On the Influence of Atmospheric Pressure upon Combustion. 235 



This law is also proved to apply to gas, the illuminating power of 

 which has been doubled by naphthalization ; and consequently it may 

 be regarded as applying to all flames in which hydrocarbons are the 

 source of light. 



The investigation has also been extended to the effect of com- 

 pressed atmospheres upon the light of combustion. Great diffi- 

 culties were experienced in this branch of the inquiry, as gas could 

 not be used, and recourse must therefore be had to other combus- 

 tibles, which, as already pointed out, are liable to certain irregularities. 

 Owing to these and other difficulties, satisfactory determinations 

 1 could only be made between one and two atmospheres. In these 

 determinations, the lamp which replaced the experimental gas-flame 

 was supplied with amylic alcohol — a liquid which, whilst affording 

 an appreciable amount of light under one-atmosphere pressure, was 

 found to burn under two atmospheres without smoke, although at 

 a somewhat higher pressure it began to evolve unconsumed carbon. 

 The results obtained approximate closely to those indicated by the 

 above law, deduced from the corresponding determinations in rare- 

 fied atmospheres, as will be seen from the following Table, in which, 

 the mean of eleven observations is given under each experiment ; the 

 column headed " calculated" containing the numbers deduced from 

 the rate of variation of luminosity in rarefied air : — 



Pressure. 



Illuminating Power. 



Observed. 



Calculated. 



1 Atmosphere 



100 



2637 



261-3 



100 

 253 

 253 



2 Atmospheres second. . . . 



Further determinations, in which the illuminating power at three- 

 and four-atmospheres pressure was compared, yielded results differ- 

 ing widely from this law, and indicating a much more rapid increase 

 of light ; but as the liability to errors increases greatly at these 

 higher pressures, little confidence is placed in the numbers. The 

 lamp was fed with a mixture of five parts of vinic alcohol and one 

 part of amylic alcohol ; it had no appreciable illuminating effect 

 under ordinary atmospheric pressure : — 



Pressure. 



Illuminating Power. 



Observed. 



Calculated. 



3 Atmospheres 



406 

 959 



406 

 559 



R2 



