ALCOHOL, the name applied to any member of a class of organic compounds (see ALcoHoLs). The word is of Arabic origin, being derived from the particle al and the word kohl, an impalpable powder used in the East for painting the eyebrows. For many centuries the word was used to designate any fine pow der; its present day application is of comparatively recent date. Thus Paracelsus and Libavius both used the term to denote a fine powder, the latter speaking of an alcohol derived from antimony. Paracelsus also used the term to denote a volatile liquid; alcool and alcool vini occur often in his writings, and once he adds id est vino ardente.
The word is commonly applied to one particular member of the class (ethyl alcohol or ethanol) having the formula C21-180. Alcohol, as an article of widespread consumption aird use, has various other names, e.g., "Spirits of Wine," "Eau de Vie," "Aqua Vitae." Ethyl alcohol does not occur in appreciable quantities in na ture except under abnormal conditions, the most common in stances being the urine of persons suffering from diabetes or those addicted to excessive consumption of alcoholic beverages. In the vegetable kingdom it occurs, mixed with ethyl butyrate, in the unripe seeds of Heracleum giganteum and H. sphondylium. In consequence, however, of its ready formation by the fermenta tion of saccharine juices of vegetable origin, it has been known, in its impure state, from ancient times. It was not until 1808 that its constitution was determined by de Saussure, although Lavoisier had previously established its qualitative composition. Sir Edward Frankland, by demonstrating its relation to the hydrocarbon ethane (C113.CH3), proved it to be CI-13.CH2OH, one hydrogen atom of the ethane molecule being replaced by the hydroxyl group. Ethyl alcohol may be synthetically prepared by any of the general methods described in the article ALcoHoLs. The mechan ism of alcoholic fermentation is discussed in the article FERMEN TATION, and the manufacture of alcohol from fermented liquors in the article SPIRITS.
Properties.—Pureethyl alcohol is a mobile colourless liquid having an agreeable ethereal odour. It boils at 78.3° C at a pres sure of 76omm. of mercury ; at —9o° C it is a thick liquid, whilst at —13o° C it solidifies to a white mass. Its specific gravity at various temperatures is as follows, the gravities being compared with water at 4° C: Its high coefficient of thermal expansion, coupled with its low freezing point, renders it a valuable thermometric fluid, especially when the temperatures to be measured are below —39° C when the mercury thermometer cannot be used. It burns readily in air with a blue smokeless flame, producing water and carbon dioxide. Since its combustion is attended with the evolution of great heat, alcohol is used extensively as a fuel.
Ethyl alcohol is miscible with water in all proportions, the mixing being accompanied by a contraction in volume and a rise in temperature. The maximum contraction corresponds approxi mately to a mixture of three molecules of alcohol and one of water. Owing to the energy with which it absorbs moisture from the air, it is difficult to obtain or preserve ethyl alcohol in a com pletely anhydrous state. Commercial alcohol, which usually con tains about 95% of the pure alcohol and 5% of water, can be obtained by fractional distillation of spirituous liquors. This method of purification fails to remove the last traces of water, which can only be effected by distilling the commercial product after it has stood in contact with a dehydrating agent such as quick-lime, baryta, or anhydrous copper sulphate, or by taking advantage of its peculiar behaviour when mixed with benzene. Calcium chloride must not be used, as it forms a crystalline com pound with alcohol, the latter playing the rOle of water of crystal lization. The presence of water in alcohol may be detected in several ways. Aqueous alcohol, when mixed with benzene, carbon disulphide, or paraffin oil, becomes turbid. A more delicate meth od is the addition of a small quantity of anthraquinone and sodium amalgam, when absolute alcohol gives a green coloration, but in the presence of minute traces of water a red coloration is obtained.
Traces of ethyl alcohol can be detected by converting it into ethyl benzoate on shaking with benzoyl chloride and caustic soda; by warming it with iodine and potassium hydroxide and thus pro ducing iodoform, which is recognized by its characteristic odour ; or by oxidation to acetaldehyde. The latter test is elaborated by distillation into a strong solution of sodium hydroxide, when an "aldehyde resin" easily recognized by appearance and smell is formed.
Determination.—Thequantity of alcohol present in a mixture of alcohol and water can readily be determined. If other sub stances are present, it is usually necessary to separate them by distillation and sometimes by preliminary chemical treatment. The determination may be made by ascertaining the vapour ten sion or by finding the boiling point. The most common and con venient method, however, is the determination of the specific gravity of the aqueous mixture. This can be ascertained by means of some form of pyknometer or hydrometer, standard tables being available which correlate gravities with proportion of alco hol. The latter may be expressed in various forms, depending upon the requirements of the Government or other authority by whom the tables have been prepared. The usual form is percentage of absolute alcohol by weight or by volume. The former has cer tain advantages as it is independent of temperature, whilst the latter, owing to the difference in the coefficients of expansion of the two ingredients, is subject to thermal variation. In the United Kingdom and in America arbitrary standards called "Proof Spirit" are used. British "Proof Spirit" is that mixture of alcohol and water which at the temperature of 51° F weighs exactly 4-1 of an equal measure of distilled water also at 51° F. It contains 49-28% of alcohol by weight, and at 6o° F it contains 57.10% of alcohol by volume and has a specific gravity of 0.91976. The "quantity at proof" is given by the formula: (quantity of sample) of proof spirit).
United States "Proof Spirit" is ioo that which at 15.6° C contains exactly one-half its volume of alcohol.
The hydrometer used varies considerably and may indicate directly specific gravity, proportion of alcohol, or have an arbi trary scale, the readings of which have to be referred to tables. Sikes's hydrometer, the British legal instrument, is of the last mentioned type. It was devised by Bartholomew Sikes, an English excise officer, at the end of the i8th century. The tables now used with it, however, are of modern compilation, and were legalized in 1915. Sikes's system has been extended by the addition of two hydrometers "A" and "B" to cover all strengths up to absolute alcohol at 84° F.
Yet another physical property which is frequently used for detecting and estimating ethyl alcohol is the refractive index. Holmes (see Trans. Chem. Soc., 1913, 103, p. 2,165) gives the following indices of refraction ("D) at 15.5 ° C for molecular mix tures of alcohol with water, that of pure alcohol being 1.36316: Alcohol Water Alcohol Water (mots.) . (mols.) . "D (mols.) . (mols.) . nD 4 I I 2 1•36408 2 I 1.36651 I 3 1.36152 I I 1.3663o I 4 1.35883 Holmes found the maximum value 1.36661 to correspond to a mixture containing 79.2 % of alcohol by weight.
Uses.—Themost important industrial application of ethyl alcohol is as a solvent. It dissolves a large number of solid and liquid organic compounds, resins, hydrocarbons, fatty acids, and many mineral salts. Potassium and sodium readily dissolve in it, yielding alcoholates (ethoxides) in the form of voluminous white powders. With sulphuric acid it yields ethyl sulphuric acid and with sulphuric anhydride diethyl sulphate. The phosphorus haloids give the corresponding ethyl haloids. It is readily oxidized into acetaldehyde and acetic acid by such agents as manganese per oxide and sulphuric acid. With bleaching powder it yields chloro form, whilst with iodine and potassium hydroxide it reacts to give iodoform. Most gases dissolve in it more readily than in water ; for instance zoo volumes will dissolve seven volumes of hydro gen, 25 volumes of oxygen or 16 volumes of nitrogen. (For industrial uses, see ALCOHOL IN INDUSTRY.) Pharmacology, Toxicology and Therapeutics of Alcohol. —The great solvent power of alcohol is of high medicinal value in the preparation of solutions of alkaloids, resins, volatile oils, iodoform, etc. The effect of alcohol when applied externally to the human body depends upon the strength of the solution and the conditions of application. When of a strength above io% it is antiseptic. If applied in such a manner that evaporation can take place readily, it has a cooling effect of which advantage is often taken by bathing the forehead with perfume to soothe headache. If on the other hand evaporation is retarded, the af finity of alcohol for water causes its extraction from the tissues, which become hardened. Thoroughly rubbed into the skin, alcohol dilates the blood vessels and produces a mild counter-irritant effect. Many alcoholic liniments are therefore employed for the relief of pain, especially lumbago and other forms of so-called "muscular rheumatism." When taken internally alcohol is com pletely and rapidly absorbed from the stomach and intestines and distributed by the blood to different organs of the body. The rate of absorption is checked if the alcohol is diluted either with water or with food taken immediately before drinking. A variable but small proportion of alcohol escapes unchanged in the breath and urine. The remainder is slowly oxidized in the body, disap pearing at a uniform rate of about 0.185 cu.cm. per kg. of body per hour. None is known to be converted into substances which the body can retain.
The effects of consumption of alcohol are almost all due (di rectly or indirectly) to its action upon the nervous system. Thus the immediate sensation of well-being is due to the flushing of the skin, suppressing temporarily the sense of chill and to the fact that the sensibility to minor pains and inconveniences becomes blunted ; whilst with larger doses the diminution of the power of self-control and sense of personal responsibility gives rise to ex citability. In the secondary stage the fineness of the senses (hear ing, touch, taste and vision) is affected, and this gives rise to an inability to control bodily movements such as facial expression.
In the advanced stage of drunkenness, the intellectual processes of judgment and control are suspended, and in the absence of a strong appeal to emotional tendencies the drinker sinks inert and nerveless into a heavy sleep or condition of torpor, which lasts until the alcohol absorbed has all been oxidized. (See DRUNKEN