218 SOAPS AND PROTEINS 



4. The System Gelatin/ Water 



We shall now consider a " neutral " protein which, when com- 

 pared with the fatty acids, is not " insoluble " in water (as glob- 

 ulin) but " soluble," namely gelatin. The ordinary alleged acid- 

 nnd base-free gelatin 1 mil, by itself, with water, show all the four 

 ti/pes of hydrophilic colloid systems described for the soaps. 2 



Dry gelatin absorbs water (to yield the system water-dissolved- 

 in-gelatin) and has a limited solubility in water (to yield the system 

 tfchit in-dissolvcd-in- water). Between these extremes and depend- 

 ing merely Upon the relative amounts of gelatin and water present 

 there lie the systems gelatin-solution dispersed in hydrated-gelatin 

 (gel) or, with more water, hydrated-gelatin dispersed in gelatin- 

 solution (sol). 



What is the action of alkalies (or acids) upon these systems? 



Under variously worded headings this problem has received 

 much study. The effects of alkalies (and acids) upon the lower- 

 most of the four systems may be found described under the cap- 

 tion " swelling " of gelatin in the presence of acids and alkalies; 3 

 their effects upon the system gelatin-solution-in-hydrated-gelatin 

 under the heading liquefaction and " solution " of gelatin; 4 their 

 effects upon the system hydrated-gelatin-in-gelatin-solution under 

 studies in viscosity; 5 their effects upon the system true solution 

 of gelatin-in- water as studies on the " solubility " of gelatin. 6 

 What is the relationship between all these? 



It is well to begin by inquiring into the relationship between 

 the swelling of a " soluble " " neutral " protein and its " solution." 



1 See the footnote on page 209. 



2 See page 69. 



3 See for example K. SPIRO: Hofmeister's Beitrage, 5, 276 (1904); WOLF- 

 GANG OSTWALD: Pfluger's Arch., 108, 563 (1905); MARTIN H. FISCHER: 

 (Edema and Nephritis, 3rd Ed., 75, New York (1920) where references to 

 the earlier studies may be found. 



4 MARTIN H. FISCHER: Science, 42, 223 (1915); Kolloid-Zeitschr., 17, 1 

 (1915). 



6 See for example the work of HOFMEISTER, PAULI, HARDY, VON 

 SCHROEDER, HANDovsKv, SCHORR, etc., on the viscosity of liquid proteins 

 ("sols"). 



6 MARTIN H. FISCHER: (Edema and Nephritis, 3rd Ed., 513, New York 

 (1920). As of simihir import but upon other proteins may be cited some 

 studies on wheat gluten. T. B. WOOD and W. B. HARDY (Proc. Roy. Soc., 

 London, Series B, 81, 38 (1908)) studied the "disintegration" and "solu- 

 tion" of gluten under the influence of acids while F. W. UPSON and J. W. 

 CALVIN (Jour. Am. Chem. Soc., 37, 1295 (1915)) studied its swelling under 

 similar circumstances. 



