a green hue. Ac- cording to Proust, nitrate of silver already saturated, if boiled with powdered silver, dissolves an additional quantity; and a solution is obtained, in which the silver is oxidized at a minimum. This sub- nitrate, he observes, possesses different properties from the common one.t IV. Muriatic acid does not act on silver; yet this acid takes oxide of silver from others. Thus when muriatic acid is added to nitrate of silver, a white curdy precipitate falls down in great abundance. This precipitate is decomposed by light; for, when exposed to the direct rays of the sun, its colour becomes gradually darker. (See chap. iv. part v.) If fused by a gentle heat, it forms a semi-trans- parent mass of the consistence of horn, called luna cornea, or horn silver, or more properly fused muriate of silver. The composition of fused silver has been variously stated. Ac- cording to Gay Lussac 100 grains of silver combine with 7.60 oxygen and 25.71 acid. Other chemists have given different proportions, as jppears from the following Table. / * Journ. of Science, iv. 270. f Nicholson's Journal, xv. 376. 62 METALS. CHAP. XIX. Acid. Base. 100 parts, according to Kirwan .... 16.54 . . . 83.46 -----------..----------Chenevix ... 17. ... 83. ----------------------Zaboada .... 17.7 ... 82.3 -----------„-----------Proust .... 18. ... 82. ----------------------Dr. Marcet . . . 19.05 . . . 80.95 ----------------------Gay Lussac . . . 19.28 . .' . 80.72 ------.---------------Berthollct ... 17.5 ... 82.5 ----------------------Berzelius . . . 19.035 . . . 80.965 These differences may, perhaps, in part, but not entirely, be ac- counted for, by the different states of dryness of the muriate of silver. A hundred grains, I have found, after being dried during twenty-four hours, at a temperature between 212° and 300° Fahrenheit, lose barely a grain by fusion. On the whole, 1 should be disposed to consider the determinations of Marcet, Gay Lussac, and Berzelius, as most entitled to confidence. Muriate of silver is decomposed by fusion with desiccated carbo- nate of soda. Mix one part of the former with three of the. latter salt, and let the mixture be fused in a crucible. When cold, the silver will be found reduced at the bottom of the crucible; break the mass, and separate the metal. From 100 grains of the muriate, barely 75 of pure silver are obtained. This is one of the best modes of pro- curing silver in a state of purity. V. Silver combines with chlorine, when heated in that gas, and a compound results, which, in composition, agrees with fused muriate of silver. According to the new theory of chlorine, it is, in fact, a compound of that body and metallic silver; and it has, therefore, been called by Sir H. Davy, argentane, by Gay Lussac, chlorure of silver; but its appropriate name is chloride of silver. Sir II. Davy makes the chlorine in this compound amount to 24.5 per cent., and 100 grains should therefore consist of Silver.....75.5 .... 100. Chlorine .... 24.5 .... 32.5 100. 132.5 Dr. Ure finds that 100 chlorine combine with 307.5 silver,* which scarcely "differs from the foregoing statement. According to Dr. Mar- cet's analysis, 100 grains should contain 75 of silver, for this is the quantity of metal in 80.95 grains of the oxide, taking the oxygen at 7.3 to 100 of silver. If this be admitted, 100 of silver will then be saturated by very nearly 33.5 of chlorine. It must be obvious, that, in order to convert the old statement of the composition of horn silver into the new one, it is only necessary, to suppose the oxygen taken from the oxide, and added to the muriatic acid, which gives the quan- tity of chlorine. * Thomson's Annals, x. 277. SECT. III. SILVER. G3 VI. A solution of nitrate of silver stains animal substances a deep black. Hence it has been applied to the staining of human hair; but. when thus employed, it should be very much diluted, and used with extreme caution, on account of its corrosive quality. White paper, or white leather, when stained with a solution of ni- trate of silver, in the proportion of ten parts of water to one of the r-alt, undergoes no change in the dark; but when exposed to the fight of day, it gradually acquires colour, and passes through a succession of changes lo black. The common sun-beams, passing through red i^lass, have very little effect upon it; yellow and green are more effi- cacious; but blue and violet produce the most decidedly powerful effects. Hence this property furnishes a method of copying paintings on glass, and transferring them to leather or paper, The process is described by Mr. T. Wedgwood, in Nicholson's Journal, 8vo. iii. 107. By a similar process, ivory may be covered with silver. Let a slip of ivory be immersed in a dilute solution of pure nitrate of silver, till the ivory has acquired a bright yellow colour. Then remove it into a tumbler tilled with distilled water, and expose it to the direct light of the sun. After two or three hours exposure, it will have become black; but on rubbing it a little, tie surface will be changed into a bright metallic one, "resembling a slip of pure silver. As the solutidn pene- trates deep into the ivory, the bright surface, when worn away, is re- placed by a succession of others. VII. The solution of nitrate of silver, when evaporated, forms regu- lar crystals. These crystals fuse when heated; and being poured, in this state, in4 METALS. CHAP. XIX. some hours, there appears on the surface of the amalgam a precipitate in the form of a vegetation. According to Proust, however, this com- plicated process is quite unnecessary; and all that is required is to throw mercury into nitrate of silver very much diluted. A beautiful arborization of reduced silver, he observes, will be produced without difficulty. . i i IX. The solution of silver is decomposed by charcoal, and by hy- drogen gas and its compounds. This may be shown by experiments precisely similar to those already directed to be made with muriate of gold. A stick of clean phosphorus, also, immersed in a dilute so- lution of nitrate of silver, in the course of a few days becomes beau- tifully gilt X. Precipitate nitrate of silver by lime-water, and thoroughly edul- corate and dry the precipitate. Let this be afterward put into a ves* sel of the purest liquid ammonia, in which it may remain for ten or twelve hours. It will then assume the form of a black powder, from which the fluid is to be decanted, and the black substance left to dry in the air. This is the celebrated compound termed fulminating sil- ver, which detonates with the gentlest heat, and even with the slight- est friction. It may be formed, also, by boiling any precipitated oxide of silver, for a few moments, in a mixed solution of potash and am- monia. The protoxide, however, described by Mr. Faraday, does not afford it. When once prepared, no attempt must be made to enclose it in a bottle, and it must be left undisturbed in the vessel in which it was dried. Great caution is necessary in the preparation of this substance, and in making experiments on it. It even explodes, when moist, on the gentlest friction.* XI. A new detonating compound of silver, formed by a process similar to that employed in making the fulminating mercury of Mr. Howard, has lately been described by Descotils.t It is prepared by adding alcohol, to a heated solution of silver in nitric acid, while the solution is yet going on. Considerable effervescence arises; the liquor presently becomes turbid; and a heavy, white, crystalline pow- der falls down. This, when washed and dried, is the detonating sil- ver. Heat a slight blow, or long continued friction, cause it to in- flame with a brisk detonation. Pressure alone is not sufficient unless very powerful. It detonates by the electric spark, and is set on fire with an explosion by concentrated sulphuric acid. Both in the pre- paration of this substance, and in experiments on its detonation, much caution is necessary; and only very small quantities should be employed. This preparation was originally discovered by Mr. E. How- ard. In repeating his process, Mr. Cruickshank dissolved 40 grains of silver in two ounces of strong nitric acid, diluted with an equal weight of water. Then by heating the solution with two ounces of alcohol, he obtained 60 grains of a white powder, which detonated violently. XII. A very useful solvent of silver has been discovered by Mr. Keir of Birmingham. It is formed by dissolving one part of nitre in * See Count Rumford's papers, Philosophical Transactions, 1798 f Nicholson's Journal, xviii. 140. SECT. III'. MERCURY. 65 about eight or ten parts by weight of concentrated sulphuric acid. This compound (which may be called nitro-sulphuric acid) when heated to between 100° and 200° Fahrenheit, dissolves one-fifth or one-sixth its weight of silver, with an extrication of nitrous gas; and ledtes, untouched, any copper, gold, lead, or iron, with which the sil- ver may be combined. Hence it is a most useful agent in extracting silver from old plated goods. The silver may be recovered from the so- lution by adding muriate of soda, which forms muriate of silver; and this may be decomposed by carbonate of soda, in the way which has already been described. XIII. Phosphate of silver is a compound of some importance, from its use in preparing chloric acid. Te 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 of the nitrate of silver is des- troyed, and though the phosphate contains an excess of alkali, the re- sulting liquor is acid. The precipitate is of a yellow colour. When washed and dried, it is fusible at a red heat without any farther loss of weight It consists, according to Berzelius,* of Phosphoric acid . . . 17.025 . . . 100. Oxide of silver .... 82.975 . . . 487.38 100. XIV. Silver is acted on by sulphurets of alkalies, and by sulphu- retted "hydrogen gas. Both these substances blacken silver when ex- posed to their operation; and the common tarnishing of silver by the atmosphere has been traced to a similar cause. Sulphuret of sil- ver lias been analyzed by Berzelius,and found to consist of Silver.....87.032 .... 100. Sulphur.....12.968 .... 14.9 100. 114.9 XV. Silver is capable of being united with most other metals. When alloyed with copper, in the proportion of one part to twelve, it constitutes the standard silver of this country. This combination, though its colour differs but little from that of pure silver, is much harder, and better adapted forlhe purpose of coin, and of domestic im- plements. Silver of commerce is composed of 37 parts of fine silver to 3 of copper; but the fine silver, being obtained by cupellation, contains gold, which is left after solution by acids, either in the form of purple protoxide, or black peroxide. * Ann. de Chim. et Phys. ii. 158.. Vol. II.—I 66 METALS. OHAP. XIX. SECTION IV. Mercury. •• I. Mercury, or quicksilver, is the only one of the metals that re- tains a fluid form at the ordinary temperature of the atmosphere. II. When its temperature is reduced to about 39° or 40° below- zero of Fahrenheit, it assumes a solid form. This is a degree of cold, however, that occurs only in high northern latitudes: and in this coun- try quicksilver can only be exhibited in a solid state by means of artificial mixtures. By congelation it acquires an increase of its spe- cific gravity; and, therefore, unlike other metals, the congealed por- tion sinks to the bottom of a fluid mass of mercury. Its specific gra- vity, at 47° above 0 of Fahrenheit, being 13.545, it was found in- creased by congelation, in an experiment of Mr. Biddle, to 15.612, or about one-seventh. III. At about 660° of Fahrenheit (656° according to Creighton) mercury boils, and is changed into vapour. Hence it may be driven over by distillation, and may thus be purified, though not accurately, from the admixture of other metals. When its temperature is con- siderably increased above this point, the vapour acquires great expan- sive force, and the power of bursting the strongest vessels. IV. Mercury is not oxidized, when pure, at the ordinary tempera- ture of the atmosphere; but preserves the lustre of its surface un- changed for a considerable time. There are several methods, how- ever, by which it may be brought to combine with oxygen. (a) Mercury is oxidized by long continued agitation in a bottle half filled with atmospherical air, and is converted into a black powder, to which Boerhaave gave the name of ethiops per se. When this oxide (which may be obtained, with less trouble,J>y decomposing calomel with solution of potash), is distilled in a glass retort, oxygen gas is evolved; or if a moderate heat be long continued, it acquires a red- dish colour, and a still farther dose of oxygen. The black or protox- ide consists, according to Fourcroy and Thenard, of 100 parts of me- tal united with 4 of oxygen. The protoxide of mercury, it is asserted by Guibourt, cannot be obtained perfectly pure; for when either pro- nitrate or protochloride of mercury is decomposed by potash, the pre- cipitate, even when excluded from air, contains peroxide of mercury and small globules of metal, the latter of which are discoverable by a magnifier. Nor can it be procured by triturating together the perox- ide and metal.* (b) Another oxide of mercury is obtained by exposing the fluid me- tal, for several days, to nearly its boiling temperature, in a flat glass vessel, into which air is freely admitted. After a sufficient length of time, small flaky crystals form on its surface, of a brownish red, or flea colour. This red oxide was formerly called precipitate per se. * 6 Ann. de Chim. et Phys. ii. 42?. sect, iv. ' MERCURY. ■ 67 When distilled alone in a glass retort, it yields oxygen gas, and re- turns to a metallic state. It is composed, according to Fourcroy and Thenard, of 100 metal and 8 of oxygen. Sir H, Davy, also, finds its oxygen to be exactly double that of the protoxide, which is composed of 190 mercury and 7.5 oxygen, while the peroxide consists of 190 metal and 15 oxygen. Hence the protoxide is composed of Mercury .... 96.22 .... 100. Oxygen.....3.78 .... 3.947 100. 103.947 And the peroxide of Mercury .... 92.69 . . . . 1QD. Oxygen . ..- . . . 7.31 .... 7.894 100. 107.894 It will be sufficiently near the truth, if we admit, with Dr. Wollas- ton, the black oxide to consist of 100 metal, united with 4 of oxygen, and the red of 100 mercury 4- 8 oxygen. The latter number agrees with the experiments of Guibourt; and the oxygen in the protoxide, though from his analysis it appeared, to contain 4$ in 100 mercury, may be safely taken at half that in the peroxide. This would make the atom of mercury to weigh 175, for 4: 100:: 7.5: 175. Peroxide of mercury, Guibourt finds, is decomposed by long con- tinued exposure to light It is soluble in water, and communicates to it the property of turning syrup of violets green, and of being pre- cipitated by sulphuretted hydrogen. With ammonia, the peroxide forms an amnnoniuret, decomposed by heat V. Mercury is dissolved by hot and concentrated sulphuric acid. Two parts of sulphuric acid and one of mercury are the proportions generally used; and as strong sulphuric acid acts but little on iron, the combination may be made in an iron vessel. Part of the redun- dant acid may be expelled by heat; but still the salt retains a con- siderable excess of acid, and may be called super-sulphate of mercury. It is very difficult of solution, requiring 155 parts of cold or 33 of boiling water. By repeated washings with cold water, the whole excess of acid may be removed, and the s,alt is rendered much more insoluble. When the super-sulphate is heated for some time, at a temperature exceeding that of boiling water, it loses still more acid, and is changed into a hard grey mass. When this is removed from the fire, and boiling water poured upon it, a lemon-yellow coloured powder is formed called Turbith Mineral. This substance requires for sola- 68 METALS. CHAr. XIX. tion 2000 times its weight of water. One hundred parts consist of 10 sulphuric acid, 76 mercury, 11 oxygen, and 3 water. VI. The nitric acid dissolves mercury, both with and without the assistance of heat. At the common temperature, but little nitrous gas is evolved by the action of mercury on nitric acid; and the acid becomes slowly saturated. The solution is very ponderous and colourless; and yields, by evaporation, large transparent crystals of pro-nitrate of mercury. The solution does not become milky when mingled with water. Pure fixed alkalies give a yellowish white precipitate; and ammonia a greyish black one. But if heat be used, a brisk effervescence arises, occasioned by the escape of nitrous gas, and a solution is obtained, in which the metal is more highly oxidated, constituting per-nitrate of mercury. When this solution is poured into cold water, a yellowish white sediment is formed; or, if into boiling water, an orange coloured one. Both pre- cipitates consist of nitric acid, with a great excess of oxide, forming an insoluble sub-nitrate of mercury. If the last mentioned solution be boiled with a fresh quantity of mercury, the newly added metal is taken up, without any dis- charge of nitrous gas, the metal becoming oxidized at the expense of that already dissolved. When the nitrate of mercury is exposed to a heat gradually raised to 600° or upwards, it is deprived of water and of most of its acid, and reduced to an oxide, which has the form of brilliant red scales. This substance, commonly called red precipitate, is termed more properly, the nitroxide of mercury; because it contains a small pro- portion of acid. VII. Mercury is the basis of a new fulminating compound discover- ed by Mr. E. Howard. To prepare this powder, 100 grains (or a greater proportional quantity, not exceeding 500) are to be dissolved, with heat in a measured ounce and half of nitric acid. The solution being poured cold upon two measured ounces of alcohol, previously introduced into any convenient glass vessel, a moderate heat is to be applied till effervescence is excited. A white fume then begins to undulate on the surface of the liquor, and the powder will be gradu- ally precipitated on the cessation of action and re-action. The pre- cipitate is to be immediately collected on a filter, well washed with distilled water, and cautiously dried in a heat not exceeding that of a water-bath. The immediate washing of the powder is material, be- cause it is liable to the redaction of the nitric acid; and while any of that acid adheres to it, it is very subject to be decomposed by the action of light. From 100 grains of mercury, about 120 or 130 of the fiowder are obtained*. This powder has the property of detonating oudly in a gentle heat, or by light friction. VIII. There are two views under which we may regard the salts, heretofore considered as compounds of oxide of mercury with dif- ferent proportions of muriatic acid; for it is possible that they may, in reality, be compounds of metallic mercury with different propor- * See Philosophical Transactions, 1800, page 214. SECT. IV. MERCURY. G9 tions of chlorine, for which the proper appellation is chlorides. Mer» cury, according to the former view, though not acted upon by muriatic acid, may be brought into union with* that acid by double elective affinity. Thus when sulphate of mercury and muriate of soda, both well dried, are mixed and exposed to heat, a combination of oxide of mercury and muriatic acid is obtained by sublimation. This com- pound is muriate of mercury, or the corrosive sublimate of the shops. The same components, with a still farther addition of mercury, con- stitute an insoluble substance called sub-muriate of mercury or calo- mel. The corrosive muriate requires 16 or 20 times its weight of water for solution; but is soluble in about one and one-eighth its weight of alcohol. Its solution in water is decomposed by all the fixed alkalies and alkaline salts, which throw down at first an orange, and afterwards a brie IT red precipitate. Calomel, or the sub-muriate, is formed by grinding the muriate with about half its weight of metallic quicksilver, and then repeatedly subliming the mixture. As the new compound is nearly insoluble, it maybe freed from any remains of the corrosive, muriate by repeatedly washing with water. Fourcroy and Thenard have given the follow- ing comparative view of the composition of corrosive sublimate and calomel. {100. mercury. 4.16 oxygen. 13.97 muriate acid. {100. mercury. 8.21 oxygen. 27.39 muriatic acid. Mercury unites directly with chlorine, and, if heated in the gas, burns with a pale red flame. The product is identical with corrosive sublimate, which, according to Sir H.Davy, is a compound, not of muriatic acid and oxide of mercury, but of chlorine and that metal. According to his experiments, calomel or protochloride of mercury, consists of 190 mercury and 33.5 chlorine, or of Mercury..... 85 ... . 100. Chlorine..... 15 ... . 17.6 100 And corrosive sublimate or perchloride of mercury, is composed of Mercurv.....74 ... . 100. Chlorine ..... 26 ... . 35.2 100 ?0 METALS. CHAP. XIX. The oxides of mercury are soluble in chloric acid;* and, as is the case with their combinations with chlorine, the salt formed with the peroxide is by much the more .soluble. When heated, they give out oxygen gas, and are converted into peroxide of mercury and corrosive sublimate. They may be called protochlorate and fleutochlorate of mercury. IX. The oxides of mercury are all reduced by heat alone, without the addition of any combustible substance, and afford oxygen gas. X. Mercury dissolves gold, silver, tin, and many other metals; and if these be combined with it in sufficient quantity, the mercury loses its fluidity, and forms an amalgam. A solid amalgam of lead, and another of bismuth, on admixture together, have the singular pro- perty of instantly becoming fluid. The extraordinary powers of the base of ammonia in amalgamating with mercury, have already been described in speaking of that alkali. By combination with mercury, metals that are not easily oxidized, acquire a facility of entering into union with oxygen. Thus gold and silver, when combined with mercury, are oxidized by agitation in contact with air. This fact furnishes a striking illustration of the effect of overcoming the aggregative affinity of bodies, in promoting chemical union. XI. By combination with sulphur, mercury affords two distinct compounds. By long continued trituration, these two bodies unite, and form a black sulphuret When united together by fusion, and afterwards sublimed, they constitute a red sulphuret called cinnabar, which, when powdered, affords the common pigment vermilion. The process used by the Dutch, who have long been celebrated for the preparation of cinnabar, is described in the 4th volume of the Annales de Chemie, or in Aikin's Dictionary, vol. ii. This compound also may be obtained by mixing concentrated solutions of muriate of mer- cury and hydro-sulphuret of ammonia. A brownish muddy precipi- tate is obtained, which, when left undisturbed, turns yellow in three or four days, then orange, and finally acquires a beautiful cinnabar colour.t If mercury, like other metals, unite with twice the quantity of sul- phur which it absorbs of oxygen, the proportion of ingredients on its sulphurets will be found by doubling the oxygen of the oxides, and they will be composed as follows: Mercury. Sulphur. Proto-sulphuret .... 100 . . . 7.894 Per-sulphuret .... 100 .. . 15.788 The composition of the sulphurets of mercury has been investi- ( gated experimentally by Guibert, with results very nearly approach- ing to these theoretical quantities.^ The first he obtained by acting * Vauquelin, 95 Ann. de Chim. 103. f Nicholson's Journal, 8vo. i. 299. * Ann. de Chim. et. Phys. ii. 425. SECT. V. RHODIUM AND PALLADIUM4. 71 on calomel; and the second on corrosive sublimate, with sulphuretted hydrogen. Both the resulting compounds were black; but the latter was entirely convertible into cinnabar of the usual colour by subli- mation. Analysis, by distillation with iron, showed them to consist as follows: Sulphur. . . 8.2 . . 16.0 SECTION V. Rhodium and Palladium. The discovery of these two metals was made by Dr. Wollaston, who separated them from the ore of platinum, by the following pro- cess. I. Rhodium. When a solution of the ore of platinum in nitro- muriatic acid has been precipitated, as far as possible, by muriate of ammonia (see sect 3.) it still retains a considerable degree of colour, varying with the strength and proportion of the acids that have been employed in effecting the solution. Beside iron, and a portion of the ammonia-muriate of platinum, it contains, also, other metals in very small proportion. 1. Let a cylinder, or thin plate of zinc, or iron, be immersed in the solution. It will separate all the metals that are present in the state of a black powder. Wash the precipitate (without drying it) with very dilute nitric acid, assisted by a gentle heat, which wilt dissolve the copper and lead. Digest the remainder in dilute nitro-muriatic acid; and to the solution, when completed, add a portion.of muriate of soda, equivalent in weight to about one-fiftieth the ore of platinum employed. Evaporate by a gentle heat. The dry mass contains the soda-muriates of platinum, palladium and rhodium; the two former of which may be separated by alcohol, and the salt of rhodium will remain. From its solution the rhodium may be precipitated by zinc, which throws down a black powder, amounting, in weight, to four grains from 400 of the ore. 2. When exposed to heat, the powder continues black: with borax it acquires a white metallic lustre, but appears infusible by any de- gree of heat. It is rendered fusible, however, by arsenic, and also by sulphur; both of which may be expelled by a continued heat; but the metallic button, thus obtained, is not malleable. 3. The specific gravity of rhodium, as near as it could be taken, was 11. 4. Rhodium unites readily with all the metals that have been tried, excepting mercury. It does not discolour gold, when alloyed with it. Mercury. Proto-sulphuret .... 100 . Per-sulphuret ..... 100 . ;& METALS. CHAP. XU. 5. When an alloy of silver or gold with rhodium is digested in nitric or nitro-muriatic acid, the rhodium remains untouched; but when alloyed with three times its weight of bismuth, copper, or lead, each of these alloys may.be dissolved completely, in a mixture, by measure, of two parts muriatic acid with one of nitric. The lead appears preferable, as it is reduced, by evaporation, to an insoluble muriate. The muriate of rhodium then exhibits the rose colour, from which the name of the metal has been derived. It is soluble in al- cohol. 6. Rhodium is not precipitated from its solution by prussiate of potash, nor by muriate of ammonia, nor by hydrosulphuret of ammo- nia. The carbonated alkalies produce no change; but the pure al- kalies precipitate a yellow oxide, soluble in all acids that have been tried. Berzelius has ascertained the existence of three oxides of .this me- tal, composed as follows: Metal. Oxvgen. Protoxide......100 -f 6.71 Deutoxide......100 + 13.42 Peroxide......100 -f 20.13 II. Palladium. 1. The alcoholic solution (1.1.) contains the soda- muriates of palladium and platinum. The latter metal may be pre- cipitated by muriate of ammonia; and may be obtained from the re- maining liquid palladium, by the addition of prussiate of potash, which occasions a sediment, at first of a deep orange colour, and changing afterwards to a dirty bottle green, owing, probably, to the presence of iron. The precipitate is to be ignited, and purified from iron, by cupellation with borax. 2. A more simple method of obtaining palladium has since been announced by its discoverer.* To a solution of the ore of platinum in nitro-muriatic acid, neutralized by evaporating the redundant acid, or by adding an alkali, and either before or after the separation of the platinum by muriate of ammonia, let prussiate of mercury be added. In a short time the liquid becomes yellow, and aflocculent precipitate is gradually formed of a pale yellowish white colour, which is the prussiate of palladium. This, on being heated, yields the metal in a pure state, in the proportion of four-tenths or five-tenths of a grain from every hundred grains of the ore. 3. Vauquelin has, also, proposed a method of separating rhodium and palladium from the ore of platinum. His process, which is less simple than the second method of Dr. Wollaston, is described at length in the 4th and 7th volumes of Dr. Thomson's Annals of Phi- losophy. On examining some ore of platinum, brought from the gold mines of Brazil, Dr. Wollaston has lately discovered in it small fragments of native palladium, which appear to be free from admixture with every other metal, except a very minute portion of iridium. These * Phil. Mag-, xxy. 272, or Phil. Trans. 1805. SECT. V. RHODIUM AND PALLADIUM. 'J fragments differ from the grains of platinum, in being formed of fibres, which are in some degree divergent from one extremity. This external character Dr. Wollaston deems sufficient for distinguishing the metal in situations, where recourse cannot be had to experi- ment* Mr. Cloud, assay master of the American mint, has, also, discover- ed palladium in a native alloy of gold with that metal.t The alloy contained no other metal, and was perfectly free from its common ingredients, copper and silver. # # Those who may wish to examine palladium, may now procure it in a metallic state at Messrs. Knights', Foster-lane, London. 4. The following are the properties of palladium: (a) Its colour resembles that of platinum, except that it is of a duller white. It is malleable and ductile. Its specific gravity varies from 10.972 to 11.482, Its power of conducting caloric is nearly equal to that of platinum, which it rather surpasses in expansion by heat. (b) Exposed in an open vessel, to a greater degree of heat than is required to melt gold, no oxidizement ensues; and no degree of fusion takes place. On increasing the fire considerably, a melted button is obtained, and the specific gravity is increased to 11.871. The metal, in this state, has a greyish white colour. Its hardness ex- ceeds that of wrought iron. By the file it acquires the brilliancy of platinum; and is malleable to a great degree. Berzelius has shown that 100 parts of palladium unite with 14.209 parts of oxygen. Hence the oxide consists of Palladium......87.56 Oxygen . .......12.44 100, (c) Palladium readily combines with sulphur. The compound is whiter than the separate metal, and is very brittle. It has been in- vestigated by Berzelius, and shown to be composed as follows: Palladium .... 78.03 .... 100. Sulphur.....21.97 .... 28.15 100. 128.15 (d) It unites with potash by fusion, and also with soda, but less re- markably. Ammonia, allowed to stand over it for some days, ac- quires a bluish tinge, and holds, in solution, a small portion of oxide of palladium. . (e) Sulphuric acid, boiled with palladium, acquires a beautiful blue colour, and dissolves a portion of the metal. The action of this acid, however, is not powerful; and it cannot be considered as a fit sol- vent for palladium. * Philosophical Transactions, 1809. t 74 Ann. de Chim. 99 Vol. II.—K 74 METALS. CHAP. XIX. ( f) Nitric acid acts with much greater violence on palladium. It oxidizes the metal with somewhat more difficulty than silver; and, by dissolving the oxide, forms a very beautiful red solution. During this process no nitrous gas is disengaged. Nitrous acid has even a more rapid action on palladium. From these solutions, potash throws down an orange coloured precipitate, which is probably a hydrate. , (g) Muriatic acid, by being boiled on palladium, acts upon it, ana acquires a beautiful red colour. , (h) But the true solvent of palladium is nitro-muriatic acid, which acts upon the metal with great violence, and yields a beautiful red solution. ... (i) From all these acid solutions of palladium, a precipitate may be produced by alkalies and earths. These precipitates are mostly of a fine orange colour; are partly dissolved by some of the alkalies; and that occasioned by ammonia, when thus re-dissolved, has a green- ish blue colour. Sulphate, nitrate, and muriate of potash,produce an orange precipitate in the salts of palladium, as in those of platinum; but tne precipitates from nitrate of palladium have generally a deeper shade of orange. All the metals, except gold, platinum, and silver, cause very copious precipitates in solutions of palladium. Recent muriate of tin produces a dark orange or brown precipitate, from neutralized salts of palladium, and is a very delicate test of this me- tal. Green sulphate of iron precipitates palladium in a metallic state; and, if the experiment succeeds, the precipitate is about equal in weight to the palladium employed. Prussiate of potash causes an olive-coloured precipitate. The prussiate of palladium, separated by a neutral solution of prussiate of mercury, has the property, when heated to about 500° of Fahrenheit, of detonating, with a noise simi- lar to that occasioned by firing an equal quantity of gunpowder. Hy- drosulphurets, and water impregnated with sulphuretted hydrogen gas, occasion a dark brown sediment from solutions of palladium. (k) Palladium readily combines with other metals. It has the pro- perty, in common with platinum, of destroying the colour of gold, even when in a very small proportion. Thus one part of platinum, or palladium, fused with six of gold, reduces the colour of the gold nearly to that of the white metal employed. Dr. Wollaston has furnished an alloy of gold and palladium for the graduation of the magnificent circular instrument, constructed by Mr. Troughton, for Greenwich observatory. It has the appearance of platinum, and a degree of hardness, which peculiarly fits it for re- ceiving the graduations. SECTION VI. Iridium and Osmium. When the ore of platinum has been submitted to the action of ni-> tro-muriatic acid, a part remains undissolved, in the form of a black ^EOT. VI. IRIDIUM AND OSMIUM. 75 powder, resembling plumbago. In this substance, Mr. Tennant has lately discovered two new metals. The process, which he employed to separate them, was the following: I. 1. The powder was fused in a silver crucible with pure soda, and the alkali then washed off with water. It had acquired a deep orange or brownish yellow colour, but much of the powder was undis- solved. The residue was digested in muriatic acid, and a dark blue solution obtained, which afterwards became of a dusky olive-green; and, finally, by continuing the heat, of a deep red colour. By the alternate action of the acid and alkali, the whole of the powder ap- peared capable of solution. 2. The alkaline solution contained the oxide of a volatile metal not yet described; and also a small portion of another metal. When the solution was kept some weeks, the latter metal separated spon- taneously in thin dark-coloured flakes. The acid solution contained both metals also; but principally one, which is not altered by muriate of tin; is precipitated of a dark brown colour by pure alkali; and which exhibits, during solution in muriatic acid, a striking variety of colours, arising from variations in its degree of oxidation. From this property Mr. Tennant terms it iridium. The proportion of oxygen in its oxide still remains to be determined. 3. In order to obtain muriate of iridium, free from the other metal, the acid solution (2) was evaporated, and an imperfectly crystallized mass obtained; but this, dried on blotting-paper and again dissolved and evaporated, gave distinct octahedral crystals. The watery solu- tion of these crystals had a deep red colour, inclining to orange. With infusion of galls no precipitation ensued; but the colour almost in- stantly disappeared Muriate of tin, carbonate of soda, and prussiate of potash, had the same effect Pure ammonia precipitated the oxide, but retained a part, and acquired a purple colour. All the metals, except gold and platinum, precipitated iridium of a dark colour from the muriate, which had lost its colour. 4, Iridium was obtained pure by heating the muriate, which expelled both the acid and the oxygen. It was of a white colour, and perfectly infusible. But Mr. Children has since fused it by his immense galva- nic battery into a metallic globule, which was white, very brilliant, and, though porous, had the high specific gravity of 18.68.* It did not combine with sulphur or arsenic. Lead united with it, but was separated by cupellation. Copper, silver, and gold, were severally found to combine with it, and it could not be separated from the two latter by cupellation with lead. Its other properties remain to be examined. II. 1. Osmium was procured in the state of an oxide, by simply distilling the alkaline solution, obtained as already described (I. 1«), along with any acid. It was even found to escape, in part, when water was added to the dry alkaline mass remaining in the crucible; and was manifested by a pungent and peculiar smell, somewhat re- sembling that of chlorine gas, from which property its name has been * Phil. Trans. 1815, p. 379. :6 METALS. biiap. xix. derived. The watery solution of oxide of osmium is without colour, having a sweetish taste, and the strong smell already alluded to. Another mode of obtaining, still more concentrated, the oxide of os- mium, is by distilling the original black powder with nitre. A solu- tion of oxide of osmium in water is found in the receiver, of such strength as to give a stain to the skin that cannot be effaced. The most striking test of this oxide is an infusion of galls, which presently becomes of a purple colour, and afterwards changes to a deep vivid blue. With pure ammonia, the solution becomes somewhat yellow; and slightly so with carbonate of soda. With alcohol, or still more quickly with ether, it acquires a dark colour, and, after some time, separates in the form of black films. # . M. Laugier having observed that nitro-muriatic acid, which has been employed to dissolve platinum, emits a strong odour of osmium, distilled the liquor, and saturated the product with quicklime; after which, by again distilling the liquid, he obtained a quantity of os- mium sufficient to repay the trouble of the process.* 2. The oxide of osmium, the precise composition of which is un- known, gives up its oxygen to all the metals, excepting gold and plati- num. When its solution in water is shaken with mercury, the solu- tion loses its smell; and the metal, combining with the mercury, forms an amalgam. From this, much of the redundant mercury may be separated by squeezing it through leather, which retains the amal- gam of a firmer consistence. The mercury being distilled off", the osmium remains in its metallic form, of a dark grey or blue colour. By exposure to heat, with excess of air, it evaporates with its usual smell; but, if oxidation be effectually prevented, it does not seem in any degree volatile. Being subjected to a strong white heat, in a ca- vity made in a piece of charcoal, it is not melted, nor does it undergo any change. With gold and silver it forms malleable alloys. These are easily dissolved in nitro-muriatic acid; and by distillation give the oxide of osmium with its usual properties. 3. The pure metallic osmium, which had been previously heated, does not seem to be acted upon by acids; at least no effect is pro- duced by boiling it some time in nitro-muriatic acid. By heating it in a silver cup with alkali, it immediately combines with the alkali, and this compound gives with water, a yellow solution, similar to that from which it had been procured. From this solution, acids expel the oxide of osmium, having its usual smell, and possessing the pro- perty of changing to a vivid blue the infusion of galls. Besides the black powder from which osmium is obtained, Dr. Wol- laston has discovered a separate ore of these two metals, mixed with the grains of crude platinum. The specific gravity of this ore is about 19.5, and therefore exceeds that of crude platinum itself, which is only 17.7. The grains are about the size of those of crude platinum, but are considerably harder; are not at all malleable; and appear to consist of laminae, possessing a peculiar lustre. The discovery of Mr. Tennant, if it had required any confirmation. 89 Ann.de Chim. p. 191 SECT. VII. COPPER. has lately received it from an elaborate investigation of Vauquelin, whose memoir is published in the 89th volume of the Annales de Chimie, and in the sixth volume of Dr. Thomson's Annals. SECTION VII. Copper. Copper, according to Berzelius, as it is found in commerce, is al- ways contaminated with a little charcoal and sulphur, amounting to about one half of a grain in 100 grains. Lead, antimony, and arsenic are also occasionally found in it* To fit it for the purposes of accu- racy, it may be dissolved in strong muriatic acid; and, after adding water, may be precipitated from the solution by a polished plate of iron. The metal, thus obtained, should be washed, first with diluted muriatic acid, and then with water, and may either be fused, or kept in a divided form. Copper is a metal of a beautiful red colour, and admits of a consi- derable degree of lustre. Its specific gravity varies with the opera- tions to which it has been subjected. Lewis states it at 8.830; Mr. Hatchett found that of the finest granulated Swedish copper to be 8.895; and Cronstedt states the specific gravity of Japan copper at 9. It has considerable malleability, and may be hammered into very thin leaves. It is, also, very ductile; and may be drawn into wire, which has great tenacity. At 27° Wedgwood, copper fuses, and by a sufficient increase and continuance of the heat, it evaporates in visible fumes. I. 1. Copper is oxidized by air. This may be shown by heating one end of a polished bar of copper, which will exhibit various shades of colour, according to the force of the heat. A plate of copper, exposed for ^oine time to heat, becomes covered with an oxide, which breaks off in scales when the copper is ham- mered. It is composed of 62 of the black oxide and 38 copper. This oxide, when exposed on a muffle, is farther oxidized, and assumes a deep red hue. Copper is also oxidized by long exposure to a humid atmosphere, and assumes a green colour; but the green compound holds carbonic acid in combination. The oxides of copper do not re- turn to a metallic state by the mere application of heat; but require, for their reduction, the admixture of inflammable matter. 2. Copper does not decompose water, which may even be transr mitted, in vapour, through a red hot tube of this metal, without de- composition. 3. Copper is susceptible of only two degrees of oxidizement; in its lower stage the compound is red; when oxidated to the maximum. it is black. * 47 Phil. Mag. 206. 78 * METALS. 0HAP. XIX. The black or peroxide may be obtained, either by calcining the scales of copper, which have already been alluded to, under a muffle; or by decomposing sulphate of copper by carbonate of potash, and ig- niting the precipitate; or by the simple ignition of the nitrate of cop- per. It is composed of Copper.....80......100 Oxygen.....20......25 100 To prepare the protoxide Mr. Chenevix recommends the following process. Mix together 57\ parts of black oxide of copper, and 50 parts of metallic copper precipitated from the sulphate on an iron plate. Triturate it in a mortar, and put it with 400 parts of muriatic acid into a phial, which is to be well stopped. The copper and its oxide will be dissolved with heat. When potash is poured into this solution, the oxide (or rather hydrated protoxide) of copper is precipitated of an orange colour. This oxide, when deprived of water, becomes red; but it attracts oxygen so strongly that it can scarcely be dried without absorbing more. It is composed of Copper.....88.89 .... 100. Oxygen.....11.11 .... 12.5 100. II. Copper combines with strong sulphuric acid, in a boiling heat, and affords a blue salt, called sulphate of copper. In this process, part of the sulphuric acid is decomposed, and furnishes oxygen to the metal which is dissolved. It is, therefore, better, in preparing sul- phate of copper, to use the oxide obtained by calcining copper scales with free access of air. (a) Sulphate of copper is a regularly crys- tallized salt, easily dissolved by water, (b) The solution is decom- posed by pure and carbonated alkalies. The former, however, re- dissolve the precipitate. Thus, on adding pure liquid ammonia to a solution of sulphate of copper, a precipitate appears, which, on a far- ther addition of the alkali, is re-dissolved, and affords a beautiful bright blue solution, (c) The sulphate of copper is decomposed* by iron. In a solution of this salt immerse a polished plate of iron. The iron will soon acquire a covering of copper in a metallic state, (d) It gives up its acid on the application of heat, without decomposition; and an oxide of copper remains in the retort. ( <,~ Oxygen 6.4 I black oxide $ Sulpnuric acid .... 32 Water.......36 100 SECT. VII. COPPER. 79 Exclusive of water of crystallization, Berzelius,* from his own ana- lysis, states its composition at Peroxide of copper . . 50.90 . . . 103.66 Sulphuric acid . . . 49.10 . . . 100. 100. Proust described a subsulphate of copper, formed by adding solu- tion of potash to a solution of the above sulphate. Berzelius prer pared it by the cautious addition of ammonia, and found it, on analyt sis, to be composed of Peroxide of copper . . . . 80 . . . 100 Sulphuric acid......20 . . . 25 100 Including its water of composition, the subsulphate consists of Sulphuric acid.....21.28 Peroxide of copper . . . 64.22 Water.........14.50 100. No sulphate of the protoxide is yet known; for when sulphuric acid is brought into contact with the protoxide, one half of the oxide gives up its oxygen to the other half, which thus becomes peroxide and unites with sulphuric acid. Sulphite of copper may be obtained by transmitting 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 ves- sel containing water and peroxide of copper. A green liquid is form- ed, which contains sulphite of copper, with a large excess of acid; and sulphite of copper, in very small red crystals, remains at the bot- tom of the vessel. This salt has been investigated by Chevreuljt and found to consist of Protoxide of copper . . . 63.84 Sulphurous acid .... 36.16 100. III. Copper exposed to a damp air rusts, and becomes covered with sub-carbonate of copper. The same compound is still more rea- * 77 Ann. de Chjm. t 88 Ann. de Chim. 181. 80 METALS. CHAP. XIX. dily produced by adding carbonated alkalies to the solutions of cop- J>er. The nitrate of copper, precipitated by carbonate of lime, af- brds a blue precipitate, called Verditer. This substance is nearly allied to the native blue carbonate in the nature and proportion Of its ingredients. It consists of Water ........5.9 Carbonic acid.....24.1 Peroxide of copper .... 67.6 Moisture and impurities . . 2.4 100.* Berzelius observes that subcarbonate of copper differs greatly in appearance when precipitated from a cold and from a hot solution. In the latter case its colour is yellowish green; in the former, it is bluish green, and much more bulky. It is composed of Peroxide of copper .... 71.7 Carbonic acid.....19.7 Water........8.6 100. IV. Copper dissolves readily in diluted nitric acid; and nitrous gas, holding a little copper in solution, is evolved in great abundance. The solution at first is green and muddy; but by degrees, a yellow precipitate falls to the bottom, and the liquid becomes transparent and blue. By evaporation, it yields a salt, which has the property of detonating with tin. When to the solution of this salt, or of any other salt of copper, a solution of potash is added in sufficient quan- tity, a blue powder is precipitated, consisting of the per-oxide of cop- per combined with water. This Substance has been called by Proust, hydrate of copper; but, more properly by Mr. Chenevix, hydro-oxide of copper. When collected on a filter, and dried at a heat below that of boiling water, it shrinks somewhat like alumine; but still re- tains its colour. At a higher temperature it is decomposed, its water being dissipated, and the black oxide only remaining, in the propor- tion of 75 parts from 100. This oxide cannot be brought to combine with water again by merely moistening it. Nitrate of copper is decomposed, but not entirely, by carbonated alkalies; for, after their full effect, Berzelius found that a precipitate is still occasioned, by adding water impregnated with sulphuretted hydrogen. This salt is constituted, according to Berzelius, pf * R. Phillips, Journ. of Science, iv. 279. SKOT. VII. COPPER. 81 Peroxide of copper .... 67.22 Nitric acid.......32.78 100. A sub-nitrate of copper is, also, described by the same chemist* It may be obtained either by carefully heating the nitrate; or by adding a small proportion of potash or ammonia to its solution. V. Concentrated and boiling muriatic acid acts on finely divided copper; and a green solution is obtained. In this salt the copper is oxidized to its maximum, and the salt may, therefore, be called, for the sake of brevity, permuriate of copper. It is very soluble in water, and generally deliquescent By careful evaporation and cooling, the salt crystallizes in rhomboidal prismatic parallelopipeds, which are readily soluble both in water and alcohol. It is composed, as Proust has stated, of Black oxide of copper.....40 Muriatic acid.........24 Water..........36 100 Exclusive of water, Berzelius states its composition to be Peroxide of copper.....59.8 Muriatic acid.......40.2 100. The watery solution of muriate of copper forms a kind of sympa- thetic ink. Characters written with it become yellow by warjaing, and again disappear when the paper cools. By digesting a solution of per-muriate of copper with filings of the metal, it is converted into a muriate of protoxide or pro-muriate; the fresh portion of copper being oxidized at the expense of what was previously held in solution. The solution of this salt is precipitated by merely pouring it into water. By exposure to air, it acquires oxygen, and is converted into the per-muriate. Alkalies throw down an orange precipitate. It consists of Copper 65.80 5 forming ? r,flfi Oxygen 8.08 } sub-oxide 5 /J,a8 Acid..........26.12 100. * 82 Ann. de Chim, 250. Vol. II.—L 82 METALS. CHAP. XIK. By the combustion of copper in chlorine gas, two compounds are produced at the same time, one of which is a fixed easily fusible sub- stance, resembling common rosin; the other a yellowish sublimate. The first, composed of 60 copper and 33.5 chlorine, and called by Sir H. Davy cuprane, but more properly named protochloride of copper, is insoluble in water, but becomes green by exposure to the atmos- phere. The second, called cupranea, or perchloride of copper, dis- solves in water, and gives it a greenish colour; and is composed of 60 copper to 67 chlorine. Its solution is identical with permuriate of copper; for even though it be admitted, according to the view of Sir H. Davy, to be, when solid, a compound of chlorine and metallic cop- per, yet during the solution it will decompose water, and become a true rauriated oxide of copper. VI. When corroded by long continued exposure to the fumes of vinegar, copper is converted into verdegris.—The verdegris of com- merce is composed partly of an acetate, soluble in water, and partly of a sub-acetate which is not soluble in water, consisting of 63 per- oxide + 37 acid and water. By solution in distilled vinegar and evaporation, a salt is obtained in regular crystals, which are completely soluble in water, and which consist of 39 peroxide and 61 acid anil water.—These, distilled alone, yield concentrated acetic acid, and a combination remains in the retort, containing, in 90 parts, 4.50 charcoal 78.66 copper 6.84 oxygen 90. VII. When the muriate of copper is mixed with a solution of prus- siate of potash or of lime, a beautiful reddish brown precipitate of ferro-prnjsiate of copper is obtained, which has been recommended by Mr. Hatchett as a pigment. Tincture of galls throws down, from all the solutions of copper, a dull yellow precipitate. VIII. Copper combines with sulphur. When a mixture of three parts of the metal, in the state of fine filings, with one part of sulphur, is melted in a glass tube, at the moment of combination, a brilliant inflammation ensues, exceeding, in brightness, that produced by the fusion of iron and sulphur. Copper leaf, Berzelius observes,* burns in gaseous sulphur, as bril- liantly as iron wire in oxygen gas. A compound is formed, precisely analogous to the native sulphuret of copper, and composed of Copper......80.....100. Sulphur......20.....25.6 100 125.6 * 79 Ann. de Chim. 250. See also Vauquelin on the Artificial Sulphuret of Copper, lxxx. 265. SXCT. VIII. IRON. 83 Dobereiner, by passing sulphuretted hydrogen through a solution of copper, obtaineu a precipitate composed of two parts by weight of sulphur and one of copper; and by boiling peroxide of copper with an alkaline hydrosulphuret, a dark name yellow compound was formed, consisting of equal weights of sulphur and copper.* Copper unites, by fusion, with phosphorus. The phosphuret is white, brittle, and of thespecific gravity 7.122. The analysis of Pelletier gives 20 per cent, of phosphorus. IX. Ammonia readily dissolves the oxides and hydro-oxides of copper. Nothing more is necessary than to digest them together in a phial. The solution has a beautiful deep blue colour. By evaporation in a very gentle heat, fine blue silky crystals may be obtained. X. Copper combines readily with most of the metals, and affords several compounds, which are of great use in the common arts of life. Tutenag is a white alloy of copper, zinc, and iron. Copper with about a fourth its weight of lead forms pot-metal; with about the same proportion of zinc, it composes brass, the most useful of all its alloys. Mixtures of zinc and copper form, also, the various compounds of Tombac, Dutch Gold, Similar, Prince Rupert's Metal, Pinchbeck, &c. Copper with tin, and sometimes a little zinc, forms bronze, and belUmetat, or gun-metal. And when the tin is nearly one third of the alloy, it is beautifully white, and takes a high polish. It is then called speculum-metal. Copper may, also, be alloyed with iron; but the com- pound has no useful properties/!" section vni. Iron. Iron has a bluish white colour, and admits of a high degree of polish. It is extremely malleable, though it cannot be beaten out to the same degree of thinness as gold or silver. It is much more ductile, however, than those metals; for it may be drawn out into wire as fine as a human hair; and its tenacity is such that a wire only 78-1000th of an inch in diameter is capable of supporting a weight of nearly 550 lb. Its specific gravity varies from 7.6 to 7.8. Iron is one of the most infusible of the metals. Its malting point is about 158° of Wedgwood. Its chemical properties are the following: I. 1. When exposed to the atmosphere, especially when the air is moist it slowly combines with oxygen, or, in common language, rusts. If the temperature of the metal be raised, this change goes on more rapidly; and, when made intensely hot, takes place with the appear- ance of actual combustion. Thus the small fragments, which fly from a bar of iron during forging, undergo a vivid combustion in the * Thomson's Annals, x. 148. + 49. Philos. Magazine, 107. 84. METALS. UHAP. XIX- atmosphere; and iron filings, projected upon the blaze of a torch, burn with considerable brilliancy. The oxide, obtained in these ways, is of a black colour, and is still attracted by the magnet. The same change is more rapidly produced, when ignited iron is brought into contact with oxygen gas. A vivid combustion happens, as already described in the chapter on that gas. Lavoisier made many experiments to ascertain the increase of weight, acquired by the iron, and concluded, that on an average, 100 parts of iron condense, from 32 to 35 parts of oxygen. Dr. Thomson, however, on repeating the experi- ment several times, did not find that 100 parts of iron absorbed more than 27.5 of oxygen; but he observes, that it is almost impossible to collect the whole product; and that minute portions are dissipated in sparks.* 2. By contact with water at the temperature of the atmosphere, iron becomes slowly oxidized, and hydrogen gas is evolved. When the steam of water is brought into contact with red-hot iron, the same change is produced with much greater rapidity; the iron is converted into the black oxide; and a large quantity of hydrogen gas is set at liberty, and may be collected by a proper apparatus. The iron is found to have lost all its tenacity, and may be crumbled down into a black powder, to which the name of finery cinder was given by Dr. Priestley. In composition, it does not appear to differ from the oxide of iron obtained by the action of atmospheric air, and is strongly magnetic. By a careful repetition of the process, Dr. Thomson found that 100 grains of iron, ignited in contact with the vapour of water, acquire 29.1 grains of oxygen. 3. When iron is dissolved in diluted sulphuric acid, the acid is not decomposed; but the metal is oxidized at the expense of the water, and hydrogen gas is obtained in abundance. Now as water is com- posed of two volumes of hydrogen and one of oxygen, a quantity of oxygen, equal in volume to half the hydrogen gas obtained, must have combined with the metal; that is, for every 200 cubic inches of hydro- gen, oxygen equal to 100 cubic inches or 83.8 grains, must have united with the metal. Dr. Thomson, from an experiment of this kind, cal- culated that 100 grains of iron, after the action of dilute sulphuric acid, had gained 27.5 of oxygen. It is to be considered, however, that the purity of the iron employed will materially affect the result; for if the iron contain charcoal, as is always the case, carburetted hydro- gen gas will be mixed with the hydrogen; and the hydrogen in this gas being in a condensed state, the apparent will be less than the real quantity disengaged. Iron, by the different processes which have been described, is con- verted into an oxide, of a black colour, and still retaining the magne- tic property. Its composition has been the subject of a series of ex- periments by Bucholz, who concludes that 100 parts of iron, to be- come the black oxide, condense 29.88 parts of oxygen; Dr. Wollaston assumes the oxygen to be 29 parts, and Dobereiner makes it 30. Ber- zelius's determination differs but little from these, viz. * 27Nich. Journ. 381. SECT. VIII. IRON. 85 Black oxide (Iron . . . 77.22 . . . 100. or protoxide £ Oxygen • 22.78 . . . 29.5 1 100. . When the oxide of iron, which has just been described, is dissolved in nitric acid; then boiled for some time; and, after being precipitated by ammonia, is washed, dried, and calcined in a low red heat, it is found to be converted into a red oxide. This, according to Bucholz, is composed of 100 parts of iron and 42 of oxygen; to Dobereiner of 100 iron and 45 of oxygen ; or according to Dr. Wollaston of 100 me- tal and 43.5 oxygen; but Berzelius states its composition as follows: Red oxide J lion . . 69.34 . . . 100. or peroxide I Oxygen . 30.66 . . . 44.25 100. The existence of these two oxides, and the proportions of their in- gredients, at somewhere near 30 and 45 oxygen to 100 iron, are clearly established. But besides these, it has been attempted to be proved that there is another oxide of iron. Thenard contends for a compound, containing less oxygen than the black oxide, viz. 25 parts to 100 metal; a second composed of 37.5 oxygen to 100 me- tal; and a third of 50 to 100 metal. And Gay Lussac, also, sup- ports the notion of three oxides with proportions, however, differing from those of Thenard. The first is that which is obtained by dissolv- ing iron in diluted sulphuric or muriatic acid, out of the contact of air. It is precipitated white by alkalies, and by ferro-prussiates, and is composed of 100 iron and 28.3 oxygen. The second is obtained when iron is oxidized by the vapour of water or oxygen gas, and consists of 100 iron and 57.8 oxygen. The third is the acknowledged red oxide, which is composed of 100 irort and 42.31 oxygen.* It is probable, however, that the only known oxides are the two, the com- position of which has already been stated on the authority of Bucholz, Wollaston, and Berzelius; and that the new oxide of Gay Lussac is, as Berzelius thinks, a compound of the black and red oxides. There appear to be two hydrates or hydro-oxides, corresponding to to these two oxides of iron, which are obtained whenever we precipi- tate their respective solutions in an acid, by a fixed alkali. The hy- drate of the black oxide is white, with a tinge of olive or green; that of the red oxide is orange coloured. The former hydrate passes to the latter, by exposure to the atmosphere. Ochre, it has been shown by Leidbeck, is a native hydrate of the red oxide, mechanically mixed with earthy ingredients; but exclusively of them, composed of 20.2 to 25 water, with 60 to 62 oxide of iron.t The preparation of a pure hydrate of iron was found by Berzelius to be attended with great difficulty. * 80 Ann. de Chim. 163, and 1 Ann de Chim. et Phys. 33. t 80 Ann. de Chim. 163. 86 METALS. OHAP. XIV It may be remarked, on comparing the composition of the two ox- ides of iron, that the oxygen of the red is not a multiplication of that of the black oxide by an entire, but by a fractional number; for 29.5 X 1£ = 44.25. This anomaly, as was observed in the account of the principles of the atomic system, is best got ovefby multiplying by 2 the numbers (1 and 1 £), expressing these proportions, which wilt make the ratio of 29.5 to 44.25 the same as that of 2 to 3. We are thus, however, led to the supposition, that there is an oxide inferior to the black oxide in its proportion of oxygen; and which, from theo- ry, should consist of 100 iron and 14.75 oxygen. The black oxide contains a quantity of oxygen, which is a multiplication of 14.75 by 2, and the red by 3. And if the supposed protoxide be constituted of an atom of metal and an atom of oxygen, the weight of the atom of iron will be about 50, for as 14.75 to 100 so is 7.5 to little more than 50. Dr. Thomson, in an Essay on this subject, has argued that the perox- ide of iron is a compound of 2 atoms of base 4- 3 atoms of oxygen, the protoxide being a compound of 1 atom of each of those bodies.'' Until this difficulty is cleared up, we may, however, give the name of protoxide to the black oxide of iron; and the red compound of iron and oxygen may continue to be called the peroxide. II. Whenever diluted sulphuric acid is made to act on iron, we obtain a compound of that acid with the protoxide. The solution, by evapo- ration, yields crystals, which have a beautiful green colour, and the shape of rhombic prisms, not of rhomboids, as is sometimes repre- sented.t They have a strong styptic taste; redden vegetable blue colours; and are soluble in about two parts of cold and three-fourths their weight of boiling water. The solution is precipitated of a green- ish white by alkalies, and white by prussiate of potash. The crystals, when distilled, are decomposed, and yield a strong fuming acid, called glacial sulphuric acid. The acid, in this salt, is'to the oxide, in the proportion of 100 to 88, and it is composed, according to Berzelius, of Sulphuric acid.....28.9 Protoxide of iron .... 25.7 Water........45.4 100. When a solution of green sulphate of iron is heated with access of air, part of the protoxide passes to the state of peroxide, and, com- bining with a portion of acid, falls down in the form of a yellow powder, which, according to Berzelius, is a sulphate of the peroxide with excess of base, or a sub-sulphate. The acid in this compound is to the base, as 100 to 266, and it is therefore composed of Sulphuric acid.....27.33 Peroxide of iron .... 72.67 100. * Annals of Phil. x. 102. f lb. xL 284. 3E8T. VUI. IRON. 87 Other sulphates with base of peroxide of iron have been investi- gated by Dr. Thomson,* but no sulphate of protoxide with excess of acid is yet known. The farther oxidation of the iron in the green sulphate is effected more expeditiously by boiling its solution with some nitric acid, and evaporating to dryness, care being taken not to raise the heat so as to expel the sulphuric acid. Water, added to the residuum, dissolves a salt, which is composed of sulphuric acid and peroxide. The solu- tion has a yellowish colour; does not afford crystals; but when eva- porated to dryness, forms a deliquescent mass, which is soluble in al- cohol, and may thus be separated from the green sulphate. Its solu- tion affords a blue precipitate with ferro-prussiate of potash. This salt has been called, but not with strict propriety, oxy-sulphate. Its legitimate name would be sulphate of peroxide of iron; but, as this is inconvenient from its length, it may be called the ted sulphate of iron. It consists, according to Berzelius, of Sulphuric acid .... 60.44 . . . 100. Peroxide of iron . . . 39.56 . . , 65.5 100. 165.5 The sulphurous acid, also, unites with iron and forms a sulphite; and this sulphite, taking an additional quantity of sulphur, composes a sulphuretted sulphite. The precise composition of these salts re- mains to be determined. III. Nitric acid, in its concentrated state, scarcely acts upon iron, but, when diluted with a small quantity of water, it dissolves iron with great vehemence; and with the extrication of a large quantity of impure nitrous gas. The solution, at first, is a deep green, but when nearly saturated assumes a red colour. It is not crystallizable, but, when evaporated, forms a deliquescent mass. The nitrate of iron, it was long ago shown by Sir H. Davy, may exist in two different states, the green nitrate in which the oxide is at the minimum of oxidation, and the red, in which it is at the max- imum. To obtain nitrate of iron, in which the oxide is at the minimum, acid of the specific gravity of 1.25 or less must be used; the iron must be added in large pieces, and at distant intervals; and the ope- ration carried on without the access of *air. When this solution is made on a large scale for the purposes of the dyer, it is proper to con- nect the vessel, in which it is prepared, with a large receiver; for, in the latter, a quantity of nitrous acid will be found, which is worth the trouble of collecting. Nitrate of iron, thus prepared, passes, on ex- posure to the atmosphere, to the state of that in which the oxide is at the maximum. The composition of these two nitrates has not yet been accurately determined. IV. Muriatic acid dissolves iron and its oxides with great ease: * Annals of Phil. x. 102 88 METALS. CHAP. XIX. and affords two distinct salts, differing from each other according to the state of oxidation of the metal. The muriate containing; the black oxide »is green, and that containing the oxide at the maximum red. Both these salts are deliquescent, and cannot be brought to crys- tallize. The green muriate is convertible into the red by simple exposure to the atmosphere. Berzelius describes an interesting experiment found- ed on this property. If a solution of the green muriate be exposed to the atmosphere, in a tall cylindrical glass jar, for some days, and a few drops of pure ammonia be introduced at different depths by means of a tube, the precipitate formed near the surface will be green; a little lower blue; still lower greyish; then of a dirty white; and at the bottom perfectly white, if time has not been allowed for the atmospheric oxygen to penetrate so low. When the solution of green muriate is evaporated dry, and the re- siduum is heated to redness, a compound is obtained which, accord- ing to Dr. John Davy's experiments, is composed of iron and chlorine. During ignition, the oxygen of the oxide and the hydrogen of the mu- riatic acid, are supposed to unite and form water, while the chlorine combines with the metal. The compound, termed by Dr. Davy fer- rane, is the protochloride of iron. It consists of Chlorine.....53.2.....100 Iron......46.8.....88 100. 188 When iron wire is burned in chlorine gas, a substance is formed of a bright yellowish brown colour, and with a high degree of lustre; volatile at a temperature a little above 212°, and crystallizing in small iridescent plates. It acts violently on water, and forms a solution of the red muriate. This is the perchloride of iron. It is composed of Chlorine .... 66.1.....100. Iron......33.9.....51.5 100. 151.5 V. Iron may be united, in the way of double elective affinity, with the ferro-prussic acid.* Thus, when ferro-prussiate of potash and iron and sulphate of iron, both in solution, are mixed together, the ferro-prussic acid and oxide of iron quit their former combinations and unite together. The beautiful blue precipitate is ferro-prussiate of iron. (a) Ferro-prussiate of iron is nearly insoluble in water. (6) It is not soluble in acids. * The prussic acid and ferro-prussic acid (or ferruretted chyazic acid of Mr. Porrett) will be described in the chapter on Animal Substances. MiCT. VIII. IKON. $£' (c) It is decomposed by a red heat, the ferro-prussic acid being de- stroyed, and an oxide of iron remaining. (a) It is decomposed by pure alkalies and earths, which abstract the ferro-prussic acid, and leave the iron in the state of peroxide. Thus, when pure potash is digested with ferro-prussiate of iron, its beautiful blue colour disappears, and we obtain a combination of pot- ash and ferro-prussic acid. It has been considered as a triple com- pound of prussic acid, potash, and iron; but, according to the new views of Mr. Porrett, it is a binary compound of ferro-prussic acid and peroxide of iron. Mr. Porrett has ascertained its composition to be as follows: 19.33 Protoxide of iron ? r c ■ „ •, -„ oQ „.,.- D • ., > forming ferro-prussic acid . . . 5o.o8 34.0o Prussic acid 3 Peroxide of iron serving as a base.......35.00 Water of crystallization...........11.62 100. In Nicholson's Journal (4to. iv. 30. 171), I have given an improved process for preparing the ferro-prussiate of potash. The following, after trying various modes of preparation, I find to afford the purest test. 1. To a solution of potash, deprived of its carbonic acid by quick- lime, and heated nearly to the boiling point, in an iron kettle, add, by degrees, powdered Prussian blue till its colour ceases to be dis- charged. Filter the liquor, and wash the sediment with water till it ceases to extract any thing; let the washings be all mixed together, and placed in an earthen dish in a sand-heat.—When the solution lias become hot, add a little diluted sulphuric acid, and continue the heat for about an hour. A copious precipitate will be formed of Prus- sian blue.—Let this be separated by filtration, and assay a small quantity of the filtered liquor in a wine glass, with a little dilute sulphuric acid. If an immediate production of Prussian blue should still take place, fresh sulphuric acid must be added to the whole li- quor, which must again, with this addition, be exposed to heat. These filtrations and additions of sulphuric acid must be repeated as long as any considerable quantity of Prussian blue is produced; but when this ceases, the liquor may finally be passed through a filter. 2. Prepare a solution of sulphate of copper in about four or six times its weight of warm water, and into the solution (1) pour this, as long as a reddish brown or copper-coloured sediment continues to appear. Wash this sediment, which is a ferro-prussiate of copper, with repeated effusions of warm water; and, when these come oft'co- lourless, lay the precipitate on a linen filter to drain, after which it may be dried on a chalk-stone. 3. Powder the precipitate, when dry, and add it by degrees to a solution of pure potash, prepared as described, chap. vii. sect. 4. The ferro-prussic acid will leave the oxide of copper and pass to the alkali, forming a ferro-prussiate of potash. Vol. II.—M 90 METALS. CHAP. XIX- 4. But as the salt still contains sulphate of potash, a portion of this may be separated by gentle evaporation, the sulphate crystallizing first To the remaining liquid, add a solution of barytes in warm water (chap. ix. sect. 1.) as long as a white precipitate ensues, observ- ing not to add more after its cessation. The solution of prussiate is now free, in a great measure, from iron, and entirely from sulphates; and, by gentle evaporation, will form, on cooling, beautiful crystals. These crystals are perfectly neutral; insoluble in alcohol; are not decomposed by boiling, or by the contact of carbonic acid; and give Prussian blue with solutions of peroxide of iron. For the vegetable alkali, either soda or ammonia maybe substituted in the above process, if they be preferred. If a sufficient quantity of pure barytes cannot be had, the sulphate may be precipitated by ace- tate of barytes. The acetate of potash, thus formed, not being a crys- tallizable salt, remains in the mother-liquor. (e) When the ferro-prussiate of potash is mixed with sulphate of iron, in which the metal is oxidized at the minimum, the ferro-prus- siate of iron that is formed is of a white colour, but gradually be- comes blue, as the iron, by exposure to air, passes to the state of per- oxide.* (/) The effect of a sympathetic ink may be obtained, by writing with a pen dipped in a very dilute solution of ferro-prussiate of pot- • ash. No characters will appear till the paper is moistened with sul- phate of iron, when letters of a Prussian blue colour will be apparent The experiment may be reversed, by writing with sulphate of iron, and rendering the characters legible by prussiate of potash. (g) The ferro-prussiate of potash decomposes all metallic solu- tions, excepting those of gold, platina, iridium, osmium, rhodium, tel- lurium, and antimony.t VI. When sulphate of iron is mixed with an infusion of galls, we obtain a black solution, which is a new combination of oxide of iron, with the gallic acid and tan. Both the gallate and tannate of iron are, therefore, essential constituents of inks; the other ingredients of which are chiefly added with a view of keeping these insoluble com- pounds suspended. In order that the iron may unite with the gallic acid and tan, it must be combined with the sulphuric acid in the state of red oxide; for the less oxidized iron, in the green salt, does not form a black compound with these substances. Iron filings, however, dissolve in an infusion of galls with an extrication of hydrogen gas; but the com- pound is not black till after exposure to air, which oxidizes the iron still farther. This solution, with a sufficient quantity of gum, forms an excellent ink. On the same principle may be explained the effect of metallic iron in destroying the colour of ink. When ink is digested with iron filings, and frequently shaken, its colour decays: and it also becomes colourless after having a stream of sulphuretted hydrogen gas passed through it In both these cases the oxide of iron is partly deoxidized. * See Proust's memoir, in Nicholson's Journal. f See Proust, Philosophical Magazine, xxx. 42. SECT. VIII. •IRON. 91 Characters written with ink, after this treatment, are at first illegible, but become black as the iron acquires oxygen from the air. (a) Write upon paper with an infusion of galls. The characters will not be legible till a solution of sulphate of iron is applied. This experiment may be reversed like the preceding one (V./). (6) The combination of iron, forming ink, is destroyed by pure and carbonated alkalies. Apply a solution of alkali to characters written with common ink, the blackness will disappear, and the characters will become brown, an oxide of iron only remaining on the paper. Alkalies, added cautiously to liquid ink, precipitate the black com- bination, but an excess re-dissolves the precipitate. (c) Characters, which have beeu thus defaced, may again be ren- dered legible by an infusion of galls. (d) Ink is decomposed by most acids, which separate the oxide of iron from the gallic acid in consequence of a stronger affinity. Hence ink stains are removed by dilute muriatic acid, and by some vegeta- ble acids. Hence, also, if to a saturated solution -of sulphate of iron there be added an excess of acid, the precipitate no longer appears on adding infusion of galls. When a mixture of ink is heated with nitric acid, the yellow oxa- late of iron is formed, and is precipitated on adding pure ammonia. (e) Ink is decomposed by age, partly in consequence of the farther oxidation of the iron, and partly, perhaps, in consequence of the de- struction of the acid of galls. Hence ink-stains degenerate into iron- moulds, and ihese last are immediately produced on an inked spot of linen when washed with soap, because the alkali of the soap abstracts the gallic acid, and leaves only an oxide of iron. (/) Injc is decomposed by oxymuriatic acid, which destroys the gallic acid, and the resulting muriatic acid dissolves the oxide of iron. As all writing inks, into the composition, of which iron enters, are "liable to decay by time, and to be destroyed by various agents, an ink has been proposed by Mr. Close, the basis of which is similar to that of printing ink.—Take oil of lavender 200 grains, gum copal, in pow- der, 25 grains, and lamp-black from 2£ to 3 grains. With the aid of a gentle heat dissolve the copal in the oil of lavender in a small phial, and then mix the lamp-black with the solution, on a marble slab, or other smooth surface. After a repose of some hours, the ink must be shaken before use, or stirred with an iron wire, and if too thick, must be diluted with a little oil of lavender.* This ink I have found ex- tremely useful in writing labels for bottles which contain acids, or which are exposed to acid fumes in a laboratory. VII. The phosphoric acid acts with but little energy upon iron; though a native compound of this acid and iron imparts, to some va- rieties of the metal, the singular property of being very brittle when cold, or, as it is called, cold-short. The phosphate of iron is almost insoluble in water. It is best pre- pared by mixing the solutions of green sulphate of iron and phos- phate of soda. A blue precipitate is formed, which is soluble in manv of the acids, and precipitated without change by ammonia. " See Nicholson's Journal, 8vo. ii. 145 O'J J1KMI..S. CHAP. XIX. The oxy-phospfiate of iron is, also, an insoluble salt It may be formed by mingling the solutions of phosphate of soda and oxi-sul- phate of iron. Its colour is yellowish white. Both these prepara- tions have lately derived some importance, from being recommended as remedies of cancer. VIII. The succinic acid composes with iron a brown mass, insolu- ble in water. The combination is best effected by double decompo- sition, and especially by the addition of a solution of succinate of ammonia to the salts of iron. A loose brown-red precipitate of suc- cinate of iron falls down. This precipitate Klaproth exposes to heat, first by itself, and afterwards mixed with a small quantity of linseed oil. The first operation destroys the acid, and the second reduces the metal to the state of black oxide. Now as the black oxide con- tains, in 100 parts, 70.5 of metallic iron, the precipitation of a solu- tion, by succinate of ammonia, affords a ready method of estimating the quantity of iron in any solution of that metal, or in any of its salts. IX. The acetic acid, or even common vinegar, acts slowly upon iron, and forms a solution, which is of great use in dyeing and calico- printing. The acetite of iron may, also, be obtained by a double de- composition, if we mingle the solutions of acetite of lime or of lead with one of sulphate of iron. It may be formed, also, by boiling acetite of lead with metallic iron, which precipitates the lead in a me- tallic state. This combination of iron with acetous acid may exist, like its other salts, in two different states. In the one, the oxide is at the minimum, and in the other at the maximum of oxidation. It is the latter salt only, which is adapted to the use of the dyer and calico-printer. X. Iron is dissolved by water impregnated with carbonic acid. A few iron filings, when added to a bottle of aerated water, and occa- sionally shaken up, impregnate the water with this metal. This solu- tion is decomposed by boiling, and in a less degree by exposure to air. XI. Iron combines with sulphur, and affords compounds, the cha- racters of which vary greatly according to the proportions of their components, (a) A paste of iron filings, sulphur, and water, if in sufficient quantity, will burst, after some time, into flame, (b) A mix- ture of one part of iron filings and three parts of sulphur, accurately mixed, and melted in a glass tube, at the moment of union exhibits a brilliant combustion. The best method, however, of effecting the combination of iron and sulphur is to take a bar of the metal, while of a glowing heat from a smith's forge, and lo rub it with a roll of sulphur. The compound of iron and sulphur falls down in drops, and may be preserved in a phial. Of all the compounds of sulphur, this is best adapted for affording pure sulphuretted hydrogen gas with diluted acids, (c) The sulphuret of iron, when moistened, rapidly decomposes oxygen gas, and passes to the state of sulphate, (d) When diluted sulphuric or muriatic acid is poured on it, we obtain sulphu- retted hydrogen gas. In the sulphuret made artificially by fusion, as well as in the na- tive sulphuret, iron (it has been shown by Proust and Mr. Hatchett,1 SECT. VIU. IRON. 9'i is in the metallic state. Two compounds, also, have been proved to exist, the one with a larger, the other with a smaller proportion ot sulphur. The former may be called the super-sulphuret; and the latter, which is distinguished by the property of being magnetic, the sulphuret. The super-sulphuret is known only as a natural product; it is not magnetic; is nearly insoluble in diluted sulphuric and mu- riatic acids; and gives no sulphuretted hydrogen gas with acids. But the sulphuret is readily soluble, obeys the magnet, and gives abund- ance of sulphuretted hydrogen with'dilute acids. It is composed of Iron......63.....100. Sulphur.....S7.....58.75 100 And the super-sulphuret is composed of Iron......53.92.....100 Sulphur.....46.08.....127 100. Though the artificial sulphuret varies in its composition, yet it is probable that these varieties are occasioned, by the sulphuret being mechanically mixed with different proportions of iron. The foregoing appear to be the only well ascertained and definite compounds; and the analysis of them by Berzelius, it may be observed, agrees very nearly with that of Proust, and indeed does not differ, in either case, one per cent If the sulphuret be, as is consistent with all we know at present, that compound in which sulphur exists in the smallest proportion, this would be unfavourable to the notion.of any oxide of iron with less oxygen than the black oxide. For in almost every other instance, the protoxide of a metal contains a quantity of oxygen equal to half the sulphur in the pro-sulphuret, a coincidence suffi- ciently explained by admitting both to be binary compounds, in the sense of the word annexed to it by Mr. Dalton, and that the weight of the atom of oxygen is just half the weight of the atom of sulphur. Gay Lussac contends for the existence of three sulphurets corres- ponding to his supposed three oxides of iron;" but the details of the experiments establishing their existence still remain to be published. XII. Iron combines with carbon in various proportions; and the variety of proportion occasions very different properties in the com- pound. On these varieties, and the occasional combination of a small proportion of oxygen, depend the qualities of the different kinds of iron used in the'arts, as cast iron, steel, &c. &£. The quantity of carbon, in the sub-carburets of iron, may be determined by solution in sulphurous acid, which dissolves the iron and sulphur, and has no action on carbon. An ingenious mode of analysis employed by Mr. i * 80 Ann. de China. 170. 94 » METALS. CHAP. XIX. Mushet, consists in ascertaining the quantity of litharge, which a given quantity of the iron under examination is capable of reducing, by fusion, to a metallic state. There can scarcely be a more striking example of essential dif- ferences in external and physical characters being produced by slight differences of chemical composition; for steel owes its properties to not more than from l-60th to 1-140th its weight of carbon. This ap- pears to be the only addition necessary to convert iron into steel; for though it is proved that the best steel is made from iron which has been procured from ores containing manganese, yet careful and skilful analysis discovers no manganese in steel.* Cast or crude iron, besides casual impurities, contains oxygen, carbon, and the metal of silex; but its differences depend chiefly on the various proportions of carbon, which is greatest in the black, and least in the white, variety of iron. Berzelius, indeed, denies the pre- sence of oxygen in cast iron, and says that its different kinds are produced by Variable proportions of charcoal, manganese, and the metallic bases of magnesia and silex.t By the process of refining, the carbon and oxygen, it has been supposed, unite together, and escape in the form of carbonic oxide; while another part of the oxide of iron unites to the earthy matter, and rises to the surface in the form of a dense slag. After this process, it forms malleable or bar iron, which may be considered as iron still holding some oxygen and carbon in combination, the latter of which, even in very ductile iron, amounts, according to Berzelius, to about one half per cent. Ilas- senfratz has suggested that iron, which has been manufactured with wood charcoal, may probably contain protassium, and may owe its superiority to this circumstance; and Berzelius has rendered it pro- bable that even the most ductile iron contains silicium.i If bar iron be long and slowly heated, in contact with charcoal, it loses oxygen and acquires carbon, and thus becomes steel. A small proportion only of carbon is not capable of depriving it entirely of the properties of malleable iron, for though it becomes a good deal harder, yet it may still be welded. By union with a still farther quantity of carbon, it loses altogether the property of welding;- is rendered harder and more compact; and forms the fine cast steel. Steel, there- fore, tliough like cast iron it contains carbon, yet differs from it essentially in being destitute of oxygen and earth. The charcoal, which it contains, appears in the form of a black stain, on applying a drop of almost any weak acid to the surface of polished steel. Another combination of iron and carbon, which is a true carburet of iron, is the substance called plumbago, or black-lead, used in fabricating pencils, and in covering iron to prevent rust By exposure to the combined action of heat and air, the carbon is burned off, and the oxide of iron remains. When mingled also with powdered nitrate of potash, and thrown into a crucible, a deflagration ensues; and an axide of iron may be obtained by washing oft the alkali of the nitre. * Ann. de Chim. et Phys. iii. 217 + 4° Phil. Majr. p. 245. ± 78 Ann. de Chim. p. 233. >ECT. IX. NICKEL. 95 From recent experiments of Messrs. Allen and Pepys, it appears that pure plumbago, when burnt in oxygen gas, leaves a residue of oxide of iron amounting only to about 5 per cent; and that it gives very nearly die same quantity of carbonic acid, by combustion, as the diamond and charcoal. When intensely heated in a Toricellian vacuum by a Voltaic battery, Sir H. Davy found that its characters remained wholly unaltered. Neither could any evidence of its containing oxygen be derived from the action of potassium.* But when exposed to the^ focus of a powerful lens in oxygen gas, he has lately observed that the gas became clouded during the process, and that there was a de- position of dew on the interior surface of the glass globe; a fact which indicates that plumbago, like charcoal, contains a small proportion of hydrogen. Iron unites with various other metals. With potassium and sodium, it forms alloys more fusible and whiter than iron, and which effervesce when added to water. Stromeyert has investigated the alloy of iron and silicium. It is formed by heating together iron, silex, and char- coal. The alloy is dissolved very slowly by acids, for it becomes covered with a coat of silex, which defends it from farther action, till it has been removed. Manganese forms a white and brittle alloy with iron. Iron, also, forms an alloy with tin; and iron plates, pre- viously cleaned by a dilute acid, may be covered with tin by dipping them into that metal when melted. SECTION IX. Nickel. I. To obtain nickel in a state of purity, the metal usually sold under that name maybe dissolved in diluted nitric acid; the solu- tion, evaporated to dryness; and the dry mass be again, for three or four times, alternately dissolved in the acid, and boiled to dryness. After the last evaporation, the mass may be dissolved in a solution of pure ammonia; which has been proved, by its occasioning no precipi- tation from muriate of lime, to be free from carbonic acid. The solu- tion is next to be evaporated to dryness; and, after being well mixed with twice or thrice its weight of black flux, is to be exposed to a vio- lent heat in a crucible for half or three quarters of an hour. Other processes, for obtaining and purifying nickel, are described by Richter in the 12th volume of Nicholson's Journal; by Robiquet in the 69th, and by Tupputi in the 78th, volumes of the Annales de Chimie. The last-mentioned memoir contains an elaborate investi- gation of the properties and combinations of nickel. Pure nickel has the following characters: * Philosophical Transactions, 1809. T 81 Ann. de Chim. 96 METALS. CHAP. XIX. 1. Its colour is white, and intermediate between those of silver and tin. It admits of being finely polished, and has then a lustre between those of steel and platinum. When ignited, its colour changes to that of antique bronze, which is increased every time the metal is heated. 2. It is perfectly malleable, and may be forged when hot into bars, and hammered into plates when cold. At 54£° Fahrenheit, Tourte found its specific gravity 8.402, and, after being thoroughly hammer- ed, 8.932. It is ductile, and may be drawn into very fine wire. It can- not easily be soldered, on account of the oxide which forms on its surface when heated. Its power of conducting heat is superior to that either of copper or zinc. Its magnetic property is very remark- able, and is retained when it is alloyed with a little arsenic, and, as Lampadius has shown* with other metals. In difficult fusibility by heat, it appears to equal manganese. 3. Nickel appears to be susceptible of two different states of oxi- dation. By long exposure to a red heat with free access of air, it is converted into a dark brown oxide, which is still magnetic. In oxygen gas, it burns vividly, and throws out sparkS. When precipitated from its solutions by alkalies, and moderately ignited, it becomes of an ash-grey colour with a slight tinge of blue or green, and in this state contains, according to Klaproth, 66 metal, and 34 oxygen. By far- ther ignition, it becomes blackish grey, and then consists, as stated by Richter, of 78 metal, and 22 oxygen. Tupputi, from 100 grains of nickel dissolved in nitric acid, precipitated by a fixed alkali, and cal- cined, obtained 127 grains of an ash-grey powder, which is to be con- sidered as the protoxide. Hence it is composed of Nickel........78.8 Oxygen........21.2 100. Thenard describes a black peroxide of nickel, obtained by passing a current of chlorine gas, through water, in which the hydrate is sus- pended. Its precise composition is unknown. In a sufficiently high temperature, its oxides are reducible without addition; nor is it more tarnished by a strong heat than gold, silver, or platinum. It ranks, therefore, among the noble or perfect metals. 4. The sulphuric and muriatic acids have little action on nickel. Its appropriate solvents are the nitric and nitro-muriatic acids. The nitric solution has a beautiful grass-green colour. Carbonate of pot- ash throws down an apple-green precipitate, which assumes a dark grey colour when heated. The fixed alkalies occasion a bulky green- ish white precipitate, which is a hydrate or hydro-oxide of nickel, composed of 76 per cent, of the protoxide and 24 water. 5. When pure ammonia is added to nitrate of nickel, a precipitate is formed, resembling that which is separated by ammonia from a so- * Thomson's Annals, v. 62. SECT. fit. NICKEL. 97 lution of copper, but not of so deep a hue. This colour changes, in an hour or two, to an amethyst red, and to a violet; which colours are converted to apple-green by an acid, and again to blue and violet by ammonia. If the precipitate retain its blue colour, the presence ef copper is indicated.* This precipitate, which is a hydrate, is solu- ble by an excess of ammonia; and by this property the oxide of nickel may be separated, in analyses, from those of almost all other metals. 6. Nickel, when heated in chlorine, affords an olive-coloured com- pound; and the liquid muriate, when evaporated and strongly heated, fives brilliant white scales, which consist of nickel and chlorine. 'rom analogy, the first should contain the largest proportion of chlo- rine; but the analysis of these compounds has not yet been accurately effected. 7. Solutions of all the salts of nickel are decomposed by alkaline hydro-sulphurets, with which they form black precipitates; but sul- phuretted hydrogen has no effect on them. Nickel may, however, be combined directly with sulphur by fusion, and forms a grey com- pound with a metallic lustre. It contains, according to Mr. E. Davy's experiments, 34 per cent of sulphur; and the super-sulphuret, which may be formed by heating the protoxide with sulphur, is stated, by the same chemist, to contain 43.5 per cent of sulphur. 9. From the solutions of nickel, prussiate of potash throws down a sea-green precipitate. According to Bergman, 250 parts of this con- tain 100 of metallic nickel. This statement, however, differs consi- derably from Klaproth's, according to whom 100 grains of nickel, after solution in sulphuric acid, give a precipitate by prussiate of pot- ash, which, after being ignited, weighs 300 grains. 10. Tincture of galls produces no change in these solutions. 11. The solutions of nickel do not deposit the metal either on polished iron or zinct All that takes place by the action of zinc, is the separation of a mud-coloured precipitate, consisting, for the most part of arsenic and iron, with which nickel generally abounds. Hence the green colour of the solution of nickel is greatly improved by the action of zinc. 12. Nickel may be alloyed with most of the metals, but the com- pounds have no particularly interesting qualities. An alloy of iron and nickel has been found in all the meteoric stones that have hitherto been analyzed, however remote from each other the parts of the world in which they have fallen. In these, it forms from 1J to 17 per cent of their weight It enters, also, into the composition of the large masses of native iron discovered in Siberia and in South America. To detect, in a general way, the presence of nickel in iron, Dr. Wollaston recommends that a small quantity (which need not exceed l-100th of a grain) should be filled from the specimen; dissolved in a drop of nitric acid; and evaporated to dryness. A drop or two of pure liquid ammonia, added to the dry mass and gently warmed, dis- solves any nickej that may be present The transparent part of the * See Richter in Nicholson's Journal, xii. f See Klaproth's Analytical Kssuys, i. 433. Vol. II.—N 98 METALS. CHAP. XIX. fluid is then to be led, by the end of a glass rod, to a small distance from the precipitated axide of iron; and the addition of a drop of triple prussiate of potash detects the presence of nickel by the ap- pearance of a milky cloud, which is not discernible in" the solution of a similar quantity of common wrought iron treated in the same man- ner. The method of ascertaining the quantity of nickel in its alloy with iron, employed by the same philosopher, will be described in the chapter on mineral analysis. SECTION X. Tin. The properties of tin must be examined in the state of grain-tin or block-tin; what is commonly known by the name of tin, being nothing more than iron plates with a thin covering of this metal. Several varieties are met with in commerce, for the discrimination of which, and the means of judging of their purity, Vauquelin has given useful instructions in the 77th volume ojf the Annales de Chimie. Cornish tin has been shown by Dr. Thomson to contain only a very minute proportion of foreign metals, never exceeding, and for the most part much less than l-500th part, which is chiefly copper derived from the ore.* Tin has a silvery white colour, and by exposure to the air acquires- a slight superficial tarnish, which does not appear to increase by time. Its specific gravity is about 7.9. It is extremely soft; scarcely, if at all, elastic; and when a piece of it is bent backwards and forwards, it gives a peculiar crackling noise. It is very malleable, and may be beaten into leaves, l-1000th of an inch thick. I. Tin melts on the application of a moderate heat, equal to 442* Fahrenheit, by a long continuance of which it is converted into a grey powder. This powder, which appears to be the first oxide of tin, when mixed with pure glass, forms a white enamel. It may be procured, also, by calcining, in a close vessel, the precipitate from fresh made muriate of tin by carbonate of potash. The grey oxide, when brought to a fuli red heat, takes fire; and, acquiring an increase of oxygen, passes to a pure white colour. This white oxide, when the heat is considerably raised, loses a part of its oxygen and runs into fusion. The white oxide may be obtained at once by projecting tin into a crucible intensely heated, when the oxide rises in the torm of flowers somewhat resembling those of zinc. It may, also, be procured, as Berzelius found, by distilling powdered tin with red oxide of mercury. The oxides of tin have been investigated by Gay Lussac and Ber- zelius, and their results differ so little, that either of them may be presumed to be correct Gay Lussac states the composition of the protoxide to be * Thomson's Annals x. 166. SECT. X. TIN. 99 ■Tin.....88.10......100. Oxygen .... 11.90......13.6 100. And that of the peroxide, in which he agrees with Klaproth, Tin......79......100. Oxygen.....21......27.2 100* Besides these two oxides, Berzelius suspects the existence of an intermediate one, which is formed when tin is acted on by nitro- muriatic acid; and which enters into the composition of deuto- chloride of tin.t It has a yellow colour, and, from theory, should consist of 100 metal 4- 20.4 oxygen; but he does not appear fully to have satisfied himself on the subject; and its existence is thought by Gay Lussac to be extremely questionable. The oxides of tin have, in a certain degree, the properties of acids, so as to render it doubtful whether they should not be arranged in that class of compounds. But their affinities for bases are so extremely feeble, that it seems adviseable, on the whole, to retain them in the class of oxides. The precipitates from solutions of tin by alkalies are hydrates, and have a white colour. They are soluble in an excess of fixed alkali; but the oxide is precipitated by the weakest acid, even the carbonic. The hydrates of tin are, also, decomposed by the action of boiling water. Dr. Thomson has described two hydrates, the one composed of 100 peroxide and 24 water, the other of 100 peroxide and 48 water.| II. Tin is not oxidized at common temperatures by exposure to air with the concurrence of moisture; a property which is the founda- tion of its use in covering iron. III. Tin amalgamates readily with mercury; and this compound is much used in the silvering of looking glasses. It is formed by adding gradually three parts of mercury to twelve of tin melted in an iron ladle, and stirring the mixture. IV. Tin dissolves in sulphuric acid, which takes up, when con- centrated and heated, half its weight It is dissolved also by this acid, diluted with about a fourth its weightof water, and heated. During both these processes, sulphurous acid is disengaged ; and, in the latter, a pellicle of sulphur forms on the surface of the solution, which pre- cipitates on cooling. When saturated, the solution deposits, after a while, needle-shaped crystals of sulphate of tin. If the sulphate be long boiled, a copious white precipitate subsides, which will not again * Ann. de Chim. et Phys. i. 43; and r. 151. f 87 Ann. de Chim. 50. t Annals of Phil. x. 149. 106 MBTALS. CHAP. XIX. dissolv?. It is composed of- the white oxide retaining only a small portion of acid, and constituting in fact a sub-sulphate. V. When nitric acid highly concentrated is poured upon tin filings, very little effect is produced; but when a small quantity of water is added, a violent effervescence follows; and the metal is reduced to a bulky powder, which is the white oxide retaining a little acid. If more water be added, an acid liquor is obtained, holding very little tin in solution. Tin, however, is slowly dissolved, without efferves- cence, in nitric acid greatly diluted. The solution is yellow, and deposits oxide of tin by keeping. VI. Muriatic acid, undiluted, is the proper solvent of tin. To one part of tin, in a tubulated retort, two parts of concentrated muriatic acid are to be added, and heat applied. The solution is complete, with the exception of a small quantity of black powder, which consists of protoxide of copper ;* and the acid takes up about one-fourth of its weight of tin.t The solution has always an excess of acid; is per- fectly limpid and colourless; and contains the metal at the minimum of oxidation. It has a tendency, however, to acquire a farther pro- portion of oxygen, and should, therefore, be carefully preserved from contact with the air. This property of absorbing oxygen is so re- markable, that it may even be applied to eudiometncal purposes. It has, also, the property of reducing, to a minimum of oxidation, those compounds of iron, in which the metal is fully oxidized. For exam- ple, it reduces the red sulphate to the green. It is a test also of gold and platinum, as already noticed, and blackens the solution of cor- rosive sublimate. With hydro-sulphurets it gives a black precipitate. VII. Tin may be brought to combine with chlorine, by first form- ing it into amalgam with mercury, triturating this with an equat weight of corrosive sublimate, and distilling the mixture. Or the same compound may be formed, according to Proust, by distilling a mixture of eight ounces of powdered tin and twenty-four ounces of corrosive sublimate. The result is a liquid which emits dense white fumes, when exposed to the air, and was formerly termed the fuming liquor of Libavius. Itgives no precipitate with muriate of gold or muriate of mercury—affords a yellow sediment with hydro-sulphuret of potash—dissolves a farther portion of the metal without efferves- cence, and is then changed into the common muriate. This compound, according to the researches of Adet is an oxy- muriate of tin (or, according to the theory of chlorine, a per- chlorine of tin), perfectly free from water, and having a strong affinity for that fluid. Hence arises its fuming property; for the white va- pours, which exhale when the bottle is unstopped, arise from the union of the salt with the moisture of the air. It may be formed at once, by heating tin in chlorine gas; and it consists, according to Dr. Davy, who calls it stannanea, of * Thomson's Annals, x. 71. t..°n tne preparation of muriate of tin, see Berard, Annales de Chimie, £vmvf8i or N'chobon's Journal, xxvi.; and Chaudet, Ann, de Chim. et Phys. SECT. .%#* •TIN. 101 Po„.iU ., C Tin .... 45 ... tOO Perchloride . . Jchlorine . . 55 . . . 122 100 Another compound of tin and chlorine, called by the same chemist stannane, but more properly named protochloride of tin, may be ob- tained by heating together an amalgam of tin and calomel. It dissolves in water, and forms a solution, similar to the muriate of the protoxide, which rapidly absorbs oxygen from the air, and deposits peroxide of tin. It is composed of 55 tin and 33.5 chlorine, or u ^ n i ^'Hn . . . » 62 . . . 100 Proto-chlonde . JChlorine . . S8 . . . 62 100 VIII. The nitro-muriatic acid (formed by mixing two or three parts of muriatic acid and one of nitric,) dissolves tin abundantly, with violent effervescence, and with so much heat, that it is necessary to add the metal slowly by successive portions. The solution is apt to congeal into a tremulous gelatinous mass; and if water be added, it is partly decomposed, and some oxide separated. The solution, used by the scarlet dyers, is prepared with that dilute nitric acid called single aqua-fortis, to each pound of which are added from one to two ounces of the muriate of soda or ammonia. This com- pound acid is capable of taking up about an eighth its weight of tin. IX. Acetic acid (distilled vinegar) by digestion with tin filings takes up a portion of the metal, and acquires an opalescent or milky appearance. The solution is decomposed by the action of the air, and deposits an insoluble oxide. Tin dissolves in tartaric acid; and the solution is applied to the useful purposes of wet-tinning, the process for which is described in Aikin's Dictionary, ii. 427. X. Tin unites with sulphur, but requires, for its combination, so high a temperature, that at the moment of union there is too small a quantity of sulphur present, to saturate the tin, and a mechanical mixture results of tin and sulphuret of tin. The only method of ob- taining the saturated sulphuret, is to melt the aurum musivum, which will presently be described, in close vessels. The proto-sulphuret is of a bluish colour and lamellated structure. It is composed, accord- ing to Dr. John Davy and Berzelius, of Tin.....78.6 . . . 100. Sulphur .... 21.4 . . . 27.234 100. 127.234 The second sulphuret, or per-sulphuret of tin, (aurum musivum,) *s formed by heating sulphur with peroxide of tin. It is of a beauti- 102 METALS. OHAr. XIX. ful gold colour, and flaky in its structure. Proust was of opinion that it is a sulphuretted oxide; but Dr. Davy and Berzelius have shown that the tin is in a metallic state. According to the former, it con- sists of Tin.....64.5 . . . 100. Sulphur .... 35.5 . . . 54.5 100. 154.5 Berzelius, by redistilling per-sulphuret of tin with sulphur, obtain- ed a compound of a greyish colour and metallic lustre, which he found to be composed of 100 tin and 40.851 sulphur, or exactly intermediate between the two which have been already described. It is probable, however, that it was merely a mixture of the two sulphurets, and not a distinct compound. XI. Tin forms useful alloys with many of the metals. Pewter is one of these; and the best kind of it is entirely free from lead, being composed chiefly of tin with small proportions of antimony, copper, and bismuth.* A mixture of tin and lead, in about equal parts, com- poses the common plumbers? solder. Tin enters, also, into the com- position of bell-metal and bronze; and one of the most useful appli- cations of it is to the tinning of iron plates, which is effected by dip- ping the plates into melted tin. The process, however, requires seve- ral preliminary steps, which are described in Watson's Chemical Es- says, vol. ix., and in Mr. Parkes's Chemical Catechism. SECTION XI. Lead. 0 To obtain lead in a state of purity, Berzelius dissolved it in nitric acid, and crystallized the salt several times, till the mother liquor, on adding carbonate of ammonia, gave no traces of copper. The pure nitrate of lead, mixed with charcoal, was strongly heated in a Hessian crucible; and the lead, which separated, was kept some time in a state of fusion, in order to free it entirely from charcoal. The lead, thus obtained, when redissolved in nitric acid, gave no trace of any other metal. Lead has a bluish white colour; and, when recently cut or melted, considerable lustre, which soon, however, tarnishes. Its specific gra- vity is 11.352. Its malleability is sufficient to allow its being beat into very thin leaves; and it may be drawn into wire, which has less tenacity, however, than that of most other metals. * On the alloys of tin, a memoir of M. Dussausoy may be consulted in the 5th vol. of Ann.de Chim. et Phys.; and Mr. Chaudet's paper in the same and iu the 7th volumes. t SECT. XI. LEAD. 103 The melting point of lead, according to Morveau, is 590° Fahren- heit; but according to Mr. Crichton of Glasgow, it is'612°. Exposed to a red heat, with free access of air, it smokes and sublimes, and gives a grey oxide, which collects on surrounding cold bodies. It is slowly oxidized, also, by exposure to the atmosphere at common tem- peratures; and more rapidly, when exposed alternately to the action of air and water. Lead appears to be susceptible of forming three distinct oxides. 1. The yellow oxide may be obtained by decomposing nitrate of lead with carbouate of soda, and igniting the precipitate, or by heating the nitrate to redness in a close vessel. This oxide is tasteless, inso- luble in water, but soluble in potash and in acids. When heated, it forms a yellow semi-transparent glass. Another form of the yellow oxide is that which is known in commerce by the name of massicot. The yellow or protoxide of lead has been investigated by Proust, Thomson, and Berzelius; and its composition, as determined by the last mentioned chemist, is Lead . . . 92.85 . . . 100. . . . 1298.7 Oxygen . . 7.15 .. . 7.7 .. . 1000. 100. 2. The second, or deutoxide of lead, may be obtained by exposing the protoxide of lead, or the metal itself, to heat, with a large surface and a free access of air, for some time, till, at length, it is converted into a red oxide, known in commerce by the names of minium or red lead. This, however, is an impure substance, containing sulphate of lead, muriate of lead with excess of base, oxide of copper, silex, and a portion of the yellow oxide. This, Berzelius found, may be removed by acetic acid, which does not act on the red oxide. Making allow- ance for the other impurities, he determined the composition of red oxide of lead, which may be considered as the deutoxide, to be Lead ..... 90 ... . 100. Oxygen .... 10 ... . 11.08 100 When minium is digested with nitric acid, one part of it is reduced- to the state of yellow oxide, and is dissolved by the acid; and the remainder is a brown oxide, contaminated (if pure minium has been used) with the substances which have been mentioned. This oxide may be procured, also, by passing a current of oxymuriatic acid gas through water, in which the red oxide is kept suspended, and by pre- cipitating with caustic potash, and drying the oxide. It is of a flea or puce colour; very fine and light in its texture; and insoluble in nitric acid. When strongly heated, it gives out three or four per cent of oxygen gas, and is converted into yellow oxide. It consists, accord- ing to Berzelius, of 104 METALS. CHAP. XIX. Lead .... 86.51 .... 100. Oxygen .... 13.49 .... 15.6 100. 115.6 On comparing the quantities of oxygen united with 100 parts of lead, in these three oxides, we shall find that the numbers 7.7, 11.08, and 15.6, are very nearly in the proportion of 1, 1 \, and 2. If, there- fore, we multiply these last numbers by 2, we shall have the oxygen, in the three oxides of lead, represented by 2, 3, and 4; and this view of the subject would render it probable, that there exists an oxide of lead, with less oxygen than any at present known. I have, therefore, till this can be decided, retained the names of the three oxides which are derived from their colour, viz. the yellow, the red, and the puce oxides. The yellow oxide of lead, when precipitated by pure alkalies from its compounds, forms a white hydrate, the composition of which is not exactly known. The oxides of lead are easily vitrified, and have the property of uniting with all the metals except gold and silver. Hence gold or 9ilver may be purified by melting them with lead. The mixture is to be kept, for some time, in a state of fusion in a flat cup made of bone ashes, and called a cupel or test. The lead becomes vitrified, and sinks into the cupel, carrying along with it all. the baser metals, and leaving the gold or silver on the surface of the cupel. The quan- tity of lead required for silver of various degrees of fineness may be learned from a memoir of d'Arcet, in the first volume of Annales de Chim. et Physique. The oxides of lead give up their oxygen on the application of heat When distilled in an earthen retort, they afford oxygen gas; and still more readily when distilled with concentrated sulphuric acid. To procure oxygen gas, sulphuric acid may be poured on the red oxide of lead, contained in a gas bottle, and a gentle heat applied. The gas, thus obtained, after being agitated with water, is sufficiently pure for common purposes. The oxides of lead are also reduced, by being ignited with combus- tible matter. Thus, when a mixture of red oxide of lead and char- coal is ignited in a crucible, a button of metallic lead will be found at the bottom of the vessel. Mere trituration of the peroxide in a mortar with a little sulphur, and the subsequent addition of a small bit of phosphorus, occasions a violent explosion.* II. Pure water has no action on lead; but it takes up a small pro- portion of the oxide of that metal. When left in contact with water, with the access of atmospherical air, lead soon becomes oxidized and dissolved, especially if agitation be used. Hence the danger of leaden pipes and vessels for containing water, which is intended to be drunk. * Thomson's Annals, ix. 31. SECT. XI. j( LEAD. 105 Water appears also to act more readily on lead, when impregnated with the neutral salts that are occasionally present in spring water.* III. Sulphuric acid has no action on lead, except when concen- trated and at a boiling temperature. It is then decomposed, and sul- phurous acid is formed. The insolubility of lead in sulphuric acid occasions its being employed as the material for constructing the chambers in which that acid is prepared, and even for boiling down the weak acid. Sulphate of lead, however, may be formed, either by adding sulphuric acid, or still better, sulphate of soda, to any of the salts of lead. Its insolubility renders its formation of use as a step in mineral analyses, and hence it is necessary to know its exact com- position, which is stated by Berzelius as follows:— Sulphuric acid ..... 26.34 .... 100 Yellow oxide .... 73.66 .' . . . 279 100. 379 If the whole oxygen in the sulphate of lead be supposed to be di- vided into four parts, one of these, it is remarked, by Berzelius, is combined with the lead, and three with the sulphur. In the sulphite, one third of the oxygen is united with the lead, and two thirds with the sulphur. IV. Nitric acid, a little diluted, dissolves lead, with the extrication of nitrous gas. If the acid be in small quantity, a sub-nitrate is form- ed, which becomes soluble on adding more acid. A small portion remains undissolved, which Dr. Thomson finds to be oxide of anti- mony with a little silex. The solution is not decomposed when poured into water. By evaporation, it yields large regular crystals, which are soluble in about 7\ parts of boiling water. They contain no water of crystallization, and consist, according to Berzelius, of Nitric acid .... 32,78 .... 100. Yellow oxide .... 67.22 .... 209.5 100. 309.5 Chevreul considers this salt as a super-nitrate,* and describes a scaly salt, which is the neutral nitrate, consisting of Nitric acid .... 19.86 .... 100 Yellow oxide. . . . 80.14 . . . . 403 100. 503 By boiling 4 parts of the super-nitrate, and 6 of lead, with S50 parts of water, for 14 hours, Chevreul obtained a liquid, which yielded * On the presence of lead in water, consult Dr. Lambe's " Researches re- specting Spring Water," (8vo. London, Johnson,) and also iluyton, 26 Nich. Journ. 102. f 1 Thomson's Annals, 101. Voi. II.—O 106 MRTALS. • «HAP. XIX. two sorts of crystals; the one, in the form of plates, a nitrite; and the other, in the shape of needles, a sub-nitrite. The nitrite was little soluble in cold water, and boiling water dissolved only about a tenth of its weight. It was decomposed by all the acids that were tried. Its constituents are Nitrous acid .... 18.15 .... 100 Yellow oxide .... 81.85 .... 450 100. The sub-nitrite crystallized in needles, of which 100 parts of boil- ing water dissolved about three parts, and retained one, when cooled down to 73° Fahrenheit It consisted of Nitrous acid .... 9.9 .... 100 Yellow oxide .... 90.1 .... 910 100. V. When the nitrate, or any other soluble salt of lead, is added to a solution of common salt, a precipitate takes place of muriate of lead. The same compound may, also, be obtained by heating lead in chlo- rine gas, or by treating the oxides of lead with muriatic acid. When dry, the compound is a dull semi-transparent substance, fusible at a heat below redness, and volatile at an intense heat. It has a sweet taste, and is soluble in 22 parts of cold water. It has successively re- ceived the names of horn lead, muriate of lead, and plumbane; Ber- zelius states its composition to be Muriatic acid . . . 19.64 .... 100. Yellow oxide . . . 80.36 .... 409.06 100. But according to Sir H. Davy, it is a compound of chlorine with metallic lead, or chloride of lead, composed of Chlorine.....24.62 .... 100 Lead......75.38 .... 306 100. When two parts of the red oxide of lead are mixed with one of muriate of soda, and the mixture is made into a paste with water, the common salt is decomposed, and a muriate, or probably a sub-mu- riate or sub-cftloride of lead is formed, which, on fusion, affords the substance called mineral or patent yellow. The soda is disengaged; and attracts carbonic acid from the atmosphere, but not enough to SECT. XI. LEAD. 197 convert it into a carbonate. In the large way, it is found necessary to supply carbonic acid to the soda, thus prepared, by burning it with saw-dust. VI. Carbonic acid may be brought to combine with protoxide of lead, by precipitating the nitrate of lead with carbonate of soda, or by long exposure of thin sheets of lead to the vapour of vinegar. , In the latter case, we obtain the carbonate of lead or common white lead, which Bergman has shown to contain no acetic acid, though made by its intervention. According to Berzelius, it consists of Carbonic acid.....16.5 Oxide of lead......83.5 100. VII. When carbonate of lead is dissolved in distilled vinegar, and the solution crystallized, we obtain a salt of great utility in the arts, the super-acetate, or more properly acetate, of lead, long known, from its sweet taste, under the name of sugar of lead. It is in the form of small shining needle-shaped crystals, which are nearly equally soluble in hot and in cold water, viz. to about one- fourth the weight of the fluid. The solution is decomposed by mere exposure to the air, the carbonic acid attracting the lead, and forming an insoluble carbonate. It is decomposed, also, by the carbonates and sulphates of alkali. Acetate of lead consists, according to the experiments of Berze- lius, of Acid......26.97 .... 100, Yellow oxide . . . 58.71 .... 217.662 Water.....14.32 .... 100. By boiling in water, a solution of 100 parts of acetate and 150 of finely pulverized litharge, the acetate passes to the state of sub-ace- tate. The taste of this salt is less sweet; it is less soluble in water; and crystallizes in plates. It is composed, according to Berzelius, of Acid......13.23.....100 Yellow oxide . . . 86.77.....656 # 100. The oxide in the sub-acetate is, therefore, so nearly three times that contained in the acetate, that we may consider the composition of these salts as furnishing an additional example of the law of sim- ple multiples. All the solutions of lead are decomposed by sulphuretted hydro- gen and by alkaline hydro-sulphurets. Hence these compounds are 108 METALS. CHAP. XIX. excellent tests of the presence of lead in wine or any other liquor, dis- covering it by a dark-coloured precipitate. Hence, also, characters traced with solution of acetate of lead, become legible when exposed to sulphuretted hydrogen gas. The same property explains, too, the effect of alkaline hydro-sulphurets in blackening the glass bottles, in which they are kept. The effect is owing to the action of the sulphu- retted hydrogen on the oxide of lead which all white glass contains. VIII. The yellow oxide of lead unites with phosphoric acid, either directly or by mixing the solutions of a neutral alkaline phosphate and of nitrate or acetate of lead. The compound is insoluble, and is composed, according to Berzelius, of Phosphoric acid . 20.8 . . 100. . . 26.2 Yellow oxide . . 79.2 . . 380.5 . . 100. 100. 480.5 126.2 IX. Lead unites in its metallic state with sulphur; and affords a compound of a blue colour with considerable brilliancy called ga- lena. This compound may, also, be formed artificially. It is remarked by Berzelius that the sulphur and lead, which it contains, are in such proportions, that when both are combined with oxygen, and convert- ed, the one into sulphuric acid, and the other into yellow oxide of lead, the acid and oxide exactly saturate each other. These propor- tions he found to be Sulphur . . 13.36 . . 15.42 . . . 100. Lead . . . 86.64 . . 100. ... 643.5 743.5 SECTION XII. Zinc. The zinc of commerce, known by the name of speltre, is never pure, but contains lead and sulphur. To purify it, zinc must be dis- solved in diluted sulphuric acid; a plate of zinc is then to be im- mersed'in the solution, to precipitate other metals, which it may con- tain; the solution must be decomposed by sub-carbonate of potash: and the precipitate ignited with charcoal powder. Zinc is of a brilliant white colour with a shade of blue. Its specific gravity varies from 6.86 to 7.1, the lightest being the purest By particular treatment it becomes malleable,* and may be beaten into leaves or drawn into wire. * The discovery of the malleability of zinc is announced by Mr. Silvester in the Philosophical Magazine, vol. xxiii. 100.00 115.42 bECT. XII. ZINC. 109 I. Zinc is melt -d by a moderate heat, viz. at about 680° Fahren- heit, and the fused mas*, on cooling, forms regular crystals. II. By exposure to the air, at a low temperature, it slowly acquires a coating of grey oxide; but when kept in a degree of heat, barely sufficient for its fusion, zinc becomes covered with a grey oxide. If thrown into a crucible, or deep earthen pot, heated to whiteness, it suddenly inflames; burns with a beautiful white flame; and a white and light oxide, containing some carbonate, sublimes, having a consi- derable resemblance to carded wool. This oxide, however, when once deposited, is no longer volatile; but, if exposed to a violent heat runs into glass. It has been examined with much attention by Proust, who found it to consist of 80 parts of zinc and 20 oxygen. Gay Lus- «ac* and Berzeliust have since investigated it, and agree in consider- ing it as composed of Zinc.....80.39 .... 100. Oxygen . . . . 19.61 . . . . 24.4 100. 124.4 Zinc decomposes water very slowly at common temperatures, but with great rapidity, if the vapour of vvnter be brought into contact with it when ignited. In whatever way it is oxidized, we obtain the compound already described, which is the only known oxide of zinc.J III. Zinc readily dissolves in diluted sulphuric acid, with the ex- ception of a small quantity of black powder, which Vogel found to be composed of charcoal, iron, and sulphate of lead. The acid, during its action on this metal, evolves hydrogen gas; and the gas, when obtained, besides other impurities, holds in combination a portion of the metal. A stream of it, burned in Cuthbertson's apparatus (pi. iv. fig. 34,) has been found, if recently prepared, to occasion the fusion of the platinum wire, though the pure gas is destitute of this pro- perty. This hydrogen gas, holding zinc in solution, may also be ob- tained by a process of Vauquelin. A mixture of the ore of zinc, called blende, or calamine, with charcoal, is to be put into a porcelain tube, which is to be placed horizontally in a furnace, and, when red- hot, the vapour of water is to be driven over it. The gas that is pro- duced, however, is a mixture of carbonic acid, carburetted hydrogen, and hydrozincic gas. The zinc is deposited on the surface of the water, by which this* gas is confined; but, if burned when recently prepared, the gas exhibits, in consequence of this impregnation, a blue flame. The solution of zinc in sulphuric acid, when evaporated to a due degree of density, shoots into regular crystals. This salt is soluble in 2£ parts of water; and its solution is not precipitated by any other metal. Its composition is stated by Berzelius and Wollaston as fol- lows: * 80 Ann. de Chim. 170. f 81 Ditto t Vogel in Thomson's Annals, vii. 33. 119 METALS. CHAP. XIX. Acid.....39.96 .... 27-3 Base.....32.69 .... 28.4 Water .... 36.45 .... 44.S 100* lOO.t IV. Nitric acid, moderately strong, acts on zinc with great vio- lence. The solution, by evaporation, crystallizes, and affords a deli- quescent salt V. Muriatic acid, a little diluted, acts on zinc, and evolves hydro- gen gas of great purity. The solution is clear, but cannot, by evapo- ration, be brought to crystallize. The dry salt, however, may be sublimed, and passes over in a half solid state, from which circum- stance it has been called butter of zinc. When rapidly evaporated, it yields a thick extract, which has somewhat of the viscidity of bird- lime. Only one compound of zinc and chlorine is known. It may be -formed by burning the metal in chlorine gas, or by distilling zinc filings with corrosive sublimate. It fuses at a heat a little above 212°; is volatile at a temperature below redness; and is identical with the compound, obtained by evaporating muriate of zinc. It consists, ac- cording to Dr. John Davy, as nearly as possible, of equal weights of metal and chlorine, or ol Zinc......49.5 .... 100 Chlorine .... 50.5 .... 102 100. VI. Acetate of zinc may be formed either by directly dissolving the metal or the white oxide in vinegar, or by mingling the solutions of super-acetate of lead and sulphate of zinc. An insoluble sulphate of lead is formed, and the acetate of zinc remains in solution. By evaporation it affords a crystallized and permanent salt. VII. Zinc is oxidized by being boiled with pure alkaline solutions, and a portion of the oxide remains dissolved. A similar compound may be obtained, by projecting a mixture of nitre and zinc filings into a red-hot crucible. VIII. Zinc, in its metallic state, has very litt^e affinity for sulphur. A mixture of the white oxide of zinc and flowers of sulphur combines, however, into a yellowish brown mass. Water, impregnated with sulphuretted hydrogen, decomposes, after some time, the solutions of zinc, and forms a yellow precipitate, which is probably a hydro-sul- phuret Mr. E. Davy, however, by passing the vapour of sulphur over melted zinc, obtained a white crystalline substance, resembling the natural compound of zinc and sulphur, called phosphorescent blende. The native sulphuret has been analyzed by Dr. Thomson, and found <"n consist of * Berzelius. f Wollaston. SECT. XIII. BISMUTH. Ill" Zinc . . . 67.19 . . 100. . . 214.40 Sulphur . . 32.81 . . 48.84 . . 100. 100. 148.84 314.40 IX. Zinc combines with phosphorus. The 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 degree of heat, burns like common zinc. X. Zinc is capable of furnishing alloys with most of the other me- tals. Of these the most useful, brass, has already been mentioned in the section on copper. It has been lately proposed to apply zinc to the purpose of culinary vessels, pipes for conveying water, sheathing for ships, &c; but it is rendered unfit for the first, by the facility with which the weakest acids act upon it; and for the rest by its con- siderable, though slow oxidation when exposed to air and moisture. SECOND CLASS. METALS THAT ARE BRITTLE AND EASILY FUSED. SECTION XIII. Bismuth. Bismuth has a reddish white colour, and is composed of broad brilliant plates adhering to each other. Its specific gravity is 9.822, but is increased by hammering. It breaks, however, under the ham- mer, and hence cannot be considered as malleable; nor can it be drawn out into wire. I. Bismuth is one of the most fusible metals, melting at 476° Fah- renheit; and it forms, more readily than most other metals, distinct wystals by slow cooling. II. When kept melted at a moderate heat, it becomes covered with an oxide of a greenish grey or brown colour. In a more violent heat it is volatile, and may be sublimed in close vessels; but, with the- access of air, it emits a blue flame, and its oxide exhales in the form of a yellowish smoke, condensible by cold bodies. This oxide is very fusible; and is convertible, by heat, into a yellow transparent glass. It is the only oxide, of bismuth with which we are acquainted; and consists, according to the experiments of Lagerhjelm,* of * 4 Thomson's Annals, 357 112 METALS. CHAP. XIX. . Bismuth . . . *. 89.863 . . . 100. Oxygen .... 10.137 . . . 11.28 100. III. Sulphuric acid acts on bismuth, and sulphurous acid is disen- gaged. A part of the bismuth is dissolved; and the remainder is changed into an insoluble oxide. The sulphate, on the same authority, is stated to consist of Oxide of bismuth . . . 66.353 . . . 100. --------sulphuric acid . 33.647 . . . 50.71 100. Besides the neutral sulphate, Berzelius describes a sub-sulphate ot Oxide of bismuth .... 85.5 ... 100 --------sulphuric acid . . 14.5 ... 17 100. IV. Nitric acid dissolves bismuth with great rapidity. To one part and a half of nitric acid, add, at. distant intervals, one of bis- muth, broken into small pieces. The* solution is crystallizable. It is decomposed when added to water; and a white substance is pre- cipitated, called magistery of bismuth,"br pearl-white. It consists of hydrated oxide of bismuth with a small proportion of nitric acid. This pigment is liable to be turned black by sulphuretted hydrogen, and by The vapours of putrefying substances in general. V. Muriatic acid acts on bismuth. The compound, when deprived of water by evaporation, is capable of being sublimed, and affords a soft salt, which deliquesces into what has been improperly called butter of bismuth. The same compound is obtained by introducing finely divided bismuth into chlorine gas, when the metal takes fire, and burns with a pale blue light. It is the only known combination of bismuth and chlorine, and was found, by Dr. Davy, to contain 66.4 per cent, of the metal, and 33.6 of chlorine. VI. Bismuth is capable of forming the basis of a sympathetic ink • The acid, employed for this purpose, must be one that does not act on paper, such as the acetic' Characters written with this solution be- come visible, when exposed to sulphuretted hydrogen. VII. Bismuth combines with sulphur, and forms a bluish grey sul- phuret, having a metallic lustre. Lagerhjelm has analyzed it, and found it to consist of Bismuth .... 81.619 .... 100. Sulphur . . . . 18.381 .... 22.52 100. SECT. XIV. ANTIMONY. 113 VIII. Bismuth is capable of being alloyed with most of the metals, and forms with some of them compounds of remarkable fusibility. One of these is Sir Isaac Newton's fusible metal. It consists of eight parts of bismuth, five of lead, and three of tin. When thrown into water, it melts before it is heated to the boiling point It is from this property of forming fusible alloys, that bismuth enters into the com- position of several of the soft solders, which, indeed, is its principal use. Bismuth has the singular property of depriving gold of its ductility; even when combined with it in very minute proportion. This effect is produced by merely keeping gold in fusion near bismuth raised to the same temperature. SECTION XIV. Antimony. t I. Antimony, as it occurs under that name in the shops, is a natural compound of the metal with sulphur in the proportion, as stated by Proust of 75 antimony and 25 sulphur. To obtain it in a metallic state, the native sulphuret is to be mixed with two-thirds its weight of supertartrate of potash (in the state of crude tartar), and one-third of nitrate of potash deprived of its water of crystallization. The mixture must be projected, by spoonfuls, into a recl-hot crucible; and the detonated mass poured into an iron mould greased with a little fat. The antimony, on account of its specific gravity, will be found at the bottom adhering to the scorise, from which it may be separated by a hammer. Or two parts of the sulphuret may be fused in a covered crucible with one of iron filings, and to these, when in fusion, half a part of nitre may be added. The sulphur quits the antimony, and combines with the iron. In order to obtain antimony in a state of complete purity, the metal, resulting from this operation, must be dissolved in nitro- muriatic acid, and the solution must be poured into water. A white powder will precipitate, which must be dried, mixed with twice its weight of crude tartar, and fused in a crucible, when the pure metal will be produced. II. Antimony in its metallic state (sometimes called regulus of antimony) is of a silvery white colour, very brittle, and of a plated, or scaly texture. III. 11 is fused by a heat of about 810° Fahrenheit; and crystallizes, on cooling, in the form of pyramids. In close vessels it may be volatilized, and collected unchanged. IV. It undergoes little change when exposed to the atmosphere at its ordinary temperature; but when fused, with the access of air, it emits white fumes, consisting of an oxide of the metal. This oxide had formerly the name of argentine flowers of antimony. The vapour Vol. II.—V 114 METALS. CHAP. XIX. of water, brought into contact with ignited antimony, is decomposed with so much rapidity, as to produce a series of detonations. \ V. Antimony, it has been supposed by Thenard, is susceptible of several degrees of oxidation; but these, according to Proust, may be all reduced to two. The first oxide may be obtained by pouring the muriate of antimony into water, and washing the precipitate with water containing a small quantity of potash. When dry, it is of a dirty white colour, without any lustre. It melts at a moderate red heat, and becomes opaque on cooling. It is composed of Antimony.....81.5 .... 100. Oxygen ...... 18.5 .... 22.7 100. The oxide at the maximum may be procured by collecting the flowers of antimony already described, or by causing the nitric acid to act on the metal, or by projecting it into melted and red-hot nitre. This oxide is of a white colour, and is muckless soluble in water than the protoxide. It is, also, less fusible, and may be volatilized at a lower temperature, forming white prismatic crystals of a silvery lustre. lr is composed of ■ Antimony.....77.....100 Oxygen......23.....30 100 The oxides of antimony have been investigated by Berzelius,* who describes four degrees ot oxidation in that metal. The first, or sub- oxide, is obtained by the long exposure of antimony to a humid at- mosphere, or by making that metal the positive conductor in a Gal- vanic arrangement, pure water being employed to complete the circuit. To procure the sub-oxides, the antimony must be reduced to powder, and placed under water in contact with a platinum wire, connected with the positive end of the pile. Oxygen gas is disengaged from the point of contact, and the antimony is covered with a bluish grey flocculejpt powder, which is lighter than the metal, and may be separated by washing with water. It is produced so sparingly, that enough could not be obtained for analysis, and its composition was, therefore, deduced by calculation. This second oxide (called by Berzelius the oxidule) may be ob- tained from muriate of antimony by an alkali. When the precipitate which at first is a hydrate, is dried and heated, the oxide assumes a dull white colour, verging on grey. In a red heat, it fuses into a yel- lowish fluid, which, on cooling, becomes an almost white mass, crys- tallized something like asbestus. * 86 Ann. de Chim. 225. SECT. XIV. ANTIMONY. 115 The third, or white oxide, was formed by dissolving antimony in nitric acid, and evaporating and igniting the product; or by dissolv- ing in nitro-muriatic acid, decomposing by water, washing the pre- cipitate, and calcining it in a platinum crucible. Its colour, when pro- perly prepared, is perfect or snow white. The fourth, or yellow oxide, was obtained by Berzelius in the fol- lowing manner: Powdered metallic antimony was fused, during an hour, in a silver crucible, with six times itsvweight of nitre; and the fused mass was washed, first with cold and then with boiling water. The liquid was evaporated to dryness, and digested many hours with nitric acid. The white powder, insoluble in nitric acid, was gently heated in a small platinum crucible, and assumed a fine lemon yellow colour. A similar product was obtained by mixing powdered antimony with pure oxide of mercury. An olive substance was produced, which, by long exposure to heat, assumed a straw yellow colour. This oxide, by a strong heat, loses about 6$ per cent, of oxygen, and is changed into the white oxide. The composition of these four oxides is thus stated by Berzelius: Metal. Oxvgen. Metal. Oxvgen. 1. Sub-oxide . . . 96.826 . . 3.174 . . 100 . . 4.65 2. Oxidule . . . 84.317 . . 15.683 . . 100 . . 18.60 3. White oxide . . 78. 19 . . 21. 81 . . 100 . . 24. 8 4. Yellow oxide . . 72. 85 . . 27. 15 . . 100 . . 37.20 It is probable, from the law of definite proportions, that the first or sub-oxide will prove to be a mechanical mixture of metallic antimony with the second or oxidule, which, in that case, will be the true prot- oxide. If this be established, it will afford another example of the general principle, that in protoxides, the oxygen is equal to half the sulphur of the sulphuret. The white and yellow compounds of oxygen and antimony ought, indeed, to be arranged among acids, rather than among oxides; for each of them combines with salifiable bases, and affords a class of salts. The first may be called the antimonious acid, and its com- pounds antimonites; the second the antimonic acid, and the salts which it composes antimoniates. These names appear to me prefer- able to those which have been derived, by Berzelius, from the Latin appellation stibium, viz. stibious, and stibic acids. For a detail of the properties of these saline combinations, I refer to the memoir al- ready quoted, and to the 5th volume of Ann. de Chim. et Phys. VI. Antimony combines with sulphur, and forms an artificial sul- phuret, exactly resembling the native compound, which last may be employed, on account of its cheapness, for exhibiting the properties of sulphuret of antimony. The proportions of its ingredients, as stated by Berzelius, differ from those assigned by Proust, viz. Antimony . . 72.86 .. 100. ... 270 Sulphur . . . 27.14 . . 37.25 . . 100 100. 116 METALS'. CHAT. XIX- 1. When native sulphuret of antimony (frequently called crude antimony) is slowly roasted in a shallow vessel, it gradually loses its sulphur, the metal attracts oxygen, and is mostly converted into a grey oxide. This, being melted in a strong heat, acquires a reddish colour, and runs into a glassy substance, transparent at its edges, and termed glass of antimony. It consists of eight parts of protoxide and one of sulphuret with ten per cent, of silex. The same quantity of oxide and two of sulphuret give an opaque compound, of a red colour inclining to yellow; and called crocus metallorum. With eight parts of oxide and four of sulphur, we obtain an opaque mass of a dark red colour, called liver of antimony. In all these compounds, the oxide is at its minimum of oxidation; for the peroxide is incapable of dis- solving the sulphuret. 2. When fused with potash, a triple compound is formed, com- posed of alkali, sulphur, and antimony. Or the combination may be effected, in the humid way, by boiling the powdered native sulphuret with pure potash. The solution, on cooling, deposits an hydro-sul- phuretted oxide, in which the- oxide prevails, called kermes mineral. The addition of a dilute acid to the cold solution, precipitates a com- pound, having the same ingredients, but a larger proportion of sul- phur, and called golden sulphur of antimony. 3. When the sulphuret of antimony is detonated with twice its weight or upwards, of powdered nitre, the sulphur is oxygenated by the oxygen of the nitric acid; sulphate of potash is formed, and an oxide of antimony is obtained, varying in its degree of oxidation, with the proportion of nitre which has been employed. The oxide remains, after washing away the sulphate with boiling water. If four times its weight of nitre be employed, the metal gains 32 per cent, of oxygen, and acquires somewhat of the character of an acid; since it forms, with potash, a crystallizable compound. VII. Antimony is dissolved by most of the acids. Sulphuric acid is decomposed by it; sulphurous acid being dissengaged, and an oxide formed, of which a small proportion only is dissolved by the remain- ing acid, constituting a sub-sulphate. Nitric acid dissolves this me- tal with great vehemence; but muriatic acid acts on it very feebly, even by long digestion. The most convenient solvent is the nitro- muriatic acid, which, with the aid of heat, dissolves it either in its reguline state, or as existing in the native sulphuret. With oxy-mu- riatic acid, it forms a compound of a thick consistence, formerly call- ed butter of antimony. This may be obtained, by exposing black sul- phuret of antimony to the fumes of oxy-muriatic acid, and by subse- quent distillation; or by distilling the powdered metal with twice its weight of corrosive muriate of mercury; or by the action of nitro-mu- riatic acid on metallic antimony.* It may be formed, also, by the combustion of antimony in chlorine gas, with which, according to Dr. John Davy, it unites in the following proportion: Antimony . . 66 . . 100 . . 150 Chlorine . . . 44 . . 67 . . 100 100 * Robiquet in Ann. de Chim. et Phys. iv. 165. bECT. XV. TELLURIUM. 117 On pouring this compound, which may be termed chloride of anti- mony, into water, a white hydrate, containing some muriatic acid, falls down, called powder of algaroth. This furnishes a delicate test of the presence of antimony in solutions effected by muriatic acid, and containing that metal in very small proportion, along with tin or others. VIII. Antimony enters into combination with most of the metals.. It destroys the ductility of gold, even when it composes only l-2000th of the whole mass, or when its fumes alone come into contact with melted gold. The most important of its alloys is that which it forms with lead. In the proportion of one part to sixteen of lead, it com- poses the metal for printers' types. It may be alloyed with tin, but if its proportion in the alloy exceeds one-fourth, the tin loses its duc- tility. Tin, also, by combination with more than one-twentieth of its weight of antimony, acquires the insolubility of the latter metal in muriatic acid.* In analyzing compounds of tin and antimony, it is necessary first to make an alloy, in which the antimony shall not exceed the above proportion of l-20th part for then concentrated muriatic acid, by digestion with this alloy, dissolves the tin, and leaves the antimony. SECTION XV. Tellurium. I. Tellurium was discovered, by Klaproth,t in an ore of gold. His process, for extracting it, consists in the solution of the ore by nitro-muriatic acid, dilution with water, and the addition of pure pot- „ ash, which throws down all the metals that are present; and, when added in excess, re-dissolves a white precipitate, which it at first oc- casions. To the alkaline solution, muriatic acid is then added; a precipitate again appears; and this, when dried, and heated with one-twelfth its weight of charcoal, or with a small quantity of oil, in a glass retort, yields tellurium, in the form of small brilliant metallic drops, lining the upper part of the body of the retort.—One hundred parts of the ore yield above 90 of tellurium. II. 1. The colour of this metal is tin-white, verging to lead-grey; it has considerable lustre, and a foliated or scaly fracture. It is very brittle; is fusible at a temperature below ignition; and, excepting os- mium, quicksilver, and selenium, is the most volatile of all metals. It is the lightest of the metals, the bases of the alkalies and earths excepted, having the specific gravity of only 6.185. 2. It is oxidized when heated in contact with air; and burns with a sky-blue flame, edged with green. Upon charcoal,-before the blow- pipe, it inflames with a violence resembling detonation; exhibits a * Ann. de Chim. et Phys. iii. 380. t Contributions, ii. 1. 1 18 METALS. CHAP. XIX. vivid flame; and entirely flies off in a grey smoke, having a peculiarly nauseous smell. This smoke, when condensed, and examined in quantity, is found to be white with a tint of yellow. It is fusible by a strong heat, and volatile at a still higher temperature. It not only unites as a base with acids, but also itself possesses the charac- ter of an acid, and forms a class of salts, which may be called tellu- rates. It is composed, according to Klaproth, of Tellurium . . 83 . . 100. Oxygen . . . 17 . . 20.5 100 Berzelius, however, determines the quantity of oxygen, absorbed by 100 of tellurium, when changed into oxide, to be 27.83. 3. Tellurium is soluble in nitric and nitro-muriatic acids. The saturated solution is decomposed by the mere addition of water, which throws down a white powder; but this is again dissolved on adding more water. Chlorine unites with tellurium,and forms a white semi-transparent compound, which is decomposed when added to water. It consists, according to Sir H. Davy, of 100 tellurium united with 90.5 chlorine. From its solutions it is precipitated in a metallic form, by iron, zinc, tin, and even by muriate of tin. Carbonated and pure alkalies precipitate the telluric oxide united with water, in the Form of a white hydrate; and the oxide is re-dissolved by an excess of alkali or carbonate. Alkaline sulphurets throw down a dark brown or blackish precipitate. Tincture of galls produces a flocculent yel- low precipitate. The solutions of this metal in acids are not decom- posed by prussiate of potash; a property which tellurium possesses in common with gold, platinum, iridium, osmium, rhodium, and antimony. Tellurium forms two distinct compounds with hydrogen, the onq of which is solid and the other gaseous—1st. By making tellurium the negative surface in water,in the Galvanic circuit, a brown powder is formed, which is a solid hydruret of tellurium. 2dly. By acting with dilute sulphuric acid, upon the alloy of tel- lurium ana potassium (which may be obtained by heating a mixture of solid hydrat of potash, tellurium, and charcoal,) we obtain a pecu- liar gas. This gas has a smell resembling that of sulphuretted hydrogen. It is absorbed by water, and a claret-coloured solution results, which by exposure to the air, becomes brown, and deposits tellurium. After being washed with a small quantity of water, it does not affect vege- table blue colours. It burns with a bluish flame, depositing oxide of tellurium. It unites with alkalies; precipitates most metallic solu- tions : and is instantly decomposed by chlorine gas. It may be call- ed telluretted hydrogen gas. According to Berzelius, it is constituted of 100 parts of tellurium with a little less than two parts of hydrogen. SHOT. XVI. SELENIUM. 119 SECTION XVI. Selenium. Ivthe chambers for manufacturing sulphuric acid, from the sulphur which is procured at Fahlun in Sweden, a reddish mass is deposited, which is principally sulphur. This substance, in burning, gave out an odour, which induced Berzelius to suspect that it contained tellurium, but on a minute examination he discovered, instead of that metal, one with entirely new properties, to which he has given the name of selenium. The process, by which it was extracted, is not described, and on that account, as well as of the scarcity of the substance which affords it, I shall give only a very general view of its properties. Selenium has a grey colour, and a very brilliant metallic lustre, and possesses a small but scarcely perceptible degree of transparency. It softens at 212° Faht, and completely fuses at a few degrees higher. While cooling, it has a considerable degree of ductility, and may be kneaded between the fingers, and drawn out into fine threads, which have a strong metallic lustre. When slowly cooled, it assumes a granulated fracture, and is extremely like a piece of cobalt At a temperature nearly equal to that of boiling mercury, selenium enters into ebullition; and condenses, either into opaque metallic drops, or* when a retort with a large neck is used, into flowers of a fine cinnabar colour. When heated before the blow-pipe, it tinges the flame of a fine azure blue, and exhales so strong a smell of horse-radish, that a frag- ment, not exceeding l-50th of a grain, is sufficient to fill the air of a large apartment. Selenium unites with the different metals, and the union is, in many cases, accompanied with ignition. The selenuret of potassium has a. metallic lustre, and a greyish white colour. Its solution in water has the colour of strong ale, and a smell resembling that of sulphuret of potash. Acids disengage, from this solution, a gas, which appears t<* be a solution of selenium in hydrogen gas. A small bubble of this- gas, not exceeding a pea in size, when drawn into the nostrils, excited inflammation of their membrane, and symptoms of catarrh, which did not subside for several days. Selenium unites with the fixed alkalies, both in the moist way and by fusion; and the compounds have a cinnabar-red colour. It dis- solves in fixed oils, and the solutions are red, but have not the hepatic smell of solutions of sulphur. Selenium dissolves in nitric, acid with the assistance of heat; and the resulting compound, after evaporation to dryness, may be easily sublimed into crystalline needles, which are often a foot in length. This sublimate is soluble in water and in alcohol, and has the taste and all the properties of an acid. It may, therefore, be called selenic acid, and its compounds seUniates. The alkaline seleniates are not readily crystallizable; and they attract moisture from the atmosphere. 120 ML1ALS. CHAP. XIX. If a little muriatic acid be added to the solution of a seleniate in water, and a plate of zinc be then introduced, the selenium is pre- cipitated in a metallic state. Selenic acid is decomposed by sulphu- retted hydrogen, and an orange-coloured precipitate is obtained, which becomes red when dried. When a slip of paper, moistened with solution of selenic acid, is exposed to a current of sulphurous acid gas, the selenium is revived in the form of a film resembling gold. It has been doubted whether selenium can, with propriety, be class- ed among the metals. But though it scarcely conducts caloric, and is a non-conductor of electricity, Berzelius is still of opinion, from a review of its other properties, that it is fully entitled to be considered as a metal; and that its proper place is among the acidifiable metal*, near to arsenic/ SECTION XVII. Arsenic. I. Arsenic, as it is to be found in the shops, occurs in the state of a white oxide, from which the metal may be obtained by the following process. Mix two parts of the white oxide with one part of black flux (prepared by detonating, in a crucible, one part of nitre with two of crystals of tartar;) and put the mixture into a crucible. Invert over this another crucible; lute the two together, by a mixture of clay and sand; and apply a red-heat to the lower one; keeping the upper one as cool as possible. The arsenic will be reduced; and will be found lining the inside of the upper crucible in a state of metallic brilliancy, not unlike polished steel. Its specific gravity is 8.31. It is so extremely brittle, that it may be reduced to powder in a mortar. II. Metallic arsenic is readily fusible, and is volatilized at 356°. In close vessels it maybe collected unchanged; but when thrown on a red-hot iron, it burns with a blue flame and a white smoke; and a strong smell of garlic is perceived. III. AH the mineral acids act on arsenic ; but not considerably, unless they are heated. In oxy-muriatic acid gas, however, arsenic burns vehemently. IV. A mixture of oxy-muriate of potash and arsenic furnishes a detonating compound, which takes fire with amazing rapidity. The salt and metal, first separately powdered, may be mixed by the gentlest possible triture, or rather by stirring them together on paper with a knife point If two long trains be laid on a table, the one of gunpowder and the other of this mixture, and they be placed in contact with each other at one end, so that they may be fired at once, the arsenical mixture burns with the rapidity of lightning, while the other burns with comparatively extreme slowness. * Thomson's Annals, xi. 291, 374, 447, xii. 13; and Ann. de Chim. et Phys. vii; 199. SEGT. XVII. ARSENIC. 121 V. Arsenic combines with most of the metals. It has the property of giving a white stain to copper. Let a small bit of metallic arsenic, or a mixture of the white oxide with a little black flux, be put be- tween two small plates of copper; bind these closely together with iron wire; and heat them, barely to redness, in the fire. The inside of the copper plates will be stained white. VI. Arsenic, by exposure to the air, is tarnished, and becomes con- verted into a bulky blackish powder. In three months, Berzelius found that 100 parts acquired an increase of 8.475; and he is dis- posed to consider the product as an oxidule; but it is probably nothing more than a mixture of arsenic and arsenious acid, into both which, indeed, it is resolved by heat Only two combinations of arsenic and oxygen have hitherto been clearly ascertained; and both are possess- ed of acid properties. The white oxide of arsenic has the following properties: 1. It has an acrid taste, and is highly poisonous. 2. It is soluble in water, which, at the ordinary temperature, takes up one-eightieth. According to La Grange, it is soluble in one-twen- ty-fourth of cold water, or one-fifteenth of hot. Other statements have been given considerably differing from these; and Klaproth was, therefore, induced to examine its degree of solubility with great at- tention. A thousand grains of cold water, left in contact with the white oxide during 24 nours, and frequently agitated, dissolved only 1\ grains. But 1000 grains of boiling water took up 77| grains; and, after being left three days to cool, and to deposit the crystals which separated, still retained in solution 30 grains. Bucholz has since pub- lished results, which agree, very nearly, with those of Klaproth. But the most elaborate experiments are those of Fischer of Breslau. Ac- cording to these, white oxide of arsenic is insoluble in water, and when acted upon by water, one portion of the oxide acquires oxygen from another, and becoming acidified, is rendered soluble. This is the reason why the undissolved portion loses its colour, and becomes of a dirty yellow. Of boiling water, 12.3 parts dissolve one of arsenic; but at the common temperature of the atmosphere, 66£ parts of water take up only one part* The solution of the white oxide of arsenic has an acrid taste, and reddens vegetable blue colours. When slowly evaporated, the oxide crystallizes in regular tetrahedrons. The oxide is, also, soluble in 70 or 80 times its weight of alcohol, and in oils. At 383° Fahrenheit it sublimes; or, if suddenly heated out of the contact of air, runs into glass. 3. The composition of the white oxide of arsenic, or arsenous acid, has been investigated by several chemists, with the following results. It consists, * Thomson's Annals, vii. 33. Vol. II.—Q 122 METALS. quiAr. xix. Arsenic. Oxygen. Arsenic. Oxygen. According to Proust, of.....75.2 . . 24.8 . . 100 . . 32.979 -----------Thenard, of.....------. ---- . . 100 . . 34.694 -----------Berzelius, of ... . 74.48 . . 25.52 . . 100 . . 34.263* ----------- Do. corrected .... 69.63 . . 30.37 . . 100 . . 43.616 -----------Thomson, of ... . ---- . . ---- . . 100 . . 34.930 It has been justly observed, however, by Dr. Thomson,t that the result, which Berzelius considers as the most correct, is probably the least so; not only on account of its want of accordance with other determinations, but on account of the complicated process, by which it was obtained. On the whole, it appears probable, that 100 parts of arsenic, to become the white oxide, combine with between 34 and 35 parts of oxygen. 4. Oxide of arsenic combines with the pure alkalies to saturation; and hence it fulfils one of the principal functions of an acid. It has therefore been called arsenous acid, and its compounds arsenites. They may be formed by simply boiling the arsenous acid with the respective bases and a sufficient quantity of water; or by double de- composition. Thus arsenite of lead may be prepared, by mixing the solutions of nitrate of lead and arsenite of potash; and the fine green pigment called Scheele's green, by mixing the solutions of arsenite of potash and sulphate of copper. 5. The arsenous acid, or rather the arsenic which it contains, by distillation with sulphur, affords either a yellow substance, called or- piment, or a red one, termed realgar. The oxygen, uniting with sulphur, escapes in the form of sulphurous acid. Both these com- pounds are sulphurets of arsenic, varying in the proportion of their components. Orpiment contains three parts of sulphur and four of arsenic; and realgar one part of sulphur and three of arsenic. Hence realgar, by fusion with an additional quantity of sulphur, may be changed into orpiment; and the latter, by an addition of .arsenic be- comes realgar. The opinion of Laugier, that both are sulphurets at the same degree, combined with different proportions of white arse- iuc, is combated by Berzelius, who could not extract any arsenious acid from orpimentj 6. By repeated distillation with nitric acid, arsenous acid is changed into arsenic acid. The same change is effected, also, by exposure to the vapour of oxymuriatic acid, and the subsequent expulsion, by heat, of the common muriatic acid. By both these processes, a white concrete substance is obtained, termed arsenic acid. The process recommended by Bucholz is to mix two parts by weight of muriatic acid of the spe- cific gravity 1.200, twenty-four parts of nitric acid of the specific gra- vity 1.25, and eight parts of white oxide of arsenic The whole may be evaporated to dryness, and gently ignited in a crucib'e. VII. 1. The arsenic acid has a sour, and at the same time, a me- tallic taste. It reddens vegetable blues; attracts humidity from the atmosphere; and effervesces strongly with solutions of alkaline carbo- * Corrected by him afterwards to 31.77. f Annals, iv. 171. t Ann. de Chim. et Phys. t. 179. SECT. XVII. ARSENIC. 123 nates. When evaporated, it assumes the consistence of jelly, and does not crystallize. It is a most active poison. With alkalies, earths, and oxides, the arsenic acid constitutes a class of salts called arsenates. The arsenate of potash may be obtained in a more simple manner, by detonating, in a crucible, a mixture of nitrate of potash with arsenous acid. The statements of the composition of arsenic acid differ from each other not less than those of the white oxide. It is composed, Amenic. Oxvgen. Arsenic. Oxygen. According to Proust, of . . . 65.4 . . 34.6 . . 100 . . 52.905 ----------- Thenard, of . . 64. . . 36. . . 100 . . 56.250 -----------Berzelius, of . . 66.038 . . 33.962 . . 100 . . 51.428* -----------Do. corrected . . 58.366 . . 41.634 . . 100 . . 71.333 -----------Thomson, of . . ---- . . ---- . . 100 . . 52.4 In this case, also, Dr. Thomson prefers, and it appears to me with reason, the first determination of Berzelius, as more nearly approach- ing the truth than the second. Dr. Thomson's result was obtained by the direct acidification of metallic arsenic by nitric acid; and, though not coincident with the analysis by Thenard, yet it agrees with the number, obtained by assuming the proportions, given by that chemist, for the white oxide, and with his assertion that 100 parts of arsenous acid are changed into arsenic acid, by 16 parts of oxygen. 2. When tin is dissolved in arsenic acid, an inflammable gas is dis- engaged, as was observed by Scheele, consisting of-hydrogen gas, hold- ing arsenic in solution. It may be obtained, afsqJjy adding powdered metallic arsenic to a mixture of diluted sulphuricracid and zinc filings. The greatest caution should be used to avou^ts deleterious effects, which were fatal to the late M. Gehlen.t ^ This gas (to which, perhaps the name of arsenuretted hydrogen is best adapted) has the following properties: (a) It is a permanently elastic and invisible fluid, of the specific gravity, compared with common air, of 0.5293; but its specific gra- vity is variable, in consequence of the admixture of different propor- tions of hydrogen gas. 4 (b) It has a fetid smell, resembling that of garlic. [cj It extinguishes burning bodies. (a) It is not absorbed by water in any notable degree; and has no effect on the blue colours of vegetables. (e) It burns with a lambent white flame, and a disagreeable odour; and emits, during combustion, fumes of arsenous acid. (/) When mingled with oxymuriatic acid gas, heat is produced, a diminution ensues, and metallic arsenic is deposited. Soap bubbles, blown with a mixture of this and oxygen gases, burn with a blue flame, a white smoke, and a strong alliaceous smell. (g) A stream of arsenuretted hydrogen gas, issuing from a bladder fitted with a stop-cock, and set on fire in a large receiver filled with oxygen, burns with a blue flame of uncommon splendour. • Corrected afterwards to 52.96; Ann. de Chim. et Phys. V. 179. f 95 Ann. de Chim. 110; and Ann. de Chim. et Phys. hi. 135. 124 METALS. CHAP. XIX. (h) One cubic inch of the gas contains about one-fourth of a grain of metallio arsenic. (i) When 100 measures, in an experiment of Gay Lussac, were acted upon by heated tin, 140 measures of hydrogen were evolved. Hence three volumes of hydrogen are, in this gas, condensed into al- most the space of two. A solid compound of hydrogen and arsenic may be formed, by act- ing on water with an alloy of potassium and arsenic; and, of course, much less hydrogen gas is evolved, than the same weight of uncom- bined potassium would liberate from water. It is described, by Gay Lussac, as separating in chesnut brown coloured flocks. There ap- pears, indeed, to be a strong affinity between hydrogen and arsenic; for Berzelius found that the recently prepared metal, when distilled along with oxide of tin, gave a drop or two of water. THIRD CLASS. liP.ITTLE AND DIFFICULTLY FUSED. * SECTION XVIII. • Cobalt. I. Cobalt may either be^obtained from a substanc'e, which may be purchased under the name of Zaffre, by fusing the zaffre with three times its weight of black flux; or it may be purchased, at a moderate price, in a metallic form. It has lately been found by Stromeyer in a meteoric stone from the Cape of Good Hope.* To obtain cobalt in a perfectly pure state, Tromsdorff recommends, that the zaffre should be, three times successively, detonated with one-fourth its weight of dry nitre, and one-eighth of powdered char- coal. After the last of these operations, the mass is to be mixed with an equal weight of black flux, and the cobalt reduced. The metal is then to be pulverized, and detonated with thrice its weight of dried nitre. This oxidizes the iron to its maximum; and acidifies the ar- senic; which last unites with the potash. Wash off the arsenate.of potash, and digest the residue in nitric acid. This will take up the oxide of cobalt and leave the oxide of iron. Evaporate to dryness; re-dissolve in nitric acid; filter the solution; and decompose it by a solution of potash. The oxide of cobalt now obtained, may be re- duced by the black flux, as before directed. * Thomson's Annals, ix. 249. SECT. XVIII. COBALT. 125 II. Cobalt has a greyish white colour, inclining somewhat to pink. Its specific gravity is 7.7; it is brittle and easily reduced to powder; is not fusible with a less heat than 130° of Wedgwood; and, when slowly cooled, may be obtained crystallized in irregular prisms. It is generally described to be magnetic; but this property Mr. Chenevix imputes to its contamination with a small quantity of iron. By exposure to the atmosphere cobalt is tarnished, but not oxi- dized to any extent. In an intense heat it burns with a red flame; but if pure, it is not easily oxidized by a moderate temperature. Its oxide, formed by long exposure to a strong heat, with access of air, is of a deep blue, approaching to black. This, from the experiments of Thenard, appears to be the protoxide. It may be obtained, also, by precipitating the nitrate of cobalt with potash. The precipitate, which at first is a bright blue hydrate, when dry becomes of so dark a blue as to appear black. It dissolves readily in muriatic acid, giving a so- lution which is green when concentrated, and red when diluted. Its solutions in sulphuric and nitric acids are always red. When this oxide is exposed to the atmosphere, it gradually absorbs an additional quantity of oxygen; and becomes olive green. Treated with muriatic acid, it gives oxymuriatic acid gas, and a red solution is obtained. This olive compound Sir H. Davy suspects to be a mix- ture of hydrate and oxide of cobalt, and not a peculiar oxide. When either of the two preceding oxides is heated in the open air, it passes to a flea-brown colour, which gradually becomes black. This is the metal oxidated to its maximum. The peroxide dissolves in muriatic acid, with a copious disengagement of oxymuriatic acid gas. It is insoluble, however, in sulphuric and nitric acids, till it has parted with oxygen enough, to reduce it to the minimum state. It is inca- pable, also, of being dissolved in pure alkalies, or of tinging vitrifiable mixtures blue. According to the experiments of Proust, 100 parts of the protoxide consist of Cobalt .... 83^ .... 100. Oxygen . . . . 16$ .... 19.8 100 119.8 And 100 of the peroxide of Cobalt.....75 ..... 100. Oxygen ..... 25.....33.25 100* The black or peroxide, heated for half an hour at the bottom of a crucible, loses a part of its oxygen, and is reduced to the state of protoxide. • Philosophical Magazine, xxx. 340. 126 METALS. CHAP. XIX. The oxides of cobalt require, however, farther investigation. Kla- proth states that 100 parts of cobalt absorb 18 of oxygen, to be con- verted into protoxide. But the oxygen of the peroxide does not, either on this or on Proust's data, bear the proportion to the oxygen in the protoxide, which might be expected from the law of definite proportions. If the oxide, described by Klaproth, be really that which is composed of one atom of metal and one of oxygen, the atom of co- balt will weigh 41.5; but if it be, as Sir H. Davy supposes, a deut- oxide, or compound of one atom of metal with two of oxygen, the atom of cobalt must weigh 83. On the first supposition, the peroxide should be constituted of 100 metal and 36 oxygen; and, on the second, of 100 metal and 25.8 oxygen; and as the former of these numbers corresponds most nearly with experiment, we may consider the prot- oxide as the first combination of cobalt and oxygen, and the atom of cobalt to be represented by 41.5. III. The best solvents of cobalt are the nitric and nitro-muriatic acids; and the solutions have the singular property of forming sympa- thetic inks. One part of cobalt, or, still better, of zaffre, may be di- gested, in a sand-heat for some hours, with four parts of nitric acid. To the solution, add one part of muriate of soda; and dilute with four parts of water. Characters written with this solution are illegible when cold; but when a gentle heat is applied, they assume a beauti- ful blue or green colour.* This experiment is rendered more amusing, by drawing the trunk and branches of a tree in the ordinary manner, and tracing the leaves with a solution of cobalt The tree appears leafless, till the paper is heated, when it suddenly becomes covered with beautiful foliage. IV. Oxide of cobalt is precipitated by carbonated alkalies from the nitric solution, at first of a peach-flower colour, and afterwards of a lilac hue. The crystals of nitrate of cobalt, thrown into a flask full of liquid potash, are immediately decomposed. A blue precipitate is formed, which, if the flask be immediately closed, passes to violet, and afterwards to red, by becoming the hydrate or hydro-oxide of cobalt. This compound is soluble in cold carbonate of potash and tinges it red. The oxide is not soluble in this liquid. The hydrate loses from 20 to 21 per cent, of water by heat and is reduced to protoxide. V. Oxalic acid throws down, from solutions of cobalt, a rose-colour- ed precipitate. Vl. Cobalt may be brought to combine with sulphur and with phos- phorus; but the compounds have no peculiarly interesting properties. The sulphuret is composed, according to Proust, of Cobalt......71.5 .... 100. Sulphur ..... 28.5 .... 39.8 100. * For some ingenious speculations on the cause of these phenomena, con- suit Mr. Hatchett's paper on the Carinthian molybdate of lead. (Philosophical Transactions, 1796.) SEC I. XIX. MANGANESK. 127 This confirms the view, already given, of the .atomic constitution of the protoxide ; for the oxygen, which it contains, is not far from being equal to half the sulphur in the sulphuret. VII. It may be alloyed with most of the metals, with the exception of bismuth and zinc. Cobalt, when oxidized, is the basis of zaffre. This is generally pre- pared by roasting from the ore, its volatile ingredients; and mixing, with the remainder, three parts of sand, or calcined flints. Zaffre, when fused, forms a blue glass; which, when ground and washed, is the substance termed smalts, used as a colouring substance for linen, and for imparting a blue colour to glass. SECTION XIX. Manganese. I. Manganese never occurs in a metallic state; the black sub- stance, known by that name, being a compound of manganese, with a large proportion of oxygen. The metal is obtained, by mixing this oxide, finely powdered, with pitch, making it into a ball, and putting this into a crucible, with powdered charcoal, one-tenth of an inch thick on the sides, and one-fourth of an inch deep at the bottom. The empty space is then to be filled with powdered charcoal, a cover is to be luted on, and the crucible exposed, for one hour, to the strongest heat that can be raised. II. This metal is of a dusky white colour, and bright and shining in its fracture. Its specific gravity was found by Dr. John to be 8.013. It is very brittle, and even less fusible than iron, requiring a heat of 160° Wedgwood to melt it It is not attracted by the mag- net; except when contaminated with a small quantity of iron. When exposed to the air it soon crumbles into a blackish brown powder, in consequence of its oxidation, and becomes in succession grey, violet, brown, and finally black. There is a remarkable want of agreement in different statements of the composition of oxides of manganese, and even of the number of those oxides. Sir H. Davy admits only two, one of a dark olive colour, consisting of 21 oxygen to 79 metal; the other of a dark brown colour, containing almost 10 per cent more of oxygen.* Dr. John, in a memoir published in the 2d and 3d volumes of Dr. Thomson's Annals, enumerates three oxides of manganese, the green, the brown, and the black. The green is formed by the action of metallic manganese on water, from which it takes oxygen, and disengages hydrogen gas, ap- parently holding some of the metal in solution. He finds it to be composed of * Elements of Chera. Phil. 369. 128 METALS. CHAP. XIX. Manganese. . 87 . . 100. Oxygen . . . 13 . . 14.942 100 The brown oxide was formed by exposing the last mentioned one to the air, till it ceased to gain weight, and then drying it quickly. Its colour was pure deep brown, and it was composed of Manganese . .80 . . 100 Oxygen .... 20 . . 25 100 The third or black oxide was prepared by dissolving manganese in nitric acid, evaporating, and drying by a heat sufficient to expel the nitric acid, but not to decompose the oxide. It consisted of Manganese . 71.33 . . 100. Oxygen . . 28.67 . . 40.19 100. The brown oxide still continued to absorb oxygen, when exposed to the atmosphere; but the black, when ignited, gave oxygen gas. Berzelius* admits the composition of the green oxide, as stated by Dr. John, with a slight alteration; but corrects the numbers indicating that of the second and third, and adds, also, two other oxides, the one with less oxygen, and the other with more than any of those which have been already cited. The first is obtained by exposing metallic manganese in a vessel loosely corked; but there can be little doubt, from its properties, that it is a mixture of the metal and the green oxide. The second, described by Dr. John, results from the action of water on metallic manganese; the third from the action of acids; and the fourth from calcining the nitrate. The fifth and last is the native oxide of manganese, which is become important from its use in pre- paring chlorine. By exposure to a strong heat, 100 parts of this oxide lose 11.3 of oxygen, and a red oxide remains. Berzelius's Table of the Composition of Oxides of Manganese. Metal. Oxygen. Metal. Oxygen. 1st oxide .........93.435 .... 6.565 . . . 100 . . . 7.0266 2d oxide (green) .... 87.68 . . . 12.32 . . . 100 . . . 14.0533 3d oxide (brown) .... 78.10 . . . 21.90 . . . 100 . . . 28.1077 4th oxide.........70.50 . . . 29.50 . . 100 . . . 42.16 5th oxide.........64.00 . . . 36.00 . . . 100 . . . 56.215 * 87 Ann. de Chim. 149. SECT. XIX. MANGANESE. 129 The numbers in the last column, it may be observed, stand to each other in the proportion of 1, 2, 4, 6, 8. But if the first compound (as appears to me probable) be not a distinct oxide, the ratio will then be that of 1, 2, 3, 4. Gay Lussac, indeed, has expressed his conviction, that the two first oxides do not exist; and that there are in reality only three; 1 st, the protoxide, obtained by dissolving manganese in diluted sulphuric acid, and precipitating it by a pure alkali out of the contact of air; 2d, the deutoxide, which remains after calcining the peroxide or the greater part of the salts of manganese; and 3d, the peroxide, or native black oxide. And Berzelius himself is now disposed to give up the two first.t and on the authority of his own experiments, to admit three oxides of manganese, with quantities of oxygen corres- sponding to the three last in the above table; the protoxide being green, and the two others black. The red compound of 100 parts of manganese with 37.47 oxygen, not agreeing with the law of definite proportions, he considers as a mixture of the two first.J The oxides of manganese may be combined with most of the acids. When the green or protoxide is precipitated from its solution in an acid by a carbonated alkali, we obtain a snow-white compound, which is a carbonate of manganese. It is composed, according to Dr. John, of Protoxide of manganese . . 55.84 W^ater.......10. Carbonic acid.....34.16 100. Concentrated sulphuric acid has very little action on metallic man- ganese; but the dilute acid dissolves it with an extrication of hydro- gen gas, which has a peculiar smell, resembling asafcetida, probably from its holding some of the metal in solution. The solution has a lio-ht rose colour, and gives crystals of the same colour. °The pure protoxide, and the carbonate, dissolve in the sulphuric acid in any state of concentration; and a solution is obtained, exactly resembling that which has been described. The first crystals, that shoot from the solution, are of a faint rose red colour. The last are white, and contain a great excess of acid. The red crystals are solu- ble in 24 parts of water, at 55° Fahrenheit, and are insoluble in alcohol. The alkaline carbonates, prussiates, and phosphates, occasion a white precipitate from the solution, and are almost the only salts that de- compose this sulphate. It is composed of Protoxide of manganese . . 31.00 Sulphuric acid.....33.66 Water.......35.34 100. * Ann. de Chim. et Phys. i. 39. f Ibid. v. 150. * Ibid. vi. 20'4 Vol. II.—R 130 M ETA IS. CHAP. XIX. The peroxide is not acted upon by sulphuric acid, except when concentrated, or very little diluted: and it is precipitated again by water added in considerable quantity. Nitric acid, when moderately concentrated, dissolves metallic man- ganese with an escape of nitrous gas. The solution is colourless; and by long continued evaporation, the acid is decomposed, and a black oxide is left. The green oxide and white carbonate also dissolve readily in nitric acid, and by particular management crystals may be obtained from the solutions. The crystals deliquiate by exposure to the air; and on the application of heat, melt, and are immediately decomposed. The black oxide does not dissolve in nitric acid, unless a little sugar is added, or some other similar substance. The action of muriatic acid is most important on the black native oxide. According to the old theory, part of the acid acts on one por- tion of the oxide; and first reduces it to the state of protoxide,-and then dissolves it; affording muriate of manganese. The oxygen, thus liberated, uniting with another portion of muriatic acid, composes oxy-muriatic acid. But, on the theory of chlorine, the hydrogen of the muriatic acid is attracted by the oxygen of the oxide, and the chlorine is merely set at liberty. When the muriate of manganese is evaporated to dryness, and strongly heated, it forms brilliant scales, which, according to Dr. John Davy, are identical with the compound obtained by burning manganese in chlorine, and are composed of Manganese......54 .... 100 Chlorine.......46 ... . 85 100 Muriate of manganese is a deliquescent salt; it is soluble in an equal weight of water, and soluble, also, in alcohol, by which means it may be separated from the sulphate. It may be obtained in large tabular crystals, quite transparent, and of a rose colour. If consi- dered as a compound of muriatic acid and oxide of manganese, it may be stated to consist of Protoxide of manganese . 38.50 Muriatic acid.....20.04 Water.......41.46 100. Dr. John has investigated, also, several of the combinations of oxide of manganese with vegetable and metallic acids, the details of which are contained in his paper. The black oxide of manganese has some properties, which render it the subject of amusing experiments. 1. It imparts to borate of soda, when melted with it, a violet co- lour. When this is effected by the blow-pipe, the colour may be de- SECT. XIX. MANGANESE. ISi stroyed by the interior flame, and again reproduced by the exterior one, or by a small particle of nitre.* 2. When black oxide of manganese and nitre, both reduced to powder, are mixed together, and thrown into a red-hot crucible, the nitric acid is decomposed, and we obtain a compound of highly oxi- dized manganese with potash. The same compound may be obtained by fusing together one part of the black oxide, and five or six of solid caustic potash. It has the singular property of exhibiting different colours, according to the quantity of water that is added to it. A small quantity gives a green solution; a farther addition changes it to blue; more still to purple; and a still larger quantity to a beauti- ful deep purple. 3. The experiment may be Varied, by putting equal quantities of this substance into two separate glass vessels, and pouring on the one hot, and on the other cold, water. The hot solution has a beautiful green colour, and the cold one is of a deep purple. The same mate- rial, with water of different temperatures, assumes various shades of colour. Hence this compound has been termed the chameleon mine- ral. This property is destroyed by a very small quantity of sulphu- ret of potash, and by other substances that attract oxygen. The properties of this •ingular substance have been lately investi- gated by Chevreul.t To exclude the presence of iron, on which Scheele suspected its green colour to depend, he prepared it by fu- sing, in a platinum crucible, one part of pure oxide of manganese with eight of potash, prepared with alcohol. The colour of the solution was still green, and by the addition either of more water, or of car- bonic acid or an alkaline carbonate, became successively blue, violet, indigo, purple, and red. The green solution, Chevreul supposes, is a combination of caustic potash with oxide of manganese; and the red, of potash, oxide of manganese, and carbonic acid. The intermediate colours result from the combination of these in different proportions, as may be proved by the direct mixture of a green with a red solu- tion. The agency of water, even when carefully deprived of carbonic acid, in effecting the same change, shows, however, that the tbeory does not account for all the phenomena. This fact Chevreul explains by the action of water in diminishing the attraction between the pot- ash and oxide of manganese, in which way he apprehends that car- bonic acid produces its effect. The oxide, both in the green and red compounds, he asserts, is at the same degree of oxidation, a degree probably inferior to that of the native oxide. Messrs. Chevillot and Edwards have ascertained that the colour of the chameleon mineral is owing to oxide of manganese, and not to any other metal; that the contact of oxygen g;i>; with the fused mate- rials is essential to its formation, during which oxygen is absorbed; and lastly that the chameleon compound is susceptible of assuming a regular crystallized forin.J III. Manganese, in its metallic state, cannot be brought to combine * See Klaproth, vol. i. page 243. a. | Ann. de Chim. et Phys. iv. 47. * Ibid, iv. 287. 132 METALS. CHAP. XIX. with sulphur, though a native compound of these two substances has been examined by Proust The oxide, however, unites with sulphur by fusion, in the proportion of eight of the former to three of the lat- ter; and a compound is obtained of a green colour, which gives out sulphuretted hydrogen gas by the action of acids. IV. Manganese unites with most of the metals, and composes al- loys ; hone of which are distinguished by important properties. SECTION XX. Chrome. This metal is found in an acidified state, and combined with oxide of lead, in the red-lead ore of Siberia; in the state of an oxide, in the green ore accompanying the red one; and in the emerald, to which it communicates its green colour, and in some meteoric stones. A compound of chromic acid with oxide of iron lias, also, been discovered in France and in America,* and is a much more abundant product than the lead ore of Siberia. 1. To separate the chromic acid, the red-lead ore, reduced to pow- der, is boiled with twice its weight of carbonate of potash. An orange- yellow solution, composed of potash and chromic acid, is thus ob- tained; and when, to this, a mineral acid is added, and the liquor is evaporated, we obtain, 1. the salt formed by the acid, which lias been united with the potash; 2. the acid of chrome, in long ruby-coloured prisms. From this acid the chrome may be obtained by heating it with charcoal, in the manner already often described. In the cru- cible a metallic mass is found, of a greyish white colour, formed of a number of needles crossing each other. II. This metal is very brittle, infusible, and fixed. Its specific gra- vity is 5.9. III. It is susceptible of three states of oxidizement—The first oxide is green, the second brown, and a farther proportion of oxygen gives the chromic acid. The precise quantity of oxygen in these dif- ferent compounds has not yet been ascertained." IV. The nitric acid alone exerts any remarkable action on this metal. Repeated distillation, with this acid, changes chrome into chromic acid, combinable with alkalies. The chromates of alkalies precipitate the salts of lead, of a beautiful yellow colour; which is now procured in considerable quantity from the American chromate of iron, and is highly valuable in painting. Mercury is thrown down from its solutions by chromates of alkalies, of a cinnabar-red hue; silver, of a carmine-red ; and all its metallic combinations are distin- guished by peculiar brilliancy of colour. The emerald derives its co- * Thomson's Annals, v. 75. :->E-CT. XXI. MOLYBDENUM. 133 lour from the oxide of chrome; and the spinelle ruby from the acid. This property of imparting colour has suggested its name. The combinations of the chromic acid with different bases have been fully investigated, and described by Vauquelin, in the 70th vo- lume of the Annales de Chimie, and by Dr. John, in the 4th volume of Thomson's Annals of Philosophy. It has, indeed, been lately as- serted, that the chrome acid is not a simple combination of chromic and oxygen; but that it always contains a portion of the acid, by which it has been precipitated from its alkaline compounds ; in other words, that no true chromic acid exists.* SECTION XXI. Molybdenum. I. The most common ore of molybdenum, was long mistaken for plumbago, or carburet of iron, to which it bears, externally, a strong resemblance. It is, in fact, a combination of sulphur and the oxide of molybdenum. These two components may be separated, by re- peated distillation with nitric acid. To the ore of molybdenum, in a retort, six times its weight of nitric acid are to be added, and the mixture distilled to dryness. This process must be repeated four or five times; and, at its close, both the sulphur and molybdenum will be acidified. The sulphuric acid is expelled by heating the mass in a crucible; and any remaining portions are to be washed off with dis- tilled water. The residue (molybdic acid) is a white heavy powder; which has an acid and metallic taste; has the specific gravity 3.4; is soluble in about 1000 parts of water; and forms salts with the alkalies and earths. The acid is reduced by making it into a paste with oil, and exposing it, bedded in charcoal in a crucible, to an intense heat Or (as Hielin recommends) the ore of molybdenum may be repeated- ly roasted in a moderate red-heat, till the whole is reduced to a fine powder, which may be passed through a sieve. The powder is to be dissolved in ammonia, the solution filtered, and evaporated to dry- ness. The residuum, being moderately heated with a little nitric acid, gives a white powder, which is the pure oxide of molybdenum. This may be metallized by exposure to an intense heat with oil'or powdered charcoal. II. Molybdenum has a whitish yellow colour, but its fracture is a whitish grey. It has not, hitherto, been obtained in any form, but that of small brittle grains. It is almost infusible by any artificial heat. Its specific gravity is 8.611. It is readily oxidized when heated in contact with air, and is con- verted into a white oxide, which is volatilized in small brilliant needle-shaped crystals. This compound has acid properties. * Thomson's Annals, vii. 36. 134 MV.l ALS. OHAP. XIX. III. The nitric, nitro-muriatic, and oxy-muriatic acids are the only ones that act on molybdenum. IV. The muriatic, and other acids, acton its oxides, and afford blue solutions. There appear to be only two well ascertained compounds of mo- lybdenum and oxygen. The first is the molybdic acid already de- scribed. It is composed, according to Bucholz, of Molybdenum .... 66.7 .... 100 Oxygen ...... 33.3 .... 50 100. Berzelius states the metal at 65.5, and the oxygen at 34.5 in 100 grains of molybdic acid. When one part of powdered molybdenum, and two parts of molyb- dic acid, are triturated in boiling water; then filtered; and the solu- tion evaporated at a temperature not exceeding 120° Fahrenheit, we obtain a fine blue powder, which is molybdous acid. This acid is more soluble in water than the molybdic, and its solution reddens fegetable blue colours. It is stated by Bucholz to consist of Molybdenum .... 74.5 .... 100 Oxygen......25.5 ..... 34 . 100. It seems not improbable that there is an oxide, containing a smaller proportion of oxygen than the molybdous acid; and that this acid is constituted of two atoms of oxygen to one of metal. On this supposition the atom of molybdenum must weigh about 44; and, in molybdous acid, it must be combined with two atoms of oxygen, weighing 15; and in molybdic acid with three atoms, weighing 22.5. The oxide, consisting of one atom of metal 44, and one atom of oxy- gen 7.5, remains to be investigated. The molybdous and molybdic acids unite with salifiable bases, and form distinct classes of salts. The latter acid is changed into the former by some of those metals, that powerfully attract oxygen. Thus a solution of molybdic acid, in which a small rod of tin or zinc is immersed, becomes blue, in consequence of the partial disoxygena- tion of the acid; and on the same principle recent muriate of tin throws down, from molybdate of potash, a fine blue precipitate. The molybdic acid decomposes the nitrates of silver, mercury, and lead ; and the nitrate and muriate of barytes. V. Molybdenum unites readily with sulphur, and composes a sub- stance, similar to the one from which the metal was originally ob- tained. One hundred parts of the metal combine with 67 of sulphur. • SECT. XXII. TUNGSTEN. 135 9 SECTION XXII. Uranium. I. This metal was discovered by Klaproth, in a mineral which con- tains uranium combined with sulphur. The metal is separated from the sulphur, first by roasting; then dissolving the ore in nitro-muriatic acid, and precipitating by an alkali. An orange-coloured precipitate is obtained, which is an oxide of uranium. This may be reduced to a metallic form, in the same manner as the molybdic acid. II. Uranium is of an iron grey colour; and internally of a reddish brown. It has only been obtained in small grains of considerable hardness and lustre. Its fusion is very difficultly effected. It un- dergoes no change by exposure to air, unless strongly heated, when it burns, and becomes a black oxide. III. The metal is soluble only in nitric acid. IV. Its oxide, when precipitated by potash from nitric acid, is of a yellow colour, and dissolves in acids. It is precipitated by alkalies; and is thrown down, of a reddish brown colour, by prussiates. Sul- phuret of ammonia gives a brownish yellow precipitate; and tincture of galls, a chocolate brown one. When exposed to intense galvanic action, it is fused, but not reduced. V. The yellow oxide of uranium is insoluble in alkalies, which dis- tinguishes it from the oxide of tungsten. It is soluble, however, by alkaline carbonates. There appear to be two oxides of uranium, the yellow one, which retains its colour when heated alone, and becomes the black oxide, when heated with a little oil. The first, according to Bucholz, con- sists of 80 metal and 20 oxygen; but the composition of the black oxide is not yet determined. SECTION XXIII. Tungsten. 1. Tungsten may be obtained from two different minerals. The one, consisting of the tungstic acid, united with lime, is called simply tungsten. In the other, termed Wolfram, it is united with iron and manganese.* Its extraction from the former is the most simple pro- cess. One part of the tungstate of lime, and four of carbonate of potash, are fused together, and the mass is dissolved in 12 parts of boiling water. Nitric acid is then added, which unites with the pot- ash, and precipitates tungstic acid. This acid, when reduced in the usual manner, yields tungsten; but the process is a very difficult one, • Berzelius, Ann. de Chim. et Phys. hi. 161 136 METALS. eHAP. XIX. and frequently fails of success. Professor Clarke has succeeded in effecting its reduction by the oxygen and hydrogen blow-piffc* The tungstic acid may, also, be obtained from Wolfram, by fusion with three times its weight of nitrate of potash; or with twice its weight of carbonate of potash. The fused mass, dissolved in boiling water, and filtered, gives, on the addition of nitric acid, a precipitate of tungstic acid; or Wolfram, reduced to a fine powder, may be boiled with three times its weight of muriatic acid. As soon as the acid be- comes hot, a yellow powder appears, and the liquid becomes brown. When cold, decant the clear liquid, and wash the sediment repeated- ly with water; then digest it, for some hours, with liquid ammonia, which will take up a part. Repeat these operations, till they cease to acton the substance. Evaporate the ammoniacal solution to dryness, and calcine the salt. The acid of tungsten remains, in the proportion of more than half the weight of Wolfram which has been employed. Other methods of forming tungstic acid are described by Bucholz.t II. Tungsten has the following characters: 1. It has a greyish white colour, like that of iron, and a good deal of brilliancy. It is not magnetic. Its specific gravity, according to D'Elhuyarts, is 17.6; or according to Messrs. Allen and Aikin 17.22. Bucholz makes it the mean of these two numbers, viz. 17.4. It is only, therefore, surpassed in density by gold and platinum. 2. It is extremely hard and brittle. It requires, for fusion, a tem- perature of at least 170° Wedgwood. 3., It is oxidized by the action of heat and air. Its first oxide is black. The second is yellow, and is commonly termed tungstic acid. 4. The tungstic acid has no taste; has the specific gravity 6.12; is difficultly fusible except by intense Galvanic action, which partially reduces it; it is insoluble in water; but remains suspended in it, and in this state has no action on vegetable colours. . Exposed to heat in a platinum spoon, it assumes a deep green colour. Calcined with the contact of air, its yellow colour becomes deeper, and passes to a green, and, after some hours, grey. The deficiency of several acid proper- ties induced Vauquelin to withdraw it from the class of acids, and to arrange it among the oxides. The tungstic acid is composed, as appears from the experiments of Bucholz, of 20 parts oxygen and 80 metal; and the tungstate of lime was shown by Klaproth, to contain per cent. 77.75 parts of acid, and 22.25 of lime. * Thomson's Annals, x. 376. f Thomson's Annals, vi. 198. SECT. XXIV. TITANIUM. 137 FOURTH CLASS REFRACTORY METALS. SECTION XXIV. Titanium. I. Titanium is obtained from a mineral found in Hungary, &c. call- ed red schorl, or titanite; and, also, in a substance from Cornwall, termed menachanite. It was in the latter substance that it was origi- nally discovered by Mr. Gregor of Cornwall; and its characters have since been more fully investigated by Klaproth, Vauquelin, and Hecht, Lovitz, and Lampadius. To separate it from the first compound, the mineral is to be reduced to powder, and fused with twice its weight of potash. When the fused mass, after cooling, is dissolved in water, a white oxide of titanium remains. To free it from iron, Laugier dis- solved it in muriatic acid, and added oxalic acid, which separates a white flocculent precipitate of oxalate of titanium.* The oxalic acid in this may be destroyed by calcination. Menachanite is to be first fused with potash in a similar manner; and to the alkaline solution, muriatic acid is to be added. This dis- solves the oxide of iron, and precipitates the white oxide of tita- nium, still, however, contaminated by some iron. II. The oxide of titanium fuses, but is not reduced by a powerful Galvanic battery. It is reduced, however, by exposure to an intense heat, moistened with oil, and surrounded by powdered charcoal. A blackish blistered substance is obtained, some points of which have a reddish colour. Lampadius states its colour to be that of copper, but deeper; and its lustre to be considerable. It is brittle, but when in thin plates, has considerable elasticity. When this is boiled with nitric acid, no remarkable effect ensues, but the bright spots disap- pear, and are succeeded by a white compound. Nitro-muriatic acid forms, also, a white powder, which remains suspended in it. Sulphu- ric acid exhibits a similar appearance; sulphurous acid is disengaged; and the titanium is partly changed to a white oxide, and partly dis- solved. Muriatic acid dissolves titanium, but not its oxide. III. The solution of titanium gives a white precipitate with carbo- nates of alkali; a grass green, mixed with brown with prussiate of pot- ash; and a dirty dark green, with hydro-sulphurets. Infusion of galls precipitates a reddish brown substance, which, if the solution be con- centrated, has the appearance of coagulated blood. A rod of tin, im- mersed in the solution, imparts to the liquid around it a fine red colour; and a rod of zinc a deep blue one. IV. Titanium tarnishes by exposure to the atmosphere, and is oxi- * 89 Ann. de Chim. 306 Vol. II.—S I SB METALS. CHAP. XIX. dized when heated with access of air. It is susceptible of three stages of oxidizement The first oxide is blue or purple, the second red, and the third white. The white oxide is the only one, with the compo- sition of which we are accurately acquainted. It has been shown, by Vauquelin and Hecht, to consist of 89 parts of the red oxide and U parts of oxygen. V. Titanium appears to be incapable of uniting with sulphur; but Mr. Chenevix has succeeded in combining it with phosphorus. The only alloy of any consequence, wdiich it forms, is with iron. It is of a grey colour, interspersed with brilliant particles, and is quite infusible. SECTION XXV. Columbium and Tantalum. Columbium was discovered by Mr. Hatchett, in a mineral belong- ing to the cabinet of the British Museum, supposed to be brought from Massachusetts in North America. By alternate fusion with potash, and digestion with muriatic acid, the mineral was decomposed; the acid combining with oxide of iron, and the.alkali with a peculiar metallic acid, separable by the addition of diluted nitric acid, which throw down a copious white sediment . This acid was not reduced by Mr. Hatchett, who however, from its properties, entertained little doubt that it has a metallic base. It is insoluble in nitric acid; but when fresh precipitated, it combines both with the sulphuric and muriatic. It unites also with alkalies: and both solutions are colourless. Prussiate of potash gives an olive- coloured precipitate; tincture of galls, a deep orange; and hydro- sulphuret of ammonia, one of a chocolate colour. Tantalum. This metal was discovered by Mr. Ekeberg, a Swedish chemist, in two different fossils, called Tantalite and Yttro-tantalite, both of which are found in Finland. In the one it occurs combined with iron and manganese; in the other, with the earth called yttria.* From these ores it is obtained, by treating them alternately with caustic fixed alkali, and muriatic or nitro-muriatic acid. The alkaline solution, being supersaturated with an acid, lets fall a white powder which is oxide of tantalum. The following are the characteristic properties of tantalum, as enumerated by Mr. Ekeberg: 1. It is not soluble in any acid, even the nitro-muriatic, in whatso- ever state the mineral is taken, and whatever means are employed. 2. Fixed alkalies attack it when fused with it in considerable ex- cess, and dissolve a considerable quantity, which may afterwards be precipitated by acids, even by the carbonic. * See Annales de Chimie, xliii. 281. SECT. XXV. TANTALUM. 139 3. The oxide of this metal is white, and does not acquire any colour, by exposure to a. high temperature with access of air. Its specific gravity, after being made red-hot, is 6.500. 4. It melts with phosphate of soda, and with borax, but does not impart to them any colour. 5. The oxide of tantalum, ignited with charcoal, melts and aggluti- nates. It then presents a metallic lustre, and a shining fracture of a greyish black colour. Acids change it again into a white oxide. Though the oxides of tin and of tungsten are equally soluble with that of tantalum in fixed alkalies, yet the former is easily reduced, furnishing a ductile metal; and the oxide of tungsten dissolves in ammonia, is changed to a yellow colour by acids, and communicates colour to phosphate of soda and borax. The oxide of titanium dif- fers from this, in being soluble by acids, and in tinging borax and phosphoric salts, when fused with them. Considerable doubts had been entertained by several chemists, whether any essential difference exists between columbium and tan- talum; and their identity appears now to be sufficiently established by the experiments of Dr. Wollaston. Having procured specimens of the tantalite and yttro-tantalite, from which tantalum may be se- parated, he compared its properties with those of oxide of columbium, jurnished by Mr. Hatchett, and obtained from a specimen in the Bri- tish Museum. The external characters of the mineral, which yields columbium, closely accord with those of tantalite. Both, also, yield a white oxide, combined with iron and manganese, and as nearly as possible in the same proportion. The white oxide, though not absolutely in- soluble in sulphuric, nitric, and muriatic acids, is (from whichever mi- neral it has been obtained) very nearly so. Its appropriate solvent is potash, which does not require to be absolutely free from carbonic acid. The whole of the oxide, thus dissolved, may be precipitated by an acid, and it is not re-dissolved by an excess of acid. The oxides from both minerals agree, also, in being soluble, when fresh precipi- tated, by oxalic, tartaric, and citric acids. Ekeberg, however, we are. informed by Berzelius,* discovered in a sample of the mineral from the British Museum, a considerable quantity of tungstic acid, to which it owes its acid properties, and its other constituent he found, with Dr. Wollaston, to be oxide of tantalum. Infusion of galls, prussiate of potash, and hydro-sulphuret of pot- ash, occasion no precipitation from the alkaline solution of either of these oxides; and, when a sufficient quantity of acid has been added to neutralize the redundant alkali, infusion of galls only throws down a precipitate which, in both cases, is of an orange colour. From these coincidences, there can be little room to doubt of the identity of tan- talum, with the characteristic ingredient of columbium. Tantalum has lately been reduced to a metallic form by Berzelius. His methpd consisted in introducing the oxide, which had previously * Thomson's Annals, iv. 467. 140 METALS. CHAP. XIX. been strongly heated, into a cavity about one inch and a half deep, and of the size of a goose quill, artificially formed in a piece of char- coal. To this cavity a stopper of charcoal was fitted, and the whole, enclosed in a Hessian crucible, was exposed to a violent fire during an hour. From four experiments, similarly conducted, he inferred the composition of the oxide to be Tantalum .... 94.8 .... 100. Oxygen.....5.2 ... . 5.485 100. The specific gravity of a specimen of the metal, sent by Berzelius to this country, was found by Dr. Wollaston to be 5.61, but as the mass wTas porous, its specific gravity is probably much higher. Its colour was dark grey, and when scratched with a knife, or rubbed against a fine grindstone, it assumed the metallic lustre, and the ap- pearance of iron. By trituration, it was reduced to a powder, which was destitute of metallic lustre, and completely insoluble, even by se- veral days digestion, in muriatic, nitric, or nitro-muriatic acid. Like chrome, titanium, iridium, and rhodium, it is incapable, therefore, of being oxidized by acids, and in order to be oxidized requires to be fused with caustic potash. At a red heat, the metal takes fire, and burns with a feeble flame. It detonates, also, when mixed with nitre, and projected into a red-hot crucible. With other metals, it unites and forms alloys.* SECTION XXVI. Cerium. I. Cerium was discovered, by Messrs. Berzelius and Hisinger of Stockholm, in a mineral from Bastnas, in Sweden, which had been supposed to be an ore of tungsten. This discovery has been since confirmed by Vauquelin; who, after a careful examination of the mi- neral, concurs in opinion, that it contains the oxide of an unknown metal. From the planet Ceres, discovered about the same period, it has been called Cerium; and the mineral that contains it is termed Cerite.t II. To obtain the oxide of this new metal, the cerite is dissolved in nitro-muriatic acid, after being calcined and pulverized. - The solution is filtered, neutralized with pure potash, and then precipi- tated by tartrite of potash; or, as Laugier recommends, by oxalic acid. This precipitate, well washed," and afterwards calcined, is the * Ann. de Chim. et Phys. in. 140; Thomson's Annals, viii. 233. f See Nicholson's Journal, xii. 105. SECT. XXVI. cerium. 141 oxide of cerium. The white oxide has been recently determined by Hisinger,* to consist of Cerium.....85.088 . . . . 100. Oxygen.....14.912 .... 17.41 100. And the red or peroxide is. composed of Cerium.....79.29 .... 100. 20.71 .... 26.115 100. III. Cerium appears to be susceptible of two stages of oxidize- ment; the first oxide being white, and the second of a fallow red. The white oxide, by calcination, becomes red. IV. Sulphuric acid, diluted with four times its weight of water,dis- solves the red oxide. The solution, on being evaporated, yields crys- tals, some of which are orange, and others have a lemon-yellow co- lour. The sulphate is soluble only by an excess of acid. Its taste is saccharine mixed with acid. V. Sulphuric acid readily unites with the white oxid%; the solution is nearly colourless, but has a slight rosy tinge. It has a saccharine taste, unmixed with acidity, and yields white crystals. VI. Nitric acid unites most easily with the white oxide. The solu- tion is very sweet, and is not crystallizable. When decomposed by heat, it leaves a brick-coloured oxide. VII. Muriatic acid dissolves the red oxide; and the solution crys- tallizes confusedly. The salt is deliquescent: soluble in ah equal weight of water; and in three or four parts of alcohol. When this solution is concentrated, it burns with a yellow sparkling flame. The dry salt consists of 100 parts of muriatic acid united with 197.5 of oxide of cerium. An infusion of galls produces, in muriate of cerium, a yellowish precipitate not very abundant. A few drops of ammonia throw down a very voluminous one of a brown colour, which becomes black and brilliant, by desiccation. By the action of heat, it assumes a brick- red colour. VIII. Oxide of cerium unites readily with carbonic acid. This union is best effected, by precipitating a solution of the oxide with carbonate of potash. An effervescence ensues; and a white and light precipitate is formed, which assumes, on drying, a silvery ap- pearance. It contains per cent. 57.9 parts of protoxide, 19.1 of water, and 23 of carbonic acid. IX. Sulphuretted hydrogen does not unite with cerium. X. The attempts of Vauquelin to reduce the oxide of cerium pro- duced only a small metallic globule, not larger than a pin's head. * Thomson's Annals, iv. 357. 142 VEGETABLE SUBSTANCES. CHAP. XX. This globule was not acted upon by any of the simple acids; but it was dissolved, though slowly, by nitro-muriatic acid. The solution was reddish, and gave traces of iron; but it also gave evident marks of cerium, by the white precipitate which tartrite of potash and oxa- late of ammonia threw down. The metallic globule, also, was harder, whiter, much more brittle, and more scaly in its fracture, than pure cast-iron. When exposed by Mr. Children to his powerful Galvanic battery, oxide of cerium fused; and, when intensely heated, burned with a large vivid white flame, and was partly volatilized. The fused oxide, on exposure for a few hours to the air, fell into a light brown powder, containing numerous shining particles of a silvery lustre. XI. Hence cerium appears to be a volatile metal, unless it is vola- tilized in the state of an oxide, which remains to be ascertained by future experiments. CHAPTER XX. VEGETABLE SUBSTANCES. VEGETABLE substances, though they are all distinguished from each other by peculiar characters, present several circumstances of agreement in chemical properties. Oxygen, hydrogen, and carbon are their principal ingredients, to which a certain proportion of nitrogen is occasionally added; and variations in the proportions, and mode of combination, of these elements, cause the great diversity, which sub- sists among the products of the vegetable kingdom. They are all susceptible of decomposition by heat alone; but we cannot, as in bo- dies of the mineral kingdom, proceed from a knowledge of their com- ponents to the actual formation of the substances themselves. It is not probable, indeed, that we shall ever attain the power of imitating nature in these operations. For in the functions of a living plant, a directing principle is concerned, peculiar to animated bodies, and su- perior to, and differing from, the cause which has been termed chemi- cal affinity. The distinction (as has been well observed by Berzelius*) between inorganic and organic compounds appears to be this. The former are composed either of combustible or of oxidized bodies; and, when when of the latter, each combustible base is united with a portion of oxygen, which.belongs exclusively to it, and which accompanies it, when it is detached from combination. Organic compounds, also, contain oxygen; but, in these, we have several combustible bases, united to one portion of oxygen, which cannot be said to belong more to the one, than to the other; and which would not suffice ft bring any one of those bases to its maximum of oxidation. * 80 Ann. de Chim. 37. CHAP. XX. VEGETABI.F. SUBSTANCES. 143 The productions, of which I am about to offer the chemical history, may be legarded as the immediate or proximate principles of vegeta- bles; for we may presume, generally speaking, that they exist in the living plant in a state identical with that, under which chemical pro- cesses exhibit them. It is not so when we proceed to the ultimate analysis of vegetables; for, in that case, we obtain compounds, which formed no part of the vegetable structure, and which result from a new arrangement of the elements composing it. Acetic and carbo- nic acids, for example, are obtained by the destructive distillation of several vegetable substances, in which neither of these acids existed ready formed, but only their elements. The destructive distillation of vegetables was, till lately, the only method employed to determine the proportion of their ultimate ele- ments; but more refined and perfect modes of analysis have lately been practised by Gay Lussac and Thenard, which have afforded results, much more deserving of confidence.* Their process consists in effecting the combustion of vegetable substances, in close vessels of a peculiar construction, by means of hyper-oxymuriate of potash. Berzelius, also, has considerably improved the methods of vegetable analysis. The following general laws, respecting the composition of vegeta- ble bodies, have been deduced, by Gay Lussac and Thenard, from a general review of their experiments. I. A vegetable substance is always acid, when the oxygen, which it contains, is to the hydrogen, in a proportion greater than is necessary to compose water. II. A vegetable substance is always resinous, or oily, or alcoholic, 8cc. when the oxygen, contained in it, is to the hydrogen, in a less proportion than in water. III. A vegetable substance is neither acid nor resinous, but in a state analogous to sugar, gum, starch, lignin, &c. whenever oxygen and hydrogen enter into its composition in the same proportions as in water. Without supposing then, that oxygen and hydrogen exist, as water, in vegetables, we may, for the sake of illustration, consider vegeta- ble acids, as constituted of carbon, water, and oxygen;—the resins, alcohol, ether, &c. as composed of carbon, water, and hydrogen;—and bodies of the third class, as composed of carbon and water only. It should not, however, be concealed that some exceptions to the gene- rality of these principles have lately been pointed out by Saussure.t The products of the vegetable economy are either situated in par- ticular organs or vessels, or are distributed throughout the whole plant. Sometimes they reside in the root or stalk; at others in the bark or leaves; at others they are peculiar to the fruit, the flowers, the seeds, or even to particular parts of these organs. When thus insulated, they may readily be procured in a separate state; and, in several in- stances, nothing more is required than the labour of collecting them. * Recherches Phys. Chim. ii. f Thomson's Annals, vi. 431. 144 VEGETABLE SUBSTANCES. CHAP. XX. Thus gum exudes from some trees, and manna issues from the branches of others. Sometimes, however, we are presented with a variety of substances mingled together, and requiring separation by processes which are sufficiently simple, and which consist in repose, filtration, pressure, washing, distillation at a gentle heat, solution by water and alcohol, and similar operations, that do not alter the nature of the bodies submitted to them. The number of principles, which have thus been extracted from vegetables, has of late years been greatly enlarged, and amounts at present to between thirty and forty. Of these, the greater part are certainly entitled, by a train of properties sufficiently characteristic, to rank as distinct compounds. But others seem to be so nearly allied to substances, with which we have long been acquainted, that it can serve no useful purpose to assign them a different place in'the system. The unnecessary multiplication, indeed, of vegetable prin- ciples, contributes rather to retard than to advance the progress of this difficult part of chemistry; and it is only in cases of decided and unequivocal differences of qualities, that we should proceed to the establishment of new species. SECTION I. Vegetable Extract. The term Vegetable Extract is not to be understood in the sense which is generally annexed to it, as comprehending all those parts of vegetables which may be dissolved in water, and obtained in a solid form by evaporating the solution; but is new limited to a distinct and peculiar substance. This substance may be obtained by evaporating, at a temperature below 212°, an infusion of saffron, prepared with boiling distilled water. Extract, thus procured, has the following pro- perties : 1. It is cohesive, of a brownish colour, and generally of a bitterish taste, varying with the plant, from which it has been obtained. 2. It is soluble in cold water, but more copiously in hot; and the solution is .always coloured. Hence the decoctions of certain sub- stances (Peruvian bark for example) become turbid on cooling. The solution, exposed for a long time to the air, acquires a mouldy pellicle, and undergoes a sort of putrefaction. 3. When a solution of extract is slowly evaporated, it affords a semi-transparent mass; but rapid evaporation renders it perfectly opaque. By repeated solutions in water, and evaporations, it acquires a deeper colour, and loses its property of being soluble in water, ap- parently in consequence of absorbing oxygen from the air. 4. Extract, exposed to the atmosphere, slowly imbibes moisture; or is imperfectly deliquescent. SECT. I. VEGETABLE EXTRACT. 145 5. It is soluble in alcohol and in liquid alkalies, but neither in ether nor in acids, which last even precipitate it from its solution in water. 6. Oxy-muriatic acid, poured into a solution of extract, precipitates a dark yellow powder, which is no longer soluble in water, but dis- solves in hot alcohol. 7. Extract has an affinity for alumine. When the sulphate or mu- riate of this earth is poured into one of extract, a precipitate appears, especially if the mixture be boiled. When linen or woollen thread, previously impregnated with a solution of alum, is boiled with a solu- tion of extract the thread is dyed a fawn colour, and the extract dis- appears in great part from the liquor. 8. Muriate of tin, and several other metallic salts, also precipitate extract, their oxides forming with it insoluble compounds. 9. Extract is not precipitated by a solution of tan. These are the properties of extract, in the purest form under which we have yet procured it. As commonly obtained, however, it is com- bined with one or more, and frequently with a great number of other principles. In the sap of plants, it exists united with mucilage, gallic acid, tan, acetate of potash, and other neutral salts. Of the substance called catechu, it forms, according to the experiments of Sir H.Davy, a considerable part; and being not easily dissolved by cold water, may be obtained by washing oft the more soluble parts. The infusions, also, of most vegetable substances, hold extract in solution, united with other principles. From a series of experiments on this subject Dr. Bostock is dis- posed to doubt whether there be any distinct principle, to which the title of extract can with propriety be given; and this doubt is enter- tained, also, by Braconnot* The re-agents, he finds, which have been pointed out as tests of extract, act also upon tan; and the processes, for separating extract from the other parts of vegetable infusions, ap- pear to him to be founded upon incorrect assumptions. He has not, however, examined the extract from saffron ;t but it has been the sub- ject of a series of experiments by Bouillon la Grange and Vogel, who have given it the name of polychroite, on account of the many different colours which it is capable of assuming. Thus its natural colour is yellow; and its aqueous solution is deprived of colour by exposure to the sun's rays. Sulphuric acid dropped into the aqueous solution causes a deep indigo blue colour; nitric acid a green one; and chlorine renders it colourless.^: * Thomson's Annals, xii. 34. t See Nicholson's Journal, xxiv. 204. t Ann. de Chim. Ixxx. 188. Vol. II.—T 146 VEGETABLE SUBSTANCES. CHAr. XX. SECTION II. Mucilage, or Gum. This substance, termed mucilage when fluid, is, in a solid state, generally known by the name of gum. Gum arabic may be taken as an example. It appears, however, from Dr. Bostock's experiments, that there is a considerable variety in the chemical properties of dif- ferent mucilages. 1. Gum is dry, brittle, and insipid, and undergoes no change by exposure to the atmosphere, except that the action of light destroys the yellow colour, which it frequently exhibits. Its specific gravity varies from 1300 to 1490. 2. It is readily soluble in water, and forms a viscid solution, which may be kept a long time, without undergoing any change; but finally becomes sour. 3. It is insoluble in alcohol and in ether, the former of which pre- cipitates it from water. 4. It is separated from water, in a thick curdy form, by acetate of le*d; and is thrown down by the red sulphate of iron, in the state of i rown semi-transparent jelly. Several other salts, also, have a simi- lar effect. According to Dr. Thomson's experiments, the salts, con- taining mercury and iron at the maximum of oxidation, are the most efficient in precipitating gum. The oxides of copper, antimony, and bismuth, are, also, acted upon by it; for it prevents water from pre- cipitating them in the state of sub-salts. The effects of re-agents on a solution of gum have been investigated by Dr. Bostock;* and have been found to vary considerably in the different species of gum; for example, in gum arabic, cherry-tree gum, and linseed mucilage. Ber- zelius, also, has examined the compound of gum arabic with oxide of lead, to which he has given the name of gummate of lead. He finds it to consist of Gum.....61.75 .... 100. Oxide of lead . . 38.25 .... 62.105 lOO.t 5. Gum is soluble in pure alkalies, and in lime-water, and is pre- cipitated unchanged by acids. Of the earths, silex seems to have the strongest affinity for it; a solution of silicated alkali decomposing a very dilute solution of gum. (Thomson.) Dr. Duncan, jun., however, informs me, that this precipitate is produced only by solutions of the lighter coloured specimens of gum, which have different properties from those of darker colour. The precipitation, when it does occur, * See Nicholson's Journal, xviii. 28. t 95 Ann. de Chim. 77. SECT. II. MUCILAGE. 147 Dr. Bostock suspects to take place, only in consequence of the lime which gum contains. Hence oxalic acid, also, produces a precipitate from the solution of gum arabic. 6. Diluted acids dissolve gum unchanged, and the concentrated ones decompose it. Strong sulphuric acid converts it into water, acetous acid, and charcoal; the last of which amounts to ratheiynore than one-fourth the weight of the gum, and exhibits slight tnras of artificial tan. Nitric acid dissolves gum with a disengagement of nitrous gas; and the solution, on cooling, deposits a little saccholactic or mucous acid. The production of mucous acid appears to be the characteristic property of mucilage; and Vauquelin even obtained this acid from the mucilage of linseed. Some malic acid is also form- ed; and by continuing the heat, the gum is changed by the nitric acid into oxalic acid, which bears the proportion of nearly one-half of the weight of the gum. Oxy-muriatic acid transmitted through a solution of gum, changes it into critic acid. 7. Gum and sugar readily combine; and by gentle evaporation of their mixed solutions, a transparent substance is obtained. From this, alcohol separates a part of the sugar, but the remainder continues in combination, and forms a substance, resembling that of which the nests of wasps are composed. 8. Gum, when submitted to destructive distillation in a retort, yields an acid, formerly called the pyro-mucous, but now ascertained to be merely the acetic, holding in solution a portion of essential oil, and some ammonia. Carburetted hydrogen and carbonic acid gases are also disengaged; and in the retort" there remains charcoal, mixed with lime and phosphate of lime. Gum, therefore, is composed of oxygen, hydrogen, carbon, and (as may be deduced from its yielding ammonia) a little nitrogen. It appears to differ from sugar, not only in containing a less proportion of oxygen, but also by its combination with, lime and nitrogen.* Respecting the varieties of vegetable mucilage, which appear to be pretty numerous and well marked, much valuable information may be obtained from the paper of Dr. Bostock, which has been already referred to. Cherry-tree gum, tragacanth, and some other varieties are considered as forming a distinct vegetable substance, to which the name of cerasin has been given. It imbibes water, and swells very considerably in bulk, but is not at all soluble except in boiling water, from which it again separates on cooling in the state of a jelly. Gum arabic has been analyzed by Gay Lussac and Thenard, and by Berzelius, and found to consist of Carbon .... 42M . . . 41.906 Oxygen .... 50.84 . . . 51.306 Hydrogen . . . 6.93 . . . 6.788 lOO.t 1004 * Cruickshank, Nicholson's Journal, 4to. il. 409. f Gay Lu«a- ; Berzelius. 148 VTGETABLE SUBSTAMFS. CHAP. XX. Saussure in addition to these three elements found also a minute quantity of nitrogen. From gum arabic and gum tragacanth, he ob- tained Carbon.......45.84 Oxygen.......48.26 £ Hydroiren......5.46 Azote .......0.44 100.* SECTION 111. Vegetable Jelly. Vegetable jelly may be obtained from the recently expressed juices of certain fruits, suchas the currant and gooseberry. When the ex- pressed juice of these fruits is allowed to remain, for some time, in a state of rest, it partly coagulates into a tremulous soft substance, well known by the name of jelly. The coagulum, washed with a very small quantity of water, is jelly nearly in a state of purity. Vegetable jelly, unless when tinged by the colour of the fruit is nearly colourless; has a pleasant taste, and a tremulous consistency. It is soluble in cold water; but more copiously in hot, and the solu- tion, if strongjenough, again gelatinates on cooling. By long boiling it loses this last property, and is changed into a substance analogous to mucilage. When dried it is transparent. It combines readily with alkalies. Nitric acid converts it into oxalic acid, without dis- engaging any azotic gas. Its solution in water is precipitated by in- fusion of galls. SECTION IV. Sugar and Oxalic Acid. Art. 1.—Sugar. Almost all the sugar, which is applied to the common purposes of life, is derived from a plant, the growth of hot climates, called Arundo Saccharifera. This plant produces strong canes, inclosing a soft pithy substance, which yield, by the compression of powerful machi- nery, a large proportion of sweet juice. The juice is evaporated in copper vessels, with the addition of a small quantity of slaked lime. During evaporation, a thick scum is formeJ, which is continually re- * Thomson's Annals, vi. 431. SECT. IV. SU GAR. 149 moved. The juice passes successively from larger to smaller boilers, till at length, in the last of these, it becomes thick and tenacious. When this happens, it is emptied into shallow wooden coolers, where the syrup forms a mass of small, irregular crystals, enveloped in a treacly fluid. The whole mass is drained in hogsheads, in the bot- toms of which holes are bored. The fluid, which separates, is called melasses or treacle; and the dried crystals are exported to this coun- try under the name of raw or muscovado sugar. The subsequent process,*which sugar undergoes, with the view of bringing it to the white and beautiful form of loaf-sugar, consists in its being re-dissolved in lime-water, and in being boiled with a quantity of some coagulable substance, such as the whites of eggs or bullock's blood. These substances coagulate into a thick scum, which rises to the surface, carrying along with it the principal part of the impurities of the sugar. The solution, after being evaporated to a due consistence, is let out into large conical earthen pots, with a hole at the apex of the cone, and each supported by an earthen jar. When the syrup has concreted into a solid mass, the plug is removed from the point of the cone, to allow the adhering liquid to drain off; and a mixture of pipe-clay and water is poured on the surface of the mould, and suffered to continue there four or five days. The moisture from this, slowly descending through the sugar, carries with it the remains of the darker coloured syrup; and the whole loaf, after being dried in a stove, is obtained of the proper degree of whiteness. Besides the juice of the cane, sugar may be extracted, also, from several other vegetables. The juice which flows spontaneously from incisions made in the American maple-tree, affords a quantity suffi- cient to render it a process worth following. Ripe fruits contain su- gar in considerable quantity, and by long keeping after they have been dried, it appears, in a granular state, on their surface. The juice of the carrot, and still more remarkably of the beet (beta vulgaris, Linn.) yield a considerable proportion of sugar. To obtain it from the latter vegetable, the roots, softened in water, are to be sliced, and the juice expressed. It is then to be boiled down with the addition of a little lime till about two-thirds remain, and afterwards strained. These boilings and strainings are repeated alternately, till the liquid attains the consistence of syrup, when it is left to cool. The sugar thus ex- tracted, retains somewhat of the taste of the root; but it may be puri- fied by the operation already described as used for the refining of West India sugar, and it then loses its peculiar flavour. The quanti- ty obtained varies considerably; but in general it may be stated at between four and five pounds from 100 pounds of the root, beside a pro- portion of uncrystallizable syrup. In Germany, the expense has been calculated at about three pence per pound; but this estimate is pro- bably under-rated.* From the experiment of Proustt it appears that a coarse sugar may be procured from grapes (of which many thousand tons are annually * See Chaptal on the manufacture of sugar in France, Phil. Mag. xlvii. 331 t Nicholson's Journal, xxi. 356. y 150 VEGETABLE SUBSTANCES. CHAP. XX. wasted in Spain,) at the expense of about eight pence per pound; or, under favourable circumstances, even for five, pence. In apples and pears, in the juice of liquorice, and in some other vegetable juices, sugar exists, but in a state of combination, which prevents it from assuming a crystallized form. The sugar of grapes has been analyzed by Saussure, and found to contain very nearly the same proportions of ingredients as starch sugar, stated under the article fecula.* These two kinds of sugar agree, indeed, so closely as to their properties, that they probably constitute one species. Sugar from the cane and from beet differs from these, and from all other kinds of sugar, by containing a greater proportion of carbon.t Sugar is produced also in the process of malting, which consists in the conversion of starch into sugar. The following are its chemical properties: 1. Sugar is soluble in an equal weight of cold water, and almost to an unlimited amount in hot water. The latter solution affords a liquid called syrup; from which, by long repose, transparent crystals of sugar separate, called candied sugar. Their form is that of prisms with four or six sides, bevelled at each extremity, or sometimes accu- minated by three planes. 2. Alcohol dissolves, when heated, about one-fourth its weight of sugar. The solution, by keeping, deposits large crystals of sugar. 3. Lime-water renders sugar more soluble; and, reciprocally, sugar increases the solubility of lime. Alkalies unite with it, and destroy its taste. It may be recovered, however, unchanged, by add- ing sulphuric acid, and precipitating the alkaline sulphate by alcohol, which retains the sugar in solution. It unites, also, with the alkaline earths; and with barytes so strongly, that it appears to undergo a kind of decomposition. 4. Sugar has the property of rendering oils miscible with water. 5. The sulphurets, hydro-sulphurets, and phosphurets appear to have the property of converting sugar into a substance not unlike gum.J 6. Sugar has the property of decomposing several of the metallic salts, when boiled with their solutions. Sometimes it reduces the oxide to a metallic state, as in sulphate of copper. In other instances, as in the acetate of the same metal, it merely reduces the oxide to an inferior degree of oxidation.§ With oxide of lead, it forms an inso- luble compound, called by Berzelius saccharate of lead.W 7. It is converted, by destructive distillation, into acetic acid, car- buretted hydrogen, and carbonic acid gas, and charcoal. According to Lavoisier, it is composed of 64 oxygen, 28 carbon, and 8 hydrogen: Gay Lussac, Thenard, and Berzelius, have analyzed it by combustion with hyper-oxymuriate of potash, and Dr. Prout by distillation with oxide of copper. They find it to consist of * See Sect. ix. infra. . j- Thomson's Annals, vi. 428. $ Thomson's Chemistry, iv. 214. § Vogel in Thomson's Annals, vii. 42. | 95 Ann. de Chim. 53. SECT. IV. OXALIC ACID. 151 44.200 . . 39.99 49.015 . . 53.33 6.785 . . 6.66 lOO.t 1004 It is remarkable that these are as nearly as possible the propor- tions of the ingredients of gum arabic. Beside pure sugar, there are other saccharine substances, that bear a considerable resemblance to it Manna is the inspissated juice which flows spontaneously from incisions in the bark of a species of ash (the fraxinus ornus). Sugar has been discovered, also, by Four- croy and Vauquelin, to enter largely into the composition of the juice obtained by pressure from the onion. Besides sugar, it appears, also, to contain a portion of mucilage and extract, to which its taste and other peculiar properties are owing. The same may perhaps be said of honey. When treated with nitric acid it was found, however, by Mr. Cruickshank, to give very little less oxalic acid, than was obtained from an equal weight of pure 9ugar. Proust has considered honey itself as of two distinct species. Common yellow honey is of an uniform consistence and viscid; but, besides this, there is a granulated white kind, which has a tendency to become solid. From the latter he obtained by alcohol a white sac- charine powder, which he considers as agreeing more nearly with the sugar of the grape than with common sugar. Art. 2.—Oxalic Acid. Sugar is acidified by distillation with nitric acid. To six ounces of strong nitric acid, in a stoppered retort, to which a large receiver is luted, add, by degrees, one ounce of lump-sugar, coarsely powder- ed. A gentle heat may be applied during the solution. Nitrous gas will be disengaged in great abundance. When the whole of the sugar is dissolved, distil off a part of the acid. The remaining liquor will form regular crystals (amounting to 58 parts from 100 of sugar,) which must be again dissolved in water and crystallized. Lay this second crop of crystals on blotting paper to dry. * Gay Lussac. f Berzelius. t Prout. Carbon . . . 42.47 Oxygen . . . . 50.63 Hydrogen . . . 6.90 100.* Or of carbon . . . 42.47 Oxygen and hydro-"*) gen, in the same (-„ .- proportion as in | "°" water ... J 100. 152 VEGETABLE SUBSTANCES. CHAP. XX. Oxalic acid may be procured, also, by a similar treatment of gum, and of various other vegetable, and even of some animal products. The crystals of oxalic acid have the following characters: 1. They have a strong acid taste, and act powerfully on vegetable blue colours. 2. They dissolve in twice their weight of cold, and in an equal weight of hot water. They are soluble, also, in boiling alcohol, which takes up about half its weight; and, though sparingly, in ether. 3. They effloresce in the air, and become covered with a white powder. 4. A red heat entirely decomposes them, and leaves only charcoal. During distillation, a considerable quantity of inflammable gas is ob- tained; and a portion of the acid is sublimed, unaltered, into the neck of the retort The constitution of oxalic acid, has been investigated with much skill and attention by Dr. Thomson.* The crystals, in their perfect state, he has proved to consist of Real acid.......77 Water........23 100 And from an elaborate examination of the gases, obtained by destruc- tive distillation, he concludes that 100 parts of real oxalic acid con- sist of Oygen........64 Carbon........32 Hydrogen ..*.... 4 100 Oxalic acid has since been analyzed by Gay Lussac and Thenard.t and by Berzelius.| The first mentioned chemists decomposed oxa- late of lime of known composition by oxy-muriate of potash, and ob- tained the following results: Carbon.......26.566 Oxygen.......70.689 Hydrogen......2.745 100. Or the analysis may be thus stated: Carboy..........26.566 Oxygen and hydrogen in the same > 22 g^ proportions as in water .... 5 Excess of oxygen......50.562 100. * Philosophical Tiansactions, 1808. t Recherches, ii. * 81 Ann. de Chim. and Thomson's Ann. iv. 232, and ix. 33. SECT. IV. OXALIC ACIS. 153 Berzelius, some time ago, ascertained that of the water, which en- ters into crystallized oxalic acid, only 28 per cent, can be driven off by heat but that a farther quantity may be detached, by uniting the acid with oxide of lead. Taking the latter portion into account the crystals consist of 58 acid and 42 water; and the real acid is thus constituted, according to his experiments: Oxygen. . . . 66.211 . . = 6 atoms. Carbon . . . . 33.021 . . . = 4 atoms. Hydrogen . . . 0.728 . . . = 1 atom. Oxalate of potash forms flat rhomboidal crystals, terminated by dihedral summits. Its taste is cooling and bitter. At 60° Fahren- heit, it requires three times its weight of water for solution. There is, also, a salt formed of the same base and acid, but with a considera- ble excess of the latter, called super-oxalate or binoxalate of potash. It forms beautiful four-sided prisms. The acid, which it contains, is double that in the oxalate; or if we suppose 100 parts of potash, and denote the quantity necessary to convert it into oxalate, by x, then 2 x will convert it into super-oxalate. According to Berzelius 100 parts of potash are united, in the oxa- late, with 97.3 parts of oxalic acid, and in the binoxalate, with 192.4. Exclusively of water, which, in the crystals of the oxalate, amounts to 17.31 per cent, they are composed as follows: Acid. Base. Oxalate of potash . . . 49.32 . . 50.68 Binoxalate of ditto . 65.80 . . . 34.20 Quadroxalate of potash may be composed in several methods.* It was formed by Dr. Wollaston, by digesting the super-oxalate in nitric or muriatic acid. The alkali is divided into two parts, one of which unites with the mineral acid; and the other half remains in combination with the oxalic acid. Hence tiie quadroxalate contains four times the acid that exists in the neutral oxalate, and twice as much acid as the super-oxalate; or its acid may be denoted by 4 x. Berzelius determined that in this salt, 100 parts of potash are combined with 380 parts of oxalic acid, or it consists of Potash......18.95 Acid......72.05 Water......9. 100. Salt of sorrel was found by Berard to be a true quadroxalate of potash. * See Berard, 73 Ann. de Chim. 271 Vol. II.—U 154 VEGETABLE SUBSTANCES. CHAP. XX. Oxalate of soda readily crystallizes, and has a taste nearly re- sembling that of oxalate of potash. When heated, it falls to powder, and loses the whole of its water of crystallization. Soda forms, also, with oxalic acid, a binoxalate, but no quadroxalate. In the oxalate, 100 parts of soda are combined with 143.5 parts of acid; in the binox- alate with 284.7, according to'the analysis of Berzelius. Oxalate of ammonia crystallizes in long transparent prisms, rhomboidal, and terminated by dihedral summits, which, according to Berard, contain 13 per cent of water. Its taste is bitter and unplea- sant At the temperature of 60°, 1000 grains of water dissolve only 45 grains of the salt. The solution is of great use as a re-agent; for it precipitates lime from all ills soluble combinations, and discovers it even when in very minute quantities. In oxalate of ammonia, 100 parts of real alkali are united with 26l parts of acid. A super-oxalate or binoxalate of ammonia, also, exists, which is less soluble in water than the oxalate. In this, 100 parts of base are united with 523 of acid. Oxalate of lime is an extremely insoluble salt It may be form- ed, either by dropping oxalic acid into lime-water, or by mingling the solutions of a salt with base of lime and of any of the soluble oxalates. When very slowly dried at the temperature of about 60° Fahrenheit, it is tolerably uniform as to its composition; and consists, according to Dr. Thomson, of Acid......59.2 Lime......35.5 Water.....5.3 100. « When rapidly dried, it is apt to concrete into hard lumps, which contain not less than 10 per cent, of water. It is soluble in nitric and muriatic acid; and hence, in the use of oxalate of ammonia or oxalic acid as a precipitant, it is necessary first to neutralize any excess of acid. Oxalates of barytes and strontites are white tasteless pow- ders of very sparing solubility; but these earths, with an excess of acid, form more soluble super-oxalates. One hundred parts of strontites take 83.62 of oxalic acid for satu- ration. No super-oxalate exists with this base. The oxalate of barytes is more soluble than the strontitic salt. It consists of 100 parts of base, united with 60.84 acid. A super-oxalate maybe form- ed, by heating muriate of barytes with oxalic acid. This salt, which shoots into crystals, has its elements so feebly combined, that it is decomposed by mere solution in water. It is constituted of 100 parts of base and 123 of oxalic acid. Oxalate of magnesia is a soft white powder, bearing a consider- able resemblance to oxalate of lime. It is tasteless, and not sensibly soluble in water. Yet when oxalate of ammonia is mixed with sul- phate of magnesia, no precipitate falls. It is composed of 100 parts of base and 265 of acid. SECT. v. NATIVE VEGETABLE ACIDS. 155 According to Dr. Thomson, 100 parts of oxalic acid saturate the following quantities of the several bases: Ammonia .... 34.12 Magnesia .... 35.71 Soda......57.14 Lime.....' . 60. Potash.....122.86 Strontian .... 151.51 Barytes.....142.86 And the composition of the different oxalates is shown by the fol- lowing Table: One hundred parts of ,--------A--------^ Oxalate of ammonia ---------magnesia -------- soda . . -------- lime . . -------- potash . -------- strontian -------- barytes . -------- lead . . Consist Consist per Thomson of per Berard of A .,_.. ,A. '" i t ' ^ Acid. Base. Acid. Base. 74.45 . . 25.55 *62.34 . . 27.66 73.68 . . 26.32 72.65 . . 27.35 63.63 . . 36.37 58.92 . . 41.08 62.50 . 37.50 62.00 . . 38.00 44.87 . . 55.13 49.32 . . 50.68 39.77 . . 60.23 45.54 . . 54.46 41.16 . . 58.84 37.83 . . 62.17 25.20 . 74.80 24.54 . 75.46t The above table is to be understood as applicable to the salts in their state of ordinary dryness. With the exception indeed of oxalate of potash, and perhaps of soda, Dr. Thomson is of opinion that when slowly and carefully dried, the proportion of water is so small, that it may be overlooked. SECTION V. Native Vegetable Acids. Native vegetable acids are such as are found, ready formed, in plants or their fruits, and require only pressure, and other simple pro- cesses, for their extraction. The following are the principal ones hitherto discovered: 1. Citric. 2.' Gallic. 3. Malic. 4. Sorbic. 5. Tartaric. 6. Oxalic. 7. Benzoic 8. Acetic. 9. Prussic. 10. Phosphoric. * This number should probably be 72.34; for, as it stands in the Table, the acid and base do not make up 100. X Berzelius, 94 Ann. de Chim. 180. 150 VEGETABLE SUBSTANCES. UUP. XX. Art. 1.—Citric Acid. Citric acid exists in the expressed juice of the lime and lemon, along with a quantity of extractive matter and mucilage, and with variable proportions of malic and sometimes of acetic acid. The process, for obtaining it in a separate state, we owe to the ingenuity of Scheele. To the expressed juice of the lime or lemon, contained in a vessel of earthen ware, or white wood, add, very gradually, finely powdered carbonate of lime (chalk or whiting,) and stir the mixture well after each addition. An effervescence will ensue; and as long as this arises, on adding fresh portions of chalk, more chalk will be required. The exact proportion it is impossible to assign, on account of the variable strength of the acid juice. In general, from six to eight ounces of chalk are sufficient to saturate a wine-gallon of lime- juice. When it ceases to excite effervescence, and the liquor has lost its sour taste, allow the mixture to settle; decant the liquid, and add a quantity of water. Let the powder subside; the liquor be again decanted, and thrown away; and these operations repeated, till the water comes off nearly colourless. The insoluble precipitate consists of citric acid, united with lime; add to it a quantity of sulphuric acid, of the density 1.85 or thereabouts, equal to the weight of the chalk which has been employed, and previously diluted with 10 parts of water.—Let the acid and precipitate remain together 24 hours; during which time they'must be frequently stirred with a wooden spatula. Then let the white sediment, which consists of sulphate of lime, subside; decant the clear liquor; add more water till it comes off tasteless; and mix all the liquors together. The solution, con- taining citric and sulphuric acids, and some mucilage, is to be evapo- rated first in a leaden boiler, and afterwards in shallow earthen dishes, placed in a sand-heat Reduce the liquor to about one-fourth of its bulk by evaporation; separate the sulphate of lime, which will be deposited, and again waste the liquor, by a heat not above 212°, to the consistence of syrup. Brown crystals will form on cooling, which must be set to drain; and the remaining liquor, when again evapo- rated repeatedly, will continue to yield fresh crystals. To purify these, let them be dissolved in water; and the solution be a«jain eva- porated. After the second crystallization, their colour will be im- proved; but it will require three or four crystallizations to obtain them perfectly white and well formed. In this state, they are the pure citric acid. The proportions, which I have recommended for the preparation of citric acid, differ a little from those, which have been deduced by Proust from his experiments. Four ounces of chalk saturated, he found, 94 ounces of lemon juice; the citrate of lime weighed seven ounces four drachms. But the four ounces of chalk, or 32 drachms, contained only 17^ drachms of lime; and, from the analysis of citrate of lime, it appears to contain 70 parts of citric acid in 100. Hence the seven ounces four drachms contained 41 £ drachms of citric acid. SECT. \. citric acid. 157 But to expel the carbonic acid completely from four ounces of chalk, five ounces of sulphuric acid of commerce were found necessary. This proportion, therefore, he employed in decomposing the citrate of lime. Six. ounces of the citrate, by two crystallizations, gave S£ ounces, or 28 drachms, of pretty large crystals; from whence it follows that the whole 7\ ounces would have given 4 ounces 3 drachms of citric acid.* The preparation of solid citric acid on the large scale of manufac- ture requires an attention to a number of minute circumstances, which are stated at length by Mr. Parkes in the 3d volume of his Chemical Essays, or in the 46th volume of the Philosophical Magazine. The citric acid, which is made for sale, is generally prepared from lime-juice. The quantity of solid citric acid, in a gallon of this juice, varies considerably. I have found it as high as twelve avoirdupois ounces; but about six or eight ounces to the wine gallon is a fair general average. The only method of ascertaining its proportion consists in adding, to a quantity of the juice, solution of pure potash till saturation is produced. Liquid potash, of a fit strength for this purpose, may be prepared by boiling two pounds of American potash with one pound of quicklime, previously slaked to a thin paste, and a gallon of water, in an iron pot, during half an hour. The solution may be strained through calico, and reserved for use in well stopped bottles. When employed as a test, one measure may be added to three measures of water; and it is proper to ascertain, by experiment, how much of this solution is requisite to saturate an avoirdupois ounce of white crystals of citric acid. It will then be easy, by saturating with the same alkaline liquor, an aliquot part of a wine gallon of any sample of lime or lemon juice (judging of the point of saturation by test papers) to calculate what quantity of solid acid is contained in a gallon of the juice under examination. This, of course, implies that the juice is not contaminated with any other acid. Pure citric acid forms beautiful transparent crystals, consisting of two four-sided pyramids joined base to base, or sometimes of rhom- boidal prisms. An ounce of distilled water, at 60° Fahrenheit, dis- solves an ounce and a quarter of these crystals, or at the boiling tem- perature twice its weight The crystals do not attract moisture from the atmosphere. They contain per cent, according to Berzelius, Real acid.......79 Water........21 100 Only a small part of this water, viz. about 7 per cent., can be driven oft'by a degree of heat, just below what is sufficient to decompose the acid. The real proportion of water can only be determined, by uniting the acid with some basis, oxide of lead for example. Citric acid is decomposed at a high temperature, and yields pro- ducts, which are constituted of carbon, hydrogen, and oxygen in un- * Philos. Magazine, x. 158 VEGETABLE SUBS'l ANTES. CHAP. XX. certain proportions. A better method of effecting its analysis is that practised by Gay Lussac and Thenard, viz. combustion with hyper- oxymuriate of potash. By this process, they determined it to con- sist of Carbon.......33.811 Oxygen.......59.859 Hydrogen......6.330 100. Berzelius obtained results,differing considerably from these; owing, he believes, to the want of due allowance, by Gay Lussac and The- nard, for the quantity of water of crystallization. His proportions are Carbon.......41.369 Oxygen.......54.831 Hydrogen......3.800 100.* When treated with about three times its weight of nitric acid, the citric acid is converted partly into the oxalic, of which it gives half its weight As the proportion of nitric acid is increased, that of the oxalic is diminished, till at length it disappears altogether, and acetic acid appears to be formed. Citric acid readily unites with alkalies, earths, and metallic oxides. Citrate of potash.—According to Vauquelin, 36 parts of crystal- lized citric acid, dissolved in water, require for saturation 61 of crys- tallized bi-carbonate of potash: and the result is an extremely soluble and even deliquescent salt, composed of 55% acid and 44£ alkali. Citrate of soda is a very soluble salt. Thirty-six parts of citric acid neutralize 42 of dry sub-carbonate of soda; and hence 100 parts of the citrate consist of 60.7 acid and 39.3 base. Citrate of ammonia.—The same quantity of citric acid saturates 44 parts of sub-carbonate of ammonia; and affords a soluble and dif- ficultly crystallizable salt, composed, in 100 parts, of 62 acid and 38 base. Citrate of barytes consists of equal weights of acid and base. It is an insoluble salt of little importance. Citrate of magnesia.—Thirty-six parts of crystallized acid neu- tralize 40 parts of sub-carbonate of magnesia. Hence 100 parts of the salt contain 33.34 base and 66.66 acid. The salt is soluble, but not crystallizable. Citrate of lime.—Crystallized citric acid, dissolved in water, re- quires an equal weight of chalk for saturation. The compound, when neutral, is insoluble; but with an excess of acid it becomes readily soluble. It was found by Gay Lussac and Thenard to consist of * Ann. de Chim. xciv. 172. SECT. V. GALLIC ACID. 159 68.83 31.17 IOC. The metallic citrates have been but little examined. The com- pounds of this acid with the oxides of iron are of the most impor- tance; from the use which is made of it as a discharger in calico- printing. Citrate of lead has been analyzed by Berzelius, and found to consist of Acid.......34.18 .... 100 Protoxide of lead . . . 65.82 .... 190 Art. 2.—Gallic Acid. The acid exists in the gall-nut, along with tan and other substances. In Sir H. Davy's experiments, 400 grains of a saturated infusion of galls, gave, by evaporation, 53 of solid matter, composed of nine- tenths tan and one-tenth gallic acid. The acid may be obtained by exposing an infusion of galls in water to the air. A mouldy pellicle will form on the surface of the infusion; and, after some months' ex- posure, small yellow crystals will appear on the inside of the vessel. These crystals contain both tan and gallic acid.* To purify them, they must be dissolved in alcohol, and the solution cautiously evapo- rated to dryness. s Gallic acid may also be procured^by sublimation. Pounded galls are to be put into a retort, and heat applied. The gallic acid will rise, and be condensed in the neck of the retort in a solid form. This process is recommended by Deyeux as preferable to any other. The gallic acid may be separated from the infusion of galls, by adding muriate of tin till the precipitate ceases to appear. This pre- cipitate may be reserved for the experiments detailed under the ar- ticle Tan. From the remaining solution the superabundant oxide of tin must be precipitated by sulphuretted hydrogen gas, and the clear liquor, on evaporation, yields crystals of gallic acid. From one ounce of galls, according to Haussman, about three drachms of gallic acid may be obtained. In Nicholson's 8vo. Journal, vol. i. page 236, a very simple process for obtaining gallic acid is proposed by M. Fiedler. Boil an ounce of powdered galls, in sixteen ounces of water down to eight, and strain the decoction. Precipitate also two ounces of alum, dissolved in water, with a sufficient quantity of carbonate of potash, and, after having washed the precipitate extremely well, add it to the decoction, and digest the mixture for 24 hours,shaking frequently. The alumine com- Acid Lime * Berzelius, 94 Ann de Chim. 303. 160 VEGETABLE SUBSTANCES. GHAF. XX. bines with, and carries down, both the tan and extract; and the fil- tered solution yields, by gentle evaporation, crystals of gallic acid. By none of these processes, however, can gallic acid be obtained perfectly pure; for it still, according to Sir II. Davy, is contaminated with a small portion of extract.—To purify it, Deyeux advises its sublimation. Over a glass capsule, containing the impure acid, and placed in a sand-heat, another capsule is to be inverted, and kept cool.—On the impression of the heat, the acid rises into the upper one, in the form of white needle-shaped crystals. The pure acid has the following characters: 1. Its crystals have the form ot transparent plates or octohedrons. They have an acid and somewhat astringent taste. 2. Gallic acid burns with flame, when placed on a red-hot iron, and emits an aromatic smell. 3. It is soluble in 24 parts of cold, or three of boiling water. Alco- hol, when cold, dissolves one-fourth, or an equal weight when heated. 4. The solution reddens blue vegetable colours; but Berzelius de- nies its action on the colour of turnsole. It effervesces with alkaline carbonates, but not with earthy ones. 5. Nitric acid converts the gallic into oxalic acid. 6. It unites with alkaline solutions without producing any deposit; but from watery solutions of lime, barytes, and strontites, it occa- sions a bluish precipitate. Of the combinations of earths with acids, it decomposes those only with base of glucine, yttria, and zircon. 7. It precipitates most metals from their solutions; gold, silver, and copper, of a brown colour; lead, white; mercury, orange; bismuth, yellow; and iron, deep black. The precipitate from solutions of iron is soluble in an excess of acid. It forms the basis of ink,'which, ac- cording to Deyeux, consists of carburetted oxide of iron, and gallate of iron. 8. By a moderate heat, it is sublimed without alteration, but a strong heat decomposes it; and aeriform products are formed, which show it to consist of hydrogen, oxygen, and carbon, in proportions not yet exactly determined. A full and valuable history of the gallic acid, and the process for obtaining it, by Bouillon la Grange, may be consulted in Nicholson's Journal, xvii. 58.* This chemist has, however, expressed a doubt of the claim of the gallic acid to be considered as a distinct acid, and suspects that it is only a modification of the acetic. Its properties, he remarks, differ according to the method in which it has been pre- pared.t * The reader will find, also, much important matter on this subject in Messrs. Aikin's Dictionary of Chemistry, article Gall Nut, and in Dr. Bostock's papers in Nicholson's Journal, xxiv. t Annales de Chimie, Ix. 156. SECT. V. MALIC ACID. 161 Art. 3.—Malic Acid. This acid exists in the juice of apples, gooseberries, and of some other fruits, and is found mixed with the citric, and occasionally with other acids. It may be obtained by evaporating the juice nearly to dryness, and then adding alcohol, which dissolves the acids, and leaves the mucilage. To this solution of citric and malic acids in alcohol, chalk is to°be added to saturation, and the precipitate to be washed with boiling water, which takes up the malate of lime, and leaves the citrate. The solution of the malate of lime may then be decomposed by sulphuric acid. Or the juice of the apples may be saturated with carbonate of pot- ash, and mixed with a solution of acetate of lead, till the precipitate ceases. This precipitate is to be washed with water, and dilute sul- phuric acid is to be added, till the liquor acquires an acid taste, un- mixed with any sweetness. The liquor is to be filtered, to separate the sulphate of lead, and evaporated. It yields no crystals, but a thick liquor of a cherry-red colour. A strong objection to this process is that the juice of apples contains not only malic but sorbic acid, which also gives with lead an insoluble salt. Vauquelin has shown that the malic acid may be obtained advan- tageously from the juice of house-leek (sempervivum tectorum) by adding acetate or' nitrate of lead, and decomposing the insoluble malate with sulphuric acid, added in slight excess. To remove the redundant sulphuric acid, Gay Lussac boils the liquor with a small quantity of litharge, and throws down the oxide of lead by a current of sulphuretted hydrogen. He then evaporates to the consistence of syrup, and adds alcohol, which separates the malic acid from a portion of malate of lime. The alcohol is then distilled at a gentle heat, and the residue dissolved in water. It is formed, also, by the action of nitric acid on sugar. Equal weights of the two are to be distilled together, till the mixture assumes a brown colour. The oxalic acid may be separated by adding lime-water; after which, the remaining liquor is to be saturated with lime and filtered. On the addition of alcohol, a coagulum of malate of lime is formed, which may be dis- solved in water, and decomposed, as before directed, by acetate of lead; and afterwards by sulphuric acid. This process Mr. Donovan finds to be extremely uncertain and costly. The malic acid is liquid, and incapable of being crystallized; for, when evaporated, it becomes thick and viscid, like syrup. It is scarce- ly possible to obtain it free from colour. It is very soluble in water. By keeping, it undergoes a kind of decomposition. Nitric acid con- verts it into oxalic acid. It unites with alkalies and earths. With lime it forms a salt which is almost insoluble in cold water, but readily soluble by hot; and in consequence of this last property, it may be easily separated from the oxalic, citric, and tartaric acids. When perfectly pure, Gay Lussac has shown that it does not decompose either nitrate of silver or nitrate of lead.* • Ann. de Chim. et Phys. vi. 330. Vol. II.—X 162 VEGETABLE SUBSTANCES. CHAP. XX. Art. 4.—On the Sorbic Acid. This acid was discovered by Mr. Donovan in the juice expressed from the berries of the sorbus aucuparia, or service-tree;* and its claim to be considered as a distinct acid has been established, not only by his experiments, but by the subsequent examinations of Vau- quelin and Braconnot.t It had escaped the sagacity of Scheele, who had overlooked its existence not only in the juice of the sorbus, but in that of apples, of which it forms the principal ingredient; and Bra- connot has found it, also, in the juice of unripe grapes. The fruit of the sorbus, collected about the month of October a little before it is perfectly ripe, is to be bruised in a porcelain or marble mortar, and submitted to a strong pressure. Vauquelin recommends that the juice, thus obtained, should be allowed to remain 12 or 15 days in a moderately warm place. By the fermentation, which it thus undergoes, a quantity of viscid matter is deposited, which may be separated by filtration. The clear liquor may be mixed with a solution of acetate of lead, which affords a copious precipitate. This is to be washed on a filter, first with a large quantity of cold water, to free it from colouring matter; and next with repeated quantities of boiling water, the hot washings only being reserved in a series of glass jars. After some hours, they become opaque, and deposit crys- tals of singular lustre and beauty, resembling benzoic acid. Those, which have been formed in the colourless washings, are to be collected on a filter, dried in the air, and preserved for a subsequent process. The original mass, remaining on the filter, is next to be boiled for half an hour with a slight excess of diluted sulphuric acid; and when cold is to be filtered. The clear liquor is to be mixed, a second time, with acetate of lead; the precipitate washed as before with boiling water; and the crystals selected from the'colourless washings only. The remaining mass is again to undergo the action of sulphuric acid as before. The crystals, thus collected, are to be boiled for half an hour with 2.3 their weight of sulphuric acid of the specific gravity of 1090, sup- plying water as it evaporates, and taking care to keep the materials suspended, by stirring constantly with a glass rod. The clear liquor is to be filtered off, and poured into a tall and narrow glass jar. While still hot, sulphuretted hydrogen gas is to be passed through it, till all the lead has been precipitated. The fluid is then to be filtered, and boil- ed in an open vessel, until the vapour ceases to blacken paper, on which characters have been traced with acetate of lead. The acid liquor thus obtained, when evaporated to a syrup, shoots on cooling into mamillary crystals, which have a very sour taste, and deliquiate in a moist atmosphere. Braconnot prefers obtaining the acid by the intermediation of lime rather than of oxide of lead, by which process he procures a larger pro- portion of acid.J In the juice of the sorbus, he finds that the peculiar acid is not pure, but mixed with malic acid. * Phil. Trans. 1815. f Ann. de Chim. et Phys. vi. t Ann. de Chim. et Phys. vi. 241. SECT. V. TARTARIC ACID. 163 The sorbic acid^wlien submitted to distillation, melts and yields acid vapours, and finally sublimes in white needle-shaped crystals, which are intensely sour, and are the acid somewhat altered. The watery solution of sorbic acid does not precipitate lime-water or barytes-water. From acetate of lead it throws down a white floc- culent precipitate, which, on standing, assumes a crystalline form. This is one of its most distinctive characters. It agrees, to a certain extent, with the tartaric acid in forming salts, which become less soluble by increasing their proportion of acid. But the capacity of saturation is greater in the tartaric acid, which saturates a quantity of base containing 11.94 of oxygen, while the sorbic saturates a quantity equivalent only to 11. The sorbates have been examined by Mr. Donovan, and more fully by Braconnot, whose memoir contains a detailed account of their pro- perties and composition. The sorbic acid has been analyzed by Vauquelin, by combustion with oxide of copper, and its composition is stated to be Hydrogen.......16.8 Carbon .......28.3 Oxygen.......54.9 100. Art. 5.—Tartaric Acid, and its Combinations. The tartaric acid is generally obtained from the supertartrate of pot- ash (common cream of tartar) by the following process: Let 100 parts of finely powdered cream of tartar be intimately mixed with about 30 parts of pulverized chalk. This is best done by grinding them together in a mortar, and passing the mixture through a sieve. Let the mixture be thrown, by spoonful, into eight or ten times its weight of boiling water; waiting for the cessation of the vio- lent effervescence, which is produced by each addition, before any more is thrown in. This method I find preferable to the entire solu- tion of the cream of tartar in the first instance, which requires a very large quantity of water. If it should appear, from the effect of the liquor on litmus paper, that the chalk has not been added in sufficient quantity, more may be gradually used, till the colour of the litmus is no longer reddened. By this operation, a quantity of insoluble tartrate of lime will be formed, which is to be allowed to subside, and washed, three or four times, with cold water. To the tartrate of lime, diffused through a sufficient quantity of water, concentrated sulphuric acid may be add- ed, equal in weight to the chalk which has been employed. The mix- ture may be allowed to stand for 24 hours, during which it should be frequently agitated. Assay' a little of the clear liquor, by pouring into it some solution of acetate of lead. A copious precipitate will be formed, which may either consist of tartrate of lead, or of a mixture 164 VEGETABLE SUBSTANCES. CHAT. NX. of tartrate with sulphate of lead. To determine this, add diluted nitric acid, which dissolves the tartrate, but not the sulphate. A small proportion of the latter is desirable, because the tartrate of lime can- not be wholly decomposed without an excess of sulphuric acid; but a large excess of that acid is injurious, from its re-acting on the tarta- ric acid, when heat is applied in the subsequent part of the process. The deficiency of sulphuric acid should be supplied by adding more; or a great redundance of it removed by the addition of a little chalk. The evaporation of the solution may now be carried on, in a manner precisely similar to that directed for the citric acid; and the crystals purified by a second solution and evaporation. The liquor remaining after the addition of chalk, consists of the neutral tartrate of potash. It may be decomposed by adding muriate of lime, till no farther precipitation ensues. An insoluble tartrate of lime falls down, which may be decomposed by sulphuric acid, in the way already directed. Or the tartrate of potash may be evaporated to dryness, and reserved for other purposes. If the tartrate of lime be formed by the first operation only, the product of crystallized acid amounts to between one-fourth and one-fifth the weight of the cream of tartar. But the decomposition by muriate of lime doubles the quan- tity of acid produced. Quicklime has been recommended as a substitute for chalk in this process; but I have never found that it could be employed with any advantage; for a quantity of caustic potash is set at liberty by its action, which dissolves the tartrate of lime, and prevents it from pre- cipitating. When chalk is employed for saturation, that part of the acid only is neutralized, which constitutes the super-salt; but with quicklime the operation is carried still farther, and the neutral tar- trate, also, abandons its acid. The tartaric acid forms regular crystals, the shape of which varies considerably according to the circumstances of their preparation. They require for solution five or six parts of water at 60° Fahrenheit; but are much more soluble in boiling water. The solution, like that of most other vegetable acids, acquires a mouldy pellicle by keeping. The crystals were found by Berzelius to consist of Real acid ....... 88.75 Water.......11.25 100. Bergman exposed tartaric acid to distillation with nitric acid, in the manner of obtaining oxalic acid, but without being able to pro- duce the latter acid. Hermbstadt, however, by using a very concen- trated nitric acid, succeeded in converting the tartaric into the oxalic acid, and from six drachms of the former obtained four drachms and two scruples of the latter. Westrumb, also, was successful in the same attempt, and adds that the tartaric acid may be changed into the acetic by digestion with water and alcohol. When distilled alone in a strong heat, the tartaric acid is decom- posed; it yields a quantity of dark-coloured acid liquor, which has SECT. V. TARTARIC ACID. 165 erroneously been supposed to be acetic acid; and a large quantity of combustible gas is obtained. From the experiments of Fourcroy and Vauquelin, it appears that the pyro-tartaric acid is a peculiar species. From the acetic, it differs in being less volatile and less odorous; in being crystallizable by eva- poration ; and in affording, with potash, a salt which precipitates ace- tate of lead. It is distinguished from the tartaric acid, in not occa- sioning any precipitate from the acetates of lime, of barytes, or of lead; and in not forming, with potash, an insoluble salt when the acid is in excess.—Influenced by the results of these experiments, the same chemists submitted the pyro-mucous and pyro-lignous acids to a fresh and rigid examination, which terminated in the conviction that they both consist of acetic acid, holding in combination a quantity of em- pyreumatic oil.* Tartaric acid has been analyzed by Gay Lussac and Thenard, and by Berzelius; and their results are contained in the following Table. One hundred parts consist, Carbon. Oxygen. Hydrogen. According to Gay Lussac, of . 24.050 . . 69.321 . . 6.629 ---------— Berzelius, of . . 35.98 . . 60.28 . . 3.74 The disagreement of these results arises, probably, from the omis- sion of part of the water of crystallization in the estimate of the two first-mentioned chemists. Tartaric acid unites with alkaline and earthy bases, and affords a distinct class of salts called tartrates. Tartrate of potash may be obtained by adding sub-carbonate of potash either to cream of tartar, or to the solution of the crystallized acid, till all effervescence ceases. According to Von Packen 120 grains of sub-carbonate require for saturation 112 of pure tartaric acid. Mr. R. Phillips finds that 100 parts of cream of tartar require for neutralization 43£ of sub-carbonate of potash. The resulting salt is Very soluble, and even deliquescent. It is composed, according to Berzelius, of Acid.....58.69.....100. Base.....41.31.....70.4 100. SlJPER-TARTRATE, OR BI-TARTRATE OF POTASH.--If into a Solution of the neutral tartrate, we pour a solution of tartaric acid, a white* powder falls down in great abundance, which is a compound of the neutral salt, and an additional quantity of acid. This is an example of the diminution of solubility, by an increased proportion of the acid ingredient of a salt The tartaric acid, in this proportion, has even so strong an affinity for potash, that it separates this alkali from the mineral acids. Thus by adding tartaric acid to the muriate of pot- ash, we obtain a precipitate of bi-tartrate of potash. * Annales de Chimie, lxiv. 42; or Nicholson's Journal, xxvi. 44 166 VEGETABLE SUBSTANCES. CHAP. XX. The substance, which is known in commerce under the name of tartar, is an impure variety of this salt When purified, it affords white crystals, the form of which has been described by Dr. Wollas- ton.* These crystals, by being reduced into powder, become the cream of tartar of the shops. Bi-tartrate of potash requires for its solution a very lar^je quantity of water, not less than 120 parts of water at 60° Fahrenheit or 30 at 212°. Hence its solution deposits the salt on cooling in such quanti- ty as amounts almost to precipitation. Bi-tartrate of potash, it is observed by Gay Lussact, acts, in many cases, like a simple acid, and even dissolves oxides that are insoluble in the mineral acids and in the tartaric acid. He proposes its use, therefore, in mineral analyses. From the experiments of Berzelius, its composition may be stated at Acid.....70.45.....100. Potash.....24.80.....35.2 Water.....4.75 100. This small portion of water appears to be essential to the salt; for it canno t be separated by heat, without decomposing the acid. When 100 grains of the salt are incinerated, so as to destroy the acid, the alkali obtained is exactly sufficient to neutralize 100 grains of the bi- tartrate; a proof that the potash in the acidulous salt is combined with twice as much acid, as in the neutral compound. By the destructive distillation of bi-tartrate of potash, Fourcroy and Vauquelin obtained, exclusively of acid and charcoal,! of Pure dry sub-carbonate of potash . . . 350. Tartrate of lime......... 6. Silex ............ 1.2 Alumine............ 0.25 Iron and manganese ....... 0.75 Tartrate of potash and soda may be formed by neutralizing 24 parts of cream of tartar with 18 parts of sub-carbonate of soda. The resulting salt is well known, from its being employed in medicine under the name of Rochelle Salt. It requires, for solution, about • five parts of cold water, but much less at the boiling temperature. From the experiments of Vauquelin it appears to be composed of 54 parts of tartrate of potash, and 46 parts of tartrate of soda. The eartht tartrates have no particularly interesting properties. With the exception of those of magnesia and alumine, they are inso- luble. Tartrate of lime consists of 77 \ acid and 22£ base; and tar- trate of lead of 37£ acid and 62£ oxide. * Thomson's Annals, x. 37. t Ann. de Chim. Lxiv. 48. f Ann. de Chim. et Phys. iii. 281. SECT. V. MOROXYLIC ACID. 167 Art. 6.—Benzoic Acid. This may be obtained from a substance termed gum benzoin or benjamin. The process consists in pulverizing a pound and a half of gum benzoin with four ounces of quicklime, and then boiling them For half an hour in a gallon of water, constantly stirring. When cold, the clear liquor is poured off; and what remains is boiled, a second time, in four pints of water, the liquor being poured off as before. The mixed liquids, after being boiled to one half, are filtered through paper; and muriatic acid is gradually added, until it ceases to pro- duce a precipitate. Finally, after having decanted the liquid, the powder is dried in a gentle heat, and sublimed from a proper vessel, placed in a sand-bath, into cones of writing paper. Benzoic acid has a peculiar and not disagreeable odour. Its crystals are soft and cannot be reduced to powder. It is volatilized, in white fumes, by a moderate heat. It requires for solution about 24 times its weight of boiling water, which, as it cools, lets fall 19-20ths of what it had dissolved. It is soluble in alcohol. The composition of this acid has been ascertained by Berzelius, as follows: Carbon.......74.41 Oxygen.......20.43 Hydrogen......5.16 100. The compounds, which it forms with alkaline and earthy bases, called benzoates, are fully described by Hisinger in the 40th volume of the Philosophical Magazine, and by Berzelius in the 90th volume of the Annales de Chimie. Art. 7.—The Oxalic Acid Is also found native in the juice of sorrel, forming a quadroxalate, and, as appears from the experiments of Vauquelin, in the Rheum Palmatum. Art. 8.—Moroxylic Acid. Mr. Klaproth has lately discovered a new acid, combined with lime and extract, in a saline mass, which exudes from the trunk of the white mulberry, morus alba, L. It was collected, by Dr. Thomson, from trees in tne botanic garden at Palermo; and seems peculiar to those individuals that grow in hot climates. Its characters have not been fully ascertained. From its origin, it has been called, by Klaproth, moroxylic acid, and its compounds moroxylates.* * See Nicholson's Journal, 8vo. vii. 129. 168 VEGETABLE SUBSTANCES. CHAP. XX. Art. 9.—The Laccic Acid (Which, in strictness, should be classed among animal acids) is obtained from the white lac of Madras, from which, when liquefied, it oozes out in drops. It is in the form of a reddish liquor, having a slightly bitter saltish taste; but, on evaporation, it shoots into acicular crystals. It may be raised in distillation. It combines with carbonate of lime and soda, and excites effervescence. It precipitates barytic salts; assumes a green colour with lime-water, and a purplish one with sulphate of iron. A full account of its properties, and of those of the substance that affords it, may be found in Dr. Pearson's paper in the Philosophical Transactions, 1794. Art. 10.—Phosphoric Acid Exists in almost all vegetable substances, and particularly in all the varieties of grain, not however in a free state, but in combination chiefly with potash and lime. Hence the coal of almost all kinds of seeds affords phosphorus by distillation, a fact originally observed by Margraaf, and confirmed by the experiments of Saussure.* Art. 11.—The Prussic Acid Has been discovered in water distilled from bitter almonds, from the leaves of the laurel, and from peach blossoms, and in the bark of theprunus padus. When the distilled liquid is neutralized with pot- ash, a crystallizable salt is obtained, the solution of which throws down prussian blue from the salts of iron. Vauquelin, also, obtained prussic acid by distilling water, with a very gentle heat, from the kernels of apncots.t The properties of the prussic acid will be de- scribed in the chapter on animal products. Art. 12.—Boletic Acid. This acid was first obtained by Braconnot, from the juice of the boletus pseudo-ignarius.% The juice was boiled? filtered, and evapo- rated cautiously, to the consistence of syrup. This was repeatedly digested in alcohol; the insoluble portion was dissolved in water, and precipitated by nitrate of lead. The white precipitate, thus ob- tained, was mixed with water, and decomposed by sulphuretted hydro- gen gas. The liquid, being evaporated,yielded crystals of boletic acid. The crystals, when purified by solution in alcohol, and re-crystal- lization, are white, and have the shape of irregular four-sided prisms. * Nicholson's Journal, xxv. 279. t Annales de Chimie, xlv. 206. * Thomson's Annals, ii. 469. SECT. V. RHEUMIC ACID. 169 They require 180 parts of water at 68° to dissolve them, and 45 parts of alcohol. The aqueous solution reddens vegetable blues, pre- cipitates nitrate of lead; and throws down the peroxide, but not the protoxide of iron from its solutions. Nitrates of silver and mercury afford with it a white precipitate. With the alkalies and earths, it unites, and forms a class of salts, which may be called boletates. Art. 13.—Acid discovered by Braconnot. An acid of a peculiar nature was discovered some years ago, by Braponnot, in vegetable substances,* which have undergone the acetous fermentation. He first procured it from rice, which had been left, mixed with water, at a gentle heat, till it had become sour. When drained in a woollen bag, a liquid passed through, which gave acetous acid by distillation. Continuing the evaporation, almost to dryness, a gummy substance was left, having a decidedly acid taste. This was digested in alcohol, and the solution, evaporated to the con- sistence of syrup, became a granular crystalline mass, with a strongly acid taste. It still, however, contained a salt with base of lime. The excess of acid was, therefore, neutralized by oxide of zinc; the salt obtained was decomposed by barytes; and the barytes precipitated by sulphuric acid. The liquor, being now carefully evaporated to a syrup, left an uncrystallizable, almost colourless, acid, nearly as strong to the taste as the oxalic. With potash and soda, this acid gave deliquescent salts, soluble in alcohol; and, with ammonia, a crystallizable salt It formed, with lime, a salt, which required 21 times its weight of water for solution; with strontites, a salt soluble in 8 parts of water; with barytes a gummy substance; and, with magnesia, small granular crystals, which were not soluble in less than 25 parts of water. Dr. Thomson, in the 5th edition of his System of Chemistry, has proposed for this acid the name of Zumic Acid, from tpm, leaven. Art. 14.—Rheumic Acid. A new acid was announced by Mr. Henderson as existing in the stems of garden rhubarb; but as he candidly admits the possibility of fallacy, and as his discovery has not been confirmed by the subse- quent experiments of Mr. Donovan, it may be sufficient to refer to their respective papers in Thomson's Annals, viii. 247, and ix. 103. • 86 Ann. de Chim. 84. Vol. II.—Y 170 VEGETABLE SUBSTANCES. UHAP. XX. Art. 15.—Kinic Acid. When yellow Peruvian bark is macerated in cold water, and the infusion concentrated and set apart for some time in an open vessel, a salt crystallizes from it in square or rhomboidal plates; having no taste; soluble in five parts of cold water; and insoluble in alcohol. From this salt, first obtained by M. Deschamps, jun. of Lyon, Vau- quelin separated the lime by oxalic acid, and concentrated the re- maining liquor to the consistency of a syrup, which he set aside for a week, when, on touching it with a glass rod, it crystallized at once into divergent plates. Its colour was slightly brown ; its taste ex- tremely acid and rather bitter; and it was readily soluble in water. It is distinguished from other vegetable acids by its forming a soluble salt with Jime, and by its not precipitating silver or lead from their respective solutions.* SECTION VI. Fixed Oils. 1. These oils are obtained, by pressure, from certain vegetables; as the olive, the almond, linseed, poppy-seed, rapeseed, &c. 2. As thus obtained, they are generally found combined with mu- cilage, to the spontaneous decomposition of which is chiefly owing the change that oils undergo by keeping, called rancidity. 3. They are usually coloured, but may be deprived of colour by digestion with charcoal. 4. Their specific gravity is commonly between that of alcohol and water. Hence they sink in the former, and float on the surface of the latter fluid. They cannot, by strong agitation, be brought to com- bine with water, but always separate on standing. When the seeds, however, which contain them, are rubbed with water, especially if a little sugar be added, an imperfect solution is obtained called an emul- sion. On adding an acid to this, the oil is detached, and floats on the surface. 5. The expressed oils of linseed and of olives, Mr. Brande finds, are very sparingly soluble in alcohol of specific gravity .820. Four ounce measures of alcohol dissolve a drachm of linseed oil. Castor oil is perfectly soluble in every proportion in alcohol of .820, but not in weaker alcohol.t 6. Four ounce measures of sulphuric ether of specific gravity .7563 are capable of dissolving a fluid ounce and quarter of oil of almonds; a fluid ounce and half of olive oil; and almost any proportion of cas- tor oil. (Brande.) 7. Some of the fixed oils congeal, or become solid, by a very mode- rate reduction of their temperature; and others, as palm oil, are per- manently thick, or form a soft solid like butter, at the temperature of the atmosphere. * Ann. de Chim. lix. 162. f Phil. Trans. 1811, p. 265. SECT. VI. FIXED OILS. 17.1 8. They unite with alkalies, and form soap. The soap, however, which is commonly manufactured in this country, is made by com- bining the fixed alkalies with tallow. Of the processes followed in the preparation of soap, both from vegetable and animal ois, an excel- lent description is given in Messrs. Aikins' Chemical Dictionary. A memoir of Chevreul on the Combination of Alkalies with Fat may, also, be consulted in the 88th and 94th volumes of the Annales de Chimie,&nd a paper of Colin on the manufacture of hard soap is con- tained in the 3d vol. of Annales de Chimie et de Physique. Soap is readily soluble in water. The solution is decomposed by acids, and by neutral salts with earthy bases. Hence hard vyaters, which contain earthy salts, curdle soap; their acid uniting with the alkali of the soap, and setting the oil at liberty. When a strong solution of soap is mixed with one of a metallic salt, a substance is formed termed a metallic soap. The alkali unites with the acid of the salt, and the oil with the metallic oxide. 9. Fixed oils dissolve sulphur, and form a kind ot balsam, lney act also on phosphorus. 10 Their properties are changed by boiling with metallic oxides, those of lead for example. The mucilage unites with this oxide, which probably gives up a portion of its oxygen to the oil, and the oil is rendered drying, and fit for the use of the painter. If the oxide be added in larger proportion, the mass, when cold, composes a P YtFixed oils, when distilled with a gentle heat, yield defiant and carburetted hydrogen gases. A portion of the oil passes over, also, without decomposition. Hence they cannot be considered as abso- lutely fixed, but have received this name chiefly from a comparison with the essential or volatile oils. By repeated distillations the whole of any fixed oil may finally be changed into gaseous matter. 12 Fixed oils are extremely combustible; and when burned in an apparatus, adapted for collecting the products of their combustion, they afford carbonic acid and water. It may be inferred, therefore, that they are composed of carbon and hydrogen, the proportions ot which, according to the experiments of Lavoisier, are 79 ot the former and 21 of the latter. From this statement, however, oxygen is ex- cluded, which it is probable all fixed oils contain. Its presence in- deed is almost demonstrated by Sir H. Davy's experiments. V\ hen a °4obule of potassium, he observes, is introduced into any of the. faxed oifs made hot, the first product is pure hydrogen, which arises trom the decomposition of the water absorbed by the crust of potash during exposure to the atmosphere. If the globule be previously freed from this crust, carburetted hydrogen is disengaged, coaly matter deposited, and a soap is formed. To generate the alkali, however which this soap contains, oxvgen must necessarily have been supplied by the decomposition of the oil. Sir H. Davy has also found, in the products of their destructive distillation by heat, a proportion of water, to the production of which oxygen is essential* But decisive proof of the ' Philosophical Transactions, 1808 172 VEGETABLE SUBSTANCES. OIIAP. XX. presence of oxygen in oil has lately been supplied by Gay Lussac and Thenard's analysis of olive oil, which they find to be composed of Carbon..........77.213 Oxygen..........9.427 Hydrogen.........13.360 100. The analysis may also be stated as follows: Carbon..........77.213 Oxygen and hydrogen in the propor-^ in?to tions to form water .... $ Excess of hydrogen ...... 12.075 100. 13. Nitric acid acts with great energy on the fixed oils. In a small proportion, its chief effect is to render them thicker. When distilled together with a larger proportion of acid, the oil is decomposed, and nitrous gas disengaged; oxalic acid remaining in the retort. Red and smoking nitric acid, when suddenly mixed with a fixed oil, espe- cially with the addition of a little sulphuric acid, occasions a violent combustion. Oxymuriatic acid gas, passed through them, thickens them, and renders them tenacious like wax. 14. The fixed oils have a singular property, which has led some- times to serious accidents. When mixed with lamp black, or with any light kind of charcoal, and even with several vegetable sub- stances, as cotton, wool, or flax, the mixture, after some time, heats spontaneously, and at length bursts into flame. This combustion has sometimes been observed to take place in the waste cotton, employed to wipe the oil from machinery; and has probably occasioned many of the dreadful fires, which have happened in cotton-mills, and for which no adequate cause could be assigned.* SECTION VII. Volatile or Essential Oils. With the exception of the oil from the rinds of the lemon and the orange, which are obtained by expression, the essential oils are pro- cured, by distilling the vegetables that afford them, with a proper pro- portion of water. The oil either sinks to the bottom, or swims on the surface of the water, according to its specific gravity; but if the distilled water be long kept, Bucholz finds that the oil is converted into mucilage. 1. These oils have a penetrating smell, and an acrid taste. 2. They are volatilized by a gentle heat. Hence the spot, which they leave on paper, may be removed by holding it at a small dis- tance from the fire; but the stains from expressed oils are permanent. * See Journal of Science, &.c.v. 367. SECT. VII. ESSENTIAL oils. 173 3. They can, with difficulty, be brought to unite with alkalies. 4. They are soluble in alcohol. 5. They do not unite with water. With the intervention of a little sugar, however, they are combinable, in small proportion, with water. 6. When nitric acid is poured upon these oils, especially if it has been previously mixed with one-fifth or one-sixth of sulphuric acid, the mixture bursts into a violent flame. This experiment requires caution, as the inflamed oil is apt to be scattered about 7. Several of them detonate, when rubbed with hyper-oxymuriate of potash, and take fire when poured into oxymuriatic acid gas. 8. Essential oils are thickened by long exposure to air. This is owing, as Dr. Priestley first proved, to their absorbing oxygen, a fact which accounts, in some degree, for the injurious effects of fresh painted rooms. 9. Potassium decomposes the volatile oils when heated. Alkali is formed; a small quantity of gas is evolved; and charcoal is deposited. Camphor resembles the essential oils in many properties, but is not inflamed by nitric acid, which converts it in to an acid, distinguished by peculiar properties,* and termed the camphoric acid. For this purpose, camphor is repeatedly distilled with four times its weight of nitric acid, till about 20 parts of acid have been employ- ed. At each operation, the portion of camphor, which sublimes and escapes decomposition, is to be returned into the retort. The acid is susceptible of crystallization; the crystals effloresce in the air, and are soluble in 100 times their weight of cold, or in 11 times their weight of boiling water; they are combustible; and burn with a dense, aromatic smoke; they melt and sublime with a gentle heat, and dis- solve in tlie mineral acids. They dissolve also in about six times their weight of cold alcohol, or to any amount in boiling alcohol; and are not precipitated by water. With alkalies and earths they com- pose a class of salts called camphorates. Fifty grains of the acid are saturated by 28 of carbonate of lime = 15.7 pure lime. A singular substance, very much resembling camphor in its sen- sible and chemical properties, maybe obtained by passing muriatic acid gas through essential oil of turpentine, which absorbs about a third of its weight The oil of turpentine becomes thick, from an abundance of a white crystalline substance which forms in it. This may be separated by draining off the liquid ; and is found rather to exceed the weight of the essential oil submitted to experimentt It is white, crystalline, granular, volatile in a moderate heat, and has very much the smell of camphor. By exposure to the air, it soon loses its property of reddening vegetable blue colours. As to the theory of its production, Thenard is of opinion that no decomposition of the oil of turpentine takes place; but that the muriatic acid unites to it entire. Ordinary camphor of commerce, he supposes, from ana- logy, to be a compound of an essential oil and a vegetable acid. * Bucholz, 84 Ann. de Chun. 301. | Thenard, Memoires d'Arcueil, ii, 174 VEGETABLE SUBSTANCES. CHAP. XX- SECTION VIII. Resins. Resins are the inspissated juices of certain plants, and are gene- rally obtained by wounding their bark. Copal, or lac, may be taken as an example. Dragon's blood, guaiacum, sandarach, labdanum, com- mon resin, and turpentine, are also varieties of this substance. 1. They have generally a yellow colour, and are imperfectly trans- parent In specific gravity they exceed water. 2. They are dry, brittle, and extremely inflammable. • 3. They dissolve in alcohol, ether, and essential oils; but not at all in water, which even precipitates them from the foregoing solvents. 4. Both acids and alkalies act on them; the pure alkalies most re- markably. The alkaline solution is clear, and may be diluted with water without decomposition; but acids immediately precipitate the resin. By mixing it with a solution of a metallic salt, the oxide is precipitated in combination with resin. 5. By long continued and repeated digestion with nitric acid, the resins afford a deep yellow solution, which has the property of pre- cipitating animal gelatine, and• agrees, therefore, with tannin. No oxalic acid is obtained by this process, a circumstance which distin- guishes the resins from all other vegetable substances. 6. Concentrated sulphuric acid dissolves the powdered resins. If the solution be digested in a moderate heat, sulphurous acid is first evolved; in a few days this ceases; and a black porous coal remains, equal to between a fifth and a third the weight of the resin which has been employed; whereas, by incineration in close vessels, scarcely l-100th part their weight of coal is obtained. Acetic acid dissolves resins, which are precipitated from it by the addition of water. 7. Resins are the basis of varnishes, and are much used in medicine. Balsams are liquid resins, holding in combination a proportion of Benzoic acid.- Gftt.ii Resins, along with resin, have an admixture of extractive matter. They dissolve partly in water, and partly in alcohol. They are almost solely used in medicine. Asafcetida, gum-ammoniac, aloes, gamboge, myrrh, opium, &c. are varieties of gum-resin.t Guaiacum was observed by Mr. Hatchett to differ from other resins in giving oxalic acid by the action of nitric acid, and very little tannin. In other respects, also, it has been since shown, by Mr. Brande, to possess properties that do not agree with those of resins in general.! Amber is a resin possessed of peculiar properties. By distillation it yields a distinct acid, called the succinic.—To prepare this acid, let a glass retort be half filled with powdered amber, and the remain- * See 69 Ann. de Chim. 293. f The reader, who may wish for further information respecting the gum- resins, may consult Braconnot's Memoir in the 28th vol. of Nicholson's Jour nal; and Pelletier's in the 80th vol. of Annales de Chimie. * Philosophical Transactions, 1806. ^ECT. IX. FECULA. 175 der with fine dry sand.* Lute a receiver, and apply a gentle heat A portion of water first comes over, which is succeeded by a weak acetic acid. The succinic acid then sublimes; but is contaminated by a mixture of oil. It may be purified by solution and crystalliza- tion; and it then forms transparent white shining crystals, having the form of triangular prisms. They are soluble in 24 times their weight of water, and in boiling alcohol. The solution reddens the blue colour of turnsole, but not that of violets, and has an acid taste. It combines with alkalies, &c. and forms succinates, the most import- ant of which is the succinate of ammonia. This salt decomposes all the solutions of iron; and affords an insoluble precipitate, composed of succinate of iron Hence it is highly useful in the analysis of mi- neral waters. Berzelius states the composition of the succinic acid as follows: Hydrogen......4.512 Carbon.......47.600 Oxygen.......47.888 100.t SECTION IX. Farina, Starch, or Fecula. Starch may be obtained from the flour of most varieties of grain, from the roots of the potato, and from almost every part of vegeta- bles, by a very simple process. The grain in the state of fine powder, or the root well rasped, is to be washed with a quantity of cold water which becomes turbid, and, if the fecula is white, milky. The fecula, however, is not dissolved, but merely suspended mechanically; and, after separating the fibrous and grosser parts by a sieve, it subsides to the bottom of the vessel. The liquid, which contains the soluble parts of the vegetable, is to be decanted, and the farina to be washed by repeated affusions of cold water. It may, afterwards, be dried in a gentle heat. From the analysis of Dr. PearsonJ we learn that 100 parts of the fresh potato root, deprived of skin, afford Water......68 to 72 Meal.......32 to 28 100 100 * Useful directions for this process are given by Robiquet and Colin, Ann. de Chim. et Phys. iv. 326. f 94 Ann. de Chimie, 189. i Repertory of Arts, Hi. 383. The analysis of several varieties of the potato by Lampadius may be seen in Thomson's Annals, v. 39. 176 VEGETABLE SUBSTANCES. OIIAP. XX. The meal is composed of three distinct substances, viz. Fecula......15 to 17 Fibrous matter .... 8 to 9 Kxtract or mucilage . . 5 to 6 28 32 Some useful information respecting the quantity of fecula in differ- ent varieties of the potato, and the methods of separating it, has been given by Mr. Skriinshire in the 21st volume of Nicholson's Journal. Its proportion in sound and unsound grain, and the causes of un- soundness in corn and flour, have been ably investigated by Mr. E. Davy, in a memoir published in the 49th volume of the Philosophical Magazine. Of rice, it constitutes, according to Braconnot, from 83 to 85 per cent* Common starch, though not absolutely free from gluten, may be taken as an example of fecula. It will be found to have the following qualities: 1. It is not soluble in water, unless when heated to 160°; and if the temperature be raised to 180°, the solution coagulates into a. thick tenacious transparent jelly. By evaporation at a low heat, this jelly shrinks, and at length forms a transparent brittle substance closely resembling gum. The solution of starch in a large quantity of water is precipitated by Goulard's extract of lead; but not by any other metallic salt. 2. Farina is insoluble in alcohol, and in ether. S. Pore liquid alkalies act on starch, and convert it into a trans- parent jelly. The compound is soluble in alcohol. 4. Sulphuric acid dissolves it slowly; sulphurous acid is evolved; and so much charcoal is disengaged, that the vessel may be inverted, without spilling its contents. 5. Nitric acid, at the temperature of the atmosphere, acts on starch, and dissolves .it; but no oxalic acid appears subsequently, unless heat be applied. Hot nitric acid is decomposed by starch, and oxalic acid is generated. 6. Starch, as it exists in grain, is spontaneously convertible into sugar. On this property is founded the process of malting. The grain, from which malt is most commonly prepared, is barley. In this grain, Proust has discovered, beside the ingredients of wheat, a peculiar substance, nearly resembling saw-dust, in its external cha- racters, to which he has given the name of hordein.\ This substance may be separated from starch by the action of hot water, in which it is quite insoluble. During the process of malting, its proportion is considerably diminished, and it appears to be partly converted into sugar, or into starch, as will appear from the following comparative analysis of malted and unmalted barley. * Ann. de Chim. et Phys. iv. 383. f Ann. de Chim. et Phys. v. 337. SECT. IX. FECULA. 177 In 100 parts In 100 parts of bailey. of malt. Resin..... 1.....1 Gum .....4.....15 Sugar.....5.....15 Gluten.....3.....1 Starch.....32.....56 Hordein . ... 55.....12 It appears, then, that the formation of malt consists in the increase of gum, sugar, and starch, and the diminution of gluten and hordein. The starch, that remains after malting, is found changed in its proper- ties; for it does not as before yield a viscid paste, capable of gelati- nizing on cooling. The process of malting, is not, however,essential to the production of alcohol from grain; for in the Scotch distilleries it has long been common to use a large proportion of unmalted barley; and M. Clement, by direct comparative experiments, obtained equal quantities of alcohol by fermenting the infusions of equal weights of malted and of unmalted grain.* The spirit obtained from unmalted barley has a peculiar odour, which is owing to its holding in solution a yellow solid oil, separable by careful distillationt of the alcohol. The loss of weight sustained by grain in malting, which Proust states at one-third, Dr. Thomson asserts is greatly over-rated, and that it did not on an average of 50 processes, carried on under his inspection, exceed one-fifth. The hordein of Proust, he considers as starch under some modification, w'nich is changed, by malting, partly into true starch, and partly into sugar.;); Another method of converting starch into sugar was discovered by M. Kirchoff of St. Petersburg. The change is effected by the action of sulphuric acid, which is boiled, for many hours, with starch and water. The process has been successfully repeated by several per- sons, and among the rest by M. Vogel§ and by Dr. Tuthill of Lon- don. || The latter digested a pound and half of potato starch (ob- tained from 8| pounds of potatoes) six pints of distilled water, and a quarter of an ounce by weight of sulphuric acid, in an earthen vessel, at a boiling heat; the mixture being frequently stirred and kept at an uniform degree of fluidity by the supply of fresh water. In 24 hours there was an evident sweetness, which increased till the close of the process; at the end of 34 hours, an ounce of finely powdered charcoal was added, and the boiling kept up two hours longer. The acid was then carefully saturated by recently burned lime; and the boiling continued for half an hour, after which the liquor was passed through calico, and the substance, remaining on the drainer, washed repeatedly with warm water. This, when dry, weighed seven-eighths of an ounce, and consisted of charcoal and sulphate of lime. The clear liquor, being evaporated to the consistence of syrup, and set aside, was in eight days converted into a crystalline mass, resembling common brown sugar with a mixture of treacle. The saccharine • Ann. de Chim. et Phys. v. 422. \ Thomson's Annals, xii. 35 i Annals of Philosophy, x. 389. 4 Ann. de Chim. 1. 82. i Nich. Jour. vol. 3^. Vol. II.—Z 178 VEGETABLE SUBSTANCES. CHAP. XX. matter, which Dr. Tuthill judged to be intermediate between cane sugar and grape sugar, weighed one pound and a quarter. By fer- menting one pound of this substince in the usual manner, and distil- ling and rectifying the product, fourteen drachms by measure of proof spirit were obtained. The differences between starch sugar, and common sugar from the sugar cane, have been pointed out by Nasse. Starch sugar assumes the form of spherical crystals like honey. It is not so hard, nor so sweet, nor so soluble in water, as common sugar. When it is digest- ed with an alkaline cabonate, a precipitation of mucilage takes place: and the same precipitation is occasioned from a solution of starch sugar by muriate of tin. The solution of starch suger ferments with- out the addition of yeast, which is not the case with common sugar.* It had been shown, by Professor de la Rive of Geneva, that in the formation of sugar from starch, no gas is evolved; that the alteration of the starch goes on in close vessels without the contact of air; and that no part of the sulphuric acid is either decomposed, or united to the starch as a constituent These results have been confirmed by the experiments of Saussure.t who has shown, also, that the sugar which is obtained, exceeds, by about one-tenth, the original weight of the starch. He concludes, therefore, that the conversion of starch into sugar is nothing else than the combination of starch with water in a solid state, a conclusion which is strengthened by the results of analyzing those two substances, viz. • Carbon. Oxygen. Hydr. Azote. In starch were found.....45.39 I 48.31 I 5.90 I 0.40 In starch sugar.......37.29 j 55.87 | 6.84 | 0. In 100 parts of starch, the oxygen and hydrogen are sufficient to form 50.48 parts of water, with an excess ot 3.76 oxygen. In starch sugar, the same principles exist in quantities sufficient to compose 58.44 parts of water, being an increase of nearly 8, and there is still an excess of 4.26 parts of oxygen. 7. Starch is said by Dr. Thomson to be capable of entering into chemical union with tan.J Of the existence of such a combination, however, Dr. Bostock has found reason to doubt§ 8. Starch has been analyzed by Gay Lussac and Thenard, and by Berzelius, and the near coincidence of their results, obtained by dif- ferent methods, is a strong presumption in favour of their accuracy. It consists, Carbon. Oxygen. Hydrogen. According to Gay Lussac, of . . 43.55 . . 49.68 . . 6.77 -------------Berzelius, of . . 43.481 . . 48.455 . . 7.064 9. When strongly heated, starch becomes first yellow, and after- wards a reddish brown; it softens, swells, and exhales a penetrating smell. If the process be stopped, a substance is the result, which is employed by calico-printers under the name of British gum. This * Thomson's Annals, vii. 47. f Thomson's Ann. vi. 424. t Nicholson's Journal, 8vo. ix. 74. v Mch. Journ. xviii. 3o. SECT. X. GLUTEI*. 179 substance, however, Vauquelin finds, is not a true mucilage; for with nitric acid it gives only oxalic acid, and no mucous acid. 10. When starch is distilled in close vessels, it yields an acid, wnicii has been called the pyromucous, but which, in fact, is nothing more than vinegar, with an admixture of empyreumatic oil. 11. When starch and iodine are triturated together, both ma dry state, the starch assumes a violet tint, which passes to blue or to black, according to the proportions that are employed. The colour of this toduret or iodide of starch is reddish, if the starch be in excess; a beautiful blue, when the two bodies are in due proportion; and black, when the iodine prevails. This compound is soluble in diluted sul- phuric acid, and the liquor is of a fine blue colour. Concentrated sulphuric acid, also, dissolves it, and the solution is brown, but passes to a beautiful blue on the addition of water. Jhere is( also a sub- ioduret of starch, which is white, but becomes blue by the action ot almost any acid.t SECTION X.. Gluten. Gluten may be obtained from wheat-flour, by a very simple pro- cess. The flour is first to be formed, by the gradual addition of a small quantity of water, into a soft and ductile paste. This is to be washed by a very slender stream of water, and, at the same time, to be constantly worked between the fingers. The water carries off the sLrch, andV some time is rendered milky. When lt passes off transparent the washing may be discontinued; and the pure gluten remains in the hands. The following are the properties of gluten: 1 It is of a erey colour, and has so much elasticity, that, when drawn out, it recovers itself like elastic gum. It has scarcely any taste, and does not melt or lose its tenacity in the mouth. 2. When exposed to a gentle heat, it dries very slowly, and be- comes hard, brittle, semi-transparent of a dark brown colour, and somewhat like glue. When broken it has the fracture of glass. In this state it is insoluble in water. nni„>KP 3. AVhen kept moist, it ferments and undergoes a sort ot putrefac- tion, emitting a very offensive odour. At the same time a portion ot acid is developed, which is perceivable by its smell, and which con- siderably retards the putrefaction of the gluten. In this circumstance, chiefly, it differs from animal gluten. 4. When suddenly heated, it first shrinks; then melts, blackens, and emits a smell like that of burning horn. By distillation in close vessels, it yields a portion of water impregnated with carbonate ot * 80 Ann. de Chim. 317. See also Thomson's Annals, v. 38, and Ann. de Chf Colin and Gaultier de Claubry. 90 Ann. de Chim. 100. 180 VEGETABLE SUBSTANCES. L'UAl'. XX. ammonia; a considerable quantity of brown fetid thick oil; solid sub- carbonate of ammonia; and carburetted hydrogen gas. These pro- ducts resemble, very closely, those of animal substances. 5. It is generally described to be insoluble in water, in alcohol and in ether. After fermentation, it is partially soluble in alcohol, and the solution maybe applied to the purposes of varnish. From the recent experiments of Dr. Bostock, a gluten appears, however, by long diges- tion, to be partly soluble in water. The solution is precipitated by acetate and super-acetate of lead, by muriate of tin, and by other re- agents.* 6. All acids dissolve it, and alkalies precipitate it, but considerably changed, and deprived of its elasticity. It undergoes a similar change when dissolved in pure alkalies, and precipitated by acids. 7. It exists most abundantly in wheat-flour, of which it constitutes about one-fourth, and is essential to its soundness; but it is found, also, in various vegetable juices.t Another ingredient, which was long supposed to be peculiar to animal products, viz. albumen, has been discovered in the emulsive seeds. In the almond, for instance, 30 per cent, have been found, of a substance precisely resembling animal curd.| SECTION XI. Caoutchouc, or Elastic Gum. Caoutchouc is chiefly the product of two trees, which are the growth of Brazil; the Hoevea Caoutchouc and Jatropha Elastica. When the bark of these trees is wounded, a white milky juice flows out, which speedily concretes in the air into an elastic substance; and, when the juice is applied in successive coats, upon clay moulds, it forms the globular bottles, which are brought to this country. By an immediate and careful seclusion from air, the juice may be pre- served some time from concreting, and has occasionally been brought to Europe in a liquid state. But even, when thus preserved, a part of it in the course of time, passes to a solid form. If it could easilybe imported in a fluid state, it would be invaluable, from its application to the rendering cloth, leather, and other substances impervious to water. 1. Caoutchouc is inflammable, burning with a bright flame in at- mospherical air, and with still greater brilliancy in oxygen gas, or in oxy-muriatic gas. 2. It is insoluble in water and in alcohol. If long slips of caout- chouc, however, are tied spirally round a glass or metal rod, and boiled for an hour or two, the edges cohere, and a hollow tube is formed. * Nicholson's Journal, xviii. 34. j- See Proust on the Green Fecula of Vegetables, Nicholson's Journal, 8vo. iv.273. 5 t Thomson's Annals, xii. 39. SECT. XII. WOODY FIBRE. 181 3. Caoutchouc is soluble in ether; not, however, in the ordinary state of this fluid as it is found in the shops. To render ether a fit solvent of this substance, it should be purified bv washing it with water, in the manner to be hereafter described. The solution may be applied to the purpose of forming tubes or vessels of any shape. The principal difficulty in using it arises from the great volatility of the ether, in consequence of which the brushes, or other instruments, by which it is applied, are soon clogged up, and rendered useless. 4. Caoutchouc is soluble in volatile oils; but when they have evaporated, they leave it in a glutinous state, and deprived of much of its elasticity." Petroleum dissolves it, and, when evaporated, leaves it unchanged. One of the most useful solvents, however, of caoutchouc, appears ^o be the cajeput oil, a substance lately admitted into the Pharmacopoeia of the London College of Physicians. A thick and glutinous solution is obtained, from which alcohol detaches the essen- tial oil. The caoutchouc floats on the surface in a semi-fluid state, but soon hardens, and regains its elastic powers on exposure to the atmosphere. To this process, the chief objection is the expensiveness of the solvent 5. Caoutchouc is acted on by alkalies; and, when Steeped in them for some time, loses its elasticity. 6. The sulphuric acid is decomposed by it; sulphurous acid is dis- engaged; and charcoal remains. Nitric acid acts on it with the as- sistance of heat, nitrous gas is formed; and oxalic acid crystallizes from the residuum. 7. When distilled it gives ammonia, and hence may be inferred to contain azote. A large quantity of defiant gas and of very dense car- buretted hydrogen, which burns with a remarkably bright flame, are at the same time evolved. SECTION XII.. The Woody Fibre. After removing all the soluble parts of wood, first by long boiling in water, and then by digestion in alcohol, a fibrous substance is ob- tained, to which, by some chemists, the name of Lignin has been given. From whatever variety of wood it may have been procured, its properties appear to be uniformly the same. 1. It is perfectly destitute of taste, smell, and colour. In specific gravity, it is generally inferior to water. 2. It is insoluble in water,at all temperatures. 3. The pure fixed alkalies act on the woody fibre, and render it soft, and of a brown colour. 4. Concentrated sulphuric acid immediately blackens it and, after sufficient digestion, converts it into charcoal. 5. Nitric acid decomposes it with the assistance of heat; and oxalic, malic, and acetic acids, are formed. 182 VEGETABLE SUBSTANCES. CHAP. XX. 6. When exposed to heat, it affords an acid called the pyroligneous, which has been lately proved to be identical with the acetous. This acid holds in combination a quantity of essential oil, from which it can with great difficulty be freed, and, also, a small proportion of am- monia. From the last mentioned product, it follows that the woody fibre must contain nitrogen. The charcoal, which remains in the re- tort, is greatly superior to that procured by the ordinary process; and hence distillation in iron cylinders has been, for some time past, practised as the best method of obtaining charcoal for the manufac- ture of gunpowder. 7. The woody fibre, by exposure to the atmosphere in a perfectly dry state, does not undergo any change. The action of the air upon it, however, when moistened, converts it, through various shades of colour, to a black mould. If the process be carried on in a confined portion of oxygen gas, carbonic acid is formed. When excluded from the air, even moist wood shows very little tendency to decomposition. Gay Lussac and Thenard have analysed, by their new process, the wood of oak and beech. The wood was taken from the most compact part of a log, reduced to a fine powder by a file, then sifted and wash- ed in succession, with water and alcohol; and finely dried, before its admixture with oxymuriate of potash. Carbon. Oxygen. Hydrogen. 100 parts of Oak contain 52.53 . . 41.78 . . 5.69 -----------Beech ---- 51.45 . . 42.73 . . 5.82 In both, the oxygen and hydrogen are in the proportions required to form water, and there is no excess of oxygen to acidify any part of the carbon. SECTION XIII. Colouring Matter. I. The colouring matter of vegetables presents a considerable va- riety in its relation to chemical agents, depending on the diversity of the basis, or sub-stratum, in which it resides. Chaptal has arranged the varieties of the colouring principle under four heads. 1st, As it is attached to extractive matter: 2d, As it resides in gum; in both which cases it is soluble in water: 3d, As it exists, in fanna, or fecula; and in this instance it dissolves most readily in sulphuric acid: 4th, The colouring principle is occasionally inherent in resin, and then it requires alcohol, an oil, or an alkali, for solution. II. The extraction of colouring matter from the various substances that afford it, and its fixation on wool, silk, or cotton, constitute the art of dyeing; the details of which would be foreign to the purpose of this work. In this place I shall state only a few general principles; and refer for more minute information to a paper by Mr. Henry in the third volume of the Manchester Memoirs; to the works of Berthollet SECT. XIII. COLOURING MATTER. 183 and Bancroft; and to a memoir of Thenard and Roard, in the 74th volume of Annales de Chimie. III. Of the various colouring substances, used in the art of dye- ing, some may be permanently attached to the dyed fabric, and fully communicate their colour to it, without the intervention of any other substance; while others leave a mere stain, removeable by washing with water. The latter class, however, may be durably attached by the mediation of what was formerly called a mordaunt, but has since been more properly termed, by the late Mr. Henry, a basis. The colours whieh are of themselves permanent, have been termed, by Dr. Bancroft, substantive colours; while those that require a basis, have been denominated adjective colours. IV. The most important bases, by the mediation of which colour- ing matter is united with wool or cotton, are alumine, the oxide of iron, and the oxide of tin. Alumine and oxide of iron are applied in combination with sulphuric, or acetic acids; and the oxide of tin, united with nitro-muriatic, muriatic, acetic, or tartaric acids. In dyeing, the most common method is to pass the substance to be dyed through a decoction of the colouring matter, and afterwards through a solution of the basis. The colouring principle thus becomes perma- nently fixed on the cloth, sometimes considerably changed by its union with the basis. In calico-printing, the basis, thickened with gum or flour paste, is applied to the cloth by wooden blocks, or cop- per cylinders. The cloth is then dried, and passed .through a decoc- tion of the colouring ingredient, which adheres only to that part of the cloth where the basis has been applied. From the rest of the cloth it maybe removed by simple washing with water. V. The variety of colours, observed in dyed substances, are redu- cible to four simple ones, viz. blue, red, yellow, and black. 1. Indigo is the only substance used in dyeing blue, which it does without the intervention of a basis. It is the production, chiefly, of several varieties of the plant called Indigofera, a native of America and of th* East and West Indies. The plant, after being cut a little while before the time of flowering, is steeped with water in large vats, where it undergoes fermentation. During this process, a fine pulve- rulent pulp separates, which is at first green, but becomes blue by exposure to the atmosphere. The operations, by which indigo is se- parated and collected, are rather complicated, and cannot be de- scribed without considerable minuteness. A good account of them may be seen in Messrs. Aikins' Chemical Dictionary. Indigo has been supposed to be a variety of fecula, but it differs from that principle in several important particulars. It is volatile, and may be sublimed at a temperature a little below that which is re- quired lor its decomposition.* Water, by'being boiled on it, dis- solves only about a ninth or a twelfth the weight of the indigo. The colouring matter, however, remains untouched; and the solution, which appears to consist chiefly of extract, has a reddish brown hue. It is insoluble in alcohol, ether, and in fixed and volatile oils. It« ' * Gay Lussac, 74 Ann. de Chim, 191. 184 VEGETABLE SUBSTANCES. CHAP. XX. appropriate, and indeed only, solvent appears to be sulphuric acid. When thus dissolved, it is sometimes applied directly, in a diluted state, to the fabric, and dyes what is termed a Saxon blue. But, by the abstraction of part of its oxygen, indigo becomes soluble in water; and its colour changes from blue to green. It recovers the former colour, howevet-, on exposure to the air, by again absorbing oxygen. Its de-oxydizement is effected by allowing it to ferment, along with I bran or other vegetable matter; or by decomposing, in contact with it, the green sulphate of iron. Substances dyed by indigo, thus de- prived of oxygen, are green when taken out of the vat, and acquire a blue colour by exposure to the atmosphere. By this revival, the in- digo again becomes insoluble, and fitted, therefore, for affording a permanent dye. There appears, however, to be a certain stage of oxygenizement in indigo, which is essential to the existence of its blue colour, and that any proportion, either exceeding or falling short of this, is equally destructive of its colour. Thus diluted nitric acid dissolves indigo, but the solution is yellow, and the indigo is decomposed. A thin layer of resinous matter appears, floating in the solution. If this be removed, and the solution, after evaporation to the consistence of honey, be re-dissolved, in hot water, filtered, and mixed with a so- lution of potash, yellow crystals appear, which consist of the bitter principle united with potash. These crystals, being wrapped in pa- per and struck with a hammer, detonate and emit a purple light If to a drachm or two of finely powdered indigo, we add an ounce mea- sure of fuming nitrous acid, the mixture presently becomes hot, ni- trous gas is evolved, a stream of sparks arises from it, and finally the whole bursts into flame. Muriatic acid has no action on indigo, but oxymuriatic acid de- stroys its colour. Hence a solution of indigo in sulphuric acid has been recommended for measuring the strength of watery solutions of oxymuriatic acid gas; in order to regulate their application*to the process of bleaching. * Alkalies do not act on indigo, unless it be previously reduced to that state of partial dis-oxygenation at which its green colour re- appears. And the solution exists no longer, if oxygen be absorbed, J and the blue colour restored. <■ The analysis of indigo by destructive distillation affords but little information respecting its nature. The products, usually obtained from vegetable substances, are evolved, along with a portion of am- monia. A copper-coloured sublimate, also, arises in fine needle- shaped crystals, possessed of peculiar properties. It has been called Indigogene.* 2. The substances, chiefly employed for affording red colours, arc cochineal (an insect which has been supposed to derive colour from its food, the leaves of the cactus opuntia, L.,) archil, madder, brazil- wood, and saf-flower. The first four are soluble in water; the last 3 not without the intervention of an alkali. They are all adjective co- * Phil. Mag. xlvii. 415. SECT. XIII. COLOURING MATTER. 185 lours. Cochineal, though its colour is naturally crimson, is used for dyeing scarlet; and to evolve the scarlet hue, it is necessary to em- ploy the super-tartrate of potash. The basis, by which it is attached to cloth, is the oxide of tin. This may be exhibited experimentally. A decoction of cochineal will leave only a fugitive stain on apiece of cloth; but if, in the decoction, some super-tartrate of potash has been dissolved, and a portion of nitro-muriate of tin afterwards been added, it will impart a permanent scarlet colour. 3. The yellow dyes are wild American hiccory, sumach, turmeric, fustic, and quercitron bark; which afford various colours, accord- ingly as they are combined with the cloth, by the intervention of alumine, or of oxide of iron, or tin. Thus, with the aluminous base, the quercitron bark yields a bright yellow; with oxide of tin, all the shades, from pale lemon colour to a deep orange ; and with oxide of iron, a drab colour. With the addition of indigo, it gives a green. 4. A combination of red oxide of iron, with the gallic acid and tan, is the principal black colour, which has therefore the same basis as common writing-ink. In calico-printing, white spots, or figures, on a black ground, are produced, by previously printing on the cloth a protecting paste of citric acid, thickened with gum or flour. The parts to which this paste is applied do not receive the black dye, but remain perfectly white. VI. The colouring matter of vegetables, besides being capable of fixation on cloth, may be obtained in a dry form, in combination with a base only. Thus, if to a decoction or infusion, of madder in wa- ter, a solution of sulphate of alumine be added, the colouring matter is precipitated in combination with the alumine, forming what is termed a lake. For obtaining this, the following process is given by Sir H. Englefield. Put two ounces of Dutch crop-madder into a ca- lico bag, capable of holding three or four times that quantity. Pour on it a pint of distilled water, and triturate, in a mortar, as much as can be done, without destroying the bag. The water becomes loaded with colouring matter, and is opaque and muddy. Pour off this por- tion, and repeat the operation till no more colour is obtained, which will generally happen after the fifth or sixth affusion. Pour these several washings into an earthen or well-tinned copper pan; and ap- ply heat till the liquor boils. Let it then be poured into a basin; and one ounce of alum, dissolved in a pint of water, be added, and mixed by stirring. Add an ounce and a half of saturated solution of sub-carbonate of potash; a violent effervescence will ensue, and the colouring matter will be precipitated. Stir the mixture till cold, and wash repeatedly with boiling water. About half an ounce of lake will be obtained, containing two-fifths its weight of alumine. Other lakes may be obtained, of different colours, by the substitu- tion of different dyeing-woods; and from the infusion of cochineal, the beautiful pigment called Carmine is precipitated by means of a solution of tin. Vol. II.—A a 186 VEGETABLE SUBSTANCES. CHAP. XX. SECTION XIV. Tan, Tannin, or the Tanning Principle. Tan exists abundantly in the bark of the oak, the willow, &c, and in the gall-nut The interior bark, next to the wood, contains the largest proportion; the middle and coloured part, the next; and in this it is accompanied with more extract The epidermis affords ver_> little. I. Tan may be obtained by any of the following processes; but, * according to Sir H. Davy.it is difficult to procure it in a state of per- fect purity. Indeed, it has been doubted by several chemists, and especially by Chevreul and Pelletier,* whether tan has ever been ob- tained sufficiently pure, to entitle it to be considered as a distinct vegetable principle. lt Into a strong infusion of nut-galls, pour the muriate of tin, till the yellowish precipitate, which at first falls down abundantly, ceases to appear. Wash the precipitate with a small quantity of distilled water, and afterwards add a sufficient quantity of warm water for its solution. From this solution, the oxide of tin is precipitated by a stream of sulphuretted hydrogen gas; and the tannin, which remains dissolved, may be procured by evaporation. There is reason, how- ever, Dr. Bostock informs me, to believe that, by this process, tan is so much altered as to be scarcely entitled to retain the appellation; and the same remark applies, though perhaps not in an equal degree, to the two following operations: 2. Into a saturated infusion of galls, pour a saturated solution of carbonate of potash. The yellowish white precipitate, after being washed with a small quantity of water, affords tan. When thus pre- pared, Sir H. Davy observes that tan is not perfectly pure, but con- tains a minute proportion of gallic acid, and alkali. 3. Into a similar infusion, pour sulphuric or muriatic acid. A pre- cipitate will form, which must be re-dissolved in water, and the ex- cess of sulphuric acid saturated by carbonate of potash. When a farther addition is made of the alkali, the tan falls down, and must be purified by washing with a small quantity of water. It has been discovered by Sir H. Davy, that the terra japonica, or catechu (which is to be met with under this name in the druggists' shops,) is composed of about one half tan, the remainder being a mix- ture of extract, mucilage, and earthy impurities. The purest kind of tan, we learn from the same authority, may be procured by the ac- tion of a small quantity of cold water on bruised grape seeds. A substance, lately introduced into medicine under the name of Extract of Rhatania, Dr. Bostock is of opinion, consists of tan in a purer form than catechu. * See 87 Ann. de Chim. 103; and 47 Phil. Mag. 74. SECT. XIV. TAV. 187 Tan procured from galls has been analyzed by Berzelius, and found to consist of Carbon.....41.186 Oxygen.....54.654 Hydrogen .... 4.186 100.* II. Tan has the following properties: 1. When evaporated to dryness, it forms a brown friable mass, which has much resemblance in its fracture to aloes, a sharp bitter taste, and is soluble in water, but still more readily in alcohol. 2. From this watery solution ail acids precipitate tan. 3. The alkaline carbonates have a similar effect _ 4. The watery solution, poured into one of glue (inspissated ani- mal jelly), converts it immediately into a coagulum, insoluble by boil- in"- water, which has the elastic properties of the gluten ol wheat. 'The solution of gelatine, or jelly, may be prepared for the purpose of precipitating tan, by dissolving isinglass in water, in the proportion of ten grains to two ounces. The precipitate consists of 54 jelly and 46 tan. An excess of the solution partly re-dissolves it It is this property, of forming with gelatine an insoluble compound, not liable to putrefaction, that fits tan for the purpose of converting skins into leather. Dr. Duncan, jun., who has made numerous experiments on tan, in- forms me, that the proportion of ingredients in this precipitate varies very considerably, according to the mode in which it is effected; and that insolubility in water is by no means one of its constant charac- ters. In ammonia it dissolves readily. Dr. Bostock, also, has found that fan and jelly do not unite in any constant proportion, and that the compound is not, in all cases, insoluble in water.t In this country, a preference is universally given to oak bark for the purpose of tanning, but various other substances afford it, as ap- pears from the following Table, drawn up by Sir H. Davy, from his own experiments: Table of Numbers, exhibiting the Quantity of Tan afforded by ISQlbs. of different Barks, which express nearly their relative Values: lb. Average of entire bark of middle-sized Oak, cut in spring ... 29 --------------------of Spanish Chesnut ....... 21 ____________________of Leicester Willow, large size ... 33 ____________________of Elm.............13 ____________________of common Willow, large size .... 11 ____________________of Ash............16 ____________________of Beech...........10 ______.-------------of Horse Chesnut........9 • 9A> Ann. de Chim. 322. J- See his paper on the union of Tan and Jelly, Nicholson'* Journal, xxiv. 1 188 VEGETABLE SUBSTANCES. CIlAr. X^. lb. Average of entire bark of Sycamore..........H --------------------of Lombard y Poplar.......15 --------------------of Birch...........8 --------------------of Hazel...........H --------------------of Black Thorn . •.......16 --------------------of Coppice Oak.........32 --------------------of Oak cut in autumn.......21 -------------------- of Larch cut in ditto.......8 White internal cortical layers of Oak Bark.......72 The inner cortical layers of all barks Sir II. Davy found to contain the greatest proportion of tan. The quantity, also, is greatest at the time the buds begin to open, and is smallest in winter, and after a cold spring. As a general average, four or five pounds of good oak bark are re- quired to form a pound of leather. The operation is most perfect, when performed slowly; for, if too rapidly effected, the outer surface of the 6kin is covered with a coat of leather, which defends the interior from change. In general, skins, by being; completely tanned, increase in weight about one-third, the skin and the leather being each sup- posed dry. 5. Tan forms^with fecula, or starch, a precipitate which is sparing- ly soluble in cold water, and very copiously in hot water. 6. With gluten it gives an insoluble precipitate. 7. It is precipitated by salts with earthy bases, such as the nitrates of barytes, lime, &c. 8. It is separated also by salts with metallic bases, such as acetate of lead, muriate of tin, muriate of gold, sulphate of iron, tartarized antimony, and muriate of platinum. Green sulphate of iron effects no change in the solution of tan, but the red sulphate occasions a dark bluish precipitate. This precipitate differs from gallate of iron, in being decomposed by acids, the tan being thus separated. An excess of the red sulphate re-dissolves the precipitate, and affords a black or dark blue liquor. By union with tan, the red sulphate is de-oxidized, the salt becoming the green sul- phate, and the oxygen passing to the tan. Tan may be oxygenized, by passing streams of oxymuriatic acid through its solution in water. Tan is capable, also, of uniting with oxide of lead, in different pro- portions, forming a tannate and sub-tannate of lead.* Until within the last ten years, tan had been known only as a pro- duction of nature; and the processes of chemistry had effected nothing more, than its separation from the various substances, with which it occurs combined. An important discovery, however, has been made by Mr. Hatchett, of the artificial formation of tan, from substances which unquestionably do not contain it,but only furnish its elements. The processes for its factitious production are very numerous; but they are arranged, by their author, under three heads: 1st, The synthesis * Berzelius, 94 Ann. de Chim. 319. ECT. XIV. TAW 189 of tan may be effected bv the action of nitric acid on animal or vege- table charcoal; 2dly, Bv distilling nitric acid from common resin, indigo, dragon's blood, and various other resinous substances; Sdly, By the action of sulphuric acid on common resin, elemi, asafcetida, camphor, &c. Of these various processes, I shall select the most sim- ple, referring to Mr. H-^hett's very interesting paper for a fuller detail of the experiment..* To 100 grains of powdered charcoal, contained in a matrass, add an ounce ot nitric acid (specific gr. 1.4) diluted with two ounces of water; place the vessel in a sand-heat, and continue the digestion till the charcoal appears to be dissolved. A copious discharge of nitrous gas will take place. At the end of the second day, it may be necessary to add another ounce, and sometimes even a third, of nitric acid; and to continue the digestion during five or six days. A red- dish brown solution will be obtained, which must be evaporated to dryness in a glass vessel; taking care in the latter part of the pro- cess, so to regulate the temperature, that the acid may be expelled, without decomposing the residuum. A brown glossy substance will be obtained, having a resinous fracture, and amounting, in weight, to 116 or 120 grr'is. This substance has the following properties: 1. It is speedily dissolved by cold water, and (ft alcohol. 2. It has an astringent flavour. 3 Exposed to heat, it smokes but little, swells much, and affords a bulky coal. 4. Its solution in water reddens lit- mus paper. 5. The solution copiously precipitates metallic salts, especially muriate of tin, acetate of lead, and red sulphate of iron. These precipitates, for the most part, are brown, inclining to choco- late, excepting that of tin, which is blackish grey. 6. Gold is preci- pitated from its solution in a metallic state. 7. The earthy salts are precipitated bv it. 8. Gelatine is instantly precipitated from water, in the state of coagulum, insoluble both in cold and in boiling water. The identity of this substance with tan can, therefore, be scarcely doubted, since the two bodies agree in having the same characteristic properties. The only essential circumstance of discrimination, is, that the natural tan is destroyed, while the artificial is produced, by the agency of nitric acid; and that the artificial substance, even when formed, powerfully resists the decomposing action of this acid, which readily destroys natural tan. Even, however, among the different varieties of the natural substance, Mr. Hatchett found essential differ- ences in the facility of destruction by nitric acid. Those of oak bark und catechu are less destructible; and, in general, the varieties of tan stem to be less permanent, in proportion to the quantity of mucilage which they contain. Infusions of factitious tan differ, also, it has been «aid, from those of the natural kind, in not becoming mouldy by keeping. This character, however, is not confirmed by Dr. Bostock, who has observed the artificial tan to mould. The artificial substance is a purer variety of tan than the natural one; inasmuch as it is perfectly free from gallic acid, and from ex- tract, both of which are always present in the latter. The properties » See Philosophical Transactions for 1805 an J 1806. 190 VEGETABLE SUBSTANCES. CHAP. XX. of the factitious compound vary a little, according to the mode of its preparation, principally in the colour of the precipitates, which it sepa- rates from metallic solutions. Those effected by tan, formed by pro- cesses of the first class, are always brown, and by the second, pale or deep yellow. SECTION XV. Wax. It was long supposed that bees' wax is merely the dust of the sta- mina of plants, unchanged by any process in the economy of that ani- mal. This opinion, however, has been lately shown by Huber* to be erroneous; for bees, he has proved, continue to form wax, when sup- plied with only raw sugar or honey. Little doubt, therefore, can exist that sugar contains all the principles of wax; and that wax is the re- sult of a new combination of those principles, effected by the animal. At the same time, it is equally well established, that wax is also a product of vegetation. It forms the varnish, which is conspicuous on the upper leaves of many trees, and may be extracted by first remov- ing, by water and alcohol, from the bruised leaves, every thing that is soluble in those fluids; then macerating the remainder with liquid ammonia, which dissolves the wax, and lets it fall on the subsequent addition of sulphuric acid. Wax exists, also, in the substance called lac, in combination with colouring matter; and is obtained, in consi- derable quantity, from the berries of the Myrica Cerifera, by the simple process of boiling them in water, and bruising them at the same time. The wax melts and rises to the surface in the form of a scum, which concretes on cooling.t In its ordinary state, wax of every kind has considerable colour and smell. It may be deprived of both, by exposing it, in thin lami- nae, to the action of the light and air, or still more speedily by oxy- muriatic acid gas. When bleached, it has the following properties: 1. Its specific gravity is about .960, water being 1.000. When heated, it melts at about 155° Fahrenheit, or at about 7° higher than unbleached wax, and forms a transparent fluid, which gradually ac- quires consistency, till at length it returns to a solid state. If the heat be raised, it boils; and a portion distils over. By a still higher heat, it is decomposed, and a quantity of olefiant and hydrocarburet gases is developed. The residuum of charcoal bears only a small propor- tion to the wax which has been decomposed. From the results of its combustion, Lavoisier has inferred that wax consists of 82.28 carbon 17.72 hydrogen 100. * Nicholson's Journal, ix 182. f Cadet, Ann. de Chim. vol. xliv. SI'.CT. XVI. BITTER PRINCIPLE. 191 Gay Lussac and Thenard, by an improved method of analysis, have lately shown it to consist of Carbon.......81.784 Oxygen.......5.544 Hydrogen......12.672 100. Of the hydrogen, part only is sufficient for the saturation of the oxygen; and besides this there are 11.916 in excess. 2. Wax is insoluble in water. 3. Boiling alcohol dissolves about one-twentieth its weight of wax, four-fifths of which separate on cooling; and the remainder is imme- diately precipitated by the addition of water. Boiling ether dissolves about one-twentieth of its weight 4. Caustic fixed alkalies convert it into a saponaceous compound, soluble in warm water. A heated solution of ammonia dissolves it, and forms a kind of emulsion. On cooling, the wax rises to a surface in flocculi. Myrtle wax, it appears from the experiments of Dr. Bostock, dif- fers from bees' wax in being more fusible (viz. at 109° Fahrenheit,) and in being soluble, to a greater amount, both in ether and in alcohol. The vegetable wax from Brazil, though it appears, from the experi- ments of Mr. Brande, to possess the principal characters of common wax, differs from it in some properties, and also from myrtle wax.* SECTION XVI. Tlie Bitter Principle. The bitter taste of certain vegetables appears to be owing to the presence of a peculiar substance, differing from every other in its chemical properties. It may be extracted from the wood of quassia, the root of gentian, the leaves of the hop, and several other plants, by infusing them for some time in cold water. The characters of this substance have been attentively examined by Dr. Thomson, who enu- merates them as.follows.t 1. When water, thus impregnated, is evaporated to dryness by a very gentle heat, it leaves a brownish yellow substance, which retains a certain degree of transparency. For some time it continues ductile, but at last becomes brittle. Its taste is intensely bitter. 2 When heated, it softens, swells, and blackens; then burns away without flaming much; and leaves a small quantity of ashes * Phil. Trans. 1811, p. 267. \ System of Chemistry, v. 95. 192 VEGETABLE SUBSTANCES. CHAP. XX 3. It is very soluble in water, and in alcohol. 4. It does not alter blue vegetable colours. 5. It is not precipitated by the watery solution of lime, barytes, or strontites; nor is it changed by alkalies. 6. Tincture of galls, infusion of nut-galls, and gallic acid, produce no effect. 7. Of the metallic salts, nitrate of silver and acetate of lead arc the only ones that throw it down. The effect of nitrate of silver can- not be ascribed to the presence of muriatic acid, since nitrate of lead produces no change in the solution. The precipitate by acetate of lead is very abundant; and that salt, therefore, affords the best test for discovering the bitter principle, provided no other substances be present, by which, also, it is decomposed. From recent experiments of Mr. Hatchett, it appears that the bit- ter principle is formed, along with tan, by the action of nitric a< id on indigo. Mr. Donovan has also composed it by the action of strong nitric acid on an equal weight of sugar. In the residual matter, which is thick and tenacious, its presence is disguised by the sourness of the malic acid, but becomes sensible when this is neutralized by lime. This bitter principle, he conceives, may exist in unripe fruits, and may afford, accordingly as it is modified by vegetation, either sugar or vegetable acids.* Another modification of the bitter principle has been extracted, by M. Chenevix, from unroasted coffee. The infusion of the berries was mixed with muriate of tin, when a precipitate appeared, which was well washed, then diffused through water, and decomposed by sul- phuretted hydrogen gas, which carried down the tin. The remaining liquid, evaporated to drynesss, gave a semi-transparent substance not unlike horn. This substance did not attract moisture from the air, was soluble in water and alcohol; and the solution, on adding alkali, became of a garnet red. Solution of iron gave it a fine green tinge, or, when very concentrated, threw down a green precipitate; and muriate of tin occasioned a yellow sediment. It was not affected by solution of animal gelatine. The bitter principle may, also, be formed by artificial processes, chiefly by the action of nitric acid on animal and vegetable substances. Welther obtained it by digesting silk with nitric acid ; and Mr. Hatchett has formed it from the same acid and indigo. Its colour is a deep yellow, and its taste intensely bitter. It is soluble in water and alcohol, and is susceptible of a regular crystallized form. It unites with alkalies, and composes crystallizable salts. Its compound of this substance with potash detonates when struck with a hammer, and inflames like gunpowder when thrown on hot charcoal. On the whole it appears better entitled to rank as a distinct principle, than that which is extracted, by infusion, from vegetable*. ♦ Phil. Trans. 1815. ^TICT. XVII. NARCOTIC PRINCIPLE—MORPHINE* i-S3 SECTION XVII. Narcotic Principle—Morphine. Opium, and other vegetable products possessed of narcotic power, are composed of several of the vegetables principles that have already been enumerated Besides these, however, they con- tain a peculiar one, in which the narcotic virtue resides. Its pre- paration and chemical qualities have been investigated by Derosne, whose memoir is published in the 45th volume of the Annales de Chimie I. To obtain the narcotic principle from opium by the process of Derosne, let water be digested upon it, and the strained solution be evaporated to the consistence of syrup. A gritty precipitate will begin to appear, which is considerably increased by diluting the liquid with water. This consists of three distinct substances, resin, oxygenized extract, and the narcotic principle. Boiling alco- hol dissolves the resin and narcotic principle only; the latter falls down in crystals, as the solution cools; still, however, coloured with resin. The crystals may be purified by repeated solutions and crystallizations. , II 1. The narcotic principle, thus obtained, is white. It crys- tallizes in rectangular prisms with rhomboidal bases. It is destitute of taste and smell. 2. It is insoluble in cold water, but is soluble in 400 parts of boiling water, from which it precipitates again as the solution eools. When thus dissolved, it does not affect vegetable blue colours. 3. It is soluble in 24 parts of boiling alcohol, and in 100 of cold alcohol. Water precipitates it, in the state of a white powder. 4. Hot ether dissolves, but deposits it on cooling. When heated in a spoon, it melts like wax. 5. It is soluble in acids, and precipitated by alkalies. With nitric acid it dissolves, and becomes red; and much oxalic acid is formed) a bitter substance remaining. 6. It may be combined with water and alcohol, by the interven- tion of resin and extract, the presence of which seems originally to tender it soluble in those fluids. Morphine or Morphia. A more complete investigation of the narcotic principle has since been published by M. Sertuerner, of Eimbeck in Hanover, who has shown that the substance, described by Derosne, is a compound of a peculiar base (morphine) with an acid, existing, so far as is known, only in opium. Vol. II.—B b 1*4 VEGETABLE SUBSTANCES. • HAP. XX. The following process is the one practised by Sertuerncr for obtaining Morphine.* Rub together in a mortar eight ounces of powdered opium, two or three ounce measures of acetic acid, and a little cold distilled water; then add two or three pints of water, and strain the liquor. Add to it a solution of ammonia, and evapo- rate the liquor to one fourth. The morphine is precipitated, and may be separated by filtration. The liquid part is a compound of ammonia with the acid ingredient of opium. Another method of separating morphine has been recommended by Robiquet.f A concentrated solution of a pound of opium in water is to be boiled with 10 or 12 drachms of carbonate of mag- nesia, during a quarter of an hour A grayish deposit is formed in considerable quantity, which is to be washed first with cold water, and next with hot and weak alcohol, which takes up a small quan- tity of morphine and much colouring matter. It is afterwards washed with a little cold and concentrated alcohol, and then boiled with a sufficient quantity of the same fluid, which, at that tempera- ture, dissolves morphine On cooling, it is deposited a little colour-, cd; but by repeating the operation three or four times, it may be obtained colourless, and crystallized in regular parallelopipeds with Oblique faces. Pure morphine dissolves in boiling water only in small propor- tion, but is very soluble in«heated alcohol and ether, and the solu- tions are intensely bitter. I he watery and alcoholic solutions affect test papers like an alkali, and Robiquet thought this property most distinct in morphine prepared by the intervention of magnesia, which, from its complete destruction by burning, could not contain any proportion of that earth. It forms neutral salts with acids, and appears therefore to approach most nearly in its characters to an alkali, which it also resembles in decomposing the compounds of acids with metallic oxides. Morphine fuses at a moderate heat, and resembles melted sul- phur. On cooling from this state, it crystallizes. It unites with sulphur, but is incapable of forming soap with an oxidized oil. Its effects on the human body are those of a violent poison. Three half grains, taken in succession with intervals of half an hour by the same person, produced violent vomiting and alarming faintings. Another ingredient of opium is the meconic acid, which, accord- ing to Robiquet, is best obtained from the residuum of the magne- sian salt, which is left undissolved by alcohol in the process for extracting morphine. This residue may be dissolved in very weak sulphuric acid, and to this solution muriate of barytes may be added. A rose-coloured precipitate falls, consisting of sulphate and me- conate of barytes. This is to be digested a considerable time with hot sulphuric acid largely diluted. When the filtered liquor is sufficiently reduced by evaporation, the meconic acid shoots, evefv * Ann. de Ghim. et Phys. r. 39. f Ibid. 379. NARCOTIC PRINCIPLE--MCRPHINE. 19 J before cooling, into coloured crystals. To obtain it pure, it must ke washed with a small quantity of water, then dried, and sublimed at a gentle heat. . f This acid is fusible at a temperature considerably above that ot boiling water. It reddens vegetable blues, and is extremely solu- ble in alcohol and in water. Its distinguishing character is, that it produces an intensely red colour in solutions of iron oxidized to the maximum. Sertuerner did not find that when taken into the stomach, it is capable of producing any of the effects of opium. The salt of Derosne, it appears from the experiments ot Kotn- quet, is not a compound of morphine and meconic acid. The wa- tery solution of opium, freed from morphine and meconic acid, contains another acid characterized by a different train of proper- tics, which may be separated by a process somewhat circuitous. This acid is not volatile, and has no peculiar action on the salts ot iron With morphia it affords salts that are readily soluble in alco- hol and in water Morphium and the salt of Derosne appear Irom the experiments of Robiquet to be both ingredients of opium, which are different and independent of each other. Beside the ingredients which have already been mentioned, 'opium contains extract, which forms with morphine a compound almost insoluble in water, but very soluble in acids. A considera- ble proportion of resin, and a small quantity of caoutchouc, enter also into the composition of opium. These are entirely destitute of sedative properties, when received into the stomach. They re- main after acting on opium first with water, and afterwards with muriatic acid. When the residue is digested with alcohol, the re- sinous matter is takeP up; and from the remaining mass, which has resisted the action of alcohol, the caoutchouc may be extract- ed by rectified ether. Tinctures of opium, it is observed by Sertuerner, should be pre- pared with pure alcohol, and kept in a place which is not very cold; for a low temperature precipitates morphine. The addition ol a little acetic acid prevents this inconvenience. SECTION XVIII. Suber and its Mid. This name is used to denote common cork wood,which appears to be possessed of peculiar properties, especially in its relation to '"i'Vo a quantity of cork, grated into powder, and contained in a tubulated retort, add six times its weight of nitric acid, ot the specific gravity 1.261; and distil the mixture, with a gentle heat, * Ann. de Chim. et Phys. v. p. 285. 196 VEGETABLE SUBSTANCES. CHAP. XX' % long as any red vapours escape As the distillation advances, a yellow matter, like wax, appears on the surface of the liquid. While the contents of the retort continue hot, they are to be pour- ed into a glass vessel, placed on a sand-bath, and constantly stirred with a glass rod, by which means the liquid gradually becomes thick. As soon as white penetrating vapours appear, let it be re- moved from the sand-bath, and stirred till it becomes cold. An orange-coloured mass will be obtained, of the consistence of honey, having a strong and sharp odour while hot, and a peculiar aromatic smell when cold. On this, pour twice its weight of boiling water; apply heat till it liquifies; und filter. The filtered liquor, as it cools, deposits a powdery sediment, and becomes covered with a thin pellicle. The sediment is to be separated by filtration; and the -liquid reduced, by evaporation, nearly 10 dryness This mass is the suberic acid. It may be purified, either by saturating it with alkali, and precipitating by an acid, or by boiling it with charcoal powder. II. Suberic acid has the following properties: 1. It is not crystallizable. 2. It has an acid and slightly bitter taste; and, when dissolved in boiling water, it acts on the throat, and excites coughing 3. It reddens vegetable blues, and changes the blue solution of indigo in sulphuric acid to green 4 Cold water dissolves about T|6th its weight, and boiling wa- ter half its weight. 5. It attracts moisture from the air. 6. When heated in a matrass, it sublimes, and is obtained in con- centric circles, composed of numerous small points. 7 With alkalies, earths, and metallic oxides, it forms a class of salts called Suberates. The action of nitric acid on cork, and the properties of the sube- ric acid and its compounds, have been lately investigated by Chev- reul, whose memoir may be consulted in the 23d volume of Nichol*. son's Journal. SECTION XIX. Of Bitumens, Though bitumens, on account of their origin, are, with more propriety, classed among mineral substances; yet, in chemical pro- perties, they are more closely allied to the products of the vegeta- ble kingdom Like vegetable substances in general, they burn in the open air, and with a degree of brightness that surpasses even that of resins. By distillation per se, they yield a weak acetic acid, an empyreumatic oil, some ammonia, and a considerable quantity «f carbureted hydrogen j*as, with occasionally a small proportion 3*CT. XIX. BITUMENS 197 of carbonic acid and sulphureted hydrogen. They ape neither soluV ble in water nor in alcohol, and in the latter respect they diffetf~ from resin. There can be little doubt that they have been formed originally by the decomposition of vegetables. The bitumens have been divided into liquid and solid. Formerly it was supposed that the liquid bitumens had been derived, by a . sort of natural distillation, from the solid; but Mr Hatchett has rendered it more probable that the sond bitumens result from the consolidation of the fluid ones.* The bituminous substances are Naphtha, Petroleum, Mineral Tar, Mineral Pitch, Asphaltum, Jet, Pit-Coal, Bituminous Wood, Turf, and Peat. To these some writers have added Amber and the Honey Stone. Nai iitha is a substance well known to mineralogists as a light, thin, often colourless oil, highly odoriferous and inflammable, which is found on the surface of the water of certain springs in Italy, and on the shores of the Caspian sea It has a penetrating but not disagreeable odour Its speci' c gravity is about .708, or, according to Brisson, .845. Saussure found its specific gravity in its natural state to be 836, after one rectification ."69, and after two .758; after which it could not be rendered lighter. It does not congeal at 0° Fahrenheit. Naphtha is highly inflammable, and burns with a penetrating smell and much smoke. It may be distilled without alteration. By long exposure to the air it becomes thick and coloured, and passes to the state of petroleum. The addition of a little sulphuric or nitric acid produces the same change more speedily. It is not miscible either with water or with alcohol, unless the alcohol be quite pure, and then the two fluids unite in any proportion. Naphtha appears to be the only fluid wc are acquainted with, in which oxygen does not exist in considerable proportion. This cir- cumstance renders it of great use in preserving the new metals discovered by Sir H. Davy. When recently distilled, they have no action on it; but in naphtha that has been exposed to the air, these metals soon oxidate; and alkali is formed, which unites with the naphtha into a kind of brown soap. When carefully rectified, Saussure did not find that it was at all altered by being kept three years in vials half full. Its boiling point is 186° Fahrenheit. The density of its vapour is 2 833, air being 1. A mixture of this vapour with common air burns like carbureted hydrogen gas. By the detonation of its va- pour with oxygen gas, Saussure determined the composition of naphtha to be Carbon........87 21 Hydrogen.......12.79 100. :' Linnsean Transactions, 1797. 198 VEGETABLE SUBSTANCES. cnAP. XX. It appears therefore to contain rather more carbon than is pre- sent in olefiant gas.' Petroleum is considerably thicker than naphtha, and has a greasy feci. It is either wholly or in part transparent, and of a reddish brown colour. Its specific gravity is .S78 When distilled per se, a portion of colourless naphtha is first obtained; then an empyreumatic acid liquor; next a thick brown oil; and a portion of black sftining coal remains in the retort. Petroleum is highly inflammable. Sulphuric and nitric acids convert it into a thick bitumen; and exposure to the air produces the same effect more slowly. It has the property of combining with fat and essential oils, with resins, camphor and sulphur; and, when rectified, it dissolves caoutchouc. Mineral tar is thicker and more viscid than petroleum, and of a reddish or blackish brown colour. In chemical properties it re- sembles petroleum. The solid bitumens are Maltha, Asphaltum, and Elastic Bitu- men or Mineral Caoutchouc, besides the several varieties of Coal and Peat Maltha or mineral pitch has a brownish black colour, and little or no lustre. It is so soft that it is impressed by the nails, but does not stain the fingers. Its specific gravity is from 1.45 to 2.06. It is extremely inflammable, and burns with a bright flame, leaving only a small quantity of ashes. Asphali lm is brownish black in its colour, is brittle, shining, and does not stain the fingers. Its specific gravity varies from ! 07 to 1.65. It is extremely inflammable, and burns with a yellow flame. By distillation per se, it yields a light brown oil resembling naph- tha, a portion of water impregnated with ammonia, and a quantity of carbureted hydrogen gas. It has been analyzed by Klaproth, whose accounts of it may be seen in the second volume of his *' Contributions " The appropriate solvent of asphaltum in naphtha, of which it requires five times its weight The solution is of a deep black co- lour, and forms an excellent varnish. Elastic bitumen or mineral caoutchouc is a rare production of nature, and has hitherto been found only in Derbyshire. It is inflammable, and burns with much smoke. By a gentle heat it is melted and converted into petroleum, maltha, or asphaltum. It resists the action of solvents. Retinasphalti m is also a rare production of the same county. It has no elasticity; but is brittle, and breaks with a glassy fracture. » Its colour is pale ochre yellow; its specific gravity 1.135. It melts on the application of heat, and burns with a bright flame. It is par- tially soluble in alcohol, potash, and nitric acid. One hundred parts contain 55 resin, 41 asphaltum, and 3 earthy matter. *: Thomson's Annals, x. 118. SBCT. XIX. BITUMENS. 199 Pit-coal is a general term, applied to several distinct varieties •f minerals. They have been divided into the three families of brown coal; black coal; and glance coal or mineral carbon. Brown coal is only imperfectly bitumemzed, and exhibits, dis- tinctly, the remains of the vegetables, from whose decay it has originated. It is brown, opaque, somewhat flexible and elastic, and nearly light enough to float on water. It burns with a clear flame, and with a bitumenous odour mixed with that of sulphur. In the mode of its combustion, as well as in its external appearance, it bears a considerable resemblance to wood that has been halt " Black coal is the substance which is commonly applied to the purposes of fuel. It shows no remains of the vegetables from which it has originated; but appears to be a compound of bitumen and charcoal; and according to the proportion of these two ingredients, its properties vary considerably. The best kinds melt on the appli- cation of a moderate heat, and burn almost entirely away, with a clear bright flame. By distillation, they yield a quantity of water holding carbonate and sulphuret of ammonia in solution; a large proportion of tar is obtained, which, by evaporation and fusion, forms a kind of asphaltum; and an immense production takes place of heavy carbureted hydrogen gas, which may be advantageously- applied to burning in lamps. In the retort, a hard heavy charcoal remains called coak. It contains generally a good deal ot sul- phur: and emits, during combustion, a suffocating smell ot sul- phurous aci,d. Glance coal appears to consist of almost pure charcoal without any bitumen, and combined with only a proportion of earth. It is common in some parts of this kingdom, where it is known by the name of stone coal. It burns with little or no flame; and, when submitted to distillation, yields no tar, and a carbureted hydrogen gas, which, from its inferior density, cannot be advantageously burned in lamps. In peat or turf, the remains of vegetable organization are generally very evident; and it consists, indeed, in a great measure, of fibres of several mosses, with occasionally whole branches, and even trunks, of various trees. It is extremely inflammable in the open air; and, when distilled in close vessels, yields products simi- lar to those of coal. The gas, however, which is evolved, ap- proaches more in its characters to carbonic oxide than to carbu- reted hydrogen. In an excellent account of this substance, given by Mr. Jameson in his Mineralogy of the Shetland Isles, peat is said to contain the suberic acid. The sulphates of iron, soda, and magnesia, are, also, occasionally found as ingredients of peat; and, when in considerable proportion, impair its combustibility. Meli.ii.he or honey-stone, so called from the resemblance ot its colour to that of honey, is a very rare production, and has been found, accompanying brown coal, in a very few parts of the conti- nent. It is consumed when ignited in the open air, but without 200 VEGETABLE SUBSTANCES. CHAP. XX. flame or smoke. When long boiled in water, it yields a solution, which, on being concentrated and mixed with alcohol, becomes pitchy. By continued trituration, however, it is dissolved, with the exception of some earthy flocculi. The clear liquid, decanted and evaporated, yields a brownish saline mass; from which, by two successive evaporations and solutions, needle-shaped crystals are obtained These are the pure mellitic acid The taste of this acid is sweetish, and at the same time sour, with some bitterness. It is combustible when ignited in the air; and is decomposed by nitric acid, without the production oi" any oxalic acid. Dropped into the watery solutions of lime, barytes, or strontites, it gives a precipitate, which is soluble in muriatic acid. With acetates of barytes and lead, and nitrates of mercury and iron, it gives precipitates, which are soluble in nitric acid. It neutralizes the three alkalies, and affords with them crystallizable salts. SECTION XX. Of the Vegetable Princi/iles of Asparagus, Elm-tree Gum, Elecam- pane, Mushrooms, Saffron and Cocculus Indicus. By an attentive examination of the products of vegetation, some new substances have been discovered, the properties of which do not agree with those of any that have been the subjects of the, pre- ceding sections. Hitherto, however, they have scarcely been so much investigated, as to entitle them to rank as distinct species. 1. Asparagin. From the juice of asparagus, concentrated by evaporation, Messrs. Vauquelin and Robiquet observed a consi- derable number of crystals to separate spontaneously.* Of these, some became, after repeated crystallizations, perfectly white and transparent. They were cool and slightly nauseous to the taste; were soluble in water; and neither affected the re-agents for acids nor alkalies. The infusion of galls, acetate of lead, oxalate of am- monia, muriate of barytes, and hydro-sulphuret of potash, produced no change in the solution; and no ammonia was disengaged by potash. When burned' in a platina crucible, they swelled up and emitted penetrating vapours, which affected the eyes and nose like the smoke of wood; and left a large proportion of charcoal, in which no traces of alkali could be discovered. Towards the close of the decomposition, an odour arose similar to that of animal matter, and inclining, also, to that of ammonia. It appears, therefore, that this substance, though crystallizable, cannot be considered as a neutral salt; for it contains neither alkali nor earth. Like other vegetable matters it appears to consist of hydrogen, oxygen, and charcoal, in proportions not yet determined, with perhaps some nitrogen. * Nicholson's Journal, xv. 242. SECT. XX. ULMIN, &C. 20*1' 2. Ulmin. In the year 1802, Klaproth received from Palermo, a substance which exudes spontaneously from a species of elm, and which, in external characters, bore a considerable resem- blance to gum. It dissolved in a small quantity of water, and gave a transparent solution of a blackish brown colour, which was not, however, mucilaginous, and could not be applied to the pur- pose of a paste Nitric acid precipitated from the solution a light brown substance, which was soluble in alcohol, though the gum itself resisted that solvent. Oxymuriatic acid produced a similar effect. The property, of producing a resin by the addition of a little oxygeti, is peculiar Jto this substance, and sufficiently charac- teristic. Dr. Thomson has proposed for it the name of Ulmin; and he and Mr. Smithson have recently paid much attention to the investigation of its properties.* It appears to be a very com- mon vegetable product, exuding from various trees, and existing, according to Berzelius, in the bark of most. When pure, it is tasteless; sparingly soluble in water and in alcohol; not precipi- tated by acids, gelatine or tan; and very soluble in alkaline carbo- nates, from which it is separated by acids and metallic salts 3 Inulin. When the roots of the inula heleni m or elecampane, are boiled some time in water, the decoction, after standing some hours, deposits some white powder like starch, but differing in its •hemical qualities. Rose, who was the first person that investi- gated its properties, found that it is insoluble in cold water, but that it readily dissolves in four times its weight of boiling water into a liquid which is somewhat mucilaginous and not quite trans- parent. After some hours, the substance precipitates from the water, in the form of a white powder; and it may also be thrown down by alcohol. When placed on burning coals, it melts as rea* dily as sugar; emits a similar smell; and is consumed, leaving a very small residuum of charcoal. When treated witb nitric acid, it yields oxalic and malic acids; or acetic acid if too much nitric acid be employed. It differs, however, from gum in not afford- ing, by this treatment, any saccholactic acid; and from starch (besides separating spontaneously from hot water), in yielding none of the waxy matter, which is formed when starch is digested with the same acid. Inulin has since been examined by M. Gaultier de Claubry, who has pointed out the following characters as discriminating it from fecula or starch. It is much more soluble than starch in hot water, with which it does not form a jelly, but is deposited on cooling in the form of a white powder. It dissolves, also, in four or five times its weight of water at 140° Fahrenheit, and the solu- tion, when evaporated, becomes viscous, but not gelatinous. With iodine, it forms a greenish-yellow compound, which is sponta- neously decomposed, in part at least, in a short space of time, * See his Annals of Philos. role. 1 and 2; and Mr. Smithson's paper, Phi]. Trans. 1813. Vol. II.—C r 2Q2 VEGETABLE SUBSTANCES. CHAP. XX The inulin remains lightly coloured yellow, and retains a portion of iodine. Muriatic acid, as well as solutions of pure alkalies, render starch gelatinous, but dissolve inulin without giving any jelly. Concentrated sulphuric acid, which carbonizes starch, and is at the same time converted into sulphurous acid, dissolves inu- lin without any extrication of sulphurous acid; and the inulin may be precipitated by ammonia. These properties appear to be suf- ficiently characteristic to entitle inulin to be considered as a dis- tinct vegetable substance. To obtain it in a state of purity, M. ■de Claubry recommends to boil the roots of elecampane in a suf- ficiently large quantity of water; to filter.the liquor, and to evapo- rate it to the consistence of an extract, which is to be washed with cold water. From the washings, there falls a considerable quantity of inulin, which is to be gently dried, not however on fil- tering paper, as it adheres to this too firmly to be got off.* 4. Fungin. This substance has been extracted by Braconnotf from the fleshy part of mushrooms. It may be obtained by wash- ing off the soluble ingredients with hot water, to which a little al- kali has been added. There remains a white, insipid, soft, and but little elastic substance. It has a fleshy structure, and is in a high degree nutritious, and free from deleterious properties. WThen dry, it burns vividly, and emits an odour resembling that of bread. By destructive distillation, it yields ammonia, and not an acid like wood. It differs, also, from lignin, in being insoluble in alkaline solutions, except when they are heated and very strong. Pure ammonia dissolves a portion of it, but deposits it on expo- sure to air. Weak sulphuric acid has no action on fungin. The concen- trated acid chars it, and sulphurous and acetic acids are formed. Muriatic acid dissolves it slowly, and converts it into a gelatinous' matter. When heated with diluted nitric acid, azotic gas is disen- gaged. In this property, and in the results of its putrefaction, as well as in yielding ammonia on distillation, it approaches very nearly to animal substances. 5. Polychroite. This name has been given, by Bouillon La Grange and Vogel, to the extract of saffron prepared with alco- hol. It has a very intense yellow colour, a bitter taste, and an agreeable smell. It is soluble in water and in alcohol; and the so- lution, by exposure to light, gradually loses its colour, which is destroyed, also, by oxymuriatic acid. A few drops of sulphuric acid change the colour to a beautiful blue; and nitric acid, added in like manner, to green. Polychroite unites with lime, potash, and barytes, ; ^ l I \ vol. oxygen, or ' 2 vols, vapour of charcoal, Alcohol = \ 3 vols, hydrogen. \ a volume of oxygen. e And tripling the numbers representing the elements of sugar, in order to equalize the hydrogen of both, -{: 3 vols, vapour of charcoal, Sugar = -^ 3 vols, hydrogen, 3 half volumes of oxygen. Comparing, then, the composition of sugar with that of alcohol, 214 ETHER. CHAP- XXI. it follows that to transform the former into the latter, we must remove 1 vol. of the vapour of charcoal, 1 vol. of oxygen gas, which, by combining, form 1 volume of carbonic acid. Reducing these volumes to weights, 100 pounds of sugar should afford jl.34 of alcohol and 48.66 carbonic acid.* By distillation with the more powerful acids, alcohol undergoes an important change. It is converted into a liquid considerably lighter than alcohol, and much more volatile and inflammable, and miscible only in small proportion with water. This fluid has re- ceived the generic name of euher; and the peculiar varieties are distinguished by adding the name of the acid, by the intervention of which they have been prepared. SECTION III. Ether. I. To prepare sulphuric ether, pour into a retort any quantity of alcohol, and add, at intervals sufficient to allow the mixture to cool after each addition, an equal weight of concentrated sulphuric acid, agitating them together each time, and taking care that the temperature of the mixture does not rise above 120° Fahrenheit. Let the retort be placed in a sand-bath previously heated to 200°, and be connected, by means of an adopter, with a tubulated re- ceiver. To the tubulute of the receiver, a glass tube, twice bent at right angles, may be luted; and its aperture be immersed in a cupful of water or mercury. The condensible vapour is thus confined; while the gases that are produced are allowed to escape. '1 he receiver and adopter should be kept cool by the application of ice or of moistened cloths. As soon as the materials begin to boil, ether is produced, and passes'over into the receiver. The ebullition is to be continued, till white vapours appear in the re- tort, or a smell of sulphurous acid is perceived; and the receiver is then to be removed. The liquor, which it contains, will pro- bably have a smell of sulphurous acid. To purify it, a small quantity of black oxide of manganese may be added, and the mix- lure may be kept in a bottle about 24 hours, agitating it occa- sionally. The clear liquid is then to be decanted, and distilled in a water bath, till one half has come over. This is to be preserved in a well-closed phial. It will be, to the alcohol employed, as about 1 to 3. Cay Lussac, 95 Ann. de C'bim. 311> SECT. III. ETHER. 215 If, when the ether ceases to be formed, the receiver be removed, and the heat still continued, sulphurous acid is produced abun- dantly, and a yellowish liquor, very different from ether, distils over. This may be mixed with a small quantity of liquid potash to correct the sulphurous smell, arid then submitted to a heat suffi- cient to drive off the small proportion of ether. The oil of wine re- mains swimming on the watery liquid. II. Nitric ether may be prepared as follows. To two pints of alcohol, contained in a glass retort, add, by degrees, half a pound of nitric adid; and, after each addition, cool the materials, by set- ting the retort in a vessel of cold water. Distil the liquor by a very cautiously regulated heat, till about a pint and a half have come over. In this state the ether is far from being pure, and must be redistilled, with the addition of pure potash, pieserving only the first half or three fourths that come over. Thenard prepared nitric ether by the following process: Into a retort, he put equal parts (about 16 oz. of each) of alcohol and nitric acid; and adapted to it in succession, by means of glass tubes, five tall bottles, half filled with a saturated solution of muriate of soda. In the last, was a bent tube, opening under a jar, to receive the gas. The bottles were surrounded by a mixture of pounded ice and salt, which was stirred occasionally. To commence the operation, a little fire was applied, but it soon became necessary to extinguish it, and to cool the retort. On the surface of the saline solution, in each of the bottles, was found, after the process was concluded, a yellowish liquid, equal in weight to about half the alcohol employed. That in the first bottle was impure; but the re- maining four contained nitric ether free from admixture. Nitric ether, thus prepared, is specifically lighter than water, but heavier than alcohol. It dissolves in the latter fluid, but re- quires for solution 48 parts of water. It reddens litmus; and though this property may be destroyed by a little lime, yet the ether soon becomes acid again by keeping. It is highly combusti- ble; and much more volatile than the best sulphuric ether. It is composed, in 100 parts, of 16 azote, 39 carbon, 34 oxygen, and 9 hydrogen.* III. To prepare muriatic ether, add, to a mixture of 8 parts of manganese and 24 of muriate of soda, in a retort, 12 parts of sul- phuric acid, previously mixed, with the necessary caution, with 8 of alcohol, and proceed to distillation. The ether, thus obtained, requires to be rectified by a second distillation from potash; and is still liable to be contaminated with sulphuric ether. A more cer- tain process, which is not, however, unaccompanied with some difficulty, consists in passing oxygenized muriatic gas through alcohol; and, according to Klaproth, this kind of ether may, also, be safely and effectually prepared by distilling equal parts of alco- hol and oxymuriatc of tin. The distilled liquid is to be rectified by * Nicholson's Journal, xviii. 144. 216 ethkr. UIIAP. XXI. a second distillation with caustic potash. An improved mode of preparing this ether, and an account of its properties, by Thenard, may be found in Nicholson's Journal, xviii. 177, or in the Philo- sophical Magazine, xxx. 101. IV. Chloric ether may be formed by causing a current of olefiant gas, and another of chlorine, to meet in a glass balloon, taking care that the first mentioned gas is somewhat in excess. An oily fluid condenses, which may be purified by first washing it with a little water, and then distilling it from fused muriate of lime. It is limpid and colourless, and its smell and taste are both rather agreeable. Its specific gravity is 1.2201; its boiling point 152° Fahrenheit; its vapour, at 49° Fahrenheit, supports a column of mercury 24.66 inches high; and the specific gravity of this vapour is 3.4434, air being 1. It burns with a green flame, giving out a smell of muriatic acid and much soot. It is composed of 100 chlorine -f- 38.88 ole- fiant gas; and hence it may be inferred to consist of one atom of chlorine and two atoms of olefiant gas.* V. Phosphoric ether may be obtained, by distilling a mixture of '.hick tenacious phosphoric acid and alcohol. The first product is a portion of unchanged alcohol. After this, a liquid passes over, which has an etherial smell, and a specific gravity inferior to that 6f alcohol. It is very volatile, requires for solution eight or ten parts of water; boils at 100°; and burns with a white flame, without leaving any trace of acicl.f VI. Fluoric ether has been obtained by distilling, in a leaden retort, a mixture of equal parts of fluate of lime, sulphuric acid, and alcohol. The product of this distillation was again distilled till one half had come over, to which potash was added. This preci- pitated so much silex, as to gelatinate the whole mass, which, on being again distilled, gave a light etherial liquid of the specific gravity 7204 VII. Acetic ether may be formed by repeatedly distilling con- centrated acetic acid (procured from acetate of copper) with alco- hol, and returning the distilled liquor to the charge in the retort. The ether, thus produced, may be freed from a redundance of acid, by distillation w ith a small quantity of potash. It is heavier than other ethers, its specific gravity being .866. It is volatile; boils at 128°, and burns with a yellowish white flame. During combustion, acetic acid is developed, though none can be discovered in the ether before. This process has been repeated, with considerable attention, by Mr. Chenevix. By repeatedly distilling to dryness a mixture of ten parts of alcohol with ten parts of acetic acid, he ascertained that no change in the specific gravity of the product took place after the first distillation. Seven twelfths of the acetic acid were * Thomson, Werner, Trans, vol. i.; and Robiquet and Colin, Ann de Chim. et Phys. i. and ii. ' f See Boullay, Ann. de Chim. lxii. 192. \ Nicholson's Journal, viii. 143. SECT. III. ETHER. 217 decomposed. Dry carbonate of potash, added in sufficient quantity to absorb all the water, gave a quantity of etherial liquor, which weighed 7.4 parts, and had the specific gravity of 8.621.* Sulphuric ether will be best employed to exhibit the properties of this substance, which are the following: 1. It is extremely light, having the specific gravity of .730, or, according to Lovitz, even of .632. 2. It has been observed by Girard, that ether escapes through a capillary tube with much greater velocity than water or alcohol, the relative times, for equal quantities of each fluid, being 101 seconds For ether, 349 for water, and 856 for alcohol. The compa- rative heights, to which these three fluids rose in the same capil- lary tube, were found to be nearly 6 for ether, 9 for alcohol, and 13 for water, f 3. Ether does not, like alcohol, combine with water; and when the two fluids are shaken together, they separate again on stand- ing. Water, however, retains about one tenth its weight of ether. By repeated agitation with water, ether is brought to a high degree of purity, and acquires the property of dissolving caoutchouc. The process, as performed in presence of Faujas de St. Fond, Mr. Winch of London, is described by the former as follows: Let a pint of good sulphuric ether be put into a bottle (or, in prefer- ence, into the separator, plate i. fig. 3,) along with two pints of water; agitate the two liquids repeatedly together; then let them stand till the ether has risen to the surface; and draw off the water through the lower cock b, leaving the ether in the vessel. Repeat this process three or four times, or till scarcely one third of the ether remains; and decant the residue into a well-stopped phial. In this ether the elastic gum, cut into thin slips, soon begins to swell; but its action is slow; and about the end of five days, the so- lution is completed. The method of forming tubes, &c. with this solution, is described in the first volume of Faujas de St. Fond's Travels in England, chap. i. 4. Ether is extremely volatile. A few drops, poured on the hand, evaporate instantly; and produce a sense of great cold. By pouring a small stream of ether, from a capillary tube, on a thermometer bulb filled with water, the water is frozen, even in a warm summer atmosphere. Under the pressure of the atmosphere, it boils at 98° * Fahrenheit, and in vacuo considerably below 32°. Two ounce' measures, when converted into gas at the temperature of 72£° Fahrenheit, fill the space of a cubic foot4 According to Gay Lussac, ether, of specific gravity 0.7365 at temperature 50° Fah- renheit, produces a gas, the density of which is to that of air as 2 35 to 1. * Ann. de Chim. lxix. 45. See also Thenard on the Action of Vegetable Acids on Alcohol, Mem. d'Arcueil, ii. 5, or 37 Phil. Mag. 216. f 6 Ann. de Chim. et Phys. 239. t Saussure, jun. Vol. II.—E e -218 ETHER- eiiAP. xxi. 5. A mixture of sulphuric and muriatic ethers evaporates instan- taneously, and produces a degree of cold considerably below 0 of Fahrenheit. 6. Ether assumes a solid form, by reducing its temperature to — 46" Fahrenheit. 7. Ether is converted into a gas, either by raising its tempera- ture, or diminishing the pressure of the atmosphere on its surface. The experiments proving this have already been described, chap, iii. sect. 4. 8. Ether does not dissolve the fixed alkalies, but it combines with ammonia. 9. It dissolves essential oils and resins, and takes up about a twentieth of its weight of sulphur, which is deposited as the sul- phur volatilizes. Ether dissolves, also, a small portion of phospho- rus, and the solution, when poured on the surface of warm water in the dark, emits a lambent blue flame. 10. It is highly inflammable. This is best shown by passing a few drops into a. receiver furnished with a brass cap and cock, to which a small pipe is screwed, and inverted in water of the tem- perature of 100°. The receiver will be filled with the gas of ether, which may be expelled through the pipe and set on fire. It burns with a beautiful deep blue flame. 11. When ether is previously mixed with oxygen gas, it deto- nates loudly. Into a strong two-ounce phial, filled with ox'ygen gas, and wrapped round with a cloth, let fall a drop of ether. On ap- plying the flume of a candle, a violent detonation will ensue. Or to a portion of oxygen gas, contained in the detonating tube, fig. 28, pass up a drop or two of ether. The volume of the gas will be doubled; and, on transmitting an electric spark, a violent detona- tion will ensue, which will probably shatter the tube. In an experi- ment of Mr. Cruickshank, three measures of oxygen and one of etherial gas detonated most violently, and two and one third mea- sures of carbonic acid gas were produced. The following experiment, evincing the inflammability of ether, is described by Mr. Cruickshank, in Nicholson's Journal, 4to. v. 205: Fill a bottle of the capacity of three or four pints, with pure oxymuriatic acid gas, taking care to expel the water as completely as possible. Then throw into it about a drachm or a drachm and a half of good ether, covering its mouth immediately with a piece of light wood or paper. In a few seconds white vapour will be seen moving circularly in the bottle, and this will soon be followed by an explosion, accompanied with flame. At the same time a con- siderable quantity of carbon will be deposited, and the bottle will be found to contain carbonic acid gas. The same effect is produced, but more slowly, by alcohol; and, along with the carbonic acid and carbon, a little ether is produced. 12. Sulphuric ether was first observed by M. Planche to under- go a spontaneous change when kept in a vessel not entirely full, SECT. HI. ETHER. 219 and frequently opened and exposed to the light. By this exposure ether becomes acid in consequence of the production of vinegar, and loses somewhat of its s-veet odour and its volatility.* This ob- servation has been confirmed by Gay Lussac,f who found that ether, which had been very attentively purified, so that its boiling point did not exceed 96* Fahrenheit, nor its density 07119, and which had no action on turnsole, acquired this last property by keeping, and at the same time became specifically heavier and less volatile. When a part of the ether thus altered was distilled oft", the residue evidently contained both acetic and sulphuric ether, and a peculiar kind of oil, which Gay Lussac thinks it probable exists in all ether, since that fluid, even when recently and skilfully prepared, leaves an evident spot on the glass on which a few drops are put to eva- porate. 13. During his investigations on flame, Sir H. Davy disco- vered that when a piece of fine platinum wire is heated and placed over the surface of ether in an open glass, a pale lam- bent flame plays around it, the wire becoming red, and even white hot, and frequently inflaming the ether. At the same time, peculiarly pungent fumes arise, the production of which takes place at all temperatures, from a heat rather above the boiling point of mercury, until the ether is inflamed. These vapours are extremely acrid and pungent; they resemble chlorine in smell; and affect the eyes in a manner similar to the compound of chlo- rine and nitrogen. Their nature has been examined by Mr Fara- day}: ; but under grea> disadvantages from the smallness of the quantity in which they are produced. By passing considerable quantities of a mixture of atmospheric air and ether through a heated glass tube, containing platinum in wire and leaf, he obtain- ed a clear and colourless liquor, of a slightly acid taste and strong irritating smell. It reddened litmus paper, as did, also, its va- pour. When heated it was quickly dissipated, leaving on the capsule a slight coally mark. It united to ammonia, and formed a neutral salt, which, by careful evaporation, might be obtained solid, but was volatile, even at temperatures below boiling water, producing a peculiar fetid smell. It united with potash, and form- ed a salt, from which the acid was expelled by heat alone. The acid solution expelled carbonic acid from all the alkaline carbo- nates; and salts were obtained, from which the acid was again ex- pelled by all the stronger acids. Oxygen, hydrogen, and charcoal (the last apparently in very great proportion) are the elements of which this new acid is composed; but Mr. Faraday could not ob- tain enough to.determine their proportion. 14. According to Mr. Cruickshank, the proportion of carbon to hydrogen is in alcohol as eight or nine to one, and in ether as five to one.§ M. Saussure, however, has lately submitted ether to analysis with somewhat different results. By following the same * Ann. de Chim. et Phys. iii. 213. f Ibid. ii. 98. t Journal of Science, iii. 77. $ Nicholson's Journal, 4to. r. 205, d. 2J0 El'IIER. CHAP. XXi. processes as those which have been already described, and, also, by the rapid combustion of ether with oxygen gas, he found that 100 parts of sulphuric ether, of specific gravity 0.7155 at 68" Fahrenheit, contain Carbon........67.98 Oxygen........17.62 Hydrogen .......14.40 100. The excess of hydrogen, above what is necessary to form water with 17.62 parts of oxygen, is 12.07 parts, which, when added to j the carbon (12.07 X 67.98) give 80.05 for the olefiant gas in 100 parts of ether. The remainder 19.95 parts are water. Ether, 1 therefore, is constituted of 5 atoms of olefiant gas, and 1 atom of water; or of 6 atoms of hydrogen, 5 of charcoal, and 1 of oxygen. To understand the conversion of alcohol into olefiant gas or f ether, it is necessary/fo compare the proportion of their elements. Alcohol consists'of 100 parts of olefiant gas -|- 50 water. Ether----------100 parts ditto +25 water. If then, to alcohol, we add a proportion of sulphuric acid suffi- cient to take away the whole of the water, we obtain only olefiant gas. But if we use no more sulphuric acid, than is sufficient to abstract half, the water contained in alcohol, we then obtain ether. It must not, however, be supposed that, in practice, we are ever able to effect these conversions without loss; for a certain propor- tion of the alcohol is decomposed, by the too energetic action of the acid, into its ultimate elements, especially towards the close of the process; and beside ether or olefiant gas (whichever it may be our object to prepare) we obtain sulphurous and carbonic acids, and a charry residue. It is nevertheless true that the sulphuric acid is efficient in the formation of ether, merely by abstracting water; and that nothing, by this process, is transferred from the acid to the alcohol; for if it be stopped in time, the whole of the acid may be recovered. The complete accuracy of the results obtained by Saussure has been called in question by Gay Lussac,* chiefly on theoreti- cal grounds. Reducing these results from weights to volumes, Gay Lussac finds that ether, according to Saussure, should con- sist of Olefiant gas...... 102.49 volumes Aqueous vapour .... 40. Ann. de Chim. xcv. SECT. IV. ACETIC AOID. 221 But the density of the vapour of ether was found by experiment to be 2.581, and supposing it to be constituted of 2 volumes of olefiant gas and 1 volume of aqueous vapour, and the condensa- tion of these to be two-thirds, its density should be 2.586, an agreement so near that the hypothetical view is probably the true one. Ether, then, will be constituted of SIS".8" :::::: 's,:™^™^. or Olefiant gas.........2 volumes Aqueous vapour........1 volume And since alcohol consists of Olefiant gas.........2#volumes Aqueous vapour........ ... 2 volumes . it follows that to change alcohol into ether, all that is necessary is to take away one volume of water, or, by weight, half the wa- ter which alcohol contains. Therefore 131.95 parts by weight of alcohol, if the con%rsion could be made without loss, should give 115.975 parts of ether; a proportion which, as has already been stated, can never be obtained in practice. SECTION IV. Acetous and Acetic'Acids'. These two names were applied, by the framers of the new chemical nomenclature, to denote what were supposed to be two distinct acids, common vinegar purified by distillation being term- ed the acetous, and the highly concentrated acid, formerly called radical vinegar, being denominated acetic. To account for the su- perior strength of the latter, it was supposed to hold in combina- tion a larger proportion of oxygen derived from the metallic oxide, from which acetous acid is generally distilled, when con- verted into acetic. The experiments of Adet were the first that threw doubt upon this conclusion; and though they appeared to be contradicted by the subsequent ones of Chaptal and Dabit, yet they received the fullest confirmation from the researches of Dar- racq. The last mentioned chemist succeeded in converting dis- tilled into radical vinegar, under circumstances where no farther oxygenation could possibly be effected, viz. by repeated distillation from dry muriate of lime; which can only act by abstracting water. Both terms, however, may bo retained for the sake of JH2 ACETIC ACID. CHAI'. XXI brevity; the acetous acid denoting the dilute acid obtained by fer- mentation; and the acetic, the at;a in its most dephlegmated state. . Acetous acid may be procured by exposing to the atmosphere, at a temperature between 75° and 90° ot Fahrenheit, the liquor which has been obtained, by the vinous fermentation, from malt, sugar, or other substances. The liquor soon becomes warm; a number of ropy filaments appear; and, after several days, it ac- quire* an acid taste and smell Little or no gas is evolved; but, on the contrary, an absorption of oxygen takes place. There is n essential difference, therefore, between the vinous and acetous fermentations. The latter requires the access of air as an indis- pensable condition; whereas the vinous fermentation may be performed in close vessels, or at least in vessels which only allow egress to the elastic fluids that are produced. Common vinegar may be purified, by submitting it to distilla- tion in a glass retort. The best malt vinegar, unadulterated by sulphuric acid or colouring, has a specific gravity of 1.0204. When distilled, the first eighth part is of sp. gr. 0.997 12, and con- tains so much acid, that a fluid ounce dissolves from 4.5 to 5 grains of precipitated carbonate of lime. The subsequent six eighths are of sp. gr. 1.0023, and a fluid ounce decomposes 8.12 grains of carbonate of lime. A similar quantity, of sp. gr. 1.007, decomposes from 15 to 16 grains of precipitated carbonate of lime, or 13.8 grains of marble.* By distillation, vinegar can only be imperfectly purified. The distilled liquor always contains an extractive matter, which Darracq considers as mucilage; and, also, as Mr. Chenevix has shown, a small portion of alcohol. The ex- tractive matter, it has been found by the latter chemist, cannot be removed by repeated distillations. In French vinegar, he disco- vered a larger proportion both of acid and alcohol, with less mu- cilage, than in the vinegar of this country. From four pints of distilled French vinegar, he obtained nearly an ounce measure of ardent spirit. Acetous acid is prepared, also, in very considerable quantity by the distillation of wood. The wood is inclosed in iron cylinders or retorts, which are exposed to a red heat. An immense quan- tity of inflammable gas is produced; and a liquid is condensed, which consists of acetous acid holding in solution a quantity of tar and of essential oil. These impurities it is possible to remove entirely; so that the acid, thus prepared, may be employed for all the purposes of vinegar. A process, for the decoloration of all kinds of vinegar, has been proposed by Figuer. The agent he employs is animal charcoal, which may be prepared by calcining the most compact beef or mutton bones in a crucible, to which a cover must be luted, hav- ing a small aperture, to allow the escape of the gases, and of the Philips on the London Pharm. p. 7. SECT. IV. ACETIO ACID. 223 other volatile substances. Towards the close of the calcination, when no more flame issues, this aperture must be closed, and the heat raised for half an hour To a wine quart of cold vinegar, an ounce and half of this charcoal, finely powdered, is to be added, and occasionally stirred. In 24 hours, the vinegar begins to lose its colour, and, in three or four clays, is entirely deprived of it. It is then to be filtered through paper, and it will be found (if the charcoal has been well prepared) to retain its acidity, without hav- ing acquired any unpleasant flavour. By reducing the quantity of charcoal to one half, the change is still effected, but more slowly. Acetous acid unites with alkalies, earths, and metallic oxides. When potash, saturated with this acid, is evaporated to dry- ness, the salt assumes a black colour. On being re-dissolved, however, and again evaporated, the salt is obtained white, and, when fused and suffered to cool, affords the acetate of potash. This salt strongly attracts moisture from the air, and is very soluble in water. When exposed to a pretty strong heat it is de- composed; carbonic acid and carbureted hydrogen gases come over; and, in the retort, there remains a mixture of carbon with carbonate of potash- When this salt is distilled, with half its weight of sulphuric acid, the vegetable acid is expelled in a very concentrated form, mixed with sulphurous acid. Digestion with a small portion of manganese, and subsequent distillation, affords it pure. It may be obtained, also, by distilling equal parts of acetate of lead and sulphate copper. Or The crystallized acetate of copper, contained in a glass retort, which may be nearly filled with the salt, may be submitted to dis- tillation in a sand-heat. The acid that comes over has a green co- lour, and requires to be rectified by a second distillation. Its specific gravity then varies from 1056 to 1080. If the products be reserved in separate portions, it has been observed by MM. De- rosne,* that those which are obtained towards the close, though specifically lighter than the earlier ones, are still more powerfully acid, assuming, as the test of their strength, the quantity of alkali which they are capable of saturating The last products, it was found also, when submitted to distillation, yield a liquid which has even less specific gravity than water. This liquid may be ob- tained, in a still more perfect state, by saturating the latter por- tions of acetic acid with caustic and solid potash; the acetate of potash precipitates; and a fluid swims above it, which may be rectified by distillation at a gentle heat. It is perfectly limpid; has a penetrating taste; is lighter than alcohol; evaporates rapidly with the production of cold when poured upon the hand; and is highly inflammable. It does not redden litmus. Excepting that it is miscible, in any proportion, with water, it has all the quali- * Annales de Chimie, lxiii. 267. 224 AQETIO ACID. rirtw. XXI. ties of ether, and like that fluid has the power of decomposing the nitro-muriate of gold. , MM. Derosne have proposed for it the name of pyro-acetic ether. Its production, they observe, is con- fined to the latter stages in the distillation of acetate of copper, and is owing, they suppose, not to any modification of alcohol, but to changes in the arrangement of the elements of the salt. These observations are confirmed by the subsequent ones of M. Mollerat.* Examining two portions of acetic acid, which had pre- cisely the same specific gravity, (viz. 1063,) he found that the one contained 87 per cent, of real acid, and the other only 41. The first he is disposed to consider as the strongest acetic acid that can be procured. It may be distilled at a very moderate heat with great rapidity, and without entering into ebullition. To this acid, having the specific gravity 1063 (and of which 100 grains required for saturation 250 of sub-carbonate of soda,) he gradually added water, and found, though water is lighter than the acid, yet that the density of the mixture increased till it became 1079. From this point, the additions of water occasioned a regular diminution of specific gravity. M. Chenevix has since observed the same ano- maly, in the acid produced from acetate of silver. Acetic acid, thus prepared, has several remarkable properties. Its smell is extremely pungent* and it raises a blister when applied to the skin for a sufficient length of time. When heated in a silver spoon over a lamp, its vapour may be set on fire. At the tempera- ture of about 38° Fahrenheit it becomes solid and shoots into beau- tiful crystals, which again liquify at 40°. It appears not to be easily destructible by heat; for Mr. Chenevix transmitted it five times through a red hot porcelain tube, with the effect of only a partial decomposition. Gay Lussac and Thenard, and Berzelius, have recently analyzed acetic acid; the twro first by the combustion of acetate of barytes, of known composition, with hyper-oxymuriate of potash. Their results are as follow. One hundred grains of acetic acid consist of Carbon. Oxygen. Hydrogen. According to Gay Lussac . 50.224 . 44.147 . 5.629 ------------- Berzelius . . 46.8 . . 46.9 . . 6.3 The proportions obtained by Gay Lussac and Thenard may be> stated also as follows: Carbon........... 50.224 Oxygen and hydrogen in the same) 4*01, proportions as in water .... £46-911 Excess of oxygen......; . 2.865 100. * Annales de Chimie, lxviii. 88; or Nicholson's Journal, xxr. 1 jj ,*F.CT. IV. ACETIC ACID. S&5 The acetic acid enters, like vinegar, into combination with alka- lies, earths, and metallic oxides. The acetate of potash, formed with this acid, is perfectly white; and does not, when liquefied by heat, become blackened by the separation of charcoal, like that afforded by common vinegar. It is deliquescent, and soluble in about ifs own weight of cold wa- ter; and in twice its weight of boiling alcohol. By distillation per se, its acid is decomposed and resolved into pyro-acetic ether, car- bonic acid, and carbureted hydrogen gases. Acetate of soda is crystailrzable; does not deliquesce in the air: dissolves in less than its own weight of cold water, or in twice ijs weight of boiling alcohol; and gives, by destructive distillation, similar products to the acetate of potash. Berzelius found it to oonsist of Acetic acid.......36.95 Soda.........22.94 Water........ 40.11 100. Or exclusively of water, Acid......61.689 ... 100 Soda......38.311 . . . 61.1 100. Acetate of ammonia derives its only importance from having been long employed in a liquid form in medicine, under the name of Spirit of Mindererus. The solution does not yield crystals by evaporation, but affords a deliquescent mass, which is readily solu- ble in water and in alcohol; and, in its solid form, is volatilized at 250° Fahrenheit. Acetate of lime may be made, by careful evaporation, to crys- tallize in the form of small silky needles. It is permanent in the air, and very soluble both in water and alcohol. According to Ber- zelius, it is composed of Acid......64.218 . . . 100. Lime......35.782 . . . 5 5.74 100. Acetate of barytes is a crystallizable salt, which does noj grow moist, but rather loses a portion of its water, by exposure to the air. It requires for solution about twelve parts of cold, and not quite two parts of boiling water. Alcohol dissolves only a very small proportion. By distillation per se} Mr. Chenevix finds that Vol. II—F f 226 ACETIC ACID. OUAP. XXI. it gives pure pyro-acetic ether, of the specific gravity, 0.845, co- loured by a little empyreumatic oil. Gay Lussac and Thenard state its composition to be , Acid.........43.17 Base .......... 56.83 100. Acetate of strontites is more*soluble than the last mentioned acetate, requiring only about twice its weight of cold water for so- lution. Its properties have not been fully investigated. Acetate of magnesia cannot be obtained in crystals, but only in the state of a thick viscid mass, which is extremely deliquescent, and soluble both in water and alcohol. Acetate of alumine is generally formed, by double decompo- sition, from the mixed solutions of acetate of lead or lime and sul- phate of alumine. It is a compound of considerable importance from its use in dyeing and calico-printing. When applied, how- ever, to these purposes', it contains always a quantity of common alum, and the properties of the pure combination of alumine with acetous acid are but imperfectly known. Gay Lussac,* however, has found that it has the remarkable quality of being decomposed by heat and of depositing alumine, which it re-dissolves on cooling. The effect takes place, even in vessels hermetically sealed, and when the solution has an excess of acid. It appears to bear some analogy to the coagulation of animal albumen. The metallic acetates have been, for the most part, already described in the history of the individual metals. To our know- ledge of this class of salts, some valuable additions have been made by Mr. Chenevix.t By distilling per se the different metallic ace- tates, that excellent chemist found that the salts with bases of lead, zinc, and manganese, yield a liquid lighter considerably than water, but heavier than alcohol, and containing only a very small propor- tion of acid. This degree of levity is owing to the presence of the peculiar fluid, which Derosne has termed pyro-acetic ether, but to which Mr. Chenevix is of opinion, the less definite name of pyro- acetic\spirit will be better adapted, till we obtain a more accurate knowledge of its nature and properties. Of all the metallic acetates, that of silver gave a product of the greatest specific gravity, and of greatest power in neutralizing alka- lies. In this respect, it exceeded, by about one fifth, an equal weight of the acid distilled from copper. It contained, however, none of the pyro-acetic spirit discovered in the acid from copper. The residuum in the retort contained, in every case, a proportion of charcoal. When the acetates of silver, nickel, copper, or lead, were * 74 Ann. de Chim. 93; and 6 Ann. dc Chim. etPhys. 201. f Ann tie Chim. vol. lxix, or Nicholson's Journal, vol. xxvi. WHAP. xxn. animal substances. 227 distilled, the metal was found in a metallic state; but zinc and man- ganese were left in the state of oxides. The pyro-acetic spirit, obtained from the acetate of lead, Mr. Chenevix describes as perfectly limpid and colourless. It has a taste, which at first is sharp and burning, but afterwards becomes cool and somewhat resinous. Its smell resembles that of volatile oils, but it is not easy to say of which particular one. Its specific gravity, when rectified by muriate of lime, is 0.864. It is very com- bustible, and leaves no sensible residue. Its boiling point is 138° Fahrenheit. It is miscible in all proportions, with water, with alco- hol, and with all the volatile oils, and, at a temperature considera- bly below its boiling point, with the fixed oils. When heated it dissolves sulphur and wax. CHAPTER XXII. ANIMAL SUBSTANCES. The products of vegetable and of animal life, though they agree in many of their external characters, and even in some of their chemical relations, present several circumstances of distinction, which, in general, sufficiently discriminate the two classes. Ani- mal substances are the results of still more delicate processes, and of a more refined organization; and the balance of affinities, by which they exist, is disturbed by still slighter causes. To the three great components of vegetable matter (oxygen, hydrogen, and carbon) a fourth is, in animal substances, added, and consti- tutes a large proportion of their structure. To the nitrogen, which they contain, are owing some of the most important quali- ties that distinguish this class of compounds. Hence it is, that in- stead of passing through the vinous or acetous fermentations, they are peculiarly prone to undergo putrefaction; and that, during this m change, they yield, among other products, both nitrogen gas and ammonia When exposed to a high temperature, ammonia is, also, generated, in great abundance, by their decomposition; little or no acetic acid is produced; and the coal, which remains, dif- fers from vegetable charcoal, in being much less combustible. This general description, however, though it applies to most indi- viduals of the animal kingdom, is not strictly true with respect to all. Animal jelly, for example, is rendered sour by spontaneous decomposition. A few vegetable substances, it may also be added, gluten for instance, become at once putrid; and furnish ammonia when decomposed by heat. In the analysis of animal substances, less precision had till lately been attained, than in that of mineral and vegetable pro- 228 ANIMAL SUBSTANCES. CH\r. XXlt. ducts. It may be considered as of two different kinds. By the first we obtain the proximate principles of animal matter, or cer- tain compounds which, we may presume, are separated by the simple processes used for their extraction, in a state identical with that, in which they exist in the animal structure. Thus by the long continued action of hot water on bones, we form a solu- tion, which separates spontaneously into two distinct substances, fat and gelatine; while the earthy ingredients remain undissolved. The substances, thus obtained, are not very numerous; and to dis- tinguish them from more complicated products they may be call- ed primary animal compounds. But, by spontaneous decomposi- tion, or by the agency of heat, we give origin to a set of bodies which had no existence in the subject of experiment, the ultimate elements of which are thus disunited, and are re-combined in a new manner. Bones, for example, though they contain no vola- tile alkali, are yet composed, in part, of its elements (nitrogen and hydrogen,) which, at a high temperature, unite and generate ammonia. The method of analysis, so successfully applied, by Gay Lussac and Thenard, to the products of the vegetable kingdom, has been extended, also, to animal substances;* and, in the history of each, the proportion of its ultimate elements will be stated, chiefly on their authority, or on that of Berard or Prout. Animal sub- stances, they observe, contain much more carbon than those de- rived from the vegetable world; in all of them, the hydrogen is in excess with relation to their oxygen; and lastly, the greater this excess, the more azote they contain. It is remarkable, moreover, that this azote, and the excess of hydrogen, are very nearly in the proportions required to constitute ammonia. Animal matters, then, such as fibrin, albumen, gelatine, &c. are composed of charcoal; of hydrogen and oxygen, in the proportions required to form water; and of hydrogen and azote, in the pro- portions necessary to constitute ammonia. They hold, therefore, among animal matters, the same rank that sugar, gum, lignin, 8cc. possess among vegetable substances. The animal acids, again, consist, probably, of carbon, oxygen, hydrogen, and azote, in such proportions, that the oxygen and azote are in excess relatively to the hydrogen. And the animal oils, on the other hand, will in all probability be shown to contain more hydrogen, than is sufficient to convert their oxygen into water, and their azote into ammonia. Thus animal substances will be divided, like vegetable ones, into three great classes, relatively to the quantities of hydrogen, oxy- gen, and azote, which they contain. The primary animal compounds are not very numerous; the * Ann. de Chim. xcvi. 53; and Berard, Ann. de Chim. et Phys. v. 290, where the process is fully described. See also Mr. Porrett's remarks, Phil. Trans. 1815, p. 225; and Dr. Prout's in the Medico-Chirurg. Trans, viiii 530. SECT. I. S.LT.ATINE. 229 following list comprehending, perhaps, the whole of those which arc sufficiently well characterized. 1. Gelatine. 6. Resin. 2. Albumen. 7. Sugar. 3. Mucus. 8. Oil. 4. Fibrin. 9. Acids. 5. Urea. SECTION I. Anithal Jelly, or Gelatine. Ammal jelly is an abundant ingredient, not only of the fluids of the body, but of the hard and solid parts. Berzelius, indeed, in his View of Animal Chemistry, p. 50, considers gelatine as a. pro- duct of the operation of boiling; and denies its existence in any one fluid of the body. This opinion, however, requires further evi- dence in its favour. By long continued boiling it may be extracted from the skin, membranes, ligaments, cartilages, and even from the bones. The solution, on cooling, forms a tremulent and im- perfectly cohering mass, well known by the name of jelly; and, if the watery part of this mass be dissipated by a very gentle heat, we obtain a hard semi-transparent substance, which breaks with a glassy fracture, and, according to the source from which it has been obtained, has the names of isinglass, glue, portable soup, &c; all of which are varieties of animal gelatine. M. D'Arcet pre- pares gelatine from bones, not by boiling, but by dissolving out the earthy matter by means of diluted muriatic acid. The gela- tine remains in a solid state, preserving the form of the bone. To purify it from small remains of acid and fat, it is plunged for an instant into boiling water, then exposed to a current of cold water, and quickly dried, in which state it is unalterable by keeping.* Isinglass, however, as the purest form under which gelatine com- monly occurs, will be best employed for the exhibition of its che- mical properties. I. Dry gelatine, when immersed in water, gradually absorbs it, swells considerably, and becomes soft and elastic. At common temperatures, however, it is not dissolved; all that is thus effected being the absorption of a quantity of water, which it loses again by a gentle heat. But in hot Water it dissolves slowly, yet completely; and affords a liquid which again gelatinates on cooling. These alternate solutions and desiccations may be repeated for any num- ber of times, without occasioning any change in the chemical pro- perties of the gelatine which is submitted to- them. * Phil. Mag. xlvi. 17. 230 ANIMAL sUHSiANCES. OHA?. xxir The proportion, in which gelatine forms a solution capable of concreting by cooling, has been determined by Dr. Bostock.* One part of dry gelatine to 100 parts of water gave a solution, that completely stiffened by cooling; but one part of gelatine to 150 parts of water produced a compound, which, though evidently gelatinous, did not assume the concrete form. 2. Gelatine in a solid state seems to be absolutely indestructible when kept in a dry place; but, when in the form of solution or of jelly, it is generally said to become first sour, and afterwards pu- trid. The production of acid, however, Dr. Bostock informs me; he is disposed to question. 3. Gelatine is insoluble in alcohol, but it is not precipitated, by that fluid, from its watery solution. 4. It readily dissolves in most of the acids. Isinglass, dissolved in common vinegar by the assistance of a gentle heat, forms a very useful and adhesive cement. Nitric acid, even when cold and very dilute, is a powerful solvent of gelatine. When the solu- tion is evaporated, the acid and gelatine rc-act upon each other; nitrous gas is disengaged; and, il the concentrations be not carried too far, oxalic and malic acids are obtained from the residuum. Muriatic acid dissolves gelatine, and retains it unchanged in solu- tion. If oxymuriatic acid be passed through a solution of gela- tine, white filuments appear, which, when collected, are found to be very flexible and elastic. They consist of gelatine, very little altered, and united with muriatic acid and Oxymuriatic acid. They are insipid; insoluble in water and in alcohol; not putrescible; and exert a feeble action on blue vegetable colours, although they con- tain a large proportion of acid. Exposed to the air during some days, they emit oxymuriatic acid at common temperatures; and still more abundantly when heated. In alkaline solutions they disappear, and muriatic salts are formed.f 5. Gelatine is soluble in pure liquid alkalies. The solution is a brownish viscid substance, which has none of the characters of soap,t and is not precipitated by acids. This is a property which distinguishes gelatine from albumen, fibrin, and other animal pro- ducts; and which points out a method of separating it from them in analysis. Owing to the solvent power of alkalies, they do not occasion any precipitation in acid solutions of gelatine; but when added in excess, dissolve it. 6. Several of the metallic salts and oxides have the property of precipitating gelatine; but not so unequivocally, as to be good tests of its presence. Goulard's extract of lead (prepared by boil- ing litharge in distilled vinegar) effects no change in a solution of gelatine. The same may be said of corrosive muriate of mercury. Nitrate of silver and nitro-muriate of tin produce a slight, and al- most imperceptible, opacity. The addition of nitro-muriate of * Nicholson's Journal, xi. and xiv. \ Thenard, Memoires d'Arcueil, ii. t Hatchett, Philosophical Transactions, 1800. bECI. I. GELATINE.. A } 1 gold causes a small quantity of a dense precipitate, from a solu- tion containing one 50th of gelatine, but not from more dilute solutions. 7. One of the most active precipitants of jelly is tan; and Dr. Bostock finds the extract of ihatania, digested in hot water, and filtered after it becomes cold, to be a convenient form for keeping that test. When the proportion of gelatine to water is so small, as to compose only one 5000th part of the solution, a considerable precipitate is produced by an infusion of galls 'prepared by mace- ration an ounce of galls in a pint of water.) The stronger the so- lution of jelly, the more copious is the precipitate; till at length, when the gelatine is in large proportion, a dense coagulum is form- ed, which, after being dried, in the open air, becomes a hard sub- stance with a vitreous fracture. This compound appears to be equally formed, when animal solids, composed chiefly of geHttine, are immersed in solutions of tan; as when the skins of animals, for instance, are steeped in an infusion of oak bark. It is perfectly insoluble in water, and incapable of putiifying; and it constitutes the preservative part of tanned leather, to which it imparts the property of resisting the transmission of moisture. The operation of tanning, then, consists essentially in the attraction of tan, from liquors which contain it, by the gelatine of the skins. It would have been an important step towards the accuracy of the analysis animal substances, if we could have ascertained the quantity of gelatine in any fluid, by precipitating it with tan. But to this there are two obstacles. Tan acts, also, on other animal fluids; upon albumen for instance. It appears also, that into the precipitate of tan and jelly, these substances do not enter in abso- lutely fixed proportions. In general, however, Dr. Bostock has been led to conclude that the compound, formed by the union of jelly and tan, consists of somewhat less than two parts of tan to three of gelatine. And as we always have it in our power to as- certain what quantity of tan is employed in precipitating any so- lution of jelly, we may, by an easy calculation, approximate the quantity of jelly, contained in the fluid we are examining. 8. Gelatine has been analysed by Guy Lussac and Thenard, who employed the chlorate of potash for its decomposition. One hun- dred parts were found to contain Carbon.......47.881 Oxygen.......27.207 Hydrogen......7.914 Azote........16.998 100. In this analysis, there are 4.204 parts of hydrogen, beside what is sufficient to saturate the oxygen; Wq are not acquainted with those circumstances, that occasion Ihe differences in the several kinds of animal gelatine. Some 23° ANIMAL SUBSTANCES. CHAP. XX.11. valuable remarks on them may be found in Mr. Hatchett's " Ob- servations on the component Parts of Animal Membrane.*" SECTION II. Albumen. With the exception of gelatine, no fluid appears to enter so largely into the composition of animal substances, as albumen. It forms a large proportion of the blood and of various secretions; and appears to be the chief basis of several of the solids; viz. of the thin membrane which constitutes the cellular texture, as well as • of th# skin, glands, and vessels that convey the fluids. The white of an egg, though not composed of an absolutely pure albumen, contains it sufficiently so for the exhibition of its properties. These will be found to be the following: 1. By agitation with water, the two fluids unite, and form a vis- cid liquid, the component parts of which do not separate by stand- ing. This solution gives a green tinge to vegetable blue colours; a proof of the presence of uncombined alkali. 2. At the temperature of 160° Fahrenheit, undiluted albumen becomes solid, a change which is called its coagulation. When the solid mass is cut into slices, and suffered to remain for some hours, a few drops of a brownish viscid fluid ooze out, amount to 4£ grains from 100 of the original albumen submitted to experi- ment. By a long continued gentle heat, the coagulated substance itself loses at least four fifths of its weight; and the solid matter is left behind, in the form of a hard brittle transparent substance. Hence it will follow, that 100 grains of the white of egg consist of 80 grains of water, A\ uncoagulable matter, and only 15^ of pure albumen. At a temperature below that required for its coagula- tion, Dr. Bostock finds that it may be dried, and redissolved in water.f Coagulation by heat is the distinguishing character of albumen, and affords an easy and obvious test of its presence; even when it forms a very minute proportion of certain fluids. By adding it, in gradually diminished quantity, to water, Dr. Bostock found that a solution, containing only one 1000th its weight of albumen, was rendered perceptibly opaque by a boiling temperature. For all practical purposes, therefore, this may be considered as a suffi- ciently accurate test of its presence in any fluid. The uncoagulated part of the white of egg, Dr. Bostock ascer- tained, was not affected by muriate of mercury, or by infusion off galls; but was copiously precipitated by Goulard's extract of lead. He * Philosophical Transactions, 1800. f Medico-Chir. Trans, ii. 169. SECT. II. ALBUMEN. 2Sr3 considers it as a peculiar fluid to which he has given the name of mucus. Dr. Marcet, who finds it to be an ingredient of several morbid fluids, has proposed to call it muco-extractive matter.* Albumen, which has been coagulated by heat, though perfectly insoluble in water, unless by long boiling aided by a Papin's di- gester, appears to have undergone no change in its chemical con- stitution. During coagulation, there is no absorption of oxygen; no gas is extricated; and hence there appears to be no re-action of the principles of the compound on each other. The coagulum is taken up by dilute liquid alkalies with a disengagement of ammo- nia. From this combination it is precipitated, unchanged, by acids.t By long boiling in water, however, though no apparent solution takes place, Mr. Brande obtained, from coagulated albu- men, a fluid which had alkaline properties; and which gave, after evaporation, a viscid substance, soluble in water. This fluid he apprehends to be a dilute solution of albumen in alkali.^ 3. Albumen is coagulated by alcohol, and by acids. The coagu- lum, formed by the latter, always retains in combination, according to Thenard, a portion of the acid which has been employed. That produced by nitric acid is least soluble; and hence nitric acid oc- casions a precipitate from solutions of albumen, which are so di- lute as not to be affected by other acids. The coagulum, produced by acids, is re-dissolved by pure alkalies, even, as Thenard finds, by ammonia, which does not dissolve albumen that has been co- agulated by heat. Alum, probably in consequence of its excess of acid, coagulates albumen; but does not act on very dilute solutions. One part in 500 of water is rendered slightly turbid by a solution of alum; but no precipitate is formed. 4. Albumen is coagulated by several of the metallic salts. So- lution of corrosive muriate of mercury, which has no effect on ge- latine or mucus, is a delicate test of the presence of albumen. A single drop of the solution, added to a liquor containing one 1000th its weight of albumen, renders it visibly milky; and, at the end of some hours, a flocculent precipitate falls to the bottom of the ves- sel. The same re-agent produces a sensible effect on a liquid, containing only half that quantity, or one 2000th of albumen. Solution of corrosive sublimate, however, does not separate the whole of the albumen, unless heat is employed. The precipitate is a compound of the metallic salt with albumen, in the proportion of about one of the former to three or four of the latter. From the quantity of corrosive sublimate, therefore required to decompose entirely a solution of albumen, we may infer the quantity of the latter; for three grains of the metallic salt, being entirely decom- posed, indicate 10§ grains of albumen. Nitro-muriate of tin precipitates albumen, but less actively than ' Medico-Chir. Trans, ii. 377. f Thenard, Ann. de Chim. Ixvii. 821. t Philosophical Transactions, 1809. Vol. II.—G g 2J4 ANIMAL SUBSTANCES. CHAP. XXII. the foregoing salt. Water, holding one 500th ofalbumcn; was not altered by this test, till after some hours, when it became milky- Nitrate of silver occasions a precipitate; but the effect is equivo- cal, from its precipitating, also, the muriate of soda. Nitro-mu- riate of gold, throws down a dense precipitate from a solution con- taining one 1000th of albumen. Goulard's extract occasions an abundant dense coagulum. 5. Solutions of albumen are decomposed by the addition of tan. When an infusion of galls, containing 2£ parts of solid extract in 100, is added to a liquor, of which albumen forms only one 1000th part, no immediate effect is apparent; but, after some time, a pre- cipitate ensues. If infusion of tan be poured into a concentrated solution of albumen, the precipitate has the consistence of pitch; is not susceptible of putrefaction; and, when dry, is brittle like over-tanned leather. The precipitate by tan from diluted albumen, Dr. Bostock observes, is incoherent, subsides very slowly, and can scarcely be separated by a filtre; whereas the precipitate from so- lution of jelly of the same strength is a hard dense substance, which almost immediately separates from the fluid, and may be collected in a distinct mass. 6. Albumen, in whatever way it has been coagulated, appears to be slow in undergoing putrefaction. Mr. Hatchett kept it for some weeks under water, without any tendency tp that state. Ac- cording to Scheele, a small portion of coagulated albumen is solu- ble in dilute acids, and precipitable by the some acids when con- centrated. By steeping albumen, for a month in dilute nitric acid, Mr. Hatchett converted it into a substance which was soluble in water, and affected chemical' tests like gelatine. 7. Albumen contains a portion of sulphur in intimate combina- tion, which gives it the property of blackening silver. This effect is often observed to be produced by eggs on spoons of that metal; and blood, evaporated in silver vessels, stains them with sulphuret of silver. Many theories have been formed of the cause of the coagulation of albumen; but the first probable conjecture on the subject ap- pears to have originated with Dr. Thomson.* The fluidity of al- bumen he supposed to depend on the presence of alkaline matter, and its coagulation on the removal of the alkali, or its saturation with some other substance. This suggestion has been confirmed by some well devised experiments of Mr. Brande.t When the white of an egg was exposed to the action of a galvanic battery, a rapid and abundant coagulation took place round the negative pole, while a thin film only collected at the positive wire. This more copious precipitation at the negative pole appears to have been owing to the separation of alkali; and as it required, in order to produce the effect, a comparatively high electrical power, it should * System of Chemistry, v. 489. f Philosophical Transactions, 1809. SECT. III. MUCUS. 23.5 follow that the rapid abstaction of alkali is necessary to the perfect coagulation of albumen. White of egg, then, is a compound of albumen with alkali and water. When heat is applied, the alkali is transferred to the water, and the albumen becomes insoluble. The alkaline liquor, which is thus produced, re-acts upon and dissolves.a small quantity of co- agulated albumen. When alcohol or acids are the coagulating powers the effect is owing to a like transfer of alkali. When the uncoagulable part of white of egg was exposed to a strong galvanic power, uncombined soda was found in the nega^. tive cup; and muriatic acid with a little coagulated albumen in the positive one. Hence fluid albumen contains both free soda and muriate of soda. In the experiments of Mr. Hatchett, 500 grains of dry albumen afforded 74£ of coal, of which 11^ were saline mat- ter, composed, besides the salts that have been mentioned, of phos- phate of lime and of phosphate and carbonate of soda. From the researches of Mr. Brande it appears that galvanism may be applied to the discovery of very minute quantities of albu- men, which are not rendered sensible by any other test. In this way, he produced a rapid coagulation, at the negative pole, in se- veral animal fluids, in which albumen had not been supposed to exist. It has been ascertained, also, by Sir E. Home, that albumen is coagulated by galvanic arrangements of too low a power to af- fect even the most delicate electrometer; and hence he has pro- posed albuminous fluids as tests of the presence of small quantities of electricity.* Albumen was found by Gay Lussac and Thenard, to consist of Carbon.......52.883 Oxygen.......23.872 Hydrogen.......7.540 Azote........15.705 100. Beside, therefore, tfie hydrogen required to saturate the oxygen, there are 4.285 parts in excess. SECTION III. Mucus. The term mucus had been employed in a vague and general sense, until Mr. Hatchett, in his valuable paper on the component parts of animal membrane,* attempted to assign to it a more defi- * Philosophical Transactions, 1809. f Phd- Trans. 1800. 236 ANIMAL SUBSTANCES. CHAP. XXII. nite meaning. Jelly and mucus he considers as modifications of the same substance, and as not essentially differing from each other. The latter term he restricts to that animal substance, which is soluble in cold water, and which cannot be brought to assume the gelatinous state. Dr. Bostock, however, has endeavoured to prove that mucus is a distinct fluid, characterized by a train of properties, which are entirely different from those of animal gela- tine.* Fourcroy and Vauquelin have admitted, also, its claim to be considered as a peculiar compound.t They apply the term, in an enlarged sense, to the viscid liquid, which lubricates the mouth, the oesophagus, the stomach, the intestines, and, in general, all the cavities and passages of the body. It differs, they suppose, from vegetable gum, in nothing but in containing a proportion of nitrogen. In the descriptions of its characters, however, they are much less precise than either of the English chemists Berzelius, on the other hand, seems scarcely to admit any fluid entitled to the general name of mucus; and finds that its chemical characters vary in different parts of the body, according to the purpose which it is intended to fulfil in the animal economy.! The substance on which Dr. Bostock's experiments were made, • was the saliva of the mouth, dissolved in water by agitation. No appearance of coagulation was produced by raising the tempera- ture of this liquid to 212°, nor, when the liquid was evaporated, and suffered to cool, did it show any tendency to gelatinate. "" No distinct effect was produced on the solution of mucus, by adding nitro-muriate of tin, muriate of mercury, or infusion of galls. Goulard's extract occasioned an immediate opacity, and, after some time, a flaky precipitate. Hence the effects, produced by the tanning principle and by Goulard's extract, establish a de- cided and essential difference between mucus and gelatine. Tan is a most delicate test of gelatine; but does not, in any degree, af- fect mucus. Goulard, again, is a sensible test of mucus, but not of jelly. Corrosive muriate of mercury, on the contrary, which discovers very small proportions of albumen, is not affected by either jelly or mucus. Hitherto, however, Dr. Bostock has not been able to devise a method of determining, exactly, the proportion of mucus in any compound fluid. One great obstacle to all attempts of this kind is, that mucus, beside animal matter, appears always to contain common salt, which acts upon the tests; so that it is impossible to say, how much of the effect is owing to each of these separate causes. The precipitates, thrown down from mucus by acetate of lead and nitrate of silver, Mr. Brande has found to consist both of the muriates and phosphates of those metals. For 1000 grains ©f saliva, he obtained by evaporation 120 grains of dry residuum, of which twenty grains were saline matter. The proportion of * Nicholson's Journal, xi. and xiv. f Annales de Chimie, lxvii. J View of Animal Chemistry, p. 58. SECT. IV. FIBRIN. 237 salts, in the mucus of the trachea, was even still greater. This variety of mucus, was not coagulated either by heat, by alcohol, or by acids. In order to obtain mucus free from neutral salts, it occurred to Mr. Brande to attempt their decomposition by electricity. With this view, a mixture of saliva and water was placed in a vessel in- termediate between two others, which contained water only (see i, fig. 82,) and which were connected, the one with the positive, the other with the negative, extremity of a galvanic apparatus. Fibres of cotton connected the central vessel with the two others. In about ten minutes, a considerable quantity of white coagulum was formed upon the cotton on the negative side; but none on the po- sitive. Thus albumen appears to be a constituent part of saliva, though not discoverable by the usual tests. A separation of alkali took place on the negative side; and hence Mr. Brande is disposed to consider mucus as a compound of albumen and muriate of soda, or of albumen and pure soda. The whole of this subject, how- ever, is still obscure; and requires to be illustrated by farther ex- periments. When mucus is evaporated to dryness by a gentle heat, no ma- terial change is produced in it. The result is a semi-transparent substance resembling gum, and, like it, soluble again in cold wa- ter. Neither alcohol nor ether dissolve it. By destructive distilla- tion, it yields only the common elements of animal matter. Mucus, as appears from Dr. Marcet's experiments, beside forming an ingredient of several healthy secretions, exists in some morbid fluids, particularly in that effused in all the forms of dropsy. SECTION IV. Fibrin, or Animal Gluten. » Fibrin forms the basis of the muscular or fleshy parts of ani- mals, and remains, combined with albumen, when all the soluble parts have been washed away by water. It may also be obtained from blood, by laying the coagulum on a linen strainer, and pour- ing water upon it, till a white fibrous matter alone remains. For the purpose of submitting fibrin to a series of experiments, Mr. Hatchett obtained it by digesting shreds of lean beef, during 15 days, in water, which was changed daily, the temperature being such as not to excite putrefaction. The shreds of the muscle were then boiled for five hours every day, during three weeks, changing the water at each boiling; and, finally, the residue was put into a press, and dried by the heat of a water bath. The following history of the chemical properties of fibrin is de- rived chiefly from a memoir of Berzelius. 333 \MMAL SUBSTANCES. CHVP. XXII. I. Fibrin is insoluble in cold water; but ^ iter, after being boiled upon it for some hours, is found to have acquired a milky hue, and, on the addition of infusion of tan, affords a precipitate of white and distinct flocculi, which do not cohere like those pro- duced by gelatine. The liquid, obtained by boiling fibrin, does not gelatinate, to whatever degree it may be concentrated, but gives a white, dry, hard, and friable residue, which is soluble in cold water. By long boiling in water, fibrin loses its property of softening and dissolving in acetic acid. 2. Alcohol, of the specific gravity .810, converts fibrin into a kind of adipocirous mattef, which is soluble in alcohol, and is pre- cipitated by the addition of water. When alcohol, which has been digested on fibrin, is evaporated, a fatty residue is left, which did not pre-exist in the fibrin. By the action of ether, fibrin is con- verted into an adifiocirc, similar to the preceding, but in much greater abundance, and distinguished by a much more disagreea- ble odour. 3. In concentrated acetic acid, fibrin immediately becomes soft, transparent, and, with the assistance of heat, is converted into a tremulous jelly. By the addition of warm water, this jelly is com- pletely dissolved, with the evolution of a small quantity of azotic gas. The solution is colourless, and of a mawkish and slightly acid taste. By sufficient evaporation, the gelatinous substance is reproduced, which, when completely desiccated, is a transparent mass, insoluble in water without the addition of fresh acetic -acid. The solution gives a white precipitate with ferro-prussiate of pot- ash, and with pure alkali; but a slight excess of alkali re-dissolves it. Sulphuric, nitric, and muriatic acids also occasion a precipi- tate, which consists of fibrin and the acid that has been employed. When laid on a filter and washed, a certain quantity of this acid is carried off by the water, and the remaining substance is soluble in pure water. 4. In weak muriatic acid, fibrin shrinks, and gives out a little azotic gas, but scarcely any portion is dissolved, even by boiling. Concentrated muriatic acid, when boiled on fibrin, decomposes it, and produces a red or violet coloured solution. Fibrin, that has been digested with weak muriatic acid, is hard and shrivelled. By repeatedly washing with water, it is at length converted into a gelatinous mass, which is perfectly soluble in tepid water. The solution reddens litmus paper, and yields a precipitate with acids, as well as with alkalies. 5. Concentrated sulphuric acid decomposes and carbonizes fibrin. The same acid, diluted with six times its weight of water, and di- gested with fibrin, acquires a red colour, but dissolves scarcely any thing. The undissolved portion is a compound of fibrin with an excess of sulphuric acid; and when this excess is removed by wa- ter, a neutral combination is obtained, which is soluble in water, and possesses the same characters, as the neutral compound of fibrin and muriatic acid. SECT. V. IKEA. 23§ 6. Nitric acid of the specific gravity 1.25 disengages at first azotic gas from fibrin, pure and unmixed with nitrous gas. By con- tinuing the digestion 24 hours, the fibrin is converted into a pul- verulent mass, of a pale citron colour, which, when placed on a filter and washed with a large quantity of water, becomes of a deep orange colour. This yellow substance was discovered by Fourcroy and Vauquelin, who obtained it by treating muscular flesh with nitric acid, and who gave it the name of yellow acid. Berzelius has ascertained that it is a combination of nitric and malic acids with fibrin, which is in some degree altered by the process. 7. In caustic fixed alkali, fibrin increases in bulk, and, at length, is completely dissolved. The solution is yellow with a shade of green; and is decomposed by acids; but the precipitated fibrin seems to have undergone some change, for it is not, as before, soluble in acetic acid. The compound of fibrin and alkali has not any analogy with soap, which Fourcroy asserts that it resembles. 8. Fibrin has been analyzed by Gay Lussac and Thenard, and found to consist of Carbon........53.360 Oxygen........19.685 Hydrogen.......7.021 Azote........19.934 100. Besides the oxygen and hydrogen in the proportions required to form water, there is an excess of 4.337 parts of hydrogen per cent. SECTION V. Urea. 1. Urea may be obtained by the following process: Evaporate, by a very gentle heat, a portion of human urine, voided six or eight hours after a meal, to the consistence of a thick syrup. In this state it concretes, on cooling, into a crystalline mass. Pour on this, at|different times, four times its weight of alcohol, and apply a gentle heat, which will effect the solution of the greater portion. Decant the alcoholic solution, and distil it by a water bath, till it acquires the consistence of syrup, which is to be poured out of the retort. On cooling, it forms a crystallized substance, which is the urea, not however in a state t>f complete purity. II. 1. Urea, thus obtained, has the form of crystalline plates, crossing each other in various directions. It has a yellowish white colour; a smell somewhat like that of garlic; is viscid, and difficult 'to cut; and has an acrid strong taste. It deliquiates, when exposed 240 animal substances. chat. XXIf. to the air, into a thick brown liquid. It is extremely soluble in water, and absorbs caloric during solution. Alcohol dissolves it readily, but in less proportion than water; and the alcoholic solu- tion yields crystals more readily than the watery one. Berzelius, by processes which he has not described, obtained urea quite free from colour, and forming distinct prismatic crystals like nitre.* Even in this state, he observes, it is still obstinately combined with lactic acid, lactate of ammonia, and the peculiar animal matter, which always accompanies the lactates. It is this animal matter, which gives the urine its colour. Dr. Prout was induced by the observation of Berzelius to at- tempt the preparation of pure urea, and succeeded by the following process. Fresh urine was carefully evaporated to the consistence of syrup, and to this, when quite cold, pure concentrated nitric acid was added by degrees, till the whole became a dark-coloured crystal- lized mass, which was slightly washed with cold water, and suffered to drain. To this mass, a pretty strong solution of sub-carbonate of potash or soda was added, till the whole became neutral. The solution was carefully concentrated by evaporation, and set aside, in order that the nitre might separate by crystallization. The liquor drained from these crystals was an impure solution of urea, which was mixed with a sufficient quantity of animal charcoal to form it into a thin paste. To this, ■after remaining a few hours, water was added to separate the urea, and the colourless solution was evapo- rated at a very gentle heat to dryness. From the dry mass, boiling alcohol separated the urea, and left the nitre and most of the saline substances behind, and from the alcoholic solution the urea was obtained pure by evaporation and crystallization, the solution in alcohol being repeated if the crystals were coloured. Urea thus purified most frequently assumes the form of a four- sided prism. Its crystals are transparent and colourless, and have a slight pearly lustre. It leaves a sensation of coldness on the tongue like nitre. Its smell is faint and peculiar, but not resinous. It does not affect the colours of litmus or turmeric. On exposure to the air it slightly deliquesces, but does not seem to be decomposed. At a strong heat it melts, and is partly decomposed, and partly sublimes unaltered. The specific gravity of its crystals is about 1.350. They are soluble in an equal weight of water at 60° Fah- renheit, and to any extent in boiling water. Alcohol at 60° Fah- renheit, dissolves about one fifth of its weight, and at 212° more than its weight. 2. The concentrated solution of urea in water yields, on the ad- dition of nitric acid, a copious precipitate of bright pearlrcoloured crystals, resembling the boracic acid. Oxalic acid produces the same effect; but in neither ol these compounds are the acids neu- tralized. The nitrate of urea, Dr. Prout finds to consist of * View of Animal Chemistry, 8vo. p. 101. SECT. V. UREA. 241 Nitric acid.....47 37 = 1 atom Urea.......52.63 = 2 atoms 100. 3. The concentrated solution of impure urea, in water, is brown; but becomes yellow, when largely diluted. Infusion of galls gives it a yellowish brown colour, but causes no precipitate; nor is it pre- cipitated by infusion of tan. 4. When heat is applied to urea, it melts, swells, and evaporates, with an insufferably fetid smell. By distillation, it yields above two thirds its weight of carbonate of ammonia; about one fourth of benzoic acid; besides carbureted hydrogen, and a residuum com- posed of charcoal with muriates of soda and ammonia. 5.«The solution of urea, in water, putrefies, and is slowly decom- posed; but much more rapidly, if a little gelatine be added. Am- monia and acetic acid are the products of its decomposition. If the solution, instead of being left to putrefy, be kept in a boiling tem- perature, and fresh water be added as the evaporation goes on, the urea is at length wholly decomposed. The condensed vapour is found to contain carbonate of ammonia; acetic acid is formed} and a portion of charcoal remains in the fluid contents of the retort. It has been ascertained, by those who distil the volatile alkali from urine, in manufacturing processes, that an equal quantity of am- monia is obtained whether the urine has undergone putrefaction or not. 6. When a mixture of urea, with one fourth its weight of diluted sulphuric acid is distilled, a quantity of oil appears on the surface, which concretes by cooling; acetic acid passes over into the re- ceiveri and sulphate of ammonia remains in the retort. The repe- tition of this process converts the whole of a portion of urea into ammonia and acetic acid. 7. Nitric acid when heated acts rapidly on urea; nitrous, azotic, and carbonic acid gases, are disengaged; and prussic acid and am- monia are generated. The residuum, when dried and ignited, de- tonates like nitrate of ammonia. 8. Muriatic acid dissolves urea without alteration. When a stream of oxymuriatic acid gas is passed throwgh a solution of urea, the gas is rapidly absorbed; and white flakes are formed, which soon assume a brown colour. After the solution has become satu- rated with gas, the effervescence still continues; and carbonic acid and nitrogen gases are evolved. The residuary liquid contains both carbt nate and muriate of ammonia. 9. Urea is soluble in alkaline solutions; and, at the same time, undergoes a partial decomposition. A strong smell of ammonia arises, probably from the action of the potash on the muriate of ammonia which is contained in urea. When solid potash, however, is triturated with urea, the disengagement of .mimonia is too great to be explained in this way; and can only be accounted for, by sup- Vol. II.—II h 242 ANIMAL SUBSTANCES. OHAF. XXII. posing the volatile alkali to be formed by the union of its elements. A strong solution of potash, heated with urea, produces a similar effect: a large quantity of ammonia is generated; the residuum di- luted with water effervesces violently from the escape of carbonic acid gas; a flocculent precipitate is formed, which has the qualities of a concrete oil; and the liquor, when distilled, gives both acetic and benzoic acids. 10 Urea has the property of changing the form of the crystals of muriate of soda; a solution of that salt, mixed with one of urea, affording, on evaporation, ochtohedral crystals. Muriate of ammo- nia, on the contrary, which usually crystallizes in octohedrons, has the form of its crystals altered, by similar treatment, to that of cubes. Of all the animal fluids, urea appears most readily to undergo decomposition, both from spontaneous changes in the arrangement of its elements and from the action of other substances. From a careful examination of the products of its distillation with oxide of copper, Dr. Prout has given the following as the proportions of its elements. One hundred parts consist of Oxygen .... 26.66 = 1 atom or \ volume Nitrogen .... 46.66 = 1 atom or I volume Carbon.....19.99 = 1 atom or 1 volume Hydrogen .... 6.66 = 2 atoms or 2 volumes. SECTION VI. Animal Resins. The properties of animal resins have not been fully investigated; but, so far as they have hitherto been examined, they appear to differ considerably from those of the vegetable kingdom. The resin of bile may be obtained by the following process: To 22 parts of recent ox bile, add one of concentrated muriatic acid. When the mixture has stood some hours, strain it, in order to separate a white coagulated substance. Pour the filtered liquor, which has a fine green colour, into a glass vessel, and evaporate by a gentle heat. At a certain point of concentration, a green sedi- ment falls down, which, after being separated from the liquid part, and washed, affords what has been considered as resin. Berzelius, however, (as will be more fully stated in the section on bile,) de- nies that it is a true resin. 1. The resin of bile has a dark brown colour; but, if spread out fine, on a white ground, it exhibits a bright grass-green. It is in- tensely bitter. 2. At about 122° it melts, and in a high temperature burns ra- pidly. It is soluble both in cold and hot water, and still more solu- ble in alcohol, from which it is in part precipitated by water. SECT. VII. ANIMAL SUGAR. 243 3. With pure alkalies it combines, and forms a compound, which has been compared to soap. From these it is precipitated unchanged by acids. 4. When farther oxygenized, by adding oxymuriatic acid to bile, the resinous portion has its properties considerably altered; it acquires the colour and consistence of tallow; melts at 140°; and dissolves in alcohol and in hot water. Besides this resin, there are several animal substances which possess similar qualities. Such are the ear-wax, ambergris, cas- tor, &c; for an account of which the reader may consult the fifth volume of Thomson's Chemistry. SECTION VII. Animal Sugar. Sugar enters pretty largely into the composition of milk; and into the urine, when altered by disease. It may be obtained from milk by the following process: I. Let whey be evaporated to the consistence of honey, and al- lowed to cool. It concretes into a solid mass, which is to be dis- solved in water, clarified by white of eggs, filtered, and again evaporated to the consistence of syrup. On cooling, a number of brilliant white crystals are deposited, which are the sugar of milk. 1. Sugar of milk has a sweetish taste, and no smell. 2. It requires for solution, seven parts of cold or four of boiling water; and is insoluble in alcohol. In these properties it differs from common sugar, and also in its relation to nitric acid, which will be afterwards stated, under the head of saccholactic aeid. Gay Lussac and Thenard have obtained by their analysis, the following results, which correspond, almost exactly, with those of Berzelius. Carbon........38.825 Oxygen.......53.834 Hydrogen ....... 7.341 100. The oxygen and hydrogen are in the proportions necessary to form water; and the carbon is in excess. 3. When exposed to heat, it melts and burns with the same appearances as common sugar, and with a similar smell. II. The urine of diabetic patients yields sugar on evaporation, which approaches more nearly in its characters to those of vege- table su gar, but is generally said to be incapable of crystallization. 244 ANIMAL SUBSTANCES. CHAT. XXII. By exposing the solution, however, for some time to the air, and removing occasionally the scum which is formed, I hav^ obtained beautiful white crystals, not inferior to those of vegetable sugar. Chevreul has, also, obtained similar crystals, which when drained, then pressed, and dissolved in hot alcohol, gave a solution that by slow evaporation afforded perfectly white crystals. In its proper- ties, diabetic sugar he found to approach most nearly to the sugar obtained from grapes;* and Dr. Prout, by analysis, finds its com- position precisely similar to that of vegetable sugar.t SECTION VIII. Animal Oils. Animal oils differ from the vegetable oils, in being generally solid at the temperature of the atmosphere, but are similar to them in other properties. Among animal oils, may be ranked butter, tallow, lard, suet, spermaceti, &c. I. Spermaceti (called by Chevreul^ cetine) bears some resem- blance to wax, but differs from it in other properties. It is more readily fusible, viz. at 112° Fahrenheit; and is less soluble in boil- ing alcohol, of which it requires 150 times its weight. It is co- piously dissolved by boiling ether; and the solution, on cooling, becomes a solid mass. Pure potash acts on it more remarkably than on wax; and the compound is quite soluble, forming a true soap. A heated solution of ammonia affords a liquid, which is not precipitated by cooling, or by the addition of water; but is de- composed by acids. From the solution by potash, Chevreul sepa- rated, by adding an acid, a substance, which he terms cetic acid. It is a white solid, fusible at nearly the same point as spermaceti, but which does not, on cooling, crystallize in plates. It is insolu- ble in water, but much more soluble in alcohol than spermaceti, and is susceptible of union with various bases, with which it forms salts or soaps.§ II. A singular instance of the production of animal oil from the lean or muscular part of animals, is presented by the conversion of muscle into a substance resembling spermaceti, and called by the French chemists adipocire. To effect this conversion, it is only necessary to confine the fleshy part of an animal in a box, with several holes in it, under the surface of a running stream. When thus confined, the change takes place spontaneously in the course of a few months. But it may be accomplished much sooner, by digesting animal muscle in strong nitric acid, and washing off the acid by water, as soon as the change has ensued. The sub- * 95 Ann. de Chim. 319. f Med. Chir. Trans, viii. 537. 4 \nn. de Chim. et Phys. vii. 155. {Ann. de Chim. xcv- 17- SECT. VIII. ANIMAL OILS. 24 J stance, thus obtained, may be bleached, by exposure to chlorine gas. From the experiments of Chevreul and of Gay Lussac,* the fatty matter thus obtained appears to be separated, rather than formed, by the processes which have been described. Their in- ferences, however, are not admitted by Dr. Thomson.f Adipocire has a light yellow colour, the consistence of tallow, and a homogeneous texture. It melts at an inferior temperature to either of the foregoing bodies, viz. at 92° Fahrenheit. Cold alcohol has little action, but when heated, dissolves about one- fourth or one-fifth its weight. On cooling,^ is deposited nearly white, and the alcohol has acquired a yellow tinge. Boiling ether dissolves nearly one-fourth, which separates, almost white, on cooling. Fixed alkalies act on this substance, as on wax and sper- maceti, forming with it a soluble soap. Cold ammonia scarcely attracts it, and in this respect it differs from both the preceding substances. III. The fat of animals may be separated from the membranous and other substances, with which it is united, by melting it with a gentle heat, and with the addition of a small quantity of water. Fat, which has been thus prepared, is called lard when of a soft consistence, and tallow when harder. From the whale and some other animals, the fat is obtained fluid, and is then called animal oil. Animal fat is insipid and free from smell. It cannot be com- bined either with water or with alcohol; but it unites with alkalies and forms soap. It is apt to become rancid by keeping, owing to the formation of an acid, mosj^probably by the oxygenation of ge- latine, or of some other animal substance which the fat contains. Fat melts at a very moderate heat. Lard becomes fluid at about 92° Fahrenheit, and tallow a few degrees higher. At a still higher temperature, it is decomposed, and yields, among other products, a large quantity of olefiant gas. Hence its ficness for artificial illumination. If fat be melted with about one sixteenth its weight of nitric acid, the mixture being kept fluid, and constantly stirred for some time, a considerable change is produced in its appearance. Nitric oxide and nitrogen gases are evolved; and the lard becomes gra- nular, of a firmer consistence, and soluble in alcohol. Any adher- ing acid may be removed by washing it with water. In this state, it has been called by the French chemists oxygenated fat. Melted fat dissolves both sulphur and phosphorus. It unites, also, with several metallic oxides, and forms compounds, which have nearly a solid consistence. * Ann. de Chim. et Phys. iv. 71. f Annals, xii. 41. 24-6 ANIMAL SUBSTANCES. CHAP. XXII. Stearin, Ela'in, Isfc. It has been shown by the experiments of Chevreul, which have been confirmed by those of Braconnot,* that fat is not homoge- neous, but composed of two distinct substances. When hog's lard is heated with alcohol, the fluid on cooling deposits white crystalline needles, which may be purified by again disolving thein in hot alcohol, and allowing them to crystallize a second time. To the solid thus obtained, Chevreul has given the name of stearin, from .. _ Lactate of soda and animal matter.....4 $ Substances soluble in water only: Soda, phosphate of soda, and a little animal matter 4.1 Loss.............., . . 0.9 1000. This analysis agrees very remarkably with one of Dr. Marcet, who obtained the following ingredients. The substance termed by him muco extractive matter, is doubtless impure lactate of soda; and the sulphate of potash, and earthy phosphates, were probably formed by the combustion. A thousand parts of human serum contain, 900.00 Albumen........ 86.80 Muriates of potash and soda . . 6.60 Muco-extractive matter . . . 4.00 Subcarbonate of soda .... 1.65 0.35 0.60 1000. Vogel considers sulphur as another constituent of serum; for he finds that when serum is kept for some days, at the temperature of between 75° and 90° Fahrenheit, a gas exhales from it, which 260 COMPOUND ANIMAL PRODUCTS. CHAP. XXIII. renders legible characters written on paper with acetate of lead.* This experiment was found to answer with the bile and urine; but it can scarcely be regarded as a proof, that the blood contains sul- phur as such, or in any state but that of intimate comUpation. The same chemist has endeavoured to establish the presence of carbo- nic acid in blood when recently drawnf from a vein. The crassamentum or clot is resolvable into two parts, viz. what has been called coagula'ole lymph or,/?6rin,and red globules. The separation may be accomplished by long continued washing with water, which dissolves the red globules only, and leaves the fibrin. Its properties differ scarcely at all from those of fibrin obtained by the long boiling of muscular flesh. Fibrin, as it is contained in the blood, is held in a state of solu- tion; aud it is still a question to what cause its spontaneous coagu- lation is owing. That it does not arise from the absorption of oxy- gen, is plain from the fact that blood, by exposure to oxygen gas, has its coagulation retarded. Hydrogen gas, also, delays its co- agulation; but carbonic acid, nitrous, and nitrogen gases accelerate it. In ifacuo, Mr. Hunter states that it occurs at the usual period; but it is not easy to conceive under what circumstances such an experiment could be fairly made. When intercepted in a living vessel, as by placing ligatures on a vein, Mr. liewson found that blood remained imperfectly fluid for several hours. That mere rest is not sufficient to produce its coagulation, appears, also, from the fact, that the'ljlood continues fluid in eases where the circula- tion is suspended throughout the whole system; as in fainting, and in suffocation from drowning and other causes. The coagulability of fibrin is destroyed, also, without our being able to explain the fact, in animals killed by electricity and lightning; by a blow on the stomach; by the poison of the viper; or by violent passions of the mind. In some diseases, on the contrary, its tendency to co- agulation is greatly increased. The red globules of the blood (that part to which its peculiar colour is owing) were first attentively observed and accurately de- scribed by Mr. Hewson. As their name imports, they have a glo- bular figure, which is sufficiently visible with the aid of the micro- scope. They appear to dissolve readily in water, and tinge it with their own peculiar colour; but Dr. Young finds that the globule remains entire, though colourless. They are soluble in alkalies, acids, and alcohol, but not in the serum. The watery liquid turns syrup of violets green; and, after some time, deposits a flocculent precipitate, doubtless from the coagulation of albumen, the pre- sence of which is indicated, also, by the effect of boiling the solu- tion. It seems to consist of albumen, dissolved by an excess of pure soda. When evaporated and calcined in a crucible, a resi- duum is obtained, amounting to about four lOOOths of the weight * Ann. de China, vol. huotvii. f 93 Ann. de Chim. 71. *fcCT. I. BLOOD. 261 of solid matter, and composed, according to Fourcroy and Vauque- lin, chiefly of sub phosphate of iron. It has been contended that the red colour of the blood is owing to the iron which it contains, but this opinion has been rendered extremely questionable by the experiments of Mr. Brande. Ber- zelius, indeed, had found that a quantity of oxide of iron exists in the ashes of the colouring mattter; while none, or at least an in- finitely small portion, is afforded by the other ingredients of blood. He cut the crassamentum into thin slices, and placed them on blotting paper; and after this had ceased to draw out any moisture, he dried the slices. Four hundred grains of the dried substance left, after incineration, 5 grains of ashes, which were composed . (supposing 100 to have been operated on) of Oxide of iron..............50.0 Sub-phosphate of iron...........7.5 Phosphate of lime with a small quantity of magnesia 6.0 Pure lime...............20.0 Carbonic acid and loss...........16.5 100. The iron in colouring matter is not, Berzelius admits, in such a state, as to be capable of being detected by the nicest tests of that metal, until the composition of the colouring matter is destroyed by combustion. Nor is there any truth in the synthetic proof al- leged by Fourcroy, that subphosphate of iron dissolves in albumen, and imparts to it a bright red colour, resembling that of blood. To procure the colouring matter of blood in a detached state, Mr. Brande employed venous blood, stirred during its coagulation. The fibrin is thus removed; and the colouring matter is diffused through the serum, from which it gradually subsides in a very con- centrated form. It retains, indeed, some serum; but this does not interfere with the effects of various agents upon the colouring principle. The aqueous solution has a bright red colour, and is not vefy prone to putrefaction. It is not altered by any temperature below 190° or 200° Fahrenheit; but, at higher temperatures, it becomes turbid, and deposits a pale brown sediment. If the fluid be poured upon a filtre, water passes through colourless; so that exposure to heat destroys the solubility of colouring matter. Diluted sulphuric and muriatic acids, and acetic, oxalic, citric, and tartaric acids, dissolve the colouring matter, and extract it from the crassamentum. The solution has more or less of a scarlet hue, according to the acid employed; but it is always green, when viewed, in narrow tubes, by transmitted light. Nitric acid destroys the red colour, and converts it to a brown. The pure and carbonated alkalies dissolve the red matter, the colour of which remains unimpaired. The solution in liquid am- 362 COMPLEX ANIMAL PRODUCTS. CHVP. XXIII. monia approaches nearest to scarlet. When these solutions arc supersaturated with inuriaticor sulphuric acids, the liquid acquires a colour, similar to the original solution of the colouring matter by those acids. Alumine cannot be brought to form a permanent red compound with the colouring principle of the blood. But when the colouring matter is left to stand a few days, in contact with a solution of the crystallized muriate of tin, a bright red powder precipitates, which is a combination of the colouring matter with oxide of tin. When kept in water, it sustains no change of colour; but when dried by exposure to air, it loses its brilliant tint, and assumes a dull red hue. The most effectual mordaunts, which Mr. Brande discovered for the colouring matter, are solutions of mercury (especially nitrate) and corrosive sublimate. When either of those salts was added to a watery solution of the colouring matter, a deep red compound was deposited, and the liquid became colourless. Woollen cloth, also, first impregnated in these solutions, and then dipped into the aqueous solution of colouring matter, acquired a permanent red dye, unalterable by washing with soap. It appears, therefore, that the colouring principle of the blood is an animal substance of a peculiar nature, susceptible, like the colouring matter from vegetables, of uniting with bases, and ad- mitting, probably, of important use in the art of dyeing. On exa- mining the colouring matter, distinctly from the crassamentum, Mr. Brande did not discover a greater proportion of iron, than in the other principles of blood; and the theory may, therefore, be considered as completely set aside, which accounts for the red colour of the blood by the presence of iron. The conclusions of Mr. Brande have been lately confirmed by Vauquelin, who recommends the following method of obtaining, in a separate form, the colouring matter of the blood. Let the coagulum of blood, well drained upon a hair sieve, be digested in four times its weight of sulphuric acid diluted with a double proportion of water, at the temperature of 160° Fahrenheit* for five or six hours. Filter the liquor while yet hot, and wash the residuum with a quantity of hot water, equal in weight to the acid which has been employed. Concentrate the liquor to half its bulk; then add pure ammonia, till there remains only a slight excess of acid. After having agitated the liquor, allow it to stand, and a purple sediment will be deposited. This sediment is to be washed with distilled water, till the washings cease to precipitate the nitrate of barytes. It may then be drained on filtering paper, and dried at a very gentle heat. When dry, it is destitute of taste and smell. It resembles jet in colour, fracture, and lustre. When moistened with water, it as- sumes a wine red colour, but does not dissolve in that fluid. In acid and alkaline liquids, it readily dissolves, and communicates •to them a purple coiour. Its acid solutions are not precipitated by SE0T. I. BLOOD. 263 gallic acid or by prussiate of potash, thus proving the absence of iron Infusion of galls, however, precipitates it without any change of colour. It is soluble in diluted nitric acid, without being disco- loured, nor is this efl'ect produced by nitrate of silver; but it is completely discoloured by nitrate of lead, which throws down a brown precipitate.* In opposition to these experiments,- it is still maintained by Ber- zelius, that the colouring matter of the blood contains iron, not .ndeed discoverable by re-agents, but decisively proved to exist 'n its ashes. In every respect except in containing that metal, the colouring matter of the blood agrees with fibrin'and albumen, and he seems disposed to believe that its colour, though not depending on the presence merely of an oxide of iron, may be produced by a compound of which that oxide is an essential part.f It is doubtless on the red globules,of the blood that the different gases act, which produce such remarkable changes in the colour of the entire fluid. Nlflbgen gas blackens arterial blood, and, ac- cording to Girtanner, venous blood also. In an experiment of Dr. Priestley, it appeared that the bulk of a quantity of nitrogen gas, to which arterial blood was exposed, sustained a diminution. Blood, which has had its colour thus impaired, it was found by the same philosopher, may be restored to its bright florid hue, by agitation with oxygen gas; and these changes may, at pleasure, be repeated alternately. Oxygen gas, to which blood is exposed, is diminished in volume, and contaminated by carbonic acid. Atmospheric air undergoes the same change in consequence of the oxygen which it contains; but in a less remarkable degree. Similar alterations are, also, constantly going on in the blood, during its circulation through the living body. In the veins it is of a dark red coolur, inclining to purple. In this state it arrives at the right ventricle of the heart, by the contraction cf which it is driven into the pulmonary artery. This artery is distributed, by extremely minute ramifications, over the whole surface of the air-cells of the lungs; and, in these, the blood is exposed to the action of atmos- pherical air, through the slender coats of the blood vessels. Here it acquires a bright vermillion colour; and, returning to the left ventricle of the heart by the pulmonary veins, it is distributed, by the contraction of this ventricle, through the whole body. In its course it loses its florid colour, and, after traversing the system, re- turns to the lungs, to be once more fitted for the performance of its functions. The function of respiration consists of two distinct actions, that of inspiration, by which the air is drawn into the lungs; and that of expiration, by which it is expelled, after having served the pur- pose for which it was inhaled. By an easy natural inspiration, about twenty cubic inches may, perhaps, on an average, be the quantity * Aon. de Chim. et Phys. i. 9, or Thomson's Ann. viii. 230. f Ami. de ( him. et Phys. r. 42. 264 COMPLEX ANIMAL PRODUCTS. QHAP. XXIII. taken in. It appears, also; from the recent experiments of Messrs. Allen and Pepys,* that the same quantity is expired, with little if any diminution. Atmospheric air, after being once only admitted into the lungs, returns charged with 8 or 8$ per cent, of carbonic acid gas. If the same portion be breathed repeatedly, considerable uneasiness is experienced; but the quantity of carbonic acid cannot be increased beyond 10 per cent. When the state of the expired air is examined by eudiometrical tests, a quantity of oxygen is found to have disappeared, equal in volume, according to the ex- periments of the same accurate chemists, to the carbonic acid which has been formed. Now as carbonic acid has been proved to con- tain exactly its own bulk of oxygen gas, it follows that all the oxy- gen, which disappears in respiration, must have been expended in forming this acid; and that no portion of it has united with hydro- gen to form water. It may still, however, be doubted, whether the oxygen is absorbed through the coats of tiie vessels, and displaces carbonic acid, which may be supposed to™ave pre-existed in the blood; or whether this acid be not rather generated by the union of the inspired oxygen with the carbon of that fluid. Of the two sup- positions, the latter appears to be the most probable. The only change, then, that has been satisfactorily proved to take place in respired atmospherical air, is the removal of a cer- tain quantity of oxygen (its nitrogen being wholly untouched,) and the substitution of a precisely equal volume of carbonic acid gas. When, however, pure oxygen gas is respired by an herbivorous animal, Messrs. Allen and Pepys have found that it cannot all be traced into this combination; but that a portion of oxygen has dis- appeared, and has been replaced by a corresponding quantity of nitrogen.f The addition of nitrogen appears to be made also, when a mixture of hydrogen and oxygen gases is breathed, in which the latter is in the same proportion as in atmospherical air. This mixture, it was found, may be respired for an hour without inconvenience. The substitution of nitrogen for the oxygen origi- nally inhaled, is a fact of considerable importance, and in the pre- sent state of our knowledge altogether inexplicable. Besides carbonic acid, a portion of watery vapour is emitted from the lungs, and in a quantity sufficient to be visible when the atmosphere is of a low temperature. From various experiments, jt may be inferred to amount to about three grains in a minute. Until lately the water, thus exhaled, was supposed to be generated in the lungs, by the union of the inspired oxygen with the hydro- gen of the blood; but this hypothesis is inconsistent with the ex- periments of Messrs. Allen and Pepys, which have traced the whole of the oxygen into combination with carbon. It is probably there- fore nothing more than the condensed vapour of a portion of that >fluid, which is ordinarily secreted into the bronchial cells. '" Philosophical Transactions, 1808. f Ibid, 1809. SECT. I. RESPIRATION. 265 An important purpose of the function of respiration is, that it contributes to that equable temperature, which the animal body preserves, amidst all the changes in the surrounding medium. This is peculiarly the property of living matter; for all other bodies have the same degree of heat with the substances that are in con- tact with them. In the human body, the temperature varies only a very few degrees from 96," whether it be exposed to a cold of many degrees below the freezing point, or whether it be surround- ed by an atmosphere, little short of the heat of boiling water. There must, then, be certain processes in the animal economy, by which, in the former case, caloric is reduced from a latent form to that of temperature; and, in the latter case, by which the great ex- cess of caloric is absorbed, and prevented from becoming inju- rious by its accumulation. We are ignorant of those precise differences, which constitute the distinction between venous and arterial blood, or in'what way the function of respiration converts the former into the latter. A fact, however of considerable importance, on this subject, has been discovered by Dr. Crawford. The capacity of arterial blood for caloric he found to be superior to that of venous blood, in the pro- portion of 1030 to 892. When, therefore, arterial blood is con- verted into venous, a considerable quantity of caloric must pass from a latent to a free state, and must prove an abundant source of temperature. Now this is precisely what is constantly taking place in the body. Caloric is evolved by the combination of the inspired oxygen with carbon; but as the capacity of blood for calo- ric is, at the same time, enlarged, its temperature is not raised by being thus arterialized. In its progress through the system, the blood again suffers a diminution of capacity; and the caloric, which it had carried in a latent form to the remotest extremities, is extri- cated, and applied to the support of animal temperature. This theory explains why the heat is not excessive in the lungs, but is equally distributed over the whole body. In animals, placed in a high temperature, Dr. Crawford has added the important fact, that the change of arterial into venous blood does not go on; and no addition of temperature is, therefore, derived from this source, Another cause, limiting the heat of the body under such circum- stances, is the excessive evaporation which takes place from the surface of the skin, and which is indicated by a loss of weight of no inconsiderable amount.* It is not in the lungs only that the blood exerts an action on at- mospherical air; for a similar function, it appears, belongs to the skin throughout the whole body. If the hand be confined in a por- tion of atmospherical air or oxygen gas, it has been ascertained that the oxygen disappears, and is replaced by a portion of carbo- nic acid. At the same time, a considerable qimn ity of watery fluid transpires, and may be collected by a proper apparatus. * Nicholson's Journal, xvii. 215. Vol. II.—L 1 266 COMPLEX ANIMAL PRODUCTS. CHAP. XXIII. The blood is subservient to several important uses in the animal economy. It is a source; from which are constantly prepared a variety of other substances, both solid and fluid, that are essential to our well being, and even to our existence. From the blood is derived the solid matter of the bones themselves; it does not, how- ever, exist in the blood in the state of sub-phosphate of lime or bone earth; but appears to be produced, from the ultimate ele- ments of blood, on the very spot where its presence is required.* The muscles, which are fixed to the bones, and which, acting as levers, enable us to change our situation at pleasure, are referrible to the same source; and so also is all the variety of animal fluids, which perform a necessary part in the economy of this complicated machine. The solids and fluids, thus produced, are sometimes elaborated by complicated organs called glands, and are then termed secretions. A sufficiently exact and comprehensive know- ledge of the business of secretion would have been attained if we were able to discover, in the secreted solids or fluids, substances analogous to those which are found in the blood, and no others. But in many secretions we find principles bearing no resemblance to albumen, fibrin, or any of those fluids that form the proximate elements of the blood. In these cases, nature must have gone farther in the work of separation; and, after disuniting the ultimate principles of the blood, have re-combined them in a new manner and in different proportions. This is a species of synthesis, which we have hitherto not been able to imitate in substances of the ani- mal kingdom, and in very few instances even in vegetable pro- ducts. SECTION II. Of the Secretions subservient to Digestion; viz. the Saliva, the Gastric and Pancreatic Juices, and the Bile. Saliva is a liquid secreted by certain glands, and poured into the mouth, for the purpose of being piixed with the food during mastication. It is a slightly viscid liquor, of a saltish taste, desti- tute of smell, and of a white colour; or with a slight tinge of blue. Its specific gravity, according to Haller, is as 1960 to 1875, or, ac- cording to Siebold, as 1080 to 1000. The latter author has com- pared its consistence to that of a solution of one part of gum in forty parts of water. It is neither acid nor alkaline, and has there- fore no effect on blue vegetable colours. Its quantity varies con- siderably. Nuck has estimated it at eight or ten ounces daily; and, during a mercurial salivation, several pints flow in Jhe same interval.f Saliva, when evaporated by a gentle heat to dryness, yields only * Berzclius's Animal Chemistry, p. 19. f Fourcroy, Systeme, 4to. v. 268. SECT. IL. SALIVA. 267 a very small proportion of dry extract in thin semi-transparent plates: or if the process be stopped when about a third only re- mains, crystals of muriate of soda are formed. Exposed to the air, it appears to absorb oxygen, and becomes of a thicker con- sistence, whitish flocculi at the same time separating from it. There is some difficulty in effecting the diffusion of saliva through water; but this may be accomplished by rubbing the two fluids together in a mortar. The solution, which is thus obtained, was subjected to the action of tests by Dr. Bostock.* Oxymunate of mercury produced no immediate effect; but, after some hours, a light flocculent coagulum separated, leaving the liquid nearly transparent. The same test produced a still less striking effect in the filtered portion of some saliva, which had been several days exposed to the atmosphere. Infusion of galls precipitated white flakes, from the recent but not from the filtered liquor. The fil- tered fluid was copiously precipitated by Goulard's extract, and by nitro-muriate of tin. From these experiments, Dr. Bostock infers, that saliva containsTcoagulated albumen, and also a quantity of mucus and muriate of soda, but no gelatine. To the quantities ef each, he considers the following as an approximation: Water........80 Coagulated albumen ... 8 Mucus.......H Saline substances .... I 100. Berzelius has lately published a more exact analysis of aaliva.i Its constituents are Water.......... A peculiar animal matter . . . Mucus.......... Alkaline muriates...... Lactate of soda and animal matter . Pure soda......... 1000. When exposed to the agency of galvanic electricity, Mr. Brande has found that saliva, even after being first boiled in water, gives an abundant coagulation, and a separation of alkali round the ne- gative pole, though neither acids, nor any of the common agents, showed the presence of albumen. Hence it appears that this sub- stance may form part of an animal fluid, and yet not be discovera- ble by the common tests. In saliva, Mr. Brande supposes that it 992.9 2.9 1 4 1.7 0.9 0.2 * Nicholson's Journal, xiv. 147. \ Thomson's Annals, iii. 25. 268 COMPLEX ANIMAL PRODUCTS. CHAP. XXIII. is united with an alkali (probably soda) which, in this state of com- bination, loses its property of affecting vegetable colours.* The gastric juice is a fluid which is poured out upon the inner surface of the stomach, and is possessed of very extraordinary powers as a solvent. One of the great obstacles to an accurate analysis of it is the difficulty of procuring it sufficiently pure, and free from admixture with the contents of the stomach. It has been generally collected from animals, which have been kept, for some time before being killed, without food. In this state, it is a transparent liquor, having a saline and somewhat bitter taste, and containing neither uncombined acid nor alkali. It precipitates nitrate of silver; and, when evaporated, gives a solid residuum, which is deliquescent, and has an unpleasant smell. By the action of acids, a small, proportion of albumen is discovered in it, and gelatine or mucus remains in solution. Vauquelin always found phosphoric acid in the gastric juice of herbivorous animals, whilst, on the other hand, that of man and carnivorous animals seldom gave any visible traces of free acid or alkali. This imperfect account of the properties of the gastric juice affords, however, no explanation of the solvent power, which it exerts on all animal and vegetable substances. Even out of the body it appears, from the experiments of Spallanzani, to retard the putrefaction of animal substances, and to reduce them to a state somewhat similar to that, in which they are found after hav- ing been some time in the stomach. On substances taken into that organ its solvent power is even still more remarkable. In Dr. Stevens's experiment, hollow silver spheres, perforated with small holes and containing animal and vegetable food, were swallowed by a man who possessed the faculty of doing this without injury, and with the result that the food was always dissolved, and the vessel voided in an empty state. After death, it appears from the observations of Mr. Hunter, that the stomach itself is sometimes eroded by the gastric juice, large holes having been found in it from the action of that fluid. These facts, as well as the power of the gastric juice in coagulating milk, are quite inexplicable on any known principle. The pancreatic juice has not been examined with any atten- tion. The only observations which we possess respecting it, are those of Dr. Fordyce. He found it to be a colourless liquid, slightly saline to the taste. By evaporation, muriate of soda was obtained, and the same salt was indicated also by nitrate of silver. Hence we may conclude it to be analogous^in composition to the saliva. The bile is one of those fluids, which has attracted peculiarly the notice of the chemists, and which is, therefore, better under- stood than most others. It is to the labours of Fourcroy, and still more recently of Thenard,t who has published two memoirs on * Philosophical Transactions, 1809. f Memoires d'Arcueil, vol. i. SECT. II. BILE. 269 the bile, that, wc are chiefly indebted for our knowledge of its com- position. . . The bile of the ox, from the greater quantity of it which may be procured, has been mostly the subject of experiment. Its colour is commonly yellowish green, and very rarely deep green. When mixed with syrup of violets or infusion of turnsole, it produces no other change than what any other liquid of the same colour would effect. Its' taste is bitter and at the same time sweetish, and ex- cessively nauseous. Its smell is peculiar; and something like that of melted fat. Its specific gravity is 1026; its consistence variable; from that of a thin mucilage to that of synovia. Sometimes it is limpid, and, at others, contains flocculi of a yellow matter, which may easily be separated by water. When submitted to heat, ox-bile first deposits a portion of co- agulated matter, and yields a liquid, which has the peculiar smell of bile, and which throws down a white precipitate from acetate of lead. The solid residuum has a yellowish green colour; is very bitter; somewhat deliquescent; and entirely soluble in water and in alcohol. It melts at a moderate heat, and is decomposed by a still stronger one, the products being more oil, and less carbonate of ammonia, than from animal matters in general. A very bulky coal containing several neutral salts remains in the retort. The salts ex- tracted from this coal, taking them in the order of their quantities, are muriate of soda, phosphate of soda, phosphate of lime, and sulphate of soda. Traces, also, are discovered of oxide of iron. The uncombined soda in bile does not exceed one 200th its weight; and as this very minute quantity of alkali must be quite incapable of dissolving the large proportion of resin, which exists in that fluid, Thenard was induced to turn his attention to the dis- covery of some other solvent of resin, existing as a component of bile. Acetate of lead (the common sugar of lead of commerce) precipitates, he found, not only the resin, but the peculiar sub- stance of which he was in search, in union with oxide of lead. 1 But an acetate with a larger proportion of base (formed from eight parts of sugar of lead and one of litharge) produced a diffe- rent effect; and precipitated only the albumen and the resin. When the remaining liquid was filtered, and the lead separated by sulphureted hydrogen gas, it gave, on evaporation, a residue having less bitterness and considerably sweeter. In this state, the solvent of the resin could not be considered as pure, since it retained in solution a quantity of acetate of soda, arising from the decomposition, by the acetate of lead, of the salts of soda existing in the bile. He again, therefore, precipitated the solution by ace- tate of lead saturated with oxide, and obtained an insoluble com- pound of the peculiar matter and oxide of lead. This was dis- solved in vinegar, the oxide of lead separated by sulphureted hydrogen, and the acid expelled by evaporation. This substance, to which Thenard has given the name ofpicro- mel, possesses the property of rendering the resin of bile easily 270 COMPLEX ANIMAL PRODUCTS. CHIP. XXIII. soluble in water. Three parts are sufficient to one of the resin. The characters of picromel are, that it is insoluble in water and alcohol, and incapable of being crystallized; that it precipitates ni- trate of mercury and acetate of lead with excess of oxide; and that it forms, with resin and a minute quantity of soda, a triple com- pound, which is not decomposable by acids nor by 'alkaline or earthy salts. The resin is to be considered as the cause of the smell, and, in great part, of the colour and taste of the bile. It is solid; very bitter; and, when pure, green; but when melted it passes to yel- low. It is soluble in alcohol and in pure alkalies, and is precipi- table from the former by water, and from the latter by acids. The yellow matter appears to be peculiar to the bile, and to possess characters distinct from those of other animal substances. Its presence seems to render the bile putrescent; and it is, also, the source of the concretions, which form in the gall-bladders of oxen. Insoluble by itself, it becomes soluble by the intervention of soda, resin, and picromel; and, whatever be the solvent, it is precipitated by acids.—In the analysis of bile, the first step was to separate this yellow matter, by adding nitric acid, and to free it from the portion of resin which adheres to it. Into the remainder, acetate of lead with excess of oxide (prepared as already directed) was poured, and an insoluble compound was formed, consisting of oxide of lead and resin, from which nitric acid detached the latter in the state of soft green flakes. Sulphureted hydrogen was then passed through the liquid, which was separated by filtration from the precipitate and evaporated to dryness. Deducting, from its weight, that of the acetate of soda formed by the decomposition of acetate of lead, the weight of picromel was obtained. The saline substances were determined by calcination, lixiviation, and other common processes. In this way, the composition of ox-bile was determined as follows: Water ........ 700 or a little more. Resin........ 24 Picromel....... 60.5 Yellow matter.....variable—in this case 4. Soda........ 4 Phosphate of soda . : . . 2 Muriate of soda..... 3.2 Sulphate of soda . . . . 0.8 Phosphate of lime .... 1.2 Oxide of iron........a trace. 800. The bile of the dog, the sheep, the cat, and the calf, was found e»n analysis to be precisely similar to that of the ox. The bile of SECT. II. BILE. 271 the pig, on the contrary, contained neither albumen, yellow mat- ter, nor picromel. It consisted merely of resin in great quantity, of soda, and of salts, the nature of which has not yet been ascer- tained. It was entirely decomposed by acids, and even by the weakest, the acetic. Berzelius denies the presence of resin in bile,* and asserts that it is not possible to repeat the analysis of that fluid, by the pro- cesses which Thenard has described. The substance, he alleges, which, in bile, resembles resin, is precipitable by acids; and the precipitate is a compound of the acid employed with the green colouring matter of bile. When we use sulphuric acid with heat, a green liquid is obtained resembling a resin; and after saturating the acid with carbonate of barytes, the green matter is soluble in water, to which it imparts its own colour and bitterness. This is the characteristic ingredient of bile, which Berzelius calls biliary matter. He finds bile composed of Water.............907.4 Biliary matter..........80.0 Mucus of the gall bladder...... 3.0 Alkalies and salts common to all animal fluids 9.6 1000. The bile of birds contains a large quantity of albuminous mat- ter. The picromel, which is extracted from it, is not sensibly sweet; but on the contrary has a sharp and bitter taste. It contains a mere trace of soda, and does not precipitate the super-acetate of lead. Human bile was, also, an object of Mr. Thenard's researches;' and his experiments, he is of opinion, have led him to as accurate a knowledge of it, as of any other species.—Its colour varies con- siderably; sometimes it is green, almost always brownish yellow, and sometimes it is without colour. Its taste is not very bitter. It is seldom perfectly limpid; for it generally holds suspended in it a certain quantity of yellow matter, which is sometimes even present in such quantity, as to render the bile clotted. When it is filtered, and submitted to a boiling heat, it becomes thick and emits the smell of white of egg. Evaporated to dryness, it affords an extract, which is equal to one 11th the weight of the bile. This extract, by calcination, affords precisely the same salts as are found in ox-bile, viz. uncombined soda; muriate, sulphate, and phosphate of soda; phosphate of lime; and oxide of iron. All the acids decompose human bile, and precipitate from it a large quantity of albumen and of resin. These may be separated from each other by alcohol. By the application of acetate of lead, no picromel can be discovered; nor is any other ingredient found *71 Ann.de Chim. 220. 272 COMPLEX animal PRODUCTS. (JHAP. xxiii. in human bile than yellow matter, albumen, resin, and saline sub- stances. The proportions, ascertained by Thenard, are the fol- lowing: Water............. Yellow matter, insoluble and floating in the bile, a variable quantity from 2 to . . Yellow matter in solution...... Albumen............ Resin............. Soda............... 5.6 Phosphates of soda and lime, sulphate and > muriate of soda, and oxide of iron. . . $ 1100. The yellow matter appears to be, in every respect, similar to that of ox-bile. The resin is yellowish; very fusible; very bitter, but less so than that of ox-bile; soluble in alcohol, from which it is precipitated by water; and soluble in alkalies, from which it is thrown down by acids. In water it appears scarcely to dissolve; and yet sulphuric and nitric acids occasion a precipitate from water which has been digested on it. If bile be submitted to the action of galvanism, Mr. Brande has found that coagulation takes place at the negative pole, where soda also appears. At the positive pole, muriatic and phosphoric acids are evolved. Biliary calculi. The composition of biliary concretions differs in different animals. Those of the ox contain traces of bile, which is removable by the action of water, after which they are entirely destitute of taste and smell. Their colour is a yellow of so much beauty as to render them a valuable pigment. They undergo no change at a heat below redness; but at this temperature they melt and swell, and after yielding the usual animal products, give about one sixth their weight of a white matter which is phosphate of lime. They are nearly insoluble both in water and in alcohol; and with some difficulty in alkalies, from Avhich they are precipitated, in green flocculi, by acids. Boiling muriatic acid takes up only a small quantity, and renders them green. Hence they appear to be homogeneous; and to possess properties identical with those of the yellow matter of the bile of oxen, and of human bile. The calculi of the human gall-bladder have been more atten- tively examined than those of the ox. It had been long known that they enter into fusion at a low temperature, and that the alkalies, and the fixed and volatile oils, effect their solution. One of their * These are the numbers given by Thenard (Memoires d'Arcueil, i. '>!;) but as their sum exceeds 1100. it is probable that the error will best be cor- rected by reducing the proportion of water. 1000* 10 a trace. 42 41 C£6T. HI. ftllLfc. srs distinctive characters was first pointed out by Poulletier de la Salle, viz. that of being soluble in boiling alcohol, and precipitable, on cooling, in the form of shining scales. Fourcroy afterwards disco- vered several important facts respecting them, and especially their resemblance to the substance which has been already described under the name of adipocire. Of the calculi examined by Thenard, only a small number were formed of white plates, crystalline and shining, and entirely adi- pocirous. Many consisted of yellow laminae containing from 88 to 94 per cent, of adipocire, and six or twelve of a colouring substance. A few were greenish on the outside, and yellow in the interior; several were covered, in spots at least, with a blackish brown crust) containing very little adipocire, but internally were like the rest. In all, excepting the perfectly white, there were traces of bile, dis- coverable by the action of water. Calculi from the intestines were found to be similar to those of the gall-bladder. It was, therefore, concluded by Fourcroy, that some of the cal- culi of the human gall-bladder consist entirely of adipocire; and that others are composed of the same substance, with the addition of a quantity of colouring matter, which is either yellowish or dark brown. When of the former colour, it appears not to differ from the yellow matter of the bile; and when of the latter, to be the same substance with an excess of carbon. Chevreul, however, has given to the crystalline matter of biliary calculi, the name of cholesterine, because it differs both from sper- maceti and from adipocire in not being capable of affording a soap with alkalies. He has found, also, that when heated with an equal weight of strong nitric acid, a peculiar acid is formed, which he terms the cholesteric. This acid separates on cooling in the form of a yellow substance. It is scarcely soluble in water, but dissolves in alcohol, and may be crystallized by evaporation. The salts, which it forms with potash, soda, and ammonia, are very soluble; with other bases it gives compounds which are difficultly soluble. 3y a heat above that of boiling water, it is decomposed.* SECTION III. Of Milk. The milk is a fluid, which is secreted, by animals of the class. Mammalia, for the nourishment of their young. Though differing considerably in the different species of animals, yet it admits of th« following general description: It is an opaque liquid, of a white colour, with sometimes a slight tulge of blue or yellow. Its taste is sweetish and grateful; but ra- * Ann. de Chim. et Phys. vi. 401. Voa. II.—M m 274 momplex animal products. ohap. xxiw. ries occasionally, as does its colour also, with the food of the animal. Its specific gravity is variable; that of cows' milk, according to Brisson, being about 1020, and that of ewes' milk 1040. The milk may be resolved, partly by standing, and partly by agents that do not essentially alter the nature of its components, into three proximate ingredients, the cream, curd, and whey. 1. The cream rises, as is well known, to the surface of milk after it has stood for some hours; and the proportion may be ascertained hy a very simple instrument, proposed by Mr. Johnson. It consists of a glass tube, 10 inches long, graduated into 100 equal parts, into which the recent milk is to be put, for spontaneous separation of the cream.* Cream has many of the properties of an oil; is smooth and unctuous to the touch; and stains cloth in the same manner as other fat substances. By standing for some days, it be- comes gradually thicker, and at length forms a soft solid, in which the flavour of cream is no longer perceived, and that of cheese is substituted in its place. Cream, of the specific gravity 1.0244, ifc composed, according to Berzelius, of Butter.........4.5 Cheese.........3.5 Whey.........92.0 100. But as 92 parts of whey contain 4.4 of sugar of milk and salts, it follows that cream contains 12.5 per cent, of solid matter. When cream is agitated, as is done by the common process of churning, it separates into two parts, a thick animal oil, well known by the name of butter, and a fluid which possesses exactly the same properties as milk that has been deprived of its cream. This change has been supposed to be owing to the combination of the cream with the oxygen of the atmosphere; but it takes place, though perhaps not equally well, in vessels from which the air is excluded. Butter has generally a yellow colour and a soft consistence. At the temperature of 96° or 98°, it melts, and when kept in this state for some time, a portion both of whey and curd separate from it. Its transparency is thus increased, but its taste, at the same time, rendered less agreeable. In this state, however, it may be kept longer without becoming rancid; and it is not improbable that it is in part by combination with the whey, that salt contributes to the preservation of butter. Butter, therefore, may be considered as an animal oil, united with a portion of whey and of curd. When milk, ether deprived or not of its cream, is mixed with certain substances, or even allowed to stand till it becomes sour, it undergoes a change which is called coagulation, consisting in its * Thomson's Annals, x. 3(84. SECT. III. MILK. 276 separation into a solid substance termed curd; and a fluid called whoy. This change may be effected by several agents; by all acids, and by many neutral salts; by gum, sugar, and certain vegetable juices; by the gastric fluid; and especially by the infusion of the inner coat of a calf's stomach called rennet. The precipitation by acids, Scheele has explained, by supposing that they form, with the curd, a combination which requires more water for solution than milk contains;* and accordingly the curd is found always to contain a portion of that acid by which coagulation has been pro- duced. But, in other cases, the coagulation cannot be thus ac-1 counted for; and is, indeed, altogether inexplicable. Thus the in- fusion of a piece of calf's stomach, not larger than half a crown, coagulates a quantity of milk sufficient for making a cheese of sixty pounds' weight;! although the quantity of coagulating matter cannot in this case exceed a few grains. The curd of milk, when pressed, salted, and partly dried, com- poses cheese. In good cheese, however, there is always a large proportion of butter, which is enveloped in the curd, and is not afterwards easily separable. Curd, therefore, for exhibiting its chemical properties, should be prepared from milk, which has been deprived of cream, and should be made by the intervention of rennet. It is a white solid substance, insoluble in water and in alcohol, but readily soluble in pure alkalies, and precipitable there- from by acids, though in a s'ate more like tallow than the original curd During solution in alkalies, a strong smell of ammonia is produced; and hence curd appears to be converted, by their action, into volatile alkali and fat. Liquid ammonia also dissolves curd; and it appears to be soluble by the pure alkaline earths. From the resemblance of its properties to those of the coagulated white of an egg, Scheele was induced to regard cheese as identical with albumen; and it is not improbable that if the curd could be obtained perfectly pure, their properties would exactly agree. By the com- bustion and calcination of curd, it appears, however, to afford a larger proportion of phosphate of lime and other saline substances, than is obtained from the coagulated white of an egg. Berzelius found that the ashes, obtained by incinerating cheese, amount to 6.5 per cent, of its weight. The ash consists chiefly of earthy phosphates, with a little pure lime; but contains neither alkali nor oxide of iron. Cheese, digested with muriatic acid, loses its earthy phosphates, and afterwards burns without leaving any ash. The presence of so large a quantity of the earthy phosphates, in the most nutritious part of milk, may be regarded, Berzelius justly observes, as a wise provision of nature; and peculiarly adapts milk to the nutrition of young animals, in whose economy there exists the greatest demand for the earthy phosphates, for the pur- pose of ossification. * Essays, p. 267. f Holland'* Cheshire Report, p. 268. 276 COMPLEX ANIMAL PRODUCTS. CHAP. XXI11. Cheese is generally considered as insoluble in water; but if it be precipitated from milk by sulphuric acid, then well pressed, and digested with carbonate of barytes, cheese affords with water a yellowish solution resembling a solution of gum. The solution boiled in an open vessel becomes covered, with a white pellicle, precisely as milk does, and acquires the smell of boiled milk. Cheese produces, with the mineral acids, the same combinations as albumen and fibrin, though its neutral compounds are less solu- ble than those of fibrin. A great excess of acetic acid is required to dissolve cheese, and the neutral compound formed with this acid appears to be insoluble. "When it has not been completely separa- ted from butter, this floats upon the surface of its solution in acetic acid. Alcohol converts cheese into an adipocirous and foetid sub- stance. The whey, or liquid which remains after the separation of all the curd is a thin and almost transparent fluid, of a yellowish green colour and a pleasant sweetish taste. It still contains, generally, a portion both of curd and of butter; the former of which may be separated by a boiling heat, in the form of a coagulum. The but- tery matter, also, separates by heat, especially if the whey be pre- viously allowed to become sour.* Whey contains, indeed, in its , recent state, some uncombined acetic acid. When whey which has been deprived, as much as possible, of the butter and curd, is slowly evaporated, it yields the substance, already described under the name of sugar of milk. Besides this substance, it contains, also, several saline bodies, viz. muriate of potash, phosphates of lime and of iron, and sulphate of potash; and a peculiar animal matter, which gives a precipitate, with infusion of galls, and affords carbonate of ammonia by distillation. Sour whey contains also a peculiar acid called the lactic. From this account of the composition of milk, several proper- ties of the entire fluid may be understood. When fresh milk is boiled, its albuminous part is not coagulated into a mass like the white of an egg, 6n account of the large quantity of water, through which it is diffused; but a thin pellicle forms on the surface, which, if removed, is immediately replaced by another; and thus the whole of the albumen may be separated in successive portions. If the pellicle fall to the bottom, it becomes burnt, and gives the milk a peculiar flavour. In order to procure butter from milk, it is not necessary, in the first place, to separate the cream; for butter may be obtained at once by the churning of milk, and has then the name of milk-but- ter. It is inferior, however to butter made from cream, in con- sequence of its containing a larger proportion both of whey and of curd. Milk is susceptible of the vinous fermentation, and is employed, by the Tartars, in making a sort of wine, which they call Koumiss^ it is prepared chiefly from mares' milk, and has an agreeable * Cheshire Report, page 262. f 37 Phil. Mag. 6. »KOT. III. CHYLE. 277 sweetish taste. By distillation, it yields a considerable quantity of alcohol. What is most remarkable with respect to this fer- mented liquor, is that it does not appear to owe its origin to the saccharine part of the fluid; for Fourcroy and Vauquelin have found that milk, after fermentation, yields as much sugar of milk as before. There appears to be a considerable difference in the quality of the milk of different animals. Human milk is sweeter than that of cows; and yields a larger proportion of cream; but from this the-butter cannot be separated by agitation. It deposits, also, a part of its curd by mere repose. Asses' milk bears a stronger re- semblance to human milk than to any other. The cream is but in small quantity, and yields a soft white and nearly tasteless but- ter. The curd is so abundant, as even to separate on standing, before the milk becomes sour. Goat's milk yields a remarkably thick and unctuous cream, and abounds also in curd. The milk of sheep bears a strong resemblance to that of cows, and yields a large proportion of curd of a fat and unctuous kind. Mares' milk is thin, insipid, and affords very little cream, from which it is very difficult to separate any butter by agitation. The constituents of skimmed cows' milk are stated by Berze- lius as follows:* Water.......... Cheese, with a trace of butter . . Sugar of milk....... Muriate of potash...... Phosphate of potash ...;.. Lactic acid, lactate of potash, and a trace of lactate of iron Earthy phosphates..... 1000. Of Chyle. The chyle has been lately examined by Mr. Brande, who ob- tained it from the thoracic duct of an animal, about four hours after taking food. If taken at a longer interval, it is mixed with a greater or less proportion of lymph. When unmixed with blood, it has the following properties. I. It is an opaque fluid of a perfectly white colour, without smell, and having a slightly salt taste, accompanied by some de- gree of sweetness. 2. It does not affect the colour of litmus or turmeric, but it slowly changes violet paper to green. 3. Its specific gravity somewhat exceeds that of water, but is less than that of blood. 928.75 28.00 35.00 1.70 0.25 6.00 0.30 * Thomson's Annals, iii. 27. 278 COMPLEX ANIMAL PRODUCTS. OH A P. XXIII. » 4. In about ten minutes after being taken from the duct, it as- sumes the appearance of a stiff jelly, which in the course of 24 hours separates into two parts, producing a firm and contracted coagulum, surrounded by a transparent colourless fluid Its spon- taneous changes, indeed, bear a striking resemblance to those which take place in blood. The coagulated portion has a closer resemblance to the cheese of milk, than to fibrin. It is rapidly dissolved both by pure and subcarbonated alkalies, forming pale brown compounds. Its solu- tion in liquid ammonia is of a reddish hue. The acids throw clown a substance intermediate between fat and albumen, which an ex- cess of nitric acid redissolvcs in the cold; and sulphuric, muriatic, and acetic acids, by boiling for a short time. Sulphuric acid, diluted, dissolves the coagulum, unless the wa- ter be increased to six times the weigh of the acid. Alkalies do not precipitate the solution. It is transparent, of a pale brown colour, and, after the addition of alkali, is decomposed by infu- sions of tan. Wrhen the coagulum is kept some weeks in one part of nitric acid, and 15 of water, it is converted into adipocire. Muriatic, acetic, and oxalic acids dissolve the coagulum; but neither citric nor tartaric have any action on it. The serous part of the chyle, when heated, becomes slightly turbid, and deposits flakes of albumen. The clear liquid, by eva- poration to half its bulk, deposits crystals, bearing a strong resem- blance to sugar of milk. They are soluble in 20 parts of water at 60° Fahrenheit, or in four of boiling water, and the taste of the solution is extremely sweet. By nitric acid, they are converted into a white powder, having the properties of saccholactic acid as described by Scheele. The destructive distillation of the serous part of chyle afforded a minute quantity of charcoal, with traces of phosphate of lime and of muriate and carbonate of soda. From these experiments, it appears that chyle bears a striking analogy to milk, not only in its external appearance, but in chemi- cal properties and composition. It must be acknowledged, how- ever, that the results, which have been described, are not perfectly coincident with those obtained by Emmert and Vauquelin, each -of whom submitted to analysis the chyle of the horse. Emmert was unable to discover the smallest trace of sugar of milk;* and Vauquelin found also, 1st, a large proportion of albumen; 2d, a smaller one of fibrin; 3d, a fatty substance, which gives to the chyle the appearance of milk; and 4thly, several salts, such as potash, muriate of potash, and pro-phosphate of iron.f Berzelius, also, appears to distrust the analogy between chyle and milk.} * 80 Ann. de Chimie, 81. \ 81 Ann. de Chimie, 113. X View of Animal Chemistry, p. 74. SKOT. IV. T,EAKS. 279 SECTION IV. Of the Mucus of the N.se; the Tears; the Humours of the Eye; and the Liquor of Surfaces and of Cavities. 1. The mucus of the nose was examined by Fourcroy and Vauquelin, in the state in which it is discharged during catarrh. Its principal qualities appear to be owing to the large proportion, which it contains, of the substance termed by Dr. Bostock animal mucus. By exposure to the air, this substance becomes viscid; but, when recently secreted, its consistence does not appear to be thicker than that of tears. It contains, besides other neutral salts, a small proportion of carbonate of soda; and hence it precipitates the solution of barytes and of lime. Water does not dissolve it, and it can only be brought into a state of diffusion by agitation. The acids thicken it, when used in small quantity; but in a larger pro- portion they dissolve it. Pure liquid alkalies decompose it, and extricate ammonia. Oxy-muriatic acid renders it thick and dry; itnj reckices it to a state almost resembling parchment. Eerzelius found the mucus of the nose to consist of Water.......... Mucus matter........ Muriates of potash and soda . . . Impure lactate of soda..... Albumen and animal matter, insoluble in water, but'soluble in alcohol . 1000. "2. The tears appear to differ from the mucus of the nose in n® Kespect, except in being of a more fluid consistence. They are perfectly pellucid, have a saline taste, and a specific gravity rather greater than that of water. They change the colour of syrup of violets to green, owing to their containing a portion of uncombi- ned soda. Mr. Hunter found that when tears are exposed to a tem- perature of 160°, a coagulum is formed; and that a substance still remains in solution, which is coagulable by Goulard's extract of lead. These properties indicate the presence both of albumen and of mucus. By evaporation, the tears afford a yellow extract, which is insoluble in water, but is readily soluble in alkalies. Sulphuric acid disengages from this extract both carbonic acid and muriatic acid gases. After its combustion, phosphate of soda and phos- phate of lime are also discovered in it. Frtsh tears are decom- posed by oxy-muriatic acid, and a precipitate is thrown down in flakes, which resembles the matter obtained by evaporation. Tears, therefore, are composed of water; an animal fluid resem- 933.7 5.6 0.9 280 COMPLEX ANIMAL PRODUCTS. 9HAP. XXIII. bling albumen; another fluid which is probably mucus; and various neutral salts. 3. The humours of the eye. The aqueous humour is a clear transparent liquid, of the specific gravity 1009. It has little smell or taste, and scarcely affects blue vegetable colours. By evapora- tion it leaves a residuum, amounting to about 8 per cent. Boiling occasions a slight coagulation; and tan precipitates it, both before and after being heated. Nitrate of silver precipitates muriate of silver from it, but no other metallic salts affect it. Hence it may be inferred, that the aqueous humour consists of a large proportion of water; and of albumen, gelatine, and several neutral salts. The vitreous humour agrees with the aqueous as to the nature of its ingredients, and differs only in their proportion. In the crys- talline lens, both albumen and gelatine are present in considerably larger quantity. It is soluble in cold water; but the solution is coagulated by heat, and by the addition of tan. Its specific gravity is nearly 1100. It appears, therefore, that all the humours of the eye are composed of the same ingredients, and differ only in the proportion which they bear to each other. A recent analysis of the humours of the eye by Berzelius, hast determined their composition as follows: Aqueous Humour. Vitreous Humour. Water........98.10 ... . 98.40 Albumen.......a trace . . . . 0.16 Muriates and lactates ... 1.15 ... . 1.42 Soda with animal matter solu- ble in water 0.75 .... 0.02 100. 100. The lens of the eye was found to be composed of Water...............58 Peculiar matter .........., . 35.9 Muriates, lactates, and animal matter soluble in > alcohol............ . 5 2-4 Animal matter soluble only in water . .... 1.3 Insoluble membrane..........2.4 100. In the ashes of the crystalline lens, Berzelius found only minute traces of iron; but in those of the black matter which covers the choroid coat, he discovered a large proportion of the oxide of that metal.* 4. Liquor of surfaces. On the surface of every cavity through- out the body a fluid is constantly poured out, in sufficient quantity * Ann. de Chim. et Phys. v. 51. SECT. IV. LIQ.UOR OF SURFACKS. 281 to lubricate the parts; and occasionally, also, to keep certain cavi- ties in a state of distension. To this head may be referred the fluid which moistens the pleura and the peritonaeum, and the contents of the pericardium, of the ventricles of the brain, and of the amnios. It is only a part of these, however, that have been accurately ex- amined. The liquor of the pericardium has been analyzed by Dr. Bostock. It had the appearance of the serum of the blood; and when exposed to the heat of boiling water, became opaque and gelatinous. By slow evaporation it left a residuum equal to one 13th of the whole. It was precipitated by oxymuriate of mercury; after the action of which infusion of galls had no effect, but a copious sediment was produced by Goulard's extract. From these characters Dr. Bostock is disposed to consider it as a compound of albumen and mucus with muriate of soda and water, but without any gelatine. The following proportions he assigns as approximations: Water.........93 Albumen ....'.... 5.5 Mucus.........2 Muriate of soda......0.5 100.* The liquor of the amnios, or the fluid which surrounds the foetus, is stated by Vauquelin and Buniva to be remarkable, in the cow, for affording a peculiar acid, already described under the name of the amniotic; but Dr. Prout, who has lately examined this liquor with much attention, was not able to detect any such principle.! The liquor, on which he made his experiments, had the sp. gr. 1.013. Its taste was bland and sweetish like fresh whey; and, when concentrated by evaporation, it yielded crystals of sugar of milk. It consisted of Water..........977 Albumen........, 2.6 Substance soluble in alcohol . . . 16.6 Saline substances and sugar of milk 3.8 1000. In the human subject, the composition of the liquor of the am- nios is entirely different; none of the amniotic acid appearing to exist in it. The only ingredients, that are found in it, are albumen, gelatine, with a portion of muriate and carbonate of soda and some phosphate of lime. It is precipitated by heat, by acids, by alcohol, and by infusion of galls. * Nicholson's Journal, xiv. 147. f Thomson's Ann. ?. 417. Vol. II.—N n £82 COMPLEX ANIMAL PRODUCTS. CHAP. XX11I. 5. Lymph. The fluid found in the thoracic duct of animals that have been kept 24 hours without food, is perfectly transparent and colourless, and seems to differ, in no respect, from that which is contained in the lymphatic vessels. Its properties are described by Mr. Brande as follows: 1. It is miscible in every proportion with water. 2. It produces no change in vegetable colours. 3. It is neither coagulated by heat, by acids, nor by alcohol, but is rendered slightly turbid by the last mentioned agent. 4. It gives, on evaporation, a very sparing residuum, which turns the colour of violet paper green. By incineration, this matter gives a very little muriate of soda, but no iron. 5. When submitted to electrical action, there was an evolution of alkali, and a^separation of albumen, at the negative pole. At the positive wire, muriatic acid only seemed to be evolved* 6. Synovia. This fluid, which is found in the cavities of the joints, may, from its office in lubricating the parts in which it is found, be described in this place, though in composition it differs considerably from the liquor of surfaces. It is at first a viscid liquid, but soon becomes gelatinous; and, after remaining some time in this state, again assumes a fluid form and deposits a fibrous matter. Alcohol separates from it a portion of albumen, but the re- maining liquid remains viscid. Acetic acid destroys its viscidity, and precipitates a quantity of white threads, which have a striking resemblance to vegetable gluten. The same substance is precipi- tated by the mineral acids, but not unless they are diluted with a large quantity of water; for in their concentrated form, they have the power of dissolving it. By continuing the analysis, several neu- tral salts may be obtained, and the proportions of the entire fluid have thus been stated by Margueron:* Fibrous matter......11.86 Albumen........4.52 Muriate of soda......1.75 Soda......... 0.71 Phosphate of lime.....0.70 Water.........80.46 100. 7. The fluid of perspiration has been examined by Berzelius. but under the disadvantage of operating on a very small quantity; A few drops, collected and evaporated on a watch glass, left a yel- lowish residue, having all the appearance, under the microscope, of the usual mixture of muriates of potash and soda with lactic acid, lactate of soda, and its accompanying animal matter. It red- dened litmus, and dissolved in alcohol; and was, without doubt, of * Annales de Chim. xiv. 283 SECT. V. URINE. the same nature as the analogous matter found in other animal fluids. The acetic acid, which 1 henard supposed he had disco- vered in the fluid of perspiration, was most probably a product ot his mode of operating. SECTION V. ' Of the Urine and Urinary Calculi. The urine, though one of the most complicated fluids of the animal bodv!containing at least a dozen different substances is nerhans one of those, the composition of which is now best under- stood For a long period of time, the attention of chemists seems o have been limited to the extraction of phosphorus and neutral alts from urine; but a new direction was given to their labours by the valuable discoveries of Fourcroy and Vauquelin.* The ana- vs's of the urine has been prosecuted, also, with great success in hs country by Cruickshank;t in Spain by Proust; and recently by t^t indefatigable philosopher, professor Berzelius of Stock- holm^ And though some important facts have b-.en contributed bv other persons, yet it is chiefly to these writers that we are in- debted for the materials of its chemical history. The external properties of the urine need no description; and indeed none would apply universally to I fluid, which is constantly varyingrnot only in The diseased but in the healthy state of the body The following account of its chemical properties is to be understood as applying to the urine which is voided e^rly in the morning, or at leas/several hours after a meal. In this state it has Heen fellow colour, and an intensely bitter taste. Its specific gravfy is variable. Dr. Bryan Robinson fixes it at 10SO, water be- ine 1000; and M. Cruickshank found it to vary from 1005 to 1033. From my own experiments, I am disposed to consider the num- ber stated by Dr. Robinson as a fair general average. The substances, which appear to me to have been satisfactorily proved to exist in healthy urine, are the following: Water. n- Albumen. o Free phosphoric acid. 12. Lactate of ammonia. 3' Phosphate of lime. 13. Sulphate of potash. 4 Phosphate of magnesia. 14. Sulphate of soda. 5. Fluoric acid. 15. Fluate of lime. 6. Uric acid. 16- Muriate of soda. 7 Benzoic acid. 17. Phosphate of soda. 3 Lactic acid. 18- Phosphate of ammonia. 9. Urea. 19- fdphiir. 10. Gelatine. 20. Silex. * \nnales de Chimie, xxxi. 48. t J™- Maf • »■ 24°' .. [ Annales de Chimie, xxxvi. 258. $ Thomson's Annals, n. 416. 2S4 COMPLEX ANIMAL PRODUCTS. OH\P. XXIII. The presence of an uncombined acid in urine is shown by its in- variably, when recently voided, reddening blue vegetable colours. This effect is owing partly to the phosphoric, and partly to the lac- tic and uric acids, which urine contains; and Vogel has lately en- deavoured to show that carbonic acid is, also, one of its constitu- ents.* The lactic and phosphoric acids form the solvent, by which the phosphate of limeys retained in solution; and, if this portion of acid be saturated, the earthy salt is precipitated. Hence a few drops of pure ammonia, added to recent urine, occasion a white cloud, and a sediment of neutral phosphate of lime falls, in the proportion of about two grains from four ounces of urine. If lime-water be mixed with urine, a still larger quantity of phos- phate of lime is deposited; for the newly added earth unites with the free phosphoric acid, and a quantity of phosphate of lime is generated, in addition to that which before existed in solution. In the precipitate, formed by either of these processes, a small proportion of magnesia is discoverable, which existed, no doubt, in combination with phosphoric acid. The sediment contains, also, according to Berzeliusf, fluate of lime. The presence of the last-mentioned substance was ascertained by adding sulphuric acid, which set at liberty vapours of fluoric acid, in sufficient quantity to corrode glass. When the urine has stood for about 24 hours at a mean tem- perature, the uric acid and phosphate of lime are in a great mea- sure deposited; and still more speedily and completely, if the urine be first evaporated to half its bulk. They may be separated from each other, either by diluted nitric acid, which leaves the uric acid, and takes \fp only the phosphate of lime; or by calcining the mix- ture in a red-heat, which destroys the uric acid, but not the calca- reous phosphate. By this operation, the uric acid is found to vary considerably; but the phosphate of lime is pretty constantly in the proportion of a grain from two ounces of urine. • The quantity of uric acid, obtained from urine, is greatly increased by adding to that fluid almost any other acid, and allowing it to stand for some days; at the end of which time small crystalline grains will be found lining the inner surface of the vessel.} The existence of salts, containing sulphuric acid, in urine, is proved by adding muriate of barytes, to urine acidulated with mu- riatic acid. This excess of acid prevents the precipitation of the phosphates, which would otherwise be decomposed by the barytic salt. From the weight of the precipitate, Berzelius computes that the proportion of sulphuric acid in urine exceeds that of phosphoric acid.—If nitrate of barytes, with an excess of nitric acid, be employed, and if the urine, after depositing the sulphate of barytes, be evaporated, a further portion of sulphate of barytes is deposited in small hard crystals. Now the sulphuric acid, which * 93 Ann. de Chim. 71. f Anna!, s de Chimie, lxi. 256; and Thomson's Annals, ii. 416. j Egan, Philosophical Magazine, xxiii. 298. SECT. V. URINE. 285 occasions this second production of the barytic sulphate, must have been formed during evaporation; and can only be accounted for by supposing, that a portion of sulphur, existing in the urine, has been acidified by the excess of nitric acid. When urine, which has deposited its phosphate of lime and uric acid, is submitted to distillation, a liquid condenses in the receiver, which has a very peculiar and nauseous smell, and effervesces strongly with acids, in consequence of its containing carbonate of ammonia. In the retort there remains a residuum, which, if eva- porated to the consistence of honey, composes from one 24th to one 36th the weight of the urine. When a little of this extract is added to a quantity of nitric acid, diluted with an equal weight of water, a number of shining white or yellowish scales are deposit- ed, resembling the boracic acid, and in the proportion of five 8ths or seven 8ths the weight of the extract. This precipitate is occa- %ioned by the action of the nitric acid on the urea, which is con- tained in urine; and to thev decomposition of the same substance is owing the carbonate of ammonia, obtained from urine by distilla- tion. (See the section on Urea.) From the extract of urine, the peculiar substance, called the urea, may be separated by digesting the extract repeatedly with alcohol, and decanting the solutions, which are to be gently eva- porated. Its proportion varies very considerably; but it has been stated, by Mr. Cruickshank, at about one 70th the weight of the urine, or one half the inspissated extract. The undissolved residue contains lactic acid and a number of neutral salts, consisting of muriate of potash, muriate of soda, phosphate of soda, and phos- phate and lactate of ammonia. Muriate of ammonia, is, also, oc- casionally found, and is dissolved, along with the urea, by the alcohol. These salts admit of being separated from each other by solution and evaporation. The muriates, at a certain degree of concentration, form a pellicle, which is to be removed while the liquor is hot. The solution, when cold, deposits two sets of crystals; rhomboidal prisms, which are the phosphate of ammonia; and rectangular tables, consisting of phosphate of soda. Along with the urea, a portion of benzoic acid is, also, taken up by the alcohol. The presence of this acid in urine may be shown, by evaporating it to the consistence of syrup, and pouring in mu- riatic acid; when a precipitate appears, which consists of benzoic acid. In human urine its proportion is small, and Berzelius could not even discover a trace of it; but in that of herbivorous quadru- peds, so large a quantity exists as to be worth extraction. On the average, Vauquelin has shown that it forms about one 300th of the urine of this class of animals.* If human urine be evaporated to the consistence of syrup only, and alcohol be added, the substance remaining undissolved is acid. This acid combines with ammonia, and the compound is soluble * Annales de Chimie, lxix. 311 236 COMPLEX AMMAL PRODUCTS. CHAP. XXIII. in alcohol. From this solution the ammonia is disengaged by lime; and from the new salt thus formed, the lime may be precipi- tated by oxalic acid, which leaves the lactic acid dissolved in wa- ter. By this process, a small part only of the lactic acid is obtain- ed from urine; the greater portion of it being dissolved by the alcohol, together with the lactate of ammonia. Albumen, gelatine, and mucus exist, alio, in the urine, but in very variable proportion. When urine is heated nearly to the boiling temperature, a white flocculent precipitate often forms in it. This is in part phosphate of lime, thrown down by the ammo- nia resulting from the decomposition of urea; but it also contains coagulated albumen, which remains after adding muriatic acid to dissolve the calcareous phosphate. In dropsy, the proportion of albumen is often sufficient to produce a distinct coagulation both by hoat and acids. Gelatine is discovered, on adding infusion of galls, by a precipitate which amounts, according to Mr. Cruick-^ shank, to one 240th part the weight of the urine. Mucus, also, is suspended in all newly evacuated urine, and affects its perfect transparency. If the urine be voided in different portions, the mucus, which naturally lines the urinary passages, is most abundant in the first, and less so in the subsequent por- tions. When recent urine is filtered, the mucus remains on the filter, in the form of transparent and colourless flocculi. The cloud, which appears in the urine during fever, is merely this mucus, which subsides more slowly than usual, in consequence of the increased specific gravity of the urine. From urine filtered when warm, a grayish white sediment falls in cooling, which gra- dually acquires a reddish hue and a crystalline form. The grayish powder is soluble in caustic potash, without any evolution of am- monia; but, as it becomes red and crystallized, potash disengages ammonia fiom it in abundance. Berzelius considers it, therefore, as urate of ammonia with excess of acid. The deposit is partly soluble, also, in acetic acid, which extracts a substance having the characters of mucus. There appears, indeed, to be an affinity be- tween uric acid and mucus; for that acid separates most abun- dantly from urine, which has not been deprived of mucus by fil- tration. In some diseases of the bladder, its mucous secretion appears to undergo a considerable change, and to assume a puru- lent appearance.* Sulphur was first discovered in urine by Proust. This fluid, he observes, blackens silver vessels in which it is evaporated, and scales are detached which consist of sulphuret of silver. Sulphu- reted hydrogen gas, he finds also, is disengaged from urine which has been kept about fifteen days; a remark, which has since been made, also, by Vogel. The same distinguished chemist supposed that he had discover- ed carbonic acid in urine, by examining the air bubbles which arise * Berzelius in Thomson's Annals, ii. 420. SECT. V. URINE. 287 from this fluid during ebullition. There can be little doubt, how- ever, that the carbonic acid, thus detected, arises from the decom- position of urea by the increased temperature. To the same source, also, (urea) may be refered the carbonate of lime, found by Proust on the surface of casks in which urine had been kept. By the decomposition of urea, carbonate of ammonia is formed; and this, re-acting on the phosphate of lime contained in urine, would doubtless compose carbonate of lime. The occasional pre- sence of the sulphate of soda rests on better evidence; for it fre- quently happens that only a part of the precipitate, formed by adding muriate of barytes to urine, is dissolved by muriatic acid; thus indicating the formation of sulphate of barytes. The acetic acid and resinous matter, which Proust imagined he had discovered in urine, may be accounted for by supposing, that they were produced, rather than separated, by the processes which he employed. At least their existence in healthy urine is equivo- cal; and it is not improbable that this excellent chemist mistook the lactic for acetic acid. The acetic acid he obtained by distil- ling a fresh extract of urine with sulphuric acid; and the resinous matter by diluting the residue of this distillation when beginning to grow thick, with a large quantity of cold water; the excess of acid being afterwards removed by a little alkali. The resin thus produced he found to bear a striking resemblance to castor. Berzelius discovered siliceous earth in urine by treating extract of urine, first with alcohol, then with water, and finally with mu- riatic acid. The silex remained in the form of a gray powder, which, by fusion with soda, became glass. Its source he appre- hends to be in the water, which we drink, which almost universally contains silex. With regard to the proportion of the different ingredients of urine, Berzelius finds that it differs essentially in the same indivi- dual, even from causes which have little influence on health. The following Table may be considered as showing its average com- position. Water ............933.00 Urea............ . 3(5.10 Sulphate of potash........ 3.71 ■----------soda......... 3.16 Phosphate of soda......... 2.94 ------------ammonia....... 1.65 Muriate of soda . *........ 4.45 - ammonia........ 1.50 Free Lactic acid......... "] Lactate of ammonia........ Animal matter soluble in alcohol and accom- ! _ panying the lactates....... Animal matter insoluble in alcohol . . . Urea not separable from the above . . . 288 COMPLEX ANIMAL PRODUCTS. OHAP. XXIII, Earthy phosphates with a trace of Fluate of Lime............ Uric acid........... Mucus of the Bladder....... Silex............. 1000. The 17.14 parts of lactic acid, Sec. contain a quantity of water, which cannot be abstracted without decomposing those bodies. The uric acid is extremely variable; but in the particular instance, which furnished the above results, it was deposited on cooling. The earthy phosphates contain 11 per cent, more magnesia, than exists in the earth of bones, or in the ashes of blood. Much more potash is discoverable, also, in urine and in milk, than in blood. The putrefaction of urine is attended with a series of changes, somewhat analogous to those accompanying its distillation. The urea, which it Contains, is decomposed and converted into carbo- nate of ammonia, which neutralizes all the redundant acids, and precipitates phosphate of lime. At the same time, the ammonia, uniting with the phosphate of magnesia, composes a salt, which settles in white crystals on the inner surface of the vessel. This salt is the ammoniaco-magnesian phosphate, which constitutes so large a part of some urinary calculi. The albumen and gelatine contained in the urine also undergo decomposition, and flakes are deposited, which consists of both these substances. Acetic acid is generated, and becomes saturated with ammonia. Acetate and carbonate of ammonia, and the ammoniaco-magnesian phosphate appear, therefore, to be the principal substances generated by the putrefaction of urine. Some important facts have been ascertained by Mr. Cruick- shank, respecting the changes that the urine undergoes in diffe- rent diseases. In dropsy, the urine was coagulated so completely by heat and by acids, as to differ but little from the serum of the blood. When this disease, however; arose from a morbid state of the liver, the urine was not coagulable; but was observed to be small in quantity, high coloured, and to deposit a considerable por- tion of pink sediment (probably the substance rosacee of Proust.) In inflammatory affections, the urine was found to be loaded with albumen. In gout, towards the end of the paroxysm, the urine deposited a lateritious sediment, which consisted of a very minute quantity of uric acid, a larger quantity of phosphate of lime, and some peculiar animal fluid not soluble in water. The urine of jaundiced persons contained a small quantity of bile, which was discoverable by the addition of muriatic acid. Hysterical urine was remarkable for a larger proportion of saline ingredients, but had scarcely any animalized matter. The composition of the urine differs essentially in the different classes of animals. Urea appears to be a constituent of the urine 1.00 1.00 0.32 0.03 sF.rr. V. URINARY CALCULI. 289 Of all animals, so far as it has hitherto been examined; but the uric acid is not found in herbivorous quadrupeds, the urine of which contains, instead of it, a lari>e proportion of benzoic acid. That of the horse and of the rabbit are remarkable for becoming milky afu.-r being voided, in consequence of the deposition of car- bonate of lime. The urine ot" the rabbit contains, also, carbonates of magnesia and potash, and sulphates of potash and lime. The urine of the cow, besides a larger proportion of benzoic acid, holds in solution carbonate and sulphate of potash and muriate of potash.—The urine of domestic fowls, which is voided through the same passage as the excrement, was found by Fourcroy and Vauquelin, and more lately by Chevreul, to contain uric acid. And Dr. Wollaston has determined the proporlion of uric acid to be greatest, in the urine of birds that feed on animal food. In the hawk, fed on flesh only, it was remarkably abundant; and the gan- nct, feeding solely on fish, discharged no solid matter except uric acid.* The uric acid has been found, also, by Dr. Proutf to con- stitute upwards of 90 per cent, of the excrement of an animal, be- longing to a different class, the serpent called boa constrictor. Mr. Brande, some years ago, discovered it in the urine of the camel. But, on the other hand, Vauquelin has proved that it is entirely absent from the urine of the lion and tiger, though fed on flesh, and though their urine abounds in urea4 Urinary calculi. Connected with the analysis of urine is that of the concretions, which are found in the bladder, and which oc- casion a disease, equally formidable from its symptoms^ and its remedy. Little was known respecting their chemical composition, till the time of Scheele; to whom we owe on this, as on many other subjects, the first, and therefore the most difficult steps to- wards accurate analysis. By the discovery of the uric (or, as he termed it, lithic) acid in one of the most common varieties of cal- culus, and in the ordinary urine, he paved the way to every thing that has been since ascertained, respecting other varFeties; and his experiments have been most ably followed up by those of Dr. Wollaston, and of Fourcroy and Vauquelin. It is but justice to Dr. Wollaston, however, to state, that the principal distinctions of the several species of calculus were pointed out by him in the year 1797§, in a memoir not less distinguished by the importance of its facts, than by the simplicity with which they are narrated. Two years afterwards the experiments of Fourcroy and his asso- ciate were communicated to the National Institute; so that the title to priority unquestionably belongs to our countryman. Se- veral valuable additions have been since made to our knowledge of the subject by Dr. Pearson, Mr. Brande, and others; and an excellent history of all that was before known, combined with * Phil. Trans. 1810. f Thomson's Annals, v. 413. J 82 Ann de Chim. 199. {See the Philosophical Transactions for that year. Vsl. lL—O o 290 COMPLEX ANIMAL PRODUCTS. un vi». xxiit much original matter, has been contributed by Dr. Marcet.* In the plates, which are annexed to this work, will be found the most exact representations of the several varieties of urinary concre- tions, that have yet been published. The ingredients of urinary calculi are much less numerous than those of the urine. The following appear to be (he only substances, the existence of which, in concretions of this sort, is sufficiently established; viz. uric or lithic acid; phosphate of lime; ammoniaco- magnesian phosphate; oxalate of lime; silex; and an animal matter, which serves the purpose of a cement to the earthy ingredients. To these, Proust has added the carbonate of lime;t but in this in- stance, there is reason to doubt of an authority which is in most cases unquestionable. The ingredients of rarer occurrence are the cystic oxide of Dr. Wollaston, and the xanthic oxide of Dr. Marcet. It is scarcely ever that any of these substances is found singly. Nevertheless, the predominance of some one of them gives to the concretion its peculiar characters; and determines the genus to which it should be assigned. Several arrangements of urinary calculi have been contrived. Fourcroy and Vauquelin have enumerated three genera, which they have divided again in- to no less than twelve species. In these subdivisions, however, several minute differences have been attended to, which are scarce- ly sufficient grounds for specific distinctions; and it appears to me sufficient for every purpose of arrangement to class them under the following heads. I. Calculi which are chiefly composed of uric acid: II. Calculi principally composed of the ammoniaco-magnesian phosphate: III. Calculi consisting, for the most part, of phosphate of lime: IV. Calculi which derive their characteristic property from oxalate oflime; and V. Calculi composed of the substance discovered by Dr. Wol- laston, and called by him cystic oxide. I. The calculi composed entirely of uric acid are of very rare occurrence; but those, in which it prevails, and gives the charac- ter of the species, form a very considerable proportion, perhaps one half, of urinary concretions. Calculi of this kind are of vari- ous sizes, from that of a bean to that of a large egg. Their shape is most commonly a flattened oval; but when more than one are found, they acquire, by friction against each other, several sides and angles. The best view of their internal structure is obtained by sawing them through their longest and widest diameter, when they exhibit generally a central nucleus, of more compact texture, and greater hardness and lustre, than the rest of the stone; but generally of the same figure. From this to the circumference, a number of distinct layers are perceived; and these layers, when the * " An Essay on the Chemical History and Medical Treatment of Calcu- lous Disorders." 8vo. London, 1817. f Annales de Chimie, xxxvi. ■>ECT. V. URINARY CALCULI. 291 calculus is broken, exhibit a radiated structure, the radii converg- ing towards the centre. The harder varieties, when divided by the saw, admit of some degree of polish, and bear a considerable rescmbl mce to wood. Tneir colour is various, but generally of different shades of yellow, from pale straw yellow to a deep shade of that colour, approaching brown or sometimes brown with a mixture of" red. Their specific gravity, according to Fourcroy, varies from 1.276 to 1.786; but generally exceeds 1.500. The chemical characters of calculi of this kind resemble those of the uric acid. When burned in a crucible; they emit the smell of horn, and are almost entirely consumed; a black dense coal re- maining which amounts to about one 5th the weight of the calcu- lus. They dissolve, either wholly or m great measure, in solu- tions of pure potash and pure soda, and are precipitated again by acids A very striking property of this sort of concretions is, that when a few grains are heated on a watch glass with a small quan- tity of nitric acid, and the mixture evaporated to dryness, a beauti- ful red substance remains, which dissolves in water and tinges the skin of the same colour. II. The ammoniaco-magnesian phosphate or triple calculus is scarcely ever found without an admixture of some other substance, especially of phosphate of lime. Calculi of this sort are easily discriminated, from those of the first species, by their colour, which is white, generally pure white They attain a much greater size than uric acid calculi; and, in one or two instances, have increased so as to fill the whole capacity of the bladder. The layers are distinguishable only by different degrees ot" hardness and density; and small cells are often formed by the interrupted deposition of these layers, which are lined with sparkling crystals. The calculi of this kind are soft, and their powder dissolves sufficiently in the mouth, to give a distinct sweetish taste. Boiling water acts upon the ammoniaco-magnesian phosphate; and the calculus loses about four lOths of its weight, which is de- posited on cooling, in the form of shining crystals. When ex- posed to heat it first becomes black, emits a smell of ammonia, and a white powder is left, which fuses imperfectly when the heat is more strongly urged. Most acids (even sulphuric acid of the specific gravity 1020) dissolve it rapidly, and deposit it again on the addition alkalies. Pure alkalies do not dissolve it, but disen- gage ammonia. To extract the phosphoric acid, Dr. Wollaston dissolved the calculus in acetic acid, and precipitated the phos- phoric acid by an excess of acetate of lead To the clear liquor, sulphuric acid was added, which threw down the excess of lead, and, at the same time, formed sulphate of magnesia. Evaporation to dryness removed the acetic acid; and, by raising the heat, the sulphate of ammonia and excess of sulphuric acid were expelled; leaving the sulphate of magnesia pure, and capable of forming crystals by solution and evaporation. 292 COMPLEX ANIMAL PRODUCTS. CHAr. XXIII- III. The third species of calculus, composed chiefly of phos- phate of lime, is usually, on its outer surface, of a pale brown co- lour, and so smooth as to appear polished. When sawed, it is found to be regularly laminated, and the layers adhere so slightly, as to be readily separated into concentric coats. Internally the colour is white, but not of that pure and brilliant kind, which dis- tinguishes the ammoniaco-magnesian phosphate. The small crys- tals also, which occur in the former variety, are never found in this; and its powder, when rubbed between the fingers, is considerably more harsh and rough. The phosphate of lime calculus dissolves, though slowly, in di- luted nitric, muriatic, and acetic acids (but not in the sulphuric acid of the specific gravity 1020), and is precipitated unchanged by alkalies. A small fragment put into a drop of muriatic acid, on a piece of glass over a candle, is soon dissolved; and, when the acid is evaporated, crystallizes in needles, which makes angles of 60° and 120° with each other. This property Dr. Wollaston considers as a very delicate test of the phosphate of lime. When exposed to the blow-pipe, it first blackens, but soon becomes white, and, by intenselyurging the flame, may at length be fused. When the phos- phate of lime and ammoniaco-magnesian phosphate exist together, they compose a calculus, a fragment of which may be melted with great ease by the blow-pipe into a vitreous globule; and which has therefore been called by Dr. Wollaston, the fusible calculus. This calculus, when pulverized and acted upon by acetic acid, is only partially dissolved, the amoniaco-rnagnesian phosphate being taken up by the acid, and the phosphate of lime left. In this way, it is easy to ascertain the proportion of the two phosphates. IV. Calculi of the fourth kind, though their composition was not ascertained} have been long distinguished from others, by the peculiarities of their external characters, under the name of mul- berry calculi. This epithet has been derived from their resem- blance to the fruit of the mulberry. They are usually of a much darker colour than the other varieties, and are covered, generally, with a number of projecting tubercles; but the species compre- hends, also, some perfectly smooth concretions of a pale colour. Their hardness greatly exceeds that of the other kinds; for it is not easy to reduce them to powder by scraping with a knife. They have also a greater degree of specific gravity, varying, according to Fourcroy, from 1428 to 1976. Calculi of this species when pulverized are soluble in muriatic and nitric acid; but not unless the acids are concentrated and heat- ed. The solution by muriatic acid has a deep brown colour, but deposits white crystals on cooling. Pure alkalies do not decom- pose this variety of calculus; but when it is digested with alkaline carbonates, the oxalic acid is separated and replaced by carbonic acid To exhibit the oxalic acid in a separate state, the oxalate of potash may be decomposed by acetate of barytes or super-acetate of lead, and the oxalate of lead or barytes by sulphuric acid. This SECT. V. URINARY CALCULI. 293 is the process of Fourcroy; but Dr. Wollaston disengaged the oxa- lic acid by the direct addition of sulphuric acid to the pulverized calculus, and the crystallization of the acid which was thus de- tached The presence of lime, in this variety of calculus, is demonstra- ted, in a very simple manner, by burning it in a crucible, and strongly calcining the residuum, or by exposure to the blow-pipe. By the addition of water, we obtain lime-water. Silex is a very rare ingredient, and has been discovered in calculi, in one or two instances only. V. A new species of calculus from the human bladder was dis- covered, by Dr. Wollaston, about the year 1805. It appears to be extremely rare; for in 1810, when its properties were first descri- bed in the Philosophical Transactions, only two instances of it had occurred to its discoverer. With the assistance of Dr. Wollaston's clear and accurate description, and of the proper experiments, I have recognized two other examples, in a collection of calculi now in my possession; and Dr. Marcet has since detected it in no less than three instances.* In external appearance, these calculi resemble more nearly the triple phosphate of magnesia than any other sort of calculus; but they are more compact, and do not consist of distinct laminae, but appear as one mass, confusedly crystallized throughout its sub- stance. They have a yellowish semitransparency, and a peculiar glistening lustre, like that of a body having a high refractive den- sity. Under the blow-pipe, the new calculus gives a peculiarly foetid smell, quite distinct from that of uric acid. Distilled in close ves- sels, it yields fcetid carbonate of ammonia, partly solid and partly fluid, and a heavy foetid oil; and there remains a black spongy coal, much smaller in proportion than from uric acid calculi. It is so readily acted upon by chemrcal agents, that its charac- ters are best taken from an enumeration of the few feeble powers, which it can resist. These are water, alcohol, acetic, tartaric, and citric acids, and saturated carbonate of ammonia; all which are in- capable of dissolving it, except in very minute proportion. Its solvents, on the other hand, are far more numerous. It is abundantly dissolved by muriatic, nitric, sulphuric, phosphoric, and oxalic acids; by potash, soda, ammonia, and lime water; and even by fully saturated carbonates of potash and soda. When, therefore, it is intended to separate it from acids, the carbonate of ammonia is best adapted to the purpose; and, for the same reason, the acetic and citric acids are best suited to precipitate it from al- kalies. Its combirfations.with acids crystallize in slender spiculae, radia- ting from a centre, which readily dissolve again in water. Its com- pounds with alkalies form small granular crystals. * On Urinary Calculi, p, 82. 29 4 COMPLEX ANIMAL PRODUCTS. UUAP. XXIII. As this substance does not affect vegetable colours, and has all the chemical habitudes of an oxide, Dr. Wollaston distinguishes it by the name of Cystic Oxide. This name it is not worth while to alter, though Dr. Marcet has lately met with instances, in which its origin may be clearly traced to the kidneys and not to the blad- der. VI. Amongst the urinary calculi examined by Dr. Marcet, were two, the properties of which were found to differ from those of every known species. The first was of a reddish or cinnamon co- lour; was soluble in acids, though less readily than in alkalies, and gave with nitric acid a solution, which, when evaporated to dry- ness, had the remarkable property of assuming a bright lemon colour. It was distinguished from cystic oxide, by being much less soluble in acids; and, from uric acid, by considerably greater solu- bility in water. From the colour which it affords with nitric acid, Dr. Marcet has applied to it the term of Xanthic Oxide (from gxvfloj, yellow.') The other calculus exhibited a train of properties, correspond- ing exactly with those of fibrin; and should other examples of a similar kind occur, they may be distinguished, Dr. Marcet thinks, by the epithet fibrinous calculi.* Such are the principal kinds of urinary concretions. If any addi- tion were made to the five classes, under which they have been arranged, I would propose to add two others; the sixth compre- hending those calculi, which contain several of the foregoing in- gredients, in such a state of admixture as not to be distinguishable without chemical- analysis; and the seventh those, in which the different substances are disposed in distinct layers or in concentric strata. It may be proper, however, to give an outline of the classi- fication, proposed by Fourcroy and Vauquelin, after the analysis ef more than 600 of these concretions. Genus I.—Calculi composed of one ingredient only. Species 1. Calculus of uric acid. 2. ---------urate of ammonia.f 3. ---------oxalate of lime. Genus II.—Calculi composed of two ingredients. Species 1. Calculus of uric acid and earthy phosphates in distinct layers. 2. -------of uric acid and earthy phosphates intimately mixed. * On Urinary Calculi, chap. iv. t The existence of urate of ammonia, as an ingredient of calculi, has late- ly been rendered very questionable, to say the least, by Mr. Brande, with whose expeneucc, and Dr. Marcct's, on this poiiit my own entirely agrees. S.E0T. VI. boni;s. 295 Species 3. Calculus of urate of ammonia and the phosphates in layers. 4.--------of the same ingredients intimately mixed. 5. --------of earthy phosphates mixed or else in fine layers. 6.--------of oxalate of lime and uric acid in distinct layers. 7,--------of oxalate of lime and earthy phosphates in layers. CJkxus III.—Calculi composed of three or four ingredients-. Species 1. Calculus of uric acid or urate of ammonia, earthy phos- phates, and oxalate of lime. 2.--------of uric acid, urate of ammonia, earthy phos- phates, and silex. The urinary concretions, which have been extracted from the ' bladders of inferior animals, differ from those of the human sub- ject in containing no uric acid, and in consisting chiefly of carbo- nate and phosphate of lime, cemented by animal matter. SECTION VI. Of Bones, Shells, Crusts, Horn, and Cartilage. The bones of animals are composed partly of earthy salts, which give them solidity and hardness, and partly of animal matter, which serves the purpose of a cement, and keeps the earthy ingredients in a state of union. By long continued boiling, a large part .of the animal matter is extracted, and a solution is obtained, which con- cretes, on cooling, into a gelatinous mass. Hence bones contain gelatine as one of their ingredients. But besides this animalized substance, another is discovered by the slow action of diluted nitric or muriatic acid. Either of these acids dissolve both the earthy salts and.gelatine; and a soft flexible substance remains, retaining, in a great measure, the shape of the original bone. This soft and spongy substance seems to be analogous to cartilage; and is essen- tial to the constitution of all organized bones and shells. Its pro- duction appears to be the first step in the formation of bone, and ■of the other hard coverings of animals. In chemical composition, it has been found by Mr. Hatchett (to whom we owe its discovery) most to resemble coagulated albumen. Besides the marrow, which is lodged in the hollow cavities of bones, they contain, in the most hard and solid part of their sub- stance, a proportion of oil. This oil makes its appearance in a hard and suetty form, on the surface of the gelatinous mass extracted 296 COMPLEX ANIMAL PRODUCTS. CHAP. XXIII. by boiling. It exudes, also, from the bones of recent anatomical preparations; and a portion of it passes over, in a separate but al- tered state, when bones are submitted to distillation. By this pro- cess, bones are deprived, not only of their oily part, but the other animal substances which they contain are decomposed; a quantity of carbonate of ammonia is generated; and in the retort there re- mains the earthy ingredients blackened by charcoal. By a farther combustion in the open air, this charcoal is destroyed; and the earthy ingredients are left in a perfectly white state. In this way large quantities of bones are distilled for the sake of the carbonate of ammonia, which is afterwards applied in making the muriate of that alkali. The animal oil (formerly used in medicine, under the name of DippeVs o/7,) is now, on account of its offensive smell, which unfits it for most other purposes, chiefly converted into lamp-black. W'hen diluted muriatic or nitric acid is poured upon the white ashes ot bones, an effervescence takes place, and nearly the whole is dissolved. Solution of pure ammonia, added to the filtered liquid, precipitates a white earth in great abundance; but after it has ceased to produce any effect, the addition of carbonate of ammonia occasions a fresh precipitation. What is thrown down by the pure alkali is composed of phosphate of lime and a small quantity of phosphate of magnesia; and the precipitate by the mild alkali is the carbonate of lime. The proportions, deduced from the analysis of ox-bones by Fourcroy and Vauquelin, are the following: Animal matter......51 Phosphate of lime.....37.7 Carbonate of lime.....10 Phosphate of magnesia . . . . 1.3 100. Human bones were found by Fourcroy and Vauquelin (who have given a good general formula for the analysis of bones)* to contain some iron and manganese, and a larger proportion of magnesia than exists in the bones of herbivorous quadrupeds. This, indeed, might have been expected from the large quantity of magnesia, which is constantly passing off in human urine, but not in that of other animals. Alumine and silex were, also, found, by the same chemists, in human bones. Hildebrandt, however, has lately ana- lyzed human bones, without being able to discover magnesia in them.f Besides the above ingredients, Mr. Hatchett discovered in bones a minute quantity of sulphate of lime; and Berzelius has detected a combination of fluoric acid with the same earth, which Morroc- * 72 Ann. de Chim. 282. |«8 Ann. deChim. 190. MiCT. VI. SHELLS. 297 chini had previously found in enamel. Befzeliu* has given the following tabular view of the results of his analysis.* Cartilage . . • Blood vessels . . Fluate of lime Phosphate of lime Carbonate of lime Phosphate of magnesia 1.16 Soda, muriate of soda, > j 2() c. . . $ Dry Human Bo net. 32.17 1.13 2.0 51.04 11.30 water, &c. Bmmql of Huirian Teeth. 3.2 85.3 8,0 1.5 100. 2.0 100. Dry OX Bonis. 33.30 2.90 55.45 3.85 2.05 2.45 100. Enamel ofCtf Teeth. 3.56 4.0 81.0 *.1Q 3.0 1.34 100. Human teeth are composed of the same ingredients as the ena- mel, and in the same proportion, except that, in addition to other ingredients, they contain cartilage. This cartilaginous basis Mr. Hatchett found to remain in the original shape of the tooth, aftef removing the other component parts by diluted nitric acid. The enamel, on the contrary, dissolves entirely in diluted nitric acid, and is, therefore, free from cartilage. But it probably contains gelatine, and to the solution of this animal substance (which is not afterwards precipitable by alkalies) may perhaps be ascribed the loss, which forms part of the following results ot the analysis of enamel obtained by Mr. Pepys. He found the enamel of human teeth to consist of ^ Phosphate of lime......78 Carbonate of lime......6 Loss and water.......16 100. The substance of the teeth Mr. Pepys found to be composed as follows: Phosphate of lime Carbonate of lime Cartilage . . • Loss..... Root* or the Teeth. . 58 . 4 23 10 100. Teeth of Adults. 64 6 . 20 , 10 100. First Teeth of Children. . 62 & . 20- 12 100. The shells, with which several marine and also some land ani- mals are covered, have been divided by Mr. Hatchett into two * Annales de Chimie, Ixi. 257. Vol. II.—P p 298 COMPLEX ANIMAL PRODUCTS. CHAP. XXIII. classes. The first, from their resemblance to porcelain, he has termed porcellaneous shells. To this class belong the several spe- cies of valuta, cyprtea, &c. The second class approach in their cha- racters to mother of pearl. The shell of the fresh water muscle, and of the oyster, may be arranged under this head; and pearl it- self has the same characters and chemical composition. Comparing the experiments on both classes, Mr. Hatchett concludes that por- cellaneous shells consist of carbonate of lime, cemented by a very small portion of animal matter; and that mother of pearl and pearl do not differ from these, except in containing a smaller proportion of carbonate of lime. This, instead of being merely cemented by animal matter, is intermixed with and serves to harden a membra- nous or cartilaginous substance which is capable of retaining its form, after the removal of the earthy ingredient. The covering of crustaceous animals (as echini, star-fish, lob- sters, crabs, &c.) differs in composition from marine shells, and approaches that of the eggs of birds. The shells of eggs, Mr. Hatchett found, are composed of barbonate of lime, with a small proportion of phosphate of lime, cemented by animal matter. Vauquelin has lately added, to these ingredients of egg-shells, carbonate of magnesia, iron, and sulphur.* Horn differs essentially from all the substances that have been described in this section. The proportion of earthy matter obtain- ed by its combustion, scarcely amounts to one 300th part. It ap- pears to consist principally of gelatine and coagulated albumen. Of Cartilage. Chevreul has analyzed the cartilage of the squalus peregrinus. He found it to be sparingly soluble in water; the solution was vis- cid; foamed on agitation; restored the colour of reddened litmus; and was precipitated by sulphuric, nitric, or muriatic acid, an ex- cess of which re-dissolved the precipitate. Oxymuriatic acid oc- casioned a deposit, as did also the pro-nitrate of mercury and the sub-acetate of lead. Infusion of galls produced only a slight cloud. When boiled with alcohol, the cartilage shrunk in bulk, and became opaque by losing water. The first washings had the co- lour of ammoniuret of copper, and deposited an animal matter. From the residue of the evaporation of these washings, hydrate of lime disengaged a large quantity of ammonia. Cartilage dissolved in muriatic acid, and the solution was pre- cipitated by infusion of galls. Nitric acid dissolved it, and when evaporated, gave oxalic acid, nitrate of soda, a yellow matter, dif- ferent from that of Welther, and an odorous oil. By destructive distillation, it gave the ordinary products of an! mal substances. * 81 Ann. de Chim. 304. ''-r'l. VII. MLSCLKc 29* SECTION VII. Of Muscle, Membrane, Tendon, Ligament. The muscular flesh of animals consists chiefly of the peculiar substance, which has been already described under the name of Fibrin. Though generally of a reddish colour; yet, essentially, muscular fibre is white, and may be obtained in this state, if all the soluble parts be first washed away by long continued affusions of water, which acquires a dark colour. The solution, if concen- trated by boiling, gelatinates on cooling; and hence gelatine ap- pears to be one of the constituents of muscle. Albumen is another ingredient, and makes its appearance by a deposition of coagula- ted flocculi in the heated watery solution. A portion of fat, also, frequently concretes on cooling; but this is to be considered rather as an accidental admixture. From the gelatine, when evaporated to dryness, alcohol removes a peculiar kind of extract, soluble in water and in alcohol, and first described by Thouvenal. The entire muscle, when calcined, leaves about 5 per cent, of its weight of saline matter, composed chiefly of phosphates of soda, ammonia and lime, and carbonate of lime. Lean flesh, Berzelius finds, is composed of nearly three-fourths its weight of fluid. This fluid contains a free acid; and the ex- tract, which Thouvenel described, is the same acid syrupy mass, which is met with in milk and urine, and which consists-of lactic acid, an alkaline lactate, and the animal matter, that always ac- companies the lactates. The fluids of muscle abound much more in this syrupy extract, and contain more phosphate of soda, than the blood. The solid fibre is interwoven with the cellular texture, and is furnished with minute veins and nerves. It agrees, in chemical properties, with the fibrin of the blood; and it is soluble, except the cellular texture of veins and nerves, in acetic acid. By boiling it becomes, like the fibrin of blood, insoluble in acetic acid, and imparts to the water, with which it has been boiled, a constituent part, which has a strong and pleasant taste of flesh, and cannot be gelatinized. When this is dissolved, and mixed with the uncoagulated part of the humours of the flesh, it forms what is called broth, the strength and taste of which depend, not only on the dissolved gelatine of the cellular texture, but also on the fibrin, the taste of which it retains. The taste does not depend on the extractive matter of Thouvenel; for flesh, from which this ex- tract has been separated, still gives a palatable though colourless soup. Considerable differences exist in the colour and other proper* ties of the muscular flesh of different animals; but the cause of these differences is not well understood. It depends, most pro- bablv. on the proportion which the fibrin, albumen, and other jiDD COMPLEX ANIMAL PRODUCTS. CHAP. XXIU. principles bear to each other. Gelatine appears to be most abun- dant in the flesh of young animals; and albumen and extract in that of old ones. The tendons, or sinews as they are commonly called, are the strong cords in which muscles terminate, and which connect them with the bones. They differ from muscle in the total absence of fibrin; and in being completely soluble in water by sufficiently long boiling. The solution has the properties of gelatine. The liga?nents are excessively strong bands, which tie the bones together at the different joints. They are in a great measure, but Bot completely, soluble by boiling water; and contain, therefore, beside gelatine, some other animal substance, probably coagulated albumen. Membranes are thin semi-transparent substances, which some- times form bags for containing fluids, and sometimes line the dif- ferent cavities of the body. They are for the most part, though not entirely, soluble in watery and are composed, therefore, chiefly ©f gelatine. Hence by the common process of tanning, membranes are convertible into leather. There is an essential difference, however, between cellular or serous membranes, and mucous membranes. The latter furnish no gelatine by boiling; and are sooner destroyed than any animal substance, the brain excepted, by maceration in water, or by the action of acids. SECTION VIII. Of the soft Coverings of Animals, viz. Nails, Scales, Skin, Hairt Feathers, and Wool. The nails and hoofs of animals most nearly resemble horn in chemical composition. Their basis seems to be a series of mem- branes composed of coagulated albumen, in which is deposited a quantity of gelatine. Long boiling does not entirely dissolve them. By calcination they have only a very small proportion of earthy matter. The scales ef serpents also resemble horn in their chemical eomposition and properties. The scales of fish, on the contrary, are more nearly analogous to mother of pearl, and are composed ©f alternate layers of membrane and phosphate of lime. The skin consists of two distinct parts, a tough white membrane on the outside which is almost insensible, and an internal one, full of blood vessels and nerves, and distinguished by great sensibility. Between these two, in the human body, is a soft mucous sub- stance called rete mucosum. 1. The external layer, called the euticle or epidermis, is best separated from the parts beneath by the action of a blister. It is net soluble in water, nor in acids, unless they are sufficiently con- >I.CT. VIII. WOOL. 301 centrated to decompose it. Hence it differs from gelatine. Alka- lies however dissolve it; and, in this respect, it agrees with coagu- lated albumen, which it resembles, also, in receiving a yellow tinge from nitric acid. 2. The cutis vera, which lies beneath the cuticle, consists of a number of fibres crossing each other in various directions, and has considerable firmness and elasticity. Long continued boiling in water entirely dissolves it, and a solution is obtained which ge- latinates on cooling, or, by farther evaporation, may be wholly converted into glue. The true skin is composed, therefore, almost entirely of gela- tine; but under some modification which renders it insoluble in water. It is this substance that adapts the skins of animals for two important uses, that of being converted into leather by the reception of the tanning principle, and that of furnishing glue. 3. Of the rete mucosum very little is known. It is that part of the skin, on which its colour depends; and by the sufficiently long continued application of oxymuriatic acid, it has been found that in the negro it may be entirely deprived of its colour. Hair has been examined with considerable attention by Vauque- lin- He effected a complete solution of it in water by using a Papin's digester. The application of the proper temperature re- quired, however, some caution; for if raised too high, the hair was decomposed and gave carbonate of ammonia, empyreumatic oil, and sulphureted hydrogen. The solution always contained a sort of bituminous oil, the colour of which approached to that of the hair which had been dissolved. After separating this oil, the so- lution was precipitated by infusion of galls and by oxymuriatic acid; but did not gelatinate on cooling. Acids occasioned a pre- cipitate, which was re-dissolved by adding more acid. Silver was precipitated from its solutions of a black colour, and lead of a brown. A diluted solution of potash dissolved hair, excepting a little oil, sulphur, and iron; and the compound was a sort of soap. The oil, if red hair was employed, had a yellow tinge. Alcohol, also, extracted from hair a portion of oil, the colour of which varied with that of the hair. The coal, obtained by incinerating hair, afforded phosphate, sulphate, and carbonate of lime, muriate of soda, silex, magnesia, and oxides of iron and manganese. The whole of these sub- stances bore a very small proportion to the hair, and varied in hair of different colours. Hair, therefore, appears to consist chiefly of an animal matter resembling coagulated albumen; of an oil of various colours; of sulphur, silex, carbonate and phosphate of lime; and oxides of iron, and manganese. Feathers probably agree in composition with hair. The quill, Mr. Hatchett has shown, consists of coagulated albumen without any gelatine. The composition of wool is not accurately known; but; from its jO^ complex ANIMAL PRODUCTS. CHAP. XXIII. forming a soap with pure alkalies, it probably consists of coagula- ted albumen. We are equally ignorant of the true nature of silk. It is inso- luble both in water and in alcohol, but dissolves in pure alkalies and acids. By the action of nitric acid it affords the peculiar sub- stance already described under the name of the bitter principle. SECTION IX. Of the Substance of the Brain. The medullary matter of the brain and nervous system appears to differ from all other organized substances. It was first examin- ed by M. Thouret, with a view to explain why the brain was ex- empted from the change, observed in the bodies which were interred in the CimetiZre des Jnnocens. Fourcroy afterwards add- ed many important facts, and corrected M. Thouret in several particulars; and Vauquelin has published an elaborate set of expe- riments on the same subject.* The medullary substance of the brain is of a soft censistence, and forms, when agitated with water, a sort of emulsion, that passes through the finest sieves. This fluid is coagulated by a temperature of 160°, and a quantity of a substance resembling al- bumen is separated. The same coagulation is produced by acids; but the coagulum differs, in several respects, from that which takes place from the serum of the blood. On being boiled with alcohol, it loses about six lOths of its weight; but one third of the portion, which has been dissolved, is again deposited on cooling in the form of shining crystalline plates resembling those which are obtained from biliary calculi, from spermaceti, or from adipo- cire; but differing from those substances in requiring a higher temperature for its fusion. It stains paper like a fixed oil, is so- luble in 20 times its weight of boiling alcohol; and is miscible with water into a sort of emulsion, from which it does not separate on standing, and which is not acid. From the results of its combus- tion, both alone and with nitre, Vauquelin infers that it contains uncombined phosphorus. Alcohol, by digesting with brain, acquires a greenish colour, which it retains even after filtration. By evaporation to one eighth its bulk it deposits a yellowish oily fluid, and the liquor itself is yellowish. When repeated quantities of alcohol are digested on the same portion of brain, the alcohol is tinged a sapphire blue co- lour. These colours remain, till the whole alcohol is expelled by heat, when the residuary matter acquires a yellow tinge, of ' Thomson's Annals, i. L'32. ^F.CT. IX. BRAIN. GO 3 greater or less intensity. The latter portions of alcohol, do not, like the first, deposit oil on standing. The liquid oil, after being washed with water, and evaporated to dryness at a gentle heat, has a reddish brown colour, and a smell resembling that of the brain itself, but stronger. Its taste is likp that of rancid fat. It forms, with water, an emulsion which is co- agulated by the addition of acids, and by infusion of tan. It is soluble in hot alcohol; and the greater part separates on cooling. Though freed from all acid by washing, yet it furnishes phospho- ric acid by being burnt either alone or with nitre; and hence we must admit the presence of phosphorus in this fatty matter, as well as in the crystalline substance. From the latter, indeed, it appears to differ only in containing a quantity of animal matter, which is separable by cold alcohol. The acohol, from which the fatty matter has separated, has a yellow colour, a taste of the juice of meat, and gives marks of acidi- ty. It contains super-phosphate of potash, and a peculiar animal matter, which by its solubility in cold alcohol and water; by its property of being precipitated by infusion of galls; by its reddish brown colour, its deliquescence, its taste and smell of the juice of meat, may be regarded as identical with the substance, which Rouelle formerly called saponaceous extract of meat, and to which Thenard has given the name of Osmazome. It i6 this substance which tinges the fatty matter, extracted from brain by alcohol. The portion of brain which remains after the full action of alco- hol, is a greyish white matter in the form of flocks, which resem- bles cheese externally. In drying, it assumes a gray colour, a semi-transparency, and a fracture similar to that of gum arabic. It appears, as Fourcroy supposed, to be perfectly identical with albu- men; and it is this ingredient, which occasions the coagulation of brain, when mixed with water, by heat, acids, metallic salts, &c. The alkaline solution of this part of brain precipitates acetate of lead of a dark brown colour, showing obviously the presence of sulphur. The medulla of the brain, when exposed to the air, soon under- goes spontaneous decomposition; and evolves an acid, before it passes to the putrid state; but under water it may be kept a long time without any change. Nitric acid does not produce the same effects upon it, as on other animal substances. No nitrogen is se- parated; but, when the temperature is raised, a large quantity of carbonate of ammonia is disengaged, and oxalic acid i6 found in the retort. Diluted sulphuric acid, partly dissolves brain, and coagulates another part. The acid solution becomes black when concentra- ted by evaporation; sulphurous acid is generated; and crystals are formed which consist of shlphate of ammonia. Besides this salt, sulphates of ammonia and lime, phosphoric acid, and phosphates of soda and ammonia arc found in the liquid. When brain is dried at the temperature of boiling water, it co- 304 COMPLEX ANIMAL PRODUCTS. CHAP. XXI11. agulates and some water separates from it. When distilled in close vessels, ammonia is disengaged; which, uniting with carbonic acid formed at the same time, composes carbonate of ammonia. A portion of oil is obtained also, and sulphureted and carbureted hydrogen gases are formed. In the retort a coal remains which affords traces of phosphates of lime and soda. The mass of brain, as appears from the experiments of Vauque- lin, is composed, therefore, of 1st, two fatty matters, which arc probably identical; 2dly, albumen; 3dly, osmazomc; 4thly, different salts; and, among others, phosphates of potash, lime, and magne- sia, and a little common salt; 5thly, phosphorus; 6thly, sulphur. The following is to be considered merely as an approximation to their proportions. I. Water.........80.00 2. White fatty matter.....4.53 3. Red fatty matter.....0.70 4 Albumen........7.00 5. Osmazome....... 1.12 6. Phosphorus ....... 1.50 7. Acids, salts, and sulphur . . . 5.15 100. ELEMENTS OF EXPERIMENTAL CHEMISTRY. PART II. DIRECTIONS FOR EXAMINING MINERAL WATERS, AND MINERAL BODIES IN GENERAL. CHAPTER I. ANALYSIS OF MINERAL WATERS. The complete and accurate analysis of. mineral waters, and of mineral bodies in general, is one of the most difficult subjects of chemical manipulation, and requires a very extensive acquaintance with the properties and habitudes of a numerous class of substances. Long and attentive study of the science is therefore essential to qualify any one for undertaking exact and minute determinations of the proportion of the component parts of bodies. Such minute- ness, however, is scarcely ever required in the experiments that are subservient to the ordinary purposes of life; a general know- ledge of the composition of bodies being sufficient to assist in directing the most useful applications of them. I shall not attempt, therefore, to lay down rules for accurate analysis, but shall only describe such experiments as are suited to afford an insight into the kind, but not to decide the exact proportion, of the constitu- ent principles of natural waters, and of mineral substances in ge- neral. Before proceeding to the analysis of a water, it is proper to in- quire into its natural history, and to examine attentively its physi- cal characters. The nature of the strata in the neighbourhood of the spring, will often furnish useful suggestions respecting the contents of the water; the period of the year should be stated at which the analysis was performed; and whether after a rainy or dry season. The temperature of the water miist be carefully ob- served, as it issues from the spring; and the quantity inquired into, which it yields in a given time. The sensible qualities of taste. Vol. II— Q q .106 \N.VLYSIS OF WATERS. CHAP. I smell, degree of transparency, &c. are also best ascertained at the fountain-head. The specific gravity of the water may be found by- weighing a bottle, which is capable of containing a known weight of distilled water, at a certain temperature, filled with the water, under examination, at the same temperature. It is proper, also, to examine, on the spot, the channel through which the water has flowed; to collect any deposit that may have been formed; and to investigate its nature. The ©fleets of heat on the water may be next tried. Many wa- ters lose their transparency when their temperature is raised, and let fall a considerable deposit. The quality of this may, in some degree, be conjectured from its appearance. If its colour be brown- ish yellow, it consists, either wholly or chiefly, of oxide of iron; if white, or nearly white, it is composed principally of the carbonate of lime or magnesia. A mineral water, containing iron, deposits that metal also, when exposed to the atmosphere; and a thin pelli- cle forms on its surface, whether stagnant in a natural reservoir, or collected in a separate vessel. By this exposure, iron may be sometimes discovered in a water, though not easily detected at first; because it becomes farther oxidized, and more sensible to the action of tests.- Sulphureted hydrogenous waters deposit a sedi- ment, even when preserved in a well-closed phial; the hydrogen quitting the sulphur, which settles in the form of a white powder SECTION I. Examination of Mineral Waters by Re-agents. Water is never presented by nature in a state of complete pu- rity. Even when collected as it descends in the form of rain, che- mical tests detect in it a minute'proportion of foreign ingredients. And when it has been absorbed by the earth, has traversed its dif- ferent strata, and is returned to us by springs, it is found to have acquired various impregnations. The readiest method of judging of the contents of natural waters, is by applying what are termed tests, or re-agents; i. e. substances which on being added to a water, exhibit, by the phenomena they produce, the nature of the saline, or other ingredients. For example, if, on adding infusion of litmus to any water, its colour is changed to red, we infer, that the water contains an uncombined acid: if this change ensues, even after the water has been boiled, we judge that the acid is a fixed, and not a volatile one: and if, on adding the muriated barytes, a precipitate falls down, we safely conclude that the peculiar acid; present in the water, is either entirely or in part, the sulphuric acid. I shall first enumerate the tests generally employed in examining waters, and describe their application; and, afterwards, point out by what par- ticular tests the substances) generally found in waters, may be de- tected. bEC'l. 1. ANALYSIS OF WATERS. 307 In many instances, however, a mineral water may contain a sa- line, or other ingredient, but in such small quantity as to escape discovery by tests. It is therefore advisable to apply the tests of fixed substances to the water, after reducing its bulk one half, or in some cases considerably more, by evaporation* as well as in its natural state. The use of tests, or re-agents, has been employed by Mr. Kir- wan to ascertain by a careful examination of the precipitate not only the kind, but the quantity, of the ingredients of mineral wa- ters.. This will be best understood from an example. It is an estab- lished fact, that 100 parts of crytallized muriate of soda, when comoletely decomposed by nitrate of silver, yield, as nearly as pos- sible, 240 of precipitated muriate of silver. From the weight of the precipitate, separated by nitrate of silver from a given quantity of any water, it is therefore easy, when no other muriatic salt is pre- sent, to infer what quantity of muriate of soda was contained in the water; since every hundred grains of muriated silver indicate, pretty accurately, 41$ of crystallized common salt. The same mode of estimation may be applied in various other instances; and the rule for each individual case will be stated in the following description of the use of the various re-agents. For the analysis of mineral waters, and of mineral bodies in general, tests of the utmost purity are required. It will be found extremely useful to keep the three mineral acids, the alkalies, and the alkaline carbonates, in a liquid form, and of such strength, that one measure of the one will neutralize either one measure, or some simple multiple of one, of the other. The advantage, thus obtained, is, that when it is necessary to precipitate a substance, held in so- lution by an acid, we can take just the quantity of alkali required for the purpose; a precaution of great use in all cases, where the substance to be precipitateiis re-dissolved by adding an excess of the precipitant; as happens, for instance, with respect to alumine. It is of no consequence of what precise strength these solutions are; but the following will be found of convenient density; and, though perhaps the numbers may require a little correction in some instances, yet they are sufficiently accurate for the purpose tfiey are intended to serve. Liquids, Sp gravity. Measure* for saturation. 100 Water gr. measure, contain Sulphuric acid . . 1.135 . . 1 . 15.7 gr. real Nitric acid . . . 1.143 . 1 . 23,27 gr. do. Muriatic acid . . 1.074 . . 1 . 11.89 gr. do. Potash . . . . . . 1.100 . . 2 . 9,3 gr. do. Soda . . . . . 1,070 . . 2 . ,. 6.1 gr^ do. Ammonia . .. 0.970 . . 1 Subcarb. potash . . 1.248 . . 1 . . 31. gr. dry ■ ■■ soda . . . 1.110 . . 2 .. .- 11.5 gr. dry ——-----ammo nia 1.046 . o ..08 ANALYSIS OF WATERS. CHAP. 1. The. first column of the foregoing Table expresses the specific gravity of the liquid test; the second, the number of measures of each required for saturating any of the others; and the third, the number of grains of real acid, real alkali, or solid carbonate, in 100 measures of solution, each measure being equal to a grain of water. From the last column, and with the aid of the Scale of equi- valents, it is easy to calculate how much any other test, of known composition, is required for decomposing 100 water grain mea- sures of any of the solutions in the Table. Thus 15.7 grains of real sulphuric acid will be found, by Dr. Wollaston's scale, to be capable of decomposing 41.2 grains of dry muriate of barytes (equal to 48 of the crystallized muriate.) It may be adviseable, therefore; to keep a solution of muriate of barytes, of such strength, that 400 water grain measures may contain 48 grains of the crys- tals; in which state the solution will be more convenient for use, than if it were stronger. The same plan may be extended to other tests, the quantities of which may thus be accurately adjust- ed to the purpose intended to be answered. Indeed, it would contribute very much to accuracy, as well as to economy, if all the chemical solutions, kept for purposes of research, had their speci- fic gravity, and the proportion of their ingredient in a real or solid state, marked on the labels of the bottles containing them,—a practice of which I have long experienced the advantages. When filters of paper are used for collecting precipitates, great caution is necessary that their weight should be the same, before and after the experiment. Even during the time of weighing, they acquire moisture from the atmosphere; and it is therefore neces- sary, before taking their weight correctly, to obtain an approxima- tion to it; after which, the paper being again dried, less time is oc- cupied in determining it within the fraction of a grain. The un- sized paper, which accompanies Mr.^j»Vatt's copying machines, answers the purpose extremely well. It isthis which was always employed by Berzelius, whenever he used filters at all; but their use, when the nature of the precipitate admits, he thinks should be avoided.* I am not inclined, however, to coincide in his rejec- tion of filters, and am of opinion that, when they are carefully and skilfully used, there is no better way of collecting and drying pre- cipitates. In order to wash away, completely, all soluble matter, a stream of distilled water should be directed upon the edge of the paper, when laid in the funnel, either from a dropping tube or from the bottle, fig. 25, a. L—Infusion of Litmus. Syrup of Violets, &c. The infusion of litmus is prepared by steeping this substance, first bruised in a mortar, and tied up in a linen rag, hi distilled water, which extracts its blue colour. * 78 Annales de Chimie, 31. SECT. I. ANALYSIS OF WATERS. 209 If the colour of the infusion tend too much to purple, it may be amended by a drop or two of solution of pure ammonia; but of this no more must be added than is barely sufficient, lest the delicacy of the test should be impaired. The syrup of violets is not easily obtained pure. The genuine syrup may be distinguished from the spurious by a solution of corrosive sublimate, which changes the former to green, while it reddens the latter. When it can be procured genuine, it is an ex- cellent test of acids, and may be employed in the same manner as the infusion of litmus. It indicates, also, the presence of alkalies, which turn it green. Paper stained with the juice of the March violet, or with that of the scrapings of radishes, answers a similar purpose; being turned red by acids, and green by alkalies. In 'staining paper for the purpose of a test; the paper must be used unsized; or, if sized, it must previously be well washed with warm water; because the alum, which enters into the composition of the size, will otherwise change the vegetable colour to red. In the Philosophical Magazine, vol. i. page 180, may be found some recipes for other test liquors, invented by Mr. Watt. Infusion of litmus is a test of most uncombined acids. I. If the infusion redden the unboiled, but not the boiled water, under examination; or, if the red colour, occasioned by adding the infusion to a recent water, return to blue, on boiling; we may infer, that the acid is a volatile one, and most probably the carbonic acid. Sulphureted hydrogen gas, dissolved in water, also reddens litmus, but not after boiling; and its presence is easily discovered by its offensive smell. To ascertain whether the change be produced by carbonic acid or by sulphureted hydrogen, when'experiment shows that the red- dening cause is volatile, add a little lime-water, or, in preference, barytic water. This, if carbonic acid be present, will occasion a precipitate, which will dissolve, with effervescence, on adding a little muriatic acid. Sulphureted hydrogen may also be contained, along with carbonic acid, in the same water; which will be deter- mined by the tests hereafter to be described. In some cases, when the change of colour is so slight as to be scarcely perceptible, it may be proper to use half a pint or more of the water which we are examining, and to mix it with the infu- sion of litmus in a broad shallow glass vessel, set on a sheet of white paper; using for the sake of comparison a similar vessel of distilled water, coloured by an equal quantity of the litmus infusion. 3 Paper tinged with litmus is also reddened by the presence of carbonic acid, but regains its blue colour on drying. The mineral and fixed acids redden it permanently. That these acids, however, may produce their effect, it is necessary that they should be pre- sent in a sufficient proportion.* The dark blue paper, which is * See Kirwan on Mineral Waters, pape 40. a io ANALYSIS OF WATERS. CHAP, I generally wrapped round loaves of refined sugar, is not discolour- ed by carbonic acid or sulphureted hydrogen, but only by the stronger acids. II. Infusion of Litmus reddened by Vinegar,—Spirituous Tine. ture of Brazil-wood,— Tincture of Turmeric, and Paper stain- ed with each of these three Substances,—Acid Tincture of Cab- baget—Syrup of Violets. All these different tests have one and the same object. 1. Infusion of litmus reddened by vinegar, or litmus paper red- dened by vinegar, has its blue colour restored by pure alkalies and pure earths, and by carbonated alkalies and earths. 2. Turmeric paper and tincture are changed to a reddish brown by alkalies, whether pure or carbonated, and by pure earths, but not by carbonated earths. Dr. Bostock finds that it is obviously affected by a solution, containing only one 2000th of its weight of potash. 3. The red infusion of Brazil-wood and paper stained with it, become blue by alkalies and earths, and even by the latter when' dissolvefl by an excess of carbonic acid. In the last mentioned case, however, the change will either cease to appear, or will be much less remarkable, when the water has been boiled. 4. Infusion of the leaves of red cabbage in very dilute sulphuric acid has a red colour, which is rendered blue by alkalies, when added in quantity just sufficient to neutralize the acid. Hence, if the infusion be made with a known quantity of acid, it becomes a test of the quantity of alkali in any solution. As it is apt to spoil by keeping, it should be prepared fresh when wanted, from the leaves dried carefully and preserved in corked vials. 5. Syrup of violets, when pure, is, by the same agents, turned green;* as is also paper stained with the juice of the viplet, or with the scrapings of radishes, III.— Tincture of Galls. Tincture of galls is the test generally employed for discovering iron; with all the combinations of which it produces a black tinge more or less intense according to the quantity of iron. The iron, however, in order to be detected by this test, must be in Jiie state of red oxitie, or, if oxidized in a less degree, its effect will not be apparent, unless after standing some time in contact with the air. By applying this test before and after evaporation, or * According to Mr. Accum, syrup of violets, which has lost its colour by keeping, may be restored by agitation, during a few minutes, in contact with oxygen gas. In preference to the syrup, Mr. Descroizilles recom- mends as a test the pickle of violets, prepared by adding common salt to the expressed juice. Annales de Chimie, lxvii. 80; or Nicholson's Journal, xxv. 232-. r.ECT. I. ANALYSIS OF WATERS. 31 : boiling, we may know whether the iron be held in solution by car- bonic acid, or by a fixed acid; For, 1. If it produce its effect before the application of heat, and not afterward, carbonic acid is the solvent. 2. If after, as well as before, a mineral acid is the solvent. 3. If, by the boiling, a yellowish powder be precipitated, and yef galls still continue to strike the water black, the iron, as often happens, is dissolved both by carbonic acid and by a fixed acid. A neat mode of applying the gall-test was used by M. Klaproth, in his analysis of the Carlsbad water; a slice of the gall-nut was suspended by a silken thread in a large bottle of the recent water, and so small was the quantity of iron, that it could only be disco- vered in water fresh from the spring, by a slowly-formed and dark cloud, surrounding the re-agent.* It has been remarked by Mr. R. Phillips, that the presence of carbonate of lime rather heightens the colour produced by this test, when the iron is at the minimum of oxidation; but that when the metal is in the state of per-oxide, it diminishes the effect so much, that a very minute quantity of iron may elude entirely the action of the test. IV—Sulphuric Acid. 1. Sulphuric acid discovers, by a slight effervescence, the pre- sence of carbonic acid, whether uncombined or united with alkalies or earths. 2. If lime be present, whether pure or uncombined, the addi- tion of sulphuric acid occasions, after a few days, a white precipi- tate. II from a mineral water, which has been well boiled, the addition of sulphuric acid extricates sulphureted hydrogen gas, Mr. Westrumb infers the presence of hydro-sulphuret of lime. In this case, sulphate of lime is precipitated.! 3. Barytes is precipitated instantly, in the form of a white powder. 4. Nitric and muriatic salts, in a dry state, or dissolved in very Rule water, on adding sulphuric acid, and applying heat, are de- composed; and if a^stopper, moistened with solution of pure am- monia, be held over the vessel, white clouds will appear. For distinguishing whether nitric or muriatic acid be the cause of this appearance, rules will be given hereafter. V.—-Nitric and Nitrous Acids. These acids, if they occasion effervescence, give the same indi- cations as the sulphuric. The fuming red nitrous acid has been recommended as a test distinguishing between hepatic waters that contain hydro sulphuret of potash, and those that contain only * Klaproth, vol. i. page 279. f Nicholon's Journal, xviir. 40. 312 ANALYSIS OF WATERS. LHAF. I. sulphureted hydrogen gas. In the former case, a precipitate en- sues on adding nitrous acid, and a very fetid smell arises; in the latter, a slight cloudiness only appears, and the smell of the water becomes less disagreeable. If a water, after boiling, gives a pre cipitate of sulphur, on adding nitrous acid, Westrumb concludes that this is owing to hydro-sulphuret of lime. VI.—Oxalic Acid and Oxalates. The oxalic acid is a most delicate test of lime, which it sepa- rates from all its combinations. 1. If a water, which is precipitated by oxalic acid, become milky on adding a watery solution of carbonic acid, or by blowing air through it from the lungs, by means of a quill or glass tube, we may infer, that pure lime (or barytes, which has never yet been found pure in water) is present. 2. If the oxalic acid occasion a precipitate before, but not after boiling, the lime is dissolved by an excess of carbonic acid. In this case, carbonate of lime is separated, by heating the water, in the form of a white sediment, or of a sediment tinged yellow by oxide of iron, when that metal is also present. 3. If oxalic acid occasion a precipitate even after boiling, the solvent of the lime is a fixed acid. A considerable excess of any of the mineral acids, however, prevents the oxalic acid from throwing down a precipitate, even though lime be present; be- cause some acids decompose the oxalic, and others, dissolving the oxalate of lime, prevent it from appearing.* The oxalate of ammonia, or of potash (which may easily be formed by saturating the respective carbonates of these alkalies with a solution of oxalic acid,) are not liable to the above objec- tion, and are preferable, as re-agents, to the uncombined acid. Yet even these oxalates fail to detect lime when greatly supersa- turated with muriatic or nitric acids; and, if such an excess be present, it must be neutralized, before adding the test, with pure ammonia. A precipitation will then be produced. The presence of other earths in solution, along with lime, also impedes decom- position by oxalic acid and the oxalates. Thus a watery solution of sulphate of magnesia and sulphate of lime is not precipitated by these tests. The quantity of lime contained in the precipitate may be known, by first calcining it with excess of air, which converts the oxalate into a carbonate; and by expelling from this last, its carbonic acid, by calcination, with a strong heat, in a covered crucible. Accord- ing to Dr. Marcet, 117 grains of sulphate of lime give 100 of oxa- late of lime, dried at 160° Fahrenheit. The use of oxalate of ammonia, that excellent analyst finds, is in some degree limited by its property of precipitating the salts of iron. * See Kiman on Waters, page 88. SECT. I. ANALYSIS OF WATERS. 313 The fluate of ammonia, recommended by Scheele, I find to be a most delicate test of lime. It may be prepared by adding carbo- nate of ammonia to diluted fluoric acid, in a leaden vessel, ob- serving that there be a small excess of acid. VII.—Pure Alkalies and Carbonated Alkalies. r. The pure fixed* alkalies precipitate most of the earths and all the metals, whether dissolved by volatile or fixed menstrua, but only in certain states of dilution; for example, sulphate of alumine may be present in water, in the proportion of four grains to 500, without being discovered by pure fixed alkalies; and if too much of the alkali be added to a more concentrated solution, the alut mine is re-dissolved. If the alkali be perfectly free from carbonic acid, it does not precipitate lime, strontites, or barytes, except when those earths are held in solution by carbonic acid in excess, and then in the state of carbonates. As the alkalies precipitate so many substances, it is evident that they cannot afford any very precise information, when employed as re-agents. ,F>om the colour of the precipitate, at it approaches to a pure white, or recedes from it, an experienced eye will judge, that the precipitated earth contains less or more of metallic ad- mixture; and its precise composition must be ascertained by rules which will presently be given. 2. Pure fixed alkalies also decompose all salts with basis of ammonia, which becomes evident by its smell (unless the salts are dissolved in much water,) and also by the white fumes it exhibits when a stopper, moistened with muriatic acid, is brought near. 3. Carbonates of potash and of soda have similar effects. 4. Pure ammonia precipitates most of the earthy and all the metallic salts; but if quite pure, it does not precipitate lime, barytes, or strontites, when held in solution by any acid, except the carbonic. It has this advantage as a precipitant of alumine, that it does not re-dissolve that earth when added in excess. To any liquid that contains copper or nickel in a state of solution, it imparts a deep blue colour; the precipitated oxides of those metals being re-dissolved by an excess of the volatile alkali. 5. Carbonate of ammonia has the same properties, except that it does not precipitate magnesia from its solutions at common temperatures. Hence, to ascertain whether this earth be present in any solution, add the carbonate of ammonia till no farther pre- cipitation ensues; filter the liquor; raise it nearly to 212° Fahren- heit; and then add pure ammonia. If any precipitation now occurs, we may infer the presence of magnesia. It must be acknowledged that zircon, yttria, and glucine, would escape discovery by this process; but they have never yet been found in mineral waters; and their presence can scarcely be expected. Vol. II.—R r 314 ANALYSIS OF WATERS". CHAP. I. VIII.—Lime- Wateri f. Lime-water is applied to the purposes of a test, chiefly for detecting carbonic acid. Let any liquor supposed to contain this acid be mixed with an equal bulk of lime-water. If carbonic acid be present, either free or combined, a precipitate will immediately appear, which, on adding a few drops of muriatic acid, will again be dissolved with effervescence. 2. Lime-water will also show the presence of corrosive subli- mate by a brick-dust coloured sediment. If arsenious acid (com- mon arsenic) be contained in a liquid, lime-water, when added, will occasion a precipitate, consisting of lime and arsenous acid, which is very difficultly soluble in water. This precipitate, when mixed up with oil, and laid on hot coals, yields the well-known garlic smell of arsenic. IX.—Pure Barytes, and its Solution in Water. 1. A solution of pure barytes is even more effectual than lime- water in detecting the presence of carbonic acid, and is much more portable and convenient; since, from the crystals of this earth, the barytic solution may at any time be immediately prepared. In dis- covering carbonic acid, the solution of barytes is used similarly to lime-water, and, if this acid be. present, gives, in like manner, a precipitate soluble with effervescence in dilute muriatic acid. 2. The barytic solution is also a most sensible test of sulphuric acid and its combinations, which it indicates by a precipitate not soluble in muriatic acid. Pure strontites has similar effects as a test. The quantity of the precipitated substance, indicated by the weight of the precipitate, will be stated in No. XV. X.—Metals. 1. Of the metals, silver and mercury are tests of the presence of hydro-sulphurets, and of sulphureted hydrogen gas. If a little quicksilver be put into a bottle containing water impregnated with either of these substances, its surface soon acquires a black film, and-, on shaking, the bottle, a blackish powder separates from it. Silver is speedily tarnished by the same cause. 2. The metals may be used also as tests of each other, on the principle of elective affinity. Thus, for example, a polished iron plate, immersed in a solution of sulphate of copper, soon acquires a coat of this metal; and the same in other similar examples. XI.—Sulphate of Iron. This is the only one of the sulphates, except that of silver, appli- cable to the purposes of a test. When used with this view, it is SECT. 1. ANALYSIS OF WATERS. 315 generally employed for ascertaining the presence of oxygen gas, of which a natural water may contain a small quantity. A water, suspected to contain this gas, may be mixed with a lit- tle recently-dissolved sulphate of iron, and kept corked up, in a phial completely filled by the''mixture. If an oxide of iron be pre- cipitated in the course of a few days, the water may be inferred to contain oxygen gas. XII.—Sulphate, Nitrate, and Acetate of Silver. These solutions are all in some measure applicable to similar purposes. 1. They are peculiarly adapted to the discovery of muriatic acid and of muriates. For the silver, quitting its solvent, combines with the muriatic acid, and forms a flaky precipitate, which, at first, is white, but on exposuae to the sun's light, acquires a bluish, and finally a black colour. This precipitate, dried and fused by a gentle heat, Dr. Black states to contain, in 1000 parts, as much muriatic acid as would form 42 5£ of crystallized muriate of soda, which estimate scarcely differs at all from that of Klaproth. The same quantity of muriate of silver (1000 parts) indicates, according to Kirwan, 454§ of muriate of potash. Dr. Marcet's experiments and my own indicate a larger product pf muriate of silver from the decomposition of dry muriate of soda, viz. not less than 240 grains from 100 of common salt. Hence 100 grains of fused muriate of silver denote 41.6 of muriate of soda, and about 19 grains of mu- riatic acid. A precipitation, however, may arise from other causes, which it may be proper to state. 2. The solutions of silver in acids are precipitated by carbona- ted alkalies and earths. The agency of the alkalies and earths may, however, be prevented, by previously saturating them with a few drops of the same acid in which the silver is dissolved. 3. The nitrate and acetate of silver are decomposed by the sul- phuric and sulphurous acids; but this may be prevented by adding, previously, a few drops of nitrate or acetate of barytes, and, after allowing the precipitate to subside, the clear liquor may be decant- ed, and the solution of silver added. Should a precipitation now take place, the presence of muriatic acid, or some one of its com- binations, may be inferred. To remove uncertainty, whether a precipitation be owing to sulphuric or muriatic acid, a solution of sulphate of silver may be employed in the first instance, which, when no uncombined alkali or earth is present, denotes with cer- tainty the presence of the muriatic acid. According to professor Pfaff, one part of muriatic acid of the specific gravity, 1.15, diluted with 70,000 parts of water, barely exhibits a slight opaline tinge, when tested with nitrate of silver: and, when diluted with 80,000 parts of water, it is not affected at all.* Mr. Meyer of Stettin as- ' "Nicholson's Journal, xvii. 361. 316 ANALYSIS OF WATERS. CHAP, t signs, however, a much more extensive power to nitrate of silver, as a test of muriatic acid.* 4. The solutions of silver are also precipitated by sulphureted hydrogen, and by hydro-sulphurets; but the precipitate is then reddish, or brown or black; or it may be, at first, white, and after- wards become speedily brown or black. It is soluble, in great part, in dilute nitrous acid, which is not the case if occasioned by mu- riatic or sulphuric acid. 5. The solutions of silver are precipitated by extractive matter; but, in this case, also, the precipitate has a dark colour, and is so- luble in nitrous acid. XIII.—Nitrate and Acetate of Lead. 1. Acetate of lead, the most eligible of these two tests, is pre- cipitated by sulphuric and muriatic acids; but, as of both these we have much better indicators, I do not enlarge on its application to this purpose. 2. The acetate is also a test of sulphureted hydrogen and of hydro-sulphurets of alkalies, which occasion a black precipitate; and, if a paper, on which characters are traced with a solution of acetate of lead, be held over a portion of water containing sulphu- reted hydrogen gas, they are soon rendered visible; especially when the water is a little warmed. 3. The acetate of lead is employed in the discovery of uncom- bined'boracic acid, a very rare ingredient of waters. To ascertain whether this be present, some cautions are necessary.(o) The un- combined alkalies and earths (if any be suspected) must be satu- rated with acetic or acetous acid, (b) The sulphates must be de- composed by acetate or nitrate of barytes, and the muriates by ace- tate or nitrate of silver. The filtered liquor, if boracic acid be con- tained in it, will continue to give a precipitate, which is soluble in nitric acid of the specific gravity 1.3. 4. Acetate of lead is said, also, by Pfaff, to be a very delicate lest of carbonic acid; and that it renders milky water, which con- tains the smallest possible quantity of this acid. XIV.—Nitrate of Mercury prepared with and without Heat. This solution, differently prepared, is sometimes employed as a test. 1. The solution of nitrate of mercury, prepared without heat,t has been found by Pfaff to be a much more sensible test of muria- tic acid than nitrate of silver. Its sensibility, indeed, is so great, that one part of muriatic acid, of the specific gravity 1.50, diluted with 300,000 parts of water, is indicated by a slightly dull tint en- suing on the addition of the test. * Thomson's Annals, v. 23. f See chap. xix. sect. 4, vi. • >KCT. I ANALYSIS OF WATERS. 317 2. It is, at the same time, the most sensible test of ammonia, one part of which,-with 30,000 parts of water, is indicated by a slight blackish yellow tint, on adding the nitrate of mercury* 3. The nitrate of mercury is also precipitated by highly diluted phosphoric acid; but the precipitate is soluble in an excess of phos- phoric or nitric acid, which is not the case if it has been occasion- ed by muriatic acid. XV.—Muriate, Nitrate, and Acetate of Barytes. 1." These solutions are all most delicate tests of sulphuric acid and of its combinations, with which they give a white precipitate, insoluble in dilute muriatic acid. They are decomposed, how- ever, by alkaline carbonates; but the precipitate thus occasioned is soluble in dilute muriatic or nitric acid, with effervescence, and may even be prevented by adding, previously, a few drops of the same acid as that contained in the barytic salt, which is employed. One hundred grains of dry sulphate of barytes contain (accord- ing to Klaproth, vol. i. p. 168) about 45§ of sulphuric acid of the specific gravity 1850; according to Claryfield (Nicholson's Jour- nal, 4to. iii. 38), 33 of acid, of the specific gravity 2240; according to Thenard, after colcination, about 25; and, according to Mr. Kirwan, after ignition, 23.5 of real acid. The same chemist states, that 170 grains of ignited sulphate of barytes denote 100 of dried sulphate of soda; while 136.36 of the same substance indicate 100 of dry sulphate of potash; and 100 parts result from the precipita- tion of 52.11 of sulphate of magnesia. From Klaproth's experiments, it appears, that 1000 grains of sulphate of barytes indicate 595 of desiccated sulphate of soda, or 1416 of the crystallized salt. The same chemist has shown, that 100 grains of sulphate of barytes are produced by the pre- cipitation of 71 grains of sulphate of lime, of ordinary dryness. The results of my own experiments are stated in vol. i. page 350. From these it follows, that 100 grains of ignited sulphate of barytes denote 57 of calcined sulphate of lime; or 73 of the same sul- phate, dried by a temperature of only 160° Fahrenheit. Desicc^f ted sulphate of magnesia, when decomposed by muriate of barytes, affords twice its weight of the barytic sulphate. 2. Phosphoric salts occasion a precipitate also, which is soluble in muriatic acid without effervescence. XVI__Triple or Ferro-Prussiates of Potash and of Lime. Of these two, the prussiate of potash is the most eligible. When pure, it does not speedily resume a blue colour on the addition of an acid, nor does it immediately precipitate muriate of barytes. Prussiate of potash is a very sensible test of iron; with the solu- * Saussure, Thomson's Annals, vi. 430. 318 ANALYSIS OF WATERS. CliAI'. K tions of which in acids it produces a prussian blue precipitate, in consequence of a double elective affinity. To render its effect more certain, however, it may be proper to add, previously, to any water suspected to contain iron, a little muriatic acid, with a view to the saturation of uncombined alkalies or earths, which, if pre- sent, prevent the detection of very minute quantities of iron. 1. If a water, after boiling and filtration, does not afford a blue precipitate, on the addition of prussiate of potash, the solvent of the iron may be inferred to be a volatile one, and probably the car- bonic acid. . 2. Should the precipitation ensue in the boiled water, the sol- vent is a fixed acid,«the nature of which must be ascertained by other tests. Doubts had been thrown, by several chemical writers, on the fitness of the ferro-prussiate of potash for determining the quantity of iron in solutions of that metal. But Mr. Porrett, in his able inquiry into the nature of the triple prussiates, has shown that, with certain precautions, the ferro-prussiate of potash is fully ade- quate to this purpose.* It is necessary to observe, 1st. That if the ferro-prussiate, after being dissolved in water, gives, immediately, a blue precipitate by the addition of muriatic acid, it is not pure, and will afford a fallacious result. 2dly. That if the salt, however pure, be added, in excess, to a solution of iron containing an excess of acid, and then heated, the prussian blue thrown down will weigh more than it ought; because some is furnished by the decomposition of the ferro-prussic acid, contained in that part of the salt, which has been added in excess. 3dly. That prussian blue, even after it has been formed, is ma- terially acted upon by a mixture of nitric and muriatic acids, and in some degree, by the muriatic acid alone at a boiling heat. 4thly. That prussian blue, when precipitated, often carries with it sulphate of potash, derived from the liquid from which it is thrown down; and that this sulphate adheres to it so obstinately, that several washings with water, acidulated with sulphuric acid, are necessary to detach it. ^5thly. That if the solution, to which the test is applied, contain not only iron, but alumine, oxide of copper, or any other substance, which the test is known to precipitate, that substance should be removed, by the usual means, previously to the application of the test. Suppose then, for example, that we have barytes, alumine, mag- nesia, and oxides of iron and copper, in a state of solution by nitro- muriatic acid. The solution, if not already neutral, may first be rendered so by the cautious addition of ammonia. The barytic salt may next be decomposed by a solution of sulphate of soda, added till it ceases to occasion a precipitate. Ammonia, added to the residuary liquor, throws down the other earths and oxides, and < Phil. Trans. 1814, p. 53». SECT. I. ANALYSIS OF WATERS. 219 an excess of it will re-dissolve the oxide of copper. I mm the in- soluble part, consisting of alumine, magnesia, and oxide ol iron, solution of pure potash will remove the alumine. I he oxide of iron and magnesia may then be re-dissolved in any suitable acid, and, to the solution, neutralized, or nearly so, by ammonia, if ne- cessary, the ferro-prussiate may be poured, till it ceases to pro- ducc any effect, taking care to add as little excess as possible. The precipitate washed, dried at a steam heat, and weighed, will indicate in every 100 grains, 34.235 grains of peroxide ot iron. Besides iron, the prussiated alkalies also precipitate muriate of alumine. No conclusion, therefore can be deduced, respecting the non-existence of muriate of alumine, from any process, m which the prussic test has previously been used. It will, there- fore, be proper, if a salt of alumine be indicated by other tests, to examine the precipitate affected by prussiate of potash. This may be done by repeatedly boiling it to dryness with muriatic acid, which takes up the alumine, and leaves- the prussiate of iron. From the muriatic solution, the alumine may be precipitated by a solution of carbonate of potash. .. ' According to Klaproth (ii. 55), solutions of yttra (which earth, however is not likely to be present in any mineral water) afford, with the prussian test, a white precipitate, passing to pearl-grey, which consist of prussiate of yttria. This precipitate disappears on adding an acid, and hence may be separated from prussiated iron The same accurate chemist states, .that the prussian test has no action on salts with base of glucine (ii. 55); but that it pre- cipitates zircon from its solutions (ii. 214.) The prussiated alkalies decompose, also, all metallic solutions excepting those of gold, platinum, iridium, rhodium, osmium, and antimony. XVII.—Succinate of Soda, and of Ammonia. 1 The succinate of soda was first recommended by Gehlen, and afterwards employed by Klaproth (Contributions, n. 48,) for the discoverv and separation of iron. The salt with base of am- monia has also been used for a similar purpose by Dr. Marcet, physician to Guy's Hospital, in a skilful analysis of the Brighton chalybeate, which is published in the new edition of Dr. Saunder s Treatise on Mineral Waters. The succinic test is prepared by slightly super-saturating car- bonate of soda or ammopia with succinic acid. In applying the test, it is necessary not to use more than is sufficient for the pur- pose- because an excess of it re-dissolves the precipitate. The best mode of proceeding is to heat the solution containing iron, and to add gradually the solution of succinate, until it ceases to produce any tubidness. A brownish precipitate is obtained, con- sisting of succinate of iron. This, when calcined with a little wax, in a low red heat, gives an oxide of iron, containing about 70 per 320 ANALYSIS OF WA1ERS. CHAP. I. cent, of the metal. From Dr. Marcet's experiments, it appear; that 100 grains of iron, dissolved in sulphuric acid, then precipi- tated by the succinate test, and afterwards burned with wax, give 148 of oxide of iron; that is, 100 grains of the oxide indicate about '67£ of metallic iron. 2. The succinates, however, it is stated by Dr. Marcet and Mr. Ekeberg, precipitate alumine, provided there be no considerable excess of acid in the aluminous salt. On magnesia it has no ac- tion, and hence may be successfully employed in the separation of these two earths. If 100 parts of octohedral crystals of alum be entirely decomposed by succinate of ammonia, they give precisely 12 parts of alumine calcined in a dull red heat. The succinate of ammonia, it is stated by Mr. Ekeberg,* precipitates glucine; and the same test, according to Klaproth (ii. 214,) throws down zircon from its solutions. To separate all the iron and alumine from any water, long boil- ing is necessary with free access of air, in order that the iron may be completely oxidized; for the succinates have no action on salts containing the protoxide of iron. XVIII.—Benzoic Acid, and Benzoate of Ammonia. Benzoic acid, or, still better, benzoate of ammonia, precipitates iron readily and entirely; and being much cheaper, and more rea- dily obtained, than succinate of ammonia, may be substituted for the latter salt. It has, also, one advantage, that it does not de- compose the salts of manganese.f XIX.—Phosphate of Soda. A method of completely precipitating magnesia from its solu- tions has been suggested by Dr. Wollaston. It is founded on the property which fully neutralized carbonate of ammonia possesses; first to cause the solution of the carbonate of magnesia, formed when it is added to the solution of a magnesian salt, and after- wards to yield that earth to phosphoric acid, with which and am- monia it forms a triple salt. For this purpose, a solution of car- bonate of ammonia, prepared with a portion of that salt which has been exposed, spread on a paper, for a few hours to the air, is to be added to the solution of the magnesian salt sufficiently concen- trated; or to a water suspected to contain magnesia, after being very much reduced by evaporation. No precipitate will appear, till a solution of phosphate of soda is added, when an abundant one will fall down. Let this be dried in a temperature not exceed- ing 100° Fahrenheit. One hundred grains of it will indicate 19 of pure magnesia; 44 carbonate; about 66 of muriate of magnesia; * Jourrt. des Mines, No. lxx. + Thomson's Annals, ix. 163; Phil. Mag. xl. 258. iK.CT. I. ANALYSIS OF WATERS. 321 t « and 62 of desiccated, or double that quantity of crystallized, sul- phate of magnesia. If, instead of drying the precipitate at a gentle heat, we calcine it, we may then reckon the calcined phosphate of magnesia to indicate, in every hundred grains, 38.5 of magnesia, or to be equivalent to 226 grains of the crystallized sulphate of that earth. XX.—Muriate of Lime. Muriate of lime is principally of use in discovering the presence of alkaline carbonates, which, though they very rarely occur, have sometimes been found in mineral waters. Carbonate of potash exists in the waters of Aix-la-Chapelle; that of soda, in the water. of a few^jprings and lakes; and the ammoniacal carbonate was de- tected by Mr. Cavendish in the waters of Rathbpne-place. Of all the three carbonates, muriate of lime is a sufficient indicator; for those salts separate from it a carbonate of lime, soluble with effer- vescence in muriatic acid. With respect to the discrimination of the different alkalies, pot- ash may be detected by the nitro-muriate of platinum, which dis- tinctly and immediately precipitates its compounds, and is not affected by soda. Carbonate of ammonia may be discovered by its smell; and by its precipitating a neutral salt of tiumine, while it has no action apparently on magnesian salts. XXI.—Solution of Soap in Alcohtl. This solution may be employed to ascertain the comparative hardness of waters. With distilled water it reay be mixed, with- out any change ensuing; but if added to a hard water, it produces a milkiness, more considerable as the water is fess pure; and, from the degree of this milkiness, an experienced eye will derive a tolerable indication of the quality of the vater. This effect is owing to the alkali quitting the oil, whenever there is present in a water any substance, for which the alkali has a stronger affinity than it has for oil. Thus all uncombined acids, and all salts with earthy and metallic bases, decompose soap, and occasion that pro- perty in waters which is termed hardness. XXII.—Alcohol Alcohol, when mixed with any water, in the proportion of about an equal bulk, precipitates all the salis which it is incapable of dissolving. (See Kirwan on Waters, page 263.) XXIII.—Hydro-Sulphuret of Ammonia. This and other sulphurets, as well as water saturated with sul- phureted hydrogen, may be employed.in detecting lead and arse- Vol. II.—S s o22 ANALYSIS OF WATERS CHAP. I. \ • nic; with the former of which they give a black, and with the latter a yellowish precipitate. As lead and arsenic, however, are never found in natural waters, I shall reserve, for another occasion, what I have to say of the application of these tests. TABLE, Showing the Substances that may be expected in Mineral Waters, and the Means of detecting them. Acids in general. ^Infusion of litmus.—Syrup of violets, I. Acid, boracic. Acetate of lead, XIII. 3. Acid, carbonic. Infusion of litmus, I. 1, 2.—Lime*water, VIII. 1.—Barytic water, IX. 1. Acid, muriatic. Nitrate and acetate of silver, XII Nitrate of mercury, XIV. Acid, nitric. Sulphuric acid, IV. 4. Acid, phosphoric. Solutions of barytes, XV. 2. Nitrate of mercury, XIV. 3. Acid, sulphurous. By its smell,—and destroying the colour of litmus, and of infusion of red roses:—by the cessation of the smell a few hours after the addition of the black oxide of manga- nese. Acid, sulphurtc. Solution of pure barytes, IX. Barytic salts, XV. Acetate ollead, XII. Alkalies in general. Vegetable colours, II. Muriate of lime, XX. Alumine dissolved by acids. Succinates, XVII. Ammonia, by its smell, and tests, II. Nitrate of mercury, XIV. 2. Barytes, and its compounds, by sulphuric acid, IV. Carbonates in general. Effervesce on adding acids. Earths dissolved by :arbonic acid. By a precipitation on boil- ing;—by pure alkalies, VII. Solution of soap, XXI. Hydro-sulphuret of lime. Sulphuric acid, IV. Nitrous acid, V. Iron dissolved by carbonic acid Tincture of galls, III. 1. Prussiate of potash, XVI. i. Succinate of ammonia, XVII. Ben- zoate of ammonia, XVIII, « Iron dissolved by Sutyhuric acid. Same tests, III. 3. XVI. 2. XVII. Lime in a pure state. Water saturated, with carbonic acid. Blowing air from the lungs. Oxalic acid, VI. Lime dissolved by carbonic acid. Precipitation on boiling.— Caustic alkalies, VII. Oxalic acid, VI. Lime dissolved hy sulphuric acid. Oxalate of ammonia, VI. Barytic solutions, IX. and XV. Magnesia dissolved by carbonic acid. Precipitation on boil- ing,—the precipitate soluble in dilute sulphuric acid. W»oT. II. ANALYSIS OF WATERS. 19: Magnesia dissolved by other acids. Precipitated by pure am- monia, not by the carbonate, VII. 5. Phosphate of 6oda, XIX. Muriates of alkalies. Solutions of silver, XII. ---------of lime. Solutions of silver, XIJ. Oxalic acid and Oxalate of ammonia, VI. Sulphates in general. Barytic solutions, IX. and XV. Acetate of lead, XIII. Sulphate of Alumine. Barytic solutions, IXi and XV. ' A pre- cipitate by carbonate of ammonia not soluble i* acetous acid, but soluble in pure fixed alkalies by boiling. Succinates, XVII. 2. Sulphate of lime. Barytic solutions, IX. and XV. Oxalic acid, and oxalates, VI. A precipitate by alkalies ndt soluble in dilute sulphuric acid. Sulphurets of alkalies. Polished metals X. Smell on adding sulphuric or muriatic acid. Nitrous acid, V. Sulphureted hydrogen gas. By its smell. Infusion of litmus, I. Polished metals, X. Acetate of lead, XIII. 2.* SECTION II. Analysis of Waters by Evaporation. Before proceeding to the evaporation of any natural water, its gaseous contents must be collected. This may be done by filling with the water a large glass globe or bottle, capable of holding about 50 cubical inches, and furnished with a ground stopper and bent tube. The bottle is to be placed, up to its neck, in a tin kettle filled with a saturated solution of common salt, which must be kept boiling for an hour or two, renewing, by fresh portions of hot wa- ter, what is lost by evaporation. The disengaged gas is to be con- veyed, by the bent tube, into a graduated jar, filled with, and in- verted in, mercury, where its bulk is to be determined. On the first impression of the heat, however, the water will itself be ex- panded, and portions will continue to escape into the graduated jar, till the water has attained its maximum of temperature. This portion must be measured, and its quantity be deducted from that of the water submitted to experiment. In determining, with precision, the quantity of gas, it is neces- sary to attend to the state of the parameter and thermometer, and to other circumstances already enumerated, vol. i. page 127. Rules for reducing observations made under different states of thejja- rometer tnd thermometer, to a mean standard, will be givef in the Appendix. If a considerable proportion of gas be contained in a * The vapour of putrefying animal or vegetable matter dissolved in water, according to Klaproth, vol. i p. 590, often gives a deceptive indication of eulphureted hydrogen 324 ANALYSIS OF WATERS. f'UAF. 1 mineral water, the most commodious method of receiving it is in- to a small gazometer. The gases, most commonly found in mineral waters, are carbonic acid; sulphureted hydrogen; nitrogen gas; oxygen gas; and, in the neighbourhood of volcanoes only, sulphurous acid gas. To determine the proportion of the gases, constituting a mix- ture obtained from any mineral water in the foregoing manner, the following experiments may be made. If tie use of re-agents has not detected the pTesence of sulphureted hydrogen, and there is reason to believe,from the same evidence, tfcat carbonic acid forms a part of the mixture, let a graduated tube be nearly filled with it over quicksilver. Pass up a small portion of solution of potash, and agitate this in contact with the gas. The amount of the dimi-. nution will "show how much carbonic acid lias been absorbed; and, if the quantity submitted to experiment was an aliquot part of the whole gas obtained, it is easy to infer the total quantity present in the water. The unabsorbable residuum consists, most probably, of oxygen and azotic gases; and the proportion of these two is best learned by the use of Dr. Hope's eudiometer. (See vol. i page 152.) If sulphureted hydrogen be present, along with carbonic acid. the separation of these two is a problem of some difficulty. Mr. Kirwan recommends that a graduated glass vessel, completely fill- ed with the mixture, be removed into a vessel containing nitrous acid. This instantly condenses the sulphureted hydrogen, but not the,carbonic acid gas. I apprehend, however, that a more eligible mode will be found to be, the condensation of the sulphureted hy- drogen by oxymuriatic acid gas (obtained from muriatic acid and hyper-oxymuriate of potash;) adding the latter gas very cautiously, as long as it produces any condensation. Or, perhaps abetter plan of effecting the separation will be the following: Half fill a gradu- ated phial with the mixed carbonic acid and sulphureted hydrogen gases, and expel the rest .of the water by oxymuriatic acid gas. Let the mouth of the bottle be then closed with a well-ground stopper, and let the mixture be kept twenty-four hours. Then withdraw the stopper under water, a quantity of which fluid will immediately rush in. Allow the bottle to stand half an hour with- out agitation. The redundant oxymuriatic acid gas will thus be absorbed; and very little of the carbonic acid will disappear. Sup- posing that, to ten cubic inches of the mixed gases, ten inches of oxymuriatic gas have been added, and that, after absorption by- standing over water, five indies remain: the result of this experi- ment shows, that the mixture consisted of equal parts of sulphure- ted hydrogen and carbonic acid gases. Mr. Westrumb ascertains the proportion of sulphureted hydro- gen and carbonic acid gases, by the following method. He intro- duces a known quantityof the water under examination into a glass vessel, from which proceeds a curved tube, terminating in a long cylinder, filled with lime-water. The gas is expelled by heat, and SF,CT. II. ANALYSIS OF WATERS. the precipitate collected. Every 20 grains indicate 10 cubic inches of carbonic acid. To determine the quantity of sulphureted hy- drogen, the same experiment is repeated, substituting*a solution of super-acetate of lead. Hydro-sulphuret of lead is formed, in the proportion of 19 grains to 10 cubic inches of gas. This method, for several reasons which it would take too much room to state, is perhaps inferior to the one which I have just proposed. Whenever this complicated admixture of gases occurs, as in the case of the Harrowgate-watcr, it is advisable to operate separately on two portions of gas, with the view to determine, by the one, the quantity of carbonic acid and sulphureted hydrogen; and that of nitrogen and oxygen by the other. In the latter instance, remove both the absorbable gases by caustic potash; and examine the re- mainder in the manner already directed Nitrogen gas sometimes occurs in mineral waters, almost in an unmixed state. When this happens, the gas will be known by the characters already described as belonging to it, vol. i. p. 144. Sul- phurous acid gas may be detected by its peculiar smell of burning brimstone, and by its discharging the colour of an infusion of roses, which has been reddened by the smallest quantity of any mineral acid adequate to the effect. The vessels employed for evaporation, should be of such ma- terials as are not likely to be acted on by the cofrtents of the water. I prefer those of unglazed biscuit ware, made by Messrs. Wedge- wood; but, as their surface is not perfectly smooth, and the dry mass may adhere so strongly as not to be easily scraped off, the water, when reduced to about one tenth or less, may be transferred, with any deposit that may have taken place, into a smaller vessel of glass. Here let it be evaporated to dryness. (c) The dry mass, when collected and accurately weighed, is to be put into a bottle, and alcohol poured on it, to the depth of an inch. After having stood a few hours, and been occasionally shaken, pour the whole on a filter, wash it with a little more alcohol, and dry and weigh the remainder. (b) To the undissolved residue, add eight times its weight of cold distilled water; shake the mixture frequently; and, after some time, filter; ascertaining the loss of weight. (c) Boil the residuum, for a quarter of an hour, in somewhat more than 500 times its weight of water, and afterwards filter. (rf) The residue, which must be dried and weighed, is no longer soluble in water or alcohol. If it has a brown colour, denoting the presence of iron, let it be moistened with water, and exposed to the sun's rays for some weeks. v I. The solution in alcohol (a) may contain one or all of the fol- lowing salts: Muriates of lime, magnesia, or barytes; or nitrates of the same earths. Sometimes, also, the alcohol may take up a sul- phate of iron, in which the metal is highly oxidized, as will appear from its reddish brown colour. 3J6 analysis of waters. CHAP. 1. 1. In order to discover the .Quality and quantity of the ingredi- ents, evaporate to dryness; weigh the residuum; add above half its weight of strong sulphuric acid; and apply a moderate heat. The muriatic or nitric acid will be expelled, and will be known by the colour of their fumes; the former being white, and the latter orange coloured. 2. To ascertain whether lime or magnesia be the basis of the salts, let the heat be continued till no more fumes arise, and let it then be raised, to expel the excess of sulphuric acid. To the dry mass, add twice its weight of distilled water. This will take up the sulphate of magnesia, and leave the sulphate of lime. The two sulphates may be separately decomposed, by boiling with three or four time? their weight of carbonate of potash. The car- bonates of lime and magnesia, thus obtained, may be separately dissolved in muriatic acid, and evaporated. The weight of the dry salts will inform us how much of each the alcohol had taken up. Lime and magnesia may also be separated by the use of the phosphate of soda, applied in the manner already described in the preceding section, No. XIX. The presence of barytes, which is very rarely to be expected, may be known by a precipitation ensuing on adding sulphuric acid to a portion of the alcoholic solution, which has been diluted with 50 or 60 times its bulk of pure water. Some of the salts obtained by the action of alcohol, it is supposed by Grotthuss, are actually formed by its operation. Sulphate of soda and muriate of magnesia, for example, when found in an alco- holic solution, result, he imagines, from the mutual decomposition of sulphate of magnesia and muriate of soda.* II. The watery solution (A) may contain a variety of salts, the accurate separation of which from each other is a problem of con- siderable difficulty. I. The analysis of this solution may be attempted by crystalliza- tion. For this purpose let one half be evaporated by a very gentle heat, not exceeding 80° or 90.° Should any crystals appear on the surface of the solution, while hot, in the form of a pellicle, let them be separated and dried on bibulous paper. These are mu- riate of soda or common salt. The remaining solution, on cool- ing very gradually, will, perhaps, afford crystals distinguishable by their form and other qualities. When various salts, however, are contained in the same solution, it is extremely difficult to obtain them sufficiently distinct to ascertain their kind. 2. The nature of the saline contents must, therefore, be exa- mined by tests, or re-agents. The presence of an uncombined alkali will be discovered by the • stained papers (p. 417, 418,; and of acids by the tests (p. 416,417.) The vegetable alkali, or potash, may be distinguished from the mineral, or soda, by saturation with sulphuric acid, and evapora- * Ann. de.Chim. et Phys. iv. 306. SECT. II. ANALYSIS OF WATERS. 32/ tion to dryness; the sulphate of soda being much more soluble than that of potash; or, by super-saturation, with the tartarous acid, which gives a soluble salt with soda, but not with potash. Muri- ate of platinum, also, is an excellent test of potash and its combina- tions; for, with the smallest portion of this alkali, or any of its salts, it forms a distinct and immediate precipitate; while it is not at all affected by the mineral alkali or its compounds. If neutral salts be present in the solution, we have to ascertain both the nature of the acid and of the basis. This may be done by attention to the rules already given for the application of tests, which it is unnecessary to repeat in this place. III. The solution by boiling water contains scarcely any thing beside sulphate of lime. IV. The residuum (rf) is to be digested in distilled vinegar, which takes up magnesia and lime, but leaves, undissolved, alu- mine and highly oxidized iron. Evaporate the solution to dryness. If it contain acetate of lime only, a substance will be obtained which does not attract moisture from the air; if magnesia be present, the mass will deliquiate. To separate the lime from the magnesia, proceed as in I. The residue, insoluble in acetous acid, may contain alumine, iron, and silex. The two first may be dissolved by muriatic acid, from which the iron may be precipitated first by prussiate of pot- ash, and the alumine afterward by a fixed alkali. Dr. Murray's Formula for the Analysis of Mineral Waters. Some ingenious views respecting the analysis of mineral waters • have lately been taken by Dr. Murray, of Edinburgh.* In pro- ceeding by the method of evaporation, the salts obtained are fre- quently, he conceives, the products of the operation, and not the original ingredients of the water For example, though we may obtain from a mineral water, sulphate of lime and muriate of . soda, yet it is probable, he thinks, that the water, in its natural state, held in solution both sulphate of soda and muriatg^>f lime, which, though incompatible salts, if presented to eacWother in dense solutions, may yet exist, without mutual decomposition, . when diffused through a large quantity of fluid He argues, there- fore, that we attain a much nearer approximation to the true com- position of a mineral water, by disregarding the salts resulting from its evaporation; and, instead of this, determining with extreme pre- cision the elements, or acids and bases, of which those salts are composed. The peculiar mode of combination, in which they exist in the water submitted to ananysis, can only, he thinks, be inferred by considering the most probable views of their binary composition. Having gained a general idea of the nature of any mineral wa- * Edinb. Transact, viii. 250, or Thomson's Annals, V28 ANALYSIS OF WATERS. CHAP. 1. tcr, by the agency of the tests already described, Dr. Murray re- commends that we proceed to its minute analysis in the following manner. 1. Reduce the water, by evaporation, as far as can be done without occasioning any sensible precipitation or crystallization. 2. Add a solution of muriate of barytes, as long as it occasions a precipitate, and no longer. By an experiment on a separate quantity, examine whether the precipitate effervesces with dilute muriatic acid, and whether it is entirely dissolved by that acid. If entirely soluble, dry and weigh it, and allow 22 grains of carbo- nic acid for every 100 grains. If it do not effervesce, or dissolve, we may consider it as sulphate of barytes, and reckon that it con- tains, in a dry state, 34 grains of sulphuric acid in every 100. If it be partly soluble with effervescence, and partly insoluble, it con- sists both of carbonate and sulphate, the former of which may readily be separated from the latter by dilute muriatic acid; and the precipitate being weighed in a dry state, both before and after the action of the acid, we learn the quantity of each; what remains being the sulphate only. By the evaporation, the carbonic acid is removed, and the sul- phuric acid is separated by the barytic salt. The next object is to discover the kind and quantity of the bases present; and then to find the quantity of muriatic acid, originally contained, in the water. 3. To the clear liquor add a saturated solution of oxalate of ammonia, as long as any turbid appearance is produced. Collect the precipitate, which consists of oxalate of lime; dry it; and, by calcining it at a low red heat, convert it into a carbonate, which may be changed into sulphate by a slight excess of sulphuric acid. • The sulphate of lime, after ignition, contains 41.5 of lime in 100. 4. The next step is to separate the magnesia, which may be done as follows: let the clear liquid, remaining after the precipita- tion of the oxalate of lime, be heated to 100° Fahrenheit, and, if necessary, reduce a little by evaporation; and then, add to it, first a soluti.Qii.of carbonate of ammonia, and afterwards of phosphate of ammmin, at long as any precipitation ensues. Wash the pre- cipitate, dry and calcine it at a red heat for an hour, after which I0Q grains may be estimated to contain 40 of magnesia. 5. To estimate the soda, evaporate the liquor, remaining after the preceding operations, to dryness, and expose the dry mass to heat as long as any vapours exhale, raising it, in the end, to red- ness. The residual matter is muriate of soda, 100 grains of which are equivalent to 53.3 soda, and 46.7 of ammoniatic acid. 6. It is possible that the muriatic scid, deduced from the residu- ary common salt, may exceed the true quantity, and that a part may have been introduced by the muriate of barytes. Or, on the other hand, if muriate of lime or magnesia were present in the water, the ammonia, by which those earths were separated, would form, with the muriatic acid quitted by them, a salt, which will sF.cr. tx. ANALYSIS OF WATERS. 329 have been dissipated by heat; and consequently the muriatic acid will have been stated too low. To decide this, the simple rule is, to suppose the elements, obtained by the analysis, combined in binary compounds, according to the known proportions in which they unite. The excess or deficiency of muriatic acid will then appear; and the amount of the excess, being subtracted from the quantity of muriatic acid existing in the muriate of soda obtained; or the amount of the deficit, being added to that quantity, the real quantity of muriatic acid will be apparent.— A.s a check on this operation, it may be proper to estimate directly the quantity of muriatic acid in a given portion of the water, by first abstracting any sulphuric or carbonic acid by nitrate of barytes, and then pre- cipitating the muriatic acid by nitrate of silver. The real quan- tity of muriatic acid will thus be found; and the result will form a check on the other steps of the analysis; for the other ingredients must bear that proportion to the muriatic acid which will cor- respond with the state of neutralization. Having thus discovered the different acids and bases, and de- termined their quantities, it remains to determine the state of combination in which they exist. They may either be considered as forming simultaneous combinations, or as existing in the state of binary compounds. In the latter case, it is probable that the acids and bases are so united as to form the most soluble com- pounds, and in this way we may state them. It may also be pro- per to give the quantity of binary compounds obtained by evapo- ration, or by any other direct analytic process. For example, the elements of the salts in a pint of sea-water, as determined by Dr. Murray's analysis,* are, Lime.......2.9 grains Magnesia......14.8 Soda.......96.3 Sulphuric acid .... 14.4 Muriatic acid .... 97.7 226.1 The compound salts, as obtained by evaporation, are, Muriate of soda . . . 180.5 grains ----------magnesia . 23. Sulphate of magnesia . 15.5 ------ —■■lime ... 7.1 226.1 *Edinb. Phil. Trans Vol. II.—T t *>oQ ANALYSIS OF MINERALS. CMAP. II. But the salts existing in a pint of sea-water, in its natural state, before subjecting it to evaporation, may be calculated to be Muriate of soda . . . ■ ■ ----magnesia *■ lime . . . Sulphate of magnesia . 226.1 CHAPTER II. EXAMINATION OF MINERALS. SECTION I. General Directions. The chemical analysis of minerals is attended even with greater difficulties than that of natural waters; and it would require not only a separate work, but one of considerable extent, to compre- hend rules for determining the proportions of all possible combi- nations. On the present occasion, I mean only to offer a few general directions for attaining such a knowledge of the compo- sition of mineral bodies, as may enable the chemical student to refer them to their proper place in a mineral arrangement, and to judge whether or not they may admit of application to the uses of common life. Those who are solicitous to become adepts in the art of mineral analysis, may read attentively the numerous papers of Vauquelin, Hatchett, and other skilful analysts, dispersed through various chemical collections; and also an admirable work of M. Klaproth, entitled, " Analytical Essays towards improving the Chemical Knowledge of Minerals," 2 vols. 8vo., published by Cadell and Davies, 1801. The great variety of mineral bodies, which nature presents in the composition of this globe, have been classed by late writers under a few general divisions. They may be arranged under four heads: 1st, Earths; 2d, Salts; 3d, Inflammable Fossils; and 4th, Metals, and their Ores. I. Earths.—The formation of such a definition of earths as would apply exactly to the bodies defined, and to no others, is at- tended with considerable difficulty, and indeed has never yet been effected. It would lead me into too long a discussion, to com- ment, in this place, on the definitions that have been generally 180.5 grains 18.3 5.7 21.6 SECT. I. ANALYSIS OF MINERALS. v>0* offered, and to state the grounds of objection to each of them. Sensible, therefore, that I am unable to present an unexceptiona- ble character of earthy bodies, I shall select such a one as may be sufficient for the less accurate purpose of general distinction. • " The term earth," says Mr. Kirwan, " denotes a tasteless, in- odorous, dry, brittle, uninflammable substance, whose specific gravity does not exceed 4.9 (/. e. which is never five times heavier than water,) and which gives no tinge to borax in fusion." After stating some exceptions to this definition, afforded by the strong taste of certain earths, and the solubility of others, he adds, " Since, however, a line must be drawn between salts and earths, I think it should begin where solution is scarcely perceptible; salts terminating, and earths, in strictness, commencing, where the weight of the water, requisite for the solution, exceeds that of the solvent 1000 times. But not to depart too widely from the commonly received import of words that are in constant use, sub- stances that require 100 times their weight of water to dissolve them, and have the other sensible properties of earths, may be so styled in a loose and popular sense." The simple, or primitive earths, are those which can only be resolved into oxygen and a metallic basis. Such are lime, mag- nesia, alumine, silex, &c. The compound earths are composed of two or more primitive earths, united chemically together. Sometimes the union of an earth with an acid constitutes what is vulgarly called an earth; as in the examples of sulphate of lime, fluate of lime, &c. II. Salts. Under this head Mr. Kirwan arranges " all those substance that requires less than 100 times their weight of water to dissolve them." This description, though by no means so amply characteristic of the class of salts as to serve for an exact definition, is sufficient for our present purpose. III. " By inflammable fossils," the same author observes, " are to be understood all those of mineral origin, whose princi- pal character is inflammability; a criterion which excludes the diamond and metallic substances, though also susceptible of com- bustion." IV. Metallic substances are so well characterized by exter- nal properties, as not to require any definition.—" Those on which nature has bestowed their proper metallic appearance, or which arc allowed only with other metals or semi-metals, are called na- tive metals. But those that are distinguished, as they commonly are in mines, by combination with some other metallic substances, are said to be mineralized. The substance that sets them in that state is called a mineralizer; and the compound of both, an ore." Thus, in the most common ore of copper, this metal is found oxi- dized, and the oxide combined with sulphur. The copper may be said to be mineralized by oxygen and sulphur, and the compound of the three bodies is called an ore of copper. 332 ANALYSIS OF MINERALS. CHAP. U. SECTION II. Method of examining a Mineral, the Composition of which is unknown. A mineral substance, presented to our examination without any previous knowledge of its composition, should first be referred to one ol the above four classes, in order that we may attain a gene- ral knowledge of its nature, before proceeding to analyze it mi- nutely. I. To ascertain whether the unknown mineral contain saline matter, let 100 grains, or any other determinate quantity, in the state of fine powder, be put into a bottle, and shaken up repeatedly with 30 times its weight of Avater, of the temperature of 120° or 130°. After having stood an hour or two, pour the contents of the bottle on a filtering paper, previously weighed and placed on a funnel. When the water has drained off, dry the powder on a fil- tering paper, in a heat of about 212": and, when dry, let the whole be accurately weighed. If the weight be considerably less than the joint weight of the powder before digestion and the filtering paper, we may infer that some salt has been dissolved, and the decrease of weight will indicate its quantity. In certain cases it may be advisable to use repeated portions of hoiling water, when the salt suspected to be present is difficult of solution. Should the mineral under examination be proved, by the fore- going experiment, to contain much saline matter, the kind and proportion must next be determined, by rules which will hereafter be laid down. 1;. The second class, viz. earthy bodies, are distinguished by their insolubility in water, by their freedom from taste, by their uninflammability, and by their specific gravity never reaching 5. If, therefore, a mineral be insoluble in water, when tried in the foregoing manner; and if it be hot consumed, either wholly or in considerable part, by keeping it, for some time, on a red-hot iron; we may couclude that it is neither a salt nor an inflammable body. 111. The only remaining class with which it can be confounded is ores of metais^from many of which ii may be distinguished merely by poising it in the hand, the ores of metals being always heavier than earths; or, if a doubt should still remain, it may be weighed hydros'tatically. The mode of doing this it may be proper to describe; but the principle on which the practice is founded, cannot with propriety be explained here. Let the mineral be sus- pended by a piepe of fine hair, silk, or thread, from the scale of a balance, and weighed in the air. Suppose it to weigh 250 grains. Let it next (still suspended to the balance) be immersed in a glass of distilled water, of the temperature of 60° Fahrenheit. The scale SECT. III. ANALYSIS OF MINERALS. r. 130 containing the weight will now preponderate. Add, therefore, to the scale from which the mineral hangs, as many grain-weights as are necessary to restore the equilibrium. Suppose that 50 grains arc necessary, then the specific gravity may be learned by dividing the weight in air by the weight lost in water. Thus, in the fore- going case, 250 -=- 50 = 5; or, a substance which should lose weight in water, according to the above proportion, would be five times heavier than water. It must, therefore, contain some metal, though probably in no great quantity. Any mineral, which, when weighed in the above manner, proves to be 5, 6, 7, or more times heavier than water, may, therefore, be inferred to contain a metal, and may be referred to the class of ores. i V. Inflammable substances are distinguished by their burning away, either entirely or in considerable part; on a red-hot iron; and by their detonating, when mixed with powdered nitre, and thrown into a red-hot crucible. Certain ores of metals, however, which contain a considerable proportion ot inflammable matter, answer to this test, but may be distinguished from purely inflammable substances by their greater specific gravity. i shall now proceed to offer a few general rules for the more ac- curate examination of substances of each of the above classes. SECTION III. Examination of Salts. 1. A solution of saline matter, obtained in the foregoing man- ner (see page 445,) may be slowly evaporated, and left to cool gra- dually. When cold, crystals will probably appear, which a chemist, acquainted with the forms of salts, will easily recognize. But, as several different salts may be present in the same solution, and may not crystallize in a sufficiently distinct shape, it may be neces- sary to have recourse to the evidence of tests. 2. Let the salt, in the first place, be referred to one of the fol- lowing orders. (a) Acids, or salts with excess of acid. These are known by their effect on blue vegetable colours. The particular species of acid may be discovered by; the tests described, p. 433. (b) Alkalies. These are characterized by their effect on vegeta- ble colours, and by the other properties enumerated, vol. 1. p. 212. (c) Salts with metallic bases. Metallic salts afford a very copi- ous precipitate when mixed with a solution of prussiate of potash. To ascertain the species of metal, precipitate the whole by prus- siate of potash, calcine the precipitate, and proceed according to the rules which will hereafter be given for separating metals from each other. .5-34 ANALYSIS OF MINI V.AL3. CHAl'. II. (rf) Salts with earthy bases. If a solution of salt, in which ferro- prussiate of potash occasions no precipitation, afford a precipitate, on adding pure or carbonated potash, we may infer, that a com- pound of an acid, with some one of the earths, is present in the solution. Or if, after ferro-prussiate of potash has ceased to throw down a sediment, the above-mentioned alkali precipitates a farther portion, we may infer that both earthy and metallic salts are con- tained in the solution. In the first case, add the alkaline solution, and, when it has ceased to produce any effect, let the sediment subside, decant the supernatant liquor, and wash and dry the pre- cipitate. The earths may be examined, according to the rules that will be given in the following article. In the second case, ferro- prussiate of potash must be added, as long as it precipitates any thing, and the liquor must be decanted from the sediment, which is to be washed with distilled water, adding the washing to what has been poured off. The decanted solution must next be mixed with the alkaline one, and the precipitated earths reserved for ex- periment. By this last process, earths and metals may be separated from each other. (e) Neutral salts with alkaline bases. These salts are not pre- cipitated either by prussiate or carbonate of potash. It may hap- pen, however, that salts of this class may be contained in a solu- tion, along with metallic or earthy ones. In this case the analysis becomes difficult; because the alkali, which is added to precipitate the two last, renders it difficult to ascertain whether the neutral salts are owing to this addition, or were originally present. I am not aware of any method of obviating this difficulty, except the following: Let the metals be precipitated by prussiate of ammonia, and the earths by carbonate of ammonia, in a temperature of 180° or upwards, in order to ensure the decomposition of magnesian salts, which this carbonate does not ei'lect in the cold. Separate the liquor by filtration, and boil it to dryness. Then expose the dry mass to such a heat as is sufficient to expel the ammoniacal salts.* Those with bases of fixed alkali will remain unvolatilized. By this process, indeed, it will be impossible to ascertain whether ammo- niacal salts were originally present; but this may be learned by adding to the salt under examination, before its solution in water, some pure potash, which, if ammonia be contained in the salt, will produce the peculiar smell of that alkali. The vegetable and mineral alkalies may be distinguished by adding to the solution a little tartarous acid, which precipitates the former but not the lat- ter; or by muriate of platinum, which acts only on the vegetable alkali. Having ascertained the basis of the salt, the acid will easily be * This application of heat will drive off, also, any excess of the ammonia. cal carbonate, which might have retained in solution either yttria, g-lucine, or zircon. The alkaline salts may be separated from these earths, by boiling fie mixture in u-ater, filtering-, and evaporating-. SECT. IV ANALYSIS OF NINKUALS. >'J discriminated. Muriated barytes will indicate sulphuric acid; ni- trate of silver the muriatic; and salts, containing nitric acid, may be known by a detonation ensuing on projecting them, mixed with powdered charcoal, into a red-hot crucible. SECTION IV, Examination of Earths and Stones. When a mineral, the composition of which we are desirous to discover, resists the action of water, and possesses characters that rank it among earthy bodies* the next object of inquiry is the na- ture of the earths that enter into its composition; in other words, how many of the simple earths, and which of them, it may contain. Of these earths (viz. silex, alumine, magnesia, lime, strontites, barytes, zircon, glucine, and yttria,) one or more may be expected in the composition of a mineral, beside a small proportion of me- tals, to which the colour of the stone is owing. In general, how- ever, it is not usual to find more than four of the simple earths in one mineral. The newly discovered earths, zircon, glucine, and yttria, occur very rarely. A stone, which is intended for chemical examination, should be finely powdered, and care should be taken that the mortar is of harder materials than the stone, otherwise it will be liable to abra- sion, and uncertainty will be occasioned in the result of the pro- cess. A longer or shorter time is required, according to the tex.- ture of the stone. Of the harder gems, 10O grains require two or three hour's trituration. For soft stones, a mortar of Wedgwood's ware is sufficient; but, for very hard minerals, one of agate, or hard steel is required; and the stone should be weighed both be- fore and after pulverization, that the addition, if any, may be as- certained and allowed for. Gems, and stones of equal hardness, gain generally from 10 to 13 per cent. When a stone is extremely difficult to be reduced to powder, it may sometimes be necessary to make it red-hot, and while in this state to plunge it into cold water. By this process it becomes brittle, and is afterwards easily pulverized. But this treatment is not always effectual; for Klaproth found the hardness of corundum not at all diminished by igniting it, and quenching in cold water. The chemical agents, employed in the analysis of stones, should be of the greatest possible purity. To obtain them in this state, di- rections have been given in the former part of this work. In treating of the analysis of stones, it may be proper to divide them, 1st, into such as are soluble, either wholly or in part, and with effervescence, in nitric or muriatic acids, diluted with five or six parts of water; and, 2dly, into such as do rot dissolve in these acids. >36 ANALYSIS OF MINERALS. ( HA1\ 11. I. Earths or stones, soluble with effervescence, in diluted nitrir or sulphuric acids.* (A) If it be found, on trial, that the mineral under examination effervesces with either of these acids, let a given weight, finely powdered, be digested with one of them diluted in the above pro- portion, in a gentle heat, for two or three hours. Ascertain the loss of weight, in the manner pointed out, vol. i. p. 301, and filter the solution, reserving the insoluble portion. (B) The solution, when effected, may contain lime, magnesia, alumine, barytes, or strontites. To ascertain the presence of the two last, dilute an aliquot part of the solution with 20 times it bulk of water, and add a little sulphuric acid, or in preference, solution of sulphate of soda. Should a white precipitate fall down, we may infer the presence of barytes, of strontites, or of both. (C) To ascertain which of these earths (viz. barytes or stron- tites) is present, or, if both are contained in the solution, to sepa- rate them from each other, add sulphate of soda till the precipitate ceases; decant the supernatant liquid; wash the sediment on a filter, and dry it. Then digest it, with four times its weight of pure car- bonate of potash, and a sufficient quantity of water, in a gentle heat, during two or three hours. A double exchange of principles will ensue, and we shall obtain a carbonate of barytes or strontites, or a mixture of both. Pour on these, after being well washed, ni- tric acid, of the specific gravity 1.4, diluted with an equal weight bf distilled water. This will dissolve the strontites, but not the barytes. To determine whether any strontites has been taken up by the acid, evaporate the solution to dryness, and dissolve the dry mass in alcohol. This alcoholic solution, if it contain nitrate of strontites, will burn with a deep blood-red flame. Barytes and strontites may also be separated from each other in the following manner: To a saturated solution of the two earths in an acid, add prussiate of potash, which, if pure, will occasion no immediate precipitation; but, after some time, small and insoluble crystals will form on the surface of the jar. These are the prus- siated barytes, which may be changed into the carbonate by a red heat, continued, with the access of air, till the black colour disap* pears. The strontites may be afterward separated from the solution by carbonate of potash. A third method of separating strontites from barytes is founded on the stronger affinity of barytes, than of the former earth, for acids. Hence if the two earths be present in the same solution, add a solution of pure barytes, till the precipitation ceases. The ba- rytes will seize the acid, and will throw down the strontites. The strontitic solution, in this case, should have no excess of acid, which would prevent the action of the barytic earth.f * The sulphuric acid is chiefly eligible for stones of the magnesian genus. f Klaproth separates barytes from strontites by evaporating the mixed so- lutions of both. The barytic salt, being- less soluble, separates first, and the ^trontitic is contained in the last portions. , SECT. IV. ANALYSIS OF MINERALS. 337 (D) The solution (B,) after the addition of sulphate of soda, may contain lime, magnesia, alumine, and some metallic oxides. To separate the oxides, add prussiate of potash, till its effect ceases, and filter the solution, reserving the precipitate for future experi- ments. (E) When lime, magnesia, and alumine, are contained in the same solution, proceed as follows: (a) Precipitate the solution, previously made hot, by carbonate of potash; wash the precipitate well, and dry it. It will consist of carbonate of lime, magnesia, and alumine. (b) The alumine may be separated, by digestion with a solution of pure potash, which will dissolve the alumine but not the other earths, (c) To this solution of alumine, add, very cautiously, diluted muriatic acid, till the precipitate ceases, and no longer; or, as Mr. Chenevix re- commends, substitute muriate of ammonia; decant the supernatant liquor; wash the precipitate well with distilled water, and dry it. Then expose it to a low red heat, in a crucible, and weigh it, which will give the proportion of alumine. (F) Magnesia and lime may be separated, though not with per- fect accuracy, by the following process: Evaporate the solution, in nitric or muriatic acid, to dryness. Weigh the dry mass, and pour on it, in a glass evaporating dish,* more than its own weight of strong sulphuric acid. Apply a sand-heat till the acid ceases to rise, and then raise the heat, so as to expel the excess of sulphuric acid. Weigh the dry mass, and digest it in twice its weight of cold distilled water.—This will dissolve the sulphate of magnesia, and will leave the sulphate of lime, which must be put on a filter, washed with a little more water, and dried in a low red heat. To estimate the quantity of lime, deduct, from the weight of the sulphate, 59 per cent. According to Klaproth,f crystallized sulphate of lime contains one third earth. If the lime be only in very small proportion to the magnesia, the two sulphates may be separated by evaporation, that of lime crystallizing first. From Klaproth's experiments, 100 parts of sulphuric acid, spe- cific gravity 1.850, when saturated with lime, give 160 of sul- phate. To saturate 100 parts of this acid, 55 parts of pure lime are required, or 100 of carbonate of time. The magnesia is next to be precipitated from its sulphate by the sub-carbonate of potash, in a heat approaching 212°; and the pre- cipitate, after being well washed, must be dried, and calcined for an hour. Its weight, after calcination, will give the quantity of magnesia contained in the stone. It had been recommended, when magnesia and lime are con- •The bottom of a broken Florence flask answers this purpose extremely well, and bears, without breaking, the heat necessary to expel the sulphuric acid. . | Vol. i. page 76, n. Vol. II.—IT u 338 INALYSIS OF MINEUALS. CHAP. II. tained in the same solution, to-precipitate the latter by the bi-car- bonate of potash; but it has been shown by Bucholz, that this process is defective,* a considerable proportion of the carbonate of lime remaining in solution. Dobereiner prefers adding the sub-carbonate of ammonia to the cold solution of the two earths. The carbonate of lime is thus thrown down, and carbonate of magnesia may afterwards be separated, by boiling the liquor: or, both carbonates may be precipitated together by adding sub-car- bonate of soda or of potash to the heated solution; and trom this precipitate, after being sufficiently washed, muriate of ammonia will take up the carbonate of magnesia, leaving that of lime sepa- rate. From the weights of the carbonates, it is easy to estimate those of the pure earths contained in them. (G) If magnesia and alumine only be held in solution by an acid (the absence of lime being indicated by the non-appearance of a precipitate, on adding oxalate of ammonia,) the two earths may- be separated by adding, to the cold solution, the carbonate of am- monia. This will separate the alumine, which may be collected, washed, and dried. To ascertain that a complete separation of the two earths has been accomplished, the process may be followed, recommended by Klaproth, in his Contributions, vol. i. page 418. The magnesia, remaining in solution, may be precipitated by sub- carbonate of potash; heat being applied, to expel the excess of carbonic acid. Magnesia and alumine may, also, be separated by succinate of soda, which precipitates the latter earth only.f When the solution of magnesia, of alumine, or of both, contains a small proportion of iron, this may be separated from either or both of the earths by evaporating to dryness, calcining the residue, during one hour, in a low red heat, and dissolving again in dilute nitric acid, which does not take up iron when thus oxidized. (H) The insoluble residue (A) may contain alumine, silex, and oxides of metals, so highly charged with oxygen as to resist the action of nitric and muriatic acids. (a) Add concentrated sulphuric acid,-with a small quantity of potash, and evaporate the mixture to dryness, in the vessel de- scribed in the note, p. 337. On the dry mass pour a fresh portion of the acid; boil again to dryness, and let this be done, repeatedly, three or four times. By this operation, the alumine will be con- verted into a sulphate of alumine and potash, which will be easily soluble in warm water; and from the solution, crystals of alum will shoot on evaporation.$ Let the sulphate of alumine be washed off, and the insoluble part be collected and dried. The alumine * Ann. de Chim. et Phys. iii. 403. + See sect. 1. xvii. of the chapter on Mineral Waters. | Klaproth procured crystals of alum from one fourth of a grain of alu- mine. The quantity of alumine he estimates at one tenth the weight of the r«rf tallized alum which is obtained. »KCT. IV. VNALYS1S Ol MINERALS. 339 may be precipitated by carbonate of potash; washed, dried, and ignited; and its weight ascertained. During the evaporation of a solution of alumine, which has been separated from silex, portions of the latter earth continue to fall, even to the last.* These must be collected, and washed with warm water; the collected earth added to the portion (b,) and the wash- ings to the solution (a.) Alumine may be separated from oxide of iron by a solution of pure potash. From whatever acid alumine is precipitated by fixed alkali, it is apt to retain a small portion of the precipitant. To ascertain the true quantity of this earth, it must, therefore, be re-dissolved in acetous acid, again precipitated by solution of pure ammonia, dried, and ignited. (b) The oxides (generally of iron only) may be separated from the silex in the following manner:—Let the insoluble part (a) be heated in a crucible with a little wax. This will render the oxides soluble in diluted sulphuric acid, and the silex will be left pure and white. Let it be washed, ignited, and its weight ascertained. 2. Stones insoluble in diluted nitric and muriatic acids. These stones must be reduced to powder, observing the cau- tions given in page 451. . (I) Let 100 grains, or any other determined quantity, be mixed with three times their weight of pure and dry potash. Put the whole into a crucible of pure silver, set in one of earthenware of a larger size, the interstice being filled with sand; and add a little water.t The crucible, covered with a lid, must then be gradually heated; and, as the materials swell and would boil over, they are to be stirred constantly with a rod or spatula of silver. When the moisture is dissipated, and the mass has become quite dry, raise the heat as far as can be done without melting the crucible, if of silver, and continue the heat during half an hour, or an hour. The phenomena that occur during this operation, indicate, in some degree, the nature of the mineral under examination. If the mixture undergo a perfectly liquid fusion, we may presume that the stone contains much siliceous earth; if it remain pasty and opaque, the other earths are to be suspected; and, lastly, if it have the form of a dry powder, the bulk of which has considerably in- creased, it is a sign of the predominance of alumine. If the fused mass have a dark green or brownish colour, the presence of oxide of iron is announced; a bright green indicates * Sec Klaproth, vol. i. pages 66 and 75. f Klaproth effected the disintegration of Corundum (which resisted eleven .successive fusions with alkali) by adding to the powdered stone, in a crucible, a solution of pure potash, boiling to dryness, and pushing the mixture to fu- sion. The alkali must be perfectly caustic, and must have been purified by alcohol, as recommended, yol. i. pp. 212, 213. A platinum crucible is unfit for this purpose, as it is corroded by pure alkalie*. 340 ANALYSIS OF MINERALS. OHAP. 11. manganese, especially if the colour be imparted to water; and a yellowish green the oxide of chrome. (a) The disintegration of stones, consisting chiefly of alumine, is not easily effected, however, by means of potash. Mr. Chenevix found (Philosophical Transactions, 1802) that minerals of this class are much more completely decomposed by fusion with cal- cined borax. One part of the mineral to be examined, reduced to a very fine powder, and mingled with 2$ or three times its weight of glass of borax (^see part i. chap, xvi.) is to be exposed to a strong heat for two hours in a crucible of platinum, set in a larger earthen one, and surrounded by sand. The crucible and its contents, which adhere very strongly to it, are then to be digested, for some hours, with muriatic acid, by which a perfect solution will be ac- complished. The whole of the earthy part is then to be precipi- tated by sub-carbonate of ammonia; and the precipitate after being vrell washed, is to be re-dissolved in muriatic acid. By this means, the borax is separated. The analysis is afterwards to be conduct- ed nearly in the manner which will presently be described. (K; The crucible, being removed from the fire, is to be well cleaned on the outside, and set, with its contents, in a porcelain or or glass vessel, filled with hot water, which is to be stirred and renewed, occasionally, till the whole mass is detached. The water dissolves a considerable part of the compound of alumine and si- lex with potash, and even the whole^ if added in sufficient quantity. During cooling, a sediment occasionally forms, in the filtered li- quor, of a brownish colour, which is oxide of manganese. (See Klaproth, i. 345, b.) (L) To the solution (K,) and the mass that has resisted solu- tion, in the same vessel, add muriatic acid. The first portions of acid will throw down a flocculent sediment, which consists of the earths that were held dissolved by the alkali. Then an efferves- cence ensues; and a precipitate occurs, which is no sooner formed than it is dissolved. Lastly, the portion that resisted the action of water is taken up, silently, if it contain alumine, and with effer- vescence if it be calcareous earth. (M, From the phenomena attending the action of muriatic acid, some indications may be derived. If the solution assume a purplish red colour, it is a sign of oxide of manganese; an orange red shows iron; and a gold yellow colour betokens chrome. Free- dom from colour proves, that the stone contains no metallic in- gredients. (N) When the solution is complete, it is to be evaporated te dryness in a glass vessel; but if any thing resist solution, it must be heated, as before (I,) with potash. When the liquor ap- proaches to dryness, it assumes the form of a jelly, and must then be diligently stirred till quite dry. (O) (a) Let the dry mass be digested, in a gentle heat, with three or four pints, or even more of distilled water, and filtered. (A) Wash what remains on the filter, repeatedly, till the washing ceases to precipitate the nitrate of silver, and add the washings to iEOT. IV. ATJALYSIS OF MINERALS. 341 the filtered liquor, (c) Let the residue on the filter be dried and ignited in a crucible. Its weight shows the quantity of silex. It pure, it should be perfectly white; but if it has any colour, an ad- mixture of some metallic oxide is indicated. From this it may be purified by digestion in muriatic acid, and may again be washed, ignited, and weighed. (P) The solution (O,) which, owing to the addition of the wash- ings, will have considerable bulk, is next to be evaporated, till less than a pint remains; carbonate of potash must then be added, and the liquor must be heated during a few minutes. Let the precipi- tate, occasioned by the alkali, subside; decant the liquor from above it, and wash the sediment, repeatedly, with warm water. Let it then be put on a filter and dried. (Q) The dried powder may contain alumine, lime, magnesia, barytes, or strontites; besides metallic"oxides, which may be sepa- rated from each other, by the rules already given. (it; It may be proper to examine the solution (P) after the ad- dition of carbonate of potasn, in order to discover, whether any and what acid was contained in the stone. (a) For this purpose, let the excess of alkali be neutralized by muriatic acid, and the liquor filtered. (6) Add, to a little of this liquor, a solution of muriated barytes. Should a copious precipitate ensue, which is insoluble in dilute muriatic acid, the presence of sulphuric acid is detected. And if much barytes, strontites, or lime, has been found in the precipitate (QO we may infer the presence of a sulphate of one of these three earths. (c) If, on mixing the liquid (a) with the solution of muriated barytes, a precipitate should ensue which is soluble, without effer- vescence, in muriatic acid, the phosphoric acid may be known to be present; and, if lime be also found, the phosphate of lime is in- dicated. (rf) To a portion of the liquor (a) add a solution of muriate of lime till the precipitate, if any, ceases. Collect this precipitate, wash it, dry it, and pour on it a little sulphuric acid. Should acid fumes arise, the fluoric acid may be suspected. To ascertain its presence decisively, distil a portion of the precipitate with half its weight of sulphuric acid. The fluoric acid will be known by its effects on the retort, and by the properties described, in part i. chap. xvii. ' (Sj The method of separating, from each other, the metallic oxides, usually found as the colouring ingredients of stones, re- mains to be accomplished. (a) Let the precipitate, by the prussiate of potash (D,) be ex- posed to a red heat, by which the prussic acid will be decomposed. The oxides thus obtained, if insoluble in dilute nitric or muriatic acid, will be rendered soluble, by again calcining them with the addition of a little wax or oil. (6) Or the process may be varied by omitting the precipitation 342 analysis or MINF.UA!.8. (HAP. 11 by prussiate of potash, and proceeding as directed (E.) The oxides will remain mixed with the magnesia and lime, and, after the ad- dition of sulphuric acid, will be held in solution by that acid, along with magnesia only. In both cases the same method of proceeding may be adopted; such variation only being necessary as is occasioned by the pre- sence of magnesia in the latter. (c) To the solution, (a or 6,) containing several metallic oxides dissolved by an acid, add a solution of crystallized carbonate of pot- ash, as long as any precipitation ensues. This will separate the oxides of iron, chrome, and nickel; but the oxide of manganese and the magnesia, if any be present, will remain dissolved. If a small quantity of oxide of manganese be suspected in an oxide of iron, it may be detected by mixing the oxide with nitre, and throwing the mixture into a red hot crucible. Manganese will be indicated by an amethystine red tinge in the solution of this ' nitre. To separate the oxides of iron and manganese from each other, Gehlen recommends succinic acid, which is preferred, also, by Klaproth and Bucholz. Berzelius employs for this purpose the compounds of benzoic acid. Dr. John advises the addition of oxa- late of potash to the solution of the two oxides, first rendered as neutral as possible; but Bucholz finds that this process is imperfect, and that the oxalates precipitate manganese as well as iron. Mr. Hatchett has suggested another method of separating iron from. manganese. The solution of the ore, made by muriatic acid, and filtrated, must be diluted with three or four pints of cold distilled water. r'-'o this liquid, pure ammonia must be gradually added, till it slightly restores the blue colour of reddened litmus paper The oxide of iren will thus be separated, and will remain on the filter upon which the liquor is thrown; and the oxide of manganese will pass through it, in a state of solution. The oxide of manganese may be obtained by evaporation to dryness, and by calcining in a heat sufficient to expel the muriate of ammonia.* (d) Magnesia and oxide of manganese may be separated by add- ing to their solution (c) the hydro-sulphuret of potash,! which will throw down the manganese, but not the magnesia. Th* precipita- ted manganese must be calcined with the access of air and weigh- ed. The magnesia may afterward be separated by solution ot pure potash; and, when precipitated, must be washed, dried, and calcined. (e) The oxide of chrome may be separated from those of iron and nickel, by repeatedly boiling the three to dryness, with nitric acid. This will acidify the chrome, and will render it soluble in pure potash, which does not take up the other oxides. From this combination with potash the chromic oxide may be detached by adding muriatic acid and evaporating the liquor till it assumes a * Thomson's Annals, v. 343. + See vol. i. page 370, SECT. IV. ANALYSIS OF MINERALS. 343 green colour. Then, on adding a solution of pure potash, the oxide of chrome will fall down, because the quantity of oxygen, required for its acidification, has been separated by the muriatic acid. (f) The oxides of iron and nickel are next to be dissolved in muriatic acid; and the solution evaporated to dryness. Liquid ammonia is then to be added, which acts on the oxide of nickel only. The solution may be again evaporated to dryness, which will render the oxide of iron more dense, and more easily separa- ble from the soluble portion. A fresh addition of ammonia will now readily dissolve the nickel, leaving the oxide of iron, which must be collected on a filter, dried, and weighed. If highly oxidized, it must, before weighing, be calcined with wax, in a crucible.* The oxide of nickel remains dissolved by the excess of ammonia, to which it imparts a blue colour. It may be separated by evapor rating the solution to dryness and dissolving the salt.f (g) Oxide of nickel may be separated from oxide of copper, when contained in the same solution, by immersing in the solu- tion a bar of zinc, which will precipitate the latter metal only. (h) From the ammoniacal solution.of nickel and cobalt, Mr. Phil- lips finds that the former metal is immediately precipitated by pot- ash or soda, which very slowly and sparingly throw down cobalt from the same solvent. The analysis of the stone is now completed, and its accuracy may be judged by the correspondence of the weight of the com- ponent parts with that of the stone originally submitted to experi- ment. It may be proper to observe, that certain stones, which are not soluble in diluted nitric and muriatic acids, may be decomposed by an easier process than that described (A.) Among these are the compounds of barytes, strontites, and lime, with acids, chiefly with the sulphuric, fluoric, and phosphoric. The sulphates of barytes, strontites, and lime; the fluate of lime; and the phosphate of lime; are all found native in the earth, and, except the last, are all insoluble in the above-mentioned acids. They may be known generally by their external characters. The compounds of barytes and strontites have a specific gravity greater than that of other earths, but inferior to that of metallic ores. They have, fre- quently, a regular or crystallized form, are more or less transpa- rent, have some lustre, and their hardness is such as does not prevent their yielding to the knife. The combinations of lime, with the above-mentioned acids, are distinguished by similar characters, except that they are much less heavy. To the mine- * Dr. Marcet alleges that after this operation, the iron still remains in the state of peroxide. Geolog. Transact, i. f For an example of die separation of nickel from iron, see Klaproth's Contributions, vol. i. page 422, where, also, anil page 428, is an instance of the testing of nickel for copper. 344 ANALYSIS OF MINERALS. CHAP. II. ralogist, the outward form and characters of these stones arc suf- ficient indications of their composition. Instead of the fusion with alkali, an easier process may be re- commended. Let the mineral under examination be reduced to powder, and be digested, in nearly a boiling heat, during one or two hours, with three or four times its weight of carbonate of pot- ash, and a sufficient quantity of distilled water. The acid, united with the earth, will quit it and pass to the potash, while the car- bonic acid will leave the alkali and combine with the earth. We shall obtain, therefore, a compound of the acid of the stone with potash, which will remain in solution, while the carbonated earths will form an insoluble precipitate. The solution may be assayed to discover the nature of the acid, according to the formula (I;) and the earths may be separated from each other by the processes (B,) &c. (T) In the foregoing rules for analysis I have omitted the mode of detecting and separating glucine, because this earth is of very rare occurrence. When alumine and glucine are present in a mi- neral, they may be separated from the precipitate (E a" by pure potash, which dissolves both these earths. A sufficient quantity of acid is then to be added to saturate the alkali; and carbonate of am- monia is to be poured in till a considerable excess of this carbo- nate is manifested by the smell. The alumine is thus separated, but the glucine, being soluble in the carbonate of ammonia, re- mains dissolved, and may be precipitated by boiling the solution. (U) Zircon may be separated from alumine, by boiling the mix- ed earths with pure soda, which acts only on the latter.* From an acid solution containing both earths, the alumine is thrown down by saturated carbonate of potash, which, when added in excess, re- dissolves the zircon. Glucine and zircon, or glucine and yttria, may be separated, when mixed together in solution, by prussiate of potash, which has no action on glucine, but precipitates the two other earths. (V) To separate yttria from alumine, precipitate them from a solution containing both earths, by pure ammonia; boil the pre- cipitate in a solution of pure soda, which chiefly takes up alumine: neutralize the solution with sulphuric acid, and add carbonate of soda to the solution, brought to the boiling temperature. A pre- cipitate will ensue, consisting of alumine, with some yttria. To separate the latter earth, dissolve in muriatic acid, and add an ex- cess of carbonate of ammonia, which takes up only the yttria. To ensure, still farther, the purity of the alumine, dissolve the residue in an excess of sulphuric acid: add a small portion of sulphate of potash, and crystallize the solution. The crystals of alum, that are produced, contain one tenth of alumine. (W) The presence of potash (which has lately been discovered in some stones) may be detected by boiling the powdered mineral, ; Klaproth, vol. ii. page 213. bKCT. IV. ANALYSIS OF MINERALS. 343 repeatedly to dryness, with strong sulphuric acid. Wash the dry mass with water, add a little excess of acid, and evaporate the so- lution to a smaller bulk. If crystals of alum should appear, it is a decisive proof of potash, because this salt can never be obtained, in a crystallized form, without the addition of the vegetable alkali. But since a mineral may contain potash, and little or no alumine, in which case no crystals of alum will appear, it may be necessary, in the latter case, to add a little alumine along with the sulphuric acid. Or the stone may be so hard as to resist the action of sul- phuric acid; and it will then be necessary to fuse it [in the manner directed (I,] with soda, which has also a solvent power over alu- mine and silex. The fused mass is to be dissolved in water, and supersaturated with sulphuric acid. Evaporate to dryness, redis- solve in water; and filter, to separate the silex. Evaporate the so- lution, which will first afford crystals of sulphate of soda, and af- terwards of sulphate of potash, should the latter alkali be contain- ed in the mineral. Klaproth first discovered potash in leucite, on summing up the results of its analysis, which gave a considerable loss of weight. By boiling the stone with diluted muriatic acid, and evaporation, he obtained crystals of muriate of potash. Another proof of the presence of potash was, that, when sulphuric acid was boiled with it, the solution gave crystals of alum, to which potash is essential. lie also boiled the stone with muriatic acid, and, after dissolving the muriate of alumine by alcohol, muriate of potash remained. The volcanic leucite contained less potash than other kinds. The same alkali he also detected, afterwards, in lepidolite. The potash, contained in sulphate of alumine, may be separated from the earth, by adding a solution of pure barytes as long as any precipitation is produced. The alumine and sulphate of barytes will fall down together, and the potash will remain in solution. Its presence may be known by the tests, enumerated in the first chap- ter of part ii. (sect. 2.) X. Soda may be detected in a mineral by the following experi- ments:—Let the powdered stone be treated with sulphuric acid, as in (U); wash off the solution, and add pure ammonia, till the pre- cipitation ceases; then filter, evaporate the solution to dryness, and raise the heat so as to expel the sulphate of ammonia. The sul- phate of soda will remain, and may be known by the character, vol. i. page 247. Soda was first found, by Klaproth, in chrysolite, in the large proportion of 36 per cent. This analysis was confirmed by Vau- quelin, whose mode of separating it happens to be the one I now recommend. Both the fixed alkalies have since been frequently discovered in native minerals; viz. soda in basalt (Klaproth, ii. 195); in pitch-stone (207); and in kling-stone, amounting to 8 per cent. (182.) The same skilful analyst has found potash in Hungarian pearl-stone (263); and, accompanied by soda, in pu- mice (20.) Vol. II.—X x 346 ANALYSIS OF MINERALS. OHAP. Ii A new method has been proposed by Sir H. Davy,* for analyzing stones, containing either of the fixed alkalies; viz. by means of the boracic acid. The process is sufficiently simple. One hundred grains of the stone to be examined must be fused, during half an hour, at a strong red heat, with 200 grains of boracic acid. An ounce and a half of nitric acid, diluted with seven or eight parts of water, must be digested on the mass, till the whole has been de- composed. The fluid must be evaporated, till its quantity is re- duced to ounce and half or two ounces. If the stone contain silex, this earth will be separated in the pro- cess of solution and evaporation. It must be collected on a filter, and washed well with water, till the boracic acid, and all the saline matter, are separated. The fluid, and all that has passed through the filter, must be evaporated to about half a pint; then saturated with carbonate of ammonia; and boiled with an excess of that salt, till all the materials that it contains, capable of being precipitated, have fallen to the bottom of the vessel. The solution must then be passed through a filter, which retains the earths and metallic oxides. It must then be mixed with nitric acid, till it tastes strongly sour, and evaporated till the boracic acid appears free. The fluid must next be evaporated to dryness; when by exposure to a heat of 450* Fahrenheit, the nitrate of ammonia will be decomposed, and the nitrate of potash or soda will remain in the vessel. The remaining earths and metallic oxides are separated from each other by common processes; viz. alumine by solution of pot- ash; lime by sulphuric acid; oxide of iron by succinate of ammonia; oxide of manganese by hydro-sulphuret of potash; and magnesia by pure soda. 2. Table of Substances which may be expected in Earths and Stones, aud References to the Means of separating them from each other. Acid, fluoric, R. d. phosphoric, R. c. sulphuric, R. b. Alumine from Lime and magnesia, E. its quantity, E. c. from magnesia, G. silex, H. a. metallic oxides, II. a. glucine, T. *• Barytes and Strontites from other earths, B. from strontites, C. Chrome from manganese, &c. S. c. , iron and nickel, S. e. Earths from oxides, D. * Philosophical Transactions, 1805; or Nicholson's Journal, xiii. 8*6. . SECT. V. ANALYSIS OF MINERALS. 347 Glucine from alumine, T. Iron from manganese, S. e, nickel, S.f Lime from magnesia, F. alumine, E. b. its quantity, F. Magnesia from lime, F. alumine, G. manganese, S. fi. SECT. I. DISCOVERY 0"F POISONS. nic, with which it forms a bright yellow deposit; or the acetate of copper, which affords a green precipitate. Of the two, he recom- mends the latter in preference, but advises that both should be re- sorted to in doubtful cases* Dr. Marcet, however, has replied, that the objection arising from the presence of common salt is easily obviated; for if a little dilute muriatic acid be added to the sus- pected liquid, and then nitrate of silver very cautiously till the precipitate ceases, the muriatic acid will be removed, but the ■arsenic will remain in solution, and the addition of ammonia will produce the yellow precipitate in its characteric form. It is scarcely necessary to add that the quantity of ammonia must be sufficient to saturate any excess of nitric acid which the fluid may contain.f A more important objection to nitrate of silver as a test of arse- nic is, that it affords, with the alkaline phosphates, a precipitate of phosphate of silver, scarcely distinguishable by its colour from the arsenite of that metal.t In answer to this, it is alleged by Mr. Hume,§ that the arsenite of silver may be discriminated by a curdy or flocculent figure, resembling that of fresh precipitated muriate of silver, except that its colour is yellow; while the phosphate is smooth and homogeneous. The better to discriminate these two arsenites, he advises two parallel experiments to be made, upon separate pieces of clean writing paper, spreading on the.one.a lit- tie of the fresh prepared arsenite, and on the other a little of the phosphate. When these are suffered to dry, the phosphate will gradually assume a black colour, or nearly so, while the arsenite will pass from its original vivid yellow to an Indian yellow, or nearly a fawn colour. (G) But the most decisive mode of determining the presence of arsenic, (which, though not absolutely indispensable, should always be resorted to, when the suspected substance can be ob- 'ained in sufficient quantity) is by reducing it to a metallic state; for its characters are then clear and unequivocal. For this pur- pose, let a portion of the white, sediment, collected from the con- tents of the stomach, be dried and mixed with three times its weight of black flux (see p. 120); or if this cannot be procured, with two parts of very dry carbonate ot potash (the salt of tartar of the shops,) and one of powdered charcoal. Dr. Bostock finds that for this mixture we may advantageously substitute one com- posed of half a grain of charcoal, and two drops of oil, to a grain of the sediment. Procure a tube eight or nine inches long, and one fourth or one sixth of an inch in diameter, of thin glass, sealed hermetically at one end. Then put into the tube the mixture of the powder and its flux, and if any should adhere to the inner sur- face, let it be wiped off by a feather, so that the inner surface of the upper part of the tube may be quite clean and dry. Stop the • 33 :\ich. Joiim. 306. f Phil. Mag. xli. 124. 1 Thomson's Annals, viii. 152. ' VTed. and Phys. Journ. Jan. l'Jt8 Vol. II.—-Z z o'62 DISCOVERY OF POISONS. l-UAf. I. end of the tube loosely, with a little paper, and heat the sealed end only, on a chaffing-dish of red-hot coals, taking care lo avoid breathing the fumes. The arsenic, ,if present, will rise to the upper part of the tube, on the inner surface of which it will form a thin brilliant coating. Break the tube, and scrape off the reduced me- tal. Lay a little on a heated iron, when, if it be arsenic, a dense smoke will arise, and a strong smell of garlic will be perceived. The arsenic may be farther identified, by putting a small quantity between two polished plates of copper, surrounding it by powder- ed charcoal, to prevent its escape, binding these tightly together by iron wire, and exposing them to a low red heat. If the in- cluded substance be arsenic, a Avhite stain will be left on the copper. (H) It may be proper to observe, that neither the stain on cop- per, nor the odour of garlic, is produced by the white oxide of arsenic, when heated without the addition of some inflammable ingredient. The absence of arsenic must not, therefore, be infer- red, if no smell should be occasioned by laying the white powder on a heated iron. Dr. Black ascertained, that all the necessary experiments, for the detection of arsenic, may be made on a single grain of the white oxide; this small quantity having produced, when heated in a tube with its proper flux, as much of the metal as clearly estab- lished its presence. If the quantity of arsenic in the stomach should be so small, which is not very probable, as to occasion death, and yet to re- main suspended in the washings, the whole contents, and the wa- ter employed to wash them, must be filtered, and the clear liquor assayed for arsenic by the tests (B,) (C,) (D,) and (E.) SECTION II, Discovery of Corrosive Sublimate. Corrosive sublimate (the muriate of mercury,) next to arsenic, is the most virulent of the metallic poisons. It may be collected by treating the contents of the stomach in the manner already de- scribed; but as it is more soluble than arsenic, viz. in about 19 times its weight of water, no more water must be employed than is barely sufficient, and the washings must be carefully preserved for examination. If a powder should be collected, by this operation, which proves, on examination, not to be arsenic, it may be known to be corrosive sublimate by the following characters: (A) Expose a small quantity of it, without any admixture, to heat in a coated glass tube, as directed in the treatment of arse- nic. Corrosive sublimate will be ascertained by its rising to the SECT. II DISCOVERY OF POISONS. 363 top of the tube, lining the inner surface in the form of a shining white crust. (B) Dissolve another portion in distilled water; and it may be proper to observe how much of the salt the water is capable of taking up. (C) To the watery solution add a little lime-water. A precipi- tate of an orange yellow colour will instantly appear. (D) To another portion of the solution add a single drop of a dilute solution of sub-carbonate of potash (salt or tartar.) A white precipitate will appear; but, on a still farther addition of alkali, an orange-coloured sediment will be formed. (E) The carbonate of soda has similar effects. (F) Sulphureted water throws down a dark-coloured sediment, which, when dried and strongly heated, is wholly volatilized, without any odour of garlic For the detection of corrosive sublimate, Mr. Sylvester has re- commended the application of galvanism, which exhibits the mer- cury in a metallic state. A piece of zinc wire, or if that cannot be had, of iron wire about three inches long, is to be twice bent at right angles so as to resemble the Greek letter n. The two legs of this figure should be distant about the diameter of a com- mon gold wedding-ring from each other, and the two ends of the bent wire must afterwards be tied to a ring of this description. Let a plate of glass, not less than three inches square, be laid as nearly horizontal as possible; and on one side, drop some sulphuric acid, diluted with about six times its weight of water, till it spreads to the size of a halfpenny. At a little distance from this towards the other side, next drop some of the solution supposed to contain corrosive sublimate, till the edges of the two liquids join together; and let the wire and ring prepared as above be laid in such a way that the wire may touch the acid, while the gold ring is in contact with the suspected liquid. If the minutest quantity of corrosive sublimate be present, the ring in a few minutes will be covered with mercury on the part which touched the fluid. The only mineral poison of great virulence that has not been mentioned, and which, from its being little known to act as such, it is very improbable we should meet with, is the carbonate of barytes. This, in the country where it is found, is employed as a poison for rats, and there can be no doubt would be equally destructive to human life. It may be discovered by dissolving it in muriatic acid, and by the insolubility of the precipitate which this solution yields on adding sulphuric acid, or sulphate of soda. Barytic salts, if these have been the means of poison, will be contained in the water employed to wash the contents of the stomach, and will be detected, on adding sulphuric acid, by a copious precipitate. It may be proper to observe, that the failure of attempts to dis- cover poisonous substances in the alimentary canal after death, is by no means a sufficient proof that death has not been occasioned by poison. For it has been clearly established, by experiments ^64 DISCOVERY OF POISONS. OHAP. A. made on animals, that a poison may be so completely evacuated, that no traces of it shall be found, and. yet that death may ensue from the inflammation which it has excited. SECTION III. Method of detecting Copper or Lead. Copper and lead sometimes gain admission into articles of food, in consequence of the employment of kitchen utensils of these materials. I. If copper be suspected in any liquor, its presence will be as- certained by adding a solution of pure ammonia, which will strike a beautiful blue colour. If the solution be very dilute, it may be concentrated by'evaporation; and if the liquor contain a considera- ble excess of acid, like that used to preserve pickles, as much of the alkali must be added as is more than sufficient to saturate the acid. In this, and all other experiments of the same kind, the fluid should be viewed by reflected, and not by transmitted light. II. Lead is occasionally found, in sufficient quantity to be inju- rious to health, in water that has been kept in leaden vessels, and sometimes even in pump water, in consequence of this metal being used in the construction of the pump. Acetate of lead has also been known to be fraudulently added to bad wines, with the view of concealing their defects. Lead may be discovered by adding, to a portion of the suspected water; about half its bulk of water impregnated with sulphureted hydrogen gas. If lead be present, it will be manifested by a dark brown, or blackish, tinge. This test is so delicate, that water con- densed by the leaden worm of a still-tub, is sensibly affected by it. It is also detected by a similar effect ensuing on the addition of sul- phuret of ammonia, or potash. The competency of this method, however, to the discovery of very minute quantities of lead, has been set aside by the experi- ments of Dr. Lambe,* the author of a skilful analysis of the springs of Lemington Priors, near Warwick. By new methods of exa- mination, he has detected the presence of lead in several spring- waters, that manifest no change on the addition of the sulphureted test; and has found that metal in the precipitate, separated from such waters by the carbonate of potash or of soda. In operating on these waters, Dr. Lambe noticed the following appearances: (a) The test forms sometimes a dark cloud, with the preci- pitate affected by alkalies, which has been re-dissolved in nitric acid. - # * See his "Researches into the Properties of Spring Water." 8vo. Lon- don. Johnson. 180C. .SECT. III. DISCOVERY OF POISONS. 365 (b) Though it forms, in other cases, no cloud, the precipitate itself becomes darkened by the sulphureted test. (c) The test forms a white cloud, treated with the precipitate as in (a). These two appearances may be united. (rf) The test neither forms a cloud, nor darkens the precipitate. (e) In the cases (b), (c),(d), heat the precipitate in contact with an alkaline carbonate, to redness; dissolve out the carbonate by water; and treat the precipitate as in (a). The sulphureted test then forms a dark cloud with the solution of the precipitate. In these experiments, it is essential that the acid, used to re-dissolve the precipitate, shall not be in excess; and if it should so happen, that excess must be saturated before the test is applied. It is bet- ter to use so little acid, that some of the precipitate may remain undissolved. • (f) Instead of the process (e) the precipitate may be exposed without addition, to a red heat, and then treated as in (a). In this case, the test will detect the metallic matter; but with less certain- ty than the foregoing one. The nitric acid, used in these experiments, should be perfectly pure; and the test should be recently prepared by saturating water with sulphureted hydrogen gas. Another mode of analysis, employed by Dr. Lambe, consists in precipitating the lead by muriate of soda; but.as muriate of lead is partly soluble in water, this test cannot be applied to small portions of suspected water. The precipitate must be, therefore, collect- ed, from two or three gallons, and heated to redness with twice its weight of carbonate of soda. Dissolve out the soda; add nitric acid, saturating any superfluity; and then apply the sulphureted test. Sulphate of soda would be found more effectual in this pro- cess than the muriate, on account of the greater insolubility of sul- phate of lead. This property, indeed, renders sulphate of^soda an excellent test of the presence of lead, when held in solution by- acids, for it precipitates that metal, even when present in very small quantity, in the form of a heavy white precipitate, which is not soluble by acetic acid. The third process, which is the most satisfactory of all, and is very easy, except for the trouble of collecting a large quantity of precipitate, is the actual reduction of the metal, and its exhibition in a separate form. The precipitate may be mixed with its own weight of alkaline carbonate, and exposed either with or without the addition of a small proportion of charcoal, to a heat sufficient to melt the alkali. On breaking the crucible, a small globule of lead will be found reduced at the bottom. The precipitate from about fifty gallons of water yielded Dr. Lambe about two grains of lead. For discovering the presence of lead in wines, a test invented by Dr. Hahnemann, and known by the title of Hahnemann's wine- test, may be employed. This test is prepared by putting together, into a small phial, sixteen grains of sulphuret of lime, prepared in the dry way (by exposing to a red heat, in a covered crucible, equal 366 DETECTION OF ADULTERATIONS. CHAP. 11.* weights of powdered lime and sulphur, accurately mixed,) and 20 grains of acidulous tartrite of potash (cream of tartar.) The phial is to be filled with water, well corked, and occasionally shaken for the space often minutes. When the powder has subsided, decant the clear liquor, and preserve it, in a well-stopped bottle, for use. The liquor, when fresh prepared, discovers lead by a dark colour- ed precipitate. A farther proof of the presence of lead in wines is the occurrence of a precipitate on adding a solution of the sulphate of soda. The quantity of lead, which has been detected in sophisticated wine, may be estimated at forty grains of the metal in every fifty gallons.* When a considerable quantity of acetate of lead has been taken into the stomach (as sometimes, owing to its sweet taste, happens to children,) after the exhibition of an active emetic, the hydro- sulphuret of potash or of ammonia may be given; or a solution of the common sulphuret. Mr. Sylvester has proposed the gallic acid as an excellent test of the presence of lead.f In cases'of the accidental swallowing of sulphuric acid, which also sometimes happens to children, M. Fourcroy recommends the speedy administration of a solution of soap, or a mixture of carbonate of magnesia or carbonate of lime (common chalk) with water.1. Oxalic acid has lately, in several instances, been taken by mis- take for Epsom salt, and has invariably proved fatal. We have no experience of the best antidote to its effects; but it is probable that this would consist in the immediate administration of carbonate of magnesia, or, if neither of these be at hand, of chalk or whitening of calcined magnesia. At the same time, it will be proper to dilute the contents of the stomach by drinking copiously, and to endea- vour to Excite vomiting by tickling the throat with a feather. These measures should be employed with the utmost promptitude; for the deleterious action of oxalic acid appears to exceed in rapidity even that of arsenic. CHAPTER II. RULES FOR ASCERTAINING THE PURITY OF CHEMICAL PREPARATIONS, EMPLOYED FOR THE PURPOSES OF MEDICINE, AND FOR OTHER USES. I.—Sulphuric Acid,—Acidum Sulphuricum of the London Phar- macopeia,— Oil of Vitriol. The specific gravity of sulphuric acid should be 1.8485, at 60° Fahrenheit; when stronger, there is reason to suspect the presence * Lambe, page 175. f 33 Nicholson's Journal, 310. X Svsteme, vol. i. page 240. CHAP. II. DETECTION OF ADULTERATIONS. 367 of sulphate of lead, or other impurities. It should remain per- fectly transparent when diluted with distilled water. If a sediment occur, on dilution, it is a proof of the presence of sulphate of lead. Iron may be detected in sulphuric acid, by saturating a portion of the diluted acid with pure carbonate of soda, and adding prus- siate of potash, which will manifest the presence of iron by a prus- sian blue precipitate; or it will be discovered by a purplish or blackish tinge, on the addition of tincture of galls to a similarly saturated portion. Copper may be discovered, by pouring, into a similarly saturated solution, pure solution of ammonia, which turns it blue; and lead may be detected by the sulphuret of ammonia, which causes a black precipitate. The latter metal, however, is for the most part thrown down on dilution, in combination with sulphuric acid. Sulphate of potash or of soda may be found by saturating the diluted acid with ammonia, evaporating to dryness, and applying a pretty strong heat. The sulphate of ammonia will escape, and that of potash or of soda will remain, and may be distinguished by its solubility and other characters.* II.—Nitric and Nitrous Acids,—Acidum Nitricum, P. L.—Aqua Fort is. The nitric acid should be perfectly colourless, and as limpid as water. It should be preserved in a dark place, to prevent its con- version into the nitrous kind. These acids arc most likely to be adulterated with sulphuric and muriatic acids. The sulpuric acid may be discovered by adding to a portion of the acid, largely diluted, nitrated or muriated barytes, which will occasion, with sulphuric acid, a white and insoluble pre- cipitate. The muriatic acid may be ascertained by nitrate of silver, which affords a sediment, at first white, but which becomes colour- ed by exposure to the direct light of the sun. Both these acids, however, may be present at once; and, in this case, it will be ne- cessary to add a solution of nitrate of barytes, as long as any pre- cipitate falls, which will separate the sulphuric acid. Let the sedi- ment subside, decant the clear liquor, and add the nitrate of silver. If a precipitate appear, muriatic acid may be inferred to be pre- sent also. Muriatic acid may, also, be detected by adding a solu- tion of sulphate of silver. These acids in their most concentrated state should have the specific gravity of 1.500; but they are seldom fond so heavy. HI.__Muriatic Acid,—Acidum Muriaticum, P. L.—Spirit of Salt. This acid generally contains iron, which may be known by its yellow colour; the pure acid being perfectly colourless. It may * See vol. i. page 272. S68 DETECTION OF ADULTERATIONS. CHAP. 11. also be detected by the same mode as was recommended in ex- amining sulphuric acid. Sulphuric acid is discoverable by a precipitation, on adding, to a portion of the acid, diluted with five or six parts of pure water, a solution of the muriate of barytes. The specific gravity of this acid should be 1.170. That of com- merce is generally from 1.156 to 1.160; and the latter number de- notes the strength of acid prepared according to the London Phar- macopoeia. IV.—Acetic Acid,—Acidum Aceticum,—Radical or Concentrated Vinegar. This acid is often contaminated by sulphurous and sulphuric acid. The first may be known by drawing a little of the vapour into the lungs, when, if the acid be pure, no unpleasant sensation will be felt; but, if sulphurous acid be contained in the acetic, it will not fail to be discovered in this mode. The sulphuric acid is detected by muriated barytes; copper, by supersaturation with pure ammonia; and lead, by sulphuret of ammonia. The specific gravity of this acid should be 1.060 at least; but, as I have already stated, its acidity does not keep pace with its den- sity. ^ i V.—Acetous Acid,—Acidum Aceticum, P. L.—Distilled Vinegar. If vinegar be distilled in copper vessels, it can hardly fail of be- ing contaminated by that metal; and, if a leaden worm be used for its condensation, some portion of lead will certainly be dissolved. The former metal will appear on adding an excess of solution of pure ammonia; and lead will be detected by the sulphureted am- monia, or by water saturated with sulphureted hydrogen. (See the preceding chapter.. The strength of distilled vinegar ought, ac- cording to Mr. R. Phillips, to be such, that a fluid-ounce should decompose 13.8 grains of carbonate of lime. It is not unusual, in order to increase the acid taste of vinegar, to add sulphuric acid. This acid may be immediately discovered by solutions of barytes, which, when vinegar has been thus adultera- ted, throw down a white precipitate. VI.—Bo'acic Acid,—-Sedative Salt of Homberg. Genuine boracic acid should totally dissolve in five times its weight of boiling alcohol; and the solution, when set on fire, should emit a green flame. The best boracic acid forms small hexangular scaly crystals of a shining silvery white colour. Its specific gravity is 1.480. 4 VII.— Tartaric Acid. i This acid often contains sulphuric acid; to discover which, let a \ portion be dissolved in water, and a solution of acetate of lead br CHAP. II. DETECTION OF ADULTERATION'S. 369 added. A precipitate will appear, which, if the acid be pure, is entirely re-dissolved by a few drops of pure nitric acid, or by a lit- tle pure acetic acid. If any portion remain undissolved, sulphuric acid is the cause. Muriate of barytes, also, when Lfce acid is adul- terated with sulphuric acid, but not otherwise, gives a precipitate insoluble by an excess of pure muriatic acid. VIII.—Acid of Amber. Acid of amber is adulterated, sometimes with sulphuric acid and its combinations; sometimes with tartaric acid; and at others with muriate of ammonia. Sulphuric acid is detected by solutions of barytes; tartaric acid by the cautious addition of carbonate of potash, which forms a difficultly soluble bi-tartrate; and muriate of ammonia by nitrate of silver, which discovers the acid, and by a solution of pure pot- ash,'which excites a strong smell of ammonia. Pure acid of amber is a crystalline white salt of an acid taste, soluble in twenty-four parts of cold or eight of hot water, and is volatilized, when laid on red-hot iron, without leaving any ashes or other residue. IX.—Acid of Benzoin,—Acidum Benzoicum, P. L. This acid is not very liable to adulteration. The best has a bril- liant white colour and a peculiarly grateful smell. It is soluble in a large quantity of boiling water or alcohol, and leaves no resi- due when placed on a heated iron. X.—Sub-carbonate of Potash,—Potasses Subcarbonas, P. L. The salt of tartar of the shops generally contains sulphate and muriate of potash, and siliceous and calcareous earths. It should dissolve entirely, if pure, in twice its weight of cold water: and any thing that remains undissolved may be regarded as an impu- rity. Sometimes one fourth of foreign mixtures may thus be de- tected, the greater part of which is sulphate of potash. To as- certain the nature of the adulteration, dissolve a portion of the sediment in pure and diluted nitric acid: the siliceous earth only will remain undissolved. Add, to one part of the solution, nitrate of barytes; this will detect sulphate of potash by a copious preci- pitate. To another portion add nitrate of silver, which will dis- cover muriatic salts; and, to a third, oxalate or fluate of ammonia, which will detect carbonate of lime. The solution of sub-carbonate of potash (liquor potasses sub- carbonatis, P. L.) may be examined in a similar manner. XI.—Solution of pure Potash,—Liquor Potassee, P. L. This may be assayed, for sulphuric and muriatic salts, by satu- ration with nitric acid, and by the tests recommended in speaking of carbonate of potash. A perfectly pure solution of potash should remain transparent on the addition of barytic water. If a precipi- tate should ensue, which dissolves with effervescence in dilute muriatic acid, it is owing to the presence of carbonic acid: if the Vol. II.—3 A \70 DETECTION OF ADULTERATIONS. CHAP. II. precipitate is not soluble, it indicates sulphuric acid. A redun- dancy of carbonic acid is also shown by an effervescence, on add- ing diluted sulphuric acid, and an excess of lime by a white pre- cipitate, on blowing air from the lungs, through the solution, by means of a tobaxco-pipe, or a glass tube. This solution should be of such a strength, as that an exact wine-pint may weigh 18 ounces troy. XII.—Sub-carbonate of Soda,—Soda Subcarbonas, P. L. Carbonate of soda is scarcely ever found free from muriate and sulphate of soda. These may be discovered by adding, to a little of the carbonate saturated with pure nitric acid, first nitrate of barytes, to detect sulphuric acid, and afterward adding to the fil- tered liquor a few drops of solution of nitrate of silver, to ascer- tain the presence of muriatic acid; or the latter impurity will bb indicated at once by a solution of sulphate of silver. Carbonate of potash will be shown by a precipitate ensuing on the addition of tartarotis acid to a strong solution of the alkali; for, this acid forms a difficultly soluble salt with potash, but not with soda, XIII.—Solution of Carbonate of Ammonia,-—Liquor Ammonia Carbonatis, P. L. This should have the specific gravity of LI50; should effervesce on the addition of acids: and should afford a strong coagulum on adding alcohol. XIV.— Carbonate of Ammonia,—Ammonia Carbonas, P.L. This salt should be entirely volatilized by heat. If any thing remain, when it is laid on a heated iron, carbonate of potash or of lime may be suspected; and these impurities arc most likely to be present if the carbonate of ammonia be purchased in the form of a powder. It should therefore always be bought in solid lumps. Sulphuric and muriatic salts, lime, and iron, may be discovered by adding to the alkali, saturated with nitric acid, the appropriate tests already often mentioned. XV.—Solution of pure Ammonia in Water,—Liquor Ammonia, P. L.—Strong Spirit of Sal Ammoniac. The volatile alkali, in its purest state, exists as a gas condensi- ble by water, and its solution in water is the only form under which it is applicable to useful purposes. This solution should contain nothing besides the volatile alkali; the alkali should be perfectly free from carbonic acid, and should be combined with water in the greatest possible proportion. The presence of other salts may be discovered by saturating a portion of the solution with pure nitric acid, and adding the tests for sulphuric and mu- riatic acids. Carbonic acid is shown by a precipitation on mixing the solution with one of muriate of lime; for this earthy salt is not precipitated by pure ammonia. The experiment should he made in a closed vial; for the volatile alkali, by exposure to the air, quickly gains carbonic acid enough to become a precipitant of calcareous solutions. The best mode of determining the strength CHAP. II. DETECTION OF ADULTERATIONS. 37) of the solution is by taking its specific gravity, which, at 60° Fah- renheit, should be as 905, or thereabouts, to 1000. That of the London Pharmacopoeia (edit. 1815) has the specific gravity of 0.960; and is, therefore, of very inferior strength. XVI.—Spirit of Hartshorn. This may be counterfeited by mixing the aqua ammonia purjc with the distilled spirit of hartshorn, in order to increase the pun- gency of its smell, and to enable it to bear an addition of water. The fraud is detected by adding alcohol to the sophisticated spi- rit; for, if no considerable coagulation ensues, the adulteration is proved. It may also be discovered by the usual effervescence not ensuing with acids. The solution should have the specific gravity of 1500. XVII.—Sulphate ofSoda,—Sod<£ Sulphas, P. L.— Glauber's Salt. This salt ought not to contain an excess of either acid or alkali, both of which may be detected by the vegetable infusions, p. 308, 309. Nor should it be mixed with earthy or metallic salts, the former of which are detected by carbonate, and the latter by prus- siate of potash. Muriate of soda is discovered by adding nitrate of barytes till the precipitate ceases, and afterwards nitrate of sil- ver, or more simply by a solution of sulphate of silver. Sulphate of potash is discovered by its more sparing solubility. The sul- phate of soda, however, being itself one of the cheapest salts, there is little risk of its being intentionally sophisticated. XVIII.—Sulphate of Potash,—Potasses Sulphas, P. L.— Vitriola- ted Tartar. The purity of this salt may be ascertained by the same means as that of the former one. The little value of this salt renders it pretty secure from wilful adulteration. XIX.—Nitrate of Potash,—Potasses Nitras, P. L.—Nitre or Salt Petre. Nitrate of potash is, with great difficulty, freed entirely from muriate of soda; and a small portion of the latter, except for nice chemical purposes, is an admixture of little importance. To dis- cover muriate of soda, a solution of nitrate of silver must be added as long as any sediment is produced. The precipitate, washed and dried, must be Weighed. Every hundred grains will denote about 42 \ of muriate of soda. Sulphate of. potash or soda may be discovered by nitrate or muriate of barytes. XX.—Muriate of Soda,—Common Salt. Common salt is scarcely ever found free from salts with earthy bases, chiefly muriates of magnesia and lime, which are contained in the brine, and adhere to the crystals. The earths may be pre- cipitated by carbonate of soda, and the precipitated lime and mag- nesia may be separated from each other by the rules given m page 337, / 372 DETECTION OF ADULTERATIONS. CHAP. II. XXI.—Muriate of Ammonia,—Ammonia Murias, L. P.—Sal Ammoniac. This salt ought to be entirely volatilized, by a low heat, when laid on a heated iron. It sometimes contains sulphate of ammonia, however, which, being also volatile, cannot be thus detected. To ascertain the presence of the latter salt, add the muriate or nitrate of barytes, which will indicate the sulphate by a copious and inso- luble precipitate. .XXII.—Acetate ef Potash,—Potasses Acetas, P. L. Genuine acetate of potash is perfectly soluble in four times its weight of alcohol, and may thus be separated from other salts that are insoluble in alcohol. The tartrate of potash (soluble tartar) is the adulteration most likely to be employed. This may be dis- covered by adding a solution of tartaric acid, which, if the sus- pected salt be present, will occasion a copious precipitate. The tartrate is also detected by its forming, with acetate of lead or mu- riate of barytes, a precipitate soluble in acetic or muriatic acid; and sulphates, by a precipitate with the same agents, insoluble in those acids. XXIII.—-Neutral Tartrate of Potash,—Potasses Tartaris, P. L.— Soluble Tartar. This salt should afforda very copious precipitate on adding tar- tarous acid. The only salt likely to be mixed with it is sulphate of soda, which may be detected by a precipitate with muriated barytes, insoluble in diluted muriatic acid. XXIV.—Acidulous Tartrate of Potash,—Potassa Supertartras, P. L.— Cream of Tartar. The only substance with which this salt is likely to be adulte- rated is sulphate of potash. To determine whether this be pre- sent, pour, on about half an ounce of the powdered crystals, two or three ounce measures of distilled water;"shake the mixture fre- quently, and let it stand one or two hours. The sulphate of pot- ash, being more soluble than the tartrate, will be taken up; and may be known by the bitter taste of the solution, and by a precipi- tate, on adding muriate of barytes, which will be insoluble in mu- riatic acid. .XXV.—-Compound Tartrate of Soda and Potash,—Soda Tartari- zata, P. L.—Rochelle or Seignette's Salt. Sulphate of soda, the only salt with which this may be expected to be adulterated, is discovered by adding to a solution of Rochelle salt the acetate of lead or muriate of barytes.—The former, if the sulphate be present, affords a precipitate insoluble in acetous acid, and the latter one insoluble in muriatic acid. XXVI.—Sulphate of Magnesia,—Magnesia Sulphas, P. L.— Epsom Salt. This salt is very likely to be adulterated with sulphate of soda, or Glauber's salt, which may be made to resemble the magnesian CHAP. II. DETECTION OF ADULTERATIONS. 373 salt in appearance, by stirring it briskly at the moment when it is about to crystallize. The fraud may be discovered very readily if the salt consist entirely of the sulphate of soda, because no preci- pitation will ensue on adding carbonate of potash. If only a part of the salt be sulphate of soda, detection is not so easy, but may still be accomplished; for, since 100 parts of crystallized sulphate of magnesia give between 35 and 36 of the dry carbonate, when completely decomposed by about 5 7 of sub-carbonate of potash, if the salt under examination afford a considerably less proportion, its sophistication may be fairly inferred; or, to discover the sulphate of soda, precipitate all the magnesia by pure ammonia, with the aid of heat. Decant the clear liquor from the precipitate, filter it, and, after evaporation to dryness, apply such a heat as will vola- tilize the sulphate of ammonia, when that of soda will remain fixed, and every 10 grains of the dry residue indicate about 22£ of crystals. Muriate of magnesia or of lime may be detected by the salt be- coming moist when exposed to the air, and by a precipitation with nitrated silver, after nitrate of barytes has separated all the sulphu- ric acid and magnesia, or by fumes of muriatic acid arising on the addition of a little sulphuric acid. These, if in very small quantity, will be made apparent by a stopper moistened with liquor of am- monia. Lime is discoverable by a white precipitate on the addition of liquid carbonate of ammonia. XXVII.— Sulphate of Alumine,—Alum. Perfectly pure alum should contain neither iron nor copper. The former is manifested by adding, to a solution of alum, prus- siate of potash, and the latter by any excess of pure ammonia. XXVIII.—Borate of Soda,—Sudes Boras—P. L.—Borax. Borate of soda, if adulterated at all, will probably be so with alum or fused muriate of soda. To discover these, borax must be dis- solved in water, and its excess of alkali be saturated with nitric acid. Nitrate of barytes, added to this saturated solution, will de- tect the sulphuric salt, and nitrate of silver the muriate of soda. XXIX.—Sulphate of Iron,—Ferri Sulphas, P. L.— Green Vitriol. If this salt should contain copper, which is the only admixture likely to be found in it, pure ammonia, added till a precipitation ceases, will afford a blue liquor. Any copper that may chance to be present, may be separated and the salt purified, by immersing in a solution of it a clear polished plate of iron. XXX.—Glass of Antimony. A large quantity of glass of lead was lately introduced into the London market, as glass of antimony. To discover this criminal imposition, whenever it may be practised, the following distinctive' characters of the two substances have lately been described by Mr. Luke Howard.* * Philosophical Magazine, xxxv. 236% 374 DETECTION OF ADULTERATIONS. CHAP. II. Glass of antimony has a rich brown or reddish colour, with the Usual transparency of coloured glasses. The glass of lead is of a deeper and duller colour against the light; is much less transpa- rent; and even in some samples, quite opaque. The specific gravity of the true never exceeds 4.95; that of the spurious or lead glass is 6.95; or, in round numbers, their compa- rative weights are as 5 to 7. Let twenty grains be rubbed fine in a glass mortar, adding half an ounce of good muriatic acid. The true dissolves with an hepa- tic smell; the solution is turbid but has no sediment. The spurious turns the acid yellow, giving out an oxymuriatic odour, and leaves much sediment. Let a little of each solution be separately dropped into water. The true deposits oxide of antimony in a copious white coagulum; or, if the water has been previously tinged with sulphuret of am- monia, in a fine orange precipitate. The spurious gives no pre- cipitate in water, and, in the other liquid, one of a dark brown or olive colour. A solution of the spurious in distilled vinegar has a sweet taste, together with the other properties of acetate of lead. A very small mixture of the spurious may be detected by its de- basing, more or less, the bright orange colour of the precipitate thrown down by the sulphuret of ammonia from the solution in any acid. The samples of the spurious, hitherto detected, are of a much thicker and clumsier cast than the genuine; but the appearance is not to be trusted, and no specimen should be allowed to pass with- out a trial either of the specific gravity or chemical properties. XXXI.— Tartarized Antimony,—Antimonium Tartarizatum, P. L.—Emetic Tartar. A solution of this salt should afford, with acetate of lead, a pre- cipitate perfectly soluble in dilute nitric acid. A few drops of the sulphuret of ammonia, also, should immediately precipitate a gold coloured sulphuret of antimony. XXXII.-—Muriate of Mercury,—Hydrargyri Oxymurias, P. L. Corrosive Sublimate. If there be any reason to suspect arsenic in this salt, the admix- ture, (which, however, is not likely to be practised except with the intention of its acting as a poison) may be discovered as follows: Dissolve a small quantity of the sublimate in distilled water; add a solution of carbonate of ammonia till the precipitate ceases, and filter the solution. If, on the addition of a few drops of ammoniated copper* to this solution, a precipitate of a yellowish green colour is produced, the sublimate contains arsenic. XXXIII.—Sub-muriate of Mercury,—Hydrargyri SuB-murias, P.'L.—Calomel. Calomel should be completely saturated with mercury. This * Prepared by digesting- a little verdegris in the solution of pure ammonia. CHAP. II. DETECTION OF ADULTERATIONS. 3W may be ascertained by boiling, for a few minutes, brum, P. L. This substance is rarely found adulterated, as it would be diffi- cult to find a substance well suited to this purpose. If well pre- pared, it may be totally volatilized by heat. XXXVI.—Red Oxide of Mercury by Nitric Acid,—Hydrargyri Nitrico-Oxydum, P. L.—Red Precipitate. This is very liable to adulteration with minium, or red lead. The fraud may be discovered by digesting it in acetic acid, and adding to the solution sulphureted water, or sulphuret of ammonia, either of which produces, with the compounds of lead, a dirty dark co- * See Mr. Accum's valuable papers on the detection of adulterations, in Nicholson's Journal. 4tn. 376 DEFECTION OF ADULTERATIONS CHAP. If. loured precipitaft; or by adding sulphate of soda, which throws down sulphate of lead. This oxide ought to be totally volatilized by heat. XXXVII.— White Oxide of Mercury,—Hydrargyrus Prxcipitatus Albus, P. L.— White Precipitate. White lead is the most probable adulteration of this substance, and chalk may also be occasionally mixed with it. The oxide of lead may be discovered as in the last article; and chalk, by adding to the dilute solution a little oxalic acid. XXXVIII.—Red Sulphureted Oxide of Mercury,—Hydrargyri, Sulphuretum Rubrum, P. L.—Factitious Cinnabar. This substance is frequently adulterated with red lead, which may be detected by the foregoing rules. Chalk and dragon's blood are also sometimes mixed with it. The chalk is discovered by an effervescence on adding acetic acid, and by pouring oxalic acid into the acetous solution. Dragon's blood will be left unvolatilized when the sulphuret is exposed to heat, and may be detected by its giving a colour to alcohol, when the cinnabar is digested with it. XXXIX.—Black Sulphureted Oxide of Mercury,—Ethiops Mi- neral. The mercury and sulphur, in this preparation, should be so in- timately combined, that no globules of the metal can be discovered by a magnifier; and that, when rubbed on gold, no white stain may be communicated. The admixture of ivory-black may be detected by its not being wholly volatilized by heat; or, by boiling with al- kali to extract the sulphur, and afterwards exposing the residuum to heat, which ought entirely to evaporate. XL.— Yellow Oxide or Sub-sulphate of Mercury,—Hydrargyrus Vitriolatus, P. L.— Turbith Mineral. This preparation should be wholly evaporable; and, when digest- ed with distilled water, the water ought not to take up any sulphu- ric acid, which will be discovered by muriate of barytes. XLI.—Fused Nitrate of Silver,—Argenti Nitras, P. L.—Lunar Caustic. The most probable admixture with this substance is nitrate of copper, derived from the employment of an impure silver. In mo- derate proportion this is of little importance. It may be ascertained by solution in water, and adding an excess of pure ammonia, which will detect copper by a deep blue colour. The watery solution of lunar caustic, when mingled with one of common salt, should give a copious curdy precipitate. XLII.— White Oxide of Zinc,—Zinci Oxydum, P. L.—Flowers of Zinc. Oxide of zinc may be adulterated with chalk, which is discover- able by an effervescence with acetous acid, and by the precipitation of this solution with oxalic acid. Lead is detected by adding, to u-UAP. II. DETECTION OF ADULTERATIONS. 377 the acetous solution, sulphureted water, or sulphuret of ammonia. Arsenic, to which the activity of this medicine has been some- times ascribed, is detected, also, by sulphureted water, added to the acetous solution: but in this case the precipitate has a yellow colour, and, when laid on red-hot charcoal, gives first a smell of sulphur, and afterwards of arsenic. XLIII.— White Oxide of Lead,—Plumbi Carbonas, P. L.— White Lead. * * This is frequently sophisticated with chalk; the presence of which may be detected by cold acetous acid, and by adding, to this solution, oxalic acid. Carbonate of barytes is detected by sulphate of soda added to the same solution, very largely diluted with distilled water; and sulphate of barytes, or sulphate of lead, by the insolubility of the cerusse in boiling distilled vinegar. XLIV.—Superacetate of Lead,—Plumbi Superacetas, P. L.—~ Sugar of Lead. If the acetate of lead should be adulterated with acetate of lime or of barytes, the former may be detected by adding, to a dilute solution, the oxalic acid; and the latter by sulphuric acid, or solu- tion of sulphate of soda, added to a solution very largely diluted with water. Acetate of lead ought to dissolve entirely in water, and any thing that resists solution may be regarded as an impurity. XLV.— Green Oxide, or Sub-acetate of Copper,—JErugo, P.L.— Verdegris. This substance is scarcely ever found pure, being mixed with pieces of copper, grape-stalks, and other impurities. The amount of this admixture of insoluble substances may be ascertained by boiling a portion of verdegris with 12 or 14 times its weight of distilled vinegar, allowing the undissolved part to settle, and as- certaining its amount. Sulphate of copper may be detected by boiling the verdegris with water, and evaporating the solution. Crystals of acetate of copper will first separate, and, when the so- lution has been farther concentrated, the sulphate of copper will crystallize. Or, it may be discovered by adding to the watery so- lution muriate of barytes, which will throw down a very abundant precipitate. Tartrate of copper, another adulteration sometimes met with, is discovered by dissolving a little of the verdegris in acetous acid, and adding acetate or muriate of barytes, which will afford, with the tartarous acid, a precipitate soluble in muriatic acid. XLV.— Crystallized Acetate of Copper,—Distilled or Crystallized Verdegris. This is prepared by dissolving the common verdegris in dis- tilled vinegar, and crystallizing the solution. These crystals should dissolve entirely in six times their weight of boiling water, and the solution should give no precipitation with solutions of ba- Vol. II.—3 B 378 DETECTION OF ADULTERATIONS. CHAP. IT. rytes; for, if these solutions throw down a precipitate, sulphate of copper is indicated. This impurity may be discovered by evapo- rating the solution very low, and separating the crystals of acetate of copper. Farther evaporation and cooling will crystallize the sulphate, if any be present. XL VII.—Sub-carbonate of Magnesia,—Magnesia Carbonas P. L. Carbonate of magnesia is most liable to adulteration with chalk; and, as lime forms with sulphuric acid a very insoluble salt, and magnesia one very readily dissolved, this acid may be employed in detecting the fraud. To a suspected portion of magnesia add a little sulphuric acid, diluted with eight or ten times its weight of water. If the magnesia should entirely be taken up, and the solution should remain transparent, it may be pronounced pure, but not otherwise. Another mode of discovering the deception is as follows:—Saturate a portion of the suspected magnesia with muriatic acid, and add a solution of carbonate of ammonia. If any lime be present, it will form an insoluble precipitate, but the magnesia will remain in solution. i XLVIII.—Pure Magnesia,—Magnesia, P. L.— Calcined Mag- nesia. Calcined magnesia may be assayed by the same tests as the car- bonate. It ought not to effervesce at all with dilute sulphuric acid; and, if the earth and acid be put together into one scale of a balance, no diminution of weight should ensue on mixing them together. It should be perfectly free from taste, and, when di- gested with distilled water, the filtered liquor should manifest no property of lime-water. Calcined magnesia, however, is very seldom so pure as to be totally dissolved by diluted sulphuric acid; for a small insoluble residue generally remains, consisting chiefly of siliceous earth, derived from the alkali. The solution in sul- phuric acid when largely diluted, ought not to afford any precipi- tation with oxalate of ammonia. XLIX.—Spirit of Wine, Alcohol, and JEthers. The only decisive mode of ascertaining the purity of spirit of wine and of aethers, is by determining their specific gravity. Highly rectified alcohol should have the specific gravity of 800 to 1000: rectified spirit of wine 835: proof spirit of 920: sulphuric aether 729; and as found in the shops under^the name of ather rectiflcatus it ought not to exceed 750: the spir tus atheris nitrici ; P. L. 1815), or sweet spirit of nitre, 834. The aethers, when quite pure, ought not to redden the colour of litmus, nor ought those formed from sulphuric acid to give any precipitation with solution of barytes. L.—Essential or Volatile Oils. As essential oils constitute only a very small proportion of the vegetables from which they are obtained, and bear generally a very high price, there is a considerable temptation to adulterate . H VP. III. USE OF TESTS TO ARTISTS. 379 them. They are found sophisticated, either with cheaper volatile oils, with fixed oils, or with the spirit of wine. The fixed oils are discovered by distillation with a very gentle heat, which elevates the essential oils, and leaves the fixed ones. These last may, also, be detected by moistening a little writing-paper with the suspect- ed oil, and holding it before the fire. If the oil be entirely essen- tial, no stain will remain on the paper. Alcohol, also, detects the fixed oils, because it only dissolves the essential ones, and the mixture becomes milky. The presence of cheaper essential oils is discovered by the smell. Alcohol, a cheaper liquid than some of the most costly oils, is discovered by adding water, which, if alcohol be present, occasions a milkiness. CHAPTER III. USE OF CHEMICAL RE-AGENTS TO CERTAIN ARTISTS AND MANU- FACTURERS. To point out all the beneficial applications of chemical sub- stances to the purposes of the arts, would require a distinct and very extensive treatise. In this place I have no farther view than to describe the-mode of detecting adulterations in certain articles of commerce; the strength and purity of which are essentials to the success of chemical processes. I.—Mode of detecting the Adulteration of Potashes, Pearl-ashes, and Barilla. Few objects of commerce are sophisticated to a greater extent than the alkalies, to the great loss and injury of the bleacher, the dyer, the glass-maker, the soap-boiler, and of all other artists who are in the habit of employing these substances. To detect these adulterations, by determining the strength of alkalies, several me- thods have been recommended. In the early editions of this work, I gave, as the best, that of Mr. Kirwan, described in the Transactions of the Royal Irish Academy for 1789, which consists in ascertaining the quantity of alum, decomposed by the alkali under examination. Experience, however, has since convinced me, that a better mode of making this assay is by means of sul- phuric acid; the quantity of acid, required for neutralizing a given weight of the alkali under examination, being directly as the alka- line power of the latter. An apparatus for this purpose was, several years ago, recom- mended by \1. Descroisilles.* It consists principally of a glass * 60 Ann. de Chim. 77 380 L'SE OF TES1S TO AR'lIUTS. CHAP. Ill tube, from five to six tenths of an inch diameter, sealed at one end, and inserted at this end into a pedestal which keeps it in a perpendicular position. The upper and open extremity is a little funnel-shaped, and provided with a lip, for the convenience of pouring out fluids. On this tube is engraved a scale of 72 equal parts, the first degree being at the uppermost part of the tube, and the 72d, of course, near its sealed extremity. Each degree is in- tended to contain half a French gramme (the gramme being 15$ English grains very nearly) of the acid test liquor, which is formed by diluting one part by weight of sulphuric acid,* with nine parts by weight of distilled water. As an example of the use of this alkalimeter, let us suppose that we wish to assay a sample of American pearlash. Reduce to powder a sufficient quantity of the alkali to serve as a fair average specimen; and of th's, put 10 grammes (= 154.5 grains) into three or four ounces of water, either warm or cold. Let the mixture be . agitated till the solution is complete, and filtered through paper. Of the clear solution, pour one half into a common tumbler. Next, pour diluted acid into the tube to the line marked 0; and taking the tube in the left hand, add the liquor, which it contains, very slowly to the alkaline solution in the tumbler, stirring all the while with one of the. wooden rods, and first using this rod, to re- move the drop, which adheres to the lip of the tube. When the acid is lowered in the tube to about the 40th degree, it is proper to try if the alkali be neutralized, by taking a drop on the end of a glass or wooden rod, and applying it to the proper test papers. By doing this repeatedly, the precise point of saturation will be at length attained; and the number on the tube, corresponding with the level of the remaining acid, will show the comparative strength of the alkali. The mean strength of several varieties of potash was found to be 55, denoting that they require 55 hundredths of theirweight of sulphuric acid, sp. gr. 1.842 ( = 53 of sp. gr. 1.849) for saturation; from which it may be calculated that they contained, percent, a quantity of alkali, equal to about 75 parts of sub-carbo- nate of potash. When soda or barilla is submitted to experiment, it is necessary to make the solution by means of hot water; and in all cases, it is adviseable to repeat the experiment on the half of the liquor which has been reserved. The following table, given by M. Descroisilles, shows the strength of some alkalies of commerce, commonly met with in France. The last column I have calculated from obvious data. It expresses the quantity of subcarbonate of potash or soda, to which 100 parts of the respective alkalies of commerce are equivalent; the four last only being compared with the subcarbonate of soda. * Of sp. gr. 1.842; for this density!, according to Vauquelin, corresponds with 66° of the artometre, at 55° Fahrenheit; (vid. 76 Ann. de Ch. 260.; The specific gravity of the dilute acid, I find by experiment, to be 1.066. => Subc. Potash or Soda. 81 to 86" 81 to 86 68 to 75 68 to 75 c CHAP. Ill LSE OF TEbTS TO ARTISTS. 381 Degrees. American pearlash, 1st sort . . . » 60 to 63 American potash in reddish masses, > gQ g3 1st ditto........5 American pearlash, 2nd sort . . . 50 to 55 American potash in grayish masses, } 5Q 55 2nd ditto........) White Russian potash ......52 to 58 70 to 79 White Dantzick ditto......45 to 52 60 to 79 Blue Dantzick potash......45 to 52 60 to 79 Alicant barilla........20 to 33 21 to 41 Crystals of soda of commerce ... 36 39 Natron (kelp?)........20 to 33 21 to 35 Barilla and natron (kelp?) inferior . 10 to 15|11 to 16 Improved Alkalimeter and Acidimeter. I have retained, in this edition, a description of the alkalimeter ©f Descroisilles, because it is probable that several of them may be in the possession of persons in this country; and because it is common in France to express the value of alkalies in degrees of that instrument. It has been very properly objected to it, by Dr. Ure of Glasgow,* that these degrees, being entirely arbitrary, do not denote the value of alkalies in a language universally intelligi- ble; and he has proposed an instrument, which shall, at once, and without calculation, declare the true proportion of alkali in 100 parts of any specimen. The principal deviation in the following rules, from the method of Dr. Ure, is, that while he employs sulphuric acid diluted to the same uniform degree (viz. of sp. gr. 1.060) for all the different alkalies, and consequently has a distinct scale for each, I use sul- phuric acid of different degrees of strength for the different alka- lies, and thus adapt one scale of equal parts to the several varieties of alkaline substances. Any tube of sufficient capacity, in my me- thod of proceeding, will answer the purpose; but the most conve- nient size I find to he about nine inches and a half long, and three quarters of an inch inside diameter. The tube should be formed with a lip for the convenience of pouring, and be provided with a glass foot to support it (see plate ii. fig. 28.) A tube of this kind holds 1000 grains of Water, and, (which is desirable) a little more. To graduate it, weigh into it 100 successive portions of distilled water at 60° Fahrenheit, of ten grains each; or, if the tube be of equal bore throughout, it may be sufficient to weigh into it ten successive portions of water of 100 grains each, dividing each of the intermediate spaces into ten parts by a pair of compasses. When 1000 grains of water have been weighed into the tube, a * In an Essay on Alkalimeter, which he was so good, about two years ago, as to communicate to me in manuscript, and which, 1 believe, he has not yet published. o8J USE OF TESTS TO ARilSTS. CHAP. III. line may be drawn with a file, which may be marked 0, the tenth below this 10, and so on as shown in fig. 28. The test acid, which I prefer, is made by diluting one part of oil of vitriol of commerce of sp. gr. 1.849, with four parts of water; consequently one fifth part of its weight is concentrated oil of vitriol, and its specific gravity is, as nearly as possible, 1.141. Acid of this strength does not, on farther dilution, give out any heat, that can be a source of inaccuracy. When an alkali is to be examined, find by Dr. Wollaston's Scale of Equivalents, how many grains of oil of vitriol are required to neutralize 100 grains of what may be considered the proper alka- line ingredients of the substance in question. This, in pearlash, is sub-carbonate of potash; in potash, pure potash; in barilla, or kelp, dry sub-carbonate of soda. Let us take pearlash as an ex- ample. On referring to the scale, we find that 100 grains of sub- carbonate of potash are equivalent to 71 grains of concentrated oil of vitriol.* Put, therefore, into the test tube a quantity of the di- lute acid containing 71 grains of concentrated acid, viz. 355 grains; and to spare the trouble, on any future occasion, of weighing the acid, let a line be drawn with a file on the blank side of the tube, at the level of the acid liquor, which may be marked Equiv. of Subc. Pot. Fill up the tube with water to the line marked 0, and mix the acid and and water completely by pouring them into a lipped glass vessel; stirring with a glass rod; and then returning them into the tube. Now as the whole 100 measures contain a quantity of oil of vitriol equivalent to 100 grains of sub-carbonate of potash, it is ob- vious that each measure of the liquor in the tube is adequate to the neutralization of one grain of the sub-carbonate. Let 200 grains, taken out of a fair average specimen of the pearlash to be examined, be dissolved in two ounce measures of warm distilled water, filter the solution; and wash the filter with two ounces more of water, which is best applied to the margin of the paper, by means of the dropping bottle, fig. 25, a. Add the washings to the solution; and having mixed the whole together, pour one half into a tumbler or goblet, reserving the other half for a repetition of the experiment if necessary. To the liquor in the glass goblet, add the diluted acid very gra- dually, making the additions more and more slowly towards the last. As soon as the point of neutralization is attained, which will be shown by the cessation of a change of colour in slips of litmus and of turmeric paper dipped, from time to time, into the liquor, no more acid must be added. It is proper, however, the operator should be aware, that there will often be an apparent excess of test acid, in consequence of the cabonic acid, which is disengaged, act- ing on the litmus paper. To avoid this source of error, it is ad- viseable, towards the last, to warm the liquor by setting the glass * Dr. Ure makes it 70.4. Journ. of Science, iv. 119. CHAP. III. USE OF TESTS TO ARTISTS. 383 containing it for half an hour near the fire, and while thus warmed, to add very cautiously the rest of the acid required for saturation. This point being attained, the number on the test tube, at the level of the acid remaining in it, shows at once, without any calculation, how much per cent, of sub-carbonate of potash is contained in the pearlash under examination. In the samples, I have tried, it has generally laeen about 80 per cent. In operating on barilla, kelp, or any variety of the mineral alkali, the process is exactly the same, except that as 93* of oil of vitriol are equivalent to 100 of sub-carbonate of 6oda, we must take 93 x 5 = 465 grains, of sulphuric acid of density 1.141. This may be marked on the tube, Equiv. of Subc. Soda. In a similar manner, we may mark on the tube the equivalent of pure potash, viz. 520 grains of the above diluted acid; and that of pure soda, 783 grains; with any other equivalents, that may be likely to be of use. Having ascertained the proportion of sub-carbonate of potash in any sample of pearlash, it is easy to find, by the sliding scale, its equivalent quantity of pure or caustic potash. Thus, supposing the pearlash to contain 80 per cent, of sub-carbonate, that number be- ing set to sub-carbonate of potash on the scale, the equivalent in pure potash is at once seen to be 55. To determine, by the same graduated tube, the strength of any acid whose equivalent is known, (which is the reverse of the fore- going process) we may put 100 grains of the acid, with a sufficient quantity of water, into a goblet; and use, for saturating it, its equi- valent of any alkali. For example, 100 grains of concentrated oil of vitriol requiring for saturation 108 grains of dry sub-carbonate of soda, dissolve the latter quantity of alkali in water sufficient to make up 1 0 measures of solution in the tube; then pour the alkaline so- lution to the acid liquor, till the latter is neutralized; and the num- ber of measures, which have been expended, exactly denote the strength of the acid. - It may sometimes be desirable to know the proportion, not of concentrated or of real acid, but of acid of some inferior degree of density, in a specimen of acid. The method of doing this will best be explained by an example. Suppose that we wish to know the equivalent, in muriatic acid of sp. gr. 1.160, to 100 grains of the same acid of sp. gr. 1.074; find, by the alkaline test, or by referring to the tables in the Appendix, how much real acid 100 grains of both those acids contain. In acid of sp. gr. 1.160, it will be 23.4 per cent.; in acid of sp. gr. 1.074, it will be 11. Then 23.4 : 100 :: 11 : 47. Therefore 47 grains of muriatic acid, of sp. gr. 1.160, are equivalent, in acidity, to 100 of sp. gr. 1.074. No chemical operation can be more simple, or more easily ma- naged, than the measurement of the strength of alkalies by acid liquors, and of acids by alkaline ones, in the way which has been * According to Dr. Ure, 91.4 is the true equivalent. Journ. of Science, fee. iv. 119. 384 CSE OF TESTS TO AR11S1S. CHAP. 111. described. The test-tube, which is the only instrument, required for that purpose, may be had at any glass-house, and may easily \>r graduated by any person who will take the necessary pains. Vv hen once accurately prepared, it will be found, also, useful for a variety of other purposes, which will readily present themselves to the practical chemist. II.—Mode of detecting the Adulteration of Manganese. In the section on drugs, instructions may be found for discover- ing impurities in several chemical preparations, employed by the artist, as cerusse or white lead, red lead, verdegris, Sec. No rules, however, have been given for examining manganese, which is a substance that varies much in quality, and is often sophisticated; as the bleachers experience, to their no small disappointment and loss. The principal defect of manganese arises from the admixture of chalk, which is not always an intentional adulteration, but is sometimes found along with it, as it occurs in the earth. When to this impure manganese mixed with muriate of soda, the sulphuric acid is added, the materials effervesce and swell considerably, and a large proportion passes into the receiver; in consequence of which the bleaching liquor is totally spoiled. This accident has, to my knowledge, frequently happened, and can only be prevented by so slow and cautious an addition of the acid, as is nearly incon- sistent with the business of an extensive bleaching work. The presence of carbonate of lime may be discovered in manganese, by pouring, on a portion of this substance, nitric acid diluted with 8 or 10 parts of water. If the manganese be free from chalk, no effervescence will ensue, nor will the acid dissolve any thing; but, if carbonate of lime be present, it will be taken up by the acid. To the solution add a sufficient quantity of carbonate of potash to pre- cipitate the lime, wash the sediment with water, and dry it. Its weight will show how much chalk the manganese under examina- tion contained. Another adulteration of manganese, that may, perhaps, be some- times practised, is the addition of some ores of iron. This impu- rity is less easily discovered. But if the iron be in such a state of oxidation as to be soluble in muriatic acid, the following process may discover it. Dissolve a portion, with the assistance of heat, in concentrated muriatic acid, dilute the solution largely with distilled water, and add a solution of crystallized carbonate of potash. The manganese will remain suspended, by the excess of carbonic acid, on mixing the two solutions, but the iron will be precipitated in the state of a coloured oxide. From an observation of Klaproth,* it appears that oxides of iron and manganese are separable by nitrous acid with the addition of sugar, which takes up the manganese only. * Essays, vol. i. page 572. « 38'' CHAPTER IV. APPLICATION OF CHEMICAL TESTS TO THE USES OF THE PARMER AND COUNTRY GENTLEMAN. The benefits that might be derived from the union of chemical skill, with the extensive observation of agricultural facts, are, per- haps, incalculable. At present, however, the state of knowledge a^mong farmers is not such as to enable them to reap much advan- tage from chemical experiments; and the chemist has, himself, scarcely ever opportunities of applying his knowledge to practical purposes in this way. It may, perhaps, however, be of use, to offer .1 few brief directions for the analysis of marls, lime-stones, &c« SECTION I. Lime. It is impossible to lay down any general rules respecting the fit- ness of lune for the purposes of agriculture; because much must depend on the peculiarities of soil, exposure, and other circum- stances. Hence a species of lime may be extremely well adapted For one kind of land and not for another. All that can be accom- plished by chemical meanS is to ascertain the degree of pflrity of the lime, and to infer, from this, to what kind of soil it is best adapted. Thus a lime, which contains much argillaceous earth, is better adapted than a purer one to dry and gravelly soils: and stiff clayey lands require a lime as free as possible from the Argillaceous ingredient. To determine the purity of time, let a given weight be dissolved in diluted muriatic acid. Let a little excess of acid be added, that no portion may remain undissolved owing to the deficiency of the solvent. Dilute with distilled water; let the insoluble part, if any, subside, and the clear liquor be decanted. Wash the sediment with farther portions of water, and pour it upon a filter, previously weighed. Dry the filter and ascertain its increase of weight, which will indicate how much insoluble matter the quantity of lime sub- mitted to experiment contained. It is easy to judge by the exter- nal qualities of the insoluble portion, whether argillaceous earth abounds in its composition. There is one earth, however, lately found in several lime-stones, which is highly injurious to the vegetation of plants, and is not discoverable by the foregoing process, being, equally with lime, soluble in muriatic acid. This earth is magnesia, which, by dl Vol. II.—3 C ,&b ANALYSIS OF LIME. VUIAP. IV. rect experiments,' has been ascertained to be extremely noxious to plants. Mr. Tennant, the gentleman to whom we owe this fact, was informed, that in the neighbourhood of Doncaster two kinds of lime were employed, one of which it was necessary to use very sparingly, and to spread very evenly; for it was said, that a large proportion, instead of increasing, diminished the fertility of the soil; and that, whenever a heap of it was left in one spot, all fer- tility was prevented for many years. Fifty or sixty bushels on an acre were considered to be as much as could be used with advan- tage. The other sort of lime, which was obtained from a village near Ferrybridge, though considerably dearer, froin> the distant carriage, was more frequently employed, on account of its supe- rior utility. A large quantity was never found to be injurious; and the spots which were covered with it, instead of being ren- dered barren, became remarkably fertile. On examining the com- position of these two species of lime, the fertilizing one proved to consist entirely of calcareous earth, and the noxious one of three parts lime and two magnesia. The presence of magnesia in lime proved, on farther investiga- tion, to be.a very common occurrence. The magnesian lime- stone appears to extend for 30 or 40 miles from a little south-west of Worksop, in Nottinghamshire, to near Ferrybridge, in York- shire, and it has also been found at Brcedo and Matlock, in Derby- shire, and in various other parts of England.* The magnesian lime-stone, according to Mr. Tennant, may easily be distinguished from that which is purely calcareous, by the slowness of its solution in acids, which is so considerable, that even the softest kind of the former is much longer in dissolving than marble; it has also frequently a'crystallized structure; and sometimes, though not always, small black dots may be seen dis- persed through it. In the countries where this lime stone is found, the lime is generally distinguished, from its effects in agri- culture, by«the farmers, as hot lime, in opposition to the purely- calcareous, which they term mild. To ascertain, by chemical means, the composition of a lime or time-stone suspected to contain magnesia, the following is thp easiest, though not the most accurate, process. Procure a Flo- rence flask, clean it well from oil by a little soap-lees or salt of tartar and quicklime mixed, and break it off, about the middle of the body, by setting fire to a string tied round it and moistened with oil of turpentine. Into the bottom part of this flask put 100 grains of the lime or lime-stone, and pour on it, by degrees, half an ounce of strong sulphuric acid. On each affusion of acid a vio- lent effervescence will ensue; when this ceases, stir the acid and lime together with a small glass tube, or rod, and place the flask in an iron pan, filled with sand. Set it over the fire, and continue the heat till the mass is quite dry. Scrape off the dry mass, weigh it, * See Phillips's Geology of England and Wale, page 80- t-be-I-. II. ANALYSIS OF MARLS. 387 and put it into a wine glass, which may be filled up with water. Stir the mixture, and when it has stood half an hour, pour the whole on a filtering paper, placed on a funnel, and previously weighed. Wash the insoluble part with water, as it lies on the fil- ter, and add the washings to the filtered liquor. To this liquor add a solution of half an ounce of salt of tartar in water, when, if magnesia be present, a very copious white sediment will ensue; if lime only, merely a slight milkiness. In the former case, heat the liquor by setting it in a tea-cup near the fire; let the sediment sub- side; pour off the clear liquor, which may be thrown away, and wash the white powder repeatedly with warm water. Then pour it on a filter of paper, the weight of which is known, dry it, and weigh. The result, if the lime-stone has been submitted to expe- riment, shows how much carbonate of magnesia was contained in the original stone, or, deducting 60 per cent, how much pure magnesia 100 parts of the lime-stone contained. If the burnt lime has been used, deduct from the weight of the precipitate 60 per cent, and the remainder will give the weight of the magnesia m each 100 grains of the burnt lime. SECTION II. Analysis of Marls. The ingredient of marls, on which their fitness for agricultural purposes depends, is the carbonate of lime. It is owing to the presence of this earth that marls effervesce on the addition ot acids, which is one of their distinguishing characters. In ascer- taining whether an effervescence takes place, let the marl be put into a class, partly filled with water, which will expel a portion at air contained mechanically in the marl, and thus obviate one source of fallacy. When the marl is thoroughly penetrated by the water, add a little muriatic acid, or spirit of salt. If a discharge of air should ensue, the marly nature of the earth is sufficiently cstab- llSTodfind the composition of a marl, pour a few ounces of diluted muriatic acid into a Florence flash, place them in a scale, and let Sem be balanced. Then reduce a few ounces of dry marl into powVr%nd let this powder be carefully and gradually thrown into the flask, until, after repeated additions, no farther) efferves- cence is perceived. Let the remainder of the powdered marl be weighed, by which the quantity projected will be known Let the balance be then restored. The difference of weight between the Quantity projected and that requisite to restore the balance, will sW the* weight of air lost during effervescence. If the loss amount to 13 per cent, of the quantity of marl projected, or from 3.88 ANALYSIS OF MARLS. CHAP. IV 13 to 32 per cent, the marl assayed is ealcareous marl, or marl rich in calcareous earth. Clayey marls, or those in which the argillaceous ingredient prevails, lose only 8 or 10 per cent, of their weight by this treat- ment, and sandy marls about the same proportion. The presence of much argillaceous earth may be judged by drying the marl, af- ter being washed with spirit of salt, when it will harden and form a brick. To determine, with still greater precision, the quantity of cal- careous earth in a marl, let the solution in muriatic acid be filter- ed, and mixed with a solution of carbonate of potash, till no farther precipitation appears. Let the sediment subside, wash it well with water, lay it on a filte", previously weighed, and dry it. The weight of the dry mass will show how much carbonate of liic< the quantity of lime submitted to experiment ccntcined. APPENDIX, CONSISTING OF VARIOUS USEFUL TABLES. No. I. CORRESPONDENCE BETWEEN ENGLISH AND FOREIGN WEIGHTS AND MEASURES. I.—English Weights and Measures. Troy Weight. Pound. Ounces. Drms. Scruples. Grains. Grammes. 1 ZZ 12 ZZ 96 ZZ 288 ZZ 5760 ZZ 372.96 1 ZZ 8 ZZ 24 ZZ 480 — 31.08 1 — 3 — 60 ZZ 3.885 1 ZZ 20 ZZ 1.295 1 ZZ 0.06475 Avoirdupois Weight. Pound. Ounces. Drms. Grains. Grammes. 1 ZZ 16 ZZ 256 ZZ 7000. ZZ 453 25 1 ZZ 16 ZZ 437.5 ZZ 28.328 1 ZZ 27.34375 ZZ 1.7705 Vol.—II. 3 D 390 APPENDIX Measures. Gal. Pints. Ounces. Drms. Cub. Inch Litres. I ZZ 8 ZZ 128 = 1024 ZZ 231. ZZ 3.78515 I ZZ 16 ZZ 128 ZZ '28.875 ZZ 0.47398 1 ZZ 8 ZZ 1.8047 ZZ 0.02957 1 ZZ 0.2256 ZZ 0.00396 N. B.—The English ale-gallon contains 282 cubical inches. The wine gallon contains 58176Troy grains; and the wine pint 7272 Troy grains. II.—German. 71 lbs. or grs. English troy - - - ZZ 74 lbs. or grs. German apothecaries weight. I oz. Nuremberg, medic, weight - ZZ 7 dr. 2 sc. 9 gr. English. l mark Cologne ------ zz 7oz. 2dwt. 4gr. English troy. III.—Dutch. 1 lb. Dutch ZZ 1 lb. 3 oz. 16 dwt. 7 gr. English troy. 787^ lbs. Dutch ZZ 1038 lbs. English troy. IV.-—Swedish Weights and Measures, used by Bergman and Scheele. The Swedish pound, which is divided like the English apothecary, or troy, pound, weighs 6556 grs. troy. The kanne of pure water, according to Bergman, weighs 42250 Swedish grains, and occupies 100 Swedish cubical inches. Hence the kanne of pure water weighs 48088.719444 English troy grains, or is equal to 189.9413 English cubic inches; and the Swedish longitudinal inch is equal to 1.238435 English longitudinal inches. From these data, the following rules are deduced : 1. To reduce Swedish longitudinal inches to English, multiply by 1.2384, or divide by 0.80747. 2. To reduce Swedish to English cubical inches, multiply by 1.9, or divide by 0.5265. 3. To reduce the Swedish pound, ounce, drachm, scruple, or grain, to the corresponding English troy denomination, multiply by 1.1382, or divide by .8786. 4. To reduce the Swedish kannes to English wine pints, multi- ply by .1520207, or divide by 6.57805. 5. To reduce Swedish kannes to English wine gallons, multiply by .82225, or divide by 1.216. 6. The lod, a weight sometimes used by Bergman, is the 32d part of the common Swedish pound of L6 oz. and the 24th part of the pound of 12 oz. Therefore to reduce it to the English troy pound, multiply by .03557, or divide by 28.1156. OLD FRENCH WEIGHTS. 391 V.— Correspondence of English Weights and Measures with those used in France before the Revolution. § 1.—WEIGHTS. . The Paris pound, poids de marc of Charlemagne, contains 9216 Paris grains; it is divided into 16 ounces, each ounce into 8 gros, and each gros into 72 grains. It is equal to 7561 English troy grains. The English troy pound of 12 ounces contains 5760 English troy grains, and is equal to 7021 Paris grains. The English avoirdupois pound of 16 ounces contains 7000 En- glish troy grains, and is equal to 8532.5 Paris grains. To reduce Paris grains to English troy grains, divide *") by.......-.-■"."."" ",". U 1.2189 To reduce English troy grains to Paris grains multiply f by................J To reduce Paris ounces to English troy, divide by - ? { 015734 To reduce English troy ounces to Paris, multiply by 5 Or the conversion may be made by means of the following tables : 1.__To reduce French to English Troy Weight. The Paris pound ZZ 7561 ~\ The ounce ZZ 472-5625 v> English troy grains. The gros ZZ 59.0703 f b ' b The grain ZZ .8204J 2.__To reduce English Troy to Paris Weight. The English troy pound of 12 > __ 7031. ounces.......5 " The troy ounce ------ ZZ 585.0833 The drachm of 60 grains - ZZ 73.1354 ' paris -ns The penny weight or denier of > __ 29.2541 I 24 grains......S The scruple of 20 grains - ZZ 24.3784 The grain......# = 1-™*J 3.__To reduce English Avoirdupois lo Paris Weight. The avoirdupois pound of 16 1 — g538 1 ounces, or 7000 troy grains $ "" f Paris Srains- The ounce...... 533.6250 J K II.--LONG AND CUBICAL MEASURES. To reduce Paris running feet, or inches, into En-~} glish,multiply by " 7 ; " ." - " ". |> 1.065977 English running feet, or inches, into Pans di- j vide by.......* " " * * J 392 APPENDIX. Te reduce Paris cubic feet, or inches to English,"") multiply by..........Li 211278 English cubic feet, or inches, to Paris, divide \ by.............J Or by means of the following tables : 4.—To reduce Paris Long Measure to. English. The French toise ZZ 6.3945 English feet. The Paris royal foot of 12 inches'zz 12.7977") The inch.......ZZ 1.0664 [r .... . The line, or l-12th of an inch - ZZ .0888 > EnShsh inches- The 1-12th of aline - - - - ZZ .0074 J 5.— To reduce English Long Measure to French. The English foot.....ZZ 11.2596^ The inch.......ZZ .9383 I The 1-8th of an inch - - - - zz .1173 j> Paris inches. The 1-10th of an inch - - - ZZ .0938 I The 1-13th of an inch - -► - ZZ .0782J 6.— To reduce French Cube Measure to English. I ZZ 1.211278 fEnghsh T 2093088384"J . 3 < cubical < Y ii ZZ .000700 (jett, or I 1.211378 J The Paris cube foot - - - S "i cubical <{ ^ in. The cubic inch 7.—To reduce English Cube Measure to French*. The English cube foot, or > 1427.48641 1728 cubical inches S I f . , • , rr.. u- i • u ___ ontr> /> French cubical The cubical inch - - - — .8260 \ . , The cube tenth - - - zz ^0008 J incnes- $.111--MEASURE OF CAPACITY. The Paris pint contains 58.145f English cubical inches, and the English wine pint contains 28.875 cubical inches; or the Paris pint * To convert the weight of a French cubic foot, of any particular substance given in French grains, into the corresponding weight of an English cubic foot in English troy grains, multiply the French grains by 0.6773181, and the pro- duct is the number of English troy grains contained in an English cubic foot of the same substance. f It is said by Belidor, Archit. Hydraul. to contain 31 oz. 64 grs. of water, which makes it 58.075 English inches ; but, as there is considerable uncertainty in the determinations of the weight of the French cubical measure of water, owing to the uncertainty of the standards made use of, it is better to abide by Mr. Everard's measure, which was made by the Exchequer standards, and by the proportions of the English and French foot, as established by the French Academy and Royal Society. According to Baume, the Paris pint contains 32 French ounces of water, at the temperature of 54.5W of Fahrenheit; which would make it equal to 59.729 English cubical inches. OLD FRENCH MEASURES. 393 contains 2.0171082 English pints, and the English pint contain? .49617 Paris pints ; hence, To reduce the Paris pints to the English, multi- ~] ply by.........- - - L 2 0171082 ' To reduce the English pints to the Paris, divide \ by.............J The scptisr of Paris is 773^ French, or 9370.45 English cubical inches; and the muid is 92832 French, or 912445.4 English cubi- cal inches. 394 APPENDIX, VI.—Table sfiowing the Comparison between French and English Grains. (Poid de Marc.) French grs. = English grs. English grs. = French grs. * I 0.8203 1 1.2189 2 1.6407 2 2.4378 3 2.4611 3 3.6568 4 3.2815 4 4.8757 5 4.1019 5 6.0947 6 4.9223 6 7.3136 7 5.7427 7 8.5325 8 6.5631 8 9.7515 9 7.3835 9 10.9704 10 8.203 10 12.189 20 16.407 20 24.378 30 24.611 30 36.568 40 32.815 40 48.757 50 41.019 50 60.947 60 49.223 60 73.136 70 57.427 70 85 325 80 65.631 80 97.515 90 73.835 90 109 704 100 82.03 100 121.89 200 164.07 200 243.78 300 246.11 300 365.68 400 328.15 400 487.57 500 410.19 500 609.47 600 492.23 600 731.36 700 574.27 700 853.25 800 656.31 800 975.15 900 738.35 900 1097.04 1000 820.3 1000 1218.9 2000 1640.7 2000 2437.8 3000 2461.1 3000 3656.8 4000 3281.5 4000 4875.7 5000 4101.9 5000 6094.7 6000 4922.3 6000 7313.6 7000 5742.7 7(;oo 8532.5 8000 6563.1 8000 9751.5 90C0 7383.5 9000 10970.4 * 10.000 8023.0 10 000 12189.0 * Per Farey (Nicholson's Journal, xxii. 338), 1 grain French = 0.8204 En- glish ; 10,000 ditto = 8204 ditto. FRENCH AND ENGLISH CUBICAL INCHES. 195 VII.—Table showing the Comparison between French and English Cubical Inches. Cubic Inches. Cubic Inches. French. = English. English. = French. 1 1.2136 1 0.8239 2 2.4272 2 1.6479 3 3.6408 3 2.4719 4 4.8544 4 3.2958 5 6.0681 5 4.1198 6 7.2817 6 4.9438 7 8.4953 7 5.7677 8 8.7089 8 6.5917 9 70.9225 9 7.4157 10 12.136 10 8.239 20 24.272 20 16.479 30 36.408 30 24.719 40 48.544 40 32.958 50 60.681- 50 41.198 60 72.817 60 49.438 70 84.953 70 57.677 80 97.089 80 65.917 90 109.225 90 74.157 100 121.36 100 82.39 200 342.72 200 164.79 300 364.08 300 247.19 400 485.44 400 329.58 ' 500 606.81. 500 411.98 600 728.17 600 494.38 700 849.53 700 576.77 800 970.89 800 659.17 900 1092.25 900 741.57 1000 1213.6 1000 823.9 2000 2427.2 2000 1647.9 3000 3640.8 3000 2471.9 4000 4854.4 4000 3295 8 5000 6068.1 5000 4119.8 6000 7281.7 6000 4943.8 • 7000 8495.3 7C00 5767.7 8000 9708.9 8000 6591.7 9000 10922.5 9000 7415.7 J0.000 12136.0 10,000 8239.0 ✓ •• 396 APPENDIX. VlU.—Ncw French Weights and Measures (calculated by Dr. Duncan, jun.). 1—Measures of Length : the Metre being at 32°, and the Foot at 62°. English inches. Millimetre .03937 Centimetre — .39371 Decimetre 3.93710 Metre* 39.37100 Mil. Fur. -Yds. Feet. In. Decametre ~~ 393 71000 ZZ 0 0 10 2 9.7 Hecatometre — 3937 10000 ZZ 0 0 109 1 1 Kilometre 39371.00000 ZZ 0 4 213 1 10.2 Myriometre 393710.00000 ZZ 6 1 156 0 6 2 —Measures of Capacity. Cubic inches. Millilitre ~~ .06103 Centilitre *""" .61028 English. Decilitre —- 6.10280 Tons. Hogs Wine fl. Pints. Litre 61.02800 ZZ 0 0 0. 2.1133 Decalitre — 610 28000 ZZ 0 0 2. 5.1352 Hecatolitre — 6102.80000. ZZ 0 0 26.419 Kilolitre — 61028 00000 ZZ 1 0 12.19 Myriolitre 610280.00000 = 10 1 58.9 3.—Measures of Weight. English grains. Milligramme I .0154 Centigramme I .1544 Decigramme ; 1.5444 Avoirdupois. Gramme Z j 5.4440 , Poun. Oun. Drm. Decagramme Z 154.4402 ZZ ' 0 ' 0 5 65 Hecatogramme Z I 1544.4023 ZZ' 0 3 85 Kilogramme I 154440234 ZZ 2 3 5 Myriogramme I 1544402344 ZZ 22 1 2 * Recently determined by Captain Kater to be 39.37079 inches. (Phil. Trans, 1813, p. 109.) CORRECTION OF THE VOLUME OF GASES. 397 IX.—Reduction of the Ounce Measures used by Dr. Priestley to Cubical Inches. Ounce French cubical English cubical Measures. Inches. Inches. L 1 567 1.898 2 3 134 3.796 3 4.701 5.694 4 6 268 7.592 5 7.835 9.490 6 9.402 11.388 7 10.969 13.286 8 12.536 15.184 9 14.103 17082 10 15.670 18.980 20 31.340 37.960 30 47.010 56.940 40 62.680 75.920 50 78.350 94.900 60 94.020 113.880 70 109.690 132.860 80 125.360 151.840 90 141.030 170.820 100 156.700 189.800 1000 1567.000 1898.000 X.—Rules for reducing the Volume of Gases to a mean Height of the Barometer, and mean Temperature. 1. From the space occupied by any quantity of gas under an obserued degree of pressure, to infer what its volume would be under the mean height of the barometer, taking this at 30 inches, as is now most usual. This is done by the rule of proportion ; for, as the mean height is to the observed height, so is the observed volume to the volume required. For example, if we wish to know what space would be filled, under a pressure of 30 inches of mercury, by a quantity of gas, which fills 100 inches, when the barometer is at 29 inches, 30 : 29 :: 100 : 96.66. The 100 inches would, therefore, be reduced to 96.66. 2. To estimate what would be the volume of a portion of gas, if brought to the temperature of 60° Fahrenheit- Divide the whole quantity of gas by 480 ; the quotient will show the amount of its expansion or contraction by each degree of Fahrenheit's thermometer. Multiply this by the number of de- grees, which the gas exceeds, or falls below, 60°. If the tempera- ture of the gas be above 60°, subtract, or if below 6o°, add, the pro- duct to the absolute quantity of gas ; und the remainder in the first case, or sum in the second, will be the answer. Thus, to find what Vol.—II. 3 E 398 APPENDIX. space 100 cubic inches of gas at 50° would occupy, if raised to 60c, divide 100 by 480; the quotient 0.208 multiplied by 10 gives 208, which added to 100 gives 102.08 the answer required. If the tem- perature had been 70°, and we had wished to know the volume which the gas would have occupied at 60*, the same number 2.08 must have been subtracted from 100, and 97.92 would have been the answer. 3. In some cases, it is necessary to make a double correction, or to bring the gas to a mean both of the barometer and thermometer. We must then first correct the temperature, and afterwards the pressure. Thus to know what space 100 inches of gas at 70° Fah- renheit, and 29 inches barometer, would fill at 60° Fahrenheit and 30 inches barometer, we first reduce the 100 inches, by the second process, to 97.92. Then by the first 30 : 29 :: 97.92 : 94.63. Or 100 inches thus corrected, would be only 94.63. 4. To ascertain what would be the absolute weight of a given volume of gas at a mean temperature, from the known weight of an equal volume at any other temperature; first, find by the second pro- cess what would be its bulk at a mean temperature, and then say, as the corrected bulk is to the actual weight, so is the observed bulk to the number required. Thus if we have 100 cubic inches ot ■(, gas, weighing 50 grains, at 50° Fahrenheit, if the temperature were raised to 60° they would expand to 102.08. And 102.08 : 50 :: 100 : 49. Therefore 100 inches of the same gas at 60° would weigh 49 grains. 5. To learn the absolute weight of a given volume of gas under a mean pressure, from its known weight under an observed pressure, say, as the observed pressure is to the mean pressure, so is the ob- served weight to the corrected weight. For example, having 100 inches of gas which weigh 50 grains under a pressure of 29 inches, to know what 100 inches of the same gas would weigh, the barome- ter being 30 inches, 29 : 30 :: 50 : 51.72. Then 100 inches of the same gas, under 30 inches pressure, would weigh 51.72 grains. 6. In some cases it is necessary to combine the two last calcula- tions. Thus, if 100 inches of gas at 50° Fahrenheit, and under 29 inches pressure, weigh 50 grains, to find what would be the weight of 100 inches at 60° Fahrenheit, and under 30 inches of the barome- ter, first correct the temperature, which reduces the weight to 49 grains. Then, 29 : 30 :: 49 : 50.7 One hundred inches, therefore, would weigh 50.7 grains. SPECIFIC GRAVITIES. 399 XI. Specific Gravities of Solid and Liquid Substances Spe Gi Specific 5rav GEMS. Diamond, white, oriental Topaz, qriental - - - Sapphire, oriental - - Garnet, Bohemian - - Beryl, oriental - - - Hyacinth, common - - Emerald, from Peru Cry sol it he, from Brasil - Amethyst, oriental - • Ruby, oriental - - ■ STONES, &C. Ponderous spar - - ■ Porphyry - - - - Potash - - - - Lime - - - - Magnesia - - - Alumine - - - Barytes ... Sulphate of potash .----------alumine ----------- zinc - — iron - - copper - Nitrate of potash Muriate of soda - - Acetate of lead - - Supertartrate of potash Sub-borate of Soda - Carbonate of potash - ____.-------soda ammonia 3.5212 4.0106 3.994! 4.1888 3.5489 2.6873 2.7755 2.6923 2.65 1 4 2833 STONES, &C. Jasper, brown - - - Granite, Egyptian - - Rock-crystal - - - - ;Chalcedony, bright - - Currara marble - - " Alabaster, oriental - - Carnelian - - - - - Slate, common, for roofs Flint...... Agate, oriental - - - Portland-stone - Serpentine, green, Italian 4 4300 lOpal, noble J2.7651 iPumice-stone Specific Gtav. 2 6911 2.6541 2.6530 2 6640 27168 2.73u2 2 6137 2 8535 2.5941 2.5901 2 53' 2 4295 2.144 0.9145 SALTS. Hassenfratz. Kirwan. jMutehenbrock. Newton. 1.7085 1.5233 0.3460 0 8200 2.3740 2.4073 1 7109 1.9120 1.8399 2.1943 1.9369 2.2001 2.3450 1.9153 1 7230 2.0120 1.3591 0.9660 46215 2 3908 2 3298 2.0000 4.0000 2.636 2.23 1.933 1 421 1.8245 2.3700 2.398 1 7260 19 1.88 1.901 2.0835 2.3953 1.8745 1.7170 2.749 1.5026 1714 1.712 1.900 2.143 1 714 • For the specific gravities of the metals, see Table of the Qualities of Metals, near the close of this Appendix. 400 APPENDIX. Table of Speciflc Gravities of Solid and Liquid Substances,^— Continued. GLASSES AND VITRIFICA- TIONS. Green bottle-glass - - French crystal-glass French mirror-glass, from St. Gobin - - - - English flint-glass - - China porcelain - - - INFLAMMABLES. Roll-sulphur - - - - Phosphorus - - - - Pit-coal..... Amber...... Heaviest charcoal - - Mineral Naphtha - - Camphor - - - - - Liquid ammonia - - - WATERS. Distilled water - - - Sea water..... Water from the Asphaltic Sea...... ACIDS. Sulphuric acid of com- merce ..... Sulphuric acid, real - - Nitric acid .... Muriatic acid - - - - Concentrated acetic acid SPIRITUOUS LIQUIDS. Madeira wine - - - Cyder..... Brown beer - - - - Burgundy wine - - - Champagne wine - - Brandy ------ Alcohol*..... Nitric ether - - - - Acetic ether - - - - Sulphuric etherf - - - Muriatic ether - - - Specific Grav. 2 732 2.89^2 2.4882 3.3203 23847 1.9907 1 714 1.3292 1.078U 0.441 0.7,8 09887 0.8970 1.0000 1.0263 i.2403 1.8500 2.1250 1.5800 1.1940 1.0626 1.0382 1.0181 1.0338 0.9915 0.962 0.8371 0.8293 0.9088 08664 0.7396 0.7296 ETHEREAL OILS. Oil of cinnamon - - Oil of cloves - - - Oil of lavender - - Spirit of turpentine - FAT OILS. Linseed oil - - - Poppy oil - - - - Oil of sweet almonds Olive oil - - - - ANIMAL FLUIDS. Asses' milk - - Cows' milk - - Human milk - - Human urine - - ANIMAL FATS. Spermaceti - - Butter - - Tallow - - - - Mutton suet - - Train oil - - - Hogs' lard - - - Ivory - - - - Bees'wax - - - . GUMS. Common gum Gum Arabic - - ■ Gum tragacanth - GUM resins. Asafcetida..... Scammonium, from Smyr na...... Galbanum..... resins. Guaiacum - - Jalap ... Ammoniacum Benzoe - - - • Per Chaussier 0.7980. f Per Lovitz 0.6320. SPECIFIC GRAVITIES. Table of Speciflc Gravities of Solid and Liquid Substances,— Continued RESINS. Sandaric - - - - White resin - - - Colophony - - - - Mastich - - - - Copal, transparent - Elastic resin - - - INSPISSATED JUICES. Aloe succotrina - - Opium..... Specific Grav. 1.0920 1.0819 1.0441 1.0742 1.0452 0.9335 1 3795 1.3366 WOODS. Lignum guaiacum Box wood, Dutch French box wood Ebony - - - - Heart of old oak - - - ♦ WOODS. Mahogany ( - ■ - - Olive tree - - - - Mulberry tree, Spanis Btech tree - - - 'Yew tree, Spanish iApple tree Plum tree Maple tree - - - Cherry tree - - - Quince tree - - - Orange tree - - - Walnut tree - - - 1.3330 Pear tree - - - - 1 3280 Cypress, Spanish 0912 Pine tree - - - - 1.2090 White Spanish poplar I.170w oork..... Specific Gray. tree 1.06 0.9270 0.8970 0.8520 0.8070 0.7930 0.7850 0.7550 0.7150 0.7050 0.7050 0.6710 0.6610 0.6440 0.5500 0.5294 0.2400 XII.__Rules for Calculating the Absolute from the Speciflc Gravities of Bodies. In 1696, Mr. Everard, balance maker to the Exchequer, weighed before the commissioners of the House of Commons 2145.6 cubical inches, by the Exchequer standard foot, of distilled water, at the temperature of 55° of Fahrenheit, and found it to weigh 1131 oz. 14 dts. troy, of the Exchequer standard. The beam turned with 6 grs. when loaded with 30 pounds in each scale. Hence, supposing the pound avoirdupois to weigh 7000 grs. troy, a cubic foot of water weighs 62£ pounds avoirdupois, or 1000 ounces avoirdupois, want- ing 106 grains troy. And hence, if the specific gravity of water be called 1000, the proportional specific gravities of all other bodies will nearly express the number of avoirdupois ounces in a cubic foot. Or, more accurately, supposing the specific gravity of water expressed by l,and of all other bodies in proportional numbers, as the cubic foot of water weighs, at the above temperature, exactly 437489.4 grains troy, and the cubic inch of water 253.175 grains, the absolute weight of a cubical foot or inch of any body in troy grains may be found by multiplying their specific gravity by either of the above numbers respectively. . By Everard's experiment, and the proportions of the English and French foot, as established by the Royal Society and French Academy of Sciences, the following numbers are ascertained. Paris grains in a Paris cube foot of water - - - = 645511 English grain* in a Paris cube foot of water - - = 529922 402 APPENDIX. Paris grains in an English cube foot of water - - — 533247 English grains in an English cube foot of water - — 437489.4 English grains in an English cube inch of water - ZZ 253.175 By an experiment of Picard with the measure and weight of the Chatelet, the Paris cube foot of wa- ter contains of Paris grains ...... ZZ 641326 By one of Du Hamel, made with great care - - ZZ 641376 By Homberg............ZZ 641666 These show some uncertainty in measure or in weights ; but the above computation from Everard's experiment may be relied on, because the comparison of the foot of England with that of France was made by the joint labour "of the Royal Society of Lon- don and the French Academy of Sciences: it agrees likewise very nearly with the weight assigned by M. Lavoisier, 70 Paris pounds to the cubical foot of water. XIII.—Table for reducing the Degrees of Baume's Hydrometer to the Common Standard. Baume's Hydrometer for Liquids lighter than Water. Temperature 55° Fahrenheit, or 10° Reaumur. Deg. Sp. Gr. Deg. Sp. Gr. Deg. Sp. Gr. Deg. Sp. Gr. 10 - - 1.000 18 - - .942 26 - - .892 34 - - .847 11 - - .990 19 - - .935 27 - - .886 35 - - .842 12 - - .985 20 - - .928 28 - - .880 36 - - .837 13 - - .977 21 - - .922 29 - - .874 37 - - .832 14 - - .970 22 - - .915 30 - - .867 38 - - .827 15 - - .963 23 - - .909 31 - - .861 39 - - .822 16 - - .955 24 - - .903 32 - - .856 40 - - .817 17 - - .949 25 - - .897 33 - - .852 Baume's Hydrometer for Liquids heavier than Water. Deg. . 0 n 6 9 12 15 18 Temperature 55° Fahrenheit, or 10 Reaumur. Sp. Gr. - 1.000 - 1.020 - 1.040 - 1.064 - 1.089 - 1.114 - 1.140 Deg. 21 24 27 30 33 36 39 Sp. Gr. - 1.170 - 1.200 - 1.230 - 1.261 - 1.295 54 - 1.333 j 57 - 1.373 60 Deg. 42 45 48 51 Sp. Gr. ■ 1.414 ■ 1.455 - 1.500 - 1.547 - 1.594 - 1.659 - 1.717 Deg. 63 66 69 72 Sp. Gr. - 1.779 - 1.848 - 1.920 - 2.000 403* 80RRESP0NDENCE OF THERMOMETER'S. No. II. ADMEASUREMENT AND EFFECTS OF HEAT I,—Correspondence between different Thermometers. Fahrenheit's thermometer is universally used in this kingdom. In this instrument the range between the freezing and boihrig points of water is divided into 180°; and as the greatest possible degree of cold was supposed to be that produced by mixing snow or muriate of soda, it was made the zero. ' Hence the freezing point became 32°, and the boiling point 212°. The Centrigrade thermometer places the zero at the freezing point, and divides the range between it and the boiling point into 100°. This has long been used in Sweden under the title of Cel- sius's thermometer. . Reaumur's thermometer, which was formerly used in 1' ranee, divides the space between the freezing and boiling of water into 80°, and places the zero at the freezing point. Wedgwood's pyrometer is only intended to measure very high temperatures. Its zero corresponds with 1077° of Fahrenheit's, and each degree of Wedgwood is equal to 130° of Fahrenheit. De Lisle's thermometer is used in Russia. The graduation be- gins at the boiling point, and increases towards the freezing point. The boiling point is marked 0,and the freezing point 150°. Therefore 180° F. = 100° C. = 80° R. = 150° D =B W. I. To reduce centrigrade degrees to those of Fahrenheit, multi- ply by 9 and divide by 5, and to the quotient add 32, that is, —^—- + 32 = F- F-22X5 2. To reduce Fahrenheit's degrees to centrigrade----y---=C. 3. To reduce Reaumur's to Fahrenheit's, we have the following formula, —'-g----(- 32 = F. F — 32 X 4 4. To convert Fahrenheit to Reaumur, ——§----= R- 6. To reduce De Lisle's degrees underlie boiling point, we have p _ 212 — P" x 6. To reduce those above the boiling point, F.= 212 + 5 P. X 5~ 6. And, inversely, to reduce Fahrenheit's degrees to De Lisle's, under the boiling point, 1Q6° ~ * F' =* D-; above the boiling point, F.X5- 1060 _ D *404 APPENDIX. , 7. To reduce Wedgwood's degrees to those of Fahrenheit, we have W. X 130 + 1077 = F. P — 1077 8. Inversely, to reduce Fahrenheit to Wedgwood,-^——---= W. Table showing the Correspondence between the Degrees of Fahren- heit's Thermometer and the new Scale of Mr. Dalton. (See vol. i. p. 81.) Fahrenheit's Fahrenheit's Scale, True equal In- Scale. corrected for the tervals of Tem- Expansion of Glass. perature. — 40. ...... ......— 175 — 21.12...... ......—.68 — 17.06...... ......— 58 — 12.96...... ......— 48 — 8.52...... ......— 38 — 3.76...... .......— 28 + 1.34...... ......— 18 6.78 ------ -..-.__ 8 12.63...... ......+ 2 18.74............. 12 25.21.....- ......' 22 32. ......32. _-....- 32 39.1.....39.3...... 42 46.6......47. ...... 52 54.44......55....... 62 62.55......63.3...... 72 71.04......72. ...... 82 79.84......81....... 92 89.02......90.4...... 102 98.49......101.1......- 112 108.3 -.....110. ...... 122 118.5......120.1...... 132 129. ..-.'-- 130.4...... 142 139.9......141.1 ...... 152 151. ......152....... 162 162.4......163.3...... 172 177.4......178....... 182 186.5......186.9...... 192 199. ......199.2...... 202 212. ......212. ...... 212 359.1...... ...... 312 539.8...... ...... 412 754.7 ------- ...... 512 1000. ...... ...... 612 1285. ...... ...... 712 TABLE OF THE EFFECTS OF HEAT. 403 II.—-Table of the Effects of Heat. + Fahrenheit. — 55 46 39 36 22 11 7 I 16 20 23 25 28 30 32 36 46 64 40 82 97 90 104 109 112 127 149 145 155 212 b'ahren. Wedg. 234 235 383 303 334 442 160 Vol. I.—Freezing Points of Liquids. Strongest nitric acid freezes (Cavendish) Ether and liquid ammonia Mercury Sulphuric acid (Thompson) Acetous acid % 2 Alcohol, 1 water Brandy Strongest sulphuric acid (Cavendish) Oil of turpentine (Macquer) Strong Wines Fluoric acid Oils bergamot and cinnamMi Human blood Vinegar Milk Oxymuriatic acid Water Olive oil Sulphuric acid, specific gravity 1.78 (Keir) Oil of anniseeds, 50 (Thompson) 2.—Melting Points of Solids. Equal parts of sulphur and phosphorus Adipocire of muscle Lard (Nicholson) Phosphorus Resin ofjjile Myrtle wax (Cadet) Spermaceti (Bostock) Tallow (Nicholson) 92 (Thompson) Bees' wax Ambergris (La Grange) Bleached wax (Nicholson) Bismuth 5 parts, tin 3, lead 2 Sulphur (Hope) 212 (Fourc.) 185 (Kirw.) Adipocire of biliary calculi (Fourcroy) Tin and bismuth, equal parts Camphor Tin 3, lead 2, or tin 2, bismuth 1 Tin (Chrichton) 413 (Irvine) Tin 1, lead 4 II. 3F *°6 APPENDIX. Wedg. 21 27 22 32 130 150 154 158 160 + 170 Bismuth (Irvine) Lead (Chrichton) 594 (Irv.) 540 (Newton} Zinc Antimony Brass Copper Silver Gold Cobalt Nickel Soft nails + Iron Manganese Platinum, tungsten, molybdena, uranium, titan: 3i Solids'and Liquids volatilized Ether boils Liquid ammonia boils Camphor sublimes (Venturi) Sulphur evaporates (Kirwan) Alcohol boils, 174 (Black) Water and essential oils boil Phosphorus distils (Pelletier) Muriate of lime boils (Dalton) Nitrous acid boils Nitric acid boils White arsenic sublimes Metallic arsenic sublimes Phosphorus boils Oil of turpentine boils, about 212° (Dalton) Sulphur boils * Sulphuric acid boils (Dalton) 546 (Black) Linseed oil boils, sulphur sublimes (Davy) Mercury boils (Dalton) 644 (Secondat) 600 (Black) 672 (Irvine) 4. Miscellaneous Effects of Heat. Greatest cold produced by Mr. Walker Natural cold produced at Hudson's Bay Observed on the surface of the snow at Glasgow, 1780 At Glasgow, 1780 Equal parts, snow and salt Phosphorus burns slowly MISCELLANEOUS EFFECTS OF HEAT. 407 Wedg. 1 + 2 6 14 40 57 70 86 94 102 105 112 114 121 124 J25 150 185 Vinous fermentation begins lo 135 Animal putrefaction to 80, Summer heat in this climate Vinous fermentation rapid, acetous begins Pnosphorus burns in oxygen, 104 (Gottling) Acetification ceases to 100 Animal temperature Feverish heat Phosphorus burns vividly (Fourcroy) 143 (Thorn- *on) Mbumen coagulates, 156 (Black) Sulphur burns slowly Lowest heat of ignition of iron in the dark Hydrogen burns, 1000 (Thomson) Charcoal burns (Thomson) Iron red in twilight Iron red in day light Azotic gas burns Enamel colours burned Diamond burns (M'Kenzie) 30 W. = 5000 F (Morveau) Delft ware fired Working heat of plate glass Flint glass furnace Cream-coloured ware fired Worcester china vitrified Stone ware fired Chelsea china fired Derby china fired Flint glass furnace greatest heat Bow china vitrified Plate glass greatest heat Smith's forge Hessian crucible fused Greatest heat observed 408 APrENDIX. III.—Table of the Force of Steam at different Temperatures of Fahrenheit's Scale from actual Experiment. (Betancourt in Proney's Architecture Hydraulique.) Tempera- ture. 32 • 42 ■ 52 62 72 82 92 102 112 122 132 142 152 Force in English Inches of Mercury. - - 0 - - .08 - - • .21 - - .38 . - - .58 . - - .87 . - - 1.26 . - - 1.74 - - - 2.37 . - - 3.16 . . - 4.16 - - - 5.43 . - - 7.00 Tempera- ture. 162 - 172 - 182 - 192 - 202 - 212 - 222 - 232 ■ 242 ■ 252 • 262 • 272 ■ 282 • Force in English Inches of Mercury. - - 9.07 - - 11.0 - - 14.9 - - 18.7 - - 23.7 - - 29.8 . - - 37.4 46.5 57.3 69.7 83.6 97.1 108. > , i i i i i i •••••• ' , , , , , i i ■ • i » • ■ ■ ^5 •fe JJ a.oiCT.a»a>o>o-tJ2^-!:-Z2SNM tJi —' M lO >D <0 N N OOOOO £ Cn O — CM «0 .H V5 «3 <£> <0 I I I I I I 1 I I > < I • < I I I I I I I I • ■ u c* co ■* *n 60 179.10 170.10 29610 176.90 186.50 153.00 table of chemical equivalents. 4£1 The following are the data on which the above Table is founded: 1) 2, 3. Tne specific gravities of oxygen and hydrogen gases are taken on the authority of Biot and Arago; and their propor- tions in water at 88.286 to 11.714, which numbers are in the ratio of 10 to 1 327. 4, j. The specific gravities of oxygen and carbonic acid gases are 1.1036 to 1 b 196 , or as 20 (—2 oxygen) to 27.54 ; and deduct- ing the oxygen, we obuin 7.54 for ihe equivalent of carbon. 6. Tne equivalent of sulphur is inferred irom Berzelius's analysis of galena, which makes the lead bear to the sulphur the proportion of 86,64 to 13.36 or of 129.5 to 20. 7. From the analysis of sulphate of barytes by Claproth, the sul- phuric acid is to the barytes as 34 to 66, or as 50 to 97. Deducting 30 of oxygen, we again obtain 20 for the equivalent of sulphur. 8, 9. In phosphate of lead, according to Berzelius, the litharge is to the acid as 380.56 to 100, or as 139.5 to 37.4; and deducting from this last number 20 oxygen, we have 17.4 for the equivalent of phosphorus. The same number is deducible, also, from Rose's experiments on phosphoric acid. 10. To obtain the equivalent of azote, ammonia is assumed to consist of 1 volume of azote, and 3 of hydrogen. And as the spe- cific gravity of hydrogen was found by Biot and Arago to be to that of azote as .07321 to .96913, these numbers will be in the propor- tion of 1.327 to 17.54; and 1.327 X 3 ZZ 3.98 added to 17.54, the equivalent of azote, gives 21.52 lor the equivalent of ammonia. 11. The equivalent of nitric acid is deduced from Richter's analy- sis of nitrate of potash,* which makes the potash to the acid as 46.7 to 53.3, or as 59.1 to 67.45 ; from which if we subtract one por- tion of azote 17.54, there remain 49.91, so nearly 5 portions of oxy- gen, that we may assume 17.54 + 50, or 67.54, to be perfectly cor- rect. 12. By dissolving 63 partsof carbonate of lime in muriatic acid, and evaporating to perfect dryness, we obtain 69.56 of muriate of lime; and deducting the weight of the lime, 35.46, we learn, by- means of the difference 34.1, the equivalent of dry muriatic acid. Or, if we choose to consider the dry salt as a compound of calcium and chlorine, we must transfer the weight of 10 oxygen to the mu- riatic acid, making 44.1 of oxymuriatic acid combined with 25.46 calcium. 15. In oxalate of lead, according to Berzelius, 296.6 of litharge are united with 100 oxalic acid, which are in the proportion of 139.5 to 47 oxalic acid. A result almost exactly the same was obtained by Dr. Wollaston from the analysis of binoxalate of potash. 17, 18. The equivalent of soda is inferred from the analysis of common salt, in which the muriatic acid is to the soda as 100 to 114.78, or as 34. i to 39.1. The equivalent of sodium is obtained by deducting 10 of oxygen, and is 29.1. 19, 20. In muriate of potash, the acid is to the alkali as 100 to • 2 Mem. d'Arcueil, 59, Vol. II.—3 IF 422 APPENDIX. J73.47,oras 34.1 to 59.1, from which last number, if we deduct 10 the equivalent of oxygen, we obtain 49.1 for the equivalent of po- tassium. 21. The equivalent of magnesia is inferred from the composition of the sulphate, viz. 67 acid to 33 base ; for as 67 to 33, so is 50 to 24.6. 22. The equivalent of lime is deduced from the carbonate of lime, in which the acid is to the earth as 43.7 to 56.3, or as 27.54 to 35.46; from which last number, deducting 10 oxygen, we have 25.46 for the equivalent of calcium. 24. In sulphate of strontites, the acid is to the earth as 42 to 58, or as 50 to 69. * 25. In sulphate of barytes 34 acid are united with 66 earth, which is in the proportion of 50 to 97. 26. In black oxide of iron, the oxygen is to the metal as 22.5 to 77.5, or as 10 to 34.5, to which, adding 10 oxygen, we have 44.5 for the equivalent of the oxide of iron. 27. Black oxide of copper contains 20 oxygen to 100 metal, which gives 50 for the equivalent of oxide of copper, and 40 for that of the metal. 28. In oxide of zinc, the oxygen is to the metal as 24.41 to 100, or as 10 to 41. to which last number, adding 10 oxygen, we have 51 for the equivalent of oxide of zinc. 29. In red oxide of mercury, the oxygen is to the metal as 8 to 100, or as 10 to 125. But as other statements differ a little from this, 125.5 may be taken as a mean; and adding 10 oxygen, 135.5 will denote the red oxide. 30. In carbonate of lead, the acid is to the oxide as 16.5 to 83.5, or as 27.54 to 139.5, the equivalent of litharge ; from which, deduct- ing 10 oxygen, we have 129.5 for the equivalent of lead. 31. In muriate of silver, the acid is to the oxide of silver as 19.05 to 80.9 3, or as 34.1 to 145, the equivalent of the oxide, from which, if we take lOosygen we have 135 the equivalent of silver. If we consider horn silver as a compound of 24.5 chlorine and 75.5 silver, the equivalent of silver will be 136; for 24.5 : 75.5 : :44.1 : 136. 32. The suhcarbonate of ammonia consists of acid and alkali, ac- cording to Guy Lussac, in the proportion of 56.02 to 43.98, or of 27.54 to 21.6, which, therefore, again proves to be the equivalent of ammonia. The two last numbers added together, give 49 for the equivalent of the subcarbonate. 33 In subcarbonate of soda, the acid is to the alkali as 41.24 to 58 76. or as 27.54 to 39.1; and the two last numbers, added together, expr ss rhe equivalents of'he subcarbonate. 35. The proportion of the elements of carbonate of lime is 43.7 acid to .36.3 base- or 27 54 to 35.46; and consequently carbonate of lime must be represented by those two numbers added together, viz 63. 36. In carbonate of barytes, the acid is to the earth as 100 to 352.s". nr is 27 54 10 97, which two numbers, added together, 124.5C. expi ess the equivalent of carbonate of barytes. TABLE OF CHEMICAL EQUIVALENTS. 423 37. The equivalent of carbonate of lead is obtained by adding to- gether those of oxide of lead and of carbonic acid, (see 30.) 38, 39. For the determination of the equivalent ot sulphuric acid see No. 7. The remaining numbers, expressing the equivalents of compound bodies, are obtained by adding together the equivalents of their components. Thus the equivalent of muriate of p- tash 93.2 is ob- tained by adding together the equivalents of muriatic acid 34.1 and of potash 59.1. No. IV.— Table of Incompatible Salts.* SALTS. 1. Fixed alkaline sul phates - - - - 2. Sulphate of lime 3. Alum 4. Sulphate of magnesia 5. Sulphate of iron 6. Muriate of barytes 7. Muriate of lime 3. Muriate of magnesia 9. Nitrate of lime INCOMPATIBLE WITH 5 Nitrates of lime and magnesia, I Muriates of lime and magnesia. {Alkalies, Carbonate of magnesia, Muriate of barytes. f Alkalies, ! Muriate of barytes, j Nitrate, muriate, carbonate of lime, (^Carbonate of magnesia. {Alkalies, Muriate of barytes, Nitrate and muriate of lime. {Alkalies, Muriate of barytes, Earthy carbonates. f Sulphates, < Alkaline carbonates, ^Earthy carbonates. {Sulphates, except of lime, Alkaline carlionaus, Carbonate of magnesia. C Alkaline carbonates, l Alkaline sulphates. f Alkaline carbonates, ■ 2 Carbonates of magnesia and alumine, (_ Sulphates, except of lime. • That is, salts which cannot exist together in solution, without mutual de- composition. This incompatibility, however, it is to be understood, exists only in solutions of a certain density. 424 APPENDIX. No. V— Table of the Quantity of Oil of Vitriol (sp. gr. 1.8485,) and of Dry Sulphuric Acid, in 100 Parts, by Weight of diluted Acid, at different Densities. By Dr. Ure. (Journal of Science, &c. iv. 122.) Liquid. Sp. Gr. Dry. 'l liquid. Sp. Gr. j Dry. Liquid. Sp. Gr. Dry. 100 1.8485 81.54 66 l.jjOSi 53.82 32 1.2334 26.09 99 1.8475 80.72 65 1.5390 53.00 31 1.226'- 25 28 98 i.8460 79.90 64 1.5280 52.18 30 1.2184 24.46 • 97 1.8439 79. ^'9 63 1.5170 51.37 29 1.2108 23.65 96 1.8410 78.28 62 1.5u66j 50.55 28 1.2032 22.83 95 1.8376 77.46 61 1.49601 49 74 27 1.1956 22.01 94 1.8336 76.65 60 1.4860 48.92 26 1.1876 21.20 ' 93 1.829u 75.83 59 1.4760; 48.11 25 1.1792 20.38 92 1.8233 75.02 58 1.4660 47.29 24 1.1706 19.57 91 1.8 i 79 74.20 57 1.4560 46.48 23 1.1626 18.75 90 1.8115 73.39 56 14460 45 66 22 1.1549 17.94 89 1.8 »43 72.57 55 1.4360 44.85 21 1.1480 17.12 88 1.7962 71.75 54 1.4265 44.03 20 1.141U 16.31 87 1.7870 70.94 53 1.4170 43.22 19 1.1330 15.49 86 1.7774 7012 52 1.4073 42 40 18 1.1246 14.68 8: 1.7673 69.31 51 1.3977 41 5& 17 1.1165 13.86 84 1 7570 68.49 50 1.3884 40.77 16 1.1090 13.05 83 1.7465 67.68 49 1.S788 39.95 15 1.1019 12.23 82 i.7360 66.86 48 1.3697 39 14 14 1.0953 11.41 81 1.7245 66.05 47 1.3612 38.32 13 1.0887 10 60 80 ,.7120 65.23 46 1.3530 37.51 12 1 0809 9.78 7i 1.6993 64.42 45 1.3440 36.69 11 1.0743 8.97. 78 1.6S7 > 63.60 44 1.3 45 35.88 10 1 0682 8 15 77 [.6750 62.78 43 1.3255 35.06 ■9 1.0.i 14 7 34 76 1.6630 61.97 42 1.3165 34.25 8 1.0544 6.52 75 1.65 20 6i.l5 41 1.3080 33.43 7 1.0477 5.71 74 1.6415 60.34 40 1.2999 32.61 6 1.0405 4.89 73 1.63 ill .39.5 2 39 1.2913 31.80 5 1.0336 4.08 72 1 620 . 58 71 38 1.2826 30.98 4 1.0268 3.26 71 1.609U 57.89 37 1.2740 30.17 3 1.0206 2.446 70 1.5975 57.08 36 1.2654 29.35 2 1.0 14C 1.63 69 1.5868 5o.26 35 1 2572 28 54 1 1.0074 0.8154 68 I.576C 55.45 34 1.2490 27.72 | 67 1 I 5648 54.63 33 1.2409 26.91 TABLE OF NITRIC ACID, &C 425 No. VI—Table showing the Proportion of real or dry Nitric Acidt in 100 Parts of the liquid Acid, at successive Speciflc Gravities. Hy Dr. Ure. (Journal of Science, iv. 297.) Specific Acid in Specific Acid in Specific Acid in « ' gravity. 100. gravity. 100. gravity. • 100. 1.5000 79.700 1 3783 52.602 1.1833 25.504 1.4980 78.903 1.3732 5 1.805 1.1770 24.707 1.4960 78.106 1.3681 51.068 J.1709 23.910 1.4940 77.309 1.3630 50.211 ' 1.1648 23.113 1.4910 76512 1.3579 49.414 1.1587 22.316 1.4880 75.715 1.3529 48.617 1.1526 21.519 1.4850 74.918 1.3477 47 820 1.1465 20.722 ' 1.4820 74.121 1.3427 47.023 1.1403 19.925 1.4790 73.324 1.3376 46.226 1.1345 19.128 14760 72.527 1.3323 45.429 1.1286 18 331 1.4730 71.730 13270 44.632 1.1227 17.534 1.4700 70.933 1.3216 43.835 1.1168 16.737 1.4670 70.136 1.3163 43.038 1.1109 15.940 1.4640 69.339 1.3110 42.241 1.1051 15.143 1.4600 68.542 1.3056 41.444 1.0993 14.346 1.4570 67.745 1.3001 40.647 1.0935 13.549 1 4530 66.948 1.2947 39.850 1.0878 12.752 1.4500 66.155 1.2887 39.053 1.0821 11.955 1.4460 65.354 1.2826 38 256 1.0764 11.158 1.4424 64.557 1.2765 37.459 1.0708 10.361 1.4385 63.760 1.2705 36.662 1.0651 9.564 1.4346 62 963 1.2644 35.865 1.0595 8.767 1.4306 62.166 1.2583 35.068 1.0540 7.970 1.4269 61.369 1.2523 34.271 1.0485 7.173 1.4228 60.572 1.2462 33474 1.0430 6.376 1.4189 59.775 1.2402 32.677 1 0375 5.579 1.4147 58.978 1.2341 31.880 1.0320 4.782 1.4107 58181 1.2277 31.083 10267 3.985 1.4065 57384 1.2212 30.286 1.0212 3.188 1.4023 56.587 1.2148 29.489 1.0159 2.391 1.3978 55.790 1.2084 28.692 1.0106 1.594 1.3945 54.993 1.2019 27.895 1.0053 0.797 1.3882 54.196 1.1958 27.098 1.3833 53.399 1.1895 26.301 | 426 APPENDIX. No. VII,—Table of the Quantity of real or dry Muriatic Acid in 100 Parts of the liquid Acid, at successive Speciflc Gravities. By Dr. Ure. (Thomson's Annals of Philosophy, x. 371.) ■specific 1 Acid in Specific Acid in Specific Acid in gravity. 100. gravity. 100. | gravity. 100. l.l /20 28.30 1.1272 18.68 1.0610 9.,;5 l.T'OO 28 02 1.1253 18.39 1.0390 8.77 1.1881 27.73 . 1.12.33 18.11 i 1.0571 8.49 1.1863 27.45 1.12 i 4 17.83 i 1.0552 8.21 1.18 15 27.17 1.1194 17.55 ' 1.0533 7.92 I 1827 26.88 1.1 173 17.26 1.0514 7.64 1.18 ^8 26.60 1.1 155 16.>8 1.0495 7.36 1.1790 26.32 1.1134 16.70 1.0477 7.07 1.1772 26.04 1.1115 16.41 1.0457 6.79 1.1753 25.75 1.1097 16.13 1.0438 6.5 1 1.1735 25.47 1.1077 15.85 1.0418 6.23 1.1715 25.19 1.1058 15.56 1.0399 5.94 1.1698 24.90 1.1037 15.28 1 0380 5.66 1.1679 24.62 1.1018 15.00 1.0361 5.38 1.1661 24.34 1.0999 14.72 1.0342 5.)9 1.1642 2-i, 5 1.0980 14.43 1.0324 4.81 1.1624 23.77 1.0960 14.15 i 1.03 '4 4.53 1.1605 23.49 1.0941 13.87 | 1.0285 4.24 1.1587 23.20 1.0922 13.-8 l'<)266 3.96 1.1568 22.92 !.0902 13.;>0 j 1.0247 3.68 1.1550 22.64 1.0883 13.U2 | 1.0228 3.39 1.1531 22 36 1.0863 12.73 1 1.0209 3.11 1.1510 22.07 1.0844 12.45 1 1.0190 2.83 1.1491 21.79 1 w823 12.17 i 1/171 2.55 1.1471 21.51 1 ')8-;5 11.88 1.'152 2.2 r. 1.1452 21.22 I.U785 1 1.60 1.0133 1.98 , 1.1431 20.94 1.0765 11.32 1.0114 1.70 1.1410 20.66 1.07 46 11.04 1.0095 1.4 1 1.1391 20.37 I.: 1727 10.75 1.0)76 1.13 1 1371 20.09 1.0707 10 47 1.0o56 0.85 1.1351 19.81 l.<)688 10.19 1 1 i =0 J7 0.56 1.1332 19.53 U/669 9 90 1.0019 0.28 1.1312 1924 1.0649 9.62 j 1.00.-0 0.00 1.1293 18.96 1.0629 9.34 1 PRECIPITATES FROM METALLIC SOLUTIONS. 427 # No. VIII.—Colour of the Precepitates thrown down from Metallic Solutions, by various Re agents. Metals. • Prussiated Alkalies. Tincture of Galls. Water im-pregnated with Sul-phureted Hydrogen. • Hydro-Sulphurtis Gold Yellowish-white Solution turn-ed green. Precipitate brown ot re-duced goia Yellow Yellow i i Platinum No precip.; but an mange co-inured one by pruss of nu rcury i Dark green becoming paler > Precipi-tin cl in a metallic state Silver White Yellowish bmwn Bl ck Bkrk Mercury White changing to yellow Orange yel low Black Brownish black Palladium Olive*. Deep oran^ef. Dark brown D.irk brown R .odium No precip N .jprecip Iridium No precipi-tate. Colour discharged No precipi-tate. Co-lour of so-lutionsrdis-charged Osmium Purple, changing to deep vivid blue * Chevenix. f Wollaston. *28 APPENDIX. Colour of Precipitates from Metallic Solutions, ifc— Continued. Metals. Prussiated Alkalies. Tincture of • Galls. Water im-pregnated with Sul-phureted Hydrogen. Hydro-sulphurets Copper Bright red-dish brown Brownish Black Black f" 1. Green sahs Iron < 12. Red salts • White, changing to blue. Deep blue No preci-pitate. Black. Not pre-cipitated Black • Nickel Green Grayish white Not pre-cipitated Black Tin White XT No ,precip Brown Black Lead White White Black Black Zinc White No precip Yellow White Bismuth White Orange Black Black Antimony White A white oxide merely from di-lution Orange Orange Tellurium No precip. Yeilow Blackish Arsenic White Little change Yellow Yellow Cobalt Brownish Yellow Yellowish white Not pre-cipitated Black Manganese Yellowish white No preci-pitate Not pre-cipitated White Chrome Green Brown Green Precipitates from metallic solutions. 429 Colour of Precipitates from Metallic Solutions, &c»— Continued. Metals. Prussiated Alkalies. • Tincture of Galls. Water im-pregnated with Sul-phureted Hydrogen. Hydro-sulphurets. Molybdena Brown Deep brown Brown Uranium Brownish red Chocolate Brownish yellow Tungsten Titanium Grassgreen with a tinge of brown Reddish brown Not pre-cipitated Grass green Columbium Olive Orange Chocolate Tantalium Cerium Yellowish Brown becoming deep green Vol. H. 3 1 430 APPENDIX. No. IX.-rTable of Simple Affinity.* OXYGEN. OXYGEN.f nitrogen. Arsenic Molybdena Carbon Titanium Oxygen Charcoal Manganese Sulphur? Manganese Zinc Phosphorus Zinc Iron Hydrogen POTASH, SODA, Iron Tin AND AMMONIA. Tin Antimony Uranium Molybdena Acids. Hydrogen Tungsten hydrogen. . Sulphuric Pnosphorus Cobalt Nitric Sulphur Antimony Oxygen Muriatic Arsenic Nickel Sulphur Phosphoric Nitrogen Arsenic Carbon Fluoric Nickel Chrome Phosphorus Oxalic Cobalt Bismuth Nitrogen Tartaric Copper Bisn.uth Lead Copper Arsenic Succinic Caloric Tellurium SULPHUR. Citric Mercury Platinum PHOSPHORUS? Lactic Silver Mercury Benzoic Arsenous Acid Silver Potash Sulphurous Nitric oxide Gold Soda Acetic Gold* Iron Mucic Platinum Copper Boracic Carbonic oxide Tin Nitrous Muriatic acid CARBON. Lead Carbonic White oxide, of Silver Prussic manganese Oxygen Bismuth Oil White oxide of Iron Antimony Water lead Hydrogen Mercury Sulphur * This table, it may be necessary to observe, does not express accurately the comparative affinities of bodies, but denotes merely the actual order of decomposi- tion, which, as Berthollet has shown, may often be contrary to thut of affinity, owing to the influence of various extraneous forces. f Vauquelin's table of the affinity of the metals for oxygen, according to the difficulty with which their oxides are decomposed by heat. TABLE OF AFFINITY. 431 Table of Simple Affinity,—Continued. ' BARYTES. Acids. ----------» MAGNESIA. Acids. Muriatic Citric Acids. Succinic Acids. Phosphoric Sulphurip Acetic Oxalic Lactic Oxalic Arsenic Phosphoric Benzoic Succinic Boracic Sulphuric Acetic Fluoric Carbonic Fluoric Boracic Phosphoric Water Arsenic Sulphurous Mucic Mucic Nitrous Nitric Succinic Nitric Carbonic Prussic Muriatic Suberic LIME. Muriatic Citric Tartaric Citric Tartaric Acids. Arsenic Oxalic Malic? SILEX. Lactic Sulphuric Lactic Benzoic Tartaric Benzoic Fluoric acid Acetic Succinic Acetic Potash Boracic Phosphoric Boracic Sulphurous Mucic Sulphurous Nitrous Nitric Nitrous Carbonic Muriatic Carbonic OX. OF PLATI- Prussic Suberic Prussic NUM. Sulphur Fluoric Sulphur GOLD.* Phosphorus Arsenic Gallic acid AVater Lactic Citric Muriatic Nitric Fixed oils Malic Benzoic Acetic ALUMINE. Sulphuric Arsenic Fluoric Acids. STRONTITES. Boracic Sulphuric Tartaric Sulphurous Niiric Phosphoric Acids. Nitrous Muriatic Oxalic Sulphuric Carbonic Oxalic Citric Phosphoric Prussic Arsenic Acetic Oxalic Sulphur Fluoric Succinic Tartaric Phosphorus Tartaric Prussic Fluoric Water Succinic Carbonic Nitric Fixed oil Mucic Ammonia * Omitting the oxalic, citric, succinic, and carbonic, and adding sulphureted hydrogen after ammonia. 4o2 APPENDIX. Table of Simple Affinity,— Continued. OXIDE OF SIL- fluoric Oxalic Water VER. Acetic Benzoic Tartaric Muriatic i Gallic acid Boracic Sulpiiuric Muriatic Prussic Mucic OXIDE OF IRON. Oxalic Carbonic Nitric Sulphuric Arsenic Gallic Mucic Phosphoric Phosphoric Succinic Oxalic Tartaric ^ Sulphurous OXIDE OF LEAD. Fluoric Camphoric Nitric Citric Sulphuric Arsenic Gallic Lactic Mucic Fluoric Sulphuric Acetic Muriatic Tartaric Mucic Boracic Nitric Citric Oxalic Prussic Phosphoric Lactic Arsenic Carbonic Arsenic Succinic Tartaric Fixed alkalies Fluoric Acetic Phosphoric Ammonia Succinic Prussic Muriatic Fixed oils Citric Carbonic Sulphurous Lactic Ammonia Suberic Nitric Acetic Boracic Fluoric OXIDE OF AR- Prussic Citric SENIC. Carbonic OXIDE OF MER- Malic Succinic Gallic CURY. L ctic Muriatic Gallic acid Acetic Oxalic OXIDE OF TIN*. Muriatic Benzoic Sulphuric Oxalic Boracic Nitric Gallic Succinic Prussic Tartaric Muriatic Arsenic Carbonic Phosphoric Sulphuric Pi.o phoric So.phuric Fixed oils Fluoric Oxalic Ammonia Succinic Tartaric Mucic Tartaric Citric Acetic Arsenic Phosphoric C.rric OXIDE OF COP Prussic Nitric Malic PER. Fixed alkalies Succinic Sulphurous Nitric Ammonia Fluoric Gallic Fixed oils Mucic * Bergman places the tartaric before the muriatic. TABLE OF AFFINITY. 43 3 Table of Simple Affinity,—Continued. Citric Benzoic SULPHUROUS phosphorous Lactic Oxalic ACIO. ACID. Acetic Sulpiiuric SUCCINIC f. Boracic Nitric Lime Prussic Tartaric Barytes Barytes Ammonia Mucic Lime Strontites Phosphoric Citric Potash Soda Potash Soda OXIDE OF ZINC. Succinic Strontites Ammonia Fluoric Magnesia Glucine Gallic Arsenic Ammonia Alumine Oxalic Lactic Glucine Zircon Sulphuric Acetic Alumine Metallic oxides Muriatic Mucic Boracic Prussic Zircon Metallic oxides Nitric Fixed alkalies NITRIC ACID. Tartaric Ammonia MURIATIC--§. Phosphoric Citric Succinic Barytes Potash Soda Strontites Fluoric Arsenic SULPHURIC ACID. PHOSPHORIC ACID. Lactic Acetic PRUSSIC*. CARBONlC| Lime Magnesia Boracic Barytes Barytes Ammonia Glucine Prussic Strontites Strontites Jarbonic Potash Lime Alumine Zircon Metallic oxides Fixed alkalies Ammonia Soda Lime Potash Soda Magnesia Ammonia Glucine Yttria Alumine Zircon Ammonia Magnesia Glucine Alumine Zircon Metallic oxides OXIDE OF AN-TIMONY. Gallic FLUORIC ACID. BORACIC II ARSENIC----'[ TUNGSTIC---- Muriatic Metallic oxides Silex Lime * With the omission of all after ammonia. f Ammonia should come before magnesia ; and strontites, glucine, and zir- con should be omitted. t Magnesia should stand above ammonia, and alumine and silica should be omitted. § Ammonia should stand above magnesia. j| Silex should be omitted, and instead of it, water and alcohol be inserted. ^ Except silex. 434 APPENDIX. Table of Simple Affiinity,—Continued. Barytes Strontites Magnesia Potash Soda Ammonia Glucine Alumine Zircon Silex Zircon 1 Soda Ammonia Barytes Lime Magnesia Alumine CAMPHORIC ACID. Lime Potash Soda Barytes Ammonia Alumine Magnesia Magnesia Oxide of mer-cury Other metallic oxides Alumine OXALIO ACID. TARTARIC -- CITRIC --1 Lime Barytes Strontites Magnesia Potash Soda Ammonia Alumine M talhc oxides Water Alcohol ALCOHOL. Water Ether Volatile oil Alkaline sul-pha rets ACETIC ACID. LACTIC ---- SUBERIC*. Barytes Potash Soda Strontites Lime Ammonia Magnesia Metallic oxides Glucine Alumine SULPHURETED HYDROGEN. Barytes Potash Soda Lime Ammonia Magnesia Zncon FIXED OIL. Lime Barytes Potash Soda BENZOIC ACID. Whi e oxide of arsenic Potash * With the omission of strontites, metallic oxides, glucine, and zircon. ■J- Zircon after alumine. ADDENDA. I have thought it proper to annex a short account of some disco- veries, which have been published in the different philosophical journals, while this work was passing through the press. Cadmium. A new metal, to which this name has been given, was discovered by M. Stromeyer, in the autumn of 1817. Hith- erto, it has been found only in the oxide of zinc, prepared for me- dicinal use, from an ore of zinc that came from Silesia. The pro- cess, by which it was separated, has not been published ; but the following are described as its most remarkable properties*. Cadmium resembles tin in its colour, lustre, softness, ductility, and in the sound which it emits when doubled. Its specific gra- vity is 8.6350. It melts, and volatillizes, at a temperature a few degrees below that required by tin. It is not tarnished by the air ; but, when heated, is converted into an orange coloured oxide, which is not volatile, and is easily reducible. Oxide of cadmium does not tinge borax when fused with it. It readily dissolves in acids, and forms with them s luble salts, from which it is precipitated white by alkalies, and yellow, like ars nic, by sulphureted hydrogen. From these solutions, zinc throws it down in a metallic state. Sirium Of this supposed new metal, it is unnecessary to say- more, than that it has been proved to be merely a compound of sul- phur, iron, nickel, and arsenicf. Malic and Sorbic Acids. By a careful investigation of the malic acid, M. Braconnot has been led to the conclusion, that it is essentiaUy the same with the sorbic, and that, when divested of all impurities, it exhibits the same p operties, and forms exactly the same, compounds : a conclusion supported also, by the experiments ot Houton Labillardiere$ By a process somewhat complicated,the former succeeded in detaching the pure acid of the juice of house- leek (semfiervivum tectorum, L :) from a substance with which it is associated, holding apparently a middle place between gum and sugar/and so modifying the properties of the acid, as to have led to erroneous views of its nature. In the juices of other vegetables, it i* probable that the impurities mixed with it will be found oF a different kind. * Ann. de Chim. et Phys. viii. 100; or Journal of Science, vi. 111. | Thomson's Annals, xii. 312. Faraday, in Journal of Science, x\. 112. \ Ann. de Chim. et Phys. viii. 149,214. 436 addenda. The identity of the two acids having thus been rendered un- questionable, it appears reasonable to distinguish their common ingredient, by the name originally applied to it by its discoverer Scheele, and to discontinue the appellation of sorbic acid ; s'nee the latter is nothing more than the malic deprived of impurities. The Rheumic Acid, (vol.ii. p. 230,) has been lately shown by M. Lassaignc to be merely the oxalic, disfigured by certain impurities*. Purpuric Acid. This acid has been obtained, also, (but appa- rently of less purity than by Dr. Prut) by Brii-inatclli, Juniorf. He has proposed to call it erythric acid (from egvigaiveu, to 'redden,) and its compounds erythrates. Th"Se, who are interested on the subject, will find BrugnaiediN Memoir, at full length, in the Philo- sophical Magazine, for July, 1818. New Alkali of Vegetable Origin. MM. Pelletier and Caventou, in analyzing nux vomica, and the bean of St. Ignatius, have extracted a peculiar substance, possessing alkaline proper- ties, to which the powerful action of those poisons on the animal economy appears to be owing}. The new substance is white, crystalline, and insufferably bitter. It occurs in quadrangular plates, or in prisms of four sides, termi- nated by a four-sided pyramid. It is slightly soluble in water, but readily so in alcohol. It restores the blue colour of reddened lit* mus paper, and, with the acids, forms neutral salts that are soluble in water, and more or less easily crystallizable. Hence in its che- mical properties, it seems lo present a considerable resemblance to morphium, but when taken into the stomach, it produces, in a more intense degree, the effects of the tincture of nux vomica. From the circumstance of M. Vauquelin's having observed an analogous sub- stance in the Daphne Alpina, its discoverers have proposed for it the name of Vauqueline. Triple Prussiate of Potash—Prussic Acid—and the New Gas obtained by Dr. Thomscn. By distilling triple prussiate of potash with rather more than twice its weight of strong sulphuric acid, Dr. Thomson has ob- tained a gas, which, after being freed from sulphurous acid, evolved along with it, was found to possess new properties. Its^mell is peculiar, and bears no resemblance to that of any other gas ; it is permanent over water ; has the specific gravity of 0 993, air being 1000. When slowly burned from an orifice it exhibits a deep blue flame.'By rapid combustion in a Volta's eudiometer, three volumes consume two of oxygen, and give three volumes of carbonic acid. H appears to be constituted of 3 volumes of carbonic oxide > . , • . „ , , , r i i r condensed into 3 volumes. 1 volume ot hydrogen gas } Dr. Thomson has proposed to call it hydrogureted carbonic oxide. The triple prussiate of potash has also been submitted to a fresh * Ann. de Chim. et Phys. viii. 402. f Ibid. 2;;1 ; or Phil. Mag Iii 30. * Ann. de Chim. et Phys. viii. 323 ; or Journal of Science, vi. 149. ADDENDA. 437 examination both by Dr. Thomson, and by Mr. Porrett. The.for- mer describes it as crystallizing, when perfect, in plates with be- velled edges, usually about half an inch thick, and two or three inches in diameter; the two faces of the bevelled edges being in- clined to each other at an angle of about 135°. Its colour is a fine topaz yellow. When held between the eye and the light, it is trans- parent, and appears green. Its specific gravity is 1.833. It may be split into flexible plates, parallel to the bases of its pyramids. One hundred parts of water at 54° Fahrenheit dissolve 27.8 of the salt; at 100°, 65.8 parts; at 150°, 87.6 parts; and at 200 , 90.6. In alcohol it is not soluble at all. ... r •• u According to Dr. Thomson, the salifymg principle of this salt appears, from experiment, to be constituted of half an atom of me- tallic iron with one atom of prussic (hydro-cyanic) acid; and the triple salt itself consists of . ., CIron . . • • • • •*5,0C45 90 Acld I Matter gasified by heat. 30.9 $ Potash..........4l-64 • Water..........13' 100.54 Exhibiting a small excess of 0.54 in 100 of the salt*. Since, however, the proportion of iron, as deduced from the equivalent of the acid ingredient of the triple prussiate (66.11, oxy- gen being 10,) ought to be one atom to one atom of hydro-cyanic acid, there appeared, with respect to the acid of the triple prussi- ate, to be a disagreement between the atomic theory and the re- sults of analysis. This disagreement Mr. Porrett has endea- voured to rectify by a fresh series of experiments!. He detacnea the potash, from 50 grains of the triple salt, by 70 grains of crys- tallized tartaric acid; and obtained a quantity of bi-tartrate, denot- ing 17.9 grains of potash; consequently 100 grains must contain 35 8. The water being 13 grains, the acid in 100 grains must be 51.2. This acid Mr. Porrett supposes to be a compound, not ot prussic acid and iron, according to Dr. Thomson, but of•fht^ele- ments of two atoms of prussic acid, an atom of azotet, an atom ot iron, or,' in other words, it consists of 4 atoms carbon . .30.16 1 atom azote . • • 17.54 1 atom iron . • • 34.50 2 atoms hydrogen . 2.64 Its atom, therefore, weighs . . . 84.84 When it unites with potash, one atom of acid takes ooetfomot base (59.10,) and two atoms of water (22.64,) which gives the com- position of the triple prussiate as follows : , * Annals of Philosophy, xii. 110. t ">id-xii- 214' Vol.. II 3 K 43 U ADDENDA. Acid - - - 50.93 Potash - - - 35.48 Water - - - 13.59 * 100. Mr. Porrett analyzed the acid of this salt, by distilling the triple prussiate, as Dr Thompson had done, with per-oxide ot copper, only using a larger proportion of the oxide : and he found that the resulting carbonic acid and azote agreed, as nearly as could possibly be expected, with the proportions that ought to be produced accord- ing to the theoretical view. This acid, therefore, does not appear to present any exception to the general principles of the atomic theory. As to its nomenclature, Mr. Porrett is disposed to abide by that which he formerly proposed ferrureted chyazic acid;) be- cause, according to his view the acid does not consist of prussic acid and iron ; but of a part of the elements of prussic acid in union with that metal. Oxymuriate (Chloride) of Lime. This compound has been examined by Welter,* who determines it to consist of hydrate of lime united with chlorine, in the following proportions, oxygen be- ing considered as 10: "■ f 1 atom of chlorine......44.1 2 atoms hydrate of limef 46.78 X 2 ZZ 93.56 137.66 Seven parts of hydrate of lime, fully saturated with chlorine, gave, in his experiments, 10.22 of oxymuriate of lime, which destroyed the colour of as much solution of indigo, as the chlorine itself, cal- culated to be present in the salt, would have destroyed. He con- siders it, therefore, as a true compound of chlorine, and not of chloric acid with hydrate of lime ; and if this view be correct, its proper appellation will be chloride of hydrated lime. The propor- tions in 100 parts may be calculated from the data of Welter as follows: Chlorine - - - 32.04") f 1 atom ZZ 44.10" Water - - - - 22.64 I or -j 2 atoms ZZ 22.64 Lime - - - - 70.92 J ^ 2 atoms ZZ 70.92 100. 137.66 When dissolved in water, Welter agrees with Mr. Dalton, that one atom of the hydrate of lime is separated, and that the solution contains a compound of one atom of hydrate of lime ^nd one atom * Ann. de Chim. et Phys. vii. 383. T The atoms of this hydrate containing Lime - - - 35.46 Water - - 11.32 46.78 ADDENDA. 439 of chlorine. They differ, however, so materially in the proportions of the salt (see vol. i. p. 461,) that its analysis is still deserving of further investigation. New Combinations of Oxygen with the known Acids. By treating the per-oxide of barium (vol. i. p. 255,) with acids, Thenard has succeeded in forming new combinations of those acids with oxygen.* The process consists simply in dissolving per-oxide of baritim (prepared by heating pure barytes in oxygen gas, and moistening the product with water sufficient to change it into a white powder,) in any acid intended to be oxygenated ; and then adding a due proportion of sulphuric acid. This carries down the protoxide of barium, leaving the acid united with the oxygen which the per-oxide has abandoned. Oxy-nitric acid is liquid, colourless, and resembles nitric acid in its chemical agencies. It is decomposed by being heated to the boiling temperature, and abandons its oxygen, of which, by proper management, it may be made to yield eleven times its volume. It unites with alkaline and earthy bases ; but the resulting salts are so easily decomposed, that they can scarcely be obtained in crystals. It acts on all those metals that are soluble in common nitric acid, but has no power of dissolving gold. In oxy nitric acid, the elements were determined by Thenard to be present, in the proportion of 100 volumes of nitrogen to 300 oxygen ; and hence its atomic constitution is 1 atom of nitrogen to 0 aoms of oxygen. It stands, therefore, at the head of the series given in vol. i. p. 381, 383, as the most highly oxygenated com- pound of nitrogen. The phosphoric, arsenic, and acetic acids, were oxygenated by a similar treatment, but not the sulphuric ; and contrary to what might have been expected, the muriatic acid was brought into combina- tion with oxygen, which, it might have been supposed, would have acted only on the hydrogen of that acid. Thenard was not" able, however, to obtain oxymuriatic acid in a very concentrated state. Heat decomposed it into oxygen and muriatic acid, and its salts were also easily destructible. It was very acid, colourless, almost free from smell, and strongly reddened litmusT It dissolved zinc without effervescence, but had no action on gold. With oxide of silver, it exhibited a brisk effervescence, owing to the escape of oxygen gas. By means of the oxy-muriatic acid, its discoverer succeeded in oxygenating the fluoric acid, which was found to re- tain its oxygen at the temperature of ebullition. These facts ar^extremely curious arid important, and open a wide field for new ana interesting discoveries. It is remarkable, that the oxy muriatic acid, really entitled to that name, should differ essentially in its properties from the body formerly so designated; Ann. de Chim, etPhys. viii. 306. 440 ADDENDA. and that it shoula want the leading characters of the latter, viz. its power of destroying vegetable colours, and of acting on gold. Analysis of Alum. This salt has lately been carefully analyzed by Mr. Richard Phillips, with the result that the potash exists in it, not in the state of a simple sulphate, but of bi-sulphate. The true composition of alum appears from these experiments (not yet pub- lished) to be, taking 10 for the atom of oxygen, 2 atoms sulphate of alumine ----- 164 1 atom bi-sulphate of potash - - - - - 159.1 22 atoms of water --------- 249.6 572.7 Hence 100 parts of alum consist of Alumine.....11.18} (Sulph. of alumine - 28.65 Sulph. acid - - - - 34.94f )Sulph. of potash - - 19.065 Potash......I0.33lor JSulph. acid - - - 8.735 Water......43.55/ I Water.....43.55 100.00 100.00 PI 1 <~7Yff><'iir J. n.n. 11 ■ i, i i ^ fruJitv TtrfiottfS. <' Tir&ou/- .>' J'/.IV '. ntfiotu . fit: .....V ■J—r1—'—'—'—I Inches CTtr/'fllt Sc. rt. it. F?<; ■/.» 51 \.....i JlQZL_.XX1_ -1-----'-----1 Indies I.Tl'ehvtSc'. JPIMT. r.T/Wu-i,/ t: Ff.vm <=> PYf/. M ^zr ^r H^' tux. ClUbout So.c r/..\. 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