-lis, UNITED STATES OF AMERICA M«0 FOUNDED 1836 WASHINGTON, D. C. GPO 16—67244-1 AN INAUGURAL DISSERTATION, O N T H E PHOENOMENA, CAUSES and EFFECTS *\ O F FERMENTAtl ON; Submitted to the Examination OF THE Revd. WILLIAM SMITH, S. T. P. Provost j THE I Trustees and Medical Professors, O F T H E COLLEGE of PHILADELPHIA;, FOR. THE DEGREE OF DOCTOR OF MEDICINE J OS THE SECOND DAY OF JUNE A. D. I7gOk By JOHN PENINGfTQN k &h OF PHILADLju.u*"- af #U \ ~% ^^ITtr PHILADELPHIA: ^"*~ Printed by JOSEPH JAMES, M.DCC.XC. C/UcJik^r^ T O Th e Honorable FRANCIS HOPKINSON Esq. *fVDGE of the DISTRICT COURT x OF ,T H £ V ■ ♦ «' !.\ UNITED STATES, FOR THE STATE OF PENNSYLVANIA, Member of the American Philosophical Society &c. &c. &c. This Dissertation is WITH THE GREATEST RESPECT INSCRIBED, B Y HIS MUCH OBLIGED FRIEND, The AUTHOR, Philadelphia, May 24th. 179°- HOI ^"7 2. INTRODUCTION; THE rules of the college of Philadelphia, reflecting a medical education, have, a- mong other things made it neceflary, that the candidate for the degree of Doctor of Me- dicine Ihall produce a " Thefis, written in the Latin or Englifh language, at his own op- tion". As it has been the cuftom in moft colleges, to write medical diflertations in the Latin lan- guage, 1 hope it will not appear affetledly fingular to choofe the Englifh language as the vehicle ©f mine. I have no right to expect, from its con- tents, that it will ever be read in any country, where the Englifh language is not perfectly un- derflood. Befides, the nature of my fubjecr. made it necefTary to ufe terms which I did not think myfelf authorifed to convert into an imita- tion of Latin. If I have erred in adopting the En- glifh language as the medium for communicating my opinions to the world, I hope the authority of Dr. Franklin, Mr. Hopkinfon, Dr. Rufh and many other gentlemen of abilities in the United States, in favour of a perference of a modem language for a modern publication, will fcreen me from cenfure. fermentation. THERE are perhaps few procefTes, or phoe- nomena, that fall under the obfervation of chemical enquirers, that are fo little under- ftood as the fubject of the prefent eflay. This want of certainty, we fhould fufpect, arofe more from the difficulty, than from the want of oppor- tunities, for inveftigating the fubject, becaufethe materials for experiments are not only in every one's power to obtain, but the procefs is almoft daily obtruding itfelf upon us. The chief ob- ftacle to our advancement, in the knowledge of the caufes and effects of fermentation, is that we reft fatisfied with explanations handed to us by others. The fubject appears to be of much importance, both as a curious chemical procefs, and as it refpects the economical arts, and the art of medicine, and for that reafon I have cho- fen it for the fubject of the prefent dhTertation. There are many difficulties attending the invefti- gation, as every chemift mufl confefs, and I may perhaps affign the fame reafon for thofe difficul- ties that Mr. Henry of Manchefter did, when treating of the fame'fubject, that " the obfcuri- ty and intricacy of the path, on which I am en- tering, the almoft total want of guides and my inadequate abilities to clear away the obftacles, throw light on the dark parts, and point out thofe which may be traverfed with eafe and certainty, 8 essay on place me in a fituation truly difficult". Thefe rea- fons being applicable to me, in all their force, I hope for candor and liberality, whenever I may be found to ftep afide, from the common and re- ceived opinions of chemifts, reflecting fermen- tation. Some new opinions will be found in this differtation, but as the fubject will admit of elu- cidation from experiment and as it would be wrong to admit any thing as a fact, without hav- ing afcertained it to be fo, I have introduced fome experiments to prove acknowleged facts. In handling this fubject, I fhall arrange it under different fections. SeElion I. I fhall confider the definition offer- mentation, the Subftances capable of it--and its Phoenomena. II. I fhall attempt an explanation of the Phoe- nomena attending the fermentation of vege- table fubftances. III. I fhall mention the pre ducts of fermentation. IV. I fhall diftinguifh between a mere efcapc of air and a true fermentation. V. I fhall mention the principal Zymics and Antizymics. And, VI. I fhall deliver fome analyfis of animal matter; the difference between animal unci vegetable fermentation. SECTION I. Definition of fermentation—Suhjlances capable ofi FERMENTATION is a peculiar proce which certain parts of dead animal and veg etable fubftances are difpofed to undergo, when fermentation. 9 combined with moifture, expofed to a degree of heat between 50 and 120 of Fahrenheit's ther- mometer, and in contact with air fit for combuf- tion and animal refpiration. The phenomena attending the procefs are. 1. That the fermenting mafs becomes confide- rably warmer than the atmofphere around it. 2. It emits a large quantity of a fluid, perma- nently elaftic, accompanied with an inteftine mo- tion, and 3. There is always a remarkable change and alteration in the fenfible and chemical qualities of all bodies that have actually fermented. We have here confined our definition to animal and vegetable fubftances, but we have great reafon to believe, that feveral mineral mixtures will undergo fpontaneous changes, perfectly analogous to fermentation; the gradual decompofition of the natural pyrites, and the changes which take place in an artificial mixture of the flowers of fulphur and iron filings, feem to depend upon the fame caufes, and are really attended with the fame phenomena; we have alfo taken dead ani- mal and vegetable fubftances only into our defi- nition ; this may not perhaps be quite accurate ; it is probable that animals, while alive and in health, have certain parts in them that are con ftantly putrifying or fermenting, and it is poffible that the fame thing happens in plants, but it is probable that thefe living machines have a power of expelling thefe putrid parts, as being incom- patible with their own health, befides we find in particular difeafes, efpecially in the order of Exanthemata, that a fmall quantity of a difeafed B 10 2 S S A Y 0 N fluid has a power of affimilating a considerable part of the fluids of another animal; as for in- ftance, in the fmall-pox, in which Doctor Cullen allows that a fermentation goes on in the body ; for, fpeaking of the quantity of variolous mat- ter, abforbed by common infection, he fays, " altho* it were larger than that thrown in by innoculation, it is not afcertained that the cir- cumftance of quantity would have any effect. A certain quantity of ferment is neceffary to excite fermentation in a given mafs, but that quantity given, the fermentation and affimilation are ex- tended to the whole mafs." But this kind of fer- mentation, which occurs in the living animal body^ cannot be examined here, for it is fo con- nected with life (a principle which we do not well underftand) that we can by no means imi- tate it in the dead body ; it is probable that the contagious matter acts upon the animal as an ani- mated machine, as well as matter, and that this acti- on modifies its effects j it is alfo a fubject of great curiofity both to the Phyfiologift and to the Che- mift, that the blood of a patient, labouring un- der the fmall-pox, cannot communicate the difeafe to another by innoculation, and it muft certainly be very difficult to a Chemifi to con- ceive, why after the fluids of an animal have been once fermented by the variolous matter, that the fluids of the fame animal fhall never take on that fermentation again, altho' they muft have been changed twenty times or more in the courfe of life. Moisture feemsto be an indifpenfible requi- fite in the procefs ; the moft putrefcent and fer- mentable fubftances we are acquainted with remain unchanged as long as they are kept dry j FERMENTATION. II fugar is perhaps the only part in all vegetable s capable of fermenting, and it is notorious that it may be kept for many years, and perhaps for ages unchanged, and the practice of the Indians in merely drying their venifon, in order to pre- ferve it, proves that the fame thing is true re* fpecting animal fubftances. Heat accumulated in a fenfible ft ate, to a certain degree, feems alfo indifpenfible, and a lefs degree than the loweft we have affigned ab- folutely prevents fermentation. A quantity of of fugar and water which would have complete- ly fermented in 24 hours, in an heat of 90° was kept unfermented from November laft, until the middle of February, although the thermometer for many days together, in. that time flood be- tween 50° and 60°. The prefence of pure air, fit for fupporting ani- mal life and refpiration, is fo eflential to ferment tation, that without it, it cannot be excited; this opinion is generally admitted by chemifts, and perhaps may be founded upon t:he experi- ments made by the air-pump. Natural philofo- phy teaches us, that certain fruits can be preferv- ed in a vacuum for a long time, without becom- ing acid ; but this is an entire abjlrattion of air : however, we find that the prefence of air, unlefs that air be pure, is not fuificient to excite fer- mentation. T believe feveral experiments have been made by others upon the fame fubject, but it may not be improper to relate two made by myfelf. Experiment Firjl. Part of a mixture of fugar and water, which. 12 ESSAY ON was very fermentable, was confined in a jar of inflamable air, obtained from iron-filings and di- luted vitriolic acid, and fet fo near a ftove as to vary between 80 and 9© of Fahrenheit, for thir- teen or fourteen hours of the twenty-four, the other part was fet along fide of it ; in this open veffel fermentation went on as ufual : in one week's time it had become highly acid ; in the jar fermentation had not gone on, but the fluid was perfectly fweet and unchanged. Experiment Second. The fecond experiment was with animal fub- ftances ; I confined a dead wild pigeon in a glafs jar of inflamable air, in the fame manner *s in the other experiment ; another was left in a large bowl, with fome water in it, and expofed to the heat and air in. the room : in about ten days the animal thus expofed was fo offenfive to the fmell, that I difcontinued the experiments ; at the fame time the animal in the jar was fcarce tainted in the lea ft, it was however fometvhat putrid, and had a greenijh appearance ; but I think thofe ef- fects may be fairly attributed to the fmall quanti- ty of common air confined in the cavity of the pi- gion's body, which at that time I did know how to extricate from it. We are neceffarily inclined to enquire what is the nature of the fermentable materials which characterife bodies ? and whether there is any one fimple principle in them that is the caufe of that change being effected in certain bodies ? we fee but.one character in common with them all, they are all inflamable, but the caufe of their in- flamability cannot be the caufe of their fermenta- fermentation. 13 tion, for all inflamable bodies are not fermenta- ble. In vegetables we believe that none of them are fermentable, unlefs they contain the faccha- rine principle, and I think it can be demonftrat- ed, that the products of all vegetable fermenta- tion are the fame. "What is the fermentable prin- ciple in animal fubftances, or what parts are more fufceptible of this change than the others, is yet involved in great obfcurity, and we fhall attempt to throw fome light upon it in lection fixth ; at prefent we fhall only in general remark, that the moft inflamable and foluble animal fubftances are the eafieft to ferment, or to putrify, as we fay, when the term is to be applied to animals. SECTION IL Explanation of the Phenomena attending the Fermen- tation of Vegetable Subfiances. HEAT, or a degree of it greater than that of the atmofphere, around the ferment- ing mafs, is an uniform circumftance attending fermentation ; the increafe of temperature, in my experiments however, has feldom been more than iq or 12 degrees. When we reflect that all putrefcent and fermentable fubftances are in- flamable, and during fermentation generate heat, we are immediately ftruck with its analogy to combuftion ; here let us enquire, whether the o- pinion of natural philosophers refpecting heat is well founded. They fuppofe that all heat de- pends upon motion, and that the heat produced in combuftion and fermentation is owing to the fudden destruction of the attraction of cohefion pf the particles of the body burnt or fermented. 14 ESSAY ON In the firft place, I think we have no evidence that heat and motion are the fame thing. zd. Although neither heat, nor even cold, nor any thing elfe, can be produced without mo- tion, yet all motion will not produce heat: for inftance, mercury may be agitated iu a phial tor feveral hours, without producing an increafe of one degree of heat, and the fea itfelf, altho* moft violently agitated, is ftill cold. %d. The quantity of heat generated by moti- on, is never in proportion to the rapidity of the deftruction of the attraction of cohefion, as we fee when faits are difTolved in water; (for folu- tion is faid to be owing to the fame caufe ;) for example, nitre, when finely powdered, diflblves very rapidly, and muft of confequence be at- tended with great motion, but we are fo far from generating heat, that the mixture becomes colder than the air, as we find by its finking the mercu- ry in the thermometer. 4th. Sugar diflblves very rapidly in water-, but without producing any heat, although at the inftant of folution there muft have been both mo- tion, and the deftruction of the attraction ofcohe- fion. If the mixture is fuffered to ftand, it will fer- ment and generate heat, even when there is no at- traction of cohefion to overcome, that we can be fenfible of. The heat occurring in fermentation muft, I think, be explained upon the theory of Doctor Black, refpecting latent heat: itfeems probable, that heat is a body, or fluid, fui generis,/inherent in all matter, and effential to its exiflence ; that FERMENTATION. I^ it enters into different bodies, in different propor- tions, as an ingredient in their compofition, in the fame manner as electricity is fuppofed to ex- ift in iron in contact with the earth ; whilft a cer- tain quantity of heat is attached to all bodies, and if I may be allowed the expreffion, mechanically mixed with them, in contradiftinction to the other mode of union of heat with bodies, which is then chemically combined with them, or is in a latent ftate. When the heat is in this ftate, it is called fenfible heat; becaufe it is capable of exciting a certain fenfation, of railing the mercury in the thermometer, and it is governable by certain laws, by this time pretty well afcertained. When heat enters into bodies as a principle, it is moft probably in different quantities in differ- ent bodies, and it is very remarkable, that a change in the common chemical qualities of bo- dies alters very much the capacity of bodies to contain heat as a principle, or in a latent ftate; hence it happens, that in almoft all our chemical proceffes, an alteration of temperature takes place. In fermentation, we fuppofe that the in- flamable part or principle of the fermenting bo- dy, has a tendency to combine with pure air, and we fhall juft remark in this place, that the com- buftibility of all bodies, is by Jome chemifts fup- pofed to be owing to one homogeneous principle called the principle of inflamability or phlogijlon ; this theory has had very powerful opponents, but I think we have reafon to believe, that with cer- tain modifications, it is true ; and it is moft pro- bable that this principle is inflamable air. It is alfo known, from direct experiments, particular- ly of Dr. Prieftly and Mr. Kirwan, that pure air 16 E S SA Y » O N and inflamable air form what Doctor Black calls fixed air, and Mr. Bergman the aerial acid, which is precisely the fame elaftic fluid thrown out in fermentation. The pure air we may juftly fup- pofe was derived from that great fource the at- mofphere, and for feveral reafons we may con- clude, that the inflamable air was furnifhed by the fermenting vegetable, but we by no means fuppofe that the fixed air was formally prefent in the fermenting mafs, or that it afforded all the materials to form it; now let us fuppofe that the quantity of heat in the two airs before combinati- on, was in each as ten, or in other words, that they were capable of containing that quantity in a latent ftate, effential to their exiftence as mat- ter in that form: when they unite, they form a very different kind of air, which is not capable of combining with fo mUch heat, and perhaps quite foreign to its exiftence as that kind of mat- ter ; we will fuppofe then that it can combine s with but a quantity of that heat as five, the confequence then muft be that there is a quantity of redundant heat as fifteen, and there being no bodies at hand undergoing any changes in their properties, by which their capacities to unite with heat as a principle, is increafed, it becomes mechanically diffufed among thofe bodies which are neareft to it, it gives the redundant heat to the feeling hand, to the atmofphere, to the thermo- meter and to the fermenting fluid, by that law of fenfible heat which proves that it is equally diffu- fed thro* all bodies; and as the caufe of heat con- tinues to act, fo the effect muft continue to enfue until the fermentation is compleated. With the efcape of the elaftic fluid there is an hiffing noife, and of confequence an intejiine motion; thefe phe- FERMENTATION. 1J nomena have had more attention paid to them than they deferve, and they have been fuppofed to be the moil infallible iigns that this procefs is go- ing on ; thefe we know are called the working of liquors, but they are very fallacious, and have been the fource of much error, as I apprehend, and I believe, that even the great Sir John Prin- gle, trufting to fuch appearances, has fuppofed that putrifaction had taken place in experiments, where there really was no putrifaction, but I am ftill more firm in the belief, that he was in fome inftances wrong in attempting to determine the degree of putrifaction from the degree of thefe ap- pearances ; we fhall illuftrate thefe remarks in the fourth fection. An alter at ion of the fenfible qua- lities of the fermented body is a more certain and univerfal circumftance than any other, therefore I think I am fafe in afferting that we can have no certainty of fermentation having taken place in any cafe without it, for when an animal fubftance putrifies it is changed from an inodorous body to one that is vory rank and fetid, and fugar when fermented, is capable of yielding a highly intox- icating fpirit, and if fermented longer becomes highly acid, as we know from the formation of vinegar, which we fuppofe is owing to the lofs of its phlogifton. SECTION III. Products of Fermentation. AFTER, all the phenomena above mentioned have continued for fome time, which is lon- ger or fhorter, according as the exciting caufes 18 ESSAY ON of the procefs have been more Griefs applied, the fermentation becomes for a while ftationary, and the vegetable fluid gets different names accord- ing to the nature of the vegetable itfelf: the fer- mented juices of grapes are called wines, and the juices of almoft all fruits which are fweet when ripe, are capable of affording analogous liquors when fermented, fuch as the juices of currants, apples, peaches, pears, &c. certain grains may alfo be fermented by fimilar procefles, as barley, wheat, rye, and fome others : all thefe when firft fermented, and then diftilled, yield ardent fpirit, which by repeated diftillations will afford alcohol. Brandy is the ardent fpirit ob- tained by diftilling the fermented juice of the grape, whilftn^ or fpirit, are the liquors diftilled from molaffes and water ; beer is the fermented extract of barley, to which is added a decoction of hops, which as a bitter is an antizymic, and prevents it from haflening on to the acid ftage of fermentation. There is a confiderable variety in wines which does not depend fo much upon any difference in them as fermented liquors, but in moft ca- fes', upon fome addition not effential to them as wines, for inftance, fome have a peculiar flavour which cannot be analized, and may be but in very fmall quantities in them, for who can analize the flavour of the peach ? others differ only in being weaker, that is, in having a larger quantity of water, others again have the aflrin- gent acid combined with them, hence are called rough wines-, fome from being weak foon become four, before a due degree of fermentation has ta- ken place in the whole mafs, and as for the dif- F E R MENTATION. 19 ference in colour, it is fometimes owing to cau- fes which neither influence the qualities of the wine, nor the fermentation it underwent, but the moft material difference in the qualities of rich wines, fuch I mean as have a proper quantity of water, is their age ; this excellence feems especi- ally to be owing to the more perfect fermentati- on and aflimilation of the different parts of the wine, for then the unfermented faccharine part becomes perfectly vinous, whilft the vinous part already generated is £0 ftrongly antizymic as not to fuffer any part to become acid. Wines fomewhat diluted and expofed to the neceffary conditions of fermentation go on to the fecond ftage which is called the acetous or acid fermentation, and the chief difference between this and the vinous is, that all the phenomena are in a lefs degree : the refult of this fermentati- on is vinegar ; the explanation of fome of the va- rieties of vinegar, may be underftood from what we have faid above. SECTION IV. Diftinftion between a mere Efcape of Air, and a True Fermentation. FERMENTATION is fuppofed to take place in another procefs, I mean in making bread, but I think we ought to be very cautious in ad- mitting that a true fermentation takes place, or is even neceffary in its preparation : I fhall per- haps in the courfe of this fection, ufe the common language, but when the word fermentation is ap- plied to the making of bread, I wifh it would be 20 E S S A Y O N nnderftood to exprefs nothing more than the ef- fect produced on flour by yeaft or leaven. Of the origin of fermented bread we have no certain account; I cannot however omit relating the very elegant conjecture reflecting it given us by our late chemical profeffor. He fuppofes that fome careful houfewife had mixed the unbaked fcraps of a former mixture with feme frefh dough, and he imagines her furprife at finding the bread improved by this procefs of economy ; what gives greater plaufibility to the conjecture is, that it is certain that leaven was the firft ferment ufed for raifmg bread; but fince later experiments have taught us that feveral fubftances in the act of fer- mentation will raife bread, leaven has gone out of ufe, and.yeaft, where it can be had, has almoft univerfally fupplied its place. The common idea of a ferment is, that it is capable of affimilating fubftances to its own nature : this is cutting the knot, for we fee no reafon why particular fub- ftances fhould have fuch power whilft others have not, and in fact it explains nothing. In many fuppofed cafes of affimilation, we fee fources of falacy and error, in others we muft frill affent to the common opinion. In the making of bread, we deny the idea of any fuch affimilation, or even of any true fermentation ; * but let us attend to * This opinion, fupported by experiments, was communicated to feveral gentlemen, and efpecially to Doctor Rush, fo early as January 1789. When I fubmitted this diffettatjon to the Doftor for his approbation as a profeffor of the college, he was pleafed to interline a compliment upon this difcovery. He did mc the honor to declare, that he " readily adopted it, " and aherwajds publicly taught it, with acknowledgements to the author, " m his LeElures on the application of Philofophy, Lhemijlry, Mtdicinc and Econo- " my to dome/lie and culinary purpvfes." I have made no acknowledgments for the idea to any body, but claim it ^original, although the fame featiments were afterwards publifhed in thv= FERMENTATION. 21 the procefs itfelf, and the phenomena attending it. A quantity of flour is mixed with a certain pro- portion of yeaft and water, and made of the con- fiflence of dough ; it is-then baked in a manner too fimple to be defcribed, and in one hour from the beginning to the end of the procefs, the bread is made, and is perfectly good. We are juftly furprifed at the fhort time required to ferment the bread, efpecially when we confider that fugar and water, the moft fermentable mixture known, requires twenty four hours before fermentation proceeds to any great degree in it; this reflection firft faggefted the idea that the fermentation of bread is not analogous to the fermentation of fu- gar and water, in confequence of which the fol- lowing experiments were made in December, 1788, in the prefence of my fellow candidate A. J. De Roffet, and two other gentlemen at that time ftudents of medicine, Experiment Firft. Part of a quantity of dough which had been raifed in three quarters of an hour, was put into a retort, and the procefs of diftillation performed upon it; fome liquid came over into the recipi- ent, which was not inflamable, and as taftelefs as pure water. It is allowed by all chemifts that vegetables, in the firft ftage of fermentation, yield a vinous fpirit in diftillation ; here then we muft conclude, either that the dough had not ferment- ed, or that fermented wheat flour will not yield a vinous ipirit, but the practice of this country city The difcovery may perhaps be but of little importance, I have howe- ver,'inferted this note to obvi3te any charges of plagiarifm .that might be offered againft me. 2.2 ESSAY ON proves that wheat tuillferment, and yield a vinous fpirit, when diftilled, therefore I conclude that the dough had not fermented. Experiment Second. The other,parcel of the fame dough was bak- «d, and yielded a perfectly fermented bread. Experiment 'Third. The fame dough remaining in the retort ufed in Exp. i. was rendered more fluid by the addi- tion of a little water, and kept in ? warm room : in nine hoars there were no appearances of fer- mentation ; in fixteen hours an efcape of air, a hiffing noife, &c. feemed to indicate that the pro- cefs had proceeded fome time : it was now dif- tilled again, and yielded a little acid fluid, and a (mall quantity of a weak vinous fpirit. Does it not feem true therefore, from thefe ex- periments, that flour requires even more than nine hours before it ferments, and if bread can be made in one hour, it amounts almoft to a de- monftration, that the fermentation of bread is not analogous to the vinous fermentation, ore- ven the fermentation of flour. From a variety of facts, I am induced to give the following explanation of the procefs : Yeaft is a fluid containing a large quantity of fixed air, or aerial acid, and the proportion is greater in proportion as the fluid is colder: As foon as the yeaft is mixed with the dough, heat is applied ; this extricates the air in an elaftic ftate, and as it is now diffufed through every particle of dough, F E R M E N T A T I O N. 2$ every particle muft be raifed; the vifcidity of the mafs retains it : It is now baked, and a flill grea- ter quantity of air is extricated by the increafed heat, and as the cruft forms, the air is prevent- ed from efcaping ; the water is diffipated ; the loaf is rendered fomewhat dry and folid, and be- tween every particle of bread we find a particle of air, as appears from the fpongy appearance of the bread, owing to the apparent vacancies which the air had made, by infinuating itfelf into it. But let us attend to another fact, which thofe who fupport the doctrine of fermentation will find a great difficulty in explaining: If the dough be kept longer than the proper time, without bak- ing, it falls again as it is termed, or as I would exprefs it, all the fixed air which raifed it is. diffi- pated, and then being baked we get heavy bread, exactly like the bread made with flour and water, and haftily baked, which we know is taftelefs. 1 Some will perhaps fay the fermentation is over, but this cannot be admitted; for after the vinous comes the acetous fermentation, but in this in- france we have no figns of acidity, neither can we fuppofe that any fubftance is fo fermentable as to finifh the vinous ftage of fermentation in nine hours, for we found that the fame materials in more favourable circumftances, required fixteen hours before the procefs began; fometimes, however, we do find heavy bread that is acid, but in fuch cafes I conclude that the acid came from the yeft, which had proceeded to that ftage. Another fact I would wifh to be attended to is, that fermentation alters the eflential properties of bodies, as we have fhewn in Sect. sd. and 3d. 24 ESSAY ON but bread is not chemically nor effentially differ- ent from flour, for we can actually feparate the different conftituent principles of flour from bread; befides, bread itfelf infufed in water, and expof- ed to the neceffary caufes of fermentation, will actually ferment, and no doubt yield a vinous fpi- rit in diftillation. If we might be allowed to reafon from Sir Ifaac Newton's axiom, " that no more caufes ofnatu- *' ral phenomena are to be admitted than are fuf- " ficient to explain them," we can produce three facts that will prove clearly, that fermentation is not neceffaryto make bread ; from which I infer, that it does not take place. The bakers in this city find much difficulty in getting good yeaft in ftimmer, for fermentation goes on fo rapidly in the warm weather, that it grows four in a fhort time; they can however, make it anfwer their purpofe. They diffolve a fmall quantity of pot- afh in as much water as is neceffary to make their bread ; this they mix with their yeaft and flour : in lefs than ten minutes their bread is fit to bake, and has every property of what is called the belt fermented bread. We need fcarcely explain this fact; every perfon moderately acquainted with the fubject, knows that pot-afh is an alkali united to much fixed air, and we think the acid in the yeaft fets it at liberty, which is the caufe of the raifing of the bread, as before explain- ed. A fecond fad that I fhall mention, was given us by our late chemical profeffor Doctor Rufli, in the courfe of lectures which he delivered in the winter of 1788-9,, he informs us, that near Saratoga, there are two mineral fprings, the wa- FERMENTATION. 2j" ters of which have all the properties of the famous Pyrmont water, in other words they are highly impregnated with fixed air. This water when mixed with flour into dough, is fufficient without yeaft, to make a very light and palatable bread. A third fact appears decifive; we know that a little fait is added to the bread by our'bakers ; this fuggefted the idea of fupplying it in the following- manner, which I confefs is rather fanciful: I procured fome nice chryftals of the fait formed by the foffil alkali and fixed air and diffolved them in water fufficient to make a fmall loaf of bread, to this I added a little of the marine acid commonly called fpirit of fea-falt; fixed air was generated, but was abforbed by the cold water; it was then mixed with flour, fet in a warm place to rife and fhortly after baked; and I had the exquifite pleafure to obtain a tolerably light loaf of bread, fuch as any one would have fuppofed to have been fermented, which was feafoned by the fea-falt, formed by the union of the foffil and the fpirit of fea-falt; whilft the fixed air of the foffil alkali was difengaged in order to raife it. SECTION V. Zymics and Antizymics. THIS is by far the mod difficult part of the fubject; that many fubftances have the power of exciting fermentation and others of re- tarding it, cannot be denied; but I am far from believing that chemifts are quite correct upon this fubject ; whilft the one phenomenon, the e- fcape of air, is fo much attended to as the diftin- guifhing character of fermentation, we can ne- 26 E S S A Y ON ver be accurate ; thus I fufpect that when a fmall quantity of an alkaline fait is faid to be an anti- zimic with refpect to milk it abforbs the acid that is generated in the fermentation, fo that it cannot be tailed, and hence preferves the milk fweet; chalk on the other hand is faid to be zymic and to accelerate the vinous fermentation; but is it not probable that in fuch cafes a fmall quantity of acid is generated in the vinous liquor, which unites to the chalk, fets the fixed air at liberty and it then efcapes by mere effervefcence ? Subftances that have fermented, yield a matter that is fuppofed to poffefs the properties of ex- citing fermentation in other bodies ; for in- ftance yeaft, and fuch fubftances are faid to pof- fefs a power of affimilation ; but we cannot ac- count for the operation of the yeaft in thefe cafes, for we by no means know why they tend to diffi- pate the phlogifton of fuch fubftances, neither do we fee any fimilarity in the chemical compofi- ( tion of different zymics and antizymics; that yeaft excites the vinous fermentation in liquors I muft not deny. I cannot however omit relating a fo- litary experiment; I took a quantity of fugar and water, and divided it into two equal parts, I put them into two veffels of the fame fize and fhape, and expofed them to the fame temperature of heat; to one I added yeail, to the other none ; after fome time they had both become confide- rably acid j they were then both faturated with ) an alkali, and the quantity required for that pur- pofe was almoft exactly alike in each. Here then it would feem that the yeaft was entirely paffive. I can make no remarks upon this experiment; I leave it to be confirmed or rejected as future facts fhall dictate. Mr. Henry of Manchefter, in a FERMENTATION. 27 very elegant memoir, prefented to their Philofo- phical and Literary Society, on the fubject offer- mentation, afferts that &c. ferment without any addition : I think we have great reafon to doubt the fact. But I cannot as yet difprove his idea by experiment. In the memoir above mentioned, the author feems to think that fixed air is the true caufe of fermentation in vinous liquors, and he tells us of the excellent tafte afforded to punch by being im- pregnated with it. Fixed air it is well known improves the tafte of liquors, but we cannot fuf- pect that it made the punch ferment in his expe" riment; but he cells us that he made an artificial yeaft by impregnating tlour and water with fixed air, that with this yeaft he made beer (perhaps he might have made it without it) and vinegar, and that he fermented bread with it: as for its fermenting bread, we might readily allow that it would raife bread upon the principles already laid down in Section 4. and when he tells us how quick the fermentation takes place in his liquors, when expofed to a gentle heat, may we not juft- ly fuppofe that the warmth extricated the fixed air, that he had artificially combined with it, and that from this phenomenon alone he had fuppofed fermentation to be going on in them ? Fixed air as we have already faid, is the caufe of the brifk- nefs, pungent tafte and fparkling appearance of vinous liquors; and it is remarkable that in equal circumftances the colder they are the more air they contain: I have been told as an argument againft 28 ESSAYON me in fuppofing that'brcad does not ferment be- caufe it is raifed fo quickly; that a barrel of beer may be kept in a vault in the fummer, without fermenting, but if it is hoifted up into the air it will ferment in two or three hours. But may I not juftly concludd that this apparent fermentati- on was only owing to the efcape of fixed air? but fay fome there is alfo a change of properties; the beer becomes flat and; vapid but this is the natu- ral confequence of loofing its fixed air which is the caufe of its brifknefs. It is alfo a curious fact that the fixed air in liquors muft be in a peculiar ftate, otherwife they do not poffefs that brifknefs or pungency we fpoke of: in fact it muft be on the point of affuming its elaftic form : hence li- quors are not fo brific in cold as in warm weather, and a connoiffeur in porter for inftance will tell you, that a bottle fhall open very brifk in a warm day, and upon the coming on of cold weather, all the reft fhall be flat and dead ; but let them be corked up, and kept in a warm room for a few days they will all recover their brifknefs, nay, I have feen a bottled opened in a cold day that has been quite vapid, which was made brifk and live- ly by corking it up tight again, and fetting it for ten or twelve minutes in a bafon of water little more than milk-warm, SECTION VI. Some anahfis of Animal Matter, the difference be- tween Animal and Vegetable Fermentation. HEN we confider that almoft, and perhaps all animals are ultimately derived from ve- getables, we muft be very much furprifed at the difference that fubfifts between the objects of the two kingdoms. They fliew their difference fur- W FERMENTATION. 29 prizingly in the fpontaneous changes which they undergo, when expofed to the neceffary condi- tions of fermentation, for animal fubftances emit a foetid difagreeable fmell, and the elaftic fluids is the vapor of volatile alkali. * If with Doctor Cullen we may believe that on- ly certain parts of vegetables are alimentary, we might fuppofe that the parts of the animal formed of thofe alimentary parts, would in fome meafure retain their nature;* his idea is, that it is only the acid, fugar and oil of vegetables that render them nutritious, and if that idea were juft, we ought to find them in thofe animal fluids that are im- mediately formed of the food; that an acid is prefent in the blood, at leaft neutralized by fome faline bafe, is eafily demonftrated, but it may be doubted whether it is ufeful to the animal; and we have irrefragible proofs that an oil, or at leaft the conftituent principles of an oil exift in the blood, for we obtain it by diftillation ; the tafte of the urine of diabetic patients, proves the pre- fence of fugar in the fyftem, which may have ei- ther exifted formally in the blood, or been for- med by fecretion, and the principles of it at leaft muft have been afforded by the vegetable food. I know of no direct experiments to afcertain the prefence of fugar in the blood; I am in poffeffion of one, however, that would feemto giveplaufibi- lity to that idea. AsMr. Bergman had obtained the acid of fugar from gum arabic, and from thence * Since the five laft feclions were punted off, I have met with a faft, that tends to throw much light on this fubjeft, and proves that animal and vegeta- ble matters are more allied to each other, than chemifts have heretofore ima- gined; in vol. iv. part 2. of the laft edition of the Encyclopedia Britannica, under the article China, §. 114, we find the followingobfervation. "Ano- ther kind of wine is ufed by the Chinefe or rather Tartars, called lamb-yiine. It is veryfirong, and has a difagreeable fmell; and the fame may be believed pf a kind of fpirit diflilled from the jlcjh offhcep.'\ 30 ESSAY ON FERMENTATION. concluded that it contained fugar ; I was ftruck with the analogy between gum arabic and the coag- ulable lymph of the blood; I treated tnis laft men- tioned fubftance according to the manner for ob- taining acid of fugar from fugar, gum arabic, &c. that is by boiling it with ftrong nitrous acid ; the mixture when cold yielded fome fmall chryftals, which precipitated lime from a folution in lime water in the fame manner as the acid of fugar does. It is true, the blood has not a faccharine tafte, neither has gum arabic, and perhaps fome trifling circumftances, as an intimate chemical union of fugar with an oil, may deftroy all the fenfible qualities of the fugar, yet as gum arabic yields nearly the fame refult in chemical proceffes that fugar does, it would be wrong to aflert that it contains no fugar; nay, barley has no faccha- rine or fweet tafte, yet the trifling circumftance of malting will make it remarkably fweet, and confeffedly faccharine ; and who wonld fay that barley did not contain fugar, before it was malt- ed, merely becaufe it could not be tailed ? There have been, however, fo few experi- ments made to determine the caufes of the diffe- rence of animal and vegetable fermentation, and the fubject is in itfelf fo truly difficult, that I muft candidly confefs it is far beyond my reach. FINIS. MeoL- Mist. klo PHI \i