20 DAIBr CHEMISTET 



space between the and the 10 in the scale. Each 

 small division is equal to .04 cc, or, as usually made, 

 about one and one half millimeters. The test bottles 

 can also be calibrated with water in the following 

 way: The bottles are filled with pure distilled water 

 up to the mark, and then from an accurately 

 graduated burette, graduated to gV ^^-i "^^ter is 

 added. It should require 2 cc. of water to fill the 

 test bottle from the to the 10 mark. For ordinary 

 work the bottles can all be tested with one sample 

 of milk, and all bottles rejected that show a greater 

 difference than one small division. Accurately gradu- 

 ated test bottles can usually be obtained from supply 

 houses that deal in chemical apparatus. Inaccu- 

 rately graduated test bottles are occasionally the 

 cause of much trouble and dissatisfaction in the 

 creamery. 



20. Speeding the Machine. — ■ A centrifugal of 14 

 inches' diameter should make about 900 revolutions 



Fig. 8. — Centrifugal machine. 



per minute. In order to speed the machine count 

 the number of revolutions that the test bottles make 



