III.

Grain Alcohol

Ethyl alcohol, or ethanol, C₂ H₅OH, is a clear, colourless liquid, with a burning taste and characteristic, agreeable odour. Ethanol is the alcohol in such beverages as beer, wine, and brandy. Because of its low freezing point, it has been used as the fluid in thermometers for temperatures below the freezing point of mercury -39° C (-38° F), and for other special low-temperature purposes, such as for antifreeze in car radiators.

Ethanol is normally concentrated by distillation of dilute solutions. Commercial ethanol contains 95 per cent by volume of ethanol and 5 per cent of water. Dehydrating agents remove the remaining water and produce absolute ethanol. Ethanol melts at -114.1° C (-173.4° F), boils at 78.5° C (173.3° F), and has a relative density of 0.789 at 20° C (68° F).

Ethanol has been made since ancient times by the fermentation of sugars. All beverage ethanol and more than half of industrial ethanol is still made by this process. Starch from potatoes, maize, or other cereals can be the raw material. The yeast enzyme, zymase, changes the simple sugars into ethanol and carbon dioxide. The fermentation reaction, represented by the simple equation

C6H12O6 → 2C2 H5OH + 2CO2

is actually very complex because impure cultures of yeast produce varying amounts of other substances, including fusel oil, glycerine, and various organic acids. The fermented liquid, containing from 7 to 12 per cent ethanol, is concentrated to 95 per cent by a series of distillations. In the production of beverages such as whisky and brandy, some of the impurities, which supply the flavour, are of great value. Most ethanol not intended for drinking is now made synthetically, either from ethanal (acetaldehyde) made from ethyne (acetylene), or from ethene made from petroleum. A small amount is made from wood pulp.

Ethanol can be oxidized to form first ethanal and then ethanoic (acetic) acid. It can be dehydrated to form diethyl ether. Other products made from ethanol include butadiene, used in making synthetic rubber; cloroethane, used as a local anaesthetic; and many other organic chemicals. Ethanol is miscible (mixable) with water and with most organic solvents. It is an excellent solvent for many substances and is used in making such products as perfumes, lacquer, celluloid, and explosives. Alcoholic solutions of non-volatile substances are called tinctures; if the solute is volatile, the solution is called a spirit.