but a great deal of volatile oil. When the retort is made intensely hot, lamp black is formed in considerable quantities. In both

these modes then the oil may be wasted to a considerable extent; and it seems to be decomposed most advantageously when the retort is brought to a full red heat.

THE ILLUMINATING POWER OF OIL AND COAL GAS has been differently stated by different persons. According to some, the power of the oil gas is as three and a half, the coal gas being one, while, according to others, it is only two, and even not greater. On this question, however, turns one which is of very great importance, whether oil or coal gas works are most advantageous; and we must, therefore, follow Dr. Fyfe more closely in this part of his work. He first throws doubts on some experiments of Mr. Ricardo's, and of other gentlemen, on account of their having been incorrectly made, while he seems disposed to admit the accuracy of the experiments of Messrs. Herapath and Rootsey, which do not give so high an illuminating power to oil gas. Mr. Dewey's experiments published in the Annals of Philosophy, last December, and which showed a great degree of illuminating power in oil gas, were made, it appears, as well as some other experiments, with coal gas of a very small specific gravity, only 406; and Dr. Fyfe contends, that the illuminating power of both gases, after being properly purified, is in proportion to their specific gravity. The oil gas Mr. Dewey used was 939, which is very good; and if (says Dr. Fyfe) a good oil gas is only three and a half times superior to a very inferior coal gas, its superiority must be much reduced when brought into competition with the latter, when of an equally good quality. DrHenry proposed to ascertain the illuminating power of each gas by the quantity of oxygen necessary for its combustion, and, tried by this test, he obtained the following results:

་

of the

One hundred volumes of oil gas, of the

From this it appears, that the best oil gas is to the worst coal gas as three and a half to one, while the best of both stand in the relation to another of 26 to 21. On the theory, that the alefiant gas contained in both is the principal source of light, as this may be condensed by chlorine, Dr. Fyfe proposes this as a test of the illuminating power of each. The mixture must be excluded from light to prevent any action on the carburetted hydrogen. Dr. Fyfe recommends the following method for trying this experiment: A graduated jar, inverted in a water trough, must be filled to 50 with the gas; 50 measures of chlorine must then be introduced, the tube being covered with a paper shade, to prevent any action on the other gases. In the course of from 10 to 15 minutes the condensation is complete; and as chlorine and olefiant gases combine in equal proportions, the diminution in the mixture indicates correctly the quantity of olefiant gas in the gas subjected to trial. This, Dr. Fyfe says, promises to be an accurate mode ofascertaining the comparative illuminating powers; and by this method he has found the oil gas prepared in Edinburgh to be to the coal gas as 31 to 17, or nearly 1.8 to 1. Dr. Fyfe, we see, admits that the other constituents of both gases possess some illuminating powers; and unless the proportion of these other ingredients were the same in both, we cannot see how his method can be any thing more than an approxi

mation to accuracy. He concludes this part of the subject, however, by stating, "I suspect coal gas will be found to possess, or at least may be made in general to possess, about half the illuminating power of that from oil." He has found this to be the case with those made in Edinburgh, by producing the same quantity of light and marking the quantity of gas consumed.

He then enters into some calculations to show the cost of manufacturing oil and coal gas; but this depends on so many circumstances, that we cannot follow him. Having Stated his opinion as to the quantity of light to be obtained from the two gases, we must leave it to the discretion of our readers to choose either, as they are so placed as to obtain the material at a dear or cheap rate. But though Dr. Fyfe thinks that, at present, oil gas cannot be made so advantageously as coal gas, he does not assert that it never can. "Oil gas establishments,

he says, 66 are in their infancy; and as, by the present mode of decomposing oil, there is a consider able loss of illuminating power, other and more effectual methods of decomposing it may be discovered, which will allow it to be offered at a cheaper rate, and thus bring it into competition with coal gas, provided we consider it as having three times the illuminating power; but if, as I have endeavoured to show, it is only about twice that of coal gas, I fear it never can come into competition

with it."

TO FORM WATER.
To the Editor of the Chemist.

MR. EDITOR,-You have lately shown your young readers how to decompose water; and I will, with how they may compose it of its your permission, point out to them two constituent principles. · Let them supply themselves with a glass bottle, as seen in the little drawing I send herewith. It is to be provided with a cork, through in this a glass tube is inserted. which a small hole is pierced, and They must put into the bottle a small quantity of iron filings, and pour on this about twice as much sulphuric acid, by weight, preas great a quantity of water. After viously diluted by about four times these substances are placed in the bottle, put in the cork and set fire will issue from the mouth of the to the gas, which is hydrogen, that tube. When this is done, invert over the flame a glass jar, as seen in the little drawing; and in a very short time its inside will be covered with a very fine dew, which is pure water, arising from the combustion of the hydrogen gas, produced from the materials in the bottle, and the oxygen gas of the atmosphere."

dodam, Sir, I sandraomsb to Your obedient servant, sal

A STUDENT'S FRIENDt Bethnal-green, Aug. 28 os apelioulf

DISTILLATION.
Art. III.

towod FERMENTATION. PERHAPS the most dificult part of the whole process of procuring a good spirit consists in making the materials from which it is to be extracted undergo a proper degree of fermentation. On this depends the quantity of spirit formed by the grain; the quantity extracted, indeed, will depend on what is properly called distillation. We know of more than one instance in which the results completely disappointed expectation, in consequence of t the fermentation not having been completed. No spirit can be obtained from grain until it has been fermented; this part of the process is therefore essential, bq and it is necessary that its principles should be known,ub vivoiy It is a striking distinction between the substances belonging to the animal and vegetable kingdom, and minerals, that the former are subjected to perpetual alteration, while the latter, if left to themselves, remain almost unchanged, or change so slowly that the alteration is scarcely perceptible to our senses. Vegetables and animals, while living, grow and decay; and when dead, unless under very peculiar circumstances, invariably undergo spontaneous decomposition. Chemical researches have demonstrated, that during the lifetime of plants the substances of which they aging their nature. composed are continually Mucilage in the young plant be

comes starch in an old the acid of the green fruit, as the season advances, is gradually converted into sugar. The constituent parts, then, of plants are gradually entering into new combinations and forming new compounds. This holds good after the plant has been taken from the earth and the fruit gathered from the tree. Our readers have all witnessed the change which a cabbage or some similar vegetable undergoes when taken from the ground its leaves gradually decay if thrown in a heap, and not exposed to some drying influence, they soon become moist, and after a short time emit a most noxious effluvia, a part of their constituents separating in the form of gas occasions an intolerable smell. This species of spontaneous decomposition is called putrefaction. On the other hand, when the odour is not offensive, when the products are applied to useful purposes, when the circumstances under which the process takes place are effected by art, though the decomposition may still be called spontaneous, the name of fermentation has been given to it. For a long period, the nature of these changes was involved in utter darkness; but since chemistry has been applied to analyze the substances found both in the living and the dead vegetable, and in the products of its decomposition, some light has been thrown on it cannot yet be described as perthis curious phenomenon, though fectly known. As the ultimate

constituents of all vegetable matter are oxygen, hydrogen, and carbon, all the products of the fermentation of vegetable substances are merely new compounds of these three elements. Lavoisier was the first chemist who instituted a series of experiments on right principles to investigate the phenomena of fermentation; and since then the same subject has been pursued with considerable success, though with little alteration in the results, by M.Thenard and M. Gay Lussac. The phenomena of vegetable decomposition vary in some measure, according to the nature of the sub stance decomposed. With this variety we have, on the present occasion, nothing to do, but shall content ourselves with describing that change in vegetables, the result of which produces intoxicating liquors, and which is known by the name of vinous fermentation.

When the juice of grapes, which is called must, is expressed, and left in a temperature of about 709, it soon becomes thick and muddy, its temperature increases, and carbonic acid gas is evolved; in a few days the fermentation ceases, a thick part subsides to the bottom, a scum rises to the surface, the liquid loses its sweet taste, becomes lighter, and is the substance well known under the name of wine. On analyzing must, it is found to consist principally of water, sugar, jelly, gluten, and tartaric acid, the quantity of sugar being very considerable, though varying in dif ferent grapes, Wine, however, is found to consist principally of an acid, alcohol, extractive matter, a vo+ latile oil, which gives it its peculiar flavour, and a colouring matter. The alcohol obtained from wine by distillation, as it is found in commerce, in its diluted state, is called brandy. No alcohol can be detected in must before fermentation. Grain, whether malted or not, when infused in water at a certain temperature, undergoes a change like the fermentation of must, but the resulting liquid, though it contain alcohol, is not, without farther preparation, fit for use. We have

at present nothing to do with that farther process, by which the malt, after being infused and changed into wort, is converted into beer; and shall strictly confine ourselves to describing the process which we understand to be used by the distillers.

In this country the distillers make use of both malt and grain, the proportion of the former varying from a third to a tenth part of the latter. This mixture is ground, or the malt is merely bruised and mixed with barley already ground to meal. To one bushel of this mixture from 12 to 13 gallons of water are added, at a temperature of about 150° Fahr., and the whole is subjected by mechanical means to considerable agitation, which constitutes the process of mashing, This is kept up for some time, and the heat preserved by the addition of seven or eight gallons of water, a few degrees under the boiling temperature. The infusion is called wort, is very sweet, but not quite so sweet, nor is it so clear, as that made from malt. The starch, therefore, of the grain seems to be converted by the mashing, as in the process of malting, to the nature of sugar. The wort, after being allowed to settle, is drawn off and cooled very rapidly, in extensive wooden troughs, or it is made to traverse a pipe immersed in cold water; more boiling water is then poured on the grain to extract all the saccharine matter possible. The portion of water which is poured the third time over the malt is generally reserved to be poured over fresh grain, or it is concentrated by boiling. It may be here remarked, that there is no species of manufacture which, on account of the taxes levied on it, has been so much restrained, impeded, and injured in this country by numerous and injudicious fiscal regulations as that of spirits. Fortunately for mankind, the love of gain has been too strong or too cunning for the wit of the legislator, and the art has been found of circumventing him, to the great benefit of the world. It is quite evident, if