CHEMICAL TESTS AND ANALYSES 353 



For absolutely exact results the re-extraction must be repeated. 

 This third extraction yields 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 dissolving 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 c.c. of water. The sw r eetened con- 

 densed, milk mixes ..some what difficultly with the water. Complete 

 solution is facilitated by adding the water in several install- 

 ments, shaking after each addition until condensed milk sedi- 

 ment adheres no longer to the bottom and sides of the flask. 



Specific Gravity. 



Aerometric Method by Means of Beaume Hydrometer. 



Apparatus. 



Beaume Hydrometer. Use a specially constructed Beaume 

 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 



