AGRICULTURAL CHEMISTRY AGROTECITNY. G07 



evidence enough for concluding that the transformation of casein into para- 

 casein is a process of hydrolytic splitting, one molecule of casein yielding two 

 molecules of paracasein, and that this splitting of casein is not accompanied 

 by a cleavage of any of the elements contained in the original casein molecule 

 [E. S. R.. 29, p. S05I." 



Condition of casein and salts in milk, L. L. Van Slyke and A. "W. Boswoeth 

 (New York State Sta. Tech. Bui. 39 {19U), pp. 3-17; Jour. Biol. Chem., 2a 

 (1915), No. 2, pp. 135-152). — "Milk contains two general classes of compounds, 

 those in true solution and those in suspension, or insoluble. These two por- 

 tions can be separated for study by filtering the milk through a porous earthen- 

 ware filter like the Pastour-Chamberland filtering tube. 



"Serum prepared from fresh milk is yellow with a faint greenish tinge and 

 slight opalescence. The following constituents of milk are wholly in solution in 

 the milk serum : Sugar, citric aciij, potassium, sodium, and chlorin. The follow- 

 ing are partly in solution and partly in suspension : Albumin, inorganic phos- 

 phates, calcium, magnesium. Albumin in fresh milk appears to be adsorbed to 

 a considerable extent by casein and therefore only a part of it appears in the 

 serum. In serum from sour milk and milk to which formaldehyde has been 

 added, nearly all of the albumin appears in the serum. 



"The insoluble portion of milk separated by filti'ation through Pasteur- 

 Chamberland filtering tubes is grayish to greenish white in color, of a glisten- 

 ing, slime-like appearance, and of gelatinous consistency. When shaken wath 

 water it goes into susi^ension, forming a mixture having the opaque, white 

 appearance of milk. Such a susjpension is neutral to phenolphthalein. When 

 purified, the insoluble portion consists of neutral caseinate (casein Ca<t) and 

 neutral dicalcium phosphate (CaHP04). The casein and dicalcium phosphate 

 are not in combination, as shown by a study of IG samples of milk from 13 

 individual cows, and also by a study of the deposit or ' separator slime' formed 

 by whirling milk in a cream separator. By treating fresh milk with formalde- 

 hyde and whirling in a centrifugal machine under specified conditions, it is 

 possible to effect a nearly complete separation of phosphates from casein. 



" Both fresh milk and the serum from fresh milk show a slight acid reaction 

 to phenolphthalein, but are strongly alkaline to methyl orange, indicating that 

 acidity is due, in part at least, to acid phosphates. In eight samples of fresh 

 milk the acidity of the milk and. of the milk serum was determined after 

 treatment with neutral potassium oxalate. The results show that the acidity 

 of the whole milk is the same as that of the serum, and that, therefore, the 

 constituents of the serum are responsible for the acidity of the milk. There 

 is every reason to believe that the phosphates of the serum cause the observed 

 acidity." 



In the study the Briggs apparatus for filtration (E. S. R., 14, p. 127) was 

 employed. See also notes by Schroinor and Failyer and by Rupp (E. S. R., 

 17, p. 831; 29, p. 109). 



On the basis of the data presented, taken together with many other analytical 

 data worked out by the authors, the following composition of milk is suggested: 

 "Total solids, 12.901 per cent: Fat 3.90, milk-sugar 4.90, proteins combined 

 with calcium 3.20, dicalcium phosphate (CariP04) 0.175, calcium chlorid 

 (CaCls) 0.119, monomagnesiura phosphate (MglLP-Os) 0.103, sodium citrate 

 (NaoCsHsOT) 0.222, potassium citrate (KsCeHsO:) 0.052, dipotassium phosphate 

 (KjHPOi) 0.230." The amounts are based on milk of average composition. 



On the action of coagulating enzyms on caseinogen, A. Harden and A. B. 

 Macaixum {Biochcm. Jour., 8 {IDl.'t), No. 1, pp. 90-99). — "The conversion of 

 caseinogen into casein by enzym action is accompanied by the cleavage of 

 90853°— No. 7—15 2 



