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eminent chemift alfo difcovered, the affinity ofthis acid to that portion of potafh neceflary toform the acidulum being greater than that ofthe nitric acid for potafh. In the fame mannerthe oxalic acid will partially decompofe manyother of the falts with potafh, fuch as themuriat, acetite, See. In thefe cafes the fuper-oxalat of potafh being much lefs foluble thanthe other fait, precipitates in fmall needledcryftals.
This fait however readily dilfolves in hotwater, requiring no more than about its ownweight, but the greater part feparates by cool-ing-. The folution is not decompofed l'ponta-neoufly by long keeping, b in which refpedt itdiffers from the tartareous acidulum. Thefulphuric, nitric, and muriatic acids decompofethis fait only at a boiling heat.
"When the oxalic acid is fuper-faturated withpotafh and flowly evaporated, elegant prifmaticcryftals are formed, in which neither the acidnor alkali predominate. This fait may be madeby adding to the acidulous oxalat fomewhatmore potafh than is neceflary for faturation.This fait is much more foluble in water thanthe laft mentioned. Alcohol diffolves it withdifficulty. It is partially decompofed by thefulphuric, nitric, and muriatic acids withoutheat, that is to fay, a portion of the potafh isabftradled, and the remainder paffes to theftate of the fuper-oxalat. But with the afiift-ance of heat it is entirely decompofed.
Oxalat of Soda.
The oxalic acid united to a fmaller quantityof foda than will faturate it, forms a fpecies ofacidulum which has been but little examined.Saturated with foda, a fait is produced difficultof folution, and which feparates in fmall crys-talline grains.
Oxalat of Ammonia.
Ammonia alfo unites with oxalic acid in twoproportions. When as an acidulum, it formsfait in fmall cryftals, and of difficult folubility,but when perfedtly faturated the fait cryftallizesin large four-fided prifms. Thefe lofe about -j°f their weight by a gentle heat, and are veryfoluble in water but not in alcohol. This com-bination of oxalic acid is the moft ufeful fordetecting the prefence of lime, as will bePreiently mentioned.
Betides thefe Ample falts with tlacid and alkahes, feveral triple falts
VOL. II.
* Fourcroy fyftcmc.
them cryftallizable) may be formed by faturatingthe fuper-oxalat of one alkali by a different one;thus if the fuper-oxalat of potafh is faturatedwith foda, a triple neutral fait is obtained, con-fifting of oxalic acid, potafh and foda. In likemanner ammonia readily combines with thefuper-oxalat of potafh and foda. In this as inother refpeCls, the habitudes of this acid ftrong-ly refemble thofe of the tartareous acid.
This acid forms with barytes a fait whichwhen the acid is in excefs, appears in the form ofpellucid angular cryftals. Boiling water diffolvesa fmall portion, but converts the remainderinto a white powder, rendered infoluble byloiing its excefs of acid, which the water ab-ftrafts. On cooling, moft of that portionwhich had been difl'olved feparates in fmallcryftals. This fait is decompofed by fulphu-ric acid.
Oxalat of Strontian.
By pouring oxalat of potafh into muriat offtrontian, an infoluble white powder is ob-tained, compofed according to Vauquelin 1 of5<ji ftrontian, and 40 a acid.
Oxalat of Lime.
The oxalic acid attrafts lime with greater forcethan any other acid, and therefore is capableof decompofing compleatly all the known cal-careous falts. Hence the great utility of thisacid in detecting lime in every foluble combina-tion. Oxalat of lime is infoluble in water, fothat when this acid is added to a folution con-taining lime, a white precipitate of oxalat oflime falls down, from which, when collected,wafhed, and dried in a moderate heat, theactual quantity of lime may be readily inferred.By very accurate experiments Dr. Marcet 1found that 100 parts of oxalat of lime dried ati6o # were produced from 117 of felenite, andthe quantity of lime in the latter, alfo dried at160°, may be reckoned to be about 41. Theoxalat of lime however, though infoluble inwater, diffolves in many of the acids withoutbeing decompofed, and therefore when anyconfiderable excefs of acid is prefent, lefs oxa-lat of lime will be obtained than is really-formed, and which will lead to error. On thisaccount it is neceflary to faturate any excefs ofacid before the oxalic teft is ufed, and asan additional precaution, the oxalic acid fliouldbe faturated with an alkali, which will not inthe leaft diminilh its power of precipitatinglime. The oxalat of ammonia is generallypreferred.
* Aaalyfis of Brighton Water.
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