96 
Proceedings of the Boyal Society 
excess of the density of the solution thus formed over that of water 
(unity), is not constant, but increases, with greater or less rapidity, 
from the more dilute to the more dense. The work of previous 
experimenters on the electrical resistance of liquids is then reviewed 
at some length. Their chief difficulty has always been the elec- 
trolytic polarisation of electrodes. 
The solutions under investigation were put in a glass tube, which 
was narrow along the central part, but widened at the ends for the 
reception of platinum electrodes; and by means of connecting wires 
it was made to form one of the aims of a Wheatstone’s Bridge. 
High resistances were introduced into the other arms. The bridge 
was so arranged that the effect on the galvanometer could be ob- 
served the instant the battery circuit was closed, when for an in- 
definitely short period there is no polarisation. By successive 
passages of electricity, which were alternately in opposite directions, 
and between which the tube was short-circuited, opportunity was 
obtained of adjusting the resistances in the arms of the bridge, so 
that at last there was no deflection of the galvanometer needle due 
to the passage of the current. All measurements and observations 
were made at a temperature of 10° C. 
Nineteen solutions of zinc sulphate were examined. The re- 
sistances of very dilute ones are very great, hut fall off rapidly 
as the density increases, until it reaches about 1*08, after which 
they decrease much more slowly. At the density 1*2891, the 
specific resistance ( i.e ., the resistance between opposite faces of 
a cube, whose side is 1 cm.) is 28*3 B.A. units. The resistances 
of solutions from this density to that of saturation increase, 
that of the saturated solution being 33*7 B.A.U. That solu- 
tion, therefore, whose density is 1*2891, is the solution of maximum 
conductivity. By taking as ordinates the excess of the density 
of the various solutions over unity, and as abscissae their specific 
resistances, the relation between density and resistance is shown 
graphically. The curve thus obtained is symmetrical, about an 
axis passing through the point of maximum conductivity, and the 
part of it which lies between the origin and that point is an 
hyperbola whose asymptotes are inclined at an angle less than a right 
angle. 
Eleven solutions of copper sulphate were prepared and their 
