84 EFFECTS of HEA1 



medy was found to anfwer completely, and was applied, in 

 all the experiments made at this time *. 



I now propofed, in order to keep the carbonate clean, to 

 inclofe it in a fmall vefTel ', and to obviate the difficulty of 

 removing the refult at the conclufion of the experiment, I 

 further propofed to connect that vefTel with an iron ramrod, 

 longer than the barrel, by which it could be introduced or 

 withdrawn at pleafure. 



A small tube of glafs f, or of Raumur's porcelain, about 

 a quarter of an inch in diameter, and one or two inches in 

 length, (fig. 2. A) was half filled with pounded carbonate of 



lime, rammed as hard as poflible ' y the other half of the tube 



being 



* I found it a matter of much difficulty to afcertain the proper quantity of air 

 •which ought to be thus inclofed. When the quantity was too great, the refult 

 was injured by diminution of elafticity, as I fiiall have occafion fully to mew here- 

 after. When too fmall, or when, by any accident, the whole of this included air 

 was allowed to efcape, the barrel was deftroyed. 



I hoped to afcertain the bulk of air neceffary to give liberty to the ex- 

 pansion of the liquid metal, by meafuring the actual quantity expelled by 

 known heats from an open barrel filled with it. But I was furprifed to find, 

 that the quantity thus difcharged, exceeded in bulk that of the air which, in 

 the fame heats, I had confined along with the carbonate and fufible metal in 

 many fuccefsful experiments. As the expanfion of the liquid does not feem ca- 

 pable of fenfible diminution by an oppofing force, this fact can only be accounted 

 for by a dillention of the barrel. In thefe experiments, then, the expanfive force 

 of the carbonic acid, of the included air, and of the fufible metal, acted in combi- 

 nation againft the barrel, and were yielded to in part by the diftention of the bar- 

 rel, and by the condenfation of the included air. My object was to increafe the 

 force of this mutual action, by diminifliing the quantity of air, and by other de- 

 vices to be mentioned hereafter. Where fo many forces were concerned, the 

 laws of whofe variations were unknown, much precifion could not be expected, 

 nor is it wonderful, that in attempting to carry the compreffing force to the ut- 

 moft, I fhould have deftroyed barrels innumerable. 



+ I have fince conftantly ufed tubes of common porcelain, finding glafs much 

 too fufible for this purpose. 



