391 
metrically (Van Slyke). The gravimetric method requires a large 
volume of milk and also requires considerable time. The volumetric 
method is rapid, and only small amounts of milk are required. For 
this reason the latter method was employed. Fifteen cubic centi- 
meters of the sample was placed in a Bausch and Lomb graduated 
centrifuge tube. The samples were then centrifugalized for five 
minutes. The dirt then collects on the bottom of the tube, and the 
volume of it is read. From these readings the per cent of dirt is 
calculated. 
Refractometer reading . — Milk serum has a higher index of refrac- 
tion than water. Therefore the addition of water to milk lowers the 
index of refraction of the serum. The retractometer reading of the 
several samples was obtained in the following manner: One hundred 
cubic centimeters of the sample of milk is placed in a beaker. To 
this 2 cubic centimeters of 25 per cent acetic acid is added. The 
beaker is then coveied with a watch glass and heated in a water bath 
at 70° C. for twenty minutes. It is then placed in ice water for ten 
minutes and filtered. The refractometer leading on the clear yellow- 
ish filtrate (milk serum) is then made with a Zeiss immersion refrac- 
tometer, at 20° C. A description of this instrument, together with all 
necessary directions for its use, is given by Leach (6). See also 
Wagner, B. (7). Unadulterated milks give a refractometer reading 
varying between 39 and 43 on the scale of this instrument. Accord- 
ing to Leach (8), a reading below 40 with the above conditions care- 
fully observed would be suspicious of added water, though 39 might 
more safely be placed as a limit, below which milk could be declared 
fraudulently watered. 
The following data given by Leach show the variations in the 
specific gravity, refractometer reading, chemical composition, etc., 
resulting from the addition to a whole milk of various amounts of 
water up to 50 per cent. 

Determinations on milk. 
On milk serum. 
i Added 
water. 
Total 
solids. 
Water. 
Fat. 
Solids 
not fat. 
Ash. 
Specific 
gravity at 
15° C. 
Specific 
gravity at 
15° C. 
Immersion 
refrac- 
tometer 
reading at 
20° C. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
0 
12. 65 
87. 35 
4.00 
8. 65 
0. 65 
1.0315 
1.0287 
42. 40 
10 
11. 33 
88. 67 
3.50 
7.83 
.60 
1. 0278 
1.0260 
39. 75 
20 
10. 10 
89. 90 
3. 10 
7.00 
.53 
1.0252 
1. 0230 
36.90 
30 
8. 95 
91. 05 
2.80 
6. 15 
.48 
1. 0211 
1.0200 
34. 10 
40 
7.67 
92.33 
2. 40 
5.27 
.40 
1. 0192 
1. 0167 
31. 10 
50 
1 
6.43 
93.57 
2.00 
4.43 
.38 
1. 0154 
1. 0140 
28.45 
