CHANGES PRODUCED IN MILK BY HEAT 233 



Phosphorus. There is a slight loss of phosphorus when milk 

 is heated, which appears to fall out of solution in the form of calcium 

 phosphate. 



Thus Solomin found that at 80 C. a little phosphorus falls out, 

 and at I3o-I40 C. about half the ash of the milk was precipitated, 

 including all the calcium phosphate. 



Purvis, Brihaut and McHattie obtained varying results, which 

 were further affected by the method of heating. Less loss was 

 found if the vessel used was closed. Among their experiments 

 they found a loss of phosphorus amounting to II per cent, in milk 

 kept at 100 C. for half an hour and 6 per cent, of the total in 

 sterilised milk. 1 



On the Question of Citric Acid in Milk, and its Reduction by 

 Heating. Many statements have been made in regard to the 

 connection between the citric acid in milk, its diminution as a 

 result of heating, and the consequent production of scurvy. A 

 number of these statements have been entirely unsupported by 

 facts, and the connection appears to have been hailed with some 

 degree of satisfaction, as affording a possible solution of a difficult 

 question. Recently, however, less has been heard of the reduction 

 in the amount of citric acid as a result of heating milk, owing 

 probably to the generally favourable results which are obtained 

 by feeding infants upon boiled or dried cows' milk. 



The discovery of citric acid in cows' milk appears to have been 

 first made by Scheibe and Henkel, whose work was communicated 

 to a medical society by Soxhlet. These investigators found that 

 citric acid was present in cows' milk to the extent of about o-i 

 per cent, and that nine-tenths of this total amount appeared to 

 be attached to calcium. They were unable to obtain any evidence 

 of the presence of citric acid in several samples of human milk 

 which were examined by them. They believed that the difference 

 between the two milks can be accounted for by the fact that the 

 cow is a herbivorous animal. 



Netter (i) states that human milk contains -5 mgm. of citrates 

 per litre, while cows' milk contains from two to three times as 

 much. 



Obermaier studied the effect of boiling upon the citric acid 

 content of cows' milk. He clarified the milk with a variety of 

 earth until the nitrate was no longer opalescent. The filtrate 

 was then acidified with sulphuric acid to remove the calcium 

 from the citric acid. Excess of the sulphuric acid was then removed 

 with baryta and the citric acid converted to the barium citrate. 

 Evaporation was carried out and the citric acid freed with 

 a fresh addition of sulphuric acid. After further methods of 

 purification the citric acid was estimated. Obermaier found that 

 there was a considerable difference in the amount of citric acid 



1 Cp. also the work just quoted by Soldner and Grosser. 



