38 Testing Milk and Its Products. 



1 GLASSWARE. 



44. Test bottles. The test bottles should have a 

 capacity of about 50 cc., or less than two ounces; they 

 should be made of well-annealed glass that will stand 

 sudden changes of temperature without breaking, and 

 should be sufficiently heavy to withstand the maximum 

 centrifugal force to which they are likely to be subjected 

 in making tests. This force may on the average not be 

 far from 30.65 Ibs. (see 66), which is the pressure exerted 

 in whirling the bottles filled with milk and acid in a 

 centrifugal machine of 18 inches diameter at a speed of 

 800 revolutions per minute. 



Special forms of test bottles used in testing cream and 

 skim milk are described under the heads of cream and 

 skim milk testing (89, 90, 91, 99). 



When 17.6 cc., or 18 grams of milk (48), are measured 

 into the Babcock test bottle, the scale on the neck of the 

 bottles shows directly the per cent, of fat found in the 

 milk. The scale is graduated from to 10 per cent. 

 10 per cent, of 18 grams is 1.8 grams. As the specific 

 gravity of pure butter fat (i. e. its weight compared 

 with that of an equal quantity of pure water) at the 

 temperature at which the readings are made (about 140 

 F.), is 0.9, then 1.8 grams of fat will occupy a volume 

 of - l< =2 cubic centimeters. The space between the and 

 10 per cent, marks on the necks of the test bottles must 

 therefore hold 2 cc., if correctly made. The scale is 

 divided into 10 equal parts, each part representing one 

 per cent., and each of these is again sub- divided into 

 five equal parts. Each one of the latter divisions there- 



