290 Report of the Department of Chemistry of the 



original untreated milk used in the experiments, and then, following, 

 the amounts of soluble and insoluble calcium in the milk after treat- 

 ment with amounts of sodium citrate varying from 0.130 to 1.040 

 gm. per 100 c.c. of milk (equivalent to 0.55 to 4.40 grains per ounce 

 of milk). As previously stated, the soluble calcium is the portion 

 appearing in the serum after filtering the milk under pressure through 

 a Chamberland filter, while the insoluble calcium is that which fails 

 to pass through the filter. An examination of the figures in the table 

 shows that the amount of soluble calcium in 100 c.c. of the original 

 milk is 0.045 gm. and this increases quite uniformly after each addi- 

 tion of increasing amounts of sodium citrate, the insoluble decreasing 

 in essentially the same amounts. The only interpretation of these 

 results that we can give is that some of the calcium of the caseinate 

 or phosphate in the milk has been replaced by the sodium of the 

 added citrate in the manner already discussed. 



2. Changes in solubility of phosphorus. — The question suggests 

 itself as to whether or not the increase of soluble calcium may come 

 from action of sodium citrate on the insoluble calcium phosphate in the 

 milk, forming sodium phosphate and caloium citrate. An examination 

 of the figures in the columns under " Phosphorus " shows that there 

 is no increase of soluble phosphorus until we have added more than 

 0.520 gm. of sodium citrate per liter of milk (equivalent to 2.20 grains 

 per ounce), an amount sufficient to prevent curdling and even with 

 larger additions the increase of soluble phosphorus is relatively 

 small. The increase of soluble calcium comes, therefore, largely 

 from the calcium that is combined with casein in the milk. 



3. Changes in solubility of magnesium. — Owing to the small amount 

 of magnesium in milk, the observed increase of solubility is slight 

 but is in the direction shown by calcium, which would be expected. 



In Table II we give the results obtained by treating 100 c.c. of 

 milk with 2 c.c. of rennet solution (Shinn's liquid rennet) at 37° C. 

 (98.8° F.). The rennet test was applied to untreated milk and also 

 to samples of milk containing the varying amounts of crystallized 

 sodium citrate given in the table. 



Inspection of the results in this table makes it obvious that the 

 presence of sodium citrate in milk, even in small amounts, delays 

 very markedly the time of rennet curdling, while increase of citrate 

 increases the time required for curdling, until we reach a point 

 (0.400 gm. per 100 c.c. of milk or 1.7 grains per ounce), where no 

 curdling takes place under the conditions of our experiments. It 

 should be stated, in addition, that the character of the curdled milk 

 varied in a characteristic way with the amount of sodium citrate 

 added. Sample 1, untreated milk, gives a firm curd; the treated 

 samples give curd of increasing softness with increase of sodium 

 citrate. 



The experimental results embodied in Tables I and II show that 

 when sodium citrate is added to normal milk, (1) the amount of 



