Mil. S. W. J. SMITH ON THE NATURE OF ELECTRQCAPILLAKY 1'IIKM'Mi \ \ 



more definite and more accurately measurable than tin- ascending jMU-tinns ; hut unless 

 the concentnition E.M.K. within the electrolyte is supposed to be the same for quite 

 different liquids subjected to very different degrees of polarization, there does not 

 seem to l>e any simple method of reconciling the results with the Warburg theory. 

 G. MEYER* has attempted to complete WARBURG'S theory of the phenomena by 

 supposing that the descending portions of the curves :uv produced by formation of an 

 amalgam between the mercury and the element forming the kation of tin- solution, 

 while Li i. . IN I has endeavoured to show that the descending branch of the curve 

 is absent when the solution does not contain hydrogen. The experimental evidence 

 adduced in favour of these views is mainly qualitative in nature. An extended 

 examination of the quantitative relation between the capillary curves for differently 

 concentrated solutions of the same salt shows that difficulties arise in the quantitative 

 application of the idea that the surface tension in the descending branch de]*nds 

 only upon the concentration of the amalgam ujxin the electrode surface. 



While it is unnecessary to deal with the nature of these difficulties at present, since 

 they do not immediately concern the experiments first discussed, it may be jointed 

 out that if the first hypothesis of the Helmholtz theory be true, it is possible to trace 

 (by means of the capillary curves) the relation U'tween the variation of the jx.tetitial 

 difference at the capillary electrode, the surface tension and the nature and concen- 

 tration of the electrolyte. Probably it is only by the investigation of the relation 

 l>etween these quantities that the value of the capillary curves, as a method of 

 determining "single potential differences" in voltaic phenomena, can be definitely 

 fixed. 



THE DISCREPANCY BKTWKKN mi: LIIM-MXXN HKLMHOLTZ THEORY AND THE NERNST- 

 PLANCK THEORY OF THE POTENTIAL DIFFEI:KS< i: BETWEEN SOLUTIONS. 



The result, derived from the Helmholtz theory, that the E.M.F. which must be 

 applied between the terminals of the electrometer to cause the capillary electrode to 

 assume its maximum surface tension, is equal to the natural potential difference 

 between the large electrode and the solution, is so important, if true, that this E.M.F. 

 has been observed for a large number of solutions. It is, however, impossible to test 

 directly the validity of the numbers so found, since no other independent means <.f 

 determining single potential differences has, up to the present, been discovered if we 

 except the dropping electrode method (which will Ixj referred to later). 



We may set up and measure the E.M.F. of a cell of the type 



MX. 



MX. 



* MrvKi:, WiM. Ann.,' 45, 1892. 

 t Luooix, ' Zeita. f. Physik. Chemie.,' 16, 1896. 

 I 2 



