fired gun-powder. 6i

132. The theorem 9962 n S = P where n expresses the

elasticity of the fluid, and S the surface acted on, shews thatif in this eprouvette the diameter E F of the cylinder be■sV of a foot, S will be = T j - s : then substituting 1800 in theplace of n, 9962 « 8 — 9962 x 1800 x 23048^ : the

weight QjVI N Q_ should not be less, that it may just yieldto the action of the fluid in its highest state of elasticity;but as such a weight is very ponderous and unmanageable,it may be measured by a lighter mass, by lessening the valueof S without diminishing the size of the cylinder, as follows :

133. In the eprouvette A B C D, make a hollow cylinderCI KD of such a depth, (Fig. 8.) that on applying the screwG C P D H of a sufficient length to resist the greatest effortsof the powder, the height G I of the space I K G H benearly equal to the diameter G H. In the centre of thescrew drill a cylindrical canal O P, and introduce a pinof polished iron of the same form, fitting so exactly thatthe fluid cannot pass between it and the sides of the canal,with a ledge at P to prevent its falling into the chamberwhere the powder is lodged; the axis V P of the cylinderbeing vertical, place upon the head of the iron pin a weightof which the centre of gravity is in the axis V P with teethto slide up and down in the grooves of two uprights parallelto V P as in (Fig. 7.) Having filled the space G I K Hwith powder, and applied fire by the vent X, the elasticfluid acting on every point of the superficies, will raise upthe pin O P, and consequently the superincumbent weight ;which may be increased or diminished (131) till the forceof the powder be only just sufficient to raise it. The heightto which it is raised, will shew the pressure of the fluid*for the weight being expressed in pounds, the value of Sis equal to the base O in the pin O P. Thus the valueof n expressing the elasticity of the fluid may be easilyfound.

134. There are different methods of ascertaining the great-est force of powder, by the cohesion of the constituent partsof bodies. For example, fill with powder a cylinder ofhomogeneous metal, the sides of which are of equal thick-ness, secure the ends so firmly with strong screws thatthey will resist the utmost force of the fluid, and set fire tothe powder by a small vent made in the middle of the lengthof the cylinder, that the inflammation may be as sudden andgeneral as possible. The vessel will then hurst longitudi-