TECHNIQUE OF ELECTROCHEMICAL MEASUREMENTS 459 



in series, very satisfactory. The potential derived from these is 

 measured against a standard Weston cell just before and just after 

 every reading. The potential provided by the Gladstone-Lalande 

 cells is quite sufficiently constant during the progress of an obser- 

 vation, provided they are always short-circuited for 15 to 20 

 minutes beforehand. 



The electrodes are platinized with Lummer and Kurlbaum's 

 solution. They are very carefully washed, both within and with- 

 out, between the observations, first in a stream of distilled water 

 and then in the solution in which they are about to be immersed; 

 every few days, if they are in constant use, they should also be 

 washed in chromic and sulphuric acid solution and then, after 

 thorough washing in a stream of distilled water, allowed to soak 

 for 12 hours in distilled water. From time to time they should be 

 replatinized. 



Induct or iiim 



Weston Cell 



Gas Chain 



-Hllh- 



Dry Cells 



Short Circuiting Key 



,1 



Bridge Wire 



Telephone 



Gladstone-Lalande Cells 



The conductivity-vessel which I employ is of the Kohlrausch- 

 Holborn type, with a thermometer dipping into the fluid between 

 the electrodes. This is immersed in the same water-bath as the 

 gas-chain, and the conductivities of the solutions are measured at 

 exactly 30 degrees. The electrodes are platinized with Lummer 

 and Kurlbaum's solution. The same bridge-wire is employed for 

 determining the conductivities and for determining potentials. A 

 telephone is employed to detect the zero-point and the alternating 



