MODIFIED by COMPRESSION. 113 



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

 the trouble of this laft precaution. 



It was now of confequence to protect the tube, thus prepa- 

 red, from being touched during the experiment, by any fub- 

 ftance, 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 (k), and its cylinder of lump-chalk ( /',), 

 was dropt into a large tube of porcelain (/> k, 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 (m) was 

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

 one end of it being rudely 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 

 beyond what could poilibly fall between the cylindrical part 

 and the tube, and preffed them down with a blunt tool, by 

 which the chalk being at the fame time crufhed and rammed 

 into the angle, was forced into a mafs of fome folidity, which 

 effectually prevented any thing from palling between the large 

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

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

 the chalk, thus rammed, with a ftratum of pounded flint (s), 

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

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

 layers of filex and chalk 3 the muzzle being always occu- 

 pied with chalk, which was eafily prefied into a mafs of to- 

 lerable firmnefs, and, fuffering no change in very low heats, 

 excluded the fufible metal in the firft ftages of the experiment. 



The large tube, thus filled, was placed in the cradle, fome- 

 tirnes with the muzzle upwards, and fometimes the reverfe. I 



Vol. VI. -P. I. P have 



