766 
1.32 m.m. + 0.025 C,0,” + 0.025 (2 Na”)—0.0115 Ca\—0.0115 €,0,” = 1.347 m.m. 
The total concentration of ions therefore does not increase by 0.05 mm but 
only by 0.027 mm. 
With the 6th addition we get a value for the undissociated CaC,O, of: 
0,050 + V4 <x 0,55 + 0,05? 
9 
a 
10,055 — 0,024 mm. 
The total concentration of ions after the 6th addition is 1.372 m.m., the increase 
is 0.025 mm. 
After the 7th addition it is found, calculated in the same way, that the total 
concentration of the ions is 1.402, the increase 0.03 mm, 
It appears thus that the ion concentration with the first 4 additions 
increases regularly by 0.05 m.m. From the 5th addition onward, 
however, it increases only by 0.025 to 0.030 m.m. If now the 
electrical conductivity be examined after every addition it must 
appear to increase also in analogy with the increase of the total 
concentration of ions. Should it be found now that after the first 4 
additions the conductivity increases only by half of the original 
value, then it is a proof that the true value bas been found for the 
solubility product. 
II. Determination of the concentration of Calcium ions in a solution 
of pure CaCl, 6 aq. 
In 8 tubes with ground stoppers are brought respectively 0.0010, 
0.0015, 0.0020, 0.0025, 0.0030, 0.0035, 0.0040, 0.0045 c.c. of a 
0.05 N solution of Na,C,O,. Consequently the tubes are placed in 
a waterbath for some time till the oxalate solutions are evaporated 
down to dryness. Hereupon into each tube there is introduced 1 ec. 
of a CaCl, 6 aq. solution which contains 125 mgr. per L. After an 
hour the result is observed. 
The solution of CaCl, .6 aq. was made from a chemically pure substance (The 
British Drug Houses); the strength of the solution was controlled by chlorine 
determination. The salt was dissolved in carefully boiled distilled water. All obser- 
vations were made in small tubes of 2 ce. contents with ground stoppers. 
The Na,C,0, solution was made from pure Na,C,O, after SöRENSEN (KAHLBAUM). 
It contains no water of crystallisation, is not hygroscopic and is not affected by 
temperatures below 200°. 
It appears that the first 6 tubes have remained perfectly clear but 
that the tubes with 0.040 and 0.045 ¢.c. oxalate solution show a 
faint turbidity. 
The solubility product was reached thus, if, on an average, 0.0375 c.c. 
N 
50 Na,C,O, solution was added to 1 c.c. of a solution of CaCl, 6 aq. ; 
werg 
