74 MILK PRODUCTS 
In the examination of cream a third extraction 
is necessary, but with evaporated and condensed 
milk the third extraction does not recover more 
than 0.02 or 0.03 % of fat, and may be omitted. 
Evaporate the liquid slowly on a steam bath 
and dry the fat in steam oven until its weight is 
constant. Weigh after one hourand then at half- 
hour intervals. Assoon as the fat begins to gain 
in weight stop drying and take the next previous 
weight. Increase of weight is due to oxidation 
after all moisture and alcohol are gone. In all 
cases the drying should be completed the day it 
is begun. 
Double Extraction.—The following is given as a 
provisional A. O. A. C. method: Extract with 
ether, as usual, about 5 grams of a 40% solution, 
dry, leave the tubes in a dish containing at least 
500 c.c. of water, dry, extract again with ether for 
four hours. 
Sugars.—If regard is to be given to the 
presence of invert-sugar, a special method must 
be followed. The processes first given consider 
lactose and sucrose only. The heating employed 
in the manufacture of condensed milk may 
reduce the rotatory power of lactose sufficiently 
to cause error in the polarimetric method. The 
reducing power with alkaline copper solutions 
is not seriously affected. 
Determination of sucrose may be made by 
