Effects of Heat modified by Compression. 147 



of another mode of applying the compressing weight with 

 the muzzle of the barrel downwards, by which I expected 

 to repeat, with a determinate weight, all the experiments 

 formerly made in barrels closed by congealed metal ; and 

 that, by making use of an air-tube, the air, rising to the 

 breech, would secure the contents of the tube from any 

 contamination. In this view, the barrel was introduced 

 from below into the muffie with its breech upwards, and 

 retained in that position by means of a hook fixed to the 

 furnace, till the collar was made to press up against the grate, 

 by an iron lever, loaded with a weight, and resting on a 

 support placed in front. In some experiments made in this 

 wav, the result was obtained very clean, as had been ex- 

 pected ; but the force had been too feeble, and when it was 

 increased, the furnace yielded upwards by the mechanical 

 strain. 



I found it therefore necessary to use a frame of iron (as 

 in fig. 38, the frame being represented separately in fig. 39), 

 by which the brick-work was relieved from the mechanical 

 strain. This frame consisted of two bars (ab and fe, figs. 

 38 and 3D), fixed into the wall (at a andy'), parsing hori- 

 zontally under the furnace, one on each side of the muffle, 

 turning downwards at the front (in b and e), and meeting 

 at the cround, with a flat bar (cd) uniting the whole. In 

 this manner, a kind of stirrup {bede) was formed in front 

 of the furnace, upon the cross bar (cd) of which a block of 

 wood (hit, fig. 38) was placed, supporting an edge of iron, 

 upon which the lever rested, the working end of the lever (g) 

 acting upwards. A strain was exerted, by means of the 

 barrel and its collar, against the horizontal bars (ab and/V), 

 which was effectually resisted by the wall (at candy') at 

 one end of these bars, and by the upright bars (cb and de) 

 at the other end. In this manner the whole strain was sus- 

 tained by the frame, and the furnace stood without injury. 



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

 Bhapc of a cup (atg), and halt' filled with lead, the smooth 

 surface 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 the whole ten feet in length. 

 K 2 In 



