176 c*. 



THE BABCOCK TEST 35 



serum. Hence this heavy mixture is 

 forced to the outside, which is the bottom 

 of the bottle, while the much ligher 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 material 

 are used in making the tests (i) Test-bot- 

 tles, (2) pipette for measuring milk, (3) 

 acid-measure, (4) tester or centrifugal 

 machine, and (5) sulphuric acid, 



TEST-BOTTLES 



The usual forms of bottle used in test- 

 ing milk are shown in Fig. 7 and 7a. The 

 neck of the bottle is marked with a scale 

 so graduated that each small division re- 

 presents .2 per cent, and five of these divi- 

 sions, making one large division, represent 

 I per cent., when we use 17.5 cc.* or 18 

 grams of milk. The marks extend from o 

 to 8 or 10 per cent. Why do these divisions 

 represent exact percentages by weight of 

 fat in milk, when no weighing is done in 

 testing milk?' We use, in testing, 17.5 cc. of 

 milk, which is known to weigh almost ex- 

 actly 18 grams. The graduated portion of 

 the neck of the test-bottle is made to hold 



FIG. 8 * cc - ' 1S ti 16 abbreviation for cubic centimeters 



PIPETTE (see p. 273). 



