ii2 EFFECTS of HEAT 



number of bars of that iron, which fully anfwered my expec- 

 tations. 



By the experiments laft mentioned, a very important point 

 was gained in this inveftigation ; the complete fufibility of the 

 carbonate under preiliire being thereby eftablifhed. But from 

 this very circumflance, a neceflity arofe of adding fome new 

 devices to thofe already defcribed : for the carbonate, in fu- 

 fion, fpreading itfelf on the infide of the tube containing it, 

 and the two uniting firmly together, fo as to be quite infe- 

 parable, it was impoffible, after the experiment, to afcertain 

 the weight of the carbonate by any method previoufly ufed. 

 I therefore determined in future to adopt the following ar- 

 rangement. 



A small tube of porcelain (2 k, fig. 23.) was weighed by 

 means of a counterpoife of fand, or granulated tin ; then the car- 

 bonate was firmly rammed into the tube, and the whole weighed 

 again : thus the weight of the carbonate, previous to the ex- 

 periment, was afcertained. After the experiment, the tube, 

 with its contents, was again weighed ; and the variation of 

 weight obtained, independently of any mutual a&ion that had 

 taken place between the tube and the carbonate. The balance 

 which I ufed, turned, in a conftant and fteady manner, with 

 one hundredth of a grain. When pounded chalk was rammed 

 into this tube, I generally left part of it free, and in that 

 fpace laid a fmall piece of lump-chalk fij, drefled to a cy- 

 linder, with the ends cut flat and fmooth, and I ufually cut a 

 letter on each end, the more effectually to obferve the effects 

 produced by heat upon the chalk ; the weight of this piece 

 of chalk being always eftimated along with that of the powder 

 contained in the tube. In fome experiments, I placed a cover 

 of porcelain on the muzzle of the little tube, (this cover being 

 weighed along with it), in order to provide againft the cafe of 



ebullition : 



