Effect of Heat on Cow's Milk. 



139 



phates which, on heating, pass to tricalcium phosphate and are 

 thus precipitated. This explanation has apparently never been 

 submitted to critical examination. Monocalcium phosphate is 

 readily soluble in water and its solutions decompose on boiling giv- 

 ing rise to dicalcium phosphate whose solubility is so low that a 

 heavy precipitation of phosphates occurs. The solubility of di- 

 calcium phosphate is, however, only 0.135 to 0.561 part per 1000 

 of water, depending on the saturation of the water with C0 2 . 

 The more highly concentrated solution naturally gives up some 

 of its calcium phosphate on heating, due to the loss of C0 2 . The 

 solution in pure water also clouds up on boiling. 



The facts just cited seem to support, in general, Soldner's 

 theory. However, the experimental results of Grosser 4 and Rupp, 7 

 cited above, show that there is actually little if any decrease in 

 the calcium phosphates dissolved in milk when the milk is held 

 at pasteurization temperatures or boiled for some minutes. At 

 the same time there is abundant evidence, as indicated, that heat 

 does precipitate calcium phosphates from milk. How are these 

 divergencies in results to be explained? 



It occurred to the writer that a simple explanation of these 

 divergencies is afforded by the experimental evidence brought 

 forth by Van Slyke and Bosworth 1 that the calcium phosphate 

 of cow's milk is wholly in the form of dicalcium phosphate, amount- 

 ing to about 1.75 parts per 1000, on the average. These figures 

 are greatly in excess of the maximum solubility of dicalcium 

 phosphate, even in water saturated with CO2. These investi- 

 gators found, moreover, that the dicalcium phosphate of cow's 

 milk was retained on the Pasteur-Chamberland filter when milk 

 is filtered through this medium. The natural conclusion to be 

 drawn from these results is that the calcium phosphate of cow's 

 milk, which appears to be wholly in the form of CaHP0 4 , is 

 present in colloidal solution, and that the aggregates of particles 

 are sufficiently large that they do not pass through the Pasteur- 

 Chamberland filter, or even through the Bechloidt filter used by 

 Grosser, or the clay filter used by Rupp. This conclusion coin- 

 cides with the results of Grosser and Rupp who obviously were 



*Van Slyke, L. L., and Bosworth, A. W., N. Y. Agr. Exp. Sta. Tech. Bull., 

 1914, xxxix, 1-17. 



