466 Fifty Years of Explosives. [Jan. 18, 



lighting is not required, this vibration can easily be prevented by 

 compressing the spring to a point a little short of the expected 

 pressure. Taking first the '25 density, and noting that the 

 maximum pressure is 22*4 tons per square inch, you will note that 

 the pressure and temperature are approximately halved in 2i seconds. 

 With '2 density, the maximum pressure is 17*8 tons, and this 

 pressure is approximately halved in a second and a half. Density 

 •15 gives a pressure of 12 '5 tons per square inch, and that pressure 

 is halved in a little over a second, while the pressure due to the 

 density of • 1 is halved in a little less than a second. In this last 

 density you see there is no vibration of the pen, and the pressure is 

 identical with that given by the crusher gauge. 



I now throw on the screen the last diagram, which gives the 

 times that the charges, the rate of cooling of which you have just 

 seen, take to completely burn. 



You will understand that the curves for densities '1 and '15 are 

 facsimiles of the curves traced by the explosion. The densities '2 

 and -25 are also traced by the explosion, but the vertical heights are 

 doubled in order to have the four curves on the same scale. The 

 vertical line gives the pressures in tons per square inch. 



The actual times from firing the charge are given by the black 

 figures, but I have also shown separately the time taken to consume 

 the cordite after the charge was fully lighted. For the densities -15, 

 •2 and '25, these times are approximately fifteen thousandths of a 

 second, eleven thousandths of a second, and a little less than ten 

 thousandths of a second ; while the times taken fully to light are 

 approximately nine thousandths of a second, fifteen thousandths of 

 a second, and thirteen thousandths of a second ; the smallest charge, 

 probably due to a stronger primer, being the most quickly lighted. 

 The red lines drawn on density '2 and "25, mark the increment in 

 the rate of burning each as compared with the previous experiment. 

 The black lines across, mark the maximum pressure and the time 

 taken to reach it. 



Earher to-night I referred to the improvements in velocity and 

 energy obtained with the old propellants. I conclude my lecture by 

 pointing out that the new propellants give an additional velocity of 

 nearly 1000 feet per second, and more than double the energy of the 

 projectile. 



[A. N.] 



