Alcohol (Arab. al-koh'l, originally designating a collyrium, a very fine powder of antimony for staining the eyelids; afterwards 'essence,' 'spirits'). Ordinary or ethyl alcohol is a limpid, colourless liquid, of a hot pungent taste, and having a slight but agreeable smell. It is the characteristic ingredient of fermented drinks, gives them their intoxicating quality, and is obtained from them by distillation. If we look at the extraordinary consumption of these liquors for various purposes, it is seen to be one of the most important substances produced by art.
Alcohol occurs in nature in several growing plants, and must therefore be regarded as an occasional constituent of plant-juices which have not undergone fermentation. It has been found in the fruit and pedicels of Heracleum giganteum, the fruit of the parsnip, and the unripe fruit of Anthriscus cerefolium. For practical purposes, there is, however, only one source of alcohol—namely, the fermentation of sugar or other saccharine matter. Sugar is the produce of the vegetable world. Some plants contain free sugar, and still more contain starch, which can be converted into sugar. The best vegetable substances, then, for yielding alcohol are those that contain the greatest abundance of sugar or of starch. See DIASTASE, FERMENTATION, and DISTILLATION.
Owing to the attraction of alcohol for water, it is impossible to procure pure alcohol by distillation alone. Common spirits, such as brandy, whisky, &c. contain 50 or 52 per cent. of alcohol; in other words, they are about half alcohol, half water. Proof-spirit, which is the standard by means of which all mixtures of alcohol and water are judged, contains 57·27 per cent. by volume, and 49·50 per cent. by weight of alcohol. The specific gravity of proof-spirit is .9186; and when a spirit is called above proof, it denotes that it contains an excess of alcohol; thus, spirit of wine, or rectified spirit, with specific gravity .838, is 54 to 58 overproof, and requires 54 to 58 per cent. of water to be added to it to bring the strength down to that of proof-spirit; whilst the term under-proof has reference to a less strong spirit than the standard (see HYDROMETER). The most primitive method of learning the strength of alcohol was to drench gunpowder with it, set fire to the spirit, and if it inflamed the gunpowder as it died out, then the alcohol stood the test or proof, and was called proof-spirit. The highest concentration possible by distillation gives 90 per cent. of alcohol, still leaving 10 per cent. of water. In order to remove this, fused chloride of calcium, quicklime, or fused carbonate of potash, is added to the alcoholic liquid, the whole allowed to stand for twelve hours, and then the spirit may be distilled off practically free from water. Spirit of wine may also be deprived of its remaining water by suspending it in a bladder in a warm place; the bladder allows much of the water to pass through and evaporate, but little of the alcohol. The latter method is called Soemmering's process, and depends on the different degrees of rapidity with which the bladder admits of water and alcohol passing through it. Thus, introduce into one bladder eight ounces of water, and into a second eight ounces of alcohol, and allow both bladders to be similarly exposed on a sandbath till all the water has evaporated through the pores of the membrane, which will be accomplished in about four days; and it will then be observed that whilst eight ounces of water have made their exit from the bladder, only one ounce of alcohol has thus evaporated, and seven ounces still remain in the bladder. This experiment explains why smugglers, a few generations ago, could supply a whisky which was stronger, and hence esteemed preferable, as they carried the whisky in bladders around their persons, and the water escaping therefrom in much greater proportion than the alcohol, a stronger spirit was left.
Absolute or anhydrous alcohol has a specific gravity of .793 at the temperature of 60° F. (15·5° C.). It boils at 173° F. (78·4° C.), and has not been frozen by any cold hitherto produced. Reduced to a temperature of -130° F. (-72° C.), alcohol becomes of an oily and greasy consistence; at -146° F. (-81° C.), it assumes the aspect of melted wax; and at -166° F. (-92° C.), it gets still thicker, but does not congeal at the lowest attainable temperature. This property of non-freezing at any degree of cold to which the earth is subjected, has led to the employment of alcohol coloured red by cochineal, in the thermometers sent out to the arctic regions. It is highly inflammable, its combustion yielding only carbonic acid and water. It has a very strong attraction for water, and when mixed with it, much heat is evolved and a contraction in volume takes place. Thus 2 gallons of alcohol and 1 of water measure less than 3 gallons. Its poisonous action when taken internally in large quantity has been referred to this same property, the idea being that it removes water from the tissues, and thus destroys them. The formula of alcohol is C2H5OH. In 100 pounds, therefore, of alcohol, about 53 are carbon, 13 hydrogen, and 34 oxygen. Besides the alcohol consumed in wine, beer, and spirits, it is much employed in pharmacy and in the arts. It is a powerful solvent for resins and oils; and hence is employed in the preparation of varnishes. In Germany, a cheap spirit made from potatoes is much used for cooking on a small scale.
During recent years, our knowledge of the properties of ordinary alcohol, and of the general class of bodies to which the term ALCOHOLS is applied, in consequence of their resemblance, in certain chemical reactions, to ordinary alcohol, has been very much enlarged. The alcohols are all compounds of carbon, hydrogen, and oxygen, and are perfectly neutral to test-papers. Many of them are produced along with ordinary alcohol in the process of fermentation, and alter the flavour of the resulting beverage; such are amylic (fusel oil) and butylic alcohol. They are chiefly characterised by yielding, on treatment with acids, neutral bodies called ethers, the formation of water being a part of the reaction. According to the theory of Types (see CHEMISTRY, Vol. III., p. 150), the alcohols are divided into monatomic (comprising the important series of methyl, ethyl, propyl, and other alcohols, which are referred to further below) and polyatomic. According to their behaviour on oxidation, they are further divided into primary, secondary, and tertiary.
In a nearly anhydrous state, alcohol has little tendency to oxidation, but when freely diluted, and exposed to the air, it rapidly becomes oxidised into acetic acid. This conversion is, however, not a direct one, an intermediate compound, termed Aldehyde (q.v.), being first formed, which is rapidly oxidised into acetic acid. The oxidation of alcohol into aldehyde is represented by the equation,
and the further oxidation of aldehyde into acetic acid is represented by
In the first reaction, alcohol loses two atoms of hydrogen, water being formed; in the second, aldehyde takes up one atom of oxygen.
Every alcohol which like ordinary alcohol yields on oxidation an aldehyde, and on further oxidation an acid having the same number of carbon atoms as the alcohol itself, is termed a primary alcohol. To take another example, primary propyl alcohol, , is oxidised first into propyl aldehyde, , and then into propionic acid, . Primary alcohols are subdivided into normal and iso-alcohols, but it would lead us too far to explain the meaning of this distinction.
Secondary alcohols on oxidation lose two atoms of hydrogen, and are converted into bodies known as acetones or ketones, which differ from aldehydes inasmuch as they are not converted on oxidation into acids having the same number of carbon atoms, but are split up into acids having a smaller number of carbon atoms. Thus secondary propyl alcohol is oxidised into acetone, and on further oxidation, acetone splits up into formic and acetic acids,
It will be observed that propyl alcohol and secondary propyl alcohol, propyl aldehyde and acetone, are respectively isomeric (see ISOMERISM).
Tertiary alcohols on oxidation give neither aldehydes nor ketones, but split up into acids having a smaller number of carbon atoms. Thus tertiary butyl alcohol, , which is isomeric, with primary and with secondary butyl alcohol, splits up on oxidation into acetic and formic acids. Only a comparatively small number of secondary and tertiary alcohols are at present known, and their properties and reactions have not been so thoroughly studied as those of the much more numerous class of primary alcohols. Theoretical considerations, however, lead to the belief that their number will be largely increased.
Ordinary or ethyl alcohol is monatomic—i.e. it may be regarded as being derived from the type , by the substitution of its radical ethyl, , for one atom of hydrogen. This view is expressed by the formula .
The monatomic alcohols are more abundant than all the polyatomic alcohols put together. There are several series of them, of which the most important are alcohols whose radical is of the formula (as methyl, ; ethyl, ; propyl, , &c.), and which are represented by the formula . They are intimately related to the fatty acids, whose general formula is , and which may be formed from the alcohols by oxidation, being replaced by . The three highest alcohols of this set, cetyl, cerylic, and melissyl alcohols, have the formulae , , and , and are solid, waxy, or fatty matters.
Of the polyatomic alcohols, diatomic alcohols belong to the secondary water type, or . Thus the most important diatomic alcohol, glycol, , is represented, according to the theory of types, by the formula , its radical, , being marked with two dashes to indicate that it replaces two atoms of hydrogen. So also there are tri, tetra, and hexatomic alcohols corresponding to 3, 4, and 6 molecules of water, examples of which are glycerine, ; erythrite (obtained from litmus), ; and mannite (from manna), .
Dry chlorine and absolute alcohol react on each other in a singular manner—the final product being a solid compound of alcohol with a very remarkable colourless oily fluid, called chloral, having a peculiar penetrating and irritating odour, and having the formula . By treatment with strong sulphuric acid, this chloral is set free, and may be changed into chloroform by warming with an alkali. Dilute alcohol, distilled with chloride of lime (bleaching-powder), yields chloroform; and this is the most economical process for obtaining this invaluable compound. Heated with an excess of sulphuric acid, alcohol loses all its oxygen in the form of water, and is converted into ethylene, the result being shown by the equation,
A less complete dehydration, under the action of sulphuric acid, converts alcohol into ether. The process is a complicated one, but the final result is expressed by the equation,
The best tests for discovering the presence of alcohol are—(1) Its hot pungent taste, its odour, and its great volatility. (2) Absorbed in asbestos, it burns with a pale blue flame, which deposits no carbon on white porcelain; and when burned in the mouth of an inverted test-tube, containing a few drops of solution of baryta, it produces a well-marked deposit of carbonate of baryta—carbonic acid and water being the products of its combustion. (3) When boiled with sulphuric acid, and a few drops of a saturated solution of bichromate of potash, it reduces this salt to green sulphate of chromium. The chromium test, originally discovered by Dr Thomson in 1846, is that on which the French physiologists Lallemand, Perrin, and Duroy relied in their investigations regarding the presence of alcohol in the blood, urine, expired air, &c. (4) The least trace of alcohol in an aqueous solution can be detected by adding a little chloride of benzoyl, and then a little caustic potash; benzoate of ethyl, a liquid having a very characteristic aromatic odour, is at once formed, and enables one thousandth part of alcohol in a teaspoonful of water to be detected.
Alcohol is of a double use to the chemist, inasmuch as it furnishes a cleanly and valuable fuel when used in the spirit-lamp, and possesses remarkable solvent powers without in general exerting chemical action on the dissolved substances. It dissolves many of the gases more freely than water, as, for example, nitrous oxide, carbonic acid, phosphuretted hydrogen, cyanogen, and the hydrocarbons, as, for instance, ethylene. Amongst the mineral substances which it dissolves may be mentioned iodine, bromine, boracic acid, the hydrates of potash and soda, the chlorides of calcium, strontium, magnesium, zinc, platinum, and gold, the perchloride of iron, corrosive sublimate, the nitrates of lime, magnesia, &c.; whilst amongst organic matters, it dissolves many organic acids, bases, and neutral bodies, the resins, the soaps, and the fats. The latter dissolve more freely in ether than in alcohol. The alcoholic solutions of substances used in medicine are called Essences, spirits, and tinctures. See BRANDY, WHISKY, FUSEL OIL, AMYL.
ACTIONS AND USES OF ALCOHOL.—The only alcohols which require to be taken into consideration are those belonging to the methyl, ethyl, propyl, butyl, and amyl series. It is of interest to observe that these alcohols increase in activity in direct proportion to their rise in atomic weight; amyl alcohol or potato spirit, for instance, is about five times as powerful as ethyl alcohol or spirit of wine. Ethyl alcohol alone is in general use, and it displays the most characteristic series of effects—to it, therefore, attention will here be entirely directed. When applied to the skin and allowed to evaporate, alcohol cools the surface of the body, and causes contraction of the local vessels, with diminution of the secretions. It may therefore be employed as a refrigerant and astringent, to lessen the surface temperature and check excessive perspiration. If, on the other hand, it is kept in contact with the skin without evaporation, it produces increased flow of blood in the part by penetrating through the cuticle, and it may be used in this way as a rubefacient when counter-irritation is desired. Upon the terminations of the nerves of sensation, it acts at first as a stimulant, and causes a feeling of heat and pain, but it afterwards has a depressing effect upon them, and produces numbness. In this way it is of importance as an ingredient in lotions and liniments intended for application to painful parts. When brought in contact with mucous membranes, alcohol produces effects similar in kind to those mentioned in connection with the skin, but, on account of the greater sensitiveness of the former, the effects are more marked. As alcohol coagulates albumen, it forms a film of white colour upon the mucous membranes by acting on the albuminous elements of the secretions.
When taken into the mouth, alcohol causes an increased secretion of saliva, by acting reflexly through the nerves regulating the salivary glands, and at the same time, in a similar manner, it induces a flow of the gastric juice through the nerves of the stomach. Reaching the stomach, it increases the gastric secretion, and causes dilatation of the vessels, with flushing of the surface, attended by a sense of warmth and a feeling of appetite. Taken before food, it is thus of considerable benefit in cases of impaired digestion. It also increases the muscular contractions of the stomach and intestines, and may be used for the purpose of expelling or preventing flatulence, although it is not to be recommended for this symptom. If taken in excess or in too concentrated form, alcohol causes catarrh of the stomach and bowels. Upon the digestive juices in moderately dilute solutions pure alcohol has little or no effect, and causes no retarding influence on the digestive processes. It is otherwise, however, with wines. The volatile substances which they contain exercise a powerfully inhibitory action on these processes. If it be not taken in great excess, alcohol is entirely absorbed in the stomach, none passing into the intestines. It passes into the circulation for the most part unchanged, only a very small proportion being absorbed as acetic and carbonic acids. Entering the blood, it seems to unite with the hæmoglobin of the coloured corpuscles, forming a compound which yields up oxygen to the tissues much less readily than under ordinary circumstances. In this way the oxidation of the tissues is retarded, and there is less waste, while the alcohol itself is oxidised in the tissues, acting as a food, and producing carbonic acid and water. Circulating in the blood, it gives rise to specific effects on the nervous system, and through it upon the different organs of the body. On nervous structures it produces a brief, transient stimulation, followed by depression, of their functions. Its first effect is shown by dilatation of the vessels throughout the body, with reduction of arterial pressure, and acceleration of the action of the heart—these being the consequence of depression of the vaso-motor nerves regulating the vessels, which has supervened upon the brief excitement of these nerves. The surface of the body becomes flushed and moist from the dilatation of the vessels and consequent increased secretion of the sweat glands. At the same time, from the loss of heat by radiation from the surface, the body-temperature falls. Alcohol is therefore worse than useless as a means of sustaining heat in cold climates. The respiration is accelerated by small quantities, and retarded by larger amounts, and the organs throughout the body generally are congested and stimulated to activity by alcohol, more especially the kidneys.
Upon the central nervous system, alcohol, after the brief excitement above mentioned, acts by causing a progressive impairment of the centres, from the higher or intellectual to the lower or organic; and the effects are directly proportional to the quantities taken. After the use of a quantity well within the limits of moderation, there is increased activity of these nervous centres, which shows itself by greater clearness of reasoning, strength of volition, vividness of imagination, depth of emotion, acuteness of sensibility, and force of muscular movement. As a consequence, thoughts flow swiftly, the speech becomes fluent, and is often accompanied by lively gesticulations. If the amount which has been taken, however, is beyond the limits of moderation, there is some disturbance of the various functions. The intellectual centres suffer in the first place, and while the imaginative and emotional, as well as sensory and motor functions are still stimulated, the reasoning faculties and the will become obscured and impaired. The imagination and emotions next become perverted, and, lastly, sensibility and motility are depressed. The muscles become irregular in their movements, so that the gait is staggering, or they may be paralysed, when the erect posture is an impossibility. If the quantity taken is very great, it may cause paralysis of the vital centres in the medulla oblongata, in which case death ensues from failure of respiration or circulation, or of both. Taken in moderate quantity, alcohol is, for the most part, oxidised and excreted as carbonic acid and water, only about a fifth being given off by the lungs, kidneys, and skin in an unchanged form. As a stimulant it may be employed in all diseases threatening to end in death from failure of the heart, but it is on no account to be given in cases of simple nervous depression. Alcohol is now much more sparingly used in the treatment of all wasting diseases, especially fevers, its food value being disputed, and by some wholly denied.
For the opposing views on the employment of alcohol, see a series of articles on 'The Alcoholic Question' in the Contemporary Review for 1878, 1879. For the proportions of alcohol in alcoholic beverages see WINE; also WHISKY, BRANDY, &c., and FOOD, DIET.