THE DEVIATIONS FROM THE FORMULA OF CADY. 59 



the volumes, and the heat of dilution was found to be 52 joules for an 

 amalgam equally concentrated. Hence 



* ^T ln Vj ^ = 0.00085 volt 



p = 0.00027 volt 



Difference 0.00058 volt 



This value has even a larger percentage accuracy than the one computed 

 for cadmium, and like that one can not but signify a real discrepancy. 



Because in neither case, then, the equation of Cady was found to hold 

 exactly true, it is clear that some modifying influence must be at work. It 

 does not by any means follow that the effects depicted by Cady's equation 

 do not really represent part of the influences producing electromotive force ; 

 but clearly this equation does not contain a complete or exact account of 

 all these influences. 



THE PROBABLE CAUSES OF THE DEVIATIONS. 



It becomes now a matter of great interest to speculate concerning the prob- 

 able cause of the discrepancy ; for an uncomprehended irregularity is always 

 suggestive of unknown but possibly knowable effects. 



Many possible superposed effects have been suggested as capable of modi- 

 fying results of this kind. Of these the most important may be discussed 

 in general before proceeding to particulars. 



In the first place, it has been suggested that the space occupied by the 

 dissolved substance should be taken into consideration. This was first sug- 

 gested, perhaps, by A. A. Noyes, 63 when working with Ostwald, and has 

 received striking support in the recent osmotic experiments of H. N. Morse 

 already cited. The further suggestion of Noyes, that the volume of the 

 molecules of solvent also should be subtracted, is of a more hypothetical 

 nature, and seems to receive less support from the facts. 



Secondly, the suggestion of compounds of solvent and solute (hydrates in 

 aqueous solution, or hydrargyrates in mercurial solutions) has been made to 

 explain many phenomena of the two classes of solutions. Marignac, de 

 Coppet, and Rudorff all considered this possibility and inclined toward it 

 long ago. More recently H. C. Jones has revived the theory ; and Haber's 

 recent extension of it to mercurial solutions has already been discussed. 

 There is nothing unreasonable in this idea. 



Thirdly, it is conceivable that although the amalgam holds most of its 

 dissolved metal in a monatomic form, a part remains polymerized, or in a 



Noyes, Zeitschr. Phys. Chem., 5, 53 (1890). 





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