Elements of Chemistry Part 8

libs. oz. gros grs.

Oxygen: of the water 340 0 0 0 } of the water } libs. oz. gros grs.

in the yeast 6 2 3 44.60 } 411 12 6 1.36 of the sugar 64 0 0 0 } of the dry yeast 1 10 2 28.76 } Hydrogen: of the water 60 0 0 0 } of the water } in the yeast 1 1 2 71.40 } 69 6 0 8.70 of the sugar 8 0 0 0 } of the dry yeast 0 4 5 9.30 } Charcoal: of the sugar 28 0 0 0 } of the yeast 0 12 4 59.00 } 28 12 4 59.00 Azote of the yeast - - - - } 0 0 5 2.94 -------------------------- In all 510 0 0 0

Having thus accurately determined the nature and quant.i.ty of the const.i.tuent elements of the materials submitted to fermentation, we have next to examine the products resulting from that process. For this purpose, I placed the above 510 libs. of fermentable liquor in a proper[26] apparatus, by means of which I could accurately determine the quant.i.ty and quality of gas disengaged during the fermentation, and could even weigh every one of the products separately, at any period of the process I judged proper. An hour or two after the substances are mixed together, especially if they are kept in a temperature of from 15 (65.75) to 18 (72.5) of the thermometer, the first marks of fermentation commence; the liquor turns thick and frothy, little globules of air are disengaged, which rise and burst at the surface; the quant.i.ty of these globules quickly increases, and there is a rapid and abundant production of very pure carbonic acid, accompanied with a sc.u.m, which is the yeast separating from the mixture. After some days, less or more according to the degree of heat, the intestine motion and disengagement of gas diminish; but these do not cease entirely, nor is the fermentation completed for a considerable time. During the process, 35 libs. 5 oz. 4 gros 19 grs. of dry carbonic acid are disengaged, which carry alongst with them 13 libs. 14 oz. 5 gros of water. There remains in the vessel 460 libs. 11 oz. 6 gros 53 grs. of vinous liquor, slightly acidulous. This is at first muddy, but clears of itself, and deposits a portion of yeast. When we separately a.n.a.lise all these substances, which is effected by very troublesome processes, we have the results as given in the following Tables. This process, with all the subordinate calculations and a.n.a.lyses, will be detailed at large in the Memoirs of the Academy.

TABLE IV. _Product of Fermentation._

libs. oz. gros grs.

35 libs. 5 oz. 4 gros 19 grs. { Oxygen 25 7 1 34 of carbonic acid, composed of { Charcoal 9 14 2 57

408 libs. 15 oz. 5 gros 14 grs. { Oxygen 347 10 0 59 of water, composed of { Hydrogen 61 5 4 27

{ Oxygen, combined { with hydrogen 31 6 1 64 { Hydrogen, combined 57 libs. 11 oz. 1 gros 58 grs. { with oxygen 5 8 5 3 of dry alkohol, composed of { Hydrogen, combined { with charcoal 4 0 5 0 { Charcoal, combined { with hydrogen 16 11 5 63

2 libs. 8 oz. of dry acetous { Hydrogen 0 2 4 0 acid, composed of { Oxygen 1 11 4 0 { Charcoal 0 10 0 0

4 libs. 1 oz. 4 gros 3 grs. { Hydrogen 0 5 1 67 of residuum of sugar, { Oxygen 2 9 7 27 composed of { Charcoal 1 2 2 53

{ Hydrogen 0 2 2 41 1 lib. 6 oz. 0 gros 5 grs. { Oxygen 0 13 1 14 of dry yeast, composed of { Charcoal 0 6 2 30 { Azote 0 0 2 37 --- ----------------- 510 libs. Total 510 0 0 0

TABLE V. _Recapitulation of the Products._

---------------------------------------------------------------------------- libs. oz. gros grs.

409 libs. 10 oz. 0 gros 54 grs. { Water 347 10 0 59 of oxygen contained in the { Carbonic acid 25 7 1 34 { Alkohol 31 6 1 64 { Acetous acid 1 11 4 0 { Residuum of sugar 2 9 7 27 { Yeast 0 13 1 14

28 libs. 12 oz. 5 gros 59 grs. { Carbonic acid 9 14 2 57 of charcoal contained { Alkohol 16 11 5 63 in the { Acetous acid 0 10 0 0 { Residuum of sugar 1 2 2 53 { Yeast 0 6 2 30

{ Water 61 5 4 27 71 libs. 8 oz. 6 gros 66 grs. { Water of the alkohol 5 8 5 3 of hydrogen contained { Combined with the in the { charcoal of the alko. 4 0 5 0 { Acetous acid 0 2 4 0 { Residuum of sugar 0 5 1 67 { Yeast 0 2 2 41

2 gros 37 grs. of azote in the yeast 0 0 2 37 --- --------------- 510 libs. Total 510 0 0 0

In these results, I have been exact, even to grains; not that it is possible, in experiments of this nature, to carry our accuracy so far, but as the experiments were made only with a few pounds of sugar, and as, for the sake of comparison, I reduced the results of the actual experiments to the quintal or imaginary hundred pounds, I thought it necessary to leave the fractional parts precisely as produced by calculation.

When we consider the results presented by these tables with attention, it is easy to discover exactly what occurs during fermentation. In the first place, out of the 100 libs. of sugar employed, 4 libs. 1 oz.

4 gros 3 grs. remain, without having suffered decomposition; so that, in reality, we have only operated upon 95 libs. 14 oz. 3 gros 69 grs. of sugar; that is to say, upon 61 libs. 6 oz. 45 grs. of oxygen, 7 libs. 10 oz. 6 gros 6 grs. of hydrogen, and 26 libs. 13 oz. 5 gros 19 grs. of charcoal. By comparing these quant.i.ties, we find that they are fully sufficient for forming the whole of the alkohol, carbonic acid and acetous acid produced by the fermentation. It is not, therefore, necessary to suppose that any water has been decomposed during the experiment, unless it be pretended that the oxygen and hydrogen exist in the sugar in that state. On the contrary, I have already made it evident that hydrogen, oxygen and charcoal, the three const.i.tuent elements of vegetables, remain in a state of equilibrium or mutual union with each other which subsists so long as this union remains undisturbed by increased temperature, or by some new compound attraction; and that then only these elements combine, two and two together, to form water and carbonic acid.

The effects of the vinous fermentation upon sugar is thus reduced to the mere separation of its elements into two portions; one part is oxygenated at the expence of the other, so as to form carbonic acid, whilst the other part, being deoxygenated in favour of the former, is converted into the combustible substance alkohol; therefore, if it were possible to reunite alkohol and carbonic acid together, we ought to form sugar. It is evident that the charcoal and hydrogen in the alkohol do not exist in the state of oil, they are combined with a portion of oxygen, which renders them miscible with water; wherefore these three substances, oxygen, hydrogen, and charcoal, exist here likewise in a species of equilibrium or reciprocal combination; and in fact, when they are made to pa.s.s through a red hot tube of gla.s.s or porcelain, this union or equilibrium is destroyed, the elements become combined, two and two, and water and carbonic acid are formed.

I had formally advanced, in my first Memoirs upon the formation of water, that it was decomposed in a great number of chemical experiments, and particularly during the vinous fermentation. I then supposed that water existed ready formed in sugar, though I am now convinced that sugar only contains the elements proper for composing it. It may be readily conceived, that it must have cost me a good deal to abandon my first notions, but by several years reflection, and after a great number of experiments and observations upon vegetable substances, I have fixed my ideas as above.

I shall finish what I have to say upon vinous fermentation, by observing, that it furnishes us with the means of a.n.a.lysing sugar and every vegetable fermentable matter. We may consider the substances submitted to fermentation, and the products resulting from that operation, as forming an algebraic equation; and, by successively supposing each of the elements in this equation unknown, we can calculate their values in succession, and thus verify our experiments by calculation, and our calculation by experiment reciprocally. I have often successfully employed this method for correcting the first results of my experiments, and to direct me in the proper road for repeating them to advantage. I have explained myself at large upon this subject, in a Memoir upon vinous fermentation already presented to the Academy, and which will speedily be published.

FOOTNOTES:

[26] The above apparatus is described in the Third Part.--A.

CHAP. XIV.

_Of the Putrefactive Fermentation._

The phenomena of putrefaction are caused, like those of vinous fermentation, by the operation of very complicated affinities. The const.i.tuent elements of the bodies submitted to this process cease to continue in equilibrium in the threefold combination, and form themselves anew into binary combinations[27], or compounds, consisting of two elements only; but these are entirely different from the results produced by the vinous fermentation. Instead of one part of the hydrogen remaining united with part of the water and charcoal to form alkohol, as in the vinous fermentation, the whole of the hydrogen is dissipated, during putrefaction, in the form of hydrogen gas, whilst, at the same time, the oxygen and charcoal, uniting with caloric, escape in the form of carbonic acid gas; so that, when the whole process is finished, especially if the materials have been mixed with a sufficient quant.i.ty of water, nothing remains but the earth of the vegetable mixed with a small portion of charcoal and iron. Thus putrefaction is nothing more than a complete a.n.a.lysis of vegetable substance, during which the whole of the const.i.tuent elements is disengaged in form of gas, except the earth, which remains in the state of mould[28].

Such is the result of putrefaction when the substances submitted to it contain only oxygen, hydrogen, charcoal and a little earth. But this case is rare, and these substances putrify imperfectly and with difficulty, and require a considerable time to complete their putrefaction. It is otherwise with substances containing azote, which indeed exists in all animal matters, and even in a considerable number of vegetable substances. This additional element is remarkably favourable to putrefaction; and for this reason animal matter is mixed with vegetable, when the putrefaction of these is wished to be hastened.

The whole art of forming composts and dunghills, for the purposes of agriculture, consists in the proper application of this admixture.

The addition of azote to the materials of putrefaction not only accelerates the process, that element likewise combines with part of the hydrogen, and forms a new substance called _volatile alkali_ or _ammoniac_. The results obtained by a.n.a.lysing animal matters, by different processes, leave no room for doubt with regard to the const.i.tuent elements of ammoniac; whenever the azote has been previously separated from these substances, no ammoniac is produced; and in all cases they furnish ammoniac only in proportion to the azote they contain. This composition of ammoniac is likewise fully proved by Mr Berthollet, in the Memoirs of the Academy for 1785, p. 316. where he gives a variety of a.n.a.lytical processes by which ammoniac is decomposed, and its two elements, azote and hydrogen, procured separately.

I already mentioned in Chap. X. that almost all combustible bodies were capable of combining with each other; hydrogen gas possesses this quality in an eminent degree, it dissolves charcoal, sulphur, and phosphorus, producing the compounds named _carbonated hydrogen gas_, _sulphurated hydrogen gas_, and _phosphorated hydrogen gas_. The two latter of these ga.s.ses have a peculiarly disagreeable flavour; the sulphurated hydrogen gas has a strong resemblance to the smell of rotten eggs, and the phosphorated smells exactly like putrid fish. Ammoniac has likewise a peculiar odour, not less penetrating, or less disagreeable, than these other ga.s.ses. From the mixture of these different flavours proceeds the fetor which accompanies the putrefaction of animal substances. Sometimes ammoniac predominates, which is easily perceived by its sharpness upon the eyes; sometimes, as in feculent matters, the sulphurated gas is most prevalent; and sometimes, as in putrid herrings, the phosphorated hydrogen gas is most abundant.

I long supposed that nothing could derange or interrupt the course of putrefaction; but Mr Fourcroy and Mr Thouret have observed some peculiar phenomena in dead bodies, buried at a certain depth, and preserved to a certain degree, from contact with air; having found the muscular flesh frequently converted into true animal fat. This must have arisen from the disengagement of the azote, naturally contained in the animal substance, by some unknown cause, leaving only the hydrogen and charcoal remaining, which are the elements proper for producing fat or oil. This observation upon the possibility of converting animal substances into fat may some time or other lead to discoveries of great importance to society. The faeces of animals, and other excrement.i.tious matters, are chiefly composed of charcoal and hydrogen, and approach considerably to the nature of oil, of which they furnish a considerable quant.i.ty by distillation with a naked fire; but the intolerable foetor which accompanies all the products of these substances prevents our expecting that, at least for a long time, they can be rendered useful in any other way than as manures.

I have only given conjectural approximations in this Chapter upon the composition of animal substances, which is. .h.i.therto but imperfectly understood. We know that they are composed of hydrogen, charcoal, azote, phosphorus, and sulphur, all of which, in a state of quintuple combination, are brought to the state of oxyd by a larger or smaller quant.i.ty of oxygen. We are, however, still unacquainted with the proportions in which these substances are combined, and must leave it to time to complete this part of chemical a.n.a.lysis, as it has already done with several others.

FOOTNOTES:

[27] Binary combinations are such as consist of two simple elements combined together. Ternary, and quaternary, consist of three and four elements.--E.

[28] In the Third Part will be given the description of an apparatus proper for being used in experiments of this kind.--A.

CHAP. XV.

_Of the Acetous Fermentation._

The acetous fermentation is nothing more than the acidification or oxygenation of wine[29], produced in the open air by means of the absorption of oxygen. The resulting acid is the acetous acid, commonly called Vinegar, which is composed of hydrogen and charcoal united together in proportions not yet ascertained, and changed into the acid state by oxygen. As vinegar is an acid, we might conclude from a.n.a.logy that it contains oxygen, but this is put beyond doubt by direct experiments: In the first place, we cannot change wine into vinegar without the contact of air containing oxygen; secondly, this process is accompanied by a diminution of the volume of the air in which it is carried on from the absorption of its oxygen; and, thirdly, wine may be changed into vinegar by any other means of oxygenation.

Independent of the proofs which these facts furnish of the acetous acid being produced by the oxygenation of wine, an experiment made by Mr Chaptal, Professor of Chemistry at Montpellier, gives us a distinct view of what takes place in this process. He impregnated water with about its own bulk of carbonic acid from fermenting beer, and placed this water in a cellar in vessels communicating with the air, and in a short time the whole was converted into acetous acid. The carbonic acid gas procured from beer vats in fermentation is not perfectly pure, but contains a small quant.i.ty of alkohol in solution, wherefore water impregnated with it contains all the materials necessary for forming the acetous acid.

The alkohol furnishes hydrogen and one portion of charcoal, the carbonic acid furnishes oxygen and the rest of the charcoal, and the air of the atmosphere furnishes the rest of the oxygen necessary for changing the mixture into acetous acid. From this observation it follows, that nothing but hydrogen is wanting to convert carbonic acid into acetous acid; or more generally, that, by means of hydrogen, and according to the degree of oxygenation, carbonic acid may be changed into all the vegetable acids; and, on the contrary, that, by depriving any of the vegetable acids of their hydrogen, they may be converted into carbonic acid.

Although the princ.i.p.al facts relating to the acetous acid are well known, yet numerical exact.i.tude is still wanting, till furnished by more exact experiments than any hitherto performed; wherefore I shall not enlarge any farther upon the subject. It is sufficiently shown by what has been said, that the const.i.tution of all the vegetable acids and oxyds is exactly conformable to the formation of vinegar; but farther experiments are necessary to teach us the proportion of the const.i.tuent elements in all these acids and oxyds. We may easily perceive, however, that this part of chemistry, like all the rest of its divisions, makes rapid progress towards perfection, and that it is already rendered greatly more simple than was formerly believed.

FOOTNOTES:

[29] The word Wine, in this chapter, is used to signify the liquor produced by the vinous fermentation, whatever vegetable substance may have been used for obtaining it.--E.

CHAP. XVI.