io 4 COLLOID CHEMISTRY OF THE PROTEINS 



evaluate the valency of the caseinate ion. Taking the result 

 of Laqueur and Sackur that i gm. of casein is neutralised by 

 0-881 millimols of sodium hydroxide, the equivalent weight of 



casein is ' = 1,135. This value, in the light of more recent 



O'ool 



work (see below), appears to be somewhat too high. The mole- 

 cular weight of casein is certainly greater than this, but will be 

 an integral multiple of this number. 



From consideration of a large number of mono- and poly- 

 basic organic acids (up to a basicity of five), W. Ostwald has 

 deduced the rule that the increase in conductivity when equiva- 

 lent weights of the sodium salts are diluted is proportional to 

 the valency of the anions. The relation is particularly simple 

 if the increase in conductivity at 25 for volumes of 32 litres 

 and 1,024 litres is considered. The difference A 1024 A 32 = n 

 X 10, where n is the valency of the anion. The following table 

 by W. Ostwald shows over what a wide range the rule holds 

 good. 



Table 52. 



For sodium caseinate, the values A 32 = 45, and A 1024 = 75, are 

 obtained graphically when v and A v are used as co-ordinates in 

 place of i/V and A v . The difference is 30 or 3 X 10, and thus in 

 this salt the caseinate is by Ostwald's rule tribasic. The mole- 

 cular weight itself therefore becomes 3,400. Laqueur and 

 Sackur believed the casein ions to have a low mobility, and the 

 use of the relative decrease in conductivity, (A x A 2 )/A 2 , to be 

 essential when calculating the basicity, and therefore estimated 

 the basicity of the casein to be 4 6. The normal behaviour 



