ALCOHOL. (FR., alcool ; GER., alhohol.) Formula, C21160.
Pure alcohol is a liquid substance, composed of carbon, hydrogen, and oxygen, in the following proportions :— 100.00 It is the most important member of an important series of organic compounds, all of which resemble each other closely, and possess many analogous properties. They are now classed by the chemist under the generic title of " Alcohols." The substance of which this article treats, or vinous alcohol, is the principle of all spirituous, fermented liquors. The intoxicating properties of these liquors, due to the presence of this principle, have been known since the flood, but it was not until about the beginning of the fourteenth century that it was isolated in a pure state.
Alcohol does not occur iu nature ; it is the product of the decomposition of sugar, or, more properly, of glucose, which, under the influence of certain organic, nitrogenous substances, called ferments, is split up into alcohol and carbonic anhydride. The latter is evolved in the form of gas, alcohol remaining behind mixed with water, from which it is separated by distillation. The necessary purification is effected in a variety of ways.
Pare, absolute alcohol is a colourless, mobile, very volatile liquid, baying u hot, burning taste, and a pungent and somewhat agreeable odour. It is very inflammable, burning in t,he air with a bluish-yellow flame, evolving much heat, leaving no residue, and forming vapours of carbonic anhydride and water. Its specific gravity at 0° is •8095, and at 15.5° (60° F.), •794; that of its vapour is 1.613. It boils at 78.4° (173° F.). The boiling points of its aqueous mixtures are raised iu proportion to the quantity of water preseut. Mixtums of alcohol and water when boiled give off at first a vapour rich in alcohol, and containing but little aqueous vapour ; if the ebullition be con tinued, a point is ultimately reached when all the alcohol has been driven off and nothing but pure water remains. Thus, by repeated distillation, alcohol may be obtained from its mixtures with water in an almost anhydrous state.
The following table by Otto gives the boiling points of alcoholic liquids of different strengths, and the proportions of alcohol in the vapours given off:— AbsAnto alcohol has a strong affinity for water. It absorbs moisture from the air rapidly, and thereby becomes gradually weaker ; it should therefore be kept in tightly-stoppered bottles. When brought into contact with animal tissues, it deprives them of the water necessary for their constitu tion, and acts in this way as an energetio poison. Considerable heat is disengaged when alcohol and water are brought together ; if, however, ice be substituted for water, heat is absorbed, owing to the immediate and rapid conversion of the ice into the liquid state. When 1 part of suow is mixed with 2 parts of alcohol, a temperature as low as — 2i° is reached.
When alcohol and water are mixed together, the resulting liquid occupies, after agitation, less volume than the sum of the two origioal liquids. This contraction is greatest when the mix ture is made in the proportion of volumes of alcohol and 47.7 volumes of water, the result being, instead of 100 volumes, A careful examination of the liquid when it is being agitated reveals a vast number of minute air-bubbles, which are discharged from every point of the mixture. This is due to the fact that gases which are hold in solution by the alcohol and water separately are less soluble when the two are brought together ; and the contraction described above is the natural result of the disengagement of such dissolved gases. The following table represents the contraction undergone by different mixtures of absolute alcohol and water.
Alcohol is termed "absolute" whoa it has been deprived of every trace of water, and when its composition is exactly expressed by its chemical formula. To obtain it in this nt it must be subjected to a series of delicate operations in the laboratory, which it would be impossible to perform en au industrial scale. Iu commerce, it is known only in a state of greater or less dilution.