DISTILLATION is an important process in the arts. It consists essentially in con verting a liquid into vapor in a close vessel, by means of heat, and then conveying the vapor into another cool vessel, where it is condensed again into a liquid. When applied to a solid, the process is called sublimation. The object of D. is to separate one sub stance from others with which it may be mixed. In D. proper, no chemical decompo sition takes place; when any of the substances are decomposed, it is called destructive D. (q.v.). The possibility of separating substances by vaporizing them, depends upon the fact that very few substances are volatile at the same temperature. Thus, water boils or becomes rapidly converted into vapor at 212°, alcohol at 173° sulphuric ether at 94.8, while oil of turpentine must be raised to 318°, and ineroury,A6 42'; and some sub stances, again, are altogether fixed. By applying the proper degree of heat, then, and no more, the more volatile of two substances may be expelled from the less volatile; and supposing the vapors of the two to rise mixed, as they are gradually cooled, that of the less volatile will be condensed before the other, thus affording another opportu nity of separation.
It is often, however, not so easy to obtain a perfectly pure product by distillation as might at first appear, owing to another fact in chemistry—namely, that many bodies which, when pure, require a high temperature to vaporize them, become more easily vaporized when mixed with substances more volatile than themselves. Owing to this, it is impossible to obtain, by D. alone, alcohol perfectly free from water. The circum stance, on the other hand, is sometimes turned to good account in another way. By distilling, for instance, parts of plants with water, the essential oils pass over with the steam, and are then separated from the condensed water by other processes.
The applications of D. are numerous both in chemistry and in the practical arts. Pure water is obtained by D., the most of the substances dissolved- in natural waters being fixed. Sea-water may thus be rendered drinkable, and there are apparatus for the special purpose. But wherever there are cooking-utensils, a distilling apparatus might be improvised. The pure water that descends from the clouds is produced in a way which is just the process we are speaking of on a large scale. See EVAPORATION. It is no figure of speech to say that the dews are "distilled." The extraction of zinc from the ore is a distillation; the metal, when reduced, passes over in vapor, and is condensed in a separate vessel. When the zinc ore contains cadmium, this metal, being more volatile, comes over in the first portions, and may be removed. When mercury is used to extract particles of gold from sand, the mer
cury is distilled off from the amalgam, leaving the gold, which is fixed. The mer cury being condensed, is again ready for use.
The most extensive application of distillation is in the manufacture of intoxicating spirits, and in ordinary language this is the most common use of the word. Strictly speaking, indeed, the spirits are not produced by the act of distillation; that is done by the previous step of fermentation (q.v.); and distillation merely separates the spirits from the mixture in which they already exist. But it may be as well to give some account of the whole process under this head.
All the intoxicating drinks used in ancient times seem to have been the products of fermentation merely. The art, as it has been called, of evoking the fiery demon of drunkenness from his attempered state in wine and beer, is a discovery of modern times." It is first mentioned by an Arabian physician of the 11th c., Abulkasem, though the invention is attributed by some to the northern nations. The name aqua vita, given to distilled spirits by early physicians and alchemists, shows what an estimate they made of the discovery. Raymond Lully "declares this admirable essence to be an ema nation of the divinity, an element newly revealed to man, but hid from antiquity, because the human race were thee too young to need this beverage, destined to revive the energies of modern decrepitude." Sadly have these anticipations been belied! Spirits were first distilled from wine, and hence called spirits of wine. An endless variety of substances are now used in this extensive manufacture. Alcohol (q.v.) is the essential ingredient of all spirits, and it results from the decomposition of sugar, which, by the process of fermentation, is resolved into carbonic acid and alcohol. Sugar, then, is the direct source of alcohol, and accordingly all vegetable products containing sugar, such as grapes, the sugar-cane, sweet fruits, beet-root, etc., may be used in the manu facture of spirits. But there is another more abundant vegetable substance—namely, starch—which is easily convertible into sugar, and thus becomes indirectly a source of alcohol. In malt, and in germinating seeds generally, there is found a substance called diastase (q.v.). If a small quantity of this, or of an infusion of malt, be added to. a paste of starch, it will in a short time become thin and sweet, the whole of the starch being transformed into sugar. See BEER. It is thus that grain of all kinds, potatoes, and other substances which contain little or no free sugar, are yet capable of yielding alcoholic spirits.