_ MODIFIED ly COMPRESSION. 103 
cing the barrel with its muzzle downwards, fo as to keep the 
breech above the furnace and cold, while its muzzle was 
expofed to ftrong heat in the muffle. In this manner, the 
metal was difcharged from the muzzle, and the pofition of 
the barrel being lowered by degrees, the whole metal was 
removed in fucceflion, till at laft the cradle and its contents 
became entirely loofe. As the metal was delivered, it was 
received in a crucible, filled with water, ftanding on a 
plate of iron placed over the pit, which had been ufed, 
during the firft ftage of the experiment, to contain the water- 
veffel. It was found to be of fervice, efpecially where lead 
was ufed, to give much more heat to the muzzle than fimply 
what was required to liquefy the metal it contained ; for when 
this was not done, the muzzle growing cold as the breech 
was heating, fome of the metal delivered from the breech was 
congealed at the muzzle, fo as to ftop the paflage. 
AccorDING to this method, many experiments were made 
in gun-barrels, by which fome very material fteps were gained. 
in the inveftigation, 
Ow the 24th February, I made an experiment with {par and 
chalk; the fpar being placed neareft to the breech of the bar- 
rel, and expofed to the greateft heat, fome’ baked clay inter- 
vening between the carbonates. On opening the barrel, a 
long-continued hifling noife was heard. The fpar was in a 
ftate of entire calcination; the chalk, though crumbling at 
the outfide, was uncommonly hard and firm in the vee The. 
‘temperature had rifen to 32°. 
In this experiment, we have the firft clear example, in iron 
barrels, of what I call Internal Calcination ; that is to fay, where 
the carbonic acid feparated from: the earthy ‘bafis, has been. 
accumulated in cavities within the barrel. For, fubfequently to 
the action of ftrong heat, the barrel had been'completely cooled; 
the air therefore introduced by means of the air-tube, muft 
have 
. 
