ON ELECTROLYSIS IN ITS PHYSICAL AND CHEMICAL BEABINGS. 391 

 So, equating together the above two expressions for intensity of 



current, we get 



or. 



7 dv o -p. NU 

 (I 1) 



h dv rf 



JJ,=u + v=!l X -00010352 X lO* ; 



y being the intensity of current. 



Whence the arithmetic sum of the opposite velocities of anion and 

 cation (u and v), when urged by a slope of potential of one volt per centi- 

 metre, through a solution containing N monad gramme-equivalents of 

 active substance per cubic centimetre and of specific conductivity k 

 seconds per square centimeter, is 



A- 



M -ft) =10352— centimetres per second ... (2). 



So far the ground seems to me to be perfectly firm. 



"We now proceed to apply this to special cases. To do this we assume, 

 with Kohlrausch, first, that N=r?i, the quantity of salt in unit volume 

 of the solution ; second, that the ratios of the anion and cation velocities, 

 ujv, are known for a number of substances from Hittorf's classical 

 migration experiments. On these two assumptions a table of velocities 

 can be constructed. They vary, it is true, with kim, but this number is 

 fairly constant for very dilute solutions of many substances ; if it is not, 

 the concentration must be specified. 



The latest determinations of Kohlrausch ^ give the following numbers 

 for specific ionic velocities (in centimetres per second) in an aqueous 

 solution containing one-tenth of a gramme-equivalent of salt per litre, 

 the applied E.M.F. being 1 volt per centimetre. 



Cation . . . H K NH^ Na Li Ag ^Ba ^Mg ^Zn 

 v= -00300 -00057 -00055 -00035 -00026 -00046 -0"0033 -00029 -00026 

 Anion ... OH CI I NO3 CIO3 C2H3O2 



u= -00272 -00059 -00060 -00053 -00046 -00029 



Radicles omitted from this table, like SO4, PO4, &c., are intractable 

 or anomalous. 



JN'ow in the above calculation what is there hypothetical ? Accepting 

 for the present the direct Hittorfian view of migration, the assumption 

 that N=7)i involves two hypotheses, viz. : — 



(1) That the added salt alone is the active substance, the solvent 

 conducting none of the current. 



(2) That the whole of the added salt is equally active. 



On any dissociation view of electrolysis it could hardly be expected 

 that when two substances are mixed one should be wholly inert, the other 

 wholly active. It would seem much more probable, without evidence to 

 the contrary, that the two substances should dissociate each other in some 

 ratio or other, and that the conduction should be shared between them. 



If this be so, equations (1) and (2) still remain perfectly true, but it 

 is not so easy to determine N, the amount of active substance per cc. It 



' See memoir abstracted above, p. 337. 



