DETECTION OF ADULTERATION 59 



known amounts of the preservative estimations 

 may be made. 



Hydrogen Peroxid. — Many tests have been 

 devised for detection of this substance. Among 

 the most convenient and satisfactory is the 

 reaction with vanadic acid first given by Werther. 

 It may be carried out by adding to lo c.c. of the 

 milk, 10 drops of a i% solution of vanadic acid 

 in dilute sulfuric acid. This solution may be 

 conveniently made by dissolved commercial 

 sodium orthovanadate in the dilute acid. 



In the presence of hydrogen peroxid a distinct 

 red will appear promptly. Barthel states that a 

 proportion of o.oio gram of the peroxid in loo 

 c.c. of milk can be detected positively using only 

 10 C.C; of the sample. 



Benzoates and Salicylates. — The following 

 method covers both these preservatives. 



10 c.c. of dilute sulfuric acid (s%) are added 

 to 20 c.c. of 95% alcohol and into this 50 c.c. of 

 the milk are poured in a fine stream with constant 

 stirring. After a few moments, the mixture is 

 filtered, the filtrate being returned until it passes 

 clear. A sufficient volume of the filtrate is 

 extracted in the usual manner with an equal 

 volume of ether or similar solvent. The solvent 

 is divided into two portions that are separately 

 evaporated and tested for benzoic and salicylic 

 acids respectively as given below. 



