MILK 31 
ture of 15° C. (60° F.). At higher temperatures the 
specific gravity or density is decreased, and at lower tem- 
peratures it is increased. 
The specific gravity depends not only upon the total 
quantity of solids contained in the milk, but also upon the 
relative proportion in which the individual solids are 
present, because the individual solids are of different spe- 
cific gravity. Fat shows the greatest difference, being 
much lighter than the other solids; it is even lighter than 
water. The solids not fat are all heavier than water, 
the specific gravity of the salts being 4.12, lactose 1.666, 
and proteids 1.846 (Richmond). Therefore the removal 
of fat, i.e., skimming, increases the specific gravity, and 
the addition of skim milk has the same effect, while the 
addition of water reduces the specific gravity. But the 
specific gravity has such a wide normal variation that 
it is possible to remove a small amount of fat from milk 
with a normally low specific gravity without causing the 
specific gravity to rise above the normal range, and, 
conversely, a certain amount of water may be added to 
milk with a normally high specific gravity without lower- 
ing the specific gravity below the normal limit. How- 
ever, in the first case the per cent. of fat will be decreased, 
and in the second there will be a decrease in both the per 
cent. of fat and of solids not fat. When the specific 
gravity of milk is raised above the normal by skimming 
it may be brought within the normal range by the addi- 
tion of water, but the per cent. of fat and of solids not 
fat will be decreased. Therefore, in examining market 
milk to detect skimming or the addition of skimmed 
milk or water, the per cent. of fat and of solids not fat 
must always be considered in connection with the spe- 
cific gravity. (For method of determining the specific 
