Origin

In the process of saponification, when a fixed oil and salifiable base react together, the oil is resolved into certain fatty acids, which combine with the base to form soaps, and into a substance which may be obtained separate, and which, from its sweet taste, has received the name of glycerin. For the precise method of preparing it, the reader is referred to the U. S. Dispensatory.

Properties

Glycerin is a liquid of the consistence and appearance of thin syrup, colourless or slightly yellowish, of an unctuous feel, inodorous, and of a strong, agreeable, and pure sweetness. it is heavier than water. One of its most remarkable and important properties is that it does not evaporate, and consequently retains its liquid form unchanged. A temperature sufficient to vaporize, decomposes it. At a full red heat, it is inflammable. Water and alcohol dissolve it in all proportions, but it is insoluble in ether. its own solvent powers are very extensive, and have led to its use in medicine as a menstruum. it is antiseptic like sugar, but is not susceptible of the vinous fermentation. it appears to have basic properties. its ultimate constituents are carbon, hydrogen, and oxygen; and, theoretically, it is a hydrated protoxide of a compound radical, called glyceryle (C6H7). in the oils, it is supposed to exist in combination with the fatty acids, without its equivalent of water.

Medical Effects and Uses

Like sugar, glycerin appears to be nutritive and demulcent; but is even blander in its effects on irritated surfaces than proper saccharine solutions. As a demulcent for external use, its essential liquidity renders it of great value, and places it, for some purposes, before all other substances of the class. it may not be so directly antiphlogistic as the aqueous solution of gummy matters; because the cooling effect of evaporation, and the direct sedative effects of the water are wanting; but, for preserving softness of tissue, and protecting against irritant influence from without, it is superior, or at least much more convenient; as it does not require the same constant watchfulness to prevent drying. its introduction into use for this purpose is, I believe, due to Mr. Startin, of London.

In dryness of the ear, from deficiency or too great solidity of the cerumen, and consequent deafness, glycerin is an excellent remedy. I have found it equally useful in the annoying dryness of the mucous membrane of the nostrils, which is habitual with some, and is often connected with chronic inflammation. in either of these cases, it may be introduced by means of a camel's-hair pencil, or, in the case of the external meatus, upon raw cotton. M. Foucher, of Paris, employs it much in diseases of the eyes, in order to prevent stiffness of the external parts, and the formation of crusts on the edges of the eyelids. it may be applied to the edges of the lids, by means of a hair-pencil, four or five times a day, and may be rubbed by the finger on the outer surface of the lids. {Med. T. and Gaz., Oct. 1860, p. 414.) Dr. E. R. Mayer, of Wilkesbarre, Pa., has used it, with decided advantage, in cases of pseudomembranous croup, applying it, by means of a hair-pencil, to the glottis, at the same time pressing the tongue forward and downward with the finger. {Am. Journ. of Med. Sci., April, 1858, p. 339.) M. Bouchut considers it superior to caustic applications, in diphtheric affections, believing it to be a solvent of the pseudomembranous exudation. {Med. Times and Gaz., May, 1858, p. 485.) in irritative cutaneous eruptions, it is an admirable remedy; being peculiarly adapted to lichen, prurigo, herpes, eczema, psoriasis, and lepra, but it may be used in any case of superficial irritation or inflammation of the skin, when a simple demulcent is wanted. it may be mixed with cataplasms in order to keep them moist, and answers the same useful purpose in extracts and pills, which it also guards against mustiness. But a very small proportion only must be added, or it will render the preparations too soft.

Glycerin was several years since proposed as an internal remedy by Dr. J. L. Crawcour, who considered it perfectly bland in its action on the animal economy, and possessed of the same property of supporting nutrition, and obviating the tuberculous and scrofulous tendency, which has given so much reputation to cod-liver oil. He gave from one to three drachms of it three times daily, in an ounce of water, in phthisis and strumous affections. (N. J. Med. Reporter, viii. 224, from New Orleans Med. News and Hospital Gazette.) it has since been extensively used with a view to improve nutrition and invigorate the general health; and, from the experiments of Dr. H. Lauder Lindsay, of Perth, would appear to have some effect of this kind; though it is not easy to determine how far the results obtained by him were simple consequences, and how far effects. {Ed. Med. Journ., II. 208.) it has been given also with asserted advantage in dysentery, being administered as a demulcent both by the mouth and rectum.

Some reference has been made above to its pharmaceutic uses. its solvent properties promise to render it very useful as a vehicle for other medicines, whether to be taken internally, or applied to the surface. it dissolves generally the same substances as water, and some that water does not, and so also as regards alcohol. According to MM. Cap and Garot, it approaches closely in its solvent powers to diluted alcohol. Among the medicines which it dissolves in considerable proportion, and which are insoluble, or of difficult solubility in water, are iodine of which it takes up one part in 100, biniodide of mercury, sulphate of quinia which is dissolved by it as freely as by alcohol, and gallic acid of which it dissolves one part in 12. Strychnia is soluble in 300 parts, Veratria in 96, and atropia in 50; and all much more so than in water. Tartar emetic is soluble in 30 parts. These are important facts, and suggestive of useful practical applications. {Journ. de Pharm. et de Chim., 3eser., xxvi. 81, Aug. 1854.) it has been used as a vehicle of tannic acid in leucorrhoea and fissures of the anus, and of borax in fissures of the tongue. An ointment composed of five parts of glycerin and one of starch is used by Prof. Simon, of Berlin, as an excellent excipient of medicines to be used locally. {Dub. Hosp. Gaz., Feb. 1, 1860, p. 41.)