MAXIMUM SPECIFIC ELECTRICAL CONDUCTIVITY IN CHEMISTRY. 123 
Hyprocutoric Acip AS AN ESTERIFYING AGENT. 
Consider a reaction such as that between oxalic acid and ethyl] alcohol mixed in 
equivalent proportions 
2C,H;OH + H,C,0, = (CH;).C.0,. 
The reaction from left to right is soon counterbalanced by the alteration in the 
concentration of the products, and equilibrium is reached long before the whole of the 
alcohol has been esterified. By constant withdrawal of the water formed during the 
process the esterification may approach completion. But the same end can be attained 
in another way, without the removal of the water, viz. by passing HCl gas into the 
mixture. By doing this, the chemist substitutes a system in which, as a result of the 
progress of the reaction from left to right, a great gain in specific conductivity is 
possible, for a system in which little or no such gain is possible. The tendency towards 
maximum specific conductivity is brought into play, and becomes the predominating 
factor, and the velocity of the reaction from left to right is therefore much greater. 
The possible gain in specific conductivity (y=K,,...—K) of the original mixture of 
alcohol and oxalic acid is very small, while that for the mixture containing HCl in 
addition is much greater. So long as the hydrochloric acid solution is ultramaximal, 
the dilution due to formation of water implies a gain in conductivity, but in premaximal 
solutions the case is reversed. Thus :— 
(a) In dilute premaximal solutions hydrochloric acid accelerates catalytically the 
hydrolysis of esters. 
(b) In concentrated ultramaximal solutions it favours the esterification of Alcohols 
by weak acids, instead of itself forming an ester. 
In (a) there is a gain in conductivity due to the increase of the concentration of 
hydrogen ions. In (b) there isa gain in conductivity due to the decrease in the 
number of molecules which, being mostly associated and not split up into free ions, e.g. 
(H,C,0,) and (C,H,O), lower the conductivity of the strong acid, while at the same 
time the water formed by the reaction greatly increases the specific conductivity, by 
diluting the highly concentrated ultramaximal acid solution. Were the strong acid 
itself to form an ester, there would not be this great increase in conductivity. 
#H,0,0, + 2a0,H,OH + yHCl = a(C,H,),C,0, + yHCl + 20H,0. 
Action oF HyprocEN CHLORIDE oN EruyL ALDEHYDE, ALDOL, AND 
Croronic ALDEHYDE. 
When acetaldehyde is treated with hydrochloric acid of the concentration of 
maximum conductivity, or with a rather more dilute solution, aldol is formed. 
