116 PROFESSOR H. B. DIXON OX THE RATE OF EXPLOSION IN GASES. 
These curves plainly show that the retardation of the explosion-wave depends upon 
the density of the gas added as well as upon its volume—a result in accordance with 
Berthelot’s theory. 
I think it a fair inference from these facts to conclude, when the addition of a gas 
to an explosive mixture retards the rate of explosion by an amount wdrich depends 
upon its volume and density, that such added gas is inert as far as the propagation of 
the wave is concerned, and that any change which it may undergo takes place after 
the wave-front has passed by—in other words, is a secondary change. 
§3. Oxygen Inert to Carbonic Oxide in Explosion of Carbon Compounds. 
Tliis principle can be ajjplied to determine whether, in the combustion of gaseous 
carbon, the oxidation to carbonic acid is effected in one or two stages. If, for 
instance, the carbon is first burnt to carbonic oxide, which subsequently is burnt to 
carbonic acid, the rate of the explosion-wave should correspond with the carbonic 
oxide reaction retarded by an excess of oxygen ; whereas, if the carbon burns to 
carbonic acid directly, in one stage, then the rate of the explosion-wave should 
correspond with the complete and unretarded reaction. 
Now, if we adopt Berthelot’s theory as a working hypothesis, we can calculate 
the theoretical rates of explosion of marsh gas, ethylene, or cyanogen: (1) on the 
supposition that, with sufficient oxygen, the carbon buriis direct!}^ to carbonic acid, 
and (2) on the siqjposition that the carbon burns first to carbonic oxide, and the 
further oxidation is a subsequent or secondary reaction. On the first supposition, if 
100 represents the rate of explosion of these three gases with oxygen only sufficient 
to burn them to carbonic oxide, the addition of the oxygen required to burn the gases 
to carbonic acid should increase the rate of explosion :— 
Calculated rate of explosion when burnt to COo . 
Marsh gas. 
Ethylene. 
Cyanogen. 
104 
103 . 
107 
Whereas, if these gases really burn first to carbonic oxide, and the extra oxygen is 
inert in propagating the explosion-wave, then the addition of this inert oxygen Avould 
diminish the rate of explosion :—• 
Calculated rate of explosion when burnt to CO 
with inert oxygen present 
hlarsh gas. 
Ethylene. 
Cyanogen. 
92 
88 
i 
87 j 
The experiments show that if 100 be taken as the rate of explosion when the 
