Si LABORATORY BACTERIOLOGY. 



III. Griess Colorimetric Method for Nitrites. 

 1. Reagents. 



(ft) Sulfanilie acid. 



0.5 gm. sulfanilie acid in 150 cc. of dilute acetic 

 acid (sp. gr. 1.04). 



(6) Naphthylamine acetate. 



Boil 0.1 gm. of a naphthylamine in 30 cc. of 

 water and filter through a plug of absorbent 

 cotton into 180 cc. of dilute acetic acid (sp. 

 gr. 1.04). 



(c) Nitrite reagent. 



Mix equal parts of the sulfanilie acid and 

 naphthylamine acetate. 



{d) Standard Sodium nitrite. 



0.0836 gm. pure silver nitrite dissolved in 

 water. Add a solution of NaCl until all the 

 silver is precipitated. Make up to 350 cc, 

 shake and stand until the precipitate has set- 

 tled. Dilute 10 cc. of the supernatant liquid to 

 100 cc. with water. Each cc. of this = 0.01 

 mg. NO^. 



(e) Standard colorimetric solution. 



10 cc. of the above standard nitrite solution 

 treated as described below and made up to 

 100 cc. with water. 

 3. Determination. 



To the solution to be tested add 16 cc. of the 

 nitrite reagent (c) and dilute to 100 cc. in a 

 colorimeter tube, and compare with the stand- 

 ard colorimetric solution (e) diluting the one 

 or the other as necessary. 



