Scientific Proceedings (119). 



not dealing with the colloidal matter of milk in their analyses of 

 filtrates from the clay filters which they used. The experiments 

 which have shown a gross decline in calcium phosphates or in 

 which the precipitated phosphates have been seen, when milk is 

 heated, are to be explained, therefore, solely by the effects of heat 

 on colloidal solutions of dicalcium phosphate. As a matter of 

 fact the loss of calcium and phosphorus from milk on boiling 

 observed by Soldner showed a ratio of one molecule of calcium 

 to one of phosphorus such as exists in dicalcium phosphate. 



Experimental. 



In order to determine what the effect of heat is on colloidal 

 CaHP04 solutions, such a solution was prepared by grinding 

 CaHP0 4 , which had been washed free from electrolytes, to an 

 impalpable powder in a porcelain ball mill. This powder was 

 then ground further in the mill in the presence of a 0.6 per cent, 

 gelatin solution. After settling, the supernatant fluid presented 

 a very satisfactory colloidal suspension of CaHP0 4 . It was dis- 

 tinctly milky and showed the usual Tyndall effects in a striking 

 manner. The concentration of CaHP0 4 was not, however, as 

 high as had been expected, the solution being found to contain 

 only 0.542 gram per 1000. Possibly a higher concentration would 

 have been obtained if a stronger solution of gelatin had been 

 employed or a better colloid stabilizer used. Gelatin was chosen, 

 however, because it is not coagulated by heat. 



The effect of heat on this colloidal solution of CaHP0 4 was 

 determined qualitatively only by heating a portion of it in a water 

 bath at 63 0 C. for 30 minutes. A heavy precipitation of CaHP0 4 

 resulted and the filtrate showed much less evidence of a colooidal 

 suspension. 



This simple experiment shows rather conclusively that it is 

 not necessary to assume any transformation in the composition 

 of the calcium phosphates of milk during heating to account for 

 the partial fixation of these salts. The phenomenon is readily 

 accounted for by the effect of heat on a colloidal solution of 

 CaHP0 4 which renders such a solution much less stable and 

 causes the aggregates to pass, in part at least, to the crystalloid 

 form. 



