Effects of Heat rnddrfied hy Compression. 293 



of iron placed over the pit, which had been used, during the 

 first stage of the experiment, to contain the water vessel. 

 It was fonnd to be of service, especially where lead was used, 

 to give much more heat to the muzzle than simply what 

 was required to Fiquefy the metal it contained ; for when 

 this was not done, the muzzle grov/ing cold as the breech 

 was heating, some of the metal delivered from the breech 

 was congealed at tire muzzle, so as to stop the passage. 



According to this method, many experiments were made 

 in gun-barrelsj by which some very material steps were' 

 gained in the investicration. 



On the 21th of February I made an experiment with spar 

 and chalk ; the spfer being placed nearest to the breech of 

 the barrel, and exposed to the greatest heat, some baked 

 clay intervening between the carbonates. On opening the 

 barrel, a long continued hissing noise was heard. The spar 

 was in a state of entire calcination ; the chalk, though 

 crumbling at the outside, was uncommonly hard and firm 

 in the heart. The temperature had risen to 32°. 



In this experiment we have the first clear example, in 

 iron barrels, of what I call internal calcination', that is to 

 say, where the carbonic acid, separated from the earthy basis, 

 has been accumulated in cavities within the barrel. For, 

 subsequently to the action of strong heat, the barrel had 

 been completely cooled ; the air, therefore, introduced by 

 means of the air tube, must have resumed its original bulk, 

 and by itself could have no tendency to rush out ; the heat 

 employed to open the barrel being barely sufficient to soften 

 the metal. Since, then, the opening of the barrel was ac- 

 companied by the discharge of clastic matter in great abun- 

 dance, it is evident that this must have proceeded from 

 something superadded to the air originally included, which 

 could be nothing but the carbonic acid of the carbonate. It 

 follows, that the calcination had been, in part at least, in- 

 ternal ; the separation of the acid from the earthy matter 

 being 'complete- where the heat was strongest, and only par- 

 tial where the intcnsitv was less. 



Thcr chemical principles stated in a former part of ihl.i 

 paper, authorised us to expect a result of this kind. As 

 T3 hep' 



