122 Studies on Solution. 



ki and k% are cell constants. i, 61, and a 2 and b 2 are the respective 

 readings on the bridge for the resistances w\ and w 2 . 

 Substituting the values of (3) in (2), we obtain 



" ~ 7 



2 W' 2 



Substituting now the values of (4) in (1) 



m k\a\v\ _ n k\a 2 v 2 



a 2 v 2 



(4) 



(5) 



If the same cell be used in determining the conductivities of the two 

 solutions, then ki equals k 2 , and simplifying (5) we obtain 



m a\ n a 2 



(6) 



This is the general equation, which becomes further simplified for a 

 particular case. A single illustration will make its meaning clear. 



What concentration is necessary for a calcium nitrate solution that 

 it be isohydric with regard to a molar solution of potassium nitrate? 

 At 25 C., and this temperature was used throughout the work, for 

 calcium nitrate, //^ equals 257.99, 1 and for potassium nitrate, ^"^ 

 equals 148.39. Considering the nitrate ion, m 2 and n = 1 . Therefore 



2 i az 



257.99 biwi 148.39 b 2 w 2 

 Whence 



=8693 



O 2 w 2 



Now by measuring a and 6 of the molar solution of potassium nitrate 

 for the resistance w 2 , the right-hand side of the equation becomes a 

 constant. A concentrated solution of calcium nitrate was taken in 

 different portions and diluted until, by trial, that concentration was 



found such that -^- became equal to the value for the right-hand side 



of the equation. 



The concentration of the calcium nitrate was found to be 0.698 

 molar. And so a calcium nitrate solution of this concentration contains 

 the same number of nitrate ions per unit volume as a molar solution 

 of potassium nitrate. 



SALTS. 



The majority of the salts used were the purest obtainable from 

 Kahlbaum. All the non-hydrated salts were carefully recrystallized 

 frcm conductivity water and thoroughly dried at the temperature best 



J A11 Atoo values were taken from Carnegie Inst. Wash. Pub. No. 170 (1912), but are expressed 

 here in reciprocal ohms instead of in Siemens units. 



