CHEMICAL TESTS AND ANALYSES 305 
For absolutely exact results the re-extraction must be repeated. 
This third extraction vields usually not more than about 1 mg. 
of fat (about 0.02 per cent on a 4 gram charge) if the previous 
ether-fat solutions have been drawn off closely. Evaporate the 
ethers slowly on a steam bath, then dry the fat in a boiling water 
oven to constant weight. 
Confirm the purity of the fat by disselying in a little pe- 
troleum ether. Should a risidue remain, remove the fat com- 
pletely with petroleum ether, dry the residue. weigh and deduct 
the weight. Finally correct this weight by a blank determina- 
tion on the reagents used 
SWEETENED CONDENSED MILK. 
Preparation of Sample. 
Pour the contents of the can into a bowl or on a glass plate. 
Scrape out the can thoroughly, removing all the sugar sediment 
from the top and bottom of the can. Mix thoroughly with pestle 
or spatula until a homogenous emulsion is secured. This is 
important, as it is exceedingly difficult to secure a representative 
sample otherwise. 
If it is desired to use a 40 per cent solution as directed in 
the determination of the individual ingredients, weigh accurately 
40 grams of the properly mixed contents of the can into a 100 c.c, 
graduated flask. Add 60 cc. of water. The sweetened con- 
densed milk mixes somewhat difficultly with the water. Complete 
solution is facilitated by adding the water in several install- 
ments, shaking after cach addition until condensed milk sedi- 
ment adheres no longer to the bottom and sides of the flask 
Spec'fic Gravity. 
Aerometric Method by Means of Beaumé Hydrometer. 
Apparatus. 
Beaumé Hydrometer.—lse a specially constructed Beaumé 
hydrometer with mercury bulb, and a scale of 30 to 37 degrees B., 
graduated to tenths degrees. Length over all, twelve inches; 
length of spindle, six inches; length of empty bulb, four and 
