CHAPTER XII 



THE PHENOMENA WHICH ACCOMPANY CHANGES IN THE 

 STATE OF AGGREGATION OF PROTEINS 



1. The Passage of Dry Protein into Solution. The question 

 whether or not the proteins as a class possess a definite solubility 

 in water is one which has not so far admitted of any satisfactory 

 solution. True, certain sparingly soluble salts of the proteins 

 undoubtedly are soluble only to a definite extent in water, as 

 for example the researches of Galeotti, cited in Chap. VI, reveal; 

 when this limit of solubility is overstepped the protein salt is 

 precipitated; then other forms of protein, coagulated proteins, 

 " denatured" proteins, and so forth are definitely insoluble in 

 water under the conditions which accompany their formation. But 

 the very proteins which display these phenomena under certain 

 conditions, under somewhat different conditions, either in the 

 form of free protein or of a salt, appear to be indefinitely soluble 

 in water; miscible with it in all proportions. The phenomena 

 of " solution," chemical combination with water, and of the 

 hygroscopic, possibly purely physical, retention of water, become, 

 in these cases and so far as our knowledge at present extends, 

 inextricably confused. 



On the whole it appears very probable that such proteins and 

 protein salts as gelatin and the caseinates are not only miscible 

 with water in all proportions, but also capable of entering into 

 chemical combination with water in many different proportions. 

 To this view Pauli (72), in contradistinction to Hardy (34) (35), 

 also inclines. 



Base- and acid-free casein is definitely insoluble in distilled 

 water; but in water containing a base its solubility would appear 

 to be limited only by the quantity of base which the water con- 

 tains and not by the volume of water. The casein continues 

 to dissolve until, as explained in Chaps. V and X, 11.4 X 10~ 5 

 equivalents of base are combined with each gram of casein and 

 solution of the casein stops merely because the power of the base 

 to neutralize casein is exhausted, and not because the solvent 



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