Depression of the Freezing Point of Water. 



87 



sumed to occur in other protein solutions, although the polymeri- 

 zation of the protein, which occurs when the uncombined protein is 

 set free, may not result in actual precipitation. The elaborate 

 precautions which have been taken by many observers to free the 

 protein under investigation from accompanying inorganic sub- 

 stances, have, therefore, defeated their own ends by converting the 

 protein into molecular aggregates so enormous as to possess a 

 necessarily immeasurably small osmotic pressure. 



Since it appears probable, therefore, that the dissolved salts of 

 proteins may exert a measurable osmotic pressure in solution, and 

 hence, cause an appreciable lowering of the freezing-point of water 

 in which they are dissolved, we have undertaken a series of deter- 

 minations of the lowering of the freezing-point of water, which is 

 brought about by dissolved (neutral) caseinates. 



The solutions are made up as follows : Alkali of a given con- 

 centration is shaken up with excess of casein until no more casein 

 will dissolve and the solution is then filtered through rapid-filter- 

 ing paper. The resulting solution is a solution of the " neutral 

 caseinate " of the base and is neutral to litmus.^ The cryoscopic 

 depression is estimated in the usual wa}'. The following are the 

 results which have so far been obtained : 



Experimental error of determination ± 0.0025°. 



Base. 



Concentration of base 

 " saturated " with casein. 





Indicating a concentration of 



NHpH 



w/50 



0.045 



w/41 







•OSS 





KOH 



m/so 



•0325 



^"151 



<< 



133-3 



•0375 



"1/49-3 



fi 



.0425 



m/43-7 



tt 





•0475 



w/38.9 



ft 



m/20 



■OS 



ml 31 



it 



ml IS 



.075 



m/24.6 



i< 



. I 



ml 1S.5 



LiOH 



'"159-5 



•03 



»;/6i.6 



it 



w/39.6 



• 045 



w/41 



it 



w/23.8 



.07 



ml 26.4 



t c 



w/17.8 



.08 



ml20.3 



Since these solutions are neutral and no inorganic substance is 

 introduced save the base employed to dissolve the casein it is evi- 

 dent that the compounds of bases with casein cause, in solution in 



' T. Pirailsford Robertson: Journ. of Biol, Chem., 1907, ii, 336. 



