RECENT ADVANCES IN SCIENCE 



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parison of yc values obtained from conductivity and ac values 

 obtained from electromotive force. The experimental work 

 consists of measurements of the E.M.F. of concentration cells 

 containing HC1 in aqueous solution at various concentrations 

 and temperatures, the cells being of the type 



Hydrogen electrode | HC1, Hg 2 CI 2 (solid) | Mercury electrode. 



The determinations have been carried out with extreme care 

 and cover a wide range of HC1 concentrations. If E x is the 

 E.M.F. of the above cell when the total concentration of HC1 

 is c\ and E 2 is that obtained when the HC1 concentration is 



c 2 then E2 — E1 — 2RT log 



OiCi 



a 2 c 2 



This equation involves the 



assumption that the activity of the hydrogen ion is equal 

 to that of the chlorine ion in each of the hydrochloric acid 

 solutions. If this is not valid then the calculated values of 

 ac represent the square root of the product of the activities 

 of the two ions. In the following table are given the most 



accurate data so far obtained for the conductivity ratio -JOi 



i.e., yc, and likewise for ac from E.M.F. measurements. It 

 has been provisionally assumed that at the lowest concentra- 

 tion employed, viz. 0*00167 molar, the a is substantially the 

 same as the 7, this assumption being necessary, as already 

 pointed out, in order to obtain a series of absolute values for 

 a. The conductivity values are partly those of Bray and 

 Hunt, Noyes and Falk, and Kohlrausch. 



Activity Coefficients and Conductivity-viscosity Ratios 

 for HC1 at 1 8° C. 



It will be observed that with increasing concentration the 

 values of both a and 7 fall, but a falls the more rapidly. That 

 is, the effective concentration of an ion is less than the value 



