Obituary Notices. 
545 
explaining chemical reactions, it is equally correct to represent 
such a reaction as that of hydrochloric acid on hydrate of potash, 
as consisting in an exchange of hydrogen of the one for potassium 
of the other, or of chlorine in one for peroxide of hydrogen in the 
other. In Mr Kay’s researches, as described in the following brief 
outline, this notion has obtained very striking illustrations ; for he 
has obtained a peculiar body in which the chlorine of chloroform 
is replaced by peroxide of ethyle by the action of chloroform on 
three atoms of ethylate of sodium, which product may be equally 
well conceived to be a body in which the hydrogen of three atoms 
of alcohol is replaced by the tribasic radical of chloroform. 
According to the older theories of the capacity of saturation of 
salts, this compound would contain a tribasic modification of 
formic acid, for it has the same relation to formic ether as a so- 
called tribasic phosphate has to a monobasic one.” 
It will be seen from the examples referred to that the leading 
principle of Williamson’s work was the then quite novel idea of 
the “ atomic value ” of radicals, which is exactly what we now 
call their valency, and that his favourite method was the forma- 
tion of intermediate substances as a guide to a knowledge of the 
constitution of the bodies between which they lie. This principle 
and this method led in Williamson’s hands to important develop- 
ment and simplification of chemical theory, and they still bear 
good fruit. 
Williamson’s influence on the progress of chemistry is not to be 
measured only by the work done directly by him ; every chemist 
who had the privilege of being his friend knows how much of his 
clear, intelligent knowledge of chemistry is due to Williamson. 
PEOC. ROY. SOC. EDIN. — VOL. XXVI. 
35 
