122 ; EFFECTS of HEAT 
fire was allowed to burn out till the barrel was black. The me- 
tal was difcharged irregularly. Towards the end, the inflam- 
mable air produced, burnt at the muzzle, with a lambent flame, 
during fome time, arifing doubtlefs from hydrogen gas, more 
or lefs pure, produced by the decompofition of the water. The 
upper pyrometer indicated 36°, and the lower one 19°. The 
chalk which lay in the outer part of the large tube was in a 
ftate of marble. The inner tube was united to the outer 
one, by a ftar of fufed matter, black at the edges, and f{pread- 
ing all round, furrounding one of the fragments of porcelain 
which had fallen by accident in between the tubes. The in- 
ner tube, with the ftarry matter adhering to it, but without 
the coated fragment, feemed to have fuftained a lofs of 12-per 
cent., on the original carbonate introduced. But, the fub- 
ftance furrounding the fragment being inappreciable, it was 
impoflible to learn what lofs had been really fuftained. Exa- 
mining the little tube, I found its edges clean, no boiling over 
having taken place. The top of the fmall lump of chalk had 
funk much. When the little tube was broken, its contents gave 
proof of fufion in fome parts, and in others, of the neareft ap- 
proach to it. A ftrong action of ebullition had taken place all 
round, at the contact of the tube with the carbonate: in the 
heart, the fubftance had a tranfparent granular texture, with little 
or no cryftallization. The {mall piece of lump-chalk was united. 
and blended with the rammed powder, fo that they could fcarce- 
ly be diftinguifhed. In the lower part of the carbonate, where 
the heat muft have been weaker, the rod had acted more feebly 
on the tube, and was detached from it : here the fubftance was 
firm, and was highly marked in the fracture with cryftalline 
facettes. Wherever the carbonate touched the tube, the two 
fubftances exhibited, in their mixture, much greater proofs of 
fufion than could be found in the pure carbonate. At one 
place, a ftream of this compound had penetrated a rent in 
. the 
