1892.] Pressure developed by some New Explosives. 127 



that is to say, three rounds with the breech and three with the muzzle 

 plugs, or six in all. 



In the calculation of the pressures it is assumed that before and 

 after the complete ignition of the explosive the pressures will uni- 

 formly increase and then uniformly decrease, following the laws 

 regulating the relation between the pressure and volume when per- 

 manent gases are permitted to expand with production of work. 



It is in the highest degree improbable that in any experiment 

 is this assumption strictly true. In the case of "brisante" powders, 

 and of high explosives which can be detonated, we know that even in 

 moderately-sized chambers there are wide variations in pressure; and 

 even when there is comparatively slow combustion, as with ballistite 

 and cordite, it appears probable that the generation of a consider- 

 able quantity of the gases may take place in different portions of the 

 bore, giving rise to a corresponding difference in the pressure, and it 

 may be that a portion of the discrepancies of the crusher gauge when 

 placed in forward positions in the bore, to which I shall presently 

 allude, are due to this cause. 



But such irregularities would not very seriously alter the curves 

 shown in the figure. The areas included between the final ordinate, 

 the curve, and the axis of abscissae, being the total energy impressed 

 on the projectile, would of course remain unaltered ; but the curves, 

 instead of the regular figure there shown, would have a wavy 

 outline, and would show several maxima and minima. These irregu- 

 larities of pressure are of no appreciable importance when the 

 strength of the gun, in a radial direction, is considered. 



From the same plate can be at once obtained the pressures for the 

 four explosives at any point of the bore; but for the purpose of 

 applying these results to other guns I give in the annexed table for 

 different densities of the products of explosion (1) the pressure which 

 has been determined in a closed vessel, (2) the pressure at the same 

 density, which has been found to exist in the bore of the 4r 7-inch 

 gun where the gases have been expanded, doing work on the pro- 

 jectile. 



