DETECTION OF ADULTERATION 43 
the filter and continue the filtration as usual. 
Refract the clear filtrate at 20°, by means of the 
Zeiss immersion refractometer. Areading 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 15 % inthe 
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 10.50 to 7.5% and the refraction of the 
copper serum from 36.1 to 39.5. These refrac- 
tions were distributed as follows: 
REFRACTION NuMBER oF SAMPLES 
39.0 to 39.5 6 
38.0 to 38.9 66 
37.0 to 37.9 65 
36.1 to 36.9 13 
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 
