Specific Gravity of Milk. 19 
greater in colostrum than in normal milk, and the 
percentage of fat varies very widely. Usually the 
percentage of fat is less in the colostrum than in 
the normal milk from the same cow, although oc- 
casions are not infrequent where more fat is found. 
in the milk immediately after calving than at any 
other time in the whole period of lactation. 
Specific gravity of milk.—Some of the solids of 
milk are heavier than water and some of them lighter, 
milk as a whole having a specific gravity somewhat 
greater than water. The variation in the specific 
gravity is considerable, the range usually given being 
from 1.029 to 1.035 at 60° F., the average being 
about 1.032. In general, the effect of an increase 
in the solids of the milk is to increase its specific 
gravity, though in milk extremely rich in fats (six 
per cent or above) the specific gravity is lessened. 
Formerly, more than at present, it was the custom 
to estimate the quality of the milk by determining 
its specific gravity, but as soon as it became known 
that the specific gravity depended not so much upon 
the amount as upon the character of the solids, a 
determination of the specific gravity became of little 
value. Unscrupulous dairymen soon learned that 
water could be added to milk and fat or cream 
taken from it in such proportions that the specific 
gravity would remain the same as that of normal 
milk. 
The fats.—The fat of milk, or butter fat, as it 
is often called, is a mixture of a considerable number 
of separate and distinct fats, no less than six or 
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