MODIFIED by 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 fucceilion, 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, Handing on a 

 plate of iron placed over the pit, which had been ufed, 

 during the firft flage of the experiment, to contain the water- 

 veiTel. It was found to be of fervice, efpecially where lead 

 was ufed, to give much more heat to the muzzle than limply 

 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 Hop the paflage. 



According to this method, many experiments were made 

 in gun-barrels, by which fome very material Heps were gained 

 in the invefligation. 



On the 24th February, I made an experiment with fpar 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 hilling 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 heart. The 

 temperature had rifen to 32 °. 



In this experiment, we have the firft clear example, in iron 

 barrels, of what I call Internal Calcination j 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 adion of ftrong heat, the barrel had been completely cooled; 

 the air therefore introduced by means of the air-tube, mud 



have 



