Lost Pressure in Gaseous Explosions. 29 



advance in the same ratio as the upper limit. If the lower 

 limit advanced at the same rate as the upper the efficiency 

 would not be changed by compression. 



The efficiency of explosion is seen to be raised by initial 

 compression, and it should continue to rise indefinitely, a 

 point of practical interest in internal combustion engines, 

 which has led to discussion. 



(7) Summary. 



The total action in a gaseous explosion is a multiple of 

 that which occurs in the formation of a single molecule. 

 From the consideration of a diatomic case a value of ^ was 

 obtained for the ratio of translational energies before and 

 after formation. Experiment shows that this ratio varies in 

 a definite manner and that the mean of its values over the 

 working range in coal-gas, and in many other mixtures 

 giving perfect combustion, also approaches J. 



The suggestion now made is that the "suppressed heat " 

 in gaseous explosions may be explained by the influence of 

 forces of cohesion which come into action at the moment 

 of " contact " of two combining atoms. It would explain 

 (1) the cause of the lost pressure ; (2) the variation of 

 the efficiency of combustion with strength of mixture ; 



(3) the shape of the maximum pressure-percentage curves ; 



(4) the differences between the explosion efficiency of gases 

 having different limits of inflammability ; (5) the influence 

 of initial compression in raising efficiency of explosion, 

 as a consequence of the limiting shape of the efficiency 

 curves. 



After explosion the molecular translational energy of the 

 products of combustion in a closed vessel would fall more 

 slowly than in simple cooling of a hot gas in which equi- 

 partition is already established. This would have the same 

 influence on the pressure as after-burning, and may be the 

 cause, at least in part, of the maintained pressure observed 

 by Clerk in rich mixtures (in which, as shown above, the 

 pressure efficiency should be lowest), and of the prolonged 

 radiation observed by Hopkinson after the flame stage has 

 ceased. 



