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 the 
percentage of fat content. Knowing these factors, by the use 
of the following formula given by Farrington and Woll, and 
deduced from Fleischmann’s work, the total solids, and solids 
not fat, can be found: 
Solids not fat=} lact. reading + .2 times the fat. 
Total solids =fat+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 
difference 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 
