694 



RICE 



ART. L 



anode surface is unpolarizable. Thus a potassium chloride 

 solution is saturated with mercurous chloride; a sulphate with 

 mercurous sulphate, and so on.) The simple parabolic graph 

 for 0- and E is very far from being the rule. Thus while curve I 

 (Fig. 13) shows that an iV/20 solution of KCl nearly fits a para- 

 bola, a similar solution of KI (Curve II) is too steep in its 

 ascending portion; its maximum is lower than that for KCl and 

 corresponds to a larger value of E; beyond the maximum it 

 gradually approaches and merges into the KCl graph. Accord- 

 ing to the simple Helmholtz view, the mercury in its natural 

 state ought to be higher in potential than the KCl solution by 



an amount represented by OP, about 0.6 volt; but higher than 

 the KI solution by OQ, about 0.8 volt. Now if this were so 

 we would expect to find that a cell containing these two solu- 

 tions with a mercury electrode in each would give a P.D. of 

 0.2 volt; but it is known that the P.D. is much smaller than 

 this. If then we assume that because the curve is "normal" 

 for KCl there really is a P.D. of 0.6 volt between mercury and 

 KCl in the natural state, we must admit from the evidence of 

 the cell just mentioned that the mercury must also in the 

 natural state be above the KI solution by practically the same 

 amount. Hence, at the maximum state for the latter solution 

 (represented by Q), when according to Lippmann's result the 



