ed to the influence of the winds, contains very nearly the same proportion of oxygen and nitrogen: a circumstance of great importance; for, by teaching us that the different degrees of salubrity of air do not depend upon differences in the quantities of its principal constituent parts, it ought to induce us to institute researches concerning the different substances capable of being dissolved or suspended in air, which are noxious to the human constitution; particularly as an accurate knowledge of their nature and properties would probably enable us, in a great measure, to guard against, or destroy, their baneful effects.

found it did. He accordingly brought me a small vessel with a full head of yeast upon it, assuring me, with some degree of exultation, that neither oil of vitriol with chalk, nor any portion of old yeast, had been employed on the occasion. This greatly surprised me; and I then desired he would proceed with the experiment in his own way, and endeavour to increase the quantity already made, by what additional decoction of malt and water he might think proper; insisting only that nothing but malt, water, and heat, should be employed for the purpose. He did so, and in a few days increased the original quantity till it became sufficient to work a hogshead of small-beer, which produced ten pounds weight of perfect yeast; and this, being soon after put on a vat for a hogshead of ale, was found to be augmented to forty-two pounds.

The discovery therefore is simply this: "that yeast is not (as has, I believe, been hitherto thought) some peculiar and unknown substance, necessary to be added to wort in order to put it into a fermenting state; but that malt boiled in water will generate it (as the chemists say) per se, if the following circumstances be attended to

1st, That the process be begun with a small quantity of the decoction.

2dly, That it be kept in an equal degree of heat. And,

3dly, That, when the fermentation is begun, it should be assisted and augmented with fresh decoctions of the same liquor."

The proportions and method which my servant has found generally to succeed, I will now give you, as taken from his own words, in the form of a recipe.

Procure

Procure three earthen or wooden vessels of different sizes and apertures, one capable of holding two quarts, the other three or four, and the third five or six: boil a quarter of a peck of malt for about eight or ten minutes in three pints of water; and when a quart is poured off from the grains, let it stand in a cool place, till not quite cold, but retain ing that degree of heat which the brewers usually find to be proper when they begin to work their liquor. Then remove the vessel into some warm situation near a fire, where the thermometer stands between 70 and 80 degrees (Fahrenheit,) and there let it remain till the fermentation begins, which will be plainly perceived within thirty hours; add then two quarts more of a like decoction of malt, when cool, as the first was; and mix the whole in the larger-sized vessel, and stir it well in, which must be repeated in the usual way, as it rises in a common vat: then add a still greater quantity of the same decoction, to be worked in the largest vessel, which will produce yeast enough for a brewing of forty gallons.

As I cannot conveniently send my servant to town on this occasion to produce the yeast himself, and have also some doubt whether the simplicity of the process will not make it disregarded, I have thought it best to communicate the discovery previ. ously to you, who, as my friend told me, appeared to be interested in its success; hoping you may be induced to try so easy an experiment, and to acquaint me with the result of it, before you communicate it to the society. With my brewer it has never failed, except when the failure was to be accounted for from an inequality of temperature of the

air, where the experiments were made: it seems therefore to me, that in the hands of a good practical brewer, accommodated with a place where his little vat will stand in a constant degree of proper heat, it will generally succeed, especially in the brewing seasons.

P. S. It may be proper to add, that my servant is of opinion, that a proper quantity of hops boiled in the liquor makes the fermentation proceed better; but as it may, and has actually succeeded, without such addition, I would willingly wish them to be omitted, to prevent the bread baked with it from tasting bitter. Experience only can decide this; and farther experience is still wanted, to make a perfect recipe for the operation.

of

In a second letter Mr. Mason says, that "yeast, used for the purpose brewing malt liquor, and in making bread, is a viscid, frothy substance, which arises on the surface of a simple decoction of malt in water, when in a state of fermentation; and which substance, after it has been so generated, may, by additional quantities of the same liquor, gradually supplied, be increased ad infinitum." This definition, duly attended to, will put the committee on their guard in adjudging the premium to any person who, by adding any known or unknown article to wort, offers it as a substitute for old yeast taken from a former brewing, because they will be taught that new original yeast may be obtained from wort itself without any such substitute.

With respect to the doubt you expressed in your obliging answer to my last, I can with truth assure, that in all the primary decoctions made hitherto for the purpose, coarse

earthen

earthen and glazed pots have been used,till a quantity of yeast sufficient to work a brewing of beer was produced after which, the process was carried on in a large wooden vat; and therefore, when I used in my last the epithet wooden as well as earthen, it was merely because I thought the former kind of vessels less liable to accidents.

Certain it is, that in two experiments lately made here, in York, one by myself, the other by my friend Dr. Burgh, a gentleman much more conversant in chemical matters than myself, new earthen vessels bought out of the shops were employed.

He produced excellent bread from the yeast which his decoction had generated, without any addition of hops: a small quantity of hops were boiled in mine; which, without much affecting the taste of the bread baked with it, left about four gallons of table beer, now in a small cask; which, though not fine, from having been brewed little more than a fortnight, is greatly preferable to the wretched bitter beverage sold by our common brewers, from whose vats a yeast is produced, equally unpalatable for the purpose of baking, and perhaps equally unwholesome both for baking and brewing.

I am much obliged to you for the attention which you promise to pay to the experiment; but I cannot help wishing that you had at your elbow one of our old housewives in one of our obscure Yorkshire dales, used, as they are, to very small brewings, who, after two or three little blunders, would soon bring it to a certainty.

In another letter Mr. Mason says, I write to inform you of the result of some more experiments which VOL. XLIII.

have been made here under my direction, relative to yeast; and the rather, because they were made by means of a very simple apparatus, which I think will be found very convenient on ship-board, and also in cottages, &c. It is merely a wooden box, of about twelve or fourteen inches square, open on one side, in which a vessel containing the wort is placed; and then the box is set with the open side close to a wall, heated by a fire on the other side, when the thermometer indicates the wall to be about 80°: so that I imagine the back of a chimney in a ship, or behind an oven or kitchen fire in a cottage, would be found very convenient for the process; as the vessel might be there surrounded with a small atmosphere of air, sufficiently warm at the first, and capable of being continued at the same equable temperature for a sufficient time.

A box of this kind, in which the following experiments were made, was placed on a dresser in my kitchen, more than eighteen feet from the kitchen fire, but against a thin wall, which divides the kitchen from the servants' hall, just behind the fire-place of that room; and the open side of the box turned to the heated wall, the vessels themselves uncovered. If you recollect the trouble you so obligingly took in heating your office, you will think this method, since discovered, of performing the same experiment, of considerable utility.

Experiment I. Three vessels were set at the same time in the warm box, containing a quart of liquor each, and of equal strength with respect to malt: one was a decoction without hops, another with hops, the other a pure infusion of malt: in about twenty-four hours the hopped decocᎻ Ꮒ

tion

tion produced a fine head of yeast; the other decoction fermented as well, but was twenty-four hours later, the simple infusion was near thirtysix hours later, and the yeast appear ed dark and ill-coloured, so that my housekeeper thought it spoiled; but this bad appearance was merely owing to its not having been boiled and cleared, for it made very light breakfast rolls.

This experiment, you will perceive, was made to try whether hops (as my servant imagined) were necessary; and it certainly proves that they accelerate the fermentation; but it proves, also, that neither hops nor boiling are essential to the process.

Experiment II. Four vessels from a common brewing of ale were placed in a box of longer dimensions; one contained two quarts; a second, one; a third, a pint; a fourth, half a pint: they all showed signs of fermentation at the same time, viz., in about twenty-four hours; but that in the mug or pot holding a pint appeared the strongest, which my servant thought was `owing to the smaller diameter of the vessel, which was smaller in proportion to the half-pint; but as it stood more centrally to the heat of the fire behind, I am persuaded the excess of fermentation proceeded from that cause. This proves that the quantity you begin the process with is not very material: though two quarts seem to be most convenient for the purpose of baking.

Experiment III was instituted merely to find whether an addition of sugar would accelerate the fermentation; for which purpose, two quarts of hopped liquor were tried in separate vessels, a quart in each: and the result was, that the decoc

tion, in which two large spoonfuls of coarse sugar were stirred in, did not ferment in the least, though continued in the warm box five days and nights; the other fermented in about thirty-six hours. The reason of this later fermentation than of that in the former experiments, was, that the liquor used was from a brewing of small-beer. Hence we may conclude, that a decoction of the strength of ale, if not of strongbeer, is the best to begin with.

Account of Experiments on the Generation of Yeast, made under the Inspection of the Committee of Chemistry of the Society.

Four quarts of ground malt were put into a new stone-ware vessel, and mashed, with about an equal quantity of hot water, in the usual manner for brewing.

When the mash had stood about an hour, the wort was drawn off, and three quarts of boiling water poured on the grains : when this had stood a due time, the liquor was suffered to run off, and the whole liquor boiled half an hour; being then set to cool, it was poured clear from the sediment, and then put in a room where the heat was regularly kept up to summer heat, or near 80° of Fahrenheit's thermometer. stood in this degree of heat till some signs of fermentation appeared on the surface; which came on in about three days.

It

Another brewing was then made as above described; and, when of a due heat, stirred into the former liquor. In about twenty-four hours some yeast appeared, and another brewing was then made; and, when of a due heat, mixed with the two former ones, and well beat in, the

heat

heat being still kept up to the degree above mentioned: in about two days more, five ounces of excellent yeast were collected from the surface of the liquor.

Some of this yeast being mixed with a due proportion of flour, water,and salt,answered all the purposes intended for bread; and might certainly have been equally well applied to brewing, in the common method. In fine, being pure and good yeast, it will answer all the intentions of that useful article.

Observations relative to the Means of increasing the Quantities of Heat obtained in the Combustion of Fuel. By Count Rumford. From the Journals of the Royal Institution of Great Britain.

T is a fact, which has been long IT is a fact, which has been long

other incombustible substances, when mixed with sea-coal, in certain proportions, cause the coal to give out more heat in its combustion than it can be made to produce when it is burnt pure or unmixed; but the cause of this increase of heat does not appear to have been yet investigated with that attention which so extraordinary and important a circumstance seems to demand.

Daily experience teaches us that all bodies-those which are incombustible as well as those which are combustible, and actually burn ing-throw off in all directions heat, or rather calorific (heat-making) rays, which generate heat wherever they are stopped, or absorbed; but common observation was hardly sufficient to show any perceptible difference between the quantities of calorific rays thrown off

by different bodies, when heated to the same temperature, or exposed in the same fire; although the quantities so thrown off might be, and probably are, very different.

It has lately been ascertained, that when the sides and back of an open chimney fire-place, in which coals are burned, are composed of firebricks, and heated red-hot, they throw off into the room incomparably more heat than all the coals that could possibly be put into the grate, even supposing them to burn with the greatest possibledegreeof brightness. Hence it appears that a redhot burning coal does not send off near so many calorific rays as a piece of red-hot brick or stone, of the same form and dimensions; and this interesting discovery will enable us to make very important improvements in the construction of our fire-places, and also in the management of our and a

The fuel,instead of being employed to heat the room directly, or by the direct rays from the fire, should be so disposed, or placed, as to heat the back and sides of the grate; which must always be constructed of fire-brick or fire-stone, and never of iron, or of any other metal. Few coals, therefore, when properly placed, make a much better fire than a larger quantity; and shallow grates, when they are constructed of proper materials, throw more heat into a room, and with a much less consumption of fuel, than deep grates; for a large mass of coals in the grate arrests the rays which proceed from the back and sides of the grate, and prevents their coming into the room; or, as fires are generally managed, it prevents the back and sides of the grate from ever being sufficiently heated to assist much in heating the Hh 2

room,