GLYCERINE (GLYCEROL), in pharmacy Glycerinum, was discovered by Scheele in olive oil in 1779 and named olsiiss. Chevreul studied it more fully in connection with his work on the fats about 1813 and gave it its present name (Gr. 'yAvxin, sweet) ; whilst Pelouze (1836), Berthelot and others established its formula as a trihydric alcohol, and its connection with the fats and oils, which are formed by the replacement of the hydrogen of the OH groups in glycerine by radicals of the higher fatty acids (see GLYCERIDES). In addition to the fatty oils, which are the largest source of glycerine, the latter is combined, partly with fatty acids and at the same time with derivatives of phosphoric acid (as glycerophosphatides), in certain substances characteristic of specific animal structures, such as lecithin (eggs, various organs) and kephalin (brain, liver and other organs).
Glycerine is also a normal product (about 3%) of the alcoholic fermentation of sugar by yeast, and is therefore present in wine and beer, as was originally shown by Pasteur in 1858. Neuberg (1912) and others have shown that, if the fermentation be carried out in presence of certain salts such as sodium sulphite, sugar can be made to yield as much as 2 5 % of its weight of glycerine, and this observation was utilised on a large technical scale by the Cen tral Powers in the World War. In effect this process means that, if the supply of glycerine from fats falls short of the demand, it may in future be supplemented by fermentation glycerine from molasses or other cheap sugar material.
Properties.—Glycerol (pure glycerine) is a colourless, odour less, viscous liquid with an insipid sweet taste (sp. gr. 1.2647 at 15 ° C. ; refractive index nD I .475$ at 12.5 ° C.) . It boils at 29o°C. with some decomposition at atmospheric pressure, and is unchanged under diminished pressure (e.g., 182°/2omm. and . Its melting-point is 20 ° C., but owing to the ease with which it exists in the supercooled state, it is rarely seen in the solid state. It is exceedingly hygroscopic, miscible with water or alcohol in all proportions, but less soluble in ether.
The bacterial fermentation of many fats, especially those of marine animals, in presence of water not infrequently causes some of the glycerine to be transformed into a related dihydric alcohol or glycol known as trimethylene glycol, •CH,. ; this substance can be separated from glycerine dur ing refining and finds application for certain of the purposes for which glycerine itself is used. It may be added that a simpler glycol, ethylene glycol, •CH,(OH), which can be pro duced from ethylene (in coke-oven or other gas) or alcohol, is coming to the fore as a potential competitor with glycerine.
Manufacture.—Practically the whole of the glycerine of com• merce is still derived from the fatty oils, and most of this comes into the hands of the glycerine refiner in the form of soap-lyes (see SOAP). In the ordinary soap-pan the fats have been saponi fied by means of aqueous caustic soda and the resulting soap salted out by brine; the clear aqueous (saline) liquors contain the whole of the glycerine from the fat and the latter forms about 3 to 5% of the soap-lye (as it is termed) whilst all the added salt is also present. Other means of splitting the fats are also em ployed, for example, by heating them in presence of a little lime with a current of steam at about 140°C. (12o lbs. per sq.in. steam-pressure) in autoclaves, by heating them with water and a special chemical known as the Twitchell agent, or by fermenta tion with aq enzyme (lipase) in presence of water. The aqueous lyes from the autoclave, Twitchell, or lipase processes will contain up to 15 % of glycerine and but little saline matter.
Crude glycerine is made by simple concentration of the lyes or sweet waters without distillation of the glycerine. The lyes (especially if from the soap-pan) are first of all treated with oxide of iron and/or lime to coagulate and remove traces of soap and other impurities, and the clarified liquor is then heated under a vacuum of 25-28 inches of mercury (usually in a double-effect evaporator) until the glycerine content of the residue reaches at least 8o%. After removal of any solid salts which have separated from the liquor, the product forms what is technically known as "crude glycerine." Soap-lye crude contains about Io% of salt and 8o% of glycerine; autoclave, etc., crudes contain about 86% of glycerine and less than 1 % of saline matter. But economic considerations on the fat-splitting side make saponification in the open soap-pan the more usual procedure. Most of the soap lye crude is distilled to give the more refined qualities of glycerine, but some of the other type finds use in printer's inks, in "anti freeze" compositions, plastic clays, etc.
Dynamite Glycerine.—The most important single outlet for glycerine is probably its use, after nitration, in blasting and other explosives such as dynamite, cordite, etc. (see NITRO GLYCERINE). To this end it is necessary to have glycerine free from solid impurities and containing about 95% of glycerol. This is secured by distillation of crude glycerine under much re duced pressure (28-29 inches of mercury) by the aid of a current of superheated steam. Several systems of glycerine stills are in operation, the favourite being that designed by van, Ruymbeke, in which, by means of an "expansion chamber" heated by the same steam as that which heats the centre of the still, the in jected steam regains the temperature lost by its expansion under vacuum and enters (in fine jets) into the heated crude glycerine in the still at exactly the same temperature as that of the latter. The mixed glycerine and steam vapours pass over into condensers in which they are fractionally separated and the dynamite glycer ine is collected. In later systems, such as those of Wood or Gar rigue, multiple stills are arranged in series and the distillation process made continuous; the superheated steam may be made to pass through a pre-heated spray of the crude glycerine.
Dynamite glycerine should have a sp. gr. 1 . 261-1.26 2 and con tain not more than o•o5% of mineral ash. It is usually pale yel low in colour, but can be converted into an almost white product ("industrial white glycerine") by treatment with charcoal.
Finally, chemically pure glycerine is produced by a further distillation of the once-distilled dynamite glycerine, followed by treatment with charcoal. Chemically pure (C.P.) glycerine should contain no impurity other than moisture; its sp. gr. is I•26 (97 98% glycerol) but for trade purposes it is also supplied at, for example, sp. gr. 1.25 (93%) or 1.24 (9o%). Arsenic, lead and copper must be completely absent, the mineral ash should not exceed o.oi%, and the total non-volatile residue, 0.05%.
Technical Uses.—C.P. glycerine is used very largely for medicinal and pharmaceutical purposes as a solvent for drugs, a component of emollient solutions, ointments and plasters, and in some purgative remedies; it also finds use as a preservative against fermentation and is thus employed in preserving meat and flesh products, in anatomical preparations, in vaccine lymph, etc. It is also used in the tobacco, snuff and spirit trades. In addition to its use in the manufacture of explosives dynamite glycerine (or the industrial white variety) is employed in various ways, for example, in the textile industries, as a lubricant where mineral or other oils are inadmissible, in hydraulic presses, for filling gas meters, in the preparation of plastic materials, in the paper, ink, soap and leather industries. (T. P. H.)