118 PROFESSOR JOHN GIBSON ON 
matter, is undoubtedly associated with increased conductivity,* and the decrease in the 
conductivity of the gelatine film observed is probably due to the heterogeneity result- 
ing from the formation of insoluble gelatine. It is impossible without qualification to 
apply the rule to heterogeneous systems. 
There is an apparent similarity between the action of the short-wave electro- 
magnetic vibrations called “light,” in cases such as those above cited, and the action 
of the long-wave electro-magnetic vibrations on the coherers used in wireless telegraphy. 
In this case also there is a resultant increase in the conductivity of the system. 
Tae Seectric ELEcTROLYTIC ConpucTIvITY oF Goop ELECTROLYTES. 
The line of argument developed in this paper will be greatly facilitated by frequent 
reference to the graphs in Fig. I., which are obtained by plotting as ordinates the specific 
conductivity at 18° C. (K,,) of a number of aqueous solutions of electrolytes in 
ohm™ ¢.m.* against the concentration (I) in gram equivalents per kilo of solution 
as abscisse. The advantages of this mode of representing the concentration have been 
discussed in a previous paper.t 
The graph for HCl may be taken as typical. Starting at the origin with pure 
water, the specific conductivity rises as the concentration of HCl increases, but 
reaches a maximum (Kj. max, = 0°7646) at a concentration, according to Konirauscn, of 
(I= 5'0) 18°25 per cent., at 18° C. Beyond this concentration the specific electrolytic 
conductivity of the solutions falls off as the concentration increases. 
The exact concentration corresponding to maximum conductivity is not easily 
determined, as in the neighbourhood of the maximum the conductivity varies but 
slightly with concentration. 
For the sake of brevity, solutions of strong electrolytes will be referred to in what 
follows as being either maximal, ultramaximal, or premaximal, according as their con- 
centrations are equal to, greater, or less than those having maximum specific conductivity. 
BEHAVIOUR OF AQUEOUS SOLUTIONS CONTAINING HypROGEN CHLORIDE. 
Of all known solutions none surpass hydrochloric acid, at comparable concentration, 
in specific conductivity, and none show a higher maximum of specific conductivity. It 
is probable that no other solution has a higher ionic concentration or a higher specific 
conductivity than hydrochloric acid of maximum conductivity. 
The chemical properties of hydrochloric acid vary in a remarkable manner with the 
concentration. In dilute premaximal solutions hydrochloric acid behaves as a very 
stable acid. In concentrated ultramaximal solutions it is readily oxidised and acts as 
a reducing agent. In dilute premaximal solutions it favours hydrolysis. In highly 
* This is clearly recognised by Myer, loc. cit. 
+ J. Gipson, Trans, Roy. Soc. Hdin., 1905-6, vol. xli. p. 241. 
