146 EFFECTS of HEAT 
held tight by the beam, but was rent and a little fwelled 
at the breech. The rent was wide, and fuch as has always 
appeared in the ftrongeft barrels when they failed. The car- 
bonate was quite calcined, it had boiled over the little tube, 
and was entirely in a frothy ftate, with large and diftin@ly 
rounded air-holes. The fragments of fhell which had occupied 
the upper part of the little tube, had loft every trace of their 
original fhape in the act of ebullition and fufion. 
No. 7.—Own the 26th a fimilar experiment, was made, in 
which the barrel was thrown open, in fpite of this powerful 
comprefling force, with a report like that of a gun, (as I was 
told, not having been prefent), and the bar was found in a 
ftate of ftrong vibration. The carbonate was calcined, and 
fomewhat frothy, the heart of one piece of chalk ufed was in 
a ftate of faline marble. 
Ir now occurred to me to work with a comprefling force; and 
no air-tube, trufting, as happened accidentally in one cafe, that 
the expanfion of the liquid would clear itfelf by gentle exu- 
dation, without injury to the carbonate. In this mode, it 
was neceflary, for reafons lately ftated, to place the muzzle 
upwards. Various trials made thus, at this time, afforded no 
remarkable refults. But I refumed the method, with the fol- 
lowing alteration in the application of the weight, on the 27th 
of April 1804. 
I concEIvED that fome inconvenience might arife from the 
mode of employing the weight in the former experiments. 
In them it had been applied at the end of the bar, and its 
effect propagated along it, fo as to prefs againft the barrel 
at its other extremity. It occurred to me, that the propagation 
of motion in this way, requiring fome fenfible time, a confi- 
derable quantity of carbonic acid might efcape by a fudden 
eruption, before that propagation had taken effect. I there- 
fore thought, that more effectual work might be done, by 
placing 
a 
