This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
General Impurities. - Water, fusel oil, and aldehyde. The water may have come to be present either as an accidental impurity or as an intentional adulteration. One of the most important impurities of alcohol is the presence of organic alkaloids. A good deal of spirit is made from spoiled grain, maize, etc, which cannot be used for food. In diseased grain alkaloids are formed, and these appear to pass over with the alcohol during distillation
Tests. - Water is detected by the use of the hydrometer, as any admixture of water with alcohol raises the specific gravity of the latter.
The presence of oily, fatty, or resinous substances in alcohol is recognised by diluting it with water, when these substances, being insoluble in weak spirit, are precipitated and render the solution turbid.
Traces of fusel oil and aldehyde are almost always present, and they are reckoned as impurities by the B.P. only when they rise above a certain amount. The quantity of them present in alcohol is determined by adding to 4 oz. of it 30 grain-measures of standard solution of nitrate of silver and exposing it to the sunlight for twenty-four hours. The nitrate of silver is deoxidised by these substances and a black precipitate consisting of oxide or of some organic compound is deposited.
General Action of Alcohol. - When alcohol is added in sufficient quantity to albuminous solutions it precipitates them, apparently simply by withdrawing the water from them, because when water is added to the freshly-precipitated albumin it redis-solves easily. When, however, the precipitate is kept for some time in alcohol it loses its solubility, and is no longer redissolved by water. Peptones are, however, uncoagulated by long standing under alcohol. When applied to the skin, alcohol evaporates readily, and gives rise to a sensation of cold. It renders the epidermis drier and harder, and if kept in contact with the skin, evaporation being prevented, it passes through the epidermis, and, acting upon the tissue below, stimulates it, causing an increased supply of blood to the part, and producing a feeling of warmth or burning. A similar action takes place when it is applied to a mucous membrane, e.g. when taken into the mouth. It here produces a slight precipitate of albumin on the surface and acts as an astringent, drawing the parts slightly together, and forming on the surface a whitish pellicle, which, however, rapidly disappears. It causes considerable reflex secretion of saliva. When taken into the stomach in small quantities, it has a similar action on that organ, causing increased vascularity and increased secretion, accompanied by a feeling of warmth, and it excites a feeling of appetite, for which purpose it is taken by some persons before meals. It aids the expulsion of flatulence from the stomach and intestines. In cases of diarrhoea it has a somewhat astringent action in the intestine, but in persons accustomed to take alcohol to excess the bowels are always rather loose, constipation occurring very rarely, if at all.
After absorption into the blood, it appears to form a compound with haemoglobin, which takes up and gives off oxygen less readily than haemoglobin itself (Schmiedeberg). It thus lessens the oxidising power of the blood, and will, consequently, diminish oxidation in the tissues.
Considerable dispute has arisen as to whether alcohol is a food or not. The chief argument in favour of its not being a food is that it is eliminated in the urine unchanged, but this seems to occur only when it is given in considerable quantities. In small doses it is partly eliminated by the breath, but most of it appears to undergo combustion in the body, and very little of it passes out in the urine. In this respect it agrees with other foods, such as cane-sugar. Hammond found that when on insufficient diet he was losing weight, the addition of a little alcohol not only enabled him to reach his former weight, but to add to it.
The argument in favour of alcohol being a food is that it is retained in the body, and supplies the place of other foods, so that the quantity of food which would without it be insufficient, with its aid becomes sufficient.
The conclusion to which all the evidence points is that alcohol is a food, and in certain circumstances, such as febrile conditions, it may be a very useful food; but in health, when other kinds of food are abundant, it is unnecessary, and, as it interferes with oxidation, it is an inconvenient kind of food.
After its absorption into the circulation it causes dilatation of the vessels on the surface of the body, and increases the rapidity of the pulse. From the freer circulation which thus takes place in the capillaries of the surface, the skin of the face and hands becomes more flushed. The blood flows so freely from the arteries into the veins that there is no longer time for it to become completely venous in its passage. In consequence of the capillaries being dilated, the skin is no longer mottled, but of a uniformly pink colour. The veins are distended; they fill more rapidly when emptied, and are of a lighter blue than usual, owing to the blood they contain being more arterial.
The action of alcohol upon the temperature seems to depend upon two factors. One of these is its power of lessening oxidation, but this only comes into consideration with large doses, when this factor may aid considerably in reducing the temperature. The other factor is the dilatation of the vessels on the surface (p. 419), which occurs even after moderate doses. This dilatation allows the warm blood from the interior of the body to circulate more readily near the surface, and thus subjects it to the cooling influence of the surrounding air, and also to the cooling effect of evaporation from the skin. By increasing the sweat it may lessen the temperature of the body, even when that of the surrounding air is as high or higher than it, and it will also cool the blood by freer radiation when the temperature of the atmosphere is below that of the body. It is evident that the cooling effects of alcohol will thus depend to a great extent on the atmospheric conditions of temperature and moisture to which the person taking it is subjected, as well as on the quantity of alcohol. Normally, when a person is subjected to cold, the vessels of the skin contract and prevent the warm blood in the interior of the body from approaching the surface and thus becoming cooled; but when large quantities of alcohol are taken, this mechanism becomes paralysed, the blood from the interior circulates over the surface, and is cooled down more and more until its temperature becomes so much reduced as to be incompatible with life, and the patient is frozen to death. The dangerous effects of alcohol under such circumstances are well known to the lumberers in Canada, and to Arctic voyagers, who dread alcohol, and generally avoid it altogether. The utility of this selfsame action of alcohol is very evident when a person comes from the cold atmosphere into a warm room; for here the individual may still remain cold, although in front of a fire, as the contraction of the surface vessels now continues, and the blood is no longer able to convey warmth to the interior, just as it was formerly unable to convey the cold. If alcohol be now taken, and the vessels dilated, the blood is allowed to circulate in the surface, soon becomes warm, and thus diffuses the warmth equally through the body.