102 EFFECTS of HEAT 



contributed very much both to the convenience and fafety 

 of thefe experiments. 



In this view, making ufe of the brick- furnace with the 

 vertical muffle, already defcribed in page 93. I ordered a pit 

 (a a a, fig. 20.) to be excavated under it, for the purpofe of 

 receiving a water-vefTel. This vefTel (reprefented feparately, 

 fig. 21.) was made of caft iron; it was three inches in diame- 

 ter, and three feet deep ; and had a pipe {d e) flriking off from 

 it at right angles, four or five inches below its rim, communi- 

 cating with a cup {e j ') at the diftance of about two feet. 

 The main vefTel being placed in the pit (a a) directly below the 

 vertical muffle, and the cup Handing clear of the furnace, wa- 

 ter poured into the cup flowed into the vefTel, and could thus 

 conveniently be made to ftand at any level. (The whole ar- 

 rangement is reprefented in fig. 20.) The muzzle of the barrel 

 (^) being plunged into the water, and its breech [b) reaching 

 up into the muffle, as far as was found convenient, its pofition 

 was fecured by an iron chain (gf). The heat communi- 

 cated downwards generally kept the furface of the water 

 (at c) in a flate of ebullition ; the wafle thus occafioned being 

 fupplied by means of the cup, into which, if necefTary, a con- 

 flant ffream could be made to flow. 



As formerly, I rammed the carbonate into a tube of porce- 

 lain, and placed it in a cradle of iron, along with an air-tube 

 and a pyrometer ; the cradle being fixed to a rod of iron, 

 which rod I now judged proper to make as large as the barrel 

 would admit, in order to exclude as much of the fufible me- 

 tal as poflible ; for the expanfion of the liquid metal being in 

 proportion to the quantity heated, the more that quantity 

 could be reduced, the lefs rife there w T as of deflroying the 

 barrels. 



In the courfe of practice, a fimple mode occurred of remo- 

 ving the metal and withdrawing the cradle •: it confifted in pla- 

 cing 



