38 MILK 



The correction may be made more closely by 

 calctilating the actual volune of the precipitate 

 by mtiltiplying 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 100 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 o . 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.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 = 4-7Si 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 



