CRYOSCOPIC METHOD 75 



tions of strong acids or bases, upon the addition to them of pro- 

 teins. As in the previous method, the measurement is a static 

 one, with this difference, however, that the measurement is 

 necessarily conducted at or in the neighborhood of 0° C. and 

 that the dynamical equilibrium of the system under investigation 

 is shifted to the equilibrium pertaining at this temperature. 

 Regarding the magnitude of this shift for any given temperature 

 range we have but meagre data, but in the light of results ob- 

 tained with the caseinates and with the salts of ovomucoid (Chap. 

 IX) it is probably in these instances and for the temperature- 

 range 30-0° C, not greater than the experimental error of the 

 method. 



The cryoscopic method was first employed, for this, purpose, 

 by Bugarzsky and Liebermann (5), who found that upon adding 

 6.4 grams of egg albumin ^to 100 cc. of 0.05 A^ HCl or NaOH 

 the difference between the freezing-point of the solution and that 

 of water is reduced nearly 50 per cent, indicating a diminution 

 by nearly 50 per cent of the total number of ions plus molecules 

 per liter of the solution. Upon adding similar quantities of 

 protein to solutions of sodium chloride, little or no alteration in 

 the freezing-point of the solutions could be detected. From 

 these results it is usually inferred that the proteins do not bind 

 neutral salts. This, however, is not an altogether justifiable 

 inference. Hardy (loc. cit.) has detected a slight, but what he 

 considers urmaistakable, depression in the electrical conductivities 

 of salt solutions upon saturation with serum globulin, and he 

 assumes that a compound with the neutral salt is actually formed, 

 but that it is only stable in the presence of excess of the salt, so 

 that at any given salt-concentration only a small proportion of 

 the salt is held in combination. Mellanby (28) has arrived at 

 similar conclusions. This possibility becomes more plausible 

 when we view it in the light of the Guldberg-Waage mass law. 

 Representing the reaction between protein and NaCl thus: 



Protein + NaCl ^ Protein— NaCl Compound, 



we may suppose that the station of equilibrium lies far to the 

 right. An excess of NaCl would displace this equilibrium towards 

 the left and a greater proportion of the protein would exist in 

 the solution in the form of the protein-salt compound, i.e., the 

 compound would be more "stable." Turning now, to the above- 



