306 Effects of Heat modified hy Compression. 



which had separated its acid from the most heated part of 

 the carbonate, according to the theory already stated. The 

 soundness of the barrel was proved by the complete state of 

 those carbonates which lay in less heated parts. The air- 

 tube in this experiment had a capacity of 0'29, nearly one- 

 third of a cubic inch. 



The second of these experiments was made on the 29th 

 of April, in the same barrel with the last, after it had af- 

 forded some good results. The air-tube was reduced to one- 

 third of its former bulk, that is, to one-tenth of a cubic inch. 

 The heat rose to 60". The barrel was covered externally 

 with a black spongy substance, the constant indication of 

 failure; and a small drop of white metal made its appear- 

 ance. The cr^adle was removed without any explosion or 

 hissing. The carbonates were entirely calcined. The barrel 

 had yielded, but had resisted well at first ; for the contents 

 of the little tube were found in a complete state of froth, 

 and running with the porcelain. 



The third experiment was made on the 30th of April in 

 another similar barrel. Every circumstance was the same 

 as in the two last experiments, only that the air-tube was 

 now reduced to half its last bulk, that is, to one-twentieth 

 of a cubic inch, A pyrometer was placed at each end of the 

 large tube. The uppermost gave 41", the other only 15°. 

 The contents of the inner tube had lost 16 per cent., and 

 were reduced to a most beautiful state of froth, not very 

 much injured by the internal calcination, and indicating a 

 thinner state of fusion than had appeared. 



The fourth experimerjt was made on the 2d of May, like 

 the rest in all respects, with a still smaller air-tube, of 

 0*0318, being less than one- thirtieth of a cubic inch. The 

 upper pyrometer gave 23", and the under one 16^. The 

 lowest masses of carbonate were scarcely affected by the 

 heat : the contents of the litlle tube had lost 2*9 per cent. ; 

 both. the lump and the poqnded chalk were in a fine saline 

 state, and in several places had run and spread upon the 

 inside of the tube, which I had not expected to see in such 

 a low heat. On the upper surface of the chalk rammed into 



the; 



