Alcohol is one member of a large series of organic products known by the generic term of alcohols. The lowest member of this series is methyl alcohol, which is contained in wood spirit; the next is ethyl alcohol, which is the ordinary alcohol; higher still are propyl alcohol and amyl alcohol, contained in fusel oil. There are also several others. Ordinary or ethyl alcohol is formed by the fermentation of sugar by means of yeast. There are two stages in the fermentation; in the first place, cane sugar takes up water and becomes "invert " sugar. This is then decomposed, yielding alcohol and carbonic acid. There are other minor products, but alcohol and carbonic acid are the principal ones. Starch in the form of potato starch, rice, barley, and Indian corn are also used in the preparation of alcohol, but they have first to be converted into sugar. This is done either with malt or with sulphuric acid. The alcohol produced is extremely weak; it is then distilled carefully, and leaves most of the water and all the solid matter in the still. Another distillation produces rectified spirit containing 84 per cent, by weight of alcohol.
To prepare stronger alcohol, distillation should be repeated several times with quicklime, the final distillation yielding absolute alcohol, which should contain 95 to 99 per cent, of alcohol. Proof spirit contains 49 per cent, by weight of alcohol. Methylated spirit is rectified spirit to which 10 per cent, of wood spirit, or 3/8 per cent, of petroleum naphtha, has been added to render it undrinkable; it passes free of duty for manufacturing purposes. Whisky is made from malt and distilled as for rectified spirit; rum is made from molasses, gin from malt, etc., and brandy from French wines. Brandy, whisky, and rum must not be sold weaker than 25° under proof, i.e. containing not less than 40 per cent, of alcohol; and gin not les3 than 350 below proof, containing 37 per cent, of alcohol. Potato spirit made from potatoes, and "corn " spirit made from Indian corn or maize, are common alcohols containing much fusel oil. Still commoner alcohol is made from beet treacle. The three last are made and used largely in Germany, but not much in Great Britain. Wines contain from 10 to 20 per cent, of alcohol; beer as a rule contains about 5 per cent.