YEAST is a ferment which causes alcoholic fermentation. It consists of microscopic plants, which increase by the formation of multitudes of tiny cells not more than 1/2400 of an inch in diameter. In the brewing of beer they grow in great abundance, making common brewer's yeast. Ferments or their spores float in the air ready to enter any fermentable liquid, and under favorable conditions they multiply with great activity and energy. The favorable conditions include the presence of oxygen or sugar; [Footnote: Yeast, like ordinary plants, buds and multiplies even in the absence of fermentable sugar, when it is furnished with free oxygen. This multiplication, however, is favored by the presence of sugar, which is a more appropriate element than non-fermentable hydrocarbon compounds. Yeast is also able to bud and multiply in the absence of free oxygen, but in this case a fermentable substance is indispensable.--SCHÜTZENBERGER'S _Fermentation_.] oxygen being, as we know, necessary for the development and the reproduction of all cell life (p. 107), and ferments having the power to resolve sugar, which penetrates by endosmose into the interior of the cell, into alcohol, carbonic acid, glycerine, succinic acid, and oxygen. BEER.--The barley used for making beer is first malted, _i. e._, sprouted, to turn a part of its starch into sugar. When this process has gone far enough, it is checked by heating the grain in a kiln until the germ is destroyed. The malt is then crushed, steeped, and fermented with hops and yeast. The sugar gradually disappears, alcohol is formed, and carbonic acid escapes into the air. The beer is then put into casks, where it undergoes a second, slower fermentation, and the carbonic acid gathers; when the liquor is drawn, this gas bubbles to the surface, giving to the beer its sparkling, foamy look. WINE is generally made from the juice of the grape. The juice, or _must_, as it is called, is placed in vats in the cellar, where the low temperature favors a slow fermentation. If all the sugar be converted into alcohol and carbonic-acid gas, a dry wine will remain; if the fermentation be checked, a sweet wine will result; and if the wine be bottled while the change is still going on, a brisk effervescing liquor like champagne, will be formed. All these are dangerous beverages because of the alcohol they contain. DISTILLATION.--Alcohol is so volatile that, by the application of heat, it can be driven off as a vapor from the fermented liquid in which it has been produced. Steam and various fragrant substances will accompany it, and, if they are collected and condensed in a cool receiver, a new and stronger liquor will be formed, having a distinctive odor. In this way whiskey is distilled from fermented corn, rye, barley, or potatoes; the alcohol of commerce is distilled from whiskey; brandy, from wine; rum, from fermented molasses; and gin, from fermented barley and rye, afterward distilled with juniper berries.