MODIFIED by COMPRESSION. 119 



rometer gave 25 , and the under one i6 Q : The loweft mafTes 

 of carbonate were fcarcely affected by the heat : The contents 

 of the little tube had loft 2.9 per cent, j both the lump and the 

 pounded chalk were in a fine faline ftate, and, in feveral places 

 had run and fpread upon the infide of the tube, which I had 

 not expected to fee in fuch a low heat. On the upper furface 

 of the chalk rammed into the little tube, which, after its in- 

 troduction had been wiped fmooth, were a fet of white crys- 

 tals, with mining facettes, large enough to be diftinguifhed by 

 the naked eye, and feeming to rife out of the mafs of car- 

 bonate. I likewife obferved, that the folid mafs on which 

 thefe cryftals flood, was uncommonly tranfparent. 



In thefe four experiments, the bulk of the included air was 

 fucceilively diminished, and by that means its elafticity in- 

 creafed. The confequence was, that in the firft experiment, 

 where that elafticity was the leaft, the carbonic acid was 

 allowed to feparate from the lime, in an early ftage of the 

 rifing heat, lower than the fuiing point of the carbonate, and 

 complete internal calcination was effected. In the fecond 

 experiment, the elaftic force being much greater, calcina- 

 tion was prevented, till the heat rofe fo high as to occa- 

 fion the entire fufion of the carbonate, and its aclion on 

 the tube, before the carbonic acid was fet at liberty by 

 the failure of the barrel. In the third experiment, with ftill 

 greater elaftic force, the carbonate was partly conftrained, 

 and its fufion accomplished, in a heat between 41 Q and 15 . 

 In the laft experiment, where the force was ftrongeft of all, 

 the carbonate was almoft completely protected from decom- 

 position by heat, in confequence of which it cryftallized and 

 a&ed on the tube, in a temperature between 25 ° and 16 . 

 On the other hand, the efficacy of the carbonic acid as a 

 flux on the lime, and in enabling the carbonate to act as a 

 flux on other bodies, was clearly evinced .; fince the firft ex- 

 periment 



