54 Testing Milk and Its Products. 



The Trowbridge method of calibrating milk test bot- 

 tles may 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, and from 20 to 30 per cent, 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 hold, 

 viz., 17.6 grams and 17.5 grams, respectively. The 

 necessity of previous thorough 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 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 grnm, when 

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

 water (4O); 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.) 



