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fulphat of barytes, inftead of 135.25. Thequantity of lujpMiric acid indicated by a givenquantity of fulphat of baryte is differently efti-niated as will be r.ientioned under that head,but the difference between 1-8 and 135.25 grs.in an experiment performed by two able che-mifts, as appears, preen; iy in the fame way,is not very accountable, particularly with tofixed a fubitance as lulphat of barytes, whichmay be deficcated thoroughly with fo little rifkof lofs.

Acid Sulphat of Potaflo.

If common fulphat of potafh is put into aglal's, or better, a platina veffel, and fulphuricacid poured upon it, and heat applied, the mat'sfirft melts into an uniform denfe limpid fluid,vvhicn when it has arrived at the heat at whichfulphuric acid boils, fends forth an abundanceof wdiite vapour, udiich is the excels of acidthat evaporates. This continues till the quantityof acid left in the veffel is fomewhat more thana third of the weight of the fulphat; but whenit approaches this point, the vapour graduallydiminifhes and nearly ceafes, provided the heatdoes not exceed that of low rednefs, the falinemafs in the veffel remaining all the time per-fectly fluid and limpid. It then has the ap-pearance of a very denfe tranfparent oil, and ifremoved from the fire, it fpeedily folidifies uni-formly and compleatiy, and becomes a hard,tough opake-white or greenifh-white mafs of aftriated texture, which is the fuper-fulphatof potafj. If the veffel is returned to the fire,the fait again melts quietly, and becomes tranf-parent. If the heat is raifed to full rednefs,the evaporation of the acid again begins, andby continuing the heat long enough, and withfufficient intenfity, all the excefs of acid maybe driven off, and the neutral fulphat alone willremain; but the difficulty of evaporation in-creafes as the excefs of acid leffens, fo that itwould require many hours of pretty ftrongheat to drive off all the excefs. The fufibilityof the mafs alfo decreafes as the acid evapokrates.

The fuper fulphat thus obtained (the heatnot having exceeded a low rednefs ) has aftrongly acid tafte mixed with fomewhat of bit-ternefs. It is much more foluble in water thanthe fulphat, requiring for folution no morethan twice its weight of water when cold, andlefs than its own weight when boiling. It isvery {lightly deliquefeent. If moiftened witha very little water and melted, on cooling itforms a fofter mafs than before, compofed oflong ftriw, fomewhat flexible, and often of a

filky Iuftre. The faturated folution of this faitin boiling^water cryftallizes on cooling.

Super-fulphat of potaffi is decompofed bythofe fubftances that decompoie the fulphat,and it is alfo reduced to the ftate of commonfulphat by any alkali or earth, which unites-with the excels of acid. The proportions ofits conifituent parts are only uniiorm when itis cryftallized, and it is then compofed.of abouttwo parts of fulphat of potafh, and one of ful-phuric acid.

The neutral fulphat is highly ufeful in themanufacture of Alum , and a little in medicine.The fuper-fulphat is not employed, as it is notproduced in any manufacture, and neither ofthefe falts are of fufficient value to be worth-preparing by the direct combination of theiringredients.

SuLPHAT OF SODA, or Glauber’s Salt.

This fait was firft difeovered by Glauber, in1658, in the refidue of the diltiliation of com~mon fait and fulphuric acid for procuring mu-riatic acid. This fait and Epfom fait, or fulphatof magnefia, were often confounded togetherfor fome time after the firft difeovery of each,till the real nature of the latter was afeertainedby Dr. Black.

Sulphat of foda is found native in a varietyof places and both folid and diffolved in naturalwaters, but on the whole the quantity is butfmall. The native Glauber's fait is found inHungary , in the neighbourhood of fait lakes,and is deferibed under this article. This faitis alfo contained in greater or lefs quantity inalmoft every natural water that has any falinetafte or quality, fuch as the Seltzer, Chelten-ham, &c. and particularly in many of the hotfaline fprings, combined with carbonat of foda,of which the celebrated thermal waters ofCarlfbad are ftriking inftances, and are efti-mated by fair calculation to pour out annuallyupwards of a million of pounds of this faitalong with other ingredients. Many brinefprings aifo contain this fait, which remains inthe mother water after the extraction of thecommon fait, and may then be obtained byevaporation and cryftallization on cooling.

Glauber’s fait is alfo procured in many pro-ceffes of chemical manufacture, either as a re-fidue, or an intermediate product in the prepa-ration of foda. A good deal of it is obtainedin manufacture as a refidue in the diftillationof muriatic acid from fulphuric acid and com-mon fait, or of oxymuriatic acid from fulphuricacid, common fait, and manganefe; or in the