EXPLOSIONS OF COAL-GAS AND AIR. 



:J81 



The dotted curves A' and B' in fig. 4 are the differentials of the radiation curves 

 A and H in the same figure. These curves show very plainly that the gas at the top 

 <>(' the cylinder radiates much more strongly than that at the bottom during explosion 

 (except for a moment just before the attainment of maximum pressure) as well as 



SSOO WOO S3O0 tSOO /fOO tOOO 

 Gas Temflem/are C absotuff 



Fig. 5. 



during cooling. The most interesting point, however, shown by these curves is that 

 the rate at which the gas emits radiation is less at the moment at which the mean 

 temperature of the gas is a maximum (which is the same as the moment of maximum 

 preasure) than it is some little time before. An examination of the curves shows that 

 the rate of emission of radiation is a maximum about 4*0 of a second before the 

 attainment of maximum temperature, the "time of explosion" being 0'18 second. 

 At this point the temperature of the gas is about 1600 0. (abs.), and pressure about 

 65 Ibs. per sq. in.', the maximum temperature and pressure subsequently attained 

 being 1700 C. (abs.), and 70 Ibs. per'sq. in. respectively. Prof. HOPKINSON,* 

 experimenting with a very much larger explosion vessel (of G'2 cub. ft. capacity), 

 found that in a 10-per-cent. mixture of coal-gas and air the flame completely fills the 

 vessel about 3*0 second before maximum pressure is attained, the "time of explosion" 

 being 0'2f> second. The preasure at this point was about 70 Ibs. per sq. in. and the 

 maximum pressure reached -$ of a second afterwards 82 ll>s. Thus it appeal's that 

 the maximum rate at which the gas emits radiation occurs very approximately at the 

 moment when the flame completely fills the vessel.t 



Experiments were next made with 15-per-cent. mixtures. The results are shown 

 in fig. 6, the radiation curves again showing the amount of radiation received in 

 calories per sq. cm. of surface at various times after ignition in the same three 

 positions, A, B, and C. The corresponding gas-temperature curves are also shown in 

 the same figure ; these were deduced from the preasure records after allowing for a 



* ' Roy. Soc. Proc.,' A, vol. 77, p. 389. 



t I have several records which show that the gas radiates most strongly some time before the attain 

 mi'iit of maximum pressure in explosions of from 10-per-cent. to 12-per-cent. mixtures. The period ot 

 the galvanometer is not sufficiently low to determine definitely whether the same thing happens in 

 stronger mixtures. 



