160 



MILK 



The graduations of test bottles are not always accurate and 

 should be tested. This can be accomplished in various ways. 

 A special plunger has been devised for this purpose, known as the 

 Trowbridge calibrator, which can be procured for testing 10 per 

 cent, milk test bottles and 30 per cent, cream test bottles (Fig. 49). 

 This instrument consists of two parts, connected by wire. Each 



Fig. 47. — Correct 

 way of holding pipet 

 and bottle (Van Slyke) . 



Fig. 48. — Wrong way 

 of holding pipet and bot- 

 tle (Van Slyke). 



Fig. 49. — o, Milk- 

 bottle tester; 6, test- 

 ing accuracy of milk 

 bottle (Van Slyke). 



part displaces exactly 1 c.c. of water. The bottle is filled with 

 water or some other fluid exactly to the mark and the tester 

 is inserted until the lower portion is submerged. One c.c. of the 

 fluid is displaced, and therefore the surface line should reach to 

 the 5 per cent. mark. The second portion of the plunger is now 

 lowered and the fluid should reach to the 10 per cent. mark. It is 

 assumed that when the 5 and 10 per cent, marks are correct 



