94 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



prediction was verified by experiment. Tliree similar cells were set up 

 with different electrolytes, (1) normal cadmium sulphate, (2) tenth nor- 

 mal cadmium sulphate, (3) normal cadmium iodide. The results are 

 shown in Table II. Theory demands 0.0286 instead of 0.0292. 



Cl(xss 2. 



The cells with electrodes of zinc amalgams were less constant in 

 potential than those with cadmium, and the measurements were less 

 trustworthy. Table III. gives the results with four cells of this tyjie. 

 The remarks on the preceding case apply here. 



TABLE III. Zinc Amalgams. 



Class 3. 



The measurement of the contact-potential of solid electrodes has 

 always been subject to considerable uncertainty, due to accidents of 

 crystallization, condition of surface, polarization, and other unknown 

 causes. It seemed possible that by sufficiently increasing the extent and 

 diversity of the surface an electrode might be obtained whose potential 

 would be the mean of a large number of different values, and therefore 

 constant. An electrode consisting of a quantity of finely divided metal 

 perhaps a centimeter in depth, packed loosely around a sealed-in platinum 

 wire seemed likely to satisfy the necessary conditions most nearly, and 

 experiments made with zinc and cadmium electrodes of this sort yielded 

 remarkably satisfactory results. 



