Scientia Sinica

70 : SCIENTIA SINICA Vol, V

1.0000

0.9800

1/f

Purpuro 0.9400

0.9000

0.8800 0.0000 0.0560 0.1000 C 0.1500 7 $s

Fig. 3. Plot of 1/f of n-valeric acid vs. concentrations of salts. Note: The curve for purpuro is shifted down by 0.0600 and that

for croceo by 0.1000 units to avoid disfiguration of the other three curves. 5;

From the slope of each straight line in Fig. 2, we get k, equal to k of Eq. (2). Similarly, we get k, from Fig. 3. k, 1s not identical with ¢ of Eq. (4), (4), since f in Eq. (4) is the activity coefficient of real nonelectrolyte containing no ions. Ki and k, are called salting-out constants. Positive values of Ri and k, indicate salting-out, while negative values, salting-in. Table 2 is a collection of salting-out constants of m-valeric acid by five cobaltammines. Table 2 Salting-out Constants of n-Valeric Acid by Cobalt-

ammines at 25°C

Cobaltammine Purpuro Xantho | Luteo | Flavo

DiscUSSION

- The five cobaltammines, used here, have rather low solubilities, the largest of which, ic. that of Luteo, 1s only 0.26 mol per litre at 70°C. Hence in our experiments, the highest concentration used is only 0.15 mol per litre. But the lower the concentration of cobaltammine is, the smaller will be the salt effect and the larger will be the experimental error. Moreover, the colouring of the solution by cobaltammine decreases the sensitivity of the indicator and increases the analytical error. Hence it is difficult to get accurate saltingout constants at low concentrations of these salts. Nevertheless, we get fairly

gcod straight lines in Figs, 2 and 3, and the salting-out results are essentially in agreement with the theories of Debye McAulay and of Debye.