324 Dr. W. T. David on Heat-loss by Conduction 



Table IV. — Heat-loss by Conduction in a 9'7 per cent. 



mixture of Coal-gas and Air. 



Heat of Combustion of Coal-gas in Vessel = 10,600 calories. 









Heat lost by Con- 



Time 



Mean 



Heat lost by Con- 



duction expressed as a 



after 



Gas 



duction per eq. cm. 



percentage of the 



Ignition 



Temp. 



of Wall-surface. 



Heat of Combustion 



(sees.). 



(° C. abs.). 



(Calories.) 



of the Coal-gas in 

 Vessel. 



018 



16G0 

 (max.temp.) 



0-20 



11-0 



02 



1650 



0-31 



12-8 



0-25 



3580 



04 



165 



0-3 



1520 



0-47 



19-4 



04 



1390 



0-59 



24-4 



05 



1310 



067 



27-7 



The conduction- loss up to the moment of maximum tem- 

 perature, it will be noticed, amounts to 5*1 per cent, of the 

 heat of combustion in the 15 per cent, mixture, 5*5 per cent, 

 in the 12*4 per cent, mixture, and 11*0 per cent, in the 

 9*7 per cent, mixture. The much greater proportion of the 

 heat of combustion lost by conduction to the vessel-walls up 

 to the moment of maximum temperature in the weakest 

 mixture is due to the much greater "time of explosion" 

 which occurs in this mixture ; it amounts to 0*18 sec, 

 whereas in the 15 per cent, mixture it was only 0'05 sec. 



At 0'5 sec. after ignition the 15 per cent, mixture has lost 

 by conduction about 38 per cent, of its heat of combustion. 

 The 12*4 per cent, mixture at the same instant has lost about 

 34 per cent, and the 9*7 per cent, mixture about 28 per cent. 



The curves in fig;. 4 and data in Table V. show the rate at 

 which heat-loss by conduction is proceeding during the 

 cooling of the various mixtures after explosion. It will be 

 noticed that the weaker mixtures in the initial stages of 

 cooling lose heat by conduction rather more rapidly than the 

 stronger mixtures when they have cooled to the same mean 

 temperatures as the weaker mixtures have in this epoch *. 

 This is probably mainly due to convection currents, which, 

 having been set up during the explosion period, are more 

 vigorous in the initial stages of cooling than in the later 

 stao-es. 



* A similar result was obtained in an investigation into the radiation 

 loss (Phil. Trans. A. vol. ccxi.). 



