QUALITATIVE AND QUANTITATIVE ANALYSIS 59 



Place 10 to 15 cubic centimeters of the test solution in a test 

 tube. Add 5 cubic centimeters of reagent (a). Boil over free 

 flame or heat on water bath for 4 to 5 minutes. To prove that 

 all nitrites have been destroyed, add to 3 cubic centimeters of 

 the mixture a few drops of reagents (a) and (b). The lack of 

 formation of a red color indicates the destruction of all the 

 nitrites. 



The remaining solution containing the reagent (a) is cooled 

 down and used for the nitrate or hydroxylamine tests. 



DiPHENYLAMINE ReAGENT^ 



1. Dissolve 0.7 gram of diphenylamine in a mixture of 60 cubic 

 centimeters of concentrated sulphuric acid and 28.8 cubic centi- 

 meters of distilled water. 



2. Cool this mixture and add slowly 11.3 cubic centimeters of 

 concentrated hydrochloric acid (specific gravity 1.19). After 

 standing overnight some of the base separates, showing that the 

 reagent is saturated. 



Test for Nitrates. — Place 1 drop of the substance to be tested 

 in a depression on the test plate. Add 1 drop of diphenylamine 

 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 chloride, and many other 

 oxidizing agents. Diphenylbenzidine is recommended as prefer- 

 able to diphenylamine. 2 



Brucine Reagent 



Dissolve 1.0 gram of brucine in 10 cubic centimeters of 50 per 

 cent pure sulphuric acid and make up to 100 cubic centimeters 

 with distilled water. 



Test for Nitrates. — Place 1 drop of the substance to be tested 

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

 sulphuric acid. Now add 1 drop of brucine solution. If nitrates 

 are present, a red color develops quickly, which changes to orange, 



1 Withers and Ray, /. Am. Chem. Soc, 33, 708-711, 1911. 



2Snell, F. D., " Colorimetric Analysis," D. Van Nostrand Co., 1921. 



