KXI'I.OSIONS ()! ciiAI. KAS AND AIR. 



399 



n-nt. tor reflection from the blackened surface of the bolometer. In the same figure 

 an- slmwii the (dotted) curves C, I), and S taken from fig. 14, which give the intrinsic 

 r:nli;iiire from 5!) cm., 30 cm., and 15 cm. of the hot gas after explosions of 15-per- 

 cent, mixtures in the vessel with black walls. The chain-dotted curves L and N 

 show tin- \alues of the intrinsic radiance from an infinite thickness of the gaseous 

 mixture calculated on the assumption that the absorption follows an exponential law 

 (see p. 398). 



On comparing Curves C and E, or D and F, we see that the 13-per-cent. mixtures 

 radiate more strongly in the initial stages of cooling than the 15-per-cent. mixtures 

 do when they have cooled to the same temperatures as the 13-per-cent. mixtures have 

 in this epoch, although there is about 15-per-cent. more radiating gas in the latter 

 mixtures. The same result was previously obtained when comparing at the same 

 mean gas temperatures the average rate at which radiation is absorbed by the 

 blackened walls per square centimetre when mixtures of from 10 per cent, to 15 per 

 cent, were exploded in the vessel (see fig. 9). 



It will be noticed that Curves C and I) (15-per-cent. mixtures) and E and F 

 (13-per-cent. mixtures) show precisely the same peculiarities. At maximum pressure, 

 and also in the initial stages of cooling, 59 cm. emit much more strongly than 30 cm., 

 while, later on, when the gas temperatures have fallen to about 1500 C. (abs.),* the 

 emission from 30 cm. is just as great as that from 59 cm. The following table gives 

 the ratio of the intrinsic radiance from 59 cm. of the hot gas to that from 30 cm. (at 

 the same temperature) up to yj, second after maximum pressure for both the 13-per- 

 cent, and 15-per-cent. mixtures in the vessel with black walls. Gas temperatures 

 and pressures at the same times are also given. 



TABLK XIII. Mixtures of Coal-gas and Air. 



* The times after maximum pressure taken by the 13-per-cent. and 15-per-cent. mixtures to cool to 

 1500 C. (abs.) are nearly equal. 



