368 Professor Arthur Smithells [March 12, 



siderable, and the finger perceives no heat when held in the flame. 

 If the supply of phosphorus vapour be increased the number of 

 luminous molecules increases, the light becomes brighter, and the 

 temperature also rises in due proportion. 



In the case of hydrogen, which does not ignite at a low tem- 

 perature, it is impossible to get a cool sheet of flame, for by the 

 addition of a neutral gas, the molecules of nascent steam are soon 

 separated to such an extent that the energy liberated is insufficient to 

 keep the general temperature of the sheet up to the j)oint required 

 to stimulate sufficiently the combination of the incoming hydrogen. 



If the shell of burning gas, which constitutes what may be called 

 the foundation of a flame, is very hot, it is always possible that a 

 secondary source of light may be developed, due to a purely baking 

 process. This may affect the product of combustion itself, or the 

 unburned gas or some decomposition product. We might thus 

 anticipate that in the hydrogen flame light would come not only from 

 the steam, which is being formed, but also from the hydrogen within 

 the flame, which is subjected to intense roasting as it ascends. 

 This, however, does not appear to be the case. The occurrence of the 

 spectrum of hydrogen in that of the oxy-hydrogen flame was described 

 by Pliicker, but experiments undertaken by Professor Liveing,* 

 specially to test this question, have decided it in the negative. The 

 light of the oxy-hydrogen flame has been examined spectroscopically 

 by Professors Liveing and Dewar, Dr. Huggins and others, and the 

 spectrum is now attributed to water alone. 



The light of a hydrogen flame is very feeble compared with that 

 of most other flames. If we ask why this is so, we are asking almost 

 the same question that eighty years ago impelled Sir Humphry Davy 

 to the splendid researches which laid the foundation of our scientific 

 knowledge of flames. And it was the same question that fifty years 

 later led Dr. Edward Frankland to investigations of flame, which 

 rank second only to those of his illustrious predecessor. Curious to 

 know why an explosive mixture of coal gas and air within a safety 

 lamp burned with a pale blue flame, whilst coal gas ordinarily burnt 

 with a bright light, Davy, after a few simple experiments, concluded 

 that he was correct in his first surmise, viz. " that the cause of the 

 superiority of the light from the stream of coal-gas might be owing 

 to a decomposition of a part of the gas towards the interior of the 

 flame where the air was in smallest quantity, and the deposition of 

 solid charcoal which, first by its ignition and afterwards by its 

 combustion, increased in a high degree the intensity of the light." 

 Davy's final and general conclusion was that '* whenever a flame is 

 remarkably brilliant or dense it may be always concluded that some 

 solid matter is produced in it ; on the contrary, when a flame is 

 extremely feeble and transparent it may be inferred that no solid 

 matter is formed." 



* Phil. Mag. [v] 34, p. 371 (1892). 



