38 MILK 
The correction may be made more closely by 
calculating the actual volune of the precipitate 
by multiplying the fat-percentage by 1.075 
(average specific volume of fat) and the protein- 
percentage by 0.8 (average specific volume of 
coagulated proteins), deducting the sum of these 
products from too c.c. and correcting the ob- 
served reading by proportion. For ordinary 
milk, the volume of the proteins from 65.96 
grams may be taken at 1.68 c.c. Supposing 
the sample to contain 4.0% of fat and the 
polarimetric reading to be 10, the calculation 
would be thus: 
65.96 X 0.04 = 2.63 Amount of fat in milk taken 
2.63 X 1.075 = 2.82 c.c, Volume of fat in precipitate 
1.68 c.c, Est. vol. of proteins in precipitate 
4.50 ¢.c. Total volume of precipitate 
100 — 4.50 = 9.55 c.c. Actual volume of liquid. 
100 :95.5::10:9.55 9.55 +2 = 4.75, per cent. lactose. 
The employment of a factor for correcting 
for the volume of precipitate may be avoided by 
Scheibler’s method of ‘‘double dilution,” in 
which two solutions of different volume are 
compared. The following is a summary of the 
method given by Wiley & Ewell: For polari- 
meters adapted to a normal weight of 26.048 
sucrose, 65.82 grams of milk are placed in a 
100 c.c. flask, 10 c.c. of the acid mercuric nitrate 
