296 



ELECTRICAL MEASUREMENTS 



kept at a uniform temperature and not disturbed, for then the 



zinc sulphate crystals gradually 

 unite in a compact mass. 



The H Cell. A much more 

 satisfactory cell, designed by 

 Lord Rayleigh and known as 

 the H form, is shown in Fig. 

 170 which shows an hermetically 

 sealed cell; the zinc is used in 

 the form of an amalgam, and 

 the platinum terminals are 

 amalgamated to prevent acci- 

 dental contact with the elec- 

 trolyte. 



This cell has been thoroughly 

 studied by Kahle, and later in 

 this country by Wolff and 



Waters. The latest results show that with skilled manipulation 



FIG. 



170. H form of Clark 

 standard cell. 



Air Bubble 



Zinc Sulphate 



Crystals 



Paste 



Mercurous 



Sulphate 



Zinc Sulphate 



Mercury 



Zinc Sulphate 



Solution 

 Saturated 



Zinc Sulphate 

 Crystals 



Amalgam 

 10 % Zinc 



FIG. 171. Kahle H form of Clark cell, 

 it is reproducible to within a few parts in 100,000. This cell is 



