A72 TRANSACTIONS OF SECTION B. 
No flame better illustrates the relation of strueture to chemical processes than 
that of cyanogen, where the two steps in the oxidation of the carbon are clearly 
marked out in colour. Apart from hydrocarbon flames, very few others have been 
carefully explored from this point of view. There is, unfortunately, no gas 
composed of two combustible gaseous elements; and, though such gases as the 
hydrides of phosphorus and sulphur do not fall far short of this, the experimental 
difficulties of an exact exploration of their flames are very great. We are thus 
prevented from studying the flame of a composite combustible in its simplest form, 
The flames of hydrocarbons have naturally been the subject of most frequent 
investigation. The use of single hydrocarbons instead of the mixtures present in 
coal-gas and other common combustibles has simplified the study considerably. 
Two problems stand out prominently: one is to trace the steps in the oxidation of 
the hydrocarbon, the other to account for the bright patch of yellow luminosity. 
With regard to the question of the luminosity, [ do not think there is any longer 
doubt about its being due essentially to the separation within the fame of minute 
solid particles of what is practically carbon. The separation seems to be 
adequately explained by the high temperature of the blue burning walls of the 
flame, which decomposes the unburned hydrocarbon within. In a similar way 
areenic and sulphur and phosphorus are liberated within flames of their hydrides ; 
but these elements, being volatile, do not appear as solids unless a cold object be 
placed within the flame. In the case of the hydride of silicon the liberated 
element at once oxidises to form the solid non-volatile oxide, which gives a bright 
glow. 
The mode in which a hydrocarbon yields carbon by the application of a high 
temperature has been the subject of experiment and of hypothesis; but neither 
the view of Berthelot, that the carbon results from a continuous coalescence of 
hydrocarbon molecules with elimination of hydrogen, nor that of Lewes, according 
to which the formation and sudden decomposition of acetylene is the essence of 
the phenomenon, appears to me to be in harmony with the experimental facts ; and 
I am not aware that either view has secured any support from other workers 
in this field. It is certainly not easy to ascertain experimentally the changes 
undergone by a single hydrocarbon as its temperature is raised, and at the last it 
may be objected that the course of events in contact with the solid walls of a 
containing vessel is not necessarily the same as that within the gaseous envelope 
of a flame. I am glad to think that there is promise of further light on this 
subject from the work of Professor Bone. 
The course of oxidation of hydrocarbons has been the subject of very careful 
and fruitful study. The old view that a selective or preferential oxidation of the 
hydrogen always took place, that with a restricted supply of oxygen the hydrogen 
was oxidised and the carbon set free, is, I think, no longer maintained by anyone 
who has studied the question, The explosion of ethylene with its own volume 
of oxygen, which leaves us with practically all the carbon oxidised and all the 
hydrogen free, is fatal to this view. Again, when hydrocarbons are burned in a 
flame with a restricted supply of air, as is the case in the inner cone of the flame 
of a well-aérated Bunsen burner, there is clearly no separation of solid carbon, 
and the products of combustion when withdrawn and analysed disclose the 
presence of much free hydrogen and no unoxidised carbon. In describing this 
experimental fact I have spoken of it as the preferential oxidation of carbon. I 
have always thought it pedantic to quarrel with that expression; for, in speaking 
of a chemical transaction, we usually include only a description of the initial and 
final states of combination. I should be sorry, however, to detach the expression 
from the facts it describes and to exalt it into a general doctrine. That would be 
quite inadmissible, and, if there is any danger of misunderstanding, it would be 
better to avoid using the expression. 
The admirable researches carried out in the University of Manchester by 
Professor Bone and his collaborators have afforded most valuable information as 
to the oxidation of hydrocarbons at temperatures extending from those of 
incipient oxidation up to the highest ones that prevail in a flame. According to 
Professor Bone, the oxidation of a hydrocarbon involves nothing in the nature of 
