228 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

 DETERMINATION OF SPECIFIC GRAVITY 



The specific gravity of milk is determined by means 

 of Quevenne 3 s lactometer ( Fig. 31 ) or modifications of 

 this apparatus. 



After being thoroughly mixed, some of the milk to 

 be tested is poured into a high glass cylinder and the 

 lactometer is slowly and carefully lowered 

 into the fluid until it floats. Care should 

 be taken not to mix air with the milk. 

 This can be avoided by pouring the milk 

 against the side of the vessel. The lacto- 

 meter must not be permitted to touch 

 the side of the cylinder. When the 

 lactometer has become stationary, the 

 specific gravity is indicated by the 

 figures on the scale in the stem of the 

 lactometer. The reading is taken from 

 the line in the scale which is on a level 

 with the surface of the milk. The stem 

 of the lactometer draws the milk up 

 around it, forming a slight meniscus 

 which obscures the line at the surface of 

 the milk. The reading should not be 

 taken from the top of this meniscus, but 

 at the surface of the milk, the depth of 

 the meniscus being estimated. The 



Fio. 31. Quevenne 'B 



lactometer. figures on the lactometer scale do not ex- 

 press the specific gravity but Quevenne degrees. By 

 dividing Quevenne degrees by 1000 and adding 1, the 

 specific gravity is obtained. 



The temperature of the milk should be 15 C. (60 

 F. ) when the specific gravity is taken, and the tempera- 

 ture should be taken with an accurate thermometer after 



