Section no. The Solubility Values. 



309 



solubility at 100 (S 100 ) to that at 20 (S 20 ) are given in parallel columns. 

 The percentage errors in these 100 solubility values are of the same mag- 

 nitude as those in the 100 values of the specific conductances. (See end 

 of section 109.) 



Table 131. Solubility of silver chloride, sulpho- 

 cyanate, and bromide. 



*Kohlrausch, Z. phys. Chem., 50, 35C (1905). I have corrected his values to 20 

 by means of his own temperature-coefficients. 

 tCottger, Z. phys. Chem., 46, 602 (1903). 



The increase of solubility with the temperature is much less in the case 

 of silver chloride than of the other two salts. It is of some interest to 

 apply to these results the integrated form of the van't Hoff equation : 



L_ T 2 T x 



2R 



S 



lOge TT 



T X T 2 



Since there are undoubtedly considerable errors in the very small solu- 

 bility at 20 of the sulphocyanate and bromide, the best method is to use 

 the formula in calculating this solubility {S x ) from that at 100 (S 2 ) 

 with the help of the heat of solution (L). The values of the heat of pre- 

 cipitation as determined by Thomsen* at about 18 by metathesis, which 

 are equal to the heat L absorbed by the dissolving of one equivalent, are 

 15,850 cal. for AgCl. 22,400 cal. for AgSCN, and 20,100 cal. for AgBr. 

 The so calculated values of the solubility X lO' at 20 are : 8.1 for AgCl, 

 0.02 for AgSCN, and 0A7 for AgBr. The agreement with the observed 

 values is as good as could be expected in the case of the last two salts, 

 but is not very satisfactory in the case of silver chloride. It is possible, 

 of course, that the assumption involved in the integration that the heat 

 of solution remains constant through so wide a temperature-interval is 

 attended with considerable error. 



Attention may also be called to the relatively large solubility of silver 

 chloride at 100, which amounts to 21.8 milligrams per liter. This shows 

 clearly that the statement made in several text-books on quantitative 

 analysisf that this substance may be washed with hot water is a mis- 

 leading one. 



*See Ostwald's Lehrbuch, II, 1, 335, 439. 



fClassen, Ausgewahlte Methoden der analytischen Chemie, 1, 2; Fresenius, Anleit- 

 nng zur quant, chem. Analyse (6te Ann.) 1, 298-299; Jannasch, Praktischer Leit- 

 faden der Gewichtsanalyse, 1, 10. 



