TAR

TAR

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of tartar, and is employed in the fir ft lixiviationof the rough tartar.

Tartar is refined near Montpellier in thefollowing manner, according to the defcriptiongiven by M. Fizes, b which has been foundfio convenient and efficacious that little if anychange has been made in it for a century. 0

The apparatus required for this purpol'e is iff,si large copper boiler; 2d, a ftone cittern, largerthan the boiler; 3d, a number of glazed earthenpots (generally 27) which, together, hold fome-what more than the boiler ; 4th, fome ftrainersof coarfe cloth ftretched on wooden frames;5th, four fmaller copper boilers which, together,hold as much as the larger boiler, and are ufedin the refining part of the procefs; and 6th,a mill to grind the tartar.

The large copper is firtt filled with two-thirdsof mother liquor, remaining from the previousoperations, and one-third of fpring water, a quan-tity of rough tartar is then thrown in, and whenthe liquor is faturated and boiling it is (trainedinto the earthen pots. In about half an hour theliquor in tliefe pots though ftill very hot, beginsto depofit cryftals on the furface and fides ofthe pot, during which time more liquor andtartar are thrown into the large copper as atfirtt.

The liquor in the pots is then emptied intothe ftone cittern, leaving the cryftallized cruftof tartar behind ; and when the fecond boilingis faturated, the pots are again filled as before,and the large copper again charged with theclear liquor from the cittern, and frefh tartar.By thus five times alternately preparing a hotfaturated folution, and allowing it partially todepofit its tartar in the pots, the latter becomelined to a confiderable thicknefs with a cruft ofrcddifh-white tartar,much purer than at firtt,andwhich obvioufly confifts of an irregular cryftal-lizedfaline mafs,and when walhed with cold wa-ter is fit for the fecond, or proper refining procefs.For this purpofe the four imall boilers are filledwith water, in which a fmall quantity of clay isdiffufed, which renders it milky, reje&ing theftony and larger particles of earth. The half-purified tartar is then added in fuch proportionthat the water when boiling ffiall be fufficient todiffolve all the foluble part, and the ebullitionis continued for a quarter of an hour ; the fireis then withdrawn, and the liquor allowed toremain at reft till the next day. It is thenfound covered on the furface with a white hardfaline cruft, and a fimilar cruft, but more dif-tindfly cryftallized, has concreted on the fides

k Mem. de l’Acad for 1 ;

and bottom of the boiler. They are both very-pure tartar, the cruft on the iurface, whichis an amorphous mafs, is called Cream of tartar ,and the other, Cry/fa/s of tartar , but they areindifcriminately mixed.

The cruft is then broken down and falls tothe bottom, and the liquor, which is a clear palered, is poured off gently into the ftone ciftern,till it begins to run white owing to the clayat bottom, which latter portion paffes into afeparate veffel. The whole mafs of folid tartarleft in the boiler is then wafhed with coldwater, till all the foulnefs (which is merelyfuperficial) is got out, and the water comesaway quite clear, after which the purified tartaris taken out and dried on ftoves or in the fun,and is perfectly pure and white. The ordinaryrough tartar yields about three-fifths of itsweight of the white pure fait. All the residu-ary liquors are employed in fubfequent opera-tions in the way already mentioned.

The above two proceffes of purifying tartarare confiderably fimple. Tartar confifts of thepure fuper-tartrite of potaffi, or cream of tartar,united with a large quantity of extractive andcolouring matter. Of thefe, the pure fait isentirely foluble in water, and much more fo inhot than cold water, but it requires a very largeproportion of water for folution; for even at aboiling temperature one ounce of the faturatedfolution holds no more than 16 grs. or yV of itsweight of the fait, and on cooling only threeor four grains are retained in folution. Hencethe neceftity of ufing a very large bulk of fluid inthe proceffes of folution and cryftallization, andthe advantage of employing the mother liquorsor cold faturated folutions of former proceffes.In each of thefe methods the tartar is firftconfiderably purified by fimple folution, filtra-tion, and cryftallization, but the fubfequent partof the procefs differs materially. In the Vene-tian method the white of egg is doubdefs avery excellent, though fomewhat more expen-five, fubftance for clarification ; but the ufe ofthe wood-afh is not very obvious, and wouldl'eem to be fo far injurious as its alkali multneutralize a portion of the tartareous acid, anddiminifh the quantity of purified tartar by con-verting a portion of it to tartrite of potafli, orthat combination of this acid and potafli inwhich the acid and alkali are in mutual fatu-ration, and which being very foluble would re-main in folution. Whether, as has been ftatedby fome, the alkali of the afbes would renderthe whole mafs of purified tartar lefs acidulous

c Cliaptal.

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