TAR

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refidual carbonat of potafh in nitric acid, andconverting it to nitrat of potafh, which laft heeftimatcs to contain 53 per cent, of potafh. Bythe iff proccfs therefore the water of cryftalli-zation is afcertained; by the 2d, the tartareousacid; and by the 3d, the potafh.

Tartrite of Potajh and Soda, Salt of Seignette.Rochelle Salt.

This is a triple cryftallizable fait firft difco-vered by a peri'on of the name of Seignette, atLa Rochelle , and introduced by him into medi-cine. It is prepared in the following way : boilfome water, throw into it about a fifth of itsweight of cream of tartar, and then add bydegrees a quantity of carbonat of foda, as longas any eflerveicence is excited. In proportionas the excefs of acid in the cream of tartarbecomes faturated with the foda, the fait gra-dually difappears, and is finally held in perfeCtfolution in the liquid. Evaporate the whole tothe confidence of fyrup, and by cooling it willyield the triple tartrite or Rochelle fait, inlarge tranfparent beautiful cryftals, generallyof the form of eight-fided prifms. Thefe areoften found divided longitudinally through theaxis.

This fait is perfectly neutral, diffolves inabout five parts of water, has a bitterifh falinetafle, and fomewhat efflorefces by expofure tothe air. It is totally decompofed by barytesand lime, and the fupernatant liquor then con-tains a mixture of potafh and foda. It is com-pofed, according to Vauquelin, of about 54 percent, of tartrite of potafh and 46 of tartrite offoda.

It is decompofed, like the fimple tartrite ofpotafh, by the ftronger acids, and cream oftartar is produced.

Tartrite of Potajh and ^Ammonia .

This triple fait is prepared in the fame gene-ral manner as the preceding, by faturating thecream of tartar with carbonat of ammonia; andby evaporation and cooling the triple fait isfeparated. When expofed to the air it efflo-refces, and after a time lofes its ammonia, andreturns to the flate of fimple cream of tartar.

Tartrite of Potafo and Lime, Barytes , ipc.

Though lime will compleatly decompofe anyalkaline tartrite, as is fliewn in the preparationof the tartareous acid, there appears to exift acertain affinity between tartrite of potafh andlime, which tends to the formation of a triplefait. Thus though fimple tartrite of lime isinfoluble in cold water, no precipitate is pro-duced by the affufion of a fmall quantity of

lime-water into a cold folution of tartrite ofpotafh, which muft therefore be owing to thetartrite'*of lime, then formed, being renderedioluble by the remaining tartrite or rather fub-tartrite of potafh. j Even when cream of tartaris as completely as poffible decompofed by limein fubftance, in the procefs of obtaining theacid the cauftic alkaline liquor, fupernatantover the precipitated tartrite of lime, fliil holdsa fmall quantity of the latter in folution, as hasbeen remarked by Vauquelin, which may beconfidered as a triple fait of tartareous acid,lime, and potafh, the latter being in very largeexcefs.

The fame applies to barytes and- ftrontian,the folutions of which do not immediately givea precipitate with tartrite of potafh; and evenif tartrite of barytes or of ftrontian recentlyformed and ftill wet be put into a folutionof tartrite of potafh, it is foon diffolved ;though the mere quantity of liquid prefentwould be entirely unable to effe£t a folution.There is therefore fuch a ftrong affinity be-tween tartrite of potafh and thefe earthy tar-trites as may perhaps entitle us to confiderthefe compound folutions as triple falts, thoughthey have not been obtained in a cryflallizedform like the triple tartrite of potafh and foda.

Alumine unites with ftill greater eafe withtartrite of potafh : for when this earth, recentlyprecipitated from alum by a cauftic or carbon-ated alkali, and ftill wet, is transferred to a fo-lution of tartrite of potafh, it readily diflolvestherein, and forms an uncryftallizable com-pound which is ndt rendered turbid by anyaddition of potafh or its carbonat. This laftcircumftance might lead to the fuppofition thatalumine has a ftronger affinity for tartareousacid than potafh has, but it is contradicted bythe fatf, that in this cafe there is not the lealtexcefs of potafh in the liquid; fo that the alu-mine does not difplace the alkali from the tar-tareous acid, but unites with them both into atriple compound. Tl)e Rochelle fait has thefame habitude with alumine as the fimple tar-trite of potafh, which therefore forms a qua-druple compound of tartareous acid, potafh,foda, and alumine.

Tartrite of Soda. When the tartareousacid is faturated with foda, a fait is produced,which by due evaporation may be obtained infmall needled cryftals, and is the tartrite of foda.This fait (with which the Rochelle fait wasformerly confounded) is not very foluble in

j Thenard.