MODIFIED hy COMPRESSION. 109 



the powder, on ramming it into the tube : it had, to the naked 

 eye, the roughnefs and femitranfparency of the pith of a rufh 

 (tripped of its outer fkin. By the lens, this fame furface was 

 feen to be glazed all over, though irregularly, fhewing here 

 and there fome air-holes. In fracture, it was femitranfparent, 

 more vitreous than cryftalline, though having a few facettes : 

 the mafs, was feemingly formed of a congeries of parts, in them- 

 felves quite tranfparent: and, at the thin edges, fmall pieces were 

 vifible of perfect tranfparency. Thefe mufi have been produ- 

 ced in the fire \ for the fpar had been ground with water, and 

 pafied through fieves, the fame with the fineft of thofe ufed at 

 Etruria, as deicribed by Mr Wedgwood, in his paper on the 

 conflruction of his Pyrometer. 



With the fame barrel I obtained many interefting refults, 

 giving as ftrong proofs of fufion as in any former experiments ; 

 with this remarkable difference, that, in thefe laft, the fub- 

 flance was compact, with little or no trace of frothing. In 

 the gun-barrels where fufion had taken place, there had al- 

 ways been a lofs of 4 or 5 per cent., connected, probably, with 

 the frothing. In thefe experiments, for a reafon foon to be 

 ftated, the circumftance of weight could not be obferved ; but 

 appearances led me to fuppofe, that here the lofs had been 

 fmall, if any. 



On the 6th of April, I made another experiment with the 

 fquare barrel, whofe thicknefs was now much reduced by fuc- 

 ceflive fcales, produced by oxidation, and in which a fmall 

 rent began to appear externally, which did not, however, pe- 

 netrate to the bore. The heat rofe high, a pyrometer on the 

 breech of the barrel giving 37 °. On removing the metals,, 

 the cradle was found to be fixed, and was broken in the at- 

 tempts made to withdraw it. The rent was much widened 

 externally : but it was evident, that the barrel had not been 

 laid open, for part of the carbonate was in a ftate of faline 



marble j 



