334 Mixter — Partial non- explosive Combination, etc. 



Recapitulation. 



Detonating gas, a mixture of carbonic oxide and oxygen, one 

 of cyanogen and oxygen, and other explosive mixtures of gases 

 do not explode below certain pressures when sparked: and the 

 decomposition of acetylene does not propagate itself at pres- 

 sures less than two atmospheres. In the path of the spark 

 chemical changes occur which do not extend throughout the 

 gases, and the same is true of a weak spark in the gases men- 

 tioned when under a pressure at which a strong spark explodes 

 them. It appears for reasons already stated that explosions do 

 not occur in the instances given only because of the infre- 

 quency of impacts of molecules having a velocity or internal 

 energy adequate for chemical union. In the rare gas the 

 impacts are less frequent than in a dense gas, the mean free 

 path is longer, and there is more time for a molecule with 

 energy adequate for combination to lose this energy by radia- 

 tion and to attain a condition unfavorable to chemical union. 

 Some of the molecules combine, but the heat of their union is 

 not sufficient to restore the energy lost by radiation and the 

 change is therefore not self-propagating. The same explana- 

 tion holds good for the phenomena of feeble sparks in a dense 

 explosive gas where in the path of a spark there are relatively 

 few molecules with energy adequate for combination, and 

 these collide with each other less frequently than with the 

 molecules not having such energy. In a dense gas a given 

 quantity and a degree of heat, that is, sufficient frequency of 

 molecular impacts, is requisite to secure spontaneous extension 

 of the change. 





