Test bottles. The Babcock-test bottle for milk, as shown 

 in figure 1, consists of a body holding about 50 cubic centi- 

 meters and the neck graduated so that the percentage of 

 fat may be read directly. Seventeen and one-half cubic 

 centimeters are used in the test, and this volume of 

 average milk weighs almost exactly 18 grams. At the 

 temperature at which the bottles are standardized the 

 specific gravity of butterfat is about 

 0.9. Two cubic centimeters weigh twice 

 0.9, or 1.8 grams, which is just one- 

 tenth of the weight of the charge used in 

 the test bottle. The volume between 

 and 10 per cent in the neck should, there- 

 fore, be 2 cubic centimeters, if the bottle 

 has been correctly standardized. Each 

 unit per cent is represented by a volume 

 of 0.2 cubic centimeters in the neck. The 

 old types of bottles were 10 per cent bot- 

 tles, the smallest subdivision being 0.2 per 

 cent. In the more recent types^ notably 

 those made to conform to the specifica- 

 A tions of the United States Bureau of Stand- 

 ards, the necks are somewhat smaller in 

 diameter and read only to 8 per cent, and 

 the smallest subdivision is 0.1 per cent. 

 (Fig. 2.) The 8 per cent bottle is consid- 

 ered the more accurate of the two, and has 

 come into more general use. 



Milk pipette. The charge for the Bab- 

 cock test for milk is measured rather than 

 weighed, the measuring instrument being 

 a pipette graduated to deliver 17.5 cubic 

 centimeters of milk. These pipettes, filled to their 

 graduation mark, hold 17.6 cubic centimeters. The 

 extra 0.1 cubic centimeter is allowed for the milk 

 which clings to the walls. Pipettes may be obtained 

 which conform to the requirements of the United 

 States Bureau of Standards. (Fig. 3.) 



FIG. 3. Pipette 

 holding 17.6 

 cubic centi- 

 meters, used 

 in measuring 

 milk in the 

 Babcock test. 



