112 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 preflure being thereby eftablifhed. But from 
this very circumftance, 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 impoflible, 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 (74, 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 action 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 (7), 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 : 
