MILK. 433 



and of the method of separating them from each other, has been 

 given in a preceding volume of this work.* 



The composition of these three acids, according to the analy- 

 sis of Chevreul, is as follows : 



Butyric. Caproic. Capric. 



Carbon, . 62-82 . 68-33 . 74-00 

 Hydrogen, 7'01 . 9-00 . 9-75 



Oxygen, . 30-17 . 22-67 . 16-25 



100-00 100-00 100-00 



From the experiments of Chevreul it would appear that the ato- 

 mic weight of butyric acid is 9*625, that of caproic acid 13-25, 

 and that of capric acid 18-25. Hence the constituents of these 

 acids should be, 



Butyric acid, C 8 H 5 O 3 = 9-625 

 Caproic acid, C 12 H 10 O 3 =13-25 

 Capric acid, C 18 H 14 O 3 = 18-25 



But new and careful analyses would be necessary before we could 

 consider these numbers as established. 



2. When milk freed from cream is heated to 110, or a little 

 higher, and mixed with a little rennet, it coagulates and gradual- 

 ly separates into a solid white matter called curd, and a liquid 

 portion distinguished by the name of whey. 



Curd when in a state of purity is distinguished by the name 

 of casein. The mode of procuring it in a state of purity and its 

 properties have been given in a preceding chapter of this vo- 

 lume. Casein has many properties in common with the albu- 

 men of blood, and like albumen may be obtained in two states, 

 namely, uncoagulated, when it is soluble in water, and coagulated 

 when it is insoluble in that liquid. It is precipitated from its 

 aqueous solution by acetic acid, which is not the case with albu- 

 men. It is coagulated by a boiling heat, but slowly ; separating 

 in films which collect upon the surface of the liquid. 



Qoagulated casein subjected to pressure to free it from the 

 whey constitutes cheese. If cheese consist of nothing but casein, 

 it has a bluish white colour, is very hard, almost like horn, and 

 is quite insipid. Good cheese is always made from milk still re- 

 taining its cream, and in Stilton, which is one of the richest of 

 the English cheeses, the milk is not only allowed to retain its na- 

 tural quantity of cream, but an additional quantity is added. 



* See Chemistry of Inorganic Bodies, ii. 132. 



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