Studies in the Physical Chemistry of the Proteins. Ii. T~e Relation between the Solubility of Casein and Its Capacity to Combine with Base. the Solubility of Casein in Systems Containing the Protein and Sodium Hydroxide.*

"Casein is known to have the character of a weak acid; it reddens wet l i tmus paper and forms salt-like compounds with metals. ''~ Thus Laqueur and Sackur began their classic paper on casein near ly 20 years ago3 Moreover, the relat ive strength of this acid was suggested even before m o d e m methods were available for its determinat ion, since i t "has the power of expelling carbonic anhydride from soluble carbonates and bicarbonates. ''~ The amount of base with which it combines at acid, a t neutral , and at alkaline reactions has perhaps been investigated more often than any similar react ion