150 EFFECTS of HEA^ 



lead. In an experiment, made on the 28th November 1803, in 

 order to afcertain the power of the machinery, and the quantity 

 of metal driven out by the expanfion of the liquid, there being 

 nothing in the barrel but metal, I obferved, as foon as the com- 

 prefling apparatus was removed, (which on this occafion was 

 done while the lower part of the barrel was at its full heat, and 

 the barrel {landing brim full of liquid metal,) that all the leather 

 which lay on the outfide of the circular muzzle of the barrel, 

 remained, being only a little browned and crumpled by the 

 heat to which it had been expofed. What leather lay within 

 the circle, had difappeared ; and, on the furfice of the liquid 

 metal, which flood up to the lip of the barrel, I faw large drops, 

 of a mining black liquid, which, on cooling, fixed into a crifp 

 black fubftance, with a mining fracture, exactly like pitch or 

 pure coal. It burned, though not with flame. While hot, it 

 fmelt decidedly of volatile alkali. The important circumftance 

 here, is the different manner in which the heat has acted on the 

 leather, without and within the rim of the barrel. The only 

 difference confided in compreflion, to which, therefore, the dif- 

 ference of effect muft be afcribed : by its force, the volatile 

 matter of the leather which efcaped from the outward parts, 

 had within the rim, been conflrained to remain united to 

 the reft of the compofition, upon which it had acted as a 

 flux, and the whole together had entered into a liquid flate, 

 in a very low heat. Had the preflure been continued till 

 all was cool, thefe fubftances muft have been retained, pro- 

 ducing a real coal. 



On the 24th April 1803, a piece of leather ufed in a fimilar 

 manner, (the comprefling force being continued, however, till 

 all was cold,) was changed to a fubflance like glue, owing 

 doubtlefs to compreflion, in a heat under that of melting lead. 



These obfervations led me to make a feries of experi- 

 ments with animal and vegetable fubflances, and with coal; 



the 



