( 241 ) 



IX. — On the Relationship between Concentration and Electrolytic Conductivity 

 in Concentrated Aqueous Solutions. By Professor John Gibson. 



(MS. received May 11, 1905. Read November 6, 1905. Issued separately August 2, 1906.) 



Although great advances have been made during the last thirty years in our 

 knowledge of dilute solutions, there has been no corresponding advance in respect of 

 concentrated solutions. This is primarily due to the fact that hitherto no simple and 

 general relationship has been discovered between the conductivity and the concentration 

 of concentrated solutions of electrolytes. Ostwald's law of dilution holds only for 

 dilute solutions of weak electrolytes, and the formulae of Rudolphi and Van T'Hoff 

 are applicable only to dilute solutions of good electrolytes. It seems therefore 

 important to inquire whether the difficulty may not be to some extent overcome by an 

 alteration in the mode of representing the facts. 



Our knowledge of the facts is mainly derived from the classical researches of 

 Kohlrausch. The following discussion is based throughout on the data given by 

 Kohlratjsch and Holborn in Table I. of their invaluable compilation entitled 

 Leitvermogen der Electrolyte. 



The units adopted by Kohlraush are : — 



k = Specific conductivity in ohm -1 cm. -1 . 

 rj = Concentration in gram equivalents per c.c. 

 m = 1000 7] or gram equivalents per litre. 



A = - = equivalent conductivity. 



V 

 s = Specific gravity. 



Formerly the concentration was expressed in percentages, but the advantage gained 

 by expressing the concentration in terms of gram equivalents is obvious. This 

 advantage is, however, not dependent upon the adoption of the unit of volume 

 (c.c. or litre). On the contrary, by expressing the concentration of a concentrated 

 solution in terms of the number of gram equivalents of the solute per unit volume of 

 the solution, the relationship between the concentration and the mass of a concentrated 

 solution is necessarily masked, because the solution of electrolytes in water is 

 accompanied by changes in volume differing with each electrolyte and by no means 

 negligible in concentrated solutions. 



Let the following; units be taken : — 



o 



k = Specific conductivity in ohm -1 cm. -1 . 



y = Concentration in gram equivalents per gram of solution. 



T = 1000 y. 



A M = — (corresponding to A = — ). 

 7 V 



TRANS. ROY. SOC. EDIN., VOL. XLV., PART I. (NO. 9). 33 



