EXPLOSIONS OF COAL-GAS AND AIR. 



403 



Mack Ixxly at the same temperature, BO that, if we assume that the width of the CO 

 emission bauds do not change with temperature, the total emission would vary approxi- 

 mately according to PLANCK'S formula for a single wave-length of 4'4/u. At these low 

 temperatures, however, the variation of PLANCK'S formula for radiation of wave- 

 length 4'4/u with the absolute temperature 6 is very nearly proportional to the 

 variation of 8* with 6, so that it is not possible to say whether at the high tempe- 

 ratures the emission from the CO, would vary according to PLANCK'S formula or the 

 fourth power law. 



Effect of Density on the Transparency and Emissive Power. 



The same experiments were repeated with 15-per-cent. mixtures of coal-gas and air 

 at various densities varying from half an atmosphere to one and a quarter atmo- 

 spheres. The experiments were not carried further for it was questionable whether 

 the fluorite would stand very much higher pressures. These experiments showed 

 that the ratio of the emission by 59 cm. (or 30 cm.) when the walls are reflecting to 

 that when the walls are black decreases as the density increases. For example, at 

 2200 C. (abs.) this ratio for 59 cm. is 1'48 at atmosphere density, 1'25 at f atmo- 

 sphere, and 1'19 at l atmospheres, and for 30 cm. at the same temperature it is 1'35 

 at atmosphere, 1'15 at f atmosphere, and 1'06 at 1^ atmospheres. It will be noticed 

 that these ratios are always greater for 59 cm. than they are for 30 cm. thickness. This 



TABLE XVII. 15-per-cent. Mixtures of Coal-gas and Air. Fluorite Window. 



Walls Black. 



is also true of the experiments made with the gaseous mixture at atmospheric density, 

 as will be seen on comparing the figures in the second and third columns of Table XI. 

 This is partly because the transparency of the gas when enclosed in the vessel with 

 reflecting walls is greater than it is when the gas is enclosed in the black- walled 

 vessel, and probably partly because the measurements of the intrinsic radiance from 



3 F 2 



