Detection of Aduwerants and Preservatives 301 



ZEISS REFRACTOMETER READING OF COPPER SERUM. 

 TENTATIVE 



"To one volume of copper-sulphate solution (72.5 grams of cop- 

 per sulphate per liter, adjusted if necessary to read 36 at 20° C. on 

 the scale of the Zeiss immersion refractometer, or, to a specific grav- 

 ity of 1.0443 at ^°^° °- ) add four volumes of milk. Shake well and 

 filter. Determine the Zeiss refractometer reading of the clear serum 

 at 20° C. A reading below 36 indicates added water. 



(In conjunction with the copper, acetic or sour serum refraction 

 method, the determination of the ash of the sour serum or of the 

 acetic serum should be made in all cases where the indices of re- 

 fraction fall below the minimum limit so as to eliminate all possi- 

 bility of abnormal milk.)" 



DETECTION OF ARTIFICIAL COLORING ^ 



Leach's Method 



"Warm about 150 c.c. of milk in a casserole over the flame and 

 add about 5 c.c. of acetic acid, after which slowly continue the 

 heating nearly 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 or colander. Press the curd free 

 from adhering liquid, transfer to a small flask, and macerate for 

 several hours (preferably over night) in about 50 c.c. of ether, the 

 flask being tightly corked and shaken at intervals. 



1. "DETECTION OF ANNATO (IN THE ETHER EXTRACT) 



"Decant the ether extract as obtained above into an evaporating 

 dish, place on the water bath, and evaporate the ether. Make the 

 fatty residue alkaline with sodium hydroxid, 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 presence of annatto, produces 

 a characteristic pink on the orange-colored paper. 



1 United States Department of Agriculture, Bureau of Chemistry, Bulletin 

 No. 107. 



