222 SOAPS AND PROTEINS 



To illustrate, now, upon such basic (or acidic) gelatin the 

 effects of a neutral salt (in mimicry of the salting-out effects 

 observed upon soaps), Tables LXXI and LXXII are introduced. 

 They show that the addition of a neutral salt in increasing con- 

 centration to a previously liquid gelatin at first increases its viscosity 

 to an optimum point (gelation) and then decreases it. The same 

 explanation holds for this finding as in the case of the soaps. The 

 salt becomes hydrated and, as salt-water, becomes emulsified in 

 the hydrated basic (or acidic) gelatin. With salt added beyond the 

 optimum point the salt-water becomes the external phase and the 

 viscosity of the system falls. With enough salt added the whole 

 of the gelatin (as sodium gelatinate or gelatin chlorid and not as 

 " neutral " gelatin) separates off in practically anhydrous form. 



5. Supplementary and Critical Remarks 



It is necessary to keep clearly in mind that the possibilities for 

 chemical and colloid-chemical change as thus far outlined for the 

 fatty acids and the proteins constitute only a small fraction of 

 those which may be induced. 



While we have said that only alkalies will unite with the fatty 

 acids and only alkalies and acids (or their salts) with the poly- 

 merized amino-acids called proteins, the former may be sulphon- 

 ated, may be saturated with hydrogen, may be oxidized or iodized 

 while the latter may also be oxidized, hydroxylated or have acids 

 bound to them elsewhere in the molecule than at an NH2 grouping. 

 As each of these chemical changes is induced the fatty acid derivative 

 or the protein derivative assumes new properties of solubility for 

 water and in water and as this happens the colloid-chemical prop- 

 erties (like the viscosity) of the system in which such a chemical 

 change has been induced, must also change. 1 



To keep things simple we have also touched upon only the 

 grosser of the phase differences present as neutral proteins unite 

 with alkalies or acids. How much more complicated in fact are 

 the systems which have been described is apparent when reference 

 is made to Figs. 48 and 49 and the system, stearic acid/alkali/ 



1 The derivatives listed have already been partly studied in our laboratory 

 and will be reported upon later. 



