54 MODERN METHODS OF TESTING MILK 



diately before taking the sample for testing. The spe- 

 cial methods of preparing milk for sampling under 

 various conditions are fully considered in Chap. II, 

 p. 20. The fat must be evenly distributed through 

 the milk just before sampling. 



Every sample of milk should always be tested in 

 duplicate, that is, two tests should be made at the 

 same time. This insures greater accuracy. If the 

 results of the duplicate test do not agree, there is an 

 error somewhere and the work must be repeated. Also, 

 in case one test is lost and another sample can not be 

 obtained, the remaining test can be used, and the whole 

 work will not be lost. 



TAKING SAMPLES OF MILK WITH PIPETTE 



The measuring pipette (Fig. 8, p. 35), is filled at 

 once after the thorough mixing of the milk. This is 

 done by placing the lower end of the pipette well down 

 in the milk and sucking up the milk until it reaches 

 a point in the pipette somewhat above the mark around 

 its upper stem. Then the forefinger, which must be 

 dry, is quickly placed over the upper end of the pi- 

 pette before the milk runs down below the mark. By 

 lightening the pressure of the finger on the end of 

 the pipette, the milk is allowed to flow out slowly un- 

 til its upper surface just reaches the mark on the 

 stem. Some practice is necessary before one can eas- 

 ily and rapidly manipulate the pipette with accuracy. 



The pipette must be kept very clean. When sam- 

 ples of several different milks are to be drawn in suc- 

 cession, the pipette may be satisfactorily rinsed by 



