226 GENERAL SCIENCE 



Composition of Milk. Milk is composed of water, fat, casein, 

 albumen, milk sugar, ash, and a few other substances in small quan- 

 tities. The average cow's milk contains 



Water 87.1 per cent 



* Fat 3 . 9 per cent 



Casein 2 . 5 per cent 



Solids 12. 9 per cent 



Albumen . 7 per cent 

 Sugar 5 . 1 per cent 

 Ash . 7 per cent 



Fat is found in the milk in the form of small globules. About 

 6000 of them placed side by side would be required to make an inch. 

 Casein gives the milk the bluish white color and is the curd found 

 in sour milk. This casein, after treatment with certain chemicals, 

 is often used for the manufacture of knife handles, billiard balls, 

 piano keys, combs, backs of hair brushes, and countless other 

 articles. The skim milk is treated with sulphuric acid to obtain 

 the casein. 



Project 5. Look up the uses of casein, and processes for manufacturing 

 articles from it. 



Adulterations of Milk. Milk is adulterated by: 



1. Addition of water. 



2. Removal of cream. 



3. Use of preservatives. 



To tell whether the cream has been removed from the milk, and 

 to determine the solids not fat, it is necessary to test for the amount 

 of fat by the Babcock Test Method. 



Babcock Test for the Per Cent of Fat in Milk. Add strong sulphuric 

 acid to milk to dissolve all the solids except the fat which is afterwards separated 

 by means of a centrifugal machine. 



Measure exactly 17.6 c.c. of the milk into a Babcock bottle by means of a 

 milk pipette. Add exactly 17.5 c.c. of H 2 SO 4 , specific gravity 1.83, inclining the 

 bottle so that the acid will run in slowly, washing all adhering milk from 

 the neck. 



