TAR

TAR

( 4G6 )

water, and in much lefs when boiling. Thecryftals are .permanent in the air.

When heated per fe in a retort with a receiverthis acid melts, boils up, and exhales a fourpungent vapour, which condenfes in the re-ceiver into a red acid empyreumatic liquor,equal to about a quarter of the, weight of thetartareous acid.

This liquor has a pungent acid and empy-reumatic tafte, ftrongly reddens litmus, andeffervefees with the alkaline carbonats. It iscalled the Pyrotartareous acid, which has notbeen much examined. The other productsfrom the diftillation of tartareous acid, are alarge quantity of carburetted hydrogen and car-bonic acid gas, and a foft fpongy coal is left inthe retort, which, heated in the open air, burnswith fcarcely any refidue.

The tartareous acid, befides being found na-tive in fome vegetable j uices, and in the depofitfrom wine during and after fermentation, isalfo produced by the aCtion of nitric acid onalcohol. A further digeftion of tartareous withnitric acid converts the former into oxalic acid,and a ftill further digehion changes the wholeof the vegetable acid into vinegar. Thefe cu-rious experiments which were at firft noticedby Scheele , have been more fully examined byHermbflaedt and other chemifts, and are de-tailed under the article Acetous acid (p. 4.)

The compounds of the tartareous acid withthe alkaline and earthy bafes, will be mentionedin the following article.

This acid is compofed, according to Four-croy f and Vauquelin, of 70.5 of oxygen, 19of carbon, and to.5 of hydrogen, and differsfrom the oxalic acid in containing more carbonand lefs oxygen. The order of affinity of thisacid for the feveral bafes is (according to The-nard) lime, barytes, ftrontian, potafh, foda, am-monia, magnefia, and alumine.

TARTRITES.

The diftinft combinations of the tartareousacid with the feveral bafes, are particularly nu-merous, as with fome it forms two falts, dif-fering in the proportions of acid and bafe, andas it is peculiarly liable to form triple falts inwhich two bafes are united with their refpeCIiveportion of acid into one uniform compound.

All the foluble alkaline and earthy tartritesare decompofed by the falts of lead, and theacid of all is deftroyed by calcination, leavingthe bafe in the (fate of Carbonat .

Super-taRtrite of Potash . Cream ofTartar. Tartareous Acidulum.

The origin and manufacture of this fait hasbeen mentioned under the article Tartar . It iscompofed of potafh and tartareous acid in ex-cefs, and hence has an acid tafte and reddensblue vegetable colours. It is foluble with greatdifficulty, requiring about 30 parts of boilingwater, and full 120 parts of cold water, andhence a hot faturated folution begins to depofitcryflals almoft immediately after it begins tocool.

The affinity between the tartareous acid andthat proportion of potafh which conlfitutes thefuper-tartrite, is fo great that the acid of tartarwill decompofe, partially or totally, all the neu-tral falts of potafh, even the fulphat. But onthe other hand, the affinity between the fuper-tartrite and that additional quantity of potafhwhich is neceftary for complete faturation ofthis acid, (or which conlfitutes the tartrite ofpotafh,) is much weaker than that of mod otheracids for potafh, and hence arifes a great num-ber of decompofitions when tartareous acid,potafh, and any other acid are mixed in dif-ferent ways. Thus if a folution of tartareousacid is poured into a folution of fulphat of pot-afh, rather concentrated, in a few feconds themixture becomes turbid, and foon a quantityof a white granular powder falls to the bottom,which is cream of tartar, and may be diftin-guifhed as fuch (when rinced with cold water)by feeling hard and granular in the mouth,with a Rightly acidulous tafte, being muchmore foluble in boiling than in cold water, andwhen heated by the blow-pipe, blackening,fwelling up, and finally being reduced to a glo-bule of pure carbonat of potafh. The fuper-natant liquor confifts of the remainder of thepotafh of the fait, united with the whole of thelulphuric acid, and no further addition of tar-tareous acid will complete the decomp fition.Two acidulous falts therefore are produced inthis cafe, the fuper-tartrite and the fuper-ful-phat of potafh, of which the former is moftlyprecipitated, and the latter remains in folution.On the other hand, a production of cream oftartar takes place when dilute fulphuric or anyother acid is added to tartrite of potafh. Theacid added takes away from the tartrite onlythat quantity of potafh which makes the dif-ference between the tartrite and the fuper-tar-trite, and the latter is precipitated, and is notfurther aCted on by any excefs of the fulphuricacid. This property of the tartareous acid, of de-compofing the neutral falts with the bafis of pot-afh, is very ufeful in analyfis, as it diftinguilhes

1 Syfteme, kc.