34 



MODERN METHODS OF TESTING MILK 



serum, the completion of the separa- 

 tion of fat is effected by centrifugal 

 force. When the bottles containing 

 the mixture of milk and acid are 

 whirled, the centrifugal force acts 

 more strongly upon the heavier por- 

 tion, that is, the mixture of acid and 

 milk-serum. Hence this heavy mix- 

 ture is forced to the outside, which is 

 the bottom of the bottle, while the 

 much lighter fat is forced to the top. 

 A small amount of fat (.1 to .2 per 

 cent.) remains unseparated under 

 usual conditions. 



The following apparatus and ma- 

 terial are used in making the test : ( i ) 

 Test-bottles, (2) pipette for measur- 

 ing milk, (3) acid-measure, (4) tes- 

 ter or centrifugal machine, and (5) 

 sulphuric acid. 



TEST-BOTTLES 



The usual form of bottle used in 

 testing milk is shown in Fig. 7. The 

 neck of the bottle is marked with a 

 scale so graduated that each small di- 

 vision represents .2 per cent, and five 

 of these divisions, making one large 

 division, represent i per cent., when we use 17.50:.* 

 or 18 grams of milk. The marks extend from o to 10 



FIG. 7 



MILK-TESTING 

 BOTTLE 



*cc. is the abbreviation for cubic centimeters (see p. 205). 



