36 



DAIRY CHEMISTRY 



WaUrzi 



43. The Specific Gravity of Milk. — If a can holds 

 100 pounds of water, to fill it with milk would require 

 about 103.2 pounds. This is because 

 milk has a greater specific gravity than 

 water. By the specific gravity of a 

 material is meant the weight of a given 

 volume compared with the weight of an 

 equal volume of water under the same 

 conditions. Milk has a higher specific 

 gravity than water because it contains 

 in solution a number of substances, as 

 sugar, ash, casein, and albumin, which 

 increase the weight of an equal volume 

 of milk, causing it to have a higher 

 specific gravity. The fat of milk, on 

 the other hand, which is lighter than 

 water, has a tendency to lower the 

 specific gravity. As stated in a previ- 

 ous chapter, the specific gravity of milk 

 fat is about .91. Since the amount of 

 sugar, ash, casein, and albumin in differ- 

 ent samples of milk is fairly constant, 

 it follows that the specific gravity of 

 the milk serum is quite constant. Since 

 the variations in the fat content of 

 milk range between 3 and 6 per cent, it 

 follows that the variations in the gravity 

 of milk are due largely to the variations 

 in the fat content. Since the milk fats vary between 

 known limits, the specific gravity of normal milk 



Fig. 11. — Que- 

 venne's lac- 

 tometer. 



