228 MILK 



Moisten a piece of delicate turmeric paper with the solution; if 

 borax or boric acid is present, the paper on drying will acquire 

 a peculiar red color, which is changed by ammonium hydroxid to 

 a dark blue green, but is restored by acid." 



A preliminary test may be made by immersing a strip of tur- 

 meric paper in about 100 c.c. of the milk, to which about 7 c.c. of 

 concentrated hydrochloric acid has been added. 



Boric acid or borax can be detected by evaporating 10 c.c. of 

 the milk to dryness after addition of a small amount of hydro- 

 chloric acid, mixing the residue with alcohol, and lighting the 

 alcohol. A greenish color in the flame indicates the presence of 

 either boric acid or borax. 



The following test for the detection of borax and boric acid is 

 given by Shaw: " Ten c.c. of the milk is mixed with 5 c.c. of hydro- 

 chloric acid in a white cup. 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 Uquid. The dry portioii of the 

 paper will gradually become moist by capillarity, and if borax or 

 boric acid is present the paper will take on a reddish-brown tint. 

 If only a trace of the preservative 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." 



Quantitative estimation: "Render 100 grams of the sample 

 decidedly alkaline with sodium hydroxid and evaporate to dry- 

 ness in a platinum dish. Ignite the residue thoroughly, heat with 

 about 20 c.c. of water, and add hydrochloric acid, drop by drop, 

 until all is dissolved. Transfer to a 100-c.c. flask, the volume not 

 being allowed to exceed 50 to 60 c.c. Add 0.5 gram of calcium 

 chlorid and a few drops of pheriolphthalein, then a 10 per cent, 

 solution of caustic soda until a permanent slightly pink color is 

 produced, and finally add 25 c.c. of lime-water. Make the volume 

 up to 100 c.c. Mix and filter through a dry filter. To 50 c.c. of 

 the filtrate add normal sulphuric acid until the pink color dis- 

 appears, then methyl orange, and continue the addition of the 

 acid until the yellow is just changed to pink. Boil to expel car- 

 bon dioxid. Add fifth-normal caustic soda until the liquid as- 

 sumes the yellow tinge, excess of soda being avoided. Cool the 

 solution, add a little phenolphthalein, and an equal volume of 

 glycerin. Titrate with standardized sodium hydroxid until a per- 

 manent pink color is produced. 



"One cubic centimeter of fifth-normal soda solution is equal to 

 0.0124 gram of crystalhzed boric acid." 



Detection of Benzoic Acid. — Method of the Association of 

 Official Agricultural Chemists: "Add 5 c.c. of dilute hydrochloric 



