T44 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 rounp it therefore neceflary to ufe a frame of iron, (as in fig. 
38.3 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 and fe, figs. 38. and 39.), fixed 
into the wall, (at aand f,) pafling horizontally under the furnace, 
one on each fide of the muffle, turning downwards at the front, (in 
band e), and meeting at the ground, with a flat bar (¢d) uniting 
the whole. In this manner, a kind of ftirrup (dc de) was formed 
in front of the furnace, upon the crofs bar (cd) of which a 
block of wood (4 4, fig. 38.), was placed, fupporting an edge of 
iron, upon which the lever refted; the working end of the 
lever (g) ating upwards. A ftrain was exerted, by means of 
the barrel and its collar, againft the horizontal bars, (@ 4 and 
f ¢), which was effectually refifted by the wall (at a and f) at 
one end of thefe bars, and by the upright bars (¢ J and d ¢) at 
the other end. In this manner the whole ftrain was fuftained, 
by the frame, and the furnace ftood without injury. 
Tue iron bar, at its working end, was formed into the fhape 
of a cup, (at g), and half filled with lead, the fmooth furface of 
which, was applied to the muzzle of the barrel. The lever, too; 
svas lengthened, by joining to the bar of iron, a beam of wood; 
making 
