APPENDIX H 

 DETERMINATION OF NITRITE 



The nitrite is best determined by means of Ilosvay's modification 

 of Griess's test, which has the advantage that the color is more rapidly 

 developed and the reagents are less liable to change. The red color 

 produced is dne to the action of the liberated nitrous acid on the sul- 

 phanilic acid, the resulting diazo-compound being in turn converted 

 by the naphthylamine into azo-amidonaphthalenebenzenesulphonic 

 acid. 



REAGENTS REQUIRED 



1. Sulphanilic acid solution. Dissolve 0.5 g. of pure sulphanUic 

 acid in 160 cc. of dilute acetic acid (sp. gr. 1.04). 



2. Naphthylamine acetate solution. Boil 0.1 g. of a-naphthylamine 

 in 20 cc. of water and strain through a well-washed plug of absorb- 

 ent cotton into 180 cc. of acetic acid (sp. gr. 1.04). 



3. Nitrite reagent. Mix equal volumes of the sulphanilic acid so- 

 lution (1) and the naphthylamine acetate solution (2). This reagent 

 is prepared in small quantities from time to time. If a reddish tint 

 is developed on mixing the solutions, it indicates the presence of 

 nitrites. In this case the reagent is treated with zinc dust, which 

 destroys the color, and after removing the excess of zinc, it is ready 

 for use. 



4. Standard sodium nitrite solution. Dissolve 0.0836 g. of pure silver 

 nitrite in water. Add a solution of pure sodium chloride until silver 

 chloride ceases to be precipitated. The volume is then made up to 

 260 cc. and, after thorough shaking, allowed to stand in the dark 

 until the precipitate has completely settled. Dilute 10 cc. of the 

 supernatant liquid to 100 cc. with nitrite-free water. This standard 

 must be kept in a well-stoppered bottle in the dark. Each cubic cen- 

 timeter of this standard solution contains 0.01 mg. of NO^. The pure 

 silver nitrite is prepared by adding to a hot concentrated solution 

 of sixteen parts of silver nitrate a hot concentrated solution of ten 

 parts of potassium nitrite. Allow to cool, and separate the mother 



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