208 ' SOAPS AND PROTEINS 



From this it may rise to great values, as witness the amount 

 of fluid " absorbed " by neutral gelatin, by dry serum-albumin, 

 etc., when these are thrown into water. 



These characteristics of solubility in water and for water of the 

 different fatty acids and the different pure, " neutral " proteins 

 must be kept in mind if their colloid-chemistry or that of their deriva- 

 tives is to be properly understood. 



If we now write the formula of any fatty acid as: 



z-COOH 



then that of any amino-fatty-acid (or its polymer, protein) may 

 be written : 



z-COOH 



I 

 NH 2 



To produce a " soap," some base is substituted for the H in the 

 first formula written above; to produce the analogous " soap- 

 like " compound from the latter, the same base is substituted for 

 the similarly placed H of the second formula. As we produce 

 potassium, sodium, calcium and iron soaps we can also produce 

 potassium, sodium, calcium and iron proteinates. 



Every new soap and every new soap-like compound thus pro- 

 duced has solubility characteristics in water and for water different 

 from those of the original fatty acid or the original amino-fatty-acid 

 (protein) from which it was produced. 



The amino-acids have, however, wider possibilities for easy 

 union with other materials than have the fatty acids. While 

 the latter, for example, do not unite readily with acids, the former, 

 through their NH 2 groups, do. In this way there may therefore 

 be produced a second series of derivatives which may be desig- 

 nated as the chlorids, bromids, acetates, sulphates, phosphates, 

 etc., of the proteins, each again possessed of its own solubility 

 in water and solvent power for water. 



We are now in a position to consider the colloid-chemistry 

 of the pure proteins and that of their basic and acidic derivatives, 

 not only to see how these mimic the colloid-chemical behavior 

 of the pure fatty acids and their basic derivatives (the soaps) 

 but in order to obtain what seems to us a simpler general con- 

 ception of what happens when protein/water mixtures show the 

 evidences, under different circumstances, of swelling, gelation, 



