124 CHEMICAL STATICS 



the phase-rule would be out of place here, since an exposition 

 of the principles underlying its application can be found in any 

 general work on physical chemistry. 



Galeotti (17) (18) has applied the phase-rule to the systems 

 egg-albumin, CUSO4, H2O, serum-albumin CUSO4, H2O; serum- 

 albumin, AgNOs, H2O; egg-albumin, AgNOs, H2O; while Hardy 

 (25) has applied it to the systems serum-globulin, salts, H2O. 

 Both observers employ the triangular co-ordinates recommended 

 by Roozeboom, in which the three sides of an equilateral triangle, 

 each equal to unity, represent the components of the system and 

 the distances of a point P from these axes, measured in a direc- 

 tion parallel with the sides of the triangle, express the compo- 

 sition of a ternary mixture corresponding to the point. Since 

 each of the systems investigated by these observers is a system 

 consisting of two immiscible bodies, protein and salt, which are 

 both partially miscible in a third, water, they are comparable 

 with the system water, sodium chloride and succinic nitrile, 

 which has been studied by Schreinemakers (72). The form of 

 the isotherm obtained by Hardy and by Galeotti is exactly 

 that obtained by Schreinemakers in the above-named system. 



The temperature and pressure in these investigations being 

 arbitrarily fixed and the components being three in number and 

 in equilibrium with water-vapor at the pressure and temperature 

 employed, the number of degrees of freedom is 3 — r, where r 

 is the number of phases. From this it follows that for a given 

 temperature and pressure there can be, in general, not more than 

 three phases in equilibrium with water-vapor coexisting in the 

 system at one time. 



Now Galeotti, as has been mentioned above, finds that solid 

 CUSO4 + 5 H2O, solid protein and water can coexist in the sys- 

 tem at the same time, the water being saturated with CUSO4 + 

 5 H2O and'also containing some dissolved protein, as is shown by 

 the fact that dilution of the fiuid phase causes further precipitation 

 of protein. From this it follows that the protein, while in solution, does 

 not constitute a separate phase and is not divided off from the solvent 

 hy a surface enwrapping molecules which are not in physical con- 

 tact with the fluid, for otherwise there would be four coexistent 

 phases; this simple consideration appears to have been over- 

 looked by the majority of writers on colloids and by many of 

 the advocates of "adsorption." 



