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. 32). 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 



