1915] 



on Gaseous Explosions 



273 



and the chemical composition of the gas or vapour. If density of a 

 given gas and air mixture and the dimensions of the explosion vessel 

 and arrangement of the igniting point remain constant, then increase 

 in the initial temperature increases the rate of the spread of the 

 tiame. Any change in the chemical composition of the gas or vapour 

 also changes the fiame velocity. Increase in hydrogen proportion 

 generally increases flame velocity ; but it is also affected by the nature 

 of the gases forming a diluent. Even when hydrogen proportion 

 remains constant, the presence of carbonic acid gas as a diluent 

 instead of nitrogen changes the rate of flame propagation quite 

 ma-fcerially. Before considering these matters in detail, however, it is 

 desirable first to state the nature of the rising line. In all diagrams 

 from closed vessel experiments the rate of rise of pressure is first 

 slow ; then occurs a rapid increase towards the maximum pressure, 

 but the rate of increase diminishes rapidly as the maximum pressure 

 is approached. This is evident from the examination of Figs. 1, 8 

 and 4. 



Fig. 2 shows a number of rising curves taken by Messrs. Bairstow 

 and Alexander from gas and air mixtures containing 9 * 5 per cent of 

 coal gas, the initial pressures varying between 7 and 45 lbs. per 

 square inch absolute. 



Fig. 3 is a diagram taken by Prof. Petavel in a spherical bomb at 

 an initial pressure of 77*3 atmospheres or 1136 lbs. per square inch 

 and a maximum explosion pressure of 646 atmospheres or 9508 lbs. 

 per square inch, air gas ratio six. 



OO 0O5 



TIME, sees. 



Fig. 3. — Eise of Peessure dueing Explosion. (Petavel.) 



Spherical enclosure capacity, 551 • 9 c.c. Temperature of enclosure : 

 before firing, 18^ C. ; after firing, 24° C. Initial pressure, 77-3 atmos. 

 (1136 lbs. per sq. in). Maximum explosion pressure, 646 atmos. 

 (9508 lb. per sq. in.). Eatio ^^ = 6-0. Eatio - ^^^^^^^^ V^essuve 



Gas 



36. 



Initial pressure 



Fig. 5 shows the rising lines of mixtures of gas and air varying 

 from 7*79 per cent gas to 14 "98 per cent gas at an initial pressure 

 of 35*5 lbs per square inch absolute, also taken by Messrs. Bairstow 

 and Alexander, 



Fig. 6 shows a diagram taken by Prof. Hopkinson in the large 

 vessel referred to, the mixture being 9 of air to 1 of gas. On this 



