MODIFIED ly 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 ruth 
- ftripped 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, {mall pieces were 
vifible of perfect tranfparency. Thefe muft have been produ- 
ced in the fire ; for the fpar had been ground with water, and 
paffed through fieves, the fame with the fineft of thofe ufed at 
Etruria, as: defcribed by Mr Wxpewoop, in his paper on the 
conftruction of his Pyrometer. 
Wira 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- 
ftance 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 fuppote, that here the lofs had been 
fmall, if any. 
On the 6th of April, I made another nce with the 
{quare barrel, whofe thicknefs ‘was now much reduced by fuc- 
ceflive {cales, produced by oxidation, and in which a {mall 
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 ; 
