Tffeds of Heat modified by Compression. 1 97 



secure perfect tisihtness, and obviate the failure which often 

 happened in the horizontal position, from the falling of the 

 borax to the lower side. 



In this view (Plate VI I. fig. 16. )j I fiHt^d the breech in 

 the manner described above, and introduced into the muzzle 

 some borax (C) supported at the middle of the tube by a 

 quantity of silex mixed with botlle-glass (B). I placed the 

 tube so prepared, with its breech plunged into a crucible filled 

 with sand (E), and its muzzle pointing upwards. It was 

 now my object to apply heat to the the muzzle half, whilst the 

 other remained cold. In that view, I constructed a furnace 

 (fig. 14. and 15.), having a muffle placed vertically {cd), 

 surrounded on all sides with fire (ce), and open both above 

 (at r),and below (at d). The ciucible just iDcntioned, with 

 its tube, being then placed on a support directly below the 

 vertical mufHe (as represented in fig 14. at F), it was raised 

 so that the half of the tube next the muzzle was introduced 

 into the tire. In consequence of this, the borax was seen 

 from above to melt, and run down in the tube, tlie air con- 

 tained in the powder escaping in tlic fbrai of bubbles, till 

 at last the borax stood with a clear atid steady surface like 

 that of water. Some of this salt, being thnnvn in front 

 above, by means of a tube of glass, the liquid S'arface was 

 raised nearly to the muzzle, and, after all had been allowed 

 to become cold, the position of the tube was reversed ; the 

 muzzle being now plunged into the sand (as in tig. 17-)» 

 and th« breech introduced into the mufBe. In several ex- 

 periments I found it answer well, to occupy great part of 

 the space next the muzzle with a rod of sand and clav pre- 

 viously baked ((ig. 19. KK), which was either introduced 

 at first, along with the pounded borax, or, being made red 

 hot, was plunged into it when in a liquid state. In manv 

 cases I assisted the compactness of the luljc by means of an 

 internal glaze of borax ; the caibonate being placed in a 

 small tube (as sliovvn in fig. IS). 



These devices answered the end proposed. Three-fourth? 



<<< the tube next the muzzle was foruul complctelv filled with 



a mass, having a concave termination at both eiuls, (^ and :j, 



figs. 17, 18, 19.) shosvlni:; that it had stood as a licpiiil 



"N3 in 



