Crude distillation glycerin is obtained in large quantities as a by-product in the manufacture of so-called °stearin') candles. In this case the fat is not saponified by an alkali, but beef fat, or some other fat that is rich in stearin, is acted upon by superheated steam, by which the stearin, or stearate of glycerin, is resolved into free stearic acid and free glycerin. Fat under goes a similar transformation when treated with a mineral acid; but this method of producing glycerin has the disadvantage that the mineral acid is likely to combine to a certain extent, either with the glycerin, or with the liberated fatty acid, necessitating a subsequent treatment for its removal.
Glycerin is refined by distillation of the crude, and, if for dietetic or pharmaceutical purposes, is redistilled. The finest grade is triple distilled. Pure glycerin is a colorless, odorless, syrupy liquid, with an oily feel and an intensely sweet taste, and a specific gravity of about 1.27. It is insoluble in ether, but it mixes in all proportions with water and with alcohol. It has a considerable affinity for water, and absorbs moisture from the air quite readily to the extent of SO per cent of its weight.
It boils at about F,, but with partial de composition. Under reduced pressures it boils at lower temperatures. At a pressure of 12.5 millimetres of mercury, for example, it boils at 356° F., and may be distilled without change. By subjecting pure glycerin to a temperature of to F., it will solidify in rhombic crys tals, which melt at 68°. A large quantity of glycerin at 32° may be solidified by the intro duction of a few glycerin crystals. Glycerin burns with an almost colorless flame, and dis solves many organic bodies that are insoluble in water. It also dissolves iodine, and many of the metallic oxides.
The solvent properties of glycerin render it valuable in pharmacy, and it is added to baker's cake in small quantities to keep it moist. Large quantities are used in the manufacture of toilet soaps, creams and washes, as a preservative medium, and hi gas meters and other mechan ical appliances in which a liquid is needed which will not readily freeze nor evaporate, but the largest part of the production is made into dynamite, blasting gelatine and smokeless powders.