Decomposition by Shock of Endothermic Compounds. 13 



compose the carbon bisulphide vapour filling a tube 600 mm. 

 long and 15 mm. diameter. Thorpe accepts Berthelot's 

 explanation, which he gives as follows : — " The shock of the 

 explosion communicates to the layer of gaseous molecules 

 in immediate proximity to the fulminate an enormous active 

 force, whereby the ' molecular edifice ' is shaken to pieces, 

 and the initial active force is augmented to a degree corres- 

 ponding to the heat evolved in the decomposition of the 

 gas. A new shock is thereby produced in the next layer, 

 and the action is repeated, and so propagated." 



According to this view, it would seem that the explosion, 

 once initiated in cyanogen, acetylene or carbon bisulphide, 

 should travel as far as the gas extends, and that the rate of 

 explosion should conform to the laws governing the propa- 

 gation of the explosion-wave in gaseous mixtures. It 

 appeared, therefore, of interest to determine whether the 

 explosion, set up by the shock of the fulminate, was propa- 

 gated along a tube filled with one of the gases ; and, if so,. 

 to measure the rate at which the flame was propagated. 



The experiments described below were carried out by 

 one of us — Mr. J. A. Harker. 



The first gas tried was acetylene. To produce the shock, 

 a mixture of acetylene and oxygen (2 vols, to 3), one of 

 the most violently explosive gaseous mixtures, was fired in 

 contact with the acetylene. A coiled leaden pipe, 13 mm. 

 in diameter and 20 metres long, was provided with a glass 

 firing-piece and tap at one end, and, at the other, a detachable 

 tube of strong glass and a second tap. The whole was 

 first filled with acetylene, and then a mixture of acetylene 

 and oxygen was driven in at the firing end so as to 

 form a column of about a metre in length. The taps 

 were then closed, and the mixture fired by a spark. The 

 explosion made the " ping " on the walls characteristic of 

 extreme violence, but the flame did not appear at the 

 further end of the tube. On examination it was found that 



