TOLMAN. — ELECTROMOTIVE FORCE PRODUCED IN SOLUTIONS. 145 



tried by Des Coudres. The method consists in the measurement of 

 the electromotive force produced between electrodes placed at the 

 central and peripheral ends of a rotating tube containing the electro- 

 lyte. An equation can be derived, connecting this electromotive force 

 and the transference number of the salt with the speed of rotation, the 

 density of the solution, and the molecular weight and the " partial " 

 specific volume of the substances involved, quantities which can be 

 independently determined. 



Some of the details of the construction of the rotating apparatus 

 may have general interest. A distinctive feature of the apparatus was 

 the method of driving the rotator as a "spinning top," which had not 

 been specially balanced and which was hung below its fixed point of 

 support. A simple arrangement of cords was devised for steadying 

 the shaft of the rotating top and preventing precessional motion. A 

 thrust bearing suitable for high speeds is also described. It consists of 

 a series of ball bearings which distribute the total relative motion. 

 An equation is given for calculating the dimensions of a rotating arm 

 of uniform strength with the cross section increasing in size towards 

 the center of rotation. 



With this apparatus measurements were made of the electromotive 

 force produced by the rotation of molal solutions of potassium, sodium, 

 lithium, and hydrogen iodides. As predicted from the equations, the 

 electromotive force was found to increase proportionately to the square 

 of the speed of rotation. From the data the transference number 

 was calculated for the four solutions, and found to agree as well as 

 could be expected, with the available results of other methods of 

 determination. 



It was pointed out in connection with a kinetic derivation of the 

 electromotive force relation, that the production of an electromotive 

 force by centrifugal force is a proof of the presence of free ions in an 

 electrolytic solution or at least of a certain degree of electrical polar- 

 ization in the molecules. 



The writer desires to express his gratitude to Professor A. A. Noyes, 

 the Director of the Research Laboratory, whose interest and support 

 made possible the completion of this research. Thanks are also due to 

 Professor Elihu Thomson and Dr. Sanford A. Moss of the General 

 Electric Company, through whose kind offices was loaned the steam 

 turbine used in this investigation. The writer also had the benefit of 

 Dr. Moss's extensive experience with high-speed rotation, and is in- 

 debted to Professor George B. Haven of the Institute for his assistance 

 in checking a large number of calculations of machine design which 

 were made before the final apparatus was constructed. 



VOL. XL VI — 10 



