Explosive Gases and Gaseous Mixtures. 331 



molecule with internal energy adequate for combination loses 

 this energy if its free path is relatively long ; that is, given 

 sufficient time though very brief, the molecule assumes a con- 

 dition unfavorable to chemical union. 



Let us now see if other phenomena are explained by this 

 hypothesis, considering first the case of an electric spark in 

 detonating gas at a pressure too low for explosion. Here we 

 have an enormous number of molecules combining in the 

 luminous path of the spark. These radiate energy, part being 

 electrical in its origin, i. e., a portion which was derived from 

 the external work done upon the gas, and part resulting from 

 chemical union. These encounter neighboring molecules of 

 hydrogen and oxygen, imparting to some of them energy ade- 

 quate for combination. Of these last a part combine, and we 

 have now to consider a portion of gas consisting of water 

 molecules, as well as those of hydrogen and oxygen. Some of 

 the last named possess energy adequate for chemical union, but 

 their encounters are too infrequent to restore by the heat of 

 combination the energy radiated, hence the change proceeds 

 with diminishing speed and finally ceases to propagate itself. 



Feeble sparks do not explode detonating gas at a pressure of 

 half an atmosphere or even more, but they cause slow combi- 

 nation. In this case it is not necessary to consider the possi- 

 bility of the hydrogen carrying the electricity, since water 

 molecules are formed, and we need only take into account a 

 system made up of a relatively small number of nascent mole- 

 cules of water, molecules of hydrogen and oxygen having 

 energy adequate for combination, together with a relatively 

 large number of molecules of these gases not having such 

 energy. Under these conditions the impacts resulting in 

 chemical union are too infrequent to maintain by the heat of 

 their combustion the energy lost by radiation, and conse- 

 quently the change does not propagate itself and cause an 

 explosion. 



Carbonic oxide and oxygen combine slowly at pressures less 

 than an atmosphere when subjected to feeble sparks. Here 

 too the impacts of molecules with a velocity adequate for 

 chemical union are infrequent, as is evident from the fact that 

 the change does not propagate itself. 



In the case of cyanogen and oxygen either the feeble spark 

 causes no chemical union, which is improbable, or as in the 

 previous instances the change does not proceed throughout the 

 gas because of the infrequency of impacts of high velocity 

 molecules. 



The study of the phenomena of explosives involves the 

 thermal effect, but for the present purpose the heat evolved 

 by the explosion or decomposition of equal volumes will suffice. 



