88 CHEMICAL STATICS 



Although the acid function of the protamins is very weak in 

 comparison with the basic function, salts with inorganic bases are 

 nevertheless formed. The salts of the heavy metals (except cupric 

 salts) produce from alkaline solutions of free protamin precipi- 

 tates of the corresponding salts of the protein. The compound 

 with divalent copper is soluble in water, and its solutions are 

 violet in color. The compounds with monovalent copper are very 

 sparingly soluble. On adding alkali (sodium hydrate) in excess 

 of one-half the equivalent of the protein (clupein) molecule, to the 

 precipitate of the silver salt, a yellow color is produced, indicating 

 that sodium has displaced some of the silver from the molecule and 

 that the silver protaminate is now mixed with silver oxide. 



Other compounds which the protamins form will be considered 

 in the succeeding chapter. The physical properties of the pro- 

 tamins and their salts will be discussed in the chapters dealing with 

 the physical properties of protein systems. 



3. The Compounds of Casein with Bases, Acids, and Salts. 

 Casein, in the dry state, forms a white powder, the general proper- 

 ties of which have been described in Chap. II. Uncombined and 

 purified casein is insoluble in distilled water or in very dilute salt 

 solutions (11) (34) (22) (36). A suspension of casein, thoroughly 

 shaken up in distilled water, reddens litmus paper wherever the 

 suspended particles touch it, but if this suspension be filtered the 

 filtrate contains no detectable casein and is neutral to litmus. 

 Casein is therefore probably soluble to a very slight extent in dis- 

 tilled water, but this slight amount is practically entirely con- 

 centrated at the surface of the water which is in immediate contact 

 with the solid particles, owing to the diminution in surface energy 

 which is thus brought about, so that the litmus is only reddened 

 where it touches these surfaces. 



Uncombined casein is soluble in warm 5 per cent salt-solution 

 and in hot 50 per cent alcohol. When freshly prepared and 

 warmed it is very plastic and is capable of being drawn out into 

 long, fine threads (59). 



Although it is so insoluble in water, uncombined casein, when 

 suspended in water, nevertheless acts as an acid in expelling carbon 

 dioxide from carbonates and bicarbonates, forming a salt with the 

 base (51), and in this way, according to Osborne (34), the ammo- 

 nium, potassium, sodium, lithium, magnesium, strontium and 

 calcium caseinates can be prepared. The salts of the alkaline 



