HISTORICAL INTRODUCTION. 3 



It may be remarked in passing that the difference between any two electro- 

 motive forces in the first table would give at once the potential of a con- 

 centration cell containing the two corresponding amalgams. 



In his theoretical discussion Lindeck calls attention to the fact that the 

 metal silver behaves like mercury from an electrochemical standpoint. 



The following year Ramsay 6 determined the molecular weights of almost 

 all known metals by measurement of the vapor tension of mercury over 

 their amalgams. In general the results were in agreement with the accepted 

 atomic weights of the various metals. Sodium and calcium, however, ap- 

 peared unmistakably smaller, suggesting the subdivision of their atoms, and 

 causing anxiety among some upholders of the atomic theory. 



In this same year Nernst published his well-known fundamental paper on 

 " Die Electromotorische Wirksamkeit der Ionen." This paper did not dwell 

 upon amalgam cells in particular, 7 but its application thereto is manifest. 



In April, 1890, von Turin 8 published a complete theory of amalgam con- 

 centration cells, as a possible means of determining the molecular weights 

 of the metals. He first considered a cell of the type 



Mercury, Mercuric salt, Amalgam of " noble " metal. 



Applying the osmotic theory developed three years before by van't Hoff," 

 he concluded that the electromotive force E was given by the equation 



E = 1.728 X io -4 (~) when T is the absolute temperature and -^ r the 



v V 273 V 



number of kilogram molecules of the metal in a cubic meter of mercury. 



The cell of the type 



Zinc amalgam concentrated, Zinc sulphate, Zinc amalgam dilute, 



required different mathematical treatment. Pointing out the analogy be- 

 tween such an element and the cells investigated by Helmholtz, he decided 

 that 



E = 9.5636 X io 5 Tqk log- 2 



where q is the electrochemical equivalent for zinc, k the ratio between the 



molecular weights of mercury and zinc, and -? the concentration ratio of 



c i 

 the amalgams. The paper, while very able, is somewhat marred by various 



minor errors, and contains no experimental data to support the formulae 



"Journ. Chem. Soc, 55, 521 (1889). 

 'Zeit. Phys. Chem., 4, 129 (1889). 

 8 Zeit. Phys. Chem., 5,340 (1890). 

 9 Zeit. Phys. Chem., 1, 481 (1887). 



