Effects of Heat modified hy Compression. 153 



placed in contact with (A) the tube containino; the car-- 

 bonate. These articles generally occupied the whole cradle ; 

 when any space remained it was filled up by a piece of chalk 

 dressed for the purpose. (Fig. 4. represents the cradle filled, 

 as just described.) 



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

 with its muzzle upwards, was half filled with the liquid 

 fusible metal. The cradle was then introduced into the 

 barrel, and plunged to the bottom of the liquid, so that the 

 carbonate was placed very near the breech (as represented in 

 fig. 5, the fusible metal standing at o). The air-lube (B) 

 being placed so as to enter the liquid with its muzzle down- 

 wards, retained great part of the air it originally contained, 

 though some of it might be driven off by the heat, so as to 

 escape 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 fast. The barrel being then filled to the brim with 

 fusible metal, the apparatus was ready for the application of 

 heat to the breech (as shown in fig. 6). 



In the experiments made at this time, I used a square 

 brick furnace (figs. 7 and 8), having a muffle {r s) travers- 

 ing it horizontally and open at both ends. This muffle 

 being supported in the middle by a very slender prop, was 

 exposed to fire from below, as well as all round. The bar- 

 rel was placed in the muffle, with its breech in the hottest 

 part, and the end next the muzzle projecting beyond the 

 furnace, and surrounded with cloths which were drenched 

 with water from time to time. (This arrangement is 

 shown in fig. 7.) In this situation the fusible metal sur- 

 rounding the cradle being melted, the air contained in the 

 air-tube would of course seek the highest position, and 

 its first place in the air-tube would be occupied by fusible 

 metal. (Tn fig. 6., the new position of the air is shown 

 atp^.) 



At the conclusion of the experiment the metal was gene- 

 rally removed by placing the barrel in the transverse muffle, 

 with its muzzle pointing a little downwards, and so that the 

 |ieat was applied first to the muzzle, and then to the rest of 



the 



