52 MILK 



and the tubes shaken and immersed in cold 

 water, which is gradually raised to 80°. The 

 emulsion breaks up, and the alcohol, holding 

 the annatto in solution, comes to the surface. 

 The alcoholic layer is separated from the lower 

 stratum, evaporated to dryness, and the residue 

 dissolved in warm water containing a little 

 alcohol and ammonium hydroxid. Clean white 

 cotton is introduced and the liquid evaporated 

 nearly to dryness on the water-bath. The 

 cotton, which is colored a pale yellow, even with 

 pure milk, is washed and immersed in a solution 

 of citric acid, when it will be immediately red- 

 dened if the milk contains annatto. Saffron, 

 turmeric, and the coloring-matter of the marigold 

 do not give a similar reaction. 



Coal-tar colors may often be detected by dyeing 

 wool, but Lythgoe has devised the following 

 method, which is satisfactory: 15 c.c. of the 

 sample are mixed in a porcelain basin with an 

 equal volume of hydrochloric acid (sp. gr. 

 1.20), and the mass shaken gently so as to break 

 the curd into coarse lumps. If the milk con- 

 tains an azo-color, the curd will be pink; with 

 normal milk the curd will be white or yellowish. 



General Method for Colors in Milk. — Leach 

 devised a general method. 150 c.c. of the 

 sample are coagulated in a porcelain basin, 

 with the addition of acetic acid and heating, 



