85 EFFECTS of HEAT 



the whole cradle ; when any fpace remained, it was filled up 

 by a piece of chalk drefled for the purpofe. (Fig. 4. reprefents 

 the cradle filled, as juft defcribed). 



Things being thus prepared, the gun-barrel, placed erect 

 with its muzzle upwards, was half filled with the liquid fufible 

 metal. The cradle was then introduced into the barrel, and 

 plunged to the bottom of the liquid, fo that the carbonate was 

 placed very near the breech, (as reprefented in fig. 5, the fu- 

 fible metal Handing at 0). The air-tube (B) being placed fo 

 as to enter the liquid with its muzzle downwards, retained 

 great part of the air it originally contained, though fome of it 

 might be driven off by the heat, fo as to efcape through the 

 liquid. The metal being now allowed to cool, and to fix round 

 the cradle and ramrod, the air remaining in the air-tube was 

 effectually confined, and all was held fail. The barrel being 

 then filled to the brim with fufible metal, the apparatus was 

 ready for the application of heat to the breech, (as fhewn in 

 fig. 6.) 



In the experiments made at this time, I ufed a fquare brick 

 furnace (figs. 7 and 8), having a muffle (r s) traverfing it ho- 

 rizontally and open at both ends. This muffle being fupported 

 in the middle by a very flender prop, was expofed to fire from 

 below, as well as all round. The barrel was placed in the 

 muffle, with its breech in the hotteft part, and the end next 

 the muzzle projecting beyond the furnace, and unrounded with 

 cloths which were drenched with water from time to time. 

 (This arrangement is fhewn in fig. 7). In this fituation, the 

 fufible metal furrounding the cradle being melted, the air 

 contained in the air-tube would of courfe feek the higheft po- 

 fition, and its firfl place in the air-tube would be occupied 

 by fufible metal. (In fig. 6., the new pofition of the air is 

 fhewn at/> q). 



At 



