Measurement of Electrical Conductivity. 237 
revolving drums, a difficulty which has also been emphasised recently 
by Hammer (15). 
A second method in which the same principle is used, namely, 
passing an alternating current through the electrolyte and rectifying 
it when passing it through the measuring instrument, is described 
by Morgan and Hildburgh (25). Their arrangement is indicated in 
the accompanying diagram and description (Fig. 3), from which it will 
be perceived that this method is also, though in a different way, one 
in which the unknown electrolytic resistance is compared with 
standard resistances, and which is therefore open to the same 
Fig. 4. Diagram to illustrate the arrangement of Morgan and Hildburgh 
(see Text). An alternating current generated at A passes through the electro¬ 
lytic resistance X. R is a large ordinary Ohm’s resistance. The current 
m easuring instrument G is put in series with the electrolytic rectifier E and so 
measured as a direct current. The electrolytic resistance is measured by 
replacing X with standard resistances which give the same deflection of G. 
errors as the method of the revolving commutators. Morgan and 
Hildburgh describe a modification of the method by which the 
measuring instrument can be standardised, but they describe it as 
not so accurate a way as that in which the resistances are compared. 
Simpler than any of the methods so far described would be the 
use of an instrument for measuring as such the alternating current 
actually passing through the electrolyte. One would then know 
