1913-14.] Obituary Notices. 287 
ammonium bromide, lithium bromide, and sodium bromide, are those 
determined by Gibson ; whilst for these experiments he devised his 
electrically controlled thermostat, which is a very perfect instrument 
of its kind. 
The main interest of his work, however, remains as before the study of 
the relation between maximum conductivity and certain types of chemical 
change. He showed, for instance, the close relation between this and the 
precipitation of salts from solution by hydrochloric acid ; the behaviour of 
aqueous solutions of hydrogen chloride towards dissolved oxygen and 
dissolved chlorine respectively; the oxidation of hydrogen chloride in 
aqueous solution by chromic acid ; the action of hydrochloric acid as an 
esterifying agent ; and the action of hydrogen chloride on acetal- 
dehyde, aldol, and crotonaldehyde, and of hydrochloric acid on cobalt 
chloride. In addition, he investigated the decomposition of aqueous solu- 
tions of hydrogen iodide ; the behaviour of nitric acid when exposed to 
light ; and, in more detail, the action of sulphuric acid on sucrose and on 
formic acid. In all these cases he proved quite definitely that the limit to 
which the reaction was carried was fixed by the point at which the system 
as a whole reached its maximum conductivity, and that many reactions 
were reversed on each side of this maximum conductivity point, proceeding 
in opposite directions when once the maximum of the curve had been 
passed. 
It is, of course, evident that there are a large number of reactions which 
are not governed by this condition, and this is one of the reasons why for 
many years Gibson hesitated to publish his results, as he wished to get 
some definite law by which he could distinguish between reactions which 
were governed by the maximum conductivity and those that were not. 
It is probably safe to say from his results that all chemical systems 
which are electrolytes tend towards the point of maximum conductivity, 
although there may be other forces at work which are sufficiently powerful 
to conceal this tendency ; but whenever we are dealing with balanced 
reactions in which a very small change of conditions will make the re- 
action proceed the other way, we find the maximum conductivity of the 
system is the governing condition. There can be no doubt that we have 
therefore to look for the widest application of this principle when dealing 
with plant and animal life, where we have such a delicate balance constantly 
occurring between two possible directions of chemical change. 
Gibson has shown the application of his theory to the change from 
sugar to starch, and again from starch to sugar, in the leaf of the plant, 
and he also made a considerable number of experiments — which, un- 
