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, 
