PROPERTIES OF MILK. 33 
only be obtained at one given temperature, for, as the tempera- 
ture of the substance becomes higher, the density of it grows less, 
and consequently the specific gravity will be less. The tempera- 
ture at which the lactometers are standardized is 60° F. 
The variations in the specific gravity of milk will also vary 
according to the relative variation in amounts of the different 
components of milk. If a sample of milk is rich in solids not 
fat, as, for instance, skimmed milk, the specific gravity will be 
high and usually between 1.033 and 1.037. If the sample of 
milk is rich in fat, as, for instance, in cream, the specific gravity 
will be less. 
By adding water to milk, the specific gravity of it is lessened. 
Owing to this fact it was first thought that adulteration of milk 
with water could be detected by testing its specific gravity, 
But this method was soon found to be erroneous, as it is 
possible to take cream away and add water in such a proportion 
as not to alter the specific gravity of the sample. A low specific 
gravity of milk may, however, cause the suspicion that the milk 
has been adulterated, and the test for water adulteration can 
be supplemented by testing it for fat. 
As has been mentioned before, the lactometer reading should 
be taken at 60° F. If the temperature of milk is above or 
below, corrections must be made. The amount of correction 
which will give approximate results is .1 of a degree added to 
the lactometer reading for every degree Fahrenheit of tempera- 
ture the milk is above 60° F., and also .1 of a degree subtracted 
from the lactometer reading for every degree of temperature the 
milk is below 60° F. The temperature of milk when tested for 
lactometer reading should never go any lower than 10° below 
60°, nor any higher than 10° above 60°. This would leave the 
range of temperature between 50° and 70° F. 
In chemical laboratories, the specific gravity of milk is 
usually determined by the use of a picnometer. 
In practice there are three instruments in general use for 
determination of lactometer reading, or specific gravity, viz.: 
Quevenne lactometer, New York Board of Health lactometer 
