REAGENTS AND QUALITATIVE METHODS 137 



(9) Diphenylamin Reagent : 



1. Dissolve 0.7 gram of diphenylamin in a mixture of 

 60 c.c. of concentrated sulphuric acid and 28.8 c.c. of 

 distilled water. 



2. Cool this mixture and add slowly 11. 3 c.c. of con- 

 centrated hydrochloric acid (sp. gr. 1.19). After standing 

 overnight some of the base separates, showing that the 

 reagent is saturated. 



Withers and Ray, Jour. Amer. Chem. Soc, vol. xxxiii, pp. 708-711, 191 1. 



Test for Nitrates, — Place i drop of the substance to be 

 tested in a depression on the test plate. Add i drop of 

 diphenylamin solution and allow the solutions to mix 

 thoroughly. Then add 2 drops of concentrated sulphuric 

 acid. A deep blue color indicates nitrates. This test 

 cannot be made in the presence of nitrites, chloric and 

 selenic acids, ferric chlorid, and many other oxidizing 

 agents. 



In order to detect nitrates in the presence of nitrites, 

 add a concentrated solution of urea to a small amount of 

 the liquid in a test-tube. Now add in the bottom of the 

 tube (by means of a pipet) a dilute solution of sulphuric 

 acid. This should destroy a greater part of the nitrous 

 aciQ. 



CO(NH2)2 -f 2HNO2 = CO2 + 3H2O + 2N2 



(xo) Brucin Reagent. — Dissolve i.o gram of brucin in 

 10 c.c. of 50 per cent, pure concentrated sulphuric acid and 

 make up to loo c.c. with distilled water. 



Test for Nitrates. — Place i drop of the substance to be 

 tested in a depression on the test plate and add 3 drops of 

 concentrated sulphuric acid. Now add i drop of brucin 

 solution. If nitrates are present, a red color develops 



