APPENDIX 371 



Nitrate test solutions: 

 I. Phenolsulphonic acid. 



1. Mix 3 gms. of pure crystallized phenol with 37 gms. 

 of c.p. concentrated sulphuric acid (20.1 c.c., sp.gr. 1.84) 

 in a round-bottom flask. 



2. Heat for six hours in a water bath at 100 C., keeping 

 the flask submerged the whole time. 



This may crystallize on cooling, but it can be brought 

 into solution easily by heat. 



Directions for making this test will be noted in Exercise 

 45, Part I. 



II. Diphenylamin. A solution of 2% diphenylamin in 

 sulphuric acid when added to a liquid containing nitrates 

 or nitrites gives a blue color. 



Diphenylamin 2 gms. 



Sulphuric acid, c.p. cone 100 c.c. 



Nitrite test solutions: 



Solution I. 8.0 gms. sulphanilic acid dissolved in 1000 

 c.c. of 5N acetic acid (sp.gr. 1.041;. 



Solution II. 5.0 gms. a-naphthylamin dissolved in 

 1000 c.c. of 5N acetic acid. These solutions should be kept 

 separate and mixed in equal parts just before use. 



Nessler's solution, for free ammonia: 



1. Dissolve 62.5 gms. of potassium iodid in 250 c.c. of 

 distilled water. Reserve about 10 c.c. of this solution. 



2. Add gradually to the main portion a cold saturated 

 solution of mercuric chloride, stirring constantly and in- 

 creasing the quantity of mercuric chloride until a bright, 

 permanent precipitate is formed. 



3. Now add the reserved potassium iodid solution and 

 again add the saturated mercuric chloride solution, cautiously 

 and with constant stirring until a distinct though slight 

 red precipitate remains. 



4. Dissolve 150 gms. of caustic potash in 150 c.c. dis- 



