178 Mr. H. B. Dixon and Mr. J. C. Cain on the 



in a bomb has been measured by Berthelot, and found to 

 be 15 atmospheres. As calculated from Berthelot's theory, 

 the pressure in the wave should be 18 atmospheres ; 

 according to Dixon 57 atmospheres. One reason which 

 led us to dilute the explosive mixture was suggested to us 

 by Professor Osborne Reynolds. If the velocity of the 

 explosion-wave in the gas approximates to the rate at which 

 the distortion-wave in the glass is propagated, the latter 

 might be continually re-inforced, and the tube be broken 

 as the result of a pressure far less than that required to 

 break it under other conditions. The velocity of this wave 

 in glass is nearly 3,000 metres per second. The rate of 

 explosion of equal volumes of cyanogen and oxygen is 

 2,728 metres per second ; when this mixture is diluted with 

 its own volume of nitrogen, the rate of explosion falls to 

 2,163 metres per second. In the diluted mixture, therefore, 

 there could be no question of the waves coinciding in rate. 

 The reduction of pressure caused by dilution made the 

 measurement more accurate, as it enabled us to find glass 

 of more nearly equal strength holding and breaking 

 respectively. After several trials a piece of uniform tube 

 was found which broke, and a slightly thicker one which 

 held. Two pieces of the first broke at the following 

 pressures : — 



1. 950 lbs. on square inch. 



2 - 9 2 5 » 



mean 938 „ ,, ,, = 63 atmospheres. 



Two pieces of the second broke : — 



1. 1230 lbs. on square inch. 



2. 1250 „ 



mean 1240 ,, „ „ = 84 atmospheres. 



The lower limit viz., 63 atmospheres, is rather higher 

 than the pressure calculated by Dixon's formula. 



