its liberation. Thus, as far back as 1825 , Clrevreul and Gay-Lussac sketched out the idea of the process of saponillcation by superheated steam, and the method was actually carried out with certain modi- fications by various chemists and manufacturers. For example, in 1842, 15. Price 8: Co. patcnted, in the name of Jones 8: Wilson, a process of the kind, which was largely worked for some years; in this, the fatty matter freed from extraneous impurities is mixed with 6 to 8 per cent. of strong sulphuric acid, arid then heated in (‘Olrlrcl' boilers to about 180° 0., by superheated steam blown through the mass for about two hours ; after which hotter steam at about 300’ to 350’ is blown through, when fatty acids distil, but little or no glycerin passes over unaltered, almost the whole being charred or decorrrposed, forming acroleiir, &c. Here the saponillcation and destruction of glycerin are largely effected by the sulphuric acid, as well as by the steam itself. Price’s process was suggested to the inventors by Tilghnran’s method, brought out early in 1851, which consisted iii making an errrulsion of melted fatty matter and water (or solution of alkali) by agita- tion, aud then pumping it through a long coil of iron tubing kept at a temperature near that of melted lead under a pressure of about 2000 1b to the square inch. In this way complete saponification is elfected, fatty acids and an aqueous solution of glycerin being obtained when water is used, and soap with more or less water and glycerin when alkaline liquor is employed. It is noticeable that in this process it is not necessary that the alkali should be caustic, as it rrrust be for the ordinary process of soap-boiling; sodium and potassium carbonates answer just as well as their respective hydrates (caustic soda, caustic potash).
Derivatives.—Arrrorrg the numerous derivatives obtainable from glycerin by appropriate chemical reactions, may be more particu- larly mentioned intro-glycerin, which is, strictly speaking, irn- properly named, inasmuch as it does not belong to the class of true nitro-substitulioir derivatives, biit is simply constituted like tri- stearirr, the radical of nitric acid displacing the hydrogen of the OH groups. By treating glycerin with nitric acid (preferably by dropping pure glycerin into a mixture of nitric and srrlplrurie acids) the following reaction ensues, the glycerin becoming what would be systematically termed tri-uilrz'n or glyccr'otrim'lrin :—
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0112. on crrgoxog err .orr + exozorr = 311,0 + -.cn.orx'o2 C112. orr (012.0502
By treating the resulting “ intro-glycerin " with caustic potash, Kiponification ensues, potassium nitrate berrrg formed and glycerin reproduced precrsoly as when trrstearin is similarly saponified. Two other important products obtainable from glycerin are isopropyl i-uliilc and (Lilyl iodide, each of wlrrclr serves as the starting-point of a large series of chemical products, many of them of utility in tlu- arts. These substances are manufactured by heating glycerin with lrydriodic acid, and are formed in Virtue of the reactions :—
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Glycerin Isopropyl iodide. c,ir,ioii.3 a.- 31120 + C3 7I Ally] iodide. 3n._.0 + 031151 M11 2 ’21. + c,rr,iou)—. + :an = i2 +
Again, glycerin is employed in the manufacture offer-mic acid, which is prepared most conveniently by heating together glycerin and oxalic acid. The splitting up of oxalic acid into carbon dioxide and formic acid, which takes place only to a minute extent when oxalic acid is heated alone (owing to the further dccompositiori of the formic acid). then ensues with but little formation of bye- products, and especially with but little loss of formic acid through further decomposition. This arises from the occurrence of a cycle of changes highly interesting from a chemical point of view, and consisting essentially in the continual fornration of a body analo- gous to rrronostcarin, and its continual breaking up into formic acid, which distils over, and glycerin, which acts over again on a fresh portion of oxalic acid.
Technical Uses.—Besidcs its use as a starting-point in the pro- duction of “ intro—glycerin ” and other chemical products, glycerin is largely employed for a number of purposes in the arts, its appli- cation thereto being due to its peculiar physical properties. Thus its non-liability to freeze (when not. absolutely anhydrous, which it practically never is when freely exposed to the air) and its non volatility at ordinary temperatures, combined with its power of always keeping fluid and not drying up and hardening, render it valuable as a lubricating agent for clockwork, watches, &e., as a substitute for water in wet gas-meters, and as an ingredient in eataplasms. plasters. modelling clay. pasty colouring matters, dye- ing materials, moist colours for artists, and numerous other analo- gous substances which are required to be kept in a permanently soft condition. From its softening property when applied to the skin, it constitutes a chief ingredient in irrairy toilet preparations, creams, and the like. Many of these indeed, sold ,under fancy names, are nothing but glycerin diluted with water or weak alcohol, or mixed with some oleaginous emulsion or paste, and variously scented. Its solvent power for numerous substances renders it valuable in pharmacy as an ingredient in numerous preparations. In some of these the glycerin acts not merely as _a solvent but also as a prescrvative against decomposition, owing to its antiseptic qualities, which also led to its being enr- ployed to preserve untanned leather (especiall y during transit when exportcd, the hides being, moreover, kept soft and supple); to make solutions of gelatin, albumen, gum, paste, cements, &e., which will keep \vrthont decomposition; to preserve meat and other edibles; to mount anatomical preparations; to preserve vaccine lymph irri- clranged ; and for many sinrilar purposes. Its solvent power is also utilized in the production of various colouring fluids, where the colouring matter would not dissolve in water alone; thus aniline vrolet,_ the tinetorial constituents of maddcr, and various allied colouring matters dissolve in glycerin, forming liquids which remain coloured even when diluted with water, the colouring matters being either retained in suspension or dissolved by the glycerin present III the diluted fluid. It has been proposed to use glycerin as a medium for the extraction of the odoriferons principle of flowers, &e., and as a substitute for sugar in the manufacture of some sorts of tobacco, the aronra of whieh is liable to be deteriorated should fer‘inentation of the saccharine matter set in. Certain kinds of copying inks are greatly irrrproved by the substitution of glycerin, in part or entirely, for the sugar or honey usually added. In fine, the number of useful adaptations of glycerin as an ingredient in order to confer certain special properties is almost unlimited, and its use in these directions is increasing yearly.
Impurities.—F or some of these purposes it is essential that the glycerin should be of considerable purity. The chief impurities liable to be present vary with the mode of preparation. Substances made by saporrification of oils, &e., with oxide of lead or lirrre, are apt to retain nrore or less of the metallic compounds, whilst glycerin extracted from soap-leys may also contain mineral matters. Such impure substances are readil y purified by distillation with steam or under greatly diminished pressure. Glycerin prepared by saponi- fyrng clarified tallow, &c., by superheated steam, rarely contains fatty acids ; if not deprived of practically all the water with which it is nrixed in the distillate first obtained, it is less viscrd and has a lower density, so that the specillc gravity forms a good test as to whether it contains much water or not. Occasionally glycerin is met with intentionally adulterated with sugar-syrup, gnnr, mineral matters, &c., but such falsifications are comparatively rare. They may be detected by the substance being not wholly soluble in alcohol, by its leaving a residue on ignition in air, by its precipi- tating a solution of basic lead acetate (after being dissolved in water), or by other special tests, according to the nature of the impurity sought for. Thus, whilst pure glycerin does not reduce alkaline copper solutions so as to precipitate cuprous oxide when boiled therewith, the precipitation is readily produced by certain kinds of sugar, either without any previous treatment (c._r/., glucose), or after boiling for a short time with water acidulated with a mineral acid such as sulphuric acid (c.g., cane sugar).
GMELIN, Johann Georg (1709–1755), a distinguished naturalist, son of the chemist of the same narrre, was born at Tilbingen, J true 12, 1709. Having taken his degree in nredicirre, he in 1727 repaired to St Petersburg, where in 1731 he was appointed professor of elrenristry and natural history. In 1733, by order of the empress Anna, he joined Deslisle, G. F. Miiller, and Behring in an expedition for the exploration of Siberia, which was penetrated as far as the Lena. He returned to St Petersburg in 1743. In 1719 he was chosen professor of botany and chemistry at Ti‘rbingen, where he died, May 20, 1755. Linnzeus named a genus of plants Gmelz'na in his honour.
His chief works are Flora Sibr'rica (4 vols. St l‘ctci‘sburg, 1749—50), and Reiscn Burch Sibz'rz'cn (4 vols., St Petersburg, 1752).
GMELIN, Leopold (1788–1853), a celebrated chemist, was born August 2, 1788, at Gottirrgerr, in the university of which city his father, Johann Friedrich Gmelin, was professor of medicine. He studied medicine and chem- istry at Giittingeu, Tiibingen, and Vienna, and in 1813 commenced lecturing on chemistry at Heidelberg, where in 1814 he was appointed extraordinary and in 1817 ordi- nary professor of medicine and chemistry ; the latter office he held till 1850. He died at Heidelberg, April 13, 1853.
Grnelirr’s fame rests chiefly on his chemical dictionary, the Hand- buc/L dcr Clzcmz'c, the first edition of which, in yols., was pub- lished at Frankfort in 1817-19. The fourth edition (Heidelberg, 1843, Sue.) was written by Gmelin himself as far as the end of vol. v.._ was continued by Drs List and Kraut and others, and completed by an eighth volume on physiological chemistry, the work of Pro~
