ESTIMATION OF NITRIC 465 



398. Estimation of Nitric in Presence of Nitrous Acid. The 

 detection of nitrous in presence of nitric acid can be accom- 

 plished by the method proposed by Griess, as described further 

 on, through the development of azocolors with metaphenylene- 

 diamin and other bodies, which are not produced under similar 

 conditions by nitric acid. The detection and estimation of nitric 

 in the presence of nitrous acid, however, is not so easy. Lunge 

 and Lwoff propose brucin for this purpose, which, contrary to 

 most authorities, does not give the red-yellow color with nitrous 

 acid. 84 The reagent is prepared by dissolving 0.2 gram of brucin 

 in 100 cubic centimeters of pure and concentrated sulfuric acid. 

 It is almost impossible to prepare a sulfuric acid which does not 

 give a trace of color with brucin ; but with the purest acids this 

 trace may be neglected. 



A solution of nitrate is also prepared containing o.oi milli- 

 gram of nitrogen as nitric acid in one cubic centimeter. It is 

 made by dissolving 0.0721 gram of pure potassium nitrate in 100 

 cubic centimeters of distilled water, and diluting 10 cubic centi- 

 meters thereof with pure concentrated sulfuric acid to 100 cubic 

 centimeters. Both solutions are conveniently preserved in burettes 

 with glass stop-cocks. The liquid to be tested for nitric acid 

 is mixed with sulfuric acid in such a way that the mixture will 

 have a specific gravity of 1.7. If the liquid to be tested is water, 

 this concentration is reached by adding three times its volume of 

 the strong acid. For the comparison of colors, cylinders of color- 

 less glass are employed, marked at 50 cubic centimeters. They 

 are about 24 centimeters high and extend about 10 centimeters 

 above the mark. There is placed in the cylinder one cubic centi- 

 meter of the solution of nitrate in sulfuric acid, and the same 

 quantity of the brucin mixture, and it is filled to the mark with 

 pure sulfuric acid. The contents of the cylinder are poured into 

 a flask and warmed at from 70 -80, until the final yellow tint 

 is secured, and then poured into the cylinder again. The liquid 

 to be tested is treated in exactly the same way. The tints are 

 then equalized by pouring out a part of the contents of the 

 deeper colored cylinder, taking account of the volume, and filling 

 up with pure concentrated sulfuric acid. 



M Zeitschrift fiir angewandte chetnie, 1894, 7 : 347- 



