27:.' Agricultural Chemistry. 



of cane sugar. By the action of dilute acids or an enzyme known 

 as lactase, it is split into a mixture of dextrose and galactose. 



Milk sugar does not readily undergo alcoholic fermentation. 

 but is readily changed into lactic acid by certain micro-organ- 

 isms. This change in the milk sugar is the cause of milk souring. 

 The necessary lactic organisms are very abundant everywhere, 

 especially in the vicinity of dairies and barns, and as they 

 multiply in the milk, more and more lactic acid is formed. Sweet 

 milk has an acidity of from 0.12 to 0.20 per cent, expressed as 

 lactic acid. When about 0.40 per cent is present, the milk ac- 

 quires a sour taste, and when the amount reaches 0.6 to 0.7 per 

 cent, curdling commences. "With certain organisms, the amount 

 of lactic acid may reach from 2.0 to 3.0 per cent, but ordinarily 

 it does not exceed 0.9 per cent. 



The ash of milk. "When water is removed from milk by evap- 

 oration and the residue then burned, a white ash is always left 

 behind. This consists of the mineral matter and salts of the 

 milk, together with sulphates, phosphates and carbonates pro- 

 duced by the burning of the organic matter of the milk. It 

 amounts in cow's milk to about 0.7 per cent, and consists of: 



Per cent 



Potash m .... 22 to 27 



Soda ".... 10 to 12 



Lime 19 to 24 



Magnesia 1.8 to 3 



Pei' cent 



Ferric oxide traces to 0.2 



Sulphur trioxide 3.8to 4.4 



Phosphoric acid 22 to 27 



Chlorine.. .... 13 to 16 



Milk also contains traces of citric acid. This is not free, but 

 in combination with bases as citrates and amounts to about 0.1 

 per cent of the milk. 



The gases of fresh milk are chiefly carbon dioxide, oxygen and 

 nitrogen. These amount to about 85 c. c. per liter, the carbon 

 dioxide constituting approximately 90 per cent of the total gas. 

 On standing, or even during the process of milking, there is a 

 rapid exchange of gases, the carbon dioxide greatly diminishing, 

 while tin- oxygen and nitrogen rapidly increase. This increase 



