may be defined a sensible internal motion of the constituent particles of a moist fluid, mixed or compound body; by the continuance of which motion, these particles are gradually removed from their former situation or combination, and again, after some visible separation is made, joined together in a different order and arrangement, so that a new compound is formed, having qualities very sensibly different from those of the original fluid.

Fermentation, properly so called, is confined to the vegetable and animal kingdoms; for the effervescences between acids and alkalies, however much they may resemble the fermentation of vinous liquors, are nevertheless exceedingly different. It is divided into three kinds; or rather, there are three different stages of it, viz. the vinous, the acetous, and the putrefactive. Of the first, vegetables alone are susceptible; the flesh of young animals is in some slight degree susceptible of the second (A); but animal substances are particularly susceptible of the third, which vegetables do not so easily fall into without previously undergoing the first and second. The produce of the first stage is wine, or some other vinous liquor; of the second, vinegar; and of the third, volatile alkali. See BREWING, VINEGAR, &c.

Fermentation is one of the most obscure processes in nature, and no attempt has been made to solve it with any degree of probability. All that we know with regard to it is, that the liquor, however clear and transparent at first, no sooner begins to ferment, than it becomes turbid, deposits a sediment, emits a great quantity of fixed air, and throws up a scum to the top, acquiring at the same time some degree of heat. The heat of the vinous stage, however, of it, is but moderate, seldom or never exceeding that of the human body. The heat of the acetous is considerably greater; and that of the putrefactive is the greatest of all, inasmuch that putrefying substances, when heaped together in great quantities, will sometimes break forth into actual flame.

From these phenomena, fermentation would seem to be a process ultimately tending to the entire dissolution of the fermenting substance, and depending upon the action of the internal heat, etherial fluid, or whatever else we please to call it, which pervades, and makes an essential ingredient in, the composition of all bodies. From such experiments as have been made upon this subject, it appears, that whether fixed air is the bond of connection between the particles of terrestrial bodies or not, yet the emission of it from any substance is always attended with a diffusion of that substance. We cannot, however, in the present case, say that the emission of the fixed air is the cause of the fermentation. It is in fact otherwise. Fixed air hath no tendency to fly off from terrestrial substances with which it is united; on the contrary, it will very readily leave the atmosphere after it hath been united with it, to join itself to such terrestrial substances as are capable of absorbing it. The emission of it, therefore, must depend upon the action of some other fluid; most probably the fire or heat, which is dispersed thro' all substances in a latent state, and in the present case begins sensibly to manifest itself. But from what cause the heat originally begins to operate in this manner, seems to be entirely unknown and inexplicable, except that it appears somehow or other to depend on the air; for, if that is totally excluded, fermentation will not go on.

In the Memoirs of the Manchester Society, Mr Henry gives an account of some experiments, in which he produced fermentation not only in bread and wort, but in liquors which we should think quite incapable of it, viz. punch and whey. Having previously suspected, from some observations and experiments, that yeast was only a quantity of fixed air involved and detained among the mucilaginous parts of the fermenting liquor, air, he attempted to prepare it in the following manner. Having boiled wheat-flour and water to the consistence of a thin jelly, he put this viscous fluid into the middle part of Dr Nooth's machine for impregnating water with fixed air. The gas was absorbed in considerable quantity; and next day the matter was in a state of fermentation. The third day it had acquired so much of the appearance of yeast, that an experiment was made on some paste for bread; and after five or six hours baking, it

(A) Under the article CHINA, no 114, a fact is mentioned which seems to show that animal substances are likewise capable of the vinous fermentation; viz. that the Chinese make use of a certain liquor called lamb-wine, and likewise that they use a kind of spirit distilled from sheep's flesh. This is related on the credit of M. Grolier; but as he does not mention the particulars of the process, we are at liberty to suppose that the flesh of these animals has been mixed with rice, or some other ingredients naturally capable of producing a vinous liquor; so that, instead of contributing any thing to the fermentation in question, they may in reality be detrimental, and furnish only that strong and disagreeable smell complained of in the liquid. Fermentation was found to have answered the purpose tolerably well. Another experiment was made with wort; but here the artificial yeast was not made use of. Instead of this, part of the wort itself was put into Nooth's machine, and impregnated with fixed air, of which it imbibed a large quantity. On being poured into the remainder of the liquor, a brisk fermentation came on in 24 hours, "a strong head of yeast began to collect on its surface, and on the third day it seemed fit for tunning?" In prosecuting the experiment, good bread was made with the yeast taken off from the surface; and beer was produced by keeping the fermented liquor, and good ardent spirit produced by distilling it.

In another experiment, in which a fourth part of the wort was impregnated but not saturated with fixed air, the fermentation did not commence so soon, though it is probable that it would also have taken place at last without any farther addition. The experiment commenced about midnight; but in the morning there were no signs of fermentation. At five in the afternoon there was only a slight mantling on the surface. A bottle with a perforated stopper and valve containing an effervescing mixture of chalk and vitriolic acid was then let down to the bottom of the vessel; the discharge of air from this mixture was going on rapidly at nine o'clock; while the liquor at the same time seemed to be in a state of effervescence. At eleven o'clock the bottle was withdrawn, as the fermentation was commenced beyond a doubt, the liquor having a pretty strong head of yeast upon it. Next day the fermentation seemed to be on the decline, but was recovered by a second immersion of the mixture. When the vinous fermentation was finished, the liquor, by being kept too long, was found converted into vinegar; so that in the course of these experiments, ale, bread, yeast, ardent spirit, and vinegar, had all been produced.

From these experiments it would seem natural to suppose that fixed air was the cause of fermentation, contrary to what has been already laid down. But in fact there is not any contradiction here to the position just mentioned; for the quantity of fixed air introduced into the liquor on Mr Henry's experiments was too great for it to contain. Some part of the latent heat by which the elasticity of that fluid is produced may likewise have been absorbed, and disposed the liquor to run into the fermenting state sooner than it would otherwise have done. Or, perhaps, when any fluid substance of the aqueous kind contains an extraordinary proportion of fixed air, it may be thus inclined to run into the fermentative process, by some disposition of the air itself to reassume its elastic state. This seems probable from Mr Henry's experiments with Pyrmont water. Having made some punch with an artificial water of this kind, he put a pint of it into a quart bottle and stopped it with a cork. On opening it three or four days after, he found that it creamed and mantled like the briskly bottled cider; so that it was taken for some delicious liquor hitherto unknown. This length of time he found was necessary to give the briskness just mentioned to the fluid; for artificial Pyrmont water itself assumes a brisk and sparkling appearance after being kept three or four days, though it has not at first, unless a very great quantity of air be forced into it at its preparation. In like manner a quantity of whey, impregnated with fixed air, was changed into a brisk and sparkling vinous liquor by keeping for some time in a bottle looily corked.

On certain substances, however, both fluid and solid, fixed air hath a different effect. Thus, when mixed with alkaline salts, whether fixed or volatile, fluid or solid, it first neutralizes, and then renders them acid, without the least tendency to fermentation, unless an acid be added. Then indeed a great effervescence will ensue; but this, as we have already said, is not a true fermentation. On calcareous earths its effect is something singular: for these earths, when pure, are soluble in water; when joined with a certain proportion of fixed air, they become insoluble; and with an over-proportion they become soluble again; but none of them show any disposition to fermentation, though kept ever so long in either state. As water therefore contains a great quantity of latent heat which it readily parts with, the probability still is, that a disposition to unite with the solid part of fixed air exists in that element, rather than to remain combined with the water. It is likewise well known that all fermentable substances, such as the juices of ripe fruits, sugar, &c., contain much fixed air, and therefore fall spontaneously into fermentation when kept in a gentle warmth. This last circumstance supplies a quantity of sensible heat, or elementary fire acting in its expansive form, which the water more readily parts with than that which acts upon its own particles in such a manner as to keep them easily moveable upon one another, and thus occasion its fluidity. Other substances contain less fixed air, as infusion of malt, potatoes, turnips, &c., whence it is necessary to add an extraordinary quantity to them, either enveloped in mucilaginous matter which is analogous to yeast, or pure as was done by Mr Henry.

Thus we may suppose fermentation to consist in the action of elementary fire expanding the fixed air naturally contained in the fluid, or artificially introduced into it; in consequence of which certain changes are produced in the nature of the fluid itself; and it becomes a vinous, acetic, or putrid liquor, according to the degree of action which takes place. This seems to Dr Pennington coincide with the opinion of Dr Pennington of Philadelphia, who, in his inaugural dissertation on this subject, makes a change of the sensible qualities of the substance the only criterion of fermentation. Hence he denies that any true fermentation exists in the raising of bread, as is commonly supposed; and indeed his arguments on this subject seem decisive. To ascertain this, he put into a retort some dough which had been raised in three quarters of an hour; and, on applying a gentle heat, some aqueous liquid came over, which did not show the least vestige of vinous spirit, though the remainder of the same dough afforded a good and well fermented bread. On adding a little water to the dough which remained in the retort, and letting the mixture stand in a gentle warmth for nine hours, no sign of fermentation appeared; but in six hours the process seemed to have been going on for some time; and on distillation yielded a small quantity of vinous spirit. Hence it appears that flour requires more than nine hours before it ferments; but as bread frequently rises in one hour, the processes must somehow or other be essentially different. "From a variety of facts (says our author), Fermentation), I am induced to give the following explanation of the process (making of bread). Yeast is a fluid containing a large quantity of fixed air or aerial acid. As soon as the yeast is mixed with the dough, heat is applied; this extricates the air in an elastic state; and as it is now diffused through every particle of dough, every particle must be raised; the fidelity of the mass retains it: it is now baked, and a still greater quantity of air is extricated by the increased heat; and as the crust forms, the air is prevented from escaping; the water is diffused: the loaf is rendered somewhat dry and solid; and between every particle of bread we find a particle of air, as appears from the spongy appearance of the bread, owing to the apparent vacancies which the air had made by infusing itself into it." This explanation he finds also confirmed by what is called the falling of bread after it has once been raised; and which takes place so rapidly, that we cannot suppose the process of fermentation to have been finished in the time: nay, bread will fall before we are warranted from his experiment to say that the fermentation is well begun; for this, as we have seen, required between 9 and 16 hours.

That bread is raised, not by a proper fermentation, but by a mere effervescence or escape of fixed air, is likewise evident from several facts mentioned by Dr Pennington. In Philadelphia, the bakers find some difficulty in getting good yeast in the summer-time, on account of the heat of the weather, which very soon turns it sour. In this case, they dissolve a small quantity of potash in water, and mix it with their yeast; when the effervescence produced between the acid and alkali produces such a discharge of fixed air, as raises the bread in less than ten minutes. He informs us also, on the authority of Dr Rush late professor in the college of Philadelphia, that "near Saratoga there are two mineral springs, the waters of which have all the properties of the famous Pyrmont water, being highly impregnated with fixed air. When this water is mixed with flour into dough, it is sufficient, without yeast, to make a very light and palatable bread."

A third fact is still more decisive. "I procured (says the Doctor) some nice crystals of the salt formed by the felspar alkali and fixed air, and dissolved them in water sufficient to make a small loaf of bread. To this I added a little of the marine acid, commonly called spirit of sea-salt; fixed air was generated, but was absorbed by the cold-water; it was then mixed with flour, set in a warm place to rise, and shortly after baked; and I had the exquisite pleasure to obtain a tolerably light loaf of bread, such as any one would have supposed to have been fermented, which was seasoned by the sea-salt, formed by the union of the felspar alkali and spirit of sea-salt; whilst the fixed air of the felspar alkali was disengaged, in order to raise it."

To these instances mentioned by our author we shall add two others, which show that fixed air is not even necessary to the raising of bread; and of consequence we cannot suppose that fermentation, which produces a great quantity of it, is the foundation of the process. One is, that eggs, when beaten into a froth, are sometimes made use of for raising bread; but more especially for puddings, &c., in which they perform an operation similar to that of raising and rendering bread light and spongy. This is done by the rarefaction of the particles of air enveloped among the glutinous particles of the egg; and hence snow, on account of its porous and spongy nature, containing a great quantity of air enveloped amongst its particles, will do the same thing. This last particular was lately published by Dr Rotheram of Newcastle.

With regard to the other experiments of Mr Henry, His observations on Mr Henry's experiments, they seem to Dr Pennington not to be altogether conclusive. He doubts the justice of Mr Henry's idea, "that wort cannot be brought into the vinous fermentation without the addition of a ferment." When we consider the analogy betwixt the infusion of malt and other fermentable liquids, the Doctor supposes that wort, as well as they, might spontaneously fall into a state of fermentation. He says indeed, that he has not as yet been able to disprove the idea by experiment; but Captain Cook has already made the experiment, and the event has decided the matter in the Doctor's favour*. We are told by that celebrated navigator, that the insipidated wort would have an article Cook, furred the purpose excellently, provided it could have been kept from fermentation in its insipidated state. But this was found impossible: of consequence we must conclude, that wort, as well as other liquors, will fall into a state of fermentation spontaneously, though perhaps not so readily, or with such a small degree of heat, as other fermentable liquors. Hence we are not altogether certain, as Dr Pennington hints, whether the fermentation in Mr Henry's experiments might not have taken place without it. "In the memoir (Mr Henry's) above mentioned, says the Doctor, the author seems to think, that fixed air is the true cause of fermentation in vinous liquors; and he tells us of the excellent taste afforded to punch by being impregnated with it. Fixed air, it is well known, improves the taste of liquors; but we cannot suppose that it made the punch ferment in his experiment; but he tells us, that he made an artificial yeast; that with this yeast 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 raise bread, upon the principles already laid down: and when he tells us how quick the fermentation takes place in his liquors when exposed to a gentle heat, may we not justly suppose, that the warmth extricated the fixed air that he had artificially combined with it, and that from this phenomenon alone he had supposed fermentation to be going on in them? Fixed air is the cause of the briskness, pungent taste, and sparkling appearance, of vinous liquors; and it is remarkable, that, in equal circumstances, the colder they are, the more air they contain. It is also a curious fact, that the fixed air in liquors must be in a peculiar state, otherwise they do not possess that briskness or pungency we spoke of; in fact, it must be on the point of affuming its elastic form: hence liquors are not so brisk in cold as in warm weather; and a connoisseur in porter, for instance, will tell you, that a bottle shall open very briskly in a warm day; and upon the coming on of cold weather, all the rest shall 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 former briskness; nay, I have... Our author's theory of fermentation is to the following purpose. 1. The heat occurring in the mixture, he explains on Dr Black's principle of latent heat. 2. In the fermenting process, he supposes the inflammable part of the mixture to have a tendency to combine with pure air, and thus to form what is called fixed air. 3. The pure air is supposed to be derived from the atmosphere, while inflammable air is furnished by the fermenting liquor. 4. The fixed air found in such plenty above the liquid while in a state of fermentation, does not exist in its originally, but is formed by a combination of the two ingredients just mentioned. 5. On these principles the heat which takes place in the mixture may be particularly explained in the following manner. "Suppose that the quantity of heat in the two airs before combination was in each as ten; or, in other words, that they were capable of containing that quantity in a latent state essential to their existence as matter in that form; when they unite, they form a very different kind of air, which is not capable of combining with so much heat, and perhaps quite foreign to its existence as that kind of matter; we will suppose then, that it can combine with but a quantity of that heat as five; the consequence must then 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 are increased, it becomes mechanically diffused among those bodies which are nearest to it; it gives the redundant heat to the hands," &c.

We shall conclude this article with one obvious remark, viz., that the dispute concerning Mr Henry's method of inducing fermentation, may be easily decided by a comparative trial. Let, for instance, two gallons of wort, the quantity he used in his experiment, be put into a certain vessel without addition, and kept in a moderate heat for a certain time; take other two gallons, and impregnate the whole or any part of it with fixed air, according to Mr Henry's method: put the whole then into a vessel similar to the other, and set it in the same place; and if the fermentation begins in the one impregnated with fixed air sooner than the other, we have good reason to believe that the fixed air was the cause of its doing so. This experiment is easily made, and must be of considerable importance to the public; for, as Mr Henry justly observes, his experiments "may be of extensive utility, and contribute to the accommodation, the pleasure, and the health, of men in various situations, who have hitherto been precluded in a great measure from the use of fermented liquors; and be the means of furnishing important articles of diet and of medicine." Even as matters stand, we must consider this end as accomplished; though, if the mere circumstance of heat, without fixed air, would bring on fermentation, it would undoubtedly render the process considerably easier, by saving the trouble of impregnating the liquor with fixed air. With regard to bread, his method seems to be entirely decisive.

The business of fermentation is one of the great preparations to the distillery. What we usually call vicious fermentation in particular, is the kind in which it is principally concerned. By this we usually understand that physical action, or intestine commotion of the parts of a vegetable juice, tincture, or solution, which render them fit to yield an inflammable spirit on distillation.

This fermentation in the hands of the distiller differs from the common one that is used in the making of potable vinous liquors, as being much more violent, tumultuary, active, and combinatory than that. A large quantity of yeast, or other ferment, is added to the distiller's fermentation; the free air is admitted, and every thing is contrived to quicken the operation, so that it is sometimes finished in two or three days. This great dispatch, however necessary to the large dealer, has its inconveniences attending it; for the spirit is by this means always fouler, more groggy, and really terrestrial, than it would have been if the liquor had undergone a proper fermentation in a slower manner. It also suffers a diminution in its quantity, from the violent and tumultuary admixture, conflict, and agitation of the free air, both in the body and upon the surface of the liquor, especially if the liquor be not immediately committed to the still as soon as the fermentation is fairly slackened or fully ended. It is a very difficult task to render the business of fermentation at once perfect and advantageous. To ferment, in perfection, necessarily requires length of time and careful attendance, and close vessels, beside several other articles of nice management, which cannot be expected to be received and practised in the large way, on account of the trouble and expense, unless it could be proved to the distillers, as possibly it sometime may, that the quantity of spirit would be so much greater from the same quantity of materials managed thus, than by the common way, that it will more than pay its own expense; to which may be added, the very well known advantage of the spirit thus procured by perfect fermentation, being much finer than that obtained in the common way. Till this shall be made out, it may not be amiss to try how much of the more perfect art of vinous fermentation is profitably practicable by the distiller in the present circumstances of things. The improvements to be made in this affair will principally regard, 1. The preparation or previous disposition of the fermentable liquor. 2. The additions tending to the general or some particular end. 3. The admission or exclusion of the air. 4. The regulation of the external heat or cold. And, 5. A suitable degree of rest at last. When proper regard is had to these particulars, the liquor will have its due course of fermentation, and it will thence become fit to yield a pure and copious inflammable spirit by distillation. The tincture, solution, or liquor, intended for fermentation, for the still, should be considerably thin and aqueous. That sort of richness there is in the twelve-shilling small beer, is the utmost that ought to be allowed to it. This property not only fits it to ferment readily, but also to yield a larger quantity in proportion of a pure vinous spirit, than it would do if it were more rich or clammy: the grog, foul, viscid, and earthy particles of such glutinous liquors, being after fermentation apt to rise up with the boiling heat, which Fermentation which must necessarily be employed to raise the spirit; and the spirit thus of course comes over foul and fetid.

There is also another advantage attending the thinness of this liquor, which is, that it will sooner become fine by standing before fermentation; whence it may be commodiously drawn off from its feces or bottom, which must always, in case of corn, malt, or any other mealy substance, be kept out where the purity of the spirit is consulted. A certain degree of warmth seems necessary in all the northern climates, to all sorts of artificial liquors intended for immediate fermentation, especially in winter; but the natural juices of vegetables, which have never been inspissated, as that of grapes and other fruits when fully ripened, will usually ferment, as soon as they are expressed, without any external assistance. But as a certain degree of inspissation prevents all tendency to fermentation in all vegetable juices, though otherwise strongly disposed to ferment; so a long continuance, or an increase of the inspissating heat, especially if it acts immediately through a metallic or solid body upon the juice, will destroy its fermenting property; and it will do this the more effectually, as the heat employed approaches to that of scorching, or the degree capable of giving an empyreuma.

—After the same manner, several experiments make it appear that there is a certain degree of heat, the continuance or least increase of which proves detrimental or destructive to fermentation, as there is another which in a wonderful manner encourages and promotes it. These two degrees of heat ought to be carefully noted and settled by the thermometer, or other certain methods, for philosophical and chemical uses; but for common, or all economical occasions, they may be limited to what we call a tepid and fervid heat. A fervid heat is the bane of all vinous fermentation; as a tepid one, or rather imperceptible warmth, is the great promoter of them. In this neutral state, therefore, with proper contrivances to preserve and continue it, the liquor is to be put into a suitable vessel for fermentation; at which time, if it works not of itself, it must be quickened by additions; and, in general, by such things as are commonly called fermentations.

The juices of plants are strangely altered by fermentation; and are susceptible of many, and those very various, changes from it. And it is not only the juices of fruits that are thus to be wrought upon, as those of apples, pears, grapes, and the like, in the common way; but there is an artificial change to be made in the seeds of plants by what is called maling. And it is not grain alone that is thus to be wrought upon, but any other seed whatever may be made to yield its juices and virtues freely to water by this process. The juices of roots also, for instance that of liquorice, will be wrought upon in the same manner; and the juices of the bodies of trees, as of the birch, and the like. If in the month of March a hole be bored into the body of a birch-tree, and this hole be stopped with a cork, through the middle of which there is thrust a quill open at both ends, the juices of the tree will drop out at the quill at the rate of a large drop every second of a minute, and a great quantity will in time be obtained in this manner. This liquor is not unpleasant to the taste, and looks tolerably clear, resembling water into which a little milk had been spilt. There are many ways of fermenting this juice, by all of which it is converted into a fort

of wine. These are well known. But there is another remarkable property in our maples, both the common small kind and the great one, which we call the fycamore; these being tapped in the same manner, will bleed freely in winter; and their juices, after a hard frost breaks, will flow out in so copious a manner as is scarce to be conceived. The willow, the poplar, and the walnut-tree, will all bleed also; and fermentation, of which their several juices are easily susceptible, will turn them all into palatable and strong wines.