202 Effects of Heat modified by Compression, 



result being visibly improved by every approach towards 

 complete saturation. I therefore became anxious to inves- 

 tigate the cause of the partial calcinations which had always 

 taken place, to a greater or a less degree, in all these experi- 

 ments. The question naturally suggests itself, — V/hat has 

 become of the carbonic acid separated in these partial cal- 

 cinations from the earthy basis ? Has it penetrated the ves- 

 sel, and escaped entirely ; or has it been retained within it 

 Jo a gaseous,, but highly compressed state ? It occurred to 

 me, that this question might be easily resolved, by weighing 

 the vessel before and after the action of heat upon the car- 

 bonate. 



With iron, a constant and inappreciable source of irregu- 

 larity existediin the oxidation of the barrel. But with porce- 

 lain the thing was easy; and I put it in practice in all my 

 experiments with this material, which were made after the 

 question had occurred to me. The tube was weighed as soon 

 as its muzzle w as closed, and again after the breech had been 

 exposed to the fire; taking care, in both cases, to allow all 

 to cool. In every case I found some loss of weight, proving 

 that, even in the best experiments, the tubes were pene- 

 trated to a certain degree. I next wished to try if any of 

 the carbonic acid separated, remained within the tube in a 

 gaseous form ; and in that view, I wrapped the tube, which 

 had just been weighed, in a sheet of paper, and placed it, so 

 surrounded, on the scale of the balance. As soon as its 

 weijiht was ascertained, I broke the tube by a smart blow, 

 and then replaced upon the scale the paper containing all the 

 fragments. In those experiments, in which entire calcina- 

 tion had taken place, the weight was found not to be 

 changed, for all the carbonic acid had already escaped during 

 the action of heat. But in the good results I always found 

 that a loss of weight was the consequence of breaking the 

 tube. 



These facts prove, that both causes of calcination had 

 operated in the porcelain tubes ; that, in the cases of small 

 loss, part of the carbonic acid had escaped through tl)c ves- 

 sel, and that part had been retained within it. I had in 



view 



