342 Sir Andrew Noble [March 23, 



I hope to be able to determine these points when the temperature is 

 so far reduced that the wires will no longer be fused. 



The apparatus I have used for these experiments is placed on the 

 table. The cylinder iu which the explosives were made is too heavy 

 to transport here, but this photograph will sufficiently explain the 

 arrangement. The charge I used is a little more than a kilogramme, 

 aud it is fired in this cylinder iu the usual manner. 



The tension of the gas acting on the piston compresses the spring 

 and indicates the pressure on the scale here shown. But to obtain 

 a permanent record the apparatus I have mentioned is employed. 



There is, you see, a drum made to rotate by means of a small 

 motor. Its rate of rotation is given by a chronometer acting on a 

 relay, and marking seconds on the drum, while the magnitude of the 

 pressure is registered by this pencil actuated by the pressure gauge 

 1 have just described. 



To obtain with sufficient accuracy the maximum pressure, and also 

 the time taken to gasify the explosive, two observations, that is two 

 explosions, are necessary. 



If the piston be left free to move the instant of the commence- 

 ment of pressure, the outside limit of the time of complete explosion 

 will be indicated, but on account of the inertia of the moviug parts 

 the pressure indicated will be in excess of the true pressure, and the 

 excess will be, more or less, inversely as the time occupied by the ex- 

 plosion. 



If we desire to know the true pressure, it is necessary to compress 

 the gauge beforehand to a point closely approximating to the expected 

 pressure, so that the inertia of the moving parts may be as small as 

 possible — the arrangement by which this is effected is uot shown on 

 the diagram, but the gauge is retained at the desired pressure by a 

 wedge-shaped stop, held in its place by the pressure of the spring, 

 and to the stop a heavy weight is attached ; when the pressure is 

 relieved by the explosion, the weight falls and leaves the spring free 

 to act. 



I have made a large number of experiments with this instrument, 

 both with a variety of explosives and with explosives fired under 

 different conditions. Time will not permit me to do more than to 

 show you on the screen three pairs of experiments to illustrate the 

 effect of exploding cordite of different dimensions, but of precisely 

 the same composition. 



I shall commence with rifle cordite. In this diagram (Fig. VIII.) 

 the axis of abscissae has the time in seconds marked upon it, while 

 the ordinates denote the pressures, and I draw your attention to the 

 great difference, in the initial stage, between the red and the blue 

 curves. You will notice that the red curves show a maximum pres- 

 sure some 4|f tons higher than that shown by the blue curve, but 

 this pressure is not real. It is due to the inertia of the moving 

 parts. The red and blue curves in a very small fraction of a second 

 come together and remain practically together for the rest of their 



