144 EFFECTS of HEAT 



made in barrels clofed by congealed metal ; and that, by ma- 

 king ufe of an air-tube, the air, rifing to the breech, would fe- 

 cure the contents of the tube from any contamination. In 

 this view, the barrel was introduced from below into the 

 muffle with its breech upwards, and retained in that pofition 

 by means of a hook fixed to the furnace, till the collar was 

 made to prefs up againft the grate, by an iron lever, loaded 

 with a weight, and refting on a fupport placed in front. In 

 fome experiments made in this way, the refult was obtained 

 very clean, as had been expected ; but the force had been too 

 feeble, and when it was increafed, the furnace yielded up- 

 wards by the mechanical ftrain. 



I found it therefore neceflary to ufe a frame of iron, (as in fig. 

 38. ', the frame being reprefented feparately in fig. 39.), by which 

 the brick-work was relieved from the mechanical ftrain. This 

 frame confifted of two bars (a b and/V, figs. 38. and 39.), fixed 

 into the wall, (at a and/,) palling horizontally under the furnace, 

 one on each fide of the muffle, turning downwards at the front, (in 

 b and <?), and meeting at the ground, with a fiat bar (c d) uniting 

 the whole. In this manner, a kind of ftirrup (be de) was formed 

 in front of the furnace, upon the crofs bar (c d) of which a 

 block of wood [h h, fig. 38.), was placed, fupportingan edge of 

 iron, upon which the lever refted ; the working end of the 

 lever (g) acting upwards. A ftrain was exerted, by means of 

 the barrel and its collar, againft the horizontal bars, (a b and 

 / ej, which was effectually refilled by the wall (at a and/j at 

 one end of thefe bars, and by -the upright bars (c b and d e) at 

 the other end. In this manner the whole ftrain was fuftained 

 by the frame, and the furnace ftood without injury. 



The iron bar, at its working end, was formed into the fhape 

 of a cup, (at^), and half filled with lead, the fmooth furface of 

 which, was applied to the muzzle of the barrel. The lever, too, 

 was lengthened, by joining to the bar of iron, a beam of wood, 



making 



