New York Agricultural Experiment Station. 31 



showing their relation to the chemistry of the process of cheese- 

 making. The publications of the past year treat of the following 

 points: (a) Sodium citrate is often added with favorable results to 

 milk used in feeding infants and invalids in certain diseased condi- 

 tions, but no satisfactory explanation of the action has been known; 

 it has been known only that sodium citrate delays the curdling 

 action of milk when it is treated with rennet extract (rennin) and 

 forms a curd of softer than normal consistency, the softness increas- 

 ing with the amount of sodium citrate added until finally no curdling 

 takes place when the citrate is added at the rate of 0.400 gram per 

 100 cubic centimeters of milk (equal to 1.7 grains of citrate per ounce 

 of milk) . Our work shows that at the point at which rennet extract 

 fails to curdle milk we have a chemical change in the casein of the 

 milk, the normal calcium caseinate of the milk being changed into a 

 double salt, calcium-sodium caseinate, a compound which is changed 

 by rennet extract into calcium-sodium paracaseinate and this latter 

 compound, owing to the presence of sodium, is not curdled, (b) The 

 cause of acidity in fresh milk has been attributed to both the casein 

 and phosphates in milk. Our work shows that casein does not have 

 any relation to the acidity of fresh milk but that the acidity is caused 

 chiefly or solely by acid phosphates in solution. In determining the 

 acidity of milk by titration with alkali, the presence of the soluble 

 calcium salts interferes with the accuracy of the work. We find that 

 this difficulty can be overcome by treating the milk with a saturated 

 solution of neutral potassium oxalate (2 cubic centimeters per 100 

 cubic centimeters of milk) and thus removing the soluble calcium 

 before determining acid with alkali. The acidity as determined by 

 this method is found to be about half that previously reported by 

 other investigators, (c) The phosphorus content of casein has been 

 previously found to be 0.85 per ct., but our work shows former 

 methods to be inaccurate; the true percentage is about 0.71. (d) The 

 action of rennet extract (rennin) in curdling casein to form paracasein 

 is shown to be a process of hydrolysis, one molecule of casein splitting 

 into two molecules of paracasein, (e) There has been controversy 

 over the composition of milk as to what constituents are in true 

 solution. Investigation made here by improved methods shows that 

 (1) sugar, citric acid or citrates, compounds containing chlorine, 

 potassium and sodium are entirely in solution; (2) albumin, inorganic 

 phosphates and compounds of calcium and magnesium are in part 



