3-T 8 HulpkaU of Pei-^jli.—'Alum. 



If the folution of ilie fulpliite of pot-a(h, and aMb thnt of Ae oxygenated muriatic aciJ, 

 'be both conccntrateil, crjR.ils of tlie fulphate of pot-alh arc formed immediately on the 

 niiNture. 

 ■ 'Cliarcoal converts the fulphite of pot-atli into tlic fulphuret of pot-alh. 

 Salts with baftis of pot-afli do not dccoi>ipofc .'lils fait. 



Thofe withbafcs of foda, except the borate and the carbonate,are dcconipofed by the ful- 

 phite of pot-afli. 



All the other f.iUs, of which the acids are ftronger tlian the fulphureous acid, are etjually 

 decompofed by the fulphite of pot-afli. 



The fupcr-oxygcnated nitrate and muriate of pot-afli, when heated with the dry fulphite 

 of pot-afh, take fire, and are changed into fulphate. 



Several metallic oxides a£l upon this fait. Some are entirely reduced to the metallic ftate; 

 •fuch as the oxides of gold, fiiver and mercury, others .ire brought nearer that (late ; fuch as 

 thofe of lead, iron and manganefe, at the maximum of oxygenation. There are others 

 -which change the nature of the fulphite of pot-afh in an oppolite direction to thofe which 

 -take place in the foregoing cafes; that is to fay, which convert it into fulphate by depriving 

 "it of a certain quantity of fulphur, with which they form fulphurated oxides, fucli as the 

 «xides of arfenic, and of iron flightly oxlded ; but in order that riiis operation may fucceed, 

 it is neceflary to boil tliefe fubftances a long time in water, and afterwards to add to the 

 folution an acid, which occafions a coloured precipitate, at the fame time that the fmdl of 

 fulphurated hydrogene gas is emitted. 



All the metallic folutions except the caibonates are dccompofed by the fulpliite of pot- 

 afh ; and as moll of the metallic fulphites are infoluble, different coloured precipitates are 

 •formed, according to the nature of the metal and its (late of oxidation. 

 \To be continued^ 



VL 



A Memoir on the Nature af the Alum of Covimirce, on the Exijlence of Pot-nJIi in this Suit, oni 

 en various fimple or triple Combination! of A /limine with the Sulphuric Acid, Read before the 

 National Infitute of France. By Citizen Vav^'ELIN ». 



In my memoir on the leucite or white grenate, I have announced that many natural eartlis 

 and .ftones contain pot-alh in a (late of combination ; and I founded my opinion at that 

 time on the impofiibility of obtaining folid cryftallized alum in oflahedrons by the imme- 

 diate combination of fulphuric acid and pure aluniine, whatever precautions were taken to 

 clear it of the excefs of acid, without the addition of alkali. 



The nccelTity of this addition has long been known in the alum works, more particu- 

 larly in the treatment of the mother waters ; and \\ was thought that the ufe of pot-afli in 

 this circumftance was merely to faturatc the excefs of acid, which was fuppofed to prevent 

 the cryftallization of the alum. Ncverthclefs, the remark made by Bergman, that foda and 



-' This iroportau Memoir is iurcrtcd in the Annates dc Chimic, XXII. 158, whence I have tranflatcd it 



lime. 



