186 ELEMENTARY AGRICULTURAL CHEMISTRY 



Qecessary lactic organisms are very abundant everywhere, 

 especially in the neighbourhood of dairies, cow-houses, <kc., 

 and as they multiply, more and more lactic acid is produced. 

 As milk is usually sold, the acidity is less than 0*2 per cent, lactic 

 acid. When about 0*4 per cent, is present the milk acquires 

 a sour taste, and when the amount reaches about 0*7 per cent,, 

 coagulation or curdling commences. After long keeping, as 

 much as 2*0 per cent, of lactic acid may be present. 



The Ash of Milk is white, and contains the basic mineral 

 matter and salts of the milk, together with sulphates, phos- 

 phates and carbonates produced by the oxidation of the 

 sulphur, phosphorus and carbon contained in organic con- 

 stituents. Its amount in cows' milk is usually about 07 per 

 cent. 



The lime and other bases in the milk are associated with 

 the casein and citric acid. The latter substance appears to be 

 a general constituent of cov/s' milk, being present usually to the 

 extent of O'l per cent. Milk contains dissolved gases, chiefly 

 carbon dioxide, nitrrgea and a little oxygen. When fresh, 

 oxygen and nitrogen are the chief, amounting to from 1 to 

 3 c.c. per litre, but on keeping, the oxygen diminishes and 

 carbon dioxide appears, probably from fermentation of the 

 milk sugar. 



Cows' Milk. Physical Properties.— A white or yellowish- 

 white, opaque liquor, with a sweet taste. Specific gravity varies, 

 usually from 1'027 to 1*034. When fresh milk is quickly 

 cooled and its specific gravity taken at once, then again after 



