54 Testing Milk and Its Products. 



ties will also be found convenient for cream bottles and 

 the same standard measure used, the part of the scale 

 from to 10 being calibrated first, then that from 10 to 

 20, 20 to 30, 30 to 40 per cent., etc., in the same way. 



63. Pipette and acid cylinder. The pipette and the 

 acid cylinder used in the Babcock test may be calibrated 

 by any of the methods already given. Sufficiently ac- 

 curate results are obtained by weighing the quantity of 

 water which each of these pieces of apparatus will de- 

 liver, viz., 17.5 grams. The necessity of previous thor- 

 ough cleaning of the glassware is evident from what has 

 been said in the preceding. The pipette and the acid 

 measure may be weighed empty and then again when 

 filled to the mark with pure water, or the measureful of 

 water may be emptied into a small weighed vessel, and 

 this weighed a second time. In either case the weight 

 of the water contained in the pipette or acid measure is 

 obtained by difference. 1 



Calibrations of the acid cylinder are generally not 

 called for, except as a laboratory exercise, since small 

 variations in the amount of acid measured out do not 

 affect the accuracy of the test. 



2. CENTRIFUGAL MACHINES. 



64. The capacity of the testing machine to be selected 

 should be governed by the number of tests which are 

 likely to be made at one time. For factory purposes a 



1 One cubic centimeter of distilled water weighs 1 gram, when 

 weighed in a vacuum at the temperature of the maximum density of 

 water (4 C.) ; for the purpose of calibration of glassware used in the 

 Babcock test, sufficiently accurate results are, however, obtained by 

 weighing the water in the air and at a low room temperature (60 F.) 



