106 COLLOID CHEMISTRY OF THE PROTEINS 



concentrations of more than 0-06 N alkali. It can be seen from 

 Fig. 24 that a range of practically complete combination follows 

 on increasing alkali content, as new acid valencies of the casein 

 come into play almost in proportion to the quantity of alkali 

 present. 



Table 53 (Fig. 24). 



Stock Solution : 4*5 gm. Dry Casein in 500 c.c. 

 o-oi NNaOH. 



(Electrometric determination made one hour after mixing.} 



The original neutral alkali caseinate made by Laqueur and 

 Sackur by titration with phenol phthalein contained 0-9 (or 

 accurately 0-881) millimols of alkali per gram of dry casein ; 

 whereas the work of Pauli and J. Matula gives the result that 

 when excess of casein is shaken at 20 in o-oi N sodium hydroxide 

 about 2 gm. of casein dissolve in each 100 c.c. The fairly clear 

 and stable solution obtained in this way contains only 0-5 

 millimols of alkali per gram of casein. 



This somewhat complex behaviour becomes much clearer if 

 we start from this caseinate saturated with casein. In the first 

 place it is possible to dilute the above solution with half its 

 volume of alkali of the same concentration without any consi- 

 derable displacement of the H ion concentration from the 

 neutral point. A series of such results is given in Table 54 on 

 p. 107. 



It follows from these experiments that all caseinates contain- 

 ing between i and 2 gm. of casein per millimol of alkali behave 



