PROPERTIES OF MILK. 35 



specific gravity into lactometer reading the reverse process will 

 give correct results. 



The hydrometer gives the specific gravity directly. The 

 Board of Health lactometer has a special graduation. In 

 devising this lactometer it was thought that 1.029 was the 

 minimum specific gravity of unadulterated milk. The scale on 

 this lactometer was made from zero to 120; zero marking the 

 point which represents the specific gravity of water, namely, 1. 

 100 is the point which is assumed to represent the least specific 

 gravity of milk 1.029. If the specific gravity of a certain 

 sample of milk fell to 90, it indicated that there was 10% of 

 water present. If it fell to 80, it indicated that there was 20% 

 of water, etc. 



In order to calculate the total solids, and solids not fat, of 

 milk, it is necessary to know the lactometer reading, and tht 

 percentage of fat content. Knowing these factors, by the use 

 of the following formula given by Farrington and WoU, and 

 deduced from Fleischmann's work, the total soHds, and solids 

 not fat, can be found: 



Solids not fat= J lact. reading + .2 times the fat. 

 Total solids = f at + solids not fat. 



Natural Separation of Milk and Cream. — When milk is 

 allowed to stand quietly for a short time, a layer having a rich- 

 yellow color comes to the surface. This is the cream, and 

 contains most of the fat. This separation is due chiefly to the 

 differeiice in weight, or specific gravity, of the fat-globules and 

 the serum. The force which acts upon the globule of fat is the 

 difference in weight between the fat-globule and the serum 

 which it displaces, minus the resistance force with which it 

 meets in its upward passage. In milk with a high degree of 

 viscosity this force is great. In milk of a limp and liquid 

 consistency this force is smaller. By adding water the vis- 

 cosity of milk is reduced considerably, and the specific gravity 

 of the serum is also decreased. But the effect of the added 

 water upon the viscosity is greater than the effect the water has 



