392 On SODALITE, a 



new 



matter, not weighing quite o.i grain. This matter was info- 

 luble in acids; but became white. With potafh it fufed into a 

 colourlefs glafs. Hence I confider it as iilica. This experi- 

 ment fhews that no chromium was prefent. I was at a lofs to 

 account for the precipitate thrown down by the nitrate of mer- 

 cury. But Mr Allan having mown me a letter from Eke- 

 berg, in which he mentions, that he had detected muriatic 

 acid in fodalite, it was eafy to fee that the whole precipitate 

 was calomel. The white powder weighed 26 grains, indicating, 

 according to the analyfis of Chenevix, about 3 grains of mu- 

 riatic acid. 



3. The folution, thus freed from muriatic acid, being con- 

 centrated by evaporation, gelatinifed. It was evaporated near- 

 ly to drynefs ; the dry mafs, digefted in hot water acidulated 

 with nitric acid, and poured upon the filter. The powder re- 

 tained upon the filter was warned, dried, and heated to rednefs. 

 It weighed 37.2 grains, and was iilica. 



4. The liquor which had pafled through the filter, was fu- 

 perfaturated with carbonate of potafh, and the copious white 

 precipitate which fell, collected by the filter, and boiled while 

 yet moift in potafh-ley. The bulk diminifhed greatly, and the 

 undiflblved portion aflumed a black colour, owing to fome 

 oxide of mercury with which it was contaminated. 



5. The potafh-ley being pafied through the filter, to free it 

 from the undiflblved matter, was mixed with a fufHcient quan- 

 tity of fal-ammoniac. A copious white precipitate fell, which 

 being collected, waflied, dried, and heated to rednefs, weighed 

 27.7 grains. This powder being digefted in fulphuric acid, 

 diflolved, except 0.22 grain of Iilica. Sulphate of potafh being 

 added, and the folution fet afide, it yielded alum cryftals to the 

 very laft drop. Hence the 27.48 grains of diflolved powder 

 were" alumina. 



6. The 



