767 
the CaCl, 6 aq. solution contained 125 mgr. CaCl, 6 aq. or 0.57 
millimol Ca: per L. 
The concentration of oxalate, therefore, was 0.095 m.m., the 
solubility product is found to be 0.095 x 0.57 = 0.054 mm. per L. 
The temperature during all the experiments was 20°. Table I gives 
the results of a series of such experiments. 
TABLE I. 
3 Strenght of the C,O,4” conc. 
Strength of Ca con- “traf had to be added to 
| ans 
: | Solubility product. 
centration. show just a precipitate. | 
0.57 millimol. 0.095 m.m. | 0.054 
OL55nr ih. - 0.05 „ 0.052 
038 0.145 | 0.055 
GES O15)" | 0.054 
ae) | Oo 0.056 
Ne CIN 0.056 
O10.) 054 0.054 
00", | 0.056 0.056 
| 
From this table it appears thus that, with solutions of pure CaCl, 
6 aq. of different strengths, a constant solubility product of CaC,O, 
is found, namely 0.055 mm. per L. 
Let this value now be controlled by the measurement of the 
electrical conductivity as it is described above. 
The conductivity was determined in a “resistance vessel” according to HamBuraen. 
The method is found deseribed in Osmot. Druck u. lonenlehre Bd. 1, pag. 98. The 
temperature was constant at 25°. 
To 5 e.c. of a solution of CaCl, 6 aq. which contained 125 mgr. per L., repeated 
additions of a 0.05 N solution of Na,;C,0, were made. Subsequent to every 
addition the conductivity was measured after it had become constant. 
The resistance of the pure CaCl, 6 aq. solution was 
8.709 ~ 2000 C Ohm (C = capacity of the resistance vessel). 
Table II gives the decrease in the resistance after every addition 
of oxalate solution. (See Table following page). 
It is observed that after the 4'" addition of oxalate the decrease 
in resistance is diminished to less than the half. With the 4" addition, 
therefore, the solubilityproduct was reached. The C,O, concentration 
then was 0.1 millimol the Ca concentration 0.56 millimol and the 
produet thus 0.056 millimol. 
