METHODS OF EXAMINING MILK 251 
of the refractometer. The temperature of the water 
bath should be 17.5° C. After allowing 8 to 10 minutes 
for the serum in the beaker to reach the same tempera- 
ture, the prism of the refractometer is inserted in the 
beaker and the refraction number is read from the scale, 
Fia. 38.—Zeiss dipping refractometer. 
which is located in the refractometer beneath the ocular. 
On looking into the ocular it will be observed that a por- 
tion of the field is dark and the remainder light. The 
border line is usually fringed with colors and the com- 
pensator must then be rotated by means of the milled 
