400 



Mil. W. T. DAVID ON THE RADIATION IN 



The intrinsic radiance from 59 cm. is from 15 per cent, to 25 per cent, greater than 

 that from 30 cm. for both the 13-per-cent. and 15-per-cent. mixtures in the initial 

 stages of cooling. This implies that the gas is very transparent to its own radiation 

 in this epoch. Prof. CALLENDAK, from his recent experiments on the radiation 

 emitted by different thicknesses of flame at atmospheric pressure, finds that in flame 

 the exponential law of al>sorption is closely ol>eyed.* He finds practically the same 

 coefficient of absorption, viz., 0'054, for two distinct states of flame (at different 

 temperatures) produced in Meker burners by varying the air supply. Reducing my 

 results to atmospheric pressure, on the assumption that the radiation and absorption 

 of a layer of gas whose thickness is inversely proportional to the density is constant, 

 I find that at -^ second after the attainment of maximum pressure the coefficient of 

 absorption in the 13-per-cent. mixture is O'OOS (temperature of gas 1960 C. abs.), 

 and in the 15-per-cent. mixture 0'0072 (temperature of gas 2210 C. abs.), whilst at 

 the moment of maximum temperature it is in both mixtures only about yfr of the 

 value found by CALLENDAR for flame. This extremely high transparency of the 

 gaseous mixtures at the moment of maximum pressure, and in the initial stages of 

 cooling, cannot be wholly due to the higher temperatures reached in the explosions, 

 for the transparency of the 13-per-cent. mixture in the initial stages of cooling is 

 much greater than that of the 15-per-cent. mixture at temperatures which the 

 13-per-cent. mixture has in this epoch, as will be seen from the following table. This 



TABLE XIV. Walls of Vessel Black. 



table gives the proportion of incident radiation transmitted by (ff x 30) cm. of the 

 13-per-cent. mixture and 30 cm. of the 15-per-cent. mixture; a layer of the 

 13-per-cent. mixture (if* 30) cm. thick contains the same amount of absorbing gas 

 (COj. H 2 O) as 30 cm. of the 15-per-cent. mixture. 



The following table gives the observed values of the intrinsic radiance from different 

 thicknesses of the 15-per-cent. mixture after explosion (from Curves C, D, and S), 

 and directly under them are given the values for the same thicknesses calculated by 



* Prof. CALENDAR'S paper on "Radiation from Flames" is given in the 'Third Reprt of the B.A, 

 Committee on Gaseous Explosions,' Appendix A, p. 1$. 



