36 MANUAL OF MILK PRODUCTS 



is in combination with calcium alone or with some other inor- 

 ganic base in addition, and also whether milk-casein is an acid 

 salt or a neutral salt and, further, whether the insoluble phos- 

 phates are in combination with casein or not. 



The authors summarize the results of their extended studies 

 on this subject as follows : 



1. Milk contains two general classes of compounds, those in 

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

 portions can be separated for study by filtering the milk through 

 a porous earthenware filter like the Pasteur-Chamberland 

 filtering tube. 



2. Serum prepared from fresh milk is yellow with a faint 

 greenish tinge and slight opalescence. The following constitu- 

 ents of milk are wholly in solution in the milk-serum : sugar, 

 citric acid, potassium, sodium, and chlorine. The following are 

 partly in solution and partly in suspension : Albumin, inorganic 

 phosphates, 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. 



3. The insoluble portion of milk separated by filtration 

 through the Pasteur-Chamberland filtering tube is grayish to 

 greenish white in color, of a glistening, slime-like appearance 

 and gelatinous consistency. When shaken with water it goes 

 readily into suspension, forming a mixture having the opaque, 

 white appearance of milk. Such a suspension is neutral to 

 phenolphthalein. When purified, the insoluble portion con- 

 sists of neutral calcium caseinate (casein Ca 4 ) and neutral di- 

 calcium phosphate (CaHPO 4 ). The casein and di-calcium 

 phosphate are not in combination, as shown by a study of 16 

 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- 



