120 EFFECTS of HEAT 



periment proved, that quicklime by itfelf, could neither be 

 melted, nor act upon porcelain, even in the violent heat of 79 v ; 

 whereas, in the laft experiment where the carbonic acid was 

 retained, both of thefe erTe&s took place in a very low tempe- 

 rature. 



V. 



Experiments in which Water was employed to increafe the Elajlicity of 

 the included Air. — Cafes of complete Compreffion. — General Obferva- 

 tions. — Some Experiments affording interejling refults ; in particular, 

 foewing a mutual action between Silex and the Carbonate of Lime. 



Finding that fuch benefit arofe from the increafe of elafti- 

 city given to the included air in the lafl-mentioned experi- 

 ments, by the diminution of its quantity ; it now occurred to 

 me, that a fuggeftion formerly made by Dr Kennedy, of ufing 

 water to ailift the comprefling force, might be followed with 

 advantage ; That while fufficient room was allowed for the 

 expanfion of the liquid metal, a reading force of any requi- 

 red amount, might thus be applied to the carbonate. In this 

 view, I adopted the following mode, which, though attended 

 with considerable difficulty in execution, I have often pra&i- 

 fed with fuccefs. The weight of water required to be intro- 

 duced into the barrel was added to a fmall piece of chalk or 

 baked clay, previously weighed. The piece was then dropped in- 

 to a tube of porcelain of about an inch in depth, and covered with 

 pounded chalk, which was firmly rammed upon it. The tube 

 was then placed in the cradle along with the fubjecl: of expe- 

 riment, and the whole was plunged into the fufible metal, 

 previoufly poured into the barrel, and heated fo as merely 

 to render it liquid. The metal being thus fuddenly cooled, 



the 



