New York Agricultural Experiment Station. 289 



caseinate and calcium citrate? If such a reaction takes place, we 

 should be able to determine the amount of calcium thus transferred 

 from the caseinate to the citrate.- How this determination can be 

 made we will indicate briefly. 



When milk is filtered under pressure through unglazed porous 

 porcelain (in the form of a Chamberland filter), the serum contain- 

 ing the filterable soluble portions passes through the filter, while the 

 insoluble portion, consisting largely of caseinate and insoluble cal- 

 cium phosphate, remains on the filter. If, therefore, milk treated 

 with sodium citrate is filtered through a Chamberland filter, the 

 amount of calcium in the filtered serum should increase with the 

 amount of citrate added up to a certain point, provided that calcium 

 citrate (or perhaps, a double salt of calcium-sodium citrate) is formed. 

 It may be added here that calcium citrate is soluble to the extent 

 of about 0.090 gm. per 100 c.c. of water at ordinary room tempera- 

 tures, while the amount of calcium citrate formed by such a reaction 

 in milk containing 3.2 gm. of casein per 100 c.c. has been found by 

 us to be not over 0.066 gm. per 100 c.c; it all, therefore, remains 

 in solution passing through the filter into the serum. 



If, then, we determine in milk the amount of soluble and insol- 

 uble calcium and then add to the milk sodium citrate, filtering and 

 determining the calcium in the filtrate, there should, on the basis 

 of our hypothesis, be an increased amount of calcium in the filtrate, 

 showing how much calcium is transferred from the form of calcium 

 caseinate to the form of calcium citrate. 



EXPERIMENTAL WORK. 



In carrying out our experimental work, we proceeded in the fol- 

 lowing manner: Fresh separator skim-milk was used, in which the 

 amounts of casein, soluble and insoluble calcium, magnesium and 

 phosphorus were determined. To prevent bacterial action, 3 c.c. 

 of 40 per ct. formaldehyde solution was added to each liter of milk. 

 The milk was then divided into nine equal parts and to each part 

 was added, in varying amounts, crystallized sodium citrate (con- 

 taining 27.7 per ct. of water of crystallization), as indicated in the 

 table given below. The milk was then allowed to stand long enough 

 for the reaction to reach equilibrium. Each portion was then filtered 

 through a Chamberland filter and the amounts of calcium, magnesium 

 and phosphorus were determined in the filtered serum. The results 

 are given in Table I. Experiments were also made to test the effect 

 of sodium citrate on the curdling action of rennin, the results of 

 which are given in Table II. 



Attention is called to the following points in connection with a 

 study of the results contained in Table I. 



1. Changes in solubility of calcium. — In the columns headed " cal- 

 cium " we give the amounts of soluble and insoluble calcium in the 



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