39 



The Leach test, which is the more delicate test of the 

 two, is conducted as follows: To 10 cubic centimeters of 

 the milk in a porcelain evaporating dish, 10 cubic centi- 

 meters of concentrated hydrochloric acid (specific gravity 

 1.2) containing one part by volume of a 10 per cent ferric- 

 chlorid solution per 500 parts is added and the mixture 

 brought slowly to a boil over a Bunsen burner. Formalde- 

 hyde is indicated by a violet coloration in intensity with 

 the amount present. 



Borax and boric acid. Twenty-five cubic centimeters of 

 the milk is treated with limewater until a piece of red 

 litmus paper when immersed in it turns distinctly blue. 

 The mixture is evaporated to dryness in a small platinum 

 or porcelain dish and then burned to an ash. A few drops 

 (not too much) of concentrated hydrochloric acid are added 

 to the ash, and then a few drops of water. A strip of tur- 

 meric paper is then dipped in the solution. When the tur- 

 meric paper becomes dry, it will be of a cherry-red color if 

 borax or boric acid is present. The test is still more certain 

 if, when the paper is moistened with an alkaline solution, 

 it turns a dark-olive color. 



A test for the detection of borax or boric acid which is in 

 use in the dairy laboratory of the Bureau of Chemistry, 

 United States Department of Agriculture, and by which 

 the ignition of the milk is avoided, is conducted as follows: 

 Ten cubic centimeters of the milk is mixed with 5 cubic 

 centimeters of concentrated hydrochloric acid in a porce- 

 lain evaporating dish. A strip of turmeric paper about 3 

 inches long is suspended in the mixture so that at least 2 

 inches of the dry strip remain out of the liquid. The dry 

 portion of the paper will gradually become moist by capil- 

 larity, and if borax or boric acid is present the paper will 

 take on a reddish-brown tint. If only a trace of the preserv- 

 ative is present, several hours may be required for this 

 color to develop. A drop of ammonia water on the red 

 portion will produce an olive-green color, which becomes 

 lighter and finally disappears as the ammonia evaporates. 



