Lost Pressure in Gaseous Explosions. 19 



explosion cylinder remains constant for long intervals. This 

 persistence of pressure can, however, be possibly explained, 

 as shown later, by consideration o£ the transfer of energy in 

 the molecules of the products of combustion, after the act of 

 coherence by which new molecules are formed. 



In slow combustion a certain portion of the total energy 

 of combustion is given to the products as heat, the amount 

 depending eventually upon the equipartition of energy. In 

 almost all physical processes into which consideration of 

 equipartition enters, the transfer of energy is from translation 

 to rotation or vibration. But in the act of combustion 

 forces (of cohesion) are suddenly introduced which materially 

 influence the method of transfer of molecular energy from 

 one form to another. There cannot be a rise in the number 

 of degrees of freedom sufficient to account for the deficiency 

 in translational energy. In several cases a rise from 7 to 

 12 degrees each sharing the energy equally is necessary, 

 and this does not occur, for it has been shown by Hopkinson* 

 and David t that the energy radiated up to the point of 

 reaching the maximum pressure is only 3 per cent, of the 

 total energy of combustion, and further, the increase in the 

 possible degrees of rotation is at most three. 



(2) Simple case leading to a mean efficiency of 

 explosion of \. 



The mechanics of two colliding and cohering spheres show, 

 however, that in such a case there may be a rise in the 

 rotational molecular energy at the expense of the trans- 

 lational, and this of an order which may account in part 

 for the lost pressure. 



In the explosion of a hydrocarbon gas carbon monoxide is 

 probably first formed J, and the atomic weight of carbon is 

 12 and of oxygen 16. Take for simplicity of treatment two 

 spheres of equal mass moving into union with equal velocity 

 v, having angular velocity &>, and having equal translational 

 and rotational energies before collision. If their approach 

 is in opposite directions in the same straight line, the trans- 

 lational energy is all converted into vibrational energy at 

 the moment of collision, the total rotational energy either 

 remaining the same as before contact, or if cheeked also 

 adding to the latter. 



* Proc. Roy. Soc, A. vol. lxxix. p. 138. 



t Phil. Trans. Roy. Soc, A. vol. ccxi. p. 375. 



X H. B. Dixon, Phil. Trans, clxxxiv. p. 97 (1893). 



02 



