The osmotic pressure of the yolk and white of the hen's egg have been shown to be identical, by means of direct freezing point determinations, dialyses, and vapor pressure measurements.
Dialysates of egg yolk slow the rate of ice formation compared with NaCl solutions. They also show a marked change of freezing rate as the freezing point is approached. The anomalous freezing behavior of this material may lead to errors in the determination of the true freezing point which would tend to make the value for the yolk erroneously low.
The postulate of a vital activity at the yolk membrane maintaining an osmotic pressure difference is thus shown to be unnecessary, since a simple osmotic equilibrium exists between the yolk and the white.