DIFFUSIBLE PHOSPHORUS OF COW’S MILK. 261 
centrations of the substances in solution have become the 
same on each side of the membrane. 
Results. 
Having demonstrated that the process of dialysis as 
carried out in the present investigation leads to a definite 
state of equilibrium between the substances on each side 
of the membrane of the dialyser, we may now enquire what 
concentrations of substances in the dialysate are in equi- 
librium with those in the milk. In this paper I shall deal 
only with the concentrations of calcium and phosphorus. 
The amounts of calcium (expressed as CaO) were deter- 
mined in addition to the amounts of phosphorus (expressed 
as P.O;) only in the first few experiments. P.O; alone 
was determined in the later experiments as the length of 
time required for the analyses was so much increased when 
CaO was estimated as well, and as the amount of diffusible 
CaO in milk has already been determined by Rona and 
Michaelis (loc. cit.) by this method. 
For these estimations as a rule not more than 10 cc. of 
dialysate were available; in the case of milk, portions of 
20 cc. of spun milk were used, as the removal of the fat 
considerably reduces the amount of organic matter which 
has to be destroyed before proceeding to the actual estima- 
tion. The organic matter in the liquids under examination 
was destroyed, and the calcium and phosphorus oxidised by 
the acid-ashing process of Neumann (1902) as modified by 
-Plimmer and Bayliss (1906), i.e., by oxidation with a mix- 
ture of concentrated nitric and sulphuric acids. 
Use of spun milk.—It has already been shown that the 
removal of the fat of milk by mechanical means does not 
alter the freezing point (Wardlaw, loc. cit.), that is, removes 
nothing from solution in the milk. This is no justification 
for concluding however, that the percentage of any par- 
ticular constituent such as CaO or P.O; is the same in spun 
