CHEMICAL TESTS AND ANALYSES 271 



be left) into a weighed flask through a small quick-acting filter. The 

 flask should always be weighed with a similar one as a counterpoise. 

 Re-extract the liquid remaining in the tube, this time with only 15 

 c.c. of each ether, shake vigorously thirty seconds with each and al- 

 low to settle. Draw off the clear solution through the small filter 

 into the same flask as before and wash the tip of spigot, the funnel 

 and the filter with a few c.c. of a mixture of the two ethers in equal 

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

 peated. 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 petroleum 

 ether. Should a residue remain, remove the fat completely with 

 petroleum ether, dry the residue, weigh and deduct the weight. 

 Finally correct this weight by a blank determination 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 spa- 

 tula until a homogenous emulsion is secured. This is important, 

 as it is exceedingly difficult to secure a representative sample other- 

 wise. 



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 sweetened condensed 

 milk mixes somewhat difficultly with the water. Complete solution 

 is facilitated by adding the water in several installments, shaking 

 after each addition until condensed milk sediment adheres no longer 

 to the bottom and sides of the flask. 



