TARTARIC ACID. Ordinary tartaric acid, C8114010.2H0, is usually seen in the form of colorless, transparent, oblique, rhombic prisms, which are not affected by the action of the air, have an agreeable acid taste, and are soluble in water and alcohol. The crys tals when gently warmed become strongly electric, the opposite sides of the crystals exhibiting the opposite forms of electricity. On heating tartaric acid to about 310°, it fuses; and at a slightly higher temperature it becomes successively changed, without 'losing weight, into two matameric acids, metatartaric and isotartaric acids, the former of which is bibasic and the latter mouobasie. At about 374°, two atoms of the acid lose one equivalent of water, and tartralic acid, is formed. If the same tem perature be maintained a little longer, half the basic water is expelled, and tartrelic acid, is formed; and finally, all the basic water is driven off, and anhy drous tartaric acid, or tartaric anhydride, (or C16II8020, remains in the form of a white porous mass insoluble in water, alcohol, or ether. If, however, it be allowed to remain ion.. moist, it gradually becomes converted into crystallized' tartaric acid. Finally, on distilling tartaric acid in a retort at a temperature of 400° and upward, it is decomposed into certain gases and empyreumatic oily matters, water, and acetic, pyru vie (or pyroracemic) and pyrotartaric acids.
Oxidizing agents, such as peroxide of lead or nitric acid, readily act upon tartaric acid, and convert it into formic and carbonic acids; and when fused with caustic potash, it splits up into acetic and oxalic acids. It is one of the strongest of the organic acids.
This acid occurs abundantly in the vegetable kingdom both in the free and combined state. It is found as a free acid in tamarinds, grapes, the pine-apple etc.; and in com bination with potash and lime in tamarinds, grapes, mulberries, and the unripe berries of mountain-ash, and in small quantity in the juice of many other vegetables. It is, however, from argol (q.v.), a product of the fermentation of grape-juice, that the tar taric acid of commerce is obtained. The details of the process may be briefly described as follows: argol, or crude bitartrate of potash, is dissolved in boiling water, and chalk is added as long as effervescence occurs. An insoluble tartrate of lime is precipitated, and tartrate of potash remains in solution. This tartrate of potash is converted by the addition of chloride of calcium, into insoluble tartrate of lime and soluble chloride of potassium. The tartrate of lime obtained by these two operations, if treated with sul phuric acid, readily yields free tartaric acid in solution, with sulphate of lime as a precipitate. The filtered liquid, when cooled and evaporated, yields tartaric acid in crystals. • Tartaric acid is used in large quantity by calico-printers and dyers for the removal of certain mordants, and is much employed in medicine in the preparation of effervescing draughts and for other purposes.
Tartaric acid being bibasic, can form both acid and normal (or neutral) salts, accord ing to the two general MO,HO,T, and QMO,T, when M signifies any metal, and T is used as a symbol for anhydrous tartaric acid, The normal salts may con tain (1) two similar or (2) different protoxides, or (3) a protoxide and scsquioxide, or (4) a protoxide and a teroxide; as, for example—(1) Tartrate of potash, ; (2) Tartrate of potash and soda, or salt, KO,NaTT; (3) Tartrate of potash and Oa; (4) Tartrate of potash and antimony, or tartar emetic, KO, Sb09f+ Aq. The
tartrates are for the most part formed by partially or entirely saturating the free acid with an oxide or carbonate, or in the case of neutral tartrates containing two oxides, by saturating a solution of the bitartrate of one oxide with the other oxide. The most important tartrates are the following : Tartrate of potash, 2KO,T, a soluble salt, which crystallizes with difficulty, and is formed in preparing tartaric acid from bitartrate of potash, This salt is pre-' pared from argol by extraction with boiling water, which dissolves about one-sixth of its weight. As it is much more insoluble in cold water, of which it requires 240 parts, it crystallizes readily as the hot solution cools. The snowy white rhombic prisms which are thus deposited constitute cream of tartar. When heated to redness in a covered cru cible, a charred mass, consisting of carbonate of potash and charcoal in a fine powder, remains, and is used in the laboratory for reducing operations under the title of black flux; and if cream of tartar is defiagrated with twice its weight of niter, white flux, also a reducing agent, consisting solely of carbonate of potash, is obtained. Tartrate of potash and soda, has been already described in the article ROCHELLE SALT. Tartrate of potash and iron, or ferrum tartaratuin, Aq, and tartrate of ammonia and iron, or of iron, 4Aq, although the latter is not included in the pharmacopoeia, are excellent medicinal preparations of iron. For the method of preparing them, the reader is referred to Neligan's Medicines, 6th ed. p. 658. 'etc. They occur in the form of brilliant, semi-transparent, reddish-brown scales, and are soluble in about their own weight of water at 60°. Tartrate of potash and boron, known also as soluble tartar (although the term has also been applied to tartrate of potash), or soluble cream of tartar, , has been employed medicinally, but is not now used. Tartrate of antimony and potash, known also as tartarized antimony and tartar emetic, liO,SbOs`lTio 2Aq, is one of the most valuable articles in the whole Materia Medial. This salt, obtained by a process which is given in the pharmacopoeia, occurs in the form of square prisms, which are soluble in about 15 parts of cold water and in 2 parts of boiling water. This salt is somewhat efflorescent, and when dried at 212° loses all its water of crystallization; its solution slightly reddens litmus, throws down an orange-colored sulphide of antimony, if a current of sulphureted hydrogen is passed through it, and has a very peculiar nauseous, metallic taste.