Alcohol constitutes a part of all ardent spirits, wine, cider, beer, &c. in which it is combined with water, or with water and mucilaginous and colouring matter. It is formed in the vinous fermentation, and always results from the union of carbon and hydrogen. During the process, carbonic acid gas is liberated. Fermented liquors, therefore, or those which have passed through the vinous fermentation, always contain alcohol in more or less abundance, but mixed with water in many instances. In some it is accompanied with water, and saccharine, mucilaginous, and extractive matter. The different kinds of beer is an example of this fact. When liquors, which contain spirit, are submitted to distillation, the product is alcohol and water; for the volatile parts evaporate, and the fixed substances remain in the still. The spirit partakes, more or less, of a peculiar taste and flavour, by which liquors are distinguished from each other. On this subject, however, it will be sufficient to add, that brandy is procured by the distillation of wine; rum, from the fermented juice of the sugar-cane; gin, from fermented grain and juniper-berry; whiskey, from the fermented mash of grain, cider, &c. and, generally, the ardent liquors, from pears, peaches, and other substances, by the same process. Alcohol, therefore, exists in all these distilled liquors, in a greater or smaller quantity, combined with water; and the proportion it bears to the water is known by a standard, as either proof, above proof, or under proof, according as its strength is shown by the hydrometer. The process of obtaining alcohol in a pure state, (usually called rectified spirit of wine), by which the water is separated from the alcohol, consists in repeated distillations, either alone, or mixed with certain substances, which have the property of uniting with, and keeping down the water, in the act of distillation. These substances are usually potash, and dry muriate of lime, both of which substances have a great affinity for water. The specific gravity of highly concentrated alcohol, at 60° is .820, but that of common alcohol, only .837, at the same temperature. The properties of alcohol are the following: It is a transparent liquor of an agreeable flavour, and may be changed in this particular, by essential oils. It may be exposed to a low temperature without freezing. It boils at 106°, when of the specific gravity .820, and in a vacuum at 56°. It has a strong affinity for water, with which it combines in any proportion; and the specific gravity varies according to the proportion of the mixture and the temperature, on which are founded the tables of Blagden, Gilpin, and others.