206 Dr. S. W. J. Smith on the Weston Cell 



§ 16. The Concentration of the Free Electrons in Platinum. 



The fact that the values of </>, given by measurements of the 

 thermionic emission and by the heating effect, are so nearly 

 identical would seem to indicate that it does net depend very 

 much on the temperature of the metal. It has been pointed 

 out by Richardson* that the temperature variation of <f> is of 

 importance in connexion with the determination of the con- 

 centration of the free electrons in a metal. The coincidence 

 of the two values of <£ would indicate that the value of the 

 concentration deduced from experiments on the thermionic 

 emission is not far from the truth. 



§17. ( 'on elusion. 



Further measurements on a series of metals are in progress 

 and the results will be published shortly. It seems desirable 

 to postpone further discussion of the results of the present 

 paper until the whole can be considered together. 



In concluding we wish to express our thanks to Messrs. 

 Baldwin, Carter, Critchlow, Ferger, Frederick, and Gibbs, 

 Honours Students in Physics, who have assisted us in taking 

 a number of the observations. 



Palmer Laboratory, 

 Princeton University. 



XV. The Limitations of the Weston Cell as a Standard of 

 Electromotive Force. By S. W. J. Smith, M.A., D.Sc, 

 Lecturer on Physics, Imperial College of Science and 

 Technology^ . 



§1. HPHIS paper contains an attempt to explain Mr. F. 

 JL E. Smith's recent experiments on the cadmium 

 amalgams of the "Weston cells % in terms of the theory of 

 solutions. 



The manner in which, according to this theory, the amal- 

 gams crystallize is indicated, and it is shown why, with this 

 mode of crystallization, the effect of the slowness of diffusion 

 is so pronounced, and also why sudden cooling to a tempe- 

 rature below the freezing point of mercury must produce a 

 comparatively uniform alloy. 



The cause of the most obvious differences between the 

 behaviour of the "chilled" and of the "slowly cooled" 

 amalgams is then at once apparent. 



* Phil. Trans. A, vol. ccii. p. 543 (1903) ; Phys. Rev. vol. xxvii, p. 528 

 (1908). 



t Communicated by the Physical Society 

 X Phil. Mag. Feb. i910, pp. 250-276. 



