Glycerine , (Gr. sweet), the sweet principle of oils, a triatonic alcohol, the base of the compounds found in animal fats and also in some vegetable substances, discovered by Scheele in 1779. Its composition is represented by the formula C3H603. It is a colorless, transparent, sweet sirup, without odor, of specific gravity 1.28; it is inflammable, mixes freely with water, taking it from the air, is also soluble in alcohol, sparingly in ether, and dissolves salts that are soluble in water; it does not become rancid by exposure, but with animal tissue may be made to ferment. At a temperature above 600° F. it is decomposed, being converted into acroleine, acetic acid, and inflammable gases. Between 500° and 600° it may be distilled with only partial decomposition. It may be cooled to - 4° F. without freezing. Berthelot has succeeded in combining it with the fatty acids, and has thus produced the organic fatty substances, stearine, margarine, oleine, etc. This was effected by keeping the mixture of acids and glycerine at a temperature of 212° for several days in close vessels. At higher heat much less time is required. - Glycerine is a product of the process of saponification.
As prepared by the pharmaceutists, it was taken up with boiling water from its mixture in a free state with the plum-biferous soap called lead plaster, The plaster is made by boiling together litharge (oxide of lead), olive oil, and water. The oil is decomposed by the lead taking its acids, and the glycerine is thus liberated. When hot water is added in equal quantity to the plaster, the mixture is well stirred, and the liquid part is decanted; any lead that may be present is thrown down by a current of sulphuretted hydrogen, and is got rid of by filtering. The water is finally removed by evaporation at a temperature below 212°, leaving the glycerine. Various other methods of preparing it are in use. The mother liquor of the soap factories affords a convenient source of it. From this it is separated by adding a slight excess of sul-phuric acid, heating the solution with carbonate of baryta, filtering, and, after the filtrate has been concentrated by evaporation, taking up the glycerine with alcohol, which is afterward to be distilled off. A hot solution of fat has been decomposed by injecting into it superheated steam. The fatty acids and glycerine, collected in a receiver, separate in two layers, the glycerine at the bottom.
The acids can be drawn off, so as to leave the glycerine with no other mixture than water. The method of detecting the presence of glycerine when in small quantity is based on the marked qualities of the substance acroleine into which it is in part converted by heat. If the substance supposed to contain it be separated from foreign mixture as far as possible and rapidly heated, either alone or with a little anhydrous phosphoric acid, the acroleine generated, in case glycerine was present, will be detected by the pungent acrid odor, somewhat like that from the wick of a candle just extinguished. Glycerine is formed in small quantities during the process of alcoholic fermentation. C. Friedl and R. Silva have succeeded in preparing it artificially from the chloride of propylene, which in turn is made without the use of glycerine itself. - Owing to its property of long continuing moist, and its strong affinity for water, it may be applied to the skin or to mucous surfaces, when it is desired to prevent dryness and to use a bland and soothing application, as in chapped hands or lips, many skin diseases, a parched and glazed condition of the mouth, etc. If applied undiluted, it withdraws water from the moister tissues under it.
For external uses it may be advantageously combined with tannin, carbolic acid, or borax, all of which are readily dissolved by it. With starch a plasma of any required consistency may be formed, which takes the place of an ointment, and has the advantage of not being greasy, and being capable of easy removal by washing. Inferior varieties of glycerine may contain irritating impurities. Either alone or with a small proportion of carbolic acid, it is a very useful medium for the preservation of anatomical specimens in a condition of pliability, and is also of great value in microscopic anatomy. Glycerine is a powerful solvent, and may be used in pharmacy to prevent drying as well as decomposition. The vegetable alkaloids dissolve in it readily, and may be used in this form for subcutaneous injection. It has been suggested for internal use in diabetes, instead of sugar, and also as a substitute for cod-liver oil; but experience does not assign to it much value for these purposes. For use in cosmetics and perfumery it is largely manufactured, its soft agreeable qualities, without greasiness or liability to putrefy, rendering it an excellent ingredient in soaps for the toilet, pomade, hair tonics, etc.
It is lately employed in the photographic art, and its use is extending for a variety of new purposes. A glycerine ointment of much repute for chapped hands and excoriations is made as follows: 1/2 oz. of spermaceti is melted together with a drachm of white wax and 2 fluid oz. of oil of almonds, by a moderate heat; the mixture is poured into a Wedgwood mortar, when a fluid ounce of glycerine is added to it and rubbed till the ingredients are thoroughly mixed and cold. The consumption of glycerine in the manufacture of beer amounts to more than 20,000 cwt. per annum. It also finds extensive use for the following purposes: mixed with water to fill wet gas metres; to lubricate the inside of moulds for plaster casts; to prevent the shrinkage of wooden vessels; to preserve meat, fruit, candies, medicines, mustard, and tobacco; as a hair wash; in soaps and cosmetics; for the extraction of perfumes; to impart elasticity to paper; in various photographic operations; as a solvent for certain aniline colors; in calico printing; in the preparation of leather; as a substitute for oil in delicate machinery; as a float to swimming compasses; in mercurial manometers; as a substitute for alcohol in the preservation of anatomical preparations; to prevent the rusting of instruments; in the artificial production of oil of mustard; to cure wounds, burns, and bites of venomous insects; in the preparation of cements; for throat diseases; in copying ink; in chemistry to prevent the precipitations of the heavy metals; and very largely in the manufacture of the explosive compounds nitro-glycerine, dynamite, dualline, and lithofracteur. (See Explosives.)