I50 Mr. Harold B. Dixon on * 



of the molecules concerned I have made the following 

 assumptions : — 



(i) That the explosion- wave is carried forward by the 

 movements of molecules of density intermediate between 

 that of the products of combustion and that of the unburnt 

 gas ; (2) that the temperature of the gas propagating the 

 wave is double that due to the chemical reaction alone ; 

 (3) that the temperature is increased when the chemical 

 volume of the products is larger, and is diminished when 

 the chemical volume of the products is smaller, than that of 

 the initial gases ; (4) that the gases are heated at constant 

 volume, and their specific heats remain constant at high 

 temperatures. On calculating out the mean rate of transla- 

 tion of the molecules on these assumptions one arrives at 

 numbers greatly in excess of any of the observed rates of 

 explosion ; but some of the observed rates agree with tJie 

 velocity of sound m. a gas of the temperature and density so 

 calculated. For instance, when one volume of cyanogen is 

 exploded with an equal volume of oxygen, two volumes of 

 carbonic oxide are formed and one volume of nitrogen : — 



Taking the quantity of heat evolved as 126,100 calories, 

 and the specific heat at constant volume of the products 

 of combustion as 4"8x3 = i4"4, the temperature produced 

 by the chemical change is 8,694°C. If the gases were 

 initially at 13°, or 286° above absolute zero, the chemical 

 reaction would raise the temperature to 8,980°. But since 

 three molecules are formed where two previously existed, 

 the temperature is further raised by the heat developed in 

 compressing three volumes to two. This will raise the 

 temperature to 10,595°. ^t double this temperature the 

 mean rate of translation of a molecule of the mean density 

 of the burnt and unburnt gases would be 3,892 metres per 

 second. If the formula for the velocity of sound under 

 ordinary conditions held good in the explosion, the velocity 



