part ii. Materia Med re a. — Super-tartras Potasscr. 529

red or white tartar, as it is more or less coloured, owing to tlienature of the wine from which it is deposited. Besides colouringmatter, it contains extractive, potass combined with tartaricacid in excess, and tartrate of lime. It is only used for pre-paring the next article. 1

SUPER-'TAR'TRAS POTAS'SiE, Edin. Potable Su-pertartras, Lond. Tartarum Ceystalli, Dub. Super-tartrate of potass, Crystals of tartar.

Syn. Tartrate acidule de Potassc {!•'.), Gercinigter Weinstein ((;.), Cranorcrii tartaro; ossitartrato ossidulo di Potassa (I.).

This is the above-mentioned saline crust purified. It is firstreduced to powder, then dissolved in boiling water in tubs, andthe clear fluid poured oif from the sediment. The clear solu-tion is then allowed to remain at rest, when it deposits browncrystals of tartrate of potass, which are boiled in copper ves-sels with the mother liquor ; and clarified by throwing in whitesof eggs, and some finely sifted wood ashes. An effervescenceimmediately takes place, and a red scum is thrown up, whichis carefully skimmed off with a perforated skimmer; and thethrowing in of the wood ashes, with the subsequent skimming,are repeated for fourteen or fifteen times ; after which the liquoris taken from the fire, and allowed to remain at rest for threedays. On the fourth day a dirty white saline crust is removedfrom the surface, and two thirds of the liquor ladled out. Thecrystals which now form are white and clean, and require nofurther prepaiation than drying on a wicker frame. In someplaces, instead of wood ashes, a portion of pure clay is diffusedthrough the boiling solution. The exposure of the crystals oncloths to the air and light whitens them very considerably. 2

Qualities. — Super-tartrate of potass is inodorous, and whenallowed to dissolve in the mouth, which it does very slowly, andfeeling gritty under the teeth, has a harsh acid taste. Its crys-tals are small and irregular, generally run together into littlemasses, which are of a white colour, semi-transparent, brittle,and easily reduced to powder. Its specific gravity is 1'953.It requires for its solution 30 parts of boiling water, and 120 ofcold water. The solution decomposes spontaneously by keep-ing ; a mucous matter is deposited, and there remains a solutionof carbonate of potass coloured with a little oil. 3 Accordingto the analysis of Thenard, 100 parts of pure supertartrate ofpotass contain 57 of tartaric acid, 33 potass, and 7 of water 4;

1 A large quantity of tartar comes from Sicily: the white is procured chieflyfrom Palermo, Marsala, and Cnlania; the red from Mascali, Messina, Melaz~o,and Vittoria.

- Schaub says, it may be purified by simply boiling it with powdered recentcharcoal, and very white crystals obtained. Ann. de Chimie, xlix. 64.

1 This decomposition was first described by Bertholler, in 1782. Mem. Par.Thompson's Chemistry, 4th edit. vol. iii. 93.

* Aixnaks de Chimie, vol. XXXftii. p- 39-

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