265. On the use of various sera for the determination of the soluble calcium and phosphorus of milk

Abstract

A comparison of the value of various milk sera for the determination of the soluble phosphate and calcium of milk, using dialysis at 0–5° C. as a standard method, gave the following results:(i) Rennet whey was the most satisfactory; with fresh milk it yields fairly accurate values for calcium, slightly low (average 5 %) for phosphate. With increasing acidity of the milk both sets of values tend to rise somewhat relatively to those of the dialysate, phosphate approaching the true value and calcium rising slightly above it.(ii) Mercuric chloride borax serum gives high results for the soluble phosphate of fresh milk With increasing acidity of the milk, the results fall steadily.(iii) Papain whey gives somewhat low results for both the phosphate and calcium of raw and pasteurized milk, with the same tendency as rennet whey to yield higher and improved results as the acidity of the milk: increases. With boiled milk it gives abnormally high results for both constituents. The additional phosphate and calcium appear to arise from the solution of colloidal calcium phosphate.