METHODS OF EXAMINING MILK 229 
the milk has been placed in the glass cylinder and the 
lactometer introduced. The lactometer reading and the 
temperature should be taken as nearly as possible at 
the same time. If the temperature of the milk is not 
exactly 15° C. (60° F.), then the specific gravity at this 
temperature must be calculated from the lactometer and 
thermometer reading, because this is the standard tem- 
perature. Adding to the specific gravity 0.0002 for each 
degree Centigrade above 15 or 0.0001 for each degree 
Fahrenheit above 60, and subtracting the same numbers 
for each degree below the standard temperature, will 
give the approximate specific gravity at the standard 
temperature; but more accurate results will be obtained 
by using the tables on pages 230 and 231. If, for exam- 
ple, the lactometer reading is 28 and the temperature is 
17° C., locate 1.028 in the column at the extreme left and 
follow this line to the right to the column headed 17° C.; 
the figures at this point, 28.4, represent the lactometer 
reading at 15° C. To obtain exact results, the specific 
gravity should be taken with the milk at 15° C., because 
lactometers are calibrated for this temperature. After 
the specific gravity is taken the lactometer should be 
rinsed with water and wiped dry. 
The specific gravity of milk may also be determined 
by means of the Westphal balance (Fig. 82). This in- 
strument consists of a pivoted beam with a float hanging 
from one end. The milk to be tested is placed in a glass 
cylinder and the float is let down into the milk. The 
weights on the beam are then moved until equilibrium 
is established, and the specific gravity is indicated by the 
position of the weights. 
The specific gravity of normal market milk ranges 
from 1.028 to 1.034, the average being 1.032. Skimming 
