J24 ACTION OF IIEAT MODIFIED 



batTel down- is to say, with the muzzle of the barrel upwards, in some of 

 *'^ ^' which I obtained very satisfactory results ; but it was only 



by chance that the substance escaped the contamination 

 of the fusible metal ; which induced me to think 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 muffle 

 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 way, the result was obtained very 

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

 feeble, and when it was increased, the furnace yielded up-> 

 wards by the mechanical strain. 



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

 e appaia us. .^ ^^ ^^ _ ^^^ frame being represented separately in iig.39.), 

 by which the brick-work was relieved from the mechanical 

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

 38. and 39. quarto Plate III.), fixed into the wail, (at a and 

 f.J passing horizontally under the furnace, one on each side 

 of the muffle, turning downwards at the front, (in b and ej, 

 and meeting at the ground, with a liat bar ^c d) uniting the 

 whole. In this manner, a kind of stirrup (b c d c) was 

 formed in front of the furnace, upon the cross bar (c d) of 

 which a block of wood (h h, fig. 38.J, was placed, supporting 

 an edge of iron, uion 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, (a b andfej, which was effectually resisted by the wall 

 (at a and/ J at one end of these bars, and by the upright 

 bars fc b and d e) at the other end. In this manner the 

 whole strain was sustained by the frame, and the furnace 

 stood without injury. 



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

 shape of a cup, (at g ), and half filled with lead, the smooth 

 surface of wljich, was ap^ilied to the muzzle of the bar^'el. 



The 



