400 ACTION CF HEAT MODrFIEB 



were placed in a taken place between the lube and the carbonate. The balance 

 ai?the wholT ^^'^^^'^ ^ ^^^^* turned in a conftant and fteady manner, with 

 put into the iron One hundredth of a grain. Wlien pounded chalk was rammed 

 barrel, &c. [^^q tj^jj, ^^^]^f.^ j generally left part of it free, and in that 

 fpace laid a fmall piecf^ of lump-chalk (?), drefled to a cy- 

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

 letter on each end, the more effedually to obferve the effedts 

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

 pf chalk being always eftimated along with that of the powder 

 contained in the tube. Infome experiments, I placed a cover 

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

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

 ebullition : but as that did not often occur, I feldom took the 

 trouble of this laft precaution. 

 Continuation of It was now of confequence to protedl the tube, thus pre- 

 the method of pared, from being touched during the experiment, by any fub- 

 /lance, above all, by the carbonate of lime, which might adhere 

 to it, and thus confound the appreciation by weight. This was 

 provided for as follows: The fmall tube {Fig. 23, i k) with its 

 pounded carbonate (/c), and its cylinder of lump-chalk (i), 

 was dropt into a large tube of porcelain (pk, fig. 24). Upon 

 this a fragment of porcelain (/), of fuch a fize as not to fall in 

 between the tubes, was laid. Then a cylinder of chalk (ju) was 

 drefTed, fo as nearly to fit and fill up the infide of the large tube, 

 ©ne end of itbeingrudely cut into the form of a cone. This mafs 

 being then introduced, with its cylindrical end downwards, 

 was made to prefs upon the fragment of porcelain (/ ). I then 

 dropped into the fpace («), between the conical part of this 

 mafs and the tube, a fet of fragments of chalk, of a fize be- 

 yond what could poffibly fall between the cylindrical part and 

 the tube, and preflTed them down with a blunt tool, by which 

 the chalk being at the fame time crufiied and rammed into 

 the angle, was forced into a mafs of fonie folidity, which ef- 

 fedtually prevented any thing from patiing between the large 

 mafs of chalk and the tube. In pradice, I have found this 

 method always to anfwer, when done with care. I covered 

 the chalk, thus rammed, with a llratum of pounded flint (o), 

 and that again with pounded chalk {/>) firmly rammed. In 

 this manner, I filled the whole of the large tube with alternate 

 layers of fiiex and chalk; the muzzle being always occupied 

 with chalk, which was eafily prefled into a mafs of tolerable 



firmnefs 



