320 Gooch and 2fedway — Rotating Cathode in the 



Art. XXXTI1. — The Use of a Rotating Cathode in the Electro- 

 lytic Determination of the Metals ; by F. A. Gooch and 

 II. E. Medway. 



[Contributions from the Kent Chemical Laboratory of Yale University— CXV.] 



The rotating cathode has been applied usefully in the arts 

 for the purpose of securing compact metallic deposits in elec- 

 tro-plating. In this case a soluble anode is employed and the 

 electromotive force of the current is generally low. So far as 

 we are aware, however, no attempts have been made heretofore 



to apply the rotating cathode in 

 analytical separations, in which it is 

 the object to remove the metal com- 

 pletely from solution. In such pro- 

 cesses the soluble anode is not used, 

 and the comparatively high electro- 

 motive force necessary to overcome 

 the resistances and to throw down 

 the metal with rapidity liberates 

 hydrogen from the water solution 

 simultaneously with the metal, 

 and the consequence is the pro- 

 duction of a deposit lacking in 

 compactness and adhesiveness. 

 This interference on the part of 

 the evolved hydrogen with the 

 regularity of deposition appears 

 to be the chief reason why low 



% ^^ ^*6i|H intensity and low density of cnr- 



Hi>w rent must be used in the ordinary 



electrolytic processes of analysis. We have made some experi- 

 ments, therefore, to see whether it is not possible to so far 

 avoid the interfering action of hydrogen by the use of the 

 revolving cathode as to secure with high currents and in a short 

 time deposits sufficiently adherent and homogeneous for ana- 

 lytical purposes. The results, as will appear, are successful. 



For a cathode we have used an ordinary 20 cm3 platinum 

 crucible rotating at a speed of from 600 to 800 revolutions a 

 minute. The crucible is driven by a small, inexpensive electric 

 motor fastened so that its shaft is vertical. Upon this shaft 

 the crucible is fixed by pressing it over a rubber stopper bored 

 centrally and fitted tightly on the end of the shaft (fig. A). 

 To secure electrical connection between crucible and shaft, a 

 narrow strip of sheet platinum is soldered to the shaft and then 

 bent upward along the sides of the stopper, thus putting the 

 shaft in contact with the inside of the crucible when the last 



