ON GASEOUS EXPLOSIONS. 221 



of a second after ignition commences, or 0'35 cal. in the first tenth 

 after maximum pressure. These are quantities of the same order 

 of magnitude, and differ in the right direction from the value deduced 

 above. They may be regarded as confirming the validity of both 

 methods of estimating the absolute value of the radiation loss. 



In applying these results to an internal-combustion engine, it must 

 be remembered that the radiation is not in fact strictly homogeneous. 

 There are considerable variations of temperature, which affect the 

 quality of the radiation. It appears probable that luminous carbon, 

 giving a continuous spectrum, may separate in rich mixtures, especially 

 if not perfectly uniform. These variations would tend to increase the 

 effective transparency of the flame, and the increase of radiation-loss 

 with dimensions. Further investigation will, doubtless, elucidate these 

 points. But, in so far as the flame tends to absorb its own radiation 

 selectively, the theory above sketched may serve a useful purpose as a 

 first approximation. 



APPENDIX B. 



On Radiation in a Gaseous Explosion. By B. Hopkinson. 



In the First Beport of the British Association Committee on 

 Gaseous Explosions attention was drawn to the probable importance 

 of radiation in determining the rate of cooling of the mass of hot gas 

 produced by igniting an inflammable mixture in a closed vessel. In 

 the Second Beport reference was made to some experiments which I 

 had made on the effect of coating the walls of the explosion vessel with 

 bright tin-foil. It was found that if a mixture of coal-gas and air of 

 given composition were exploded in a vessel thus lined the maximum 

 pressure reached was the same within one per cent, as that given by an 

 identical mixture when the tin-foil lining was blackened, but the rate 

 of cooling was decidedly less. An experiment was also described in 

 which an attempt was made to measure the actual heat absorption of 

 the walls and the radiation by means of a bolometer of copper strip, 

 whose temperature was recorded photographically during the progress 

 of the explosion and of cooling, the strip being in different experiments 

 blackened, polished, and placed behind a gas-tight screen of rock salt. 

 A considerable difference was found between the blackened and polished 

 surfaces in respect of heat absorption, and this difference was of the 

 same order as the heat absorbed by the bolometer behind the rock-salt 

 screen. The results were strong evidence that the effect of the tin-foil 

 lining on the rate of cooling was due to radiation, and gave an indication 

 of its order of magnitude ; but, as tin-foil is not a very good reflector, and 

 as the rock-salt plate was destroyed by the explosion so that only a 

 single experiment with it was possible, I have thought it desirable to do 

 some further work in the same direction. 



I have accordingly had prepared a cylindrical cast-iron explosion 

 vessel 30 cm. long by 30 cm. diameter, the whole of the interior 

 surface of which is plated with silver, and I have compared the 



1910. Q 



