CHANGES PRODUCED IN MILK BY HEAT 231 



to deal at any length with the changes which occur in the calcium 

 content on heating. 



It is a well-established fact that a reduction in the calcium 

 content occurs when milk is heated, and this reduction has been 

 held responsible for the production of rickets in children who were 

 fed upon boiled or otherwise heated milk. The work which has 

 been dealt with in the preceding pages 1 shows that there is no 

 ground for supposing that rickets is produced by small alterations in 

 the calcium content of the milk given. 



The question of alteration in the calcium content is closely 

 connected with that of the citric acid content and also with the 

 coagulation of caseinogen by rennet. 



It will be simplest first of all to consider the changes in calcium 

 content which occur as a result of heating, and subsequently to 

 give additional work upon the citric acid content and upon the 

 coagulation of milk. 



The work upon calcium belongs to a comparatively early period 

 in the investigation of milk. Soldner, in 1888, carried out extensive 

 investigations upon the effect of heating milk, and in particular 

 upon the effect on the calcium and phosphorus content. He 

 found that when milk was just boiled the loss of calcium by 

 precipitation amounted to from 13-15 mgms. per 100 c.c. of milk. 

 Thus the amount of calcium present in 100 c.c. of raw milk was 



In one case . 80 mgms., falling to 66 on boiling, a loss of 14 mgms. 

 In another case 72 ,, 59 13 



And in another 62 47 15 



Soldner believed that the calcium was present combined with 

 phosphorus as mono- and di-calcium phosphate, which on heating 

 passed to the tri-phosphate and was precipitated. He showed 

 further that the loss of phosphorus was on similar lines : thus in 

 different 100 c.c. samples : 



96 mgms. fell to 86, i.e. a loss of 10 



77 64 13 



104 93 ii 



Boekhout and de Vries found that only from 3-5 mgms. of calcium 

 were precipitated from 100 c.c. of milk when the milk was just 

 boiled. The variations in the results may perhaps be due to 

 peculiarities in the different samples of milk, since these authors 

 found that there are some Dutch milks which will not coagulate 

 with rennet although they contain normal amounts of calcium. 

 Such milks require the addition of a large amount of calcium 

 chloride, much of which apparently becomes insoluble, in order to 

 produce a coagulation with rennet. 



Grosser has investigated more recently the effect of boiling 



1 Cps Chap.- XIII. 



