Milk. 15*7 



cow's milk is about 4 per cent. The albumen is usually about 

 1 per cent. 



The milk sugar is a body similar in composition to cane 

 sugar, but differing in many of its properties. It is not so 

 soluble as cane sugar, and consequently not so sweet. It 

 may be obtained from whey by evaporating it to a thin 

 syrup, and allowing it to stand for a long time in a cool 

 place, when it crystallizes out. It forms hai'd colourless 

 transparent four-sided prisms. When milk is kept, after 

 a variable time depending on temperature and other con- 

 ditions, the milk sugar begins to undergo a change, by 

 which it is converted into a peculiar acid — lactic acid. One 

 molecule of milk sugar and one molecule of water form 

 four molecules of lactic acid. 



[C 12 H 22 O n + H 2 = 4 C 3 H 6 0,] 



The lactic acid so formed causes the coagulation of the 

 casein ("curdling"), and is the cause of the sour taste of 

 spoiled milk. This change is caused by a peculiar ferment 

 present in the milk. The activity of this ferment is 

 destroyed for a time b}^ boiling. Hence the peculiar effect 

 of boiling milk. 



Milk sugar, like cane sugar, belongs to that class of 

 saccharine bodies which are not directly susceptible of 

 alcoholic fermentation. When a solution of cane sugar is 

 mixed with yeast, it takes up a molecule of water and is 

 converted into a fermentable sugar or glucose, which in 

 its turn splits up into alcohol and carbon dioxide. 



[C 12 H 22 O n + H 2 = 2 C c H,0 B 

 C r H 12 O c = 2 G 2 H c O + 2 CO,.] 



Similarly milk sugar, under the influence of yeast, is 

 changed first into a fermentable sugar galactose and then 

 into alcohol and carbon dioxide. These changes are utilized 

 in the preparation of koumiss, an aerated alcoholic beverage 

 obtained by fermenting milk. The alcohol which koumiss 

 contains and the carbon dioxide which gives it its sparkling 

 effervescent character are both derived from the sugar of 

 milk. 



