82 EFFECTS of HEAT 



plete compreffion : and, at the fame time, it illuftrates what 

 has happened occafionally in nature, where the bituminous 

 matter feems to have been driven by fuperior local heat, from 

 one part of a coaly bed, though retained in others, under the 

 fame compreffion. The bitumen fo driven off being found, in 

 other cafes, to pervade and tinge beds of flate and of fandftone. 



I was employed in this purfuit in fpring 1800, when an 

 event of importance interrupted my experiments for about a 

 year. But I refumed them in March 1801, with many new 

 plans of execution, and with conhderable addition to my ap- 

 paratus. 



In the courfe of my firft trials, the following mode of execu- 

 tion had occurred to me, which I now began to put in practice. 

 It is well known to chemifts, that a certain compofition of differ- 

 ent metals *, produces a fubftance fo fufible, as to melt in the 

 heat of boiling- water. I conceived that great advantage, both 

 in point of accuracy and difpatch, might be gained in thefe ex- 

 periments, by fubftituting this metal for the baked clay above 

 mentioned : That after introducing the carbonate into the 

 breech of the barrel, the fufible metal, in a liquid ftate, 

 might be poured in, fo as to fill the barrel to its brim : 

 That when the metal had cooled and become folid, the breech 

 might, as before, be introduced into a muffle, and expofed 

 to any required heat, while the muzzle was carefully kept cold. 

 In this manner, no part of the fufible metal being melted, but 

 what lay at the breech, the reft, continuing in a folid ftate, 

 would effedmally confine the carbonic acid : That after the ac- 

 tion of ftrong heat had ceafed, and after all had been allowed 

 to cool completely, the fufible metal might be removed entire- 

 ly from the barrel, by means of a heat little above that of boil- 

 ing water, and far too low to occafion any decompofition of 



the 



* Eight parts of bifmuth, five of lead, and three of tin- 



