28 MODERN METHODS OF TESTING ^IILK 



instrument the main tube is open at both ends, the 

 lower end closely fitting into a cap furnished with 

 three elliptical openings. When the sampler, open at 

 the bottom, is let down into a can of milk, the liquid 

 pours into the openings and fills the tube to the height 

 of the milk in the can. When the cap comes in con- 

 tact with the bottom of the can, the tube slides down 

 and closes the openings, after which the tube can be 

 withdrawn and its contents emptied into the com- 

 posite jar. 



The tube method of sampling possesses two marked 

 advantages over the dipper method : ( i ) It always 

 takes an aliquot portion, or uniform proportion, of 

 the milk, representing a small column of the milk 

 from top to bottom ; and (2) it provides a strictly rep- 

 resentative sample of the milk, even when sampling 

 is delayed, because it takes a uniform amount from 

 each layer of milk, going from toD to bottom. 



THE USE OF PRESERVATIVES IN COMPOSITE 

 SAMPLES 



The successful use of composite samples is made 

 possible only by the presence of some substance which 

 will keep the milk from curdling. Three preserva- 

 tives have been found especially useful for this pur- 

 pose: (i) Corrosive sublimate, (2) formalin, and 

 (3) bichromate of potash. 



Corrosive sublimate, known chemically as mercuric 

 chloride, has the advantage of being a more powerful 

 antiseptic than the other substances, much smaller 

 quantities being effective in keeping milk longer, but 

 it has the disadvantage of being a violent poison. 



