PRESIDENTIAL ADDRESS. A73 
a selective or preferential oxidation of the carbon or the hydrogen ; but it occurs 
in several well-detined stages, during which oxygen enters into and is incorporated 
with the hydrocarbon molecule, forming oxygenated intermediate products, among 
which are alcohols and aldehydes. The reaction, just referred to, between 
ethylene and an equal volume of oxygen is, according to Professor Bone, to be 
represented by the scheme: 
CH, CH.OH CH.OH H,C: 0 H,+CO 
ee -_ ee > ee —— > e 
CH, CH, CH.OH H.C: 0 H,+CO 
There can be no question about the facts on which this scheme is based, and they 
are a new and important addition to knowledge. 
It is a great aid to the study of chemical changes, when we can resolve them 
into stages, whether or not these stages be realisable under certain experimental 
conditions. In this way we can get a clear view of the relationship between the - 
action under one set of circumstances to the action under another set ; and in this 
way also we can often establish rational links between reactions which at first 
sight seem quite disconnected. Intermediate reactions are much used to elucidate 
cases of contact action, and in the processes of organic chemistry they are almost 
universally assumed. 
I am far from wishing to disparage these practices, but I think it important 
that we should realise how far we are dealing with convenient devices and how 
far with ascertained facts. The isolation of an intermediate product under one set 
of circumstances is in itself no proof that this product is transitorily formed 
when the reaction is proceeding under another set of circumstances; and if we 
were to assume generally that because we can represent a chemical transaction as 
if it were due to a successive construction and destruction of a series of molecular 
edifices it actually does take such a course, we should, I think, be making the 
same kind of mistake as to suppose that in the application of two differently 
directed forces to a body at rest, the body will move successively in the direction 
of each force instead of moving immediately in the direction of their resultant. 
I know that I may be considered hypercritical, and perhaps obstinate, in this 
matter; but I wished to state the reasons that prevent me from accepting 
entirely the interpretation which Professor Bone has given to his experimental 
results, and to draw attention to a question of general importance that has not, 
I think, received the attention it deserves. 
The mode of burning of carbon, whether in the free state or as a constituent 
of a compound, is not at all easy to determine; and notwithstanding many 
investigations, among which must be specially mentioned those of Professor H. B. 
Dixon and his collaborators, so simple-looking a question as whether carbon forms 
carbon monoxide by directly uniting with oxygen, or only by reducing carbon 
dioxide, is still a matter of uncertainty. 
Our knowledge concerning the question of flame temperatures has been much 
improved in recent times, thanks mainly to the admirable work of M. Le Chatelier. 
The well-known memoir of Mallard and Le Chatelier on the explosion of gases 
supplied the data which first permitted of a moderately exact calculation of flame 
temperatures, and the perfection of the thermo-couple by M. Le Chatelier gave 
us the first instrument that could be used directly for making a satisfactory 
measurement. The uncertainty connected with this subject may be well illustrated 
by quoting the temperatures that have at different times been ascribed to the flame 
of coal-gas when burnt in a Bunsen burner, where we have had values varying 
from 1230° to 2350° C. 
The question of calculating the temperature attained during combustion by 
reference to calorimetric values, specific heat, dissociation, and other considera. 
tions is to form the subject of a joint discussion with Section G during the present 
meeting, so that I shall not here enlarge upon it. 
With regard to the use of thermo-couples, I may remark that the practical 
difficulties have been successfully met. The chief difficulty is, of course, to secure 
that the thermo-junction attains as nearly as possible the temperature of the 
