4 ELECTROCHEMICAL INVESTIGATION OF LIQUID AMALGAMS 



In this equation P and P' represent the unknown solution-pressures, 

 whose ratio alone is to be inferred, and p the osmotic pressure of the 

 appropriate ion in the electrolyte. The latter cancels, being common to 



P 



both electrodes, and the expression becomes ir= -p ln~^i . ^ no other 



source of free energy other than osmotic effect is present, - may be taken 

 as equal to and the equation reduces to ours. In this expression the 



Cl 



absence of association in the dissolved metal is assumed. Both Nernst's 

 expression and that given above are calculated on the basis of the 

 gram-atom. 



On the other hand, von Turin 4 and Meyer" expressed their equations 

 in terms of concentration, and calculated them on the basis of the electro- 

 chemical equivalent in terms of grams per coulomb ; and both introduced 

 the molecular weight (M or jn) of the dissolved metal although, to be 

 sure, von Turin seems to have accidentally omitted this quantity from his 

 final statement. 8 Their equation, reached in different ways, reads T 



gram-atomic -weight 



Bearing m mind the fact that their q meant - and that 



vr 



we have made the additional assumption (based upon the measurements 

 of many investigators) that M = gram-atomic weight, it is seen that their 

 form is essentially identical with that given above. Our form will be 

 called in future merely " the concentration-equation," as its ascription to 

 any one author might under the circumstances seem invidious. 



Attention should be called to the fact that Helmholtz, himself, insisted 

 that his original concentration-equation holds true only when there is no 

 heat of dilution involved in the reaction, 8 a condition reiterated by von 

 Turin. The same limitation applies, of course, to the equation in its 

 present simplified form ; but this limitation does not necessarily apply to the 

 equation of Nernst, involving solution-pressures instead of concentrations. 

 The term solution-pressure must be interpreted as including combined 

 effect of all the tendencies affecting the escape of the dissolved metal from 



4 von Turin, Zeitschr. phys. Chem., 5, 340 (1890) ; 7, 221 (1891). 



B G. Meyer, Zeitschr. phys. Chem., 7, 447 (1891). 



6 See von Turin on the bottom of page 221, Zeitschrift fur physikalische Chemie, 

 7 (1891). 



T By a coincidence of misprints, of which there are many in the papers of both 

 von Turin and Meyer, the decimal point of the factor 19.1 has been misplaced in 

 each case and reads 1.91. This mistake was inadvertently copied in reporting the 

 history of their work in Publication 56 of the Carnegie Institution of Washington. 



8 Helmholtz, Berliner Monatsbericht, November, page 713 (1877). 



