150 



MILK 



nite directions. The instrument used is the Zeiss butyrore- 

 fractometer (Fig. 41). The apparatus used in this determination 

 are shown in Fig. 42. Thirty c.c. of milk are measured into the 

 stoppered flask by means of a 7.5 c.c. pipet. This pipet is so con- 

 structed that it can be placed in the sampling tube. To the 

 30 c.c. of milk 12 drops acetic acid are added to curdle the milk. 

 The flask is then shaken in a mechanical shaker for one or two 



Fig. 42. — Apparatus used in Wollny's refractometer method. 



minutes and then 3 c.c. standard alkali solution added. The 

 flask is again placed in the mechanical shaker and shaken for 

 ten minutes at a temperature of 17.5° C. After this 6 c.c. water- 

 saturated ether are added and the flask shaken for fifteen minutes. 

 Finally the flask is placed in a centrifuge and whirled for three 

 minutes. Now a few drops of ether-fat solution are placed in 

 the refractometer and theres ults read. The table on pages 151 

 and 152 gives the percentage of fat according to the reading 

 (Leach). 



