CHAPTER XLIV 

 TESTING MILK 



Milk is commonly tested for two purposes: (1) To deter- 

 mine whether or not it has been adulterated with water; 

 (2) to determine the per cent, of butter-fat. 



1. As was mentioned in a previous chapter, milk is heavier 

 than water, ordinarily .032 heavier, that is, its specific gravity 

 is 1.032. It is very rare for pure milk to have a specific grav- 

 ity less than 1.029. If water has been put into milk to any 

 extent, the specific gravity will go below 1.029. An instru- 

 ment resembling a floating thermometer has been devised 

 for determining the specific gravity of milk. This instru- 

 ment is called a lactometer. The glass tube is graduated some- 

 what like that of a thermometer. There are two common 

 forms of lactometers, the Board of Health lactometer and the 

 Quevenne (Kwi-ven') lactometer. These are graduated dif- 

 ferently, but give the same results. 



When the lactometer is put into the milk it will sink to a 

 certain point. The Board of Health lactometer should not 

 sink below 100, the Quevenne not below 29. Then by read- 

 ing the figures on the glass tube one can tell the specific 

 gravity of the milk and from these whether the milk is pure 

 or not. It should be remembered that the lactometer test is 

 not absolutely reliable, but in any case of doubt further 

 investigation can be made. 



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