THE LACTOMETER AND ITS USE 37 



varies between definite limits. The lowest specific 

 gravity of normal milk is 1.029, while the highest 

 specific gravity is 1.034. *" The richer a sample of milk 

 in casein, milk sugar, and ash, the greater its buoyant 

 power and the higher specific gravity, which results 

 in the lactometer stem not sinking to so great a depth 

 as it would if less casein, sugar, and ash were present. 

 Hence we find skim milk having a greater specific 

 gravity than normal milk. On the other hand, the 

 addition of water to milk lowers the specific gravity 

 below 1.029 almost proportionally with the amount 

 of water added. Milks very rich in fat have a lower 

 specific gravity than milks which contain less fat. 

 This is due to the additional fat in the milk lowering 

 its specific gravity. A skilled operator can readily 

 determine whether the increase or decrease in the 

 specific gravity of milk is due to variation in the 

 water or the fat content of the milk. 



44. Influence of Temperature. Whenever a lac- 

 tometer reading is made, the temperature of the milk 

 should also be recorded, because a variation of 10 

 in temperature affects the lactometer reading to the 

 extent of 1. When milk is cold, it is contracted in 

 volume and the lactometer does not sink to as great 

 a depth as if the milk were warm. This results in 

 the lactometer recording a high specific gravity. 

 On the other hand, if the milk is too warm, it is ex- 

 panded, which has the effect of diluting the milk, 

 causing the lactometer to sink to a greater depth 

 and a lower specific gravity to be secured. In mak- 



