On the depression of the freezing point of water due to dissolved caseinates

Abstract

The question whether or not proteins possess, in solution, a definite osmotic pressure has been the subject of much controversy. The original investigations of Graham 1 appeared to indicate that colloids in general exert a high osmotic pressure. Subsequent investigators, however, attribute these results to an admixture of crystalloids and the investigations of Sebanejew, 2 Tamman, 3 Dreser, 4 Koeppe 2 and others indicate that when they are carefully freed from associated inorganic substances the cryoscopic depression due to dissolved proteins is negligible, while Reid 3 finds that proteins purified by repeated recrystallization, resolution and recrystallization frequently possess, in solution, 4 no measurable osmotic pressure; and he concludes that provided every precaution be taken to exclude impurities (among which he includes inorganic constituents) from the protein solution it will be invariably found to possess no osmotic pressure whatever and that the osmotic pressures observed in solutions incompletely purified are due, not to protein, but to the associated impurities.