DETECTION OF ADULTERANTS AND PRESERVATIVES 305 



drying will acquire a peculiar red color, which is changed by am- 

 monium 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 liquid foods, to which about 7 c.c. 

 of concentrated hydrochloric acid has been added. Solid and pasty 

 goods may be heated with enough water to make them thoroughly 

 fluid, hydrochloric acid added in about the proportion of 1 to 13, 

 and tested in the same manner-" 



BENZOIC ACID 1 



"Add 5 c.c. of dilute hydrochloric acid to 50 c.c. of the milk 

 in a flask and shake to curdle. Then add 150 c.c. of efher, cork the 

 flask and shake well. Break up the emulsion which forms by aid 

 of a centrifuge, or if the latter is not available extract the curdled 

 milk by gently shaking with successive portions of ether, avoiding 

 the formation of an emulsion. Transfer the ether extract (evapo- 

 rated to small volume if large in bulk) to a separatory funnel and 

 separate the benzoic acid from the fat by shaking out with dilute 

 ammonium hydroxid, which takes out the former as ammonium 

 benzoate. Evaporate the ammoniacal solution in a dish over the 

 water bath till all free ammonia has disappeared, but before dryness 

 is reached, add a few drops of ferric chlorid reagent. The char- 

 acteristic flesh-colored precipitate indicates benzoic acid. Care 

 should be taken not to add the ferric chlorid until all the ammonia 

 has been driven off, otherwise a precipitate of ferric hydrate is 

 formed." 



SALICYLIC ACID 2 



Acidulate 20 c.c. of milk with sulphuric acid and shake with 

 ether. Evaporate the ether solution and treat the residue with al- 

 cohol and a little iron-chloride solution ; a deep violet color indi- 

 cates the presence of salicylic acid- 



HYDROGEN PEROXIDE 3 

 (Wilkinson and Peters' Method) 



Add four drops of an alcoholic solution of 4 per cent benzidine 

 (paradiamidophenyl) and 2 drops of acetic acid to 10 c.c. of milk. 

 If hydrogen peroxide is present the milk assumes a blue color. 

 .005 grams of hydrogen peroxide in 100 c.c. of milk can be detected 

 by this method. 



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

 107, 1912. 



2 Farrington & Wbll, Testing Milk and Its Products. 



3 Barthel, Milk and Dairy Products, 



