upon Gun-powder , &c. 233 
valve, and which pafle's up through the vent-hole, and is cou- 
riered with the fpring S, the valve is prefled, or rather drawn 
into its place, and the vent is clofed. The ftem of the valve 
was at Arid made cylindrical ; but, in order to make way for 
the priming to pafs down to the valve, one-half of its fubftance 
was taken away, as is reprefented in the figure. 
When this vent is primed, the fpace between the vent hole 
and the ftem of the valve is filled with fine-grained powder, 
and the valve is gently opened by preffing upon the end of the 
ftem till one or more grains of powder lodge themfelves be- 
tween the valve and the aperture ; which preventing the valve 
from clofing again,, a fmall opening is left for the paflage of the 
flame- into the chamber of the piece : therefore, when the 
priming is lighted, the fire palling down the vent, and entering 
the chamber, inflames the charge, and the fmall grains of pow- 
der that were lodged between the valve and the aperture being 
deftroyed by the flame in its paflage through the vent, the valve 
immediately doles, and prevents the efcape of any part of the 
elaftic fluid generated by the inflammation of the powder in the 
chamber of the piece. The prefiure of this fluid- upon the 
valve aflifts the addon of the fpring, by which means the valve 
is more expeditioufly and more effedlually clofed. 
The valve was very accurately fitted to the aperture by grind- 
ing them together with powdered emery, and afterwards po~ 
lifhing them one upon the other. And it is very certain, that 
no part of the elaftic fluid made its efcape by this vent ; for, 
upon firing the piece, there was only a Ample fiafh from the 
explofion of the priming, and no ftream of Are was to be feen 
iffuing from the vent, as is always to be obferved when a com- 
mon vent is made ufe of, and; in all other cafes where this fluid' 
finds a 'paflage.. 
Ill: 
