ON MILK AND MILK-TESTING 79 



vigorously 10 c. c. of milk and an equal volume of 

 ether. If annatto is present the amount will be in- 

 dicated by the depth of the yellow coloring in the 

 ether layer which forms on the surface when stand- 

 ing quiet. 



How may foreign color be detected in milk? 



The following method was developed by Leach: 



1. Warm about 150 c. c. of milk in a porcelain 

 dish and add about 5 c. c. of acetic acid, after which 

 slowly continue the heating to the boiling point 

 while stirring. Gather the curd, when possible, 

 into one mass by the stirring rod and pour off the 

 whey. If the curd breaks up into small flakes, 

 separate from the whey by straining through a 

 sieve. Press the curd free from adhering liquid, 

 transfer to a small flask, and macerate for several 

 hours (preferably overnight) in about 50 c. c. of 

 ether, the flask being tightly corked and shaken at 

 intervals. 



2. Detection of annatto in the ether extract. 

 Decant the ether as obtained above into an evapo- 

 rating dish and evaporate the ether over hot water. 

 Make the fatty residue alkaline with sodium hy- 

 droxide, and pour upon a very small wet filter while 

 still warm. After the solution has passed through, 

 wash the fat from the filter with a stream of water 

 and dry the paper. If, after drying, the paper is 

 colored orange, the presence of annatto is indicated. 

 Confirm by applying a drop of stannous chlorid 

 solution, which, in the presence of annatto, produces 

 a characteristic pink on the orange-colored paper. 



3. Detection of coal-tar color (" aniline orange ") 

 in the curd. The curd of an uncolored milk is per- 



