664 



Dr. S. R. Milner on the 



The cell used for these experiments was composed of a 

 mixture of mercurous nitrate and nitric acid with mercury 

 electrodes contained in four beakers, WXYZ (fig. 3), con- 



Fiff. 3. 



nected in series by siphons. In W was the mercury anode A 

 surrounded by a glass tube, and in X a free electrode of 

 mercury B, both under a solution of *0001 normal Hg 2 (N0 3 ) 2 

 in *1 normal HN0 3 ; in Z the cathode, C, a large mercury 

 surface under a half saturated solution of mercurous nitrate 

 in *5 normal HN0 3 (this rendered the cathode practically 

 unpolarizable) ; and in Y a solution of *1 normal HX0 3 , the 

 purpose of which was to prevent the diffusion of any appre- 

 ciable amount of mercurous nitrate from Z to X. 



The measured E.M.F. of this cell was *0545 volt; and in the 

 first experiment it was simply short-circuited through a gal- 

 vanometer of 2900 ohms resistance and of known constant. The 

 resistance of the cell itself between A and C was 4400 ohms, 

 measured with the telephone and bridge*, so that the initial 

 current produced should be 



■0545 



4400 + 2900 



7*46 x 10 -6 ampere. 



The actual current at any time can be accurately represented 

 by the equation 



C = {6'33- 1-48 log 10 (* + -172) } x 10" 6 ampere, . (30) 



^ being the time in minutes. This may be seen from the 

 following table of the observed values of the current and 

 those calculated from (30). 



* The experiments on the mercurous-nitrate cells were made in 1899, 

 but not then published; this accounts for the difference between the 

 methods of measurement used here and those already describ ed used for 

 the silver-nitrate cells. 



