Chemical and Physical Papers. 67 



THE QUANTITATIVE ESTIMATION OF IRON AND COBALT 

 BY THE ROTATING CATHODE. 



By R. W. Curtis and S. A. McReynolds. 



'^^HE application of a rotating cathode to the analytical deterrni- 

 ^ tion of metals by electrolysis was introduced by Gooch in 

 1903, and the form of apparatus devised, and experiments with the 

 same, are described in several papers from his laboratory.* 



Mention is made that a rotating cathode had already been used 

 in the arts for the purpose of secu-ing compact metallic deposits in 

 electroplating. 



Soon after the appearance of the first paper the use of a rotating 

 anode for a similar purpose was described by Exner.f 



The apparatus used by Gooch and Medway consisted of a small 

 electric motor to the shaft of which, running in a vertical position, 

 was fastened a rubber stopper. An ordinary platinum crucible was 

 slipped on the stopper, electrical contact being made through a 

 strip of platinum connecting with the shaft. A beaker containing 

 the solution to be electrolyzed was raised upon a suitable standard 

 until the crucible was immersed to within eight or nine millimeters 

 of the edge. For anode a piece of platinum foil hung upon the 

 inside of the beaker was used.* 



The crucible serving as cathode was revolved from 600 to 800 

 revolutions a minute. The current varied from 0.8 to 4.0 amperes, 

 the corresponding current density per 100 sq. cm. being from 2.7 

 to 13.3. The time required for a determination was greatly dimin- 

 ished compared with that required in former electrolytic methods 

 in which the ordinary stationary electrodes are used, being, in the 

 case of copper, fifteen minutes on the average, zinc thirty minutes, 

 etc. The results for a larije number of experiments shown left 

 nothing to be desired, varying in most cases but one- or two-tenths 

 of a milligram from the correct values. 



The metals experimented with, the results of which are shown 

 in the above papers referred to, are copper, silver, nickel, cadmium, 

 tin, zinc, and gold. 



* Gooch and Medway. Am. Jour. Sci.. XV, 320 (1903). Medway, ib., XVIII, 56, 180 (1904), and 

 Zen. amorg. Chem. 35, 414. etc. 



tExner, Jour. Am. Chem. Soc, XXV. 806 (1903). 



