[ '65 ] 



the condad of feveral manufadures, particularly to that of 

 faltpetre, and hence noticed by Mr. Lavofier, 15 An. Chy. 254. On 

 this head however I hope the Academy will foon receive the fuUcft 

 information, as our worthy member, Mr. Higgins, has at my requeft 

 undertaken to examine its .reality and extent with refped to a 

 confiderable number of the moft known among thefe falts. 



Though Bergman and Wenzel fhould have conduded their 

 experiments nearly in the fame manner, as far as we can judge 

 from the mode prefcribed by Mr. Bergman in his notes on SchefFer, 

 publifhed in 1779, yet his refults differ confiderably in many 

 inftances from thofe of Wenzel, and appear to me far more 

 faulty, the caufe of which feems to me to be, that he has in moft 

 cafes departed from the method he had originally propofed to 

 follow, and fuppofed quantities of water of cryftalHzation to exift 

 in various fubftances without fufEcient reafon, or at Icaft without 

 affigning any fuch. Thus he tells us that pellucid cakareous fpars 

 lofe only 34 per cent, of fixed air by folution in acids, whereas the 

 daily experience of all chymifts fhews them to lofe from 43 to 44 

 per cent, but 1 1 of thefe he fuppofes to be water, becaufe by diftil- 

 lation he could not obtain more than 34 per cent, of fixed air, a 

 method now well known to be defedive, as from the porofity of 

 earthen retorts, the inefiicacy of lutes, and the infufficiency of the heat 

 applicable to thofe of glafs, the true quantity of fixed air can ne- 

 ver be thus obtained. Mr. Cavendifh could obtain from 31 1 grains 



X 2 of 



