RICHARDS AND LEWIS. — ZINC AND CADMIUM AMALGAMS. 



95 



In order to justify the use of this solid electrode one must show that 

 it always gives the same potential, and that this is equal to the true 

 potential existing between metal and solution. The first experiments 

 were made with a cell whose electrolyte was cadmium sulphate and 

 whose electrodes consisted of electrolyzed cadmium, of medium fineness, 

 which had been washed successively in dilute suli^huric acid, distilled 

 water, and absolute alcohol, and then dried. The two electrodes being 

 exactly similar, the electromotive force of the cell should be zero. Tlie 

 actual electromotive force, therefore, indicates the amount of deviation 

 in potential of electrodes of this kind. Several such cells were measured. 

 The largest electromotive force found was .0004 volt, the majority being 

 about .0001 to .0002 volt. Better results were obtained with metal 

 which, instead of being dried, was washed in the electrolyte. The differ- 

 ence of potential under these circumstances never exceeded .0001 volt 

 when proper care was used in preparation. Moreover no greater difference 

 was found when two electrodes made of entirely different samples of 

 electrolyzed cadmium were used. Since, therefore, the same potential 

 is obtained from such electrodes, whether the metal be in a finely divided 

 spongy state, or consist of a coarser network of crystals, this may safely 

 be considered the true potential of metallic cadmium. Similar experi- 

 ments were made with zinc, with equally satisfactory results. The data 

 given below illustrate the constancy of these electrodes. The electrodes 

 were usually not tested for any considerable length of time, the cells 

 being prepared anew for each series of observations, which only lasted 

 a few hours. Table IV. gives the electromotive forces of cells where 

 finely divided metallic cadmium was thus pitted against a dilute cad- 

 mium amalgam containing one per cent of cadmium. ' 



TABLE IV. Cadmium versus Amalgam. 



