THE OTHER CONSTITUENTS OF MILK. 29 



Indeed, Henkel has proved that citric acid is a normal con- 

 stituent of milk. Whether, in addition to it, other organic acids not 

 yet discovered, may be present in milk, it is impossible to say. If 

 citric acid only is present, milk must contain on an average some- 

 where about '25 per cent of it. Till now, perhaps in consequence 

 of the difficulty attending the exact quantitative determination, 

 only '1 to "15 per cent has been found. The following, according to 

 Soldner, are the probable combinations in which the mineral con- 

 stituents of milk are present (neglecting the small traces of iron): 



Sodium chloride, 10'62 



Potassium chloride, ... ... ... ... 9*16 



Monopotassium phosphate, 12 -77 



Dipotassium phosphate, ... ... ... 9'22 



Potassium citrate, ... ... ... ... 5 '47 



Dimagnesium phosphate, ... ... ... 3 '7 1 



Magnesium citrate, ... ... ... ... 4*05 



Dicalcium phosphate, 7 -42 



Tricalcium phosphate, ... ... ... -8 '90 



Calcium citrate, ... ... ... ... 23*55 



Calcium oxide in combination with casein, 5'13 



100-00 



In the above combinations of the mineral salts, if they could be 

 obtained unchanged, they would form '90 per cent of milk. Accord- 

 ing to Soldner's experiments, 36 to 56 per cent of the phosphoric 

 acid present in milk, and 53 to 72 per cent of the calcium oxide, are 

 not in solution, but are in a state of suspension in the form of 

 dicalcium and tricalciuin phosphates. 



To the above-mentioned constituents the following substances must 

 be added, as present in the ash of milk: silica, iodine (in districts near 

 the sea), calcium fluoride, and calcium carbonate. The chemical combina- 

 tions of the mineral salts of milk are not constant, but vary within certain 

 limits according to the state of health, the feeding, the period of lactation, 

 and perhaps also the age of the animal. 



9. The Other Constituents of Milk. In addition to the chief con- 

 stituents of milk enumerated and described above, several other 

 substances must be briefly referred to which, although occurring as 

 normal constituents, are always present only in very small quan- 

 tities, and partly in the gaseous form. These substances, therefore, 



