86 EFFECTS of HEAT 



the following general view : If we take a hollow tube or bar- 

 rel (AD, fig. i.) clofed at one end, and open at the other, of 

 one foot or more in length ; it is evident, that by introducing 

 one end into a furnace, we can apply to it as great heat as 

 art can produce, while the other end is kept cool, or, if necef- 

 fary, expofed to extreme cold. If, then, the fubftance which 

 we mean to fubject to the combined action of heat and pref- 

 fure, be introduced into the breech or clofed end, of the barrel 

 (CD), and if the middle part be filled with fome refractory 

 fubftance, leaving a fmall empty fpace at the muzzle (AB), we 

 can apply heat to the muzzle, while the breech containing the 

 fubject of experiment, is kept cool, and thus clofe the barrel by 

 any of the numerous modes which heat affords, from the weld- 

 ing of iron to the melting of fealing-wax. Things being then 

 reverfed, and the breech put into the furnace', a heat of any 

 required intenfity may be applied to the fubject of experiment, 

 now in a flate of conftraint. 



My firfl application of this fcheme was carried on with 

 a common gun-barrel, cut off at the touch-hole, and welded 

 very flrongly at the breech by means of a plug of iron. 

 Into it I introduced the carbonate, previoufly rammed into a 

 cartridge of paper or pafteboard, in order to protect it from the 

 iron, by which, in fome former trials, the fubject of experiment 

 had been contaminated throughout during the action of heat. I 

 then rammed the reft of the barrel full of pounded clay, previouf- 

 ly baked in a flrong heat, and I had the muzzle clofed like the 

 breech, by a plug of iron welded upon it in a common forge $ 

 the reft of the barrel being kept cold during this operation, 

 by means of wet cloths. The breech of the barrel was 

 then introduced horizontally into a common muffle, heated to 

 about 25 ° of Wedgwood. To the muzzle a rope was fixed, 

 in fuch a manner, that the barrel could be withdrawn with- 

 out 



