GLYCERIN, glieer-in, GLYCEROL (from Gk. yAmcepOc, glykeros, sweet, from yi.mbc, gly kys, sweet), or PROPENYL ALcolioL, An organic chemical compound, used for a variety of purposes in the arts and in medicine. Perfect ly pure glycerin is a crystalline solid substance melting at 17° C.; but the merest traces of im purities prevent it from crystallizing, and it is therefore usually obtained in the form of a thick syrupy liquid that boils at 290° C. Small quan tities of salts cause it to decompose to some extent when distilled. Glycerin mixes in all pro portions with water and alcohol, and readily absorbs moisture if exposed to the air, but does not mix with ether, chloroform, carbon disuphide, benzene, and many other organic liquids. On the other hand, it forms an excellent solvent for a variety of substances, both inorganic and organic. It is colorless and odorless, but has a distinctly sweet taste. Its specific gravity at 15° C. is 1.265. Glycerin is obtained in large quantities in the of soap and of candles. It is well known that natural fats are largely used in the manufacture of these products, and as fats consist mainly of glycerides, i.e. compounds of glycerin with fatty acids, glycerin is set free when the fats are decomposed, or 'saponified.' It is thus obtained, in more or less dilute aqueous solution, through the saponification of fats with lime or with superheated steam. To separate the glycerin from the dilute solution, the latter is somewhat concentrated by evaporation, filtered through boneblack, and then further evaporated in vacuo. To render it fit for use in medicine and in the manufacture of nitroglycerin, the product thus obtained is further purified by dis tillation with superheated steam before it is brought into the market. Finally, to eliminate, for scientific purposes, the last traces of impuri ties in the commercial product, the latter may be again mixed with water, filtered through care fully purified boneblack, and evaporated in vacuo. In medicine glycerin is used chiefly as a vehicle for applying externally many substances, such as the alkalies, neutral salts, bromine, iodine, alkaloids, tannic acid, etc., the glycerin solutions of which are readily absorbed by the skin. It injected into the rectum, glycerin relieves con stipation, its action being speedy. painless, and followed by no constitutional disturbance. Very large doses of glycerin taken internally are liable to cause loss of muscular strength, lethargy. and even death. In the arts, glycerin is employed
mainly in the manufacture of nitroglycerin, from which many valuable modern explosives are made; nitroglycerin is the tri-nitrate of glycerin, obtained by the action of nitric acid on glycerin. Glycerin is further used as a preservative fluid for small and delicate anatomi cal preparations, and has been applied to the preservation of meat and other foods; it has been added to the water in gas-meters,.with the view of preventing it from freezing in winter and from evaporating too rapidly in summer. It is also used in the manufacture of toilet-soap, of parchment paper, and of printers' rollers, in the textile industry, etc.
Chemically glycerin is a tri-atomic alcohol, its constitutional formula being CH, ( OH ) .CH ( OH) .C11,( OH). When the hydrogen of its hy droxyl groups is replaced by metals or by organic acid radicles, alcoholates or esters, respectively, are obtained. Fats are mixtures containing, in various proportions, mainly the esters which glycerin forms with oleic, palmitic, and stearic acids. The hydroxyl groups of glycerin may be readily replaced by chlorine or bromine, one or two atoms of chlorine being thus substituted by the direct action of hydrochloric acid, while the third hydroxyl group may be replaced by chlorine by the action of phosphorus pentachloride. Be sides the method described above, by which glycerin is made on an industrial scale, it may be prepared by the action of potassium perman ganate on ally] alcohol, and it is produced in small quantities during the alcoholic fermenta tion of sugars. By the action of acid potassium sulphate or other dehydrating agents on glycerin, or simply by distilling impure glycerin under ordinary atmospheric pressure, acrolein is pro duced according to the following chemical equa tion: = 2H,0 Glycerin Acrolein Water When carefully oxidized with dilute nitric acid, glycerin is transformed into glyeeric acid, CH, ( OH) .CH (OH) .COOH. Usually, however, the products of oxidation of glycerin are oxalic, car bonic, and glycollic acids.
Glycerin was discovered by Scheele in 1779; Chevreul demonstrated its existence, in the form of glycerides, in the fats; its composition was determined by Pelouze, and its chemical consti tution by Berthelot and Wurtz. Finally, Charles Friedel, in collaboration with Silva, succeeded in effecting the complete synthesis of glycerin from its chemical elements; their method, however, is too complicated to be described here.