Lost Pressure in Gaseous Explosions. 25 



energy in terms of N = aN — VN 2 and the efficiency ratio 



a^-bW 



V = 



N? 



where q is the heat of combustion of a single molecule. 

 We should then have 



v = A-BN, 



and this is the equation of the line CD in the figure 2 

 obtained from the experimental results. 



(5) General relation of maximum pressure of explosion 

 to percentages of combustible gas. 



Let the percentage of combustible gas in a mixture be 

 represented by lengths from to M, M being 100 per cent. 

 Set up vertically at M a line MR to represent to any scale 

 unit volume of combustible gas. At set up OS to repre- 

 sent unit volume of oxygen. Join OR and MS. The 

 percentage P in the mixture giving perfect combustion is at 

 that point at which the ratio of the ordinates PQ/PT is that 

 of the volumes required for perfect combustion. P being a 

 fixed point the lengths of OS and RM are decided by taking 

 PQ and PT to a convenient scale in the correct ratio, and 

 producing MQ to S, OT to R. 



Fig. 3. 



R 



In the case of methane for example, which requires twice 

 its volume of oxygen for perfect combustion, PQ = 2PT. 

 Join OQ, then the ordinates of this line represent to a 

 certain scale the number of combustible units * in the 

 mixture below the point of perfect combustion, the ordinates 

 of QM of those above this point. Let U and L be the upper 

 and lower limits of inflammability. At the lower limit there 

 are FL combustible units, and they fail to ignite the mixture 

 because of the cooling influence of the mass of inert gas ; at 



* The combustible or explosive unit is defined as the aggregate of one 

 molecule of combustible gas and the oxj^gen molecules required for its 

 complete combustion. 



