ON GASEOUS COMBUSTION. 



479 



always appeared perfectly intact in the photograph. Dixon's subsequent 

 photographic researches have demonstrated the abrupt suddenness 

 with which the gases attain the maximum temperature in detonation, 

 the intensity and short duration of luminosity, and the subsequent rapid 

 cooling, as compared with ordinary combustion. Moreover, high as 

 is the temperature attained, there is no evidence of any considerable 

 dissociation of steam in the wave, for, despite the instantaneous cooling 

 of the products, there is less than one per cent, of the gases left uncom- 

 bined after the wave has passed through electrolytic gas (2H 2 + 2 ). 



Influence of an Excess of an Inert Gas upon the Bate of Explo- 

 sion. — Writing Chapman's formula as follows: — 



2RJ 



V 8 =^[{(m-n)0p + mC»}C /) fo-r(Cp+C 1 .)A] 



and putting 



2RJ 



= A, and the terms between the square brackets = B, 



it will be immediately perceived that the addition of an inert diatomic 

 gas (e.g., H 2 , N 2 , or OQ to a given explosive mixture will affect the 

 values of both A and B, but not necessarily in the same direction. It 

 will increase the value of /*, and diminish the values of C v and Cp 

 partly by lowering the temperature in the wave and partly also (if steam 

 or carbon dioxide be formed in the wave) by reason of its own specific 

 heat being lower than that of the undiluted products. It will also in- 

 crease the value of m without altering (ra — n). If it be assumed that the 

 molecular heats of the three diatomic gases under consideration are, for 

 all practical purposes, equal at any given temperature, it will be at once 

 seen that an equal dilution of a given explosive mixture, with any one of 

 the three gases, whilst it will have an equal effect on all terms included 

 under B, may either increase or diminish the value of A, according as to 

 whether or not the plus effect of the lower value of Cv is counterbalanced 

 by the minus effect of the increase in /*. If the latter effect be small, as 

 would be the case with hydrogen as diluent, the value of A would on 

 the whole be increased ; whereas if the increase in fi were large, as 

 would be the case with nitrogen or oxygen as the diluent, the value of A 

 would on the whole be diminished. 



As an example of the probable effects of the equal dilution of a given 

 explosive mixture with each of the three gases in question, the case of an 

 equimolecular mixture of hydrogen and nitrous oxide, fired at 10° and 

 760 mm., may be cited as follows: — 



i i 2 



