Page:The American Cyclopædia (1879) Volume XV.djvu/603

 TARTARIC ACID sxtrotartaric acid is the ordinary tartarjc acid found in grapes, tamarinds, -pineapples, and several other fruits, usually in combination with potassium, and frequently with a small portion of calcium. The acid of commerce is prepared from tartar or argol, and was first separated from it by Scheele in 1770. The present mode of manufacture is as follows. The crude tartar is dissolved in hot water in which is stirred a little pipe clay and bone black to remove coloring matter. The filtered or decanted liquid deposits on cooling crystals of cream of tartar, from which the acid may be prepared by dissolving them in boiling wa- ter, or the original solution may be employed. Powdered chalk is added as long as there is effervescence or the liquid reddens litmus. The product consists of an insoluble tartrate of calcium and a soluble normal tartrate of potassium, which latter, after separation of the calcium salt, is mixed with an excess of chloride of potassium, which throws down the remaining tartaric acid also as tartrate of calcium. Both precipitates are washed and digested with sulphuric acid diluted with eight or ten parts of water, by which means sul- phate of lime is precipitated while the tar- taric acid is left free in the solution. The filtrate is carefully evaporated to the consis- tency of a sirup, and placed in a warm situa- tion to crystallize. Liebig found that tartaric acid is produced by the action of nitric acid upon milk sugar. It may also be obtained from succinic acid by submitting the latter to the action of bromine and treating one of the products, dibromosuccinic acid, with oxide of silver and water. Tartaric acid crystallizes in transparent, oblique rhombic prisms of sp. gr. 1'75, which are inodorous, permanent in the air, and easily soluble in hot and cold water and in alcohol, but insoluble in ether. The aqueous solution soon spoils, becoming cov- ered with a fungoid growth. Tartaric acid is used in calico printing to liberate chlorine from bleaching powder, and in medicine, prin- cipally for the preparation of effervescing pow- ders. (See EFFERVESCENCE.) Other Varieties of Tartaric Acid. The grapes cultivated in certain districts of the upper Rhine and in the Vosges contain, besides ordinary tartaric acid, an isomeric acid, called paratartaric or racemic acid, which resembles it in many par- ticulars, but differs much in others; for in- stance, it is rather less soluble, and has not the power of rotating the plane of a polarized ray of light. Pasteur has made some inter- esting researches upon the subject, and finds that if racemic acid is united with single bases, a salt is formed whose crystals are all identi- cal; but if it is united with two bases, after the manner of Rochelle salt, and the solution allowed to crystallize slowly, two varieties of crystals are formed, bounded by the same num- ber of faces, inclined to one another at exactly the same angles. They however have certain hemihedral faces which are developed on op- 777 VOL. xv. 37 TARTARS 575 posite sides of the two crystals, so that one crystal is like the reflected image of the oth- er, and may be denominated morphologically right-handed and left-handed crystals. If these crystals are selected and separately recrystal- lized, each variety will produce its own partic- ular form of crystal, and one will have right- handed and the other left-handed rotatory powers on polarized light. The acids obtained from these two varieties of crystals have also corresponding right-handed and left-handed rotatory powers, one being in fact ordinary or dextrotartaric, the other laevotartaric acid. As these two acids have equal rotatory powers in opposite directions, if their solutions are min- gled in equal proportions the mixture will have no effect upon polarized light. When concen- trated solutions of the two acids are mingled, crystals of racemic acid are deposited with sensible evolution of heat. Both acids also exhibit pyro-electricity, but in opposite -direc- tions. Pasteur also found that racemic acid may be artificially produced by the action of heat upon certain compounds of tartaric acid which are capable of resisting a high tempera- ture; for instance, when tartrate of cincho- nine is exposed to a temperature of about 338 F. and afterward repeatedly boiled in water and treated with chloride of calcium, racemate of calcium is formed. Left-handed tartaric acid may in like manner be converted into racemic acid. The formation of racemic acid in these reactions is accompanied by the pro- duction of a fourth modification, which Pas- teur calls inactive acid, having, like racemic, no action on polarized light, but which, unlike racemic, cannot be resolved into right-handed and left-handed acids. TARTARS, a branch of the Mongolian or Tu- ranian division of the human race, principal- ly inhabiting Asia. The name is one of in- definite and indiscriminate application, used with varying comprehensiveness by different writers. In its widest sense it may be re- garded as embracing the Altaian group of Mongolians, according to Yirchow ; that is, all the various tribes and nations inhabiting the table lands of central and northern Asia who are not of Aryan blood, including the Tartars proper, the Kirghiz, the Calmucks, the Mantchoos (sometimes called the Mantchoo Tartars), the Mongols proper, or people of Mongolia (who, however, probably constitute a separate branch), and the Tungusians, who are thought by Huxley to share the physical characteristics of the Esquimaux. In a more restricted application of the word, ^the Tar- tars comprise the Turanian inhabitants of Turkistan and the adjacent regions. These are the nomad Kirghiz, who dwell in Khp- kan and Kashgar, on the Pamir steppe, and in the adjacent valleys ; the TJzbecks, who have advanced furthest toward settled civilization and constitute the governing class in Turkis- tan; the Kiptchaks, a semi-nomadic people living in Khokan, who travel with their flocks