THE FORCE OF
64
From the principles establilhed in the former part of this■work, it may be inferred that by increasing to a certain pointthe size of the vessel, and silling it with powder without in-creasing the size of the vent, the elasticity of the powder willbe much greater than that found by the last experiments, asthe fire will be more intense, and less of the elastic fluid inproportion to its mass will escape. To ascertain to whatdegree the elasticity will increase when powder is fired in avessel with the vent closed, a similar method may be used
(m)-
Fig. ix. Perforate the screw IEFK with a canal LM, toreceive the screw G&, which may be turned with velo-city by the winch NN- The screw G&, must be longerthan the canal LM, that as soon as its head exactlycorresponds with the superficies IK, the point & whichhas been heated red hot, passing through the orifice M,may fire the powder contained in EFGH.
138. From these methods of proving the force of powderby weight and cohesion, added to the observations on the sub-ject in the Philos. Instit. there will be no difficulty in apply-ing elasticity to the measurement of this force (127). Aspring strongly bent opposed to the movement of the ironpin will suffice for this purpose ; but the greatest force of thepowder ought only to increase the tension of the spring enoughto make an impression on soft wax, or some similar sub-stance.
139. We will conclude this chapter with remarking thedifference observable in the activity of fire on burningequal quantities of powder in vessels of different sizes. Fit ascrew EMNF to the part CDHG of the eprouvette, (Fig.8.) and perforate it with a small canal TY; at the bottomof the screw make a cavity in form of a truncated coneMRSN, and fill it with tin perforated through the middle,so as not to stop up the cavity TY : having closed the ventXI, and filled 1 KGH with powder, apply the screw EFMN,and set fire to the powder by TY, through which all theclastic fluid must of necessity pass. On unscrewing EFMN,apart of the tin will be found melted. To collect the quantitymelted in this experiment, a roughplank should be placed abouta foot distant from TY, and after the explosion, the meltedsubstance will be found sticking to it. On burning the samequantity of powder in a vessel much larger, the tin will notmelt, and if it be burned in the open air upon a sheet of pa*
per,