DETECTION OF ADULTERATION 43 



the filter and continue the filtration as usual. 

 Refract the clear filtrate at 20°, by means of the 

 Zeiss immersion ref ractometer. A reading below 

 36 indicates added water. The advantages of 

 this method over the acetic acid method are as 

 follows: It is quicker, heating of the samples is 

 unnecessary, consequently there is no error due 

 to evaporation. The range of differences in the 

 refraction of pure milk is less. 10% of added 

 water will reduce the refraction of high-grade 

 milk below the minimum, but it takes 1 5 % in the 

 acetic acid method. Lythgoe made analyses 

 of 150 samples of milk of known purity by this 

 method. The total solids ranged from 17.17 to 

 10.40%, the fat from 7.7 to 2.45%, the solids not 

 fat from^io.so to 7.5% and the refraction of the 

 copper serum from 36.1 to 39.5. These refrac- 

 tions were distributed as follows : 



150 



See also table of refractions on page 7 . 



As a result of extended experience, Lythgoe 

 has recently given the following applications 

 of some of the methods of milk analysis. 



The least variable constituents of milk are 



