ADULTERATIONS OF MILK 



217 



Added water in milk can also be determined with an im- 

 mersion refractometer. The tables on pages 218 and 219 give 

 the refractometer reading and the specific gravity of milk serum 

 according to the amount of water added to the milk. 



Determination of added water either by the use of the re- 

 fractometer or by determining the specific gravity of the serum 

 requires considerable experience to yield reliable results. Ex- 

 perts with these methods claim that 5 per cent, of added water 

 can be detected by these methods. 



Fig. 82. Feser's lactoscope (Leach). 



The Association of Official Agricultural Chemists gives the 

 following method for determining added water by the use of the 

 Zeiss immersion refractometer: 



"To 100 c.c. of milk at a temperature of about 20 C. add 2 c.c. 

 of a 25 per cent, acetic acid (spec. grav. 1.035) in a beaker, and 

 heat the beaker, covered with a watch-glass, in a water-bath for 

 twenty minutes at a temperature of 70 C. Place the beaker in 

 ice water for ten minutes and separate the curd from the serum 

 by filtering through a 12.5-cm. .folded filter. Transfer about 



