ferment; for which purpose yeaft is always ufed. If, therefore, by impregnating wort with fixed air, I could bring on the vinous fermentation, if I could carry on this fermentation fo as to produce ale, and, from the ale, procure ardent fpirit, I imagined that I fhould be able to announce to the world a mode of procuring newly-fermented liquors, in most climates and in moft fituations.

I accordingly procured from à public-houfe two gallons of strong wort. It had a difagreeable bitter tafte, owing either to bad hops, or to fome fubftitute for hops. A large part of the liquor was impregnated, in Nooth's machine, with fixed air, which it seemed to abíorb very rapidly and in large quantity. When it was thus impregnated, it was mixed with the other part, and poured into a large earthen jug, the mouth of which was ftopped with a cloth, and placed in a degree of heat, varying from 70° to 80°. In twenty-four hours the liquor was in brifk fermentation, a strong head of yeait began to colleft on its furface; and, on the third day, it appeared to be in a ftate fit for tunning. It was therefore put into an earthen veffel, fuch as is used in this country by the common people as a fubítitute for a barrel, for containing their finall brewings of fermented liquors. During the space of near a week, previous to the flopping up of this veffel, much yeaft was collected on its furface, and occafionally taken off; and by means of this yeaft, I fermented wheat flour, and procured as good bread as I could have obtained by ufing an equal quantity of any other yeaft.

The veffel was now stopped up;

and in about a month tapped. The liquor was well fermented, had a head or cream on its furface; and though, as might be expected from the defcription of the wort, not very pleasant, yet as much fo, as the generality of the ale brewed at public-houfes.

A part of the ale was fubmitted to diftillation; and, from it, a quantity of vinous fpirit was produced, which is fubmitted to the examination of the fociety. But the veffel being broken before the diftillation was finished, the quan tity it would have yielded was not afcertained. However, that which was obtained, appeared not to differ much in quantity from what an equal portion of common ale would have afforded.

As I had loft my notes, and was obliged to make out the preceding account from memory, I defigned to repeat the experiments again; but various engagements prevented me, till the latter end of Auguft 1784. Of thefe experiments the following notes are taken from my journal:

August 30, I procured two gallons of common ale wort, two quarts of which were, in the evening, impregnated, but not faturated, with fixed air. The impregnated liquor was then added to the other part, and, about midnight, placed in a large jug, within the air of the kitchen fire, where it remained during the night. In the morning no figns of fermentation. At five o'clock P. M. only a flight mantling on the surface. Apprehending the quantity of gas to have been too imali, a bottle, with a perforated flopper and valve, containing an effervefcing mixture of chalk and vitriolic acid, was let down into

the

the wort. At nine o'clock, the difcharge of air, from the bottle, was going on brifkly, and the wort feemed to be fermenting. At eleven o'clock the bottle was withdrawn, the fermentation being commenced beyond a doubt; the furface of the liquor having a pretty ftrong head. Temperature of the wort 80°-at the outside of the veffel 78°.

September ift, feven o'clock, A. M. the fire having been low during the night, the fermentation was lefs brisk- temperature of the wort reduced to 72, and probably had been lower during the night, as the fire was now increased. The liquor was ftirred up, placed in a fituation where the thermometer pointed to 82°, and the effervefcing mixture was again immerfed. It was withdrawn at noon, and the thermometer ftanding at 92°, the wort was removed farther from the fire-At four o'clock, P. M. the head of yeaft was ftrong, and at eleven o'clock was increased.

September 2d, nine o'clock, A. M. the liquor was judged to be in a proper ftate for tunning. It was accordingly removed into the veffel before described, and carried into the cellar at eleven-at noon, a high head of yeast was running over the top of the veffel-fome of it was taken of, and in two hours the head was equally strong.

September 3d, the fermentation proceeded regularly this day; and on the 4th I had collected fo much yeaft as to make a loaf with it, which, when baked, weighed about two pounds. The loaf was well fermented, good bread, having no peculiar tafte, except a flight bitternefs, proceeding from the wort having had too large a proportion of hops. Though, from the time

in which the yeaft had been collecting from fo fmall a quantity of liquor, its fermenting power might have been expected to have been impaired.

September 5th, the liquor was again covered with a plentiful head of yeaft; and the fermentation was fuffered to proceed to the 12th, when the veffel was clofed, in the usual manner.

I intended, in a few weeks, to have committed the liquor to diftillation; but my thoughts were unfortunately directed to an object which engaged my moft anxious attention; and my wort was neglected till the latter end of February; when, on tapping the veffel, the liquor, from having been kept fo long, under fuch difadvantageous circumftances, and, perhaps, from too great heat in the fermentation, and the too long continuance of it, had paffed from the vinous to the acetous ftate, and was become excellent alegar.

As I had obtained a vinous fpirit from the former parcel of wort, I was not forry for this event, as it was going a step farther than I expected. For I had now obtained yeaft, bread, ale, ardent spirit, and acetous acid. A fpecimen of the laft is now produced to the fociety.

I flatter myself that thefe experiments may be of extenfive utility, and contribute to the accommodation, the pleasure, and the health of men, in various fituations, who have hitherto, in a great degree, been precluded from the ufe of fermented liquors; and be the means of furnishing important articles of diet, and of medicine. Not only at fea, but in many fituations in the country, and at particular feafons, yeast is not to be procured.

By the means I have fuggefted, in thefe experiments, fresh bread and newly fermented malt or faccharine liquors may at any time be procured; and of how much importance this may be, and how great the improvement to the malt decoctions recommended by the late Dr. Macbride, I fhall not at prefent ftay to expatiate on; as the fubject may be too much connected with the practical part of phyfic, to come within the limitations drawn by the fociety. But, in domeftic œconomy, its uses are very obvious; and perhaps none more fo than the ready mode which the preceding experiments teach, of reviving fermentation when too languid the finking of a bottle, fuch as I have described in my effay on the prefervation of water at fea, &c. * with an effervefcing mixture of chalk and vitriolic acid, appearing to be fully adequate to the purpose, and would, I believe, be fufficient for impregnating the wort, without any other contrivance. This discovery therefore may, perhaps, be of no fmall utility in public breweries, and I would recommend it to the attention of perfons concerned in the brewing trade.

Let us now proceed to defcribe the circumstances neceffary to, and the phenomena attending fermentation, as defcribed by chemical writers; and then endeavour to form fome theory which may account for them.

Sugar, the juices of ripe fruit, and malt, are all more or less difposed to run into fermentation. But before this can take place, it is neceffary they should be diluted with water, fo as to bring them to

a liquid ftate. A due degree of heat is alfo requifite, as the fermentation fucceeds beft when the temperature varics from 70 to 80 degrees.

When the fermentation takes place, a brifk inteftine motion is obfervable in the liquor; it becomes turbid, fome fæculæ fubfide, while a frothy fcum arifes to the furface. A hiffing noife is obferved, and a quantity of gas is difcharged, which has been proved to be fixed air. The liquor acquires a vinous smell and tafte; and, from being heavier, becomes fpecifically lighter than water. During the progrefs of the procefs, the temperature of the liquor is higher than that of the furrounding atmosphere, with which it is neceflary that a communication be preserved. After fome days, these appearances begin to decline. If the procefs be rightly conducted, and ftopped at a proper period, a liquor, capable of yielding vinous or ardent fpirit, is the refult. If the procefs has been too flow, and the degree of heat infufficient, the liquor will be flat and fpiritlefs; but if thefe have been too rapid and exceffive, it will pafs into the acetous fermentation, to which indeed it is continually tending. But the more ardent fpirit is generated, the less fpeedy will be the change to the acetous state.

During the progrefs of the acetous fermentation, which will even proceed in clofely ftopped veffels, no feparation of air is obfervable, nor any striking phenomena. The liquor gradually lofes its vinous tafte, and becomes four, and a grofs fediment falls to the bottom; while a quantity of vifcid matter ftill re

mains, enveloping the acid, which may be feparated from much of the impurity by diftillation.

The progrefs of these proceffes is accelerated by the addition of ferments, to the action of which it has been fuppofed neceflary, that they fhould have paffed through the state of fermentation into which they are intended to bring the liquor to which they are added; and that it was not poffible to bring the farinaccous infufions into the vinous fermentation without the aid of matter already in that ftate. This the preceding experiments have proved to be an ill-founded notion, as it appears that fixed air, obtained from calcareous earth by means of acids, produces the effect, as perfectly as when the ferment has been taken from a fermenting li

quor.

In fermentation, it is faid, new arrangements take place in the particles of the liquor, and the properties of the fubftance become different from what it before poffeffed. But what these arrangements are, or how thefe properties are changed, we are not told. Dr. Black, I am informed, declares he is unacquainted with any fatisfactory theory.

But perhaps facts, especially fome late chemical difcoveries, may throw light on the matter, and enable us to advance fome conjectures that may tend, at leaft, to lay the foundation of a theory.

1. Sugar is an effential falt, containing much oily, vifcid matter. During its combuftion it repeatedly explodes; a proof that it contains not only much inflammable matter, but alfo a quantity of air. Malt is

faccharine, united to much vifcid mucilaginous matter.

2. If nitrous acid be added to fugar, the inflammable principle of the latter is feized by the acid; the whole, or at least one of the confituent parts of which, is thereby converted into nitrous gas, and flies off in that form. By repeated affufions of this acid, more gas is formed, and the remainder of the fugar is changed into crystals, having the properties of an acid, fui generis, and which has been denominated, by Bergman, faccharine acid*.

3. Saccharine acid is refolvable by heat into fome phlegm, a large quantity of inflammable and fixed air (both of which contain latent heat) and into a brownish refiduum, amounting to of the weight of the acid. Fixed air is fuppofed to confift of pure air united to phlo. gifton; and inflammable air, to be almoft pure phlogiston.

4. Water is found to be formed by the union of pure air, and inflammable gas, deprived of their latent heat; for, if thefe two elaftic fluids be exploded together, in a clofe veffel, over mercury, the whole is converted into water of the fame weight as that of the air and gas jointly. In the procefs much heat is evolved. Again, if water, in the form of fteam, be forced to pass through a tube, containing iron fhavings, ftrongly. heated, the water, according to Meffrs. Watt and Lavoifier, is decompofed; the phlogifton paffes off, united with heat, in the form of inflammable gas, while the humor, or dephlogisticated water, unites to the calx of the

metal,

métal, from which it may be again obtained, in the form of pure air, or of äerial acid, according to the degree in which the calx has been dephlogifticated. It has been already obferved, that faccharine matter cannot be brought to ferment without water.

5. A vinous liquor, on diftillation, yields an ardent spirit.

6. Spirit of wine has had the whole of its inflammable part diffipated by combustion; after which, Mr. Lavoifier found the watery part increased in weight, from fixteen to eighteen ounces, by the abforption of the air, decompofed by the combuftion.

7. The refiduum, after the diftillation of ardent fpirit from fermented liquors, is acid.

8. Mr. Lavoifier has fuppofed pure air to be the acidifying principle of all the acids; and that their difference from each other confifts in the bafis united to this pure air.

As our experiments were made with an infufion of malt, and with fixed air, employed as a ferment, let us endeavour to account for the feveral phenomena and refults of fermentation, as appearing in these experiments.

The wort being impregnated with fixed air, and placed in such a situation as to bring it to the degree of heat, at which wort is commonly mixed with yeaft, the gas for fome time remains in a latent or quiefcent ftate; but, from its tendency to recover its elastic form, aided by heat, it presently begins to burit from the bonds in which it was confined. By this effort the mucilaginous parts of the infufion are at tenuated; the faccharine matter is developed; and, the fame caufe continuing to act, the conftituent VOL. XXVIII.

parts of the matter are feparated; and the particles of the component principles being by this means placed beyond the fphere of their mutual attraction, begin to repel. each other. A large quantity of phlogiston is discharged, together with fome pure air. The greatest part of the inflammable principle enters into a new combination, joining the phlogistic part of the water, and, in proportion, feparating from it the pure air, while another, but much fmaller portion; uniting in its nafcent ftate with this pure air, forms fixed air; which, in its attempt to escape, carries up with it much of its vifcid confinement. In the converfion of the pure into fixed air, a confiderable portion of heat is rendered fenfible. And this heat contributes to the farther decompofition of the faccharine fubftance. The vifcid matter collecting on the surface, prevents the escape of too much of the gas, and promotes its re-abforption, that thereby the brisk and agreeable tafte of the liquor may be formed; while the inflammable principle, accumulating and becoming condenfed in it, forms the ardent fpirit.

Thus a decompofition of the water takes place, fomewhat fimilar to what Mr. Watt has fuppofed in the production of pure air from nitre. The nitrous acid, feizing on the phlogifton of the water, dephlogisticates the humor or other part of the water, which, combining with the matter of heat, paffes off in the form of pure air.

The veffel being stopped, fome of the faccharine matter being not decompofed, the liquor will continue to have a sweetish tafte. But, the fermentation ftill going on, in

a more