1911 Encyclopædia Britannica/Alcohol

From Wikisource
Jump to navigation Jump to search

ALCOHOL, in commerce, the name generally given to “spirits of wine”; in systematic organic chemistry it has a wider meaning, being the generic name of a class of compounds (hydroxy hydrocarbons) of which ordinary alcohol (specifically ethyl alcohol) is a typical member (see Alcohols).

The word “alcohol” 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 powder; its present-day application to the product of the distillation of wine is of comparatively Etymology.recent date. Thus Paracelsus and Libavius both used the term to denote a fine powder, the latter speaking of an alcohol derived from antimony. At the same time Paracelsus uses the word for a volatile liquid; alcool or alcool vini occurs often in his writings, and once he adds “id est vino ardente.” Other names have been in use among the earlier chemists for this same liquid. Eau de vie (“elixir of life”) was in use during the 13th and 14th centuries; Arnoldus Villanovanus applied it to the product of distilled wine, though not as a specific name.

Ordinary alcohol, which we shall frequently refer to by its specific name, ethyl alcohol, seldom occurs in the vegetable kingdom; the unripe seeds of Heracleum giganteum and H. Sphondylium contain it mixed with ethyl butyrate. In the animal kingdom it occurs in the urine of diabetic patients and of persons addicted Ethyl alcohol.to alcohol. Its important source lies in its formation by the “spirituous” or “alcoholic fermentation” of saccharine juices. The mechanism of alcoholic fermentation is discussed in the article Fermentation, and the manufacture of alcohol from fermented liquors in the article Spirits.

The qualitative composition of ethyl alcohol was ascertained by A. L. Lavoisier, and the quantitative by N. T. de Saussure in 1808. Sir Edward Frankland showed how it could be derived from, and converted into, ethane; and thus determined it to be ethane in which one hydrogen atom was replaced by a hydroxyl group. Its constitutional formula is therefore CH3CH2OH. It may be synthetically prepared by any of the general methods described in the article Alcohols.

Pure ethyl alcohol is a colourless, mobile liquid of an agreeable odour. It boils at 78·3° C. (760 mm.); at −90° C. it is a thick liquid, and at −130° it solidifies to a white mass. 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., for which the mercury thermometer cannot be used. It readily inflames, burning with a blue smokeless flame, and producing water and carbon dioxide, with the evolution of great heat; hence it receives considerable application as a fuel. It mixes with water in all proportions, the mixing being attended by a contraction in volume and a rise in temperature; the maximum contraction corresponds to a mixture of 3 molecules of alcohol and 1 of water. Commercial alcohol or “spirits of wine” contains about 90% of pure ethyl alcohol, the remainder being water. This water cannot be entirely removed by fractional distillation, and to prepare anhydrous or “absolute” alcohol the commercial product must be allowed to stand over some dehydrating agent, such as caustic lime, baryta, anhydrous copper sulphate, &c., and then distilled. Calcium chloride must not be used, since it forms a crystalline compound with alcohol. The quantity of alcohol present in an aqueous solution is determined by a comparison of its specific gravity with standard tables, or directly by the use of an alcoholometer, which is a hydrometer graduated so as to read per cents by weight (degrees according to Richter) or volume per cents (degrees according to Tralles). Other methods consist in determining the vapour tension by means of the vaporimeter of Geissler, or the boiling point by the ebullioscope. In the United Kingdom “proof spirit” is defined as having a specific gravity at 51° of 12/13 (·92308) compared with water at the same temperature. The “quantity at proof” is given by the formula:— quantity of sample ✕ (degrees over or under proof + 100) divided by 100.

The presence of water in alcohol may be detected in several ways. Aqueous alcohol becomes turbid when mixed with benzene, carbon disulphide or paraffin oil; when added to a solution of barium oxide in absolute alcohol, a white precipitate of barium hydroxide is formed. A more delicate method consists in adding a very little anthraquinone and sodium amalgam; absolute alcohol gives a green coloration, but in the presence of minute traces of water a red coloration appears. Traces of ethyl alcohol in solutions are detected and estimated by oxidation to acetaldehyde, or by conversion into iodoform by warming with iodine and potassium hydroxide. An alternative method consists in converting it into ethyl benzoate by shaking with benzoyl chloride and caustic soda.

Alcohol is extensively employed as a solvent; in fact, this constitutes one of its most important industrial applications. It dissolves most organic compounds, resins, hydrocarbons, fatty acids and many metallic salts, sometimes forming, in the latter case, crystalline compounds in which the ethyl alcohol plays a rôle similar to that of water of crystallization. This fact was first noticed by T. Graham, and, although it was at first contradicted, its truth was subsequently confirmed. In general, gases dissolve 7 volumes of hydrogen, 25 volumes of oxygen and 16 volumes of nitrogen.

Potassium and sodium readily dissolve in ethyl alcohol with the production of alcoholates of the formula C2H5OK(Na). These are voluminous white powders. Sulphuric acid converts it into ethyl sulphuric acid (see Ether), and sulphur trioxide gives carbyl sulphate. The phosphorous haloids give the corresponding ethyl Reactions.haloid. Ethyl chloride (from the phosphorus chlorides and alcohol) is an ethereal liquid boiling at 12·5° C., soluble in alcohol, but sparingly so in water. Oxidation of ethyl alcohol gives acetaldehyde and acetic acid. Chlorine oxidizes it to acetaldehyde, and under certain conditions chloral (q.v.) is formed.

In almost all countries heavy taxes are levied on manufactured alcohol mainly as a source of revenue. In the United Kingdom the excise duty is eleven shillings per proof gallon of alcohol, while the customs duty is eleven shillings and fivepence; the magnitude of these imposts may be more readily understood when one remembers that the Industrial alcohol.proof gallon costs only about sevenpence to manufacture. The great importance of alcohol in the arts has necessitated the introduction of a duty-free product which is suitable for most industrial purposes, and at the same time is perfectly unfit for beverages or internal application.

In the United Kingdom this “denaturized” alcohol is known as methylated spirit as a distinction from pure alcohol or “spirits of wine.” It was first enacted in 1855 that methylated spirit, a specific mixture of pure alcohol and wood-naphtha, should be duty-free; the present law is to be found in the Customs and Inland Revenue Act Methylated spirit.of 1890, and the Finance Act (sect. 8) of 1902. From 1858 to 1861 methylated spirit was duty-free when it was required for manufacturing processes, and the methylation or “denaturizing” was carried out in accordance with a prescribed process. During the next three decades (1861–1891) the law was extended, and methylated spirit was duty-free for all purposes except for use as beverages and internal medicinal applications. This spirit (“unmineralized methylated spirit”) consisted of 90 parts of alcohol of 60–66 over-proof (91–95% of pure alcohol) and 10 parts of wood-naphtha. It was found, however, that certain classes were addicted to drinking this mixture, and since 1891 the sale of such spirit has been confined to manufacturers who must purchase it in bulk from the “methylators.” For retail purposes the “ordinary” methylated spirit is mixed with ·357% of mineral naphtha, which has the effect of rendering it quite undrinkable. The Finance Act of 1902 allows a manufacturer to obtain a license which permits the use of duty-free alcohol, if he can show that such alcohol is absolutely essential for the success of his business, and that methylated spirit is unsuitable. Notwithstanding this permission there have been many agitations on the part of chemical manufacturers to obtain a less restricted use of absolute alcohol, and in 1905 an Industrial Alcohol Committee was appointed to receive evidence and report as to whether any modification of the present law was advisable. In the United States the same question was considered in 1896 by a Joint Select Committee on the use of alcohol in the manufactures and arts. Reference should be made to the reports of these committees for a full account of the use, manufacture and statistics of “denaturized” spirits in various European countries.

In Germany, the use of duty-free spirit is only allowed to state and municipal hospitals, and state scientific institutions, and for the manufacture of fulminates, fuzes and smokeless powders. The duty-free “denaturized” spirits may be divided into two groups—“completely denaturized” and “incompletely denaturized.” In the first category there are two varieties:—(1) A mixture of 100 litres of spirit and 21/2 litres of a mixture of 4 parts of wood-naphtha and 1 of pyridine bases; this spirit, the use of which is practically limited to heating and lighting purposes, may be mixed with 50 grs. of lavender or rosemary, in order to destroy the noxious odour of the pyridine bases. (2) a mixture of 100 litres of spirit, 11/4 litres of the naphtha-pyridine mixture described above, 1/4 litre of methyl violet solution, and from 2 to 20 litres of benzol; this fluid is limited to combustion in motors and agricultural engines. The second category, or “incompletely denaturized” spirits, include numerous mixtures. The “general” mixture consists of 100 litres of spirit, and 5 litres of wood spirit or 1/2 litre of pyridine. Of the “particular” varieties, we can only notice those used in the colour industry. These consist of 100 litres of spirit mixed with either 10 litres of sulphuric ether, or 1 litre of benzol, or 1/2 litre of turpentine, or ·025 litre of animal oil.

The German regulations are apparently based on a keen appreciation of the fact that while one particular denaturizing agent may have little or no effect on one industry, yet it would be quite fatal to the success of another; there is consequently a great choice of denaturizing agents, and in certain cases it is sufficient to mix the alcohol with a reagent necessary for the purpose in hand, or even with a certain amount of the final product, it being only necessary to satisfy the state that the spirit is not available as a beverage.

In France, the general denaturizing agent is wood-spirit of at least 58 over-proof, and containing 25% of acetone and 2·5% of impurités pyrogenées; 10 litres of this spirit denaturizes 100 litres of alcohol. This mixture is supplied to manufactures and corresponds to the British unmineralized methylated spirit; but the regulations are more stringent. When sold for lighting and heating purposes, it is further admixed with 0·5% of heavy benzene boiling at 150°–200° C. Provisions are also made for special denaturizing processes as in Germany.

In America the internal revenue tax on denaturized alcohol (formerly duty-free only to scientific institutions) was removed by Congress in 1906 (act of June 7th).

Pharmacology, Toxicology and Therapeutics of Alcohol.—Alcohol is of great medicinal value as a solvent, being used to form solutions of alkaloids, resins, volatile oils, iodoform, &c. In strength of about 10% and upwards it is an antiseptic. If applied to the skin it rapidly evaporates, thereby cooling the skin and diminishing the amount of sweat excreted. This refrigerant and anhidrotic action is employed to soothe many forms of headache by bathing the forehead with eau de Cologne. If, on the other hand, the alcohol be rubbed into the skin, or if its evaporation be prevented—as by a watch-glass—it absorbs water from the tissues and thus hardens them.

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 muscular pains, as in lumbago and other forms of so-called “muscular rheumatism.” Given internally in small quantities and in sufficient dilution, alcohol causes dilatation of the gastric blood-vessels, increased secretion of gastric juice, and greater activity in the movements of the muscular layers in the wall of the stomach. It also tends to lessen the sensibility of the stomach and so may relieve gastric pain. In a 50% solution or stronger—as when neat whisky is taken—alcohol precipitates the pepsin which is an essential of gastric digestion, and thereby arrests this process. The desirable effects produced by alcohol on the stomach are worth obtaining only in cases of acute diseases. In chronic disease and in health the use of alcohol as an aid to digestion is without the support of clinical or laboratory experience, the beneficial action being at least neutralized by undesirable effects produced elsewhere. The continued use of large doses of alcohol produces chronic gastritis, in which the continued irritation has led to overgrowth of connective tissue, atrophy of the gastric glands and permanent cessation of the gastric functions.

A single dose of concentrated alcohol (e.g. brandy) produces very valuable reflex effects, the heart beating more rapidly and forcibly, and the blood-pressure rising. Hence the immediately beneficial effect produced in the cases of “fainting” or syncope. After absorption, which is very rapid, alcohol exerts a marked action upon the blood. The oxygen contained in that fluid, and destined for consumption by the tissues, is retained by the influence of alcohol in its combination with the haemoglobin or colouring matter of the red blood corpuscles. Hence the diminished oxidation of the tissues, which leads to the accumulation of unused fat and so to the obesity which is so often seen in those who habitually take much alcohol. The drug exerts a noteworthy action upon the body-temperature. As it dilates the blood-vessels of the skin it increases the subjective sensation of warmth. The actual consequence, however, is that more heat than before is necessarily lost from the surface of the body. Alcohol also diminishes the oxidation which is the main source of the body-heat. It follows that the drug is an antipyretic, and it is hence largely used in fevers as a means of reducing the temperature. This reduction of the temperature, carried to an undesirable extreme, is the reason why the man who has copiously consumed spirits "to keep out the cold" is often visited with pneumonia. The largest amount of alcohol that can be burnt up within the healthy body in twenty-four hours is 11/2 oz., but it must be consumed in great dilution and divided into small doses taken every four hours. Otherwise the alcohol will for the most part leave the body unused in the urine and the expired air. In fever the case is different. The raised temperature appears to facilitate the oxidation of the substance, so that quantities may be taken and completely utilized which would completely intoxicate the individual had his temperature been normal. It follows that alcohol is a food in fever, and its value in this regard is greatly increased by the fact that it requires no primary digestion, but passes without changes, and without needing change, to the tissues which are to use it. According to Sir Thomas Fraser nothing else can compete with alcohol as a food in desperate febrile cases, and to this use must be added its antipyretic power already explained and its action as a soporific. During its administration in febrile cases the drug must be most carefully watched, as its action may prove deleterious to the nervous system and the circulation in certain classes of patient. The state of the pulse is the best criterion of the action of alcohol in any given case of fever. The toxicology of alcohol is treated in other articles. It includes acute alcoholism (i.e. intoxication), chronic alcoholism, delirium tremens, and all the countless pathological changes—extending to every tissue but the bones, and especially marked in the nervous system—which alcohol produces. (See Drunkenness; Delirium).

After death the presence of alcohol can be detected in all the body fluids. Its especial affinity for the nervous system is indicated by the fact that, when all traces of it have disappeared elsewhere, it can still be detected with ease in the cerebro-spinal fluid.