294 Effects of Heat modified by Compression. 



heat, by increasing the volatility of the acid, tended to se- 

 parate it from the earth, we had reason to expect, that, 

 under the same compression, but in different temperatures, 

 one portion of the carbonate might be calcined, and another 

 not : and that the least heated of the two would be least ex- 

 posed to a change, not only from want of heat, but likewise 

 in consequence of the calcination of the other mass ; for the 

 carbonic acid disengaged bv the calcination of the hottest 

 of the two, must have added to the elasticity of the confined 

 elastic fluid, so as to produce an increase of compression. 

 Bv this means the calcination of the coldest of the two 

 might be altogether prevented, and that of the hottest might 

 be hindered from making any further advancement. This 

 reasoning seemed to explain the partial calcinations which 

 had frequently occurred where there was no proof of leak- 

 ace ; and it opened some new practical views in these expe- 

 riments, of which I availed myself without loss of time. If 

 the internal calcination of one part of an inclosed mass pro- 

 motes the compression of other masses included along with 

 it, I conceived that we might forward our views very much 

 by placing a small quantity of carbonate, carefully weighed, 

 in the same barrel with a large quantity of that substance j 

 and by arranging matters so that the small fiducial part 

 should undergo a moderate heat, while a stronger heat, ca- 

 pable of producing interna! calcination, should be applied to 

 the rest of the carbonate. In this nianner I made many 

 experiments, and obtained results which seemed to confirm 

 this reasoning, and which were often very satisfactory, 

 though the heat did not always exert its greatest force where 

 I intended it to do so. 



On the 28ll) of February I introduced some carbonate, 

 accurately weighed, into a small porcelain tube, placed 

 within a larger one, the rest of the large tube being filled 

 with pounded chalk ; these carbonates, together with some 

 pieces of chalk, placed along with the large tube in the cra- 

 dle, weighing in all 193-7 grains. On opening the barrel, 

 air rushed out with a long-continued hissing noise. The 

 contents of the little tube were lost by the intrusion qf some 

 borax which had been introduced over the silex in order to 



fxcludc 



