DETERMINATION OF ALIPHATIC AMINO GROUPS 103 



During the process the following reaction also takes place, the 

 nitrous acid solution decomposing spontaneously with the forma- 

 tion of nitric oxide. 



2HN0 2 = HNO 3 +NO. 



This latter reaction is utilized in displacing all the air of the appa- 



ratus with nitric oxide. The amino solution is then introduced, 



evolution of nitrogen mixed 



with nitric oxide resulting. 



The oxide is absorbed with 



alkaline permanganate solu- 



tion and the pure nitrogen 



measured in a special gas 



burette shown in the figure. 



Procedure. The determi- 

 nation is carried out in three 

 stages : 



1. Displacement of Air by 

 Nitric Oxide. Water from F 

 (see Figs. 2 and 3), fills the 

 capillary leading to the Hem- 

 pel pipette and also the other 

 capillary as far as c. Into A 

 one pours a volume of glacial 

 acetic acid sufficient to fill 

 one-fifth of D. For conven- 

 ience, A is etched with a mark 

 to measure this amount. The 

 acid is run into D, cock c being 

 turned so as to let the air 



FIG. 2. Van Slyke Amino Nitrogen 

 Apparatus . (Hawk . ) 



escape from D. Through A 

 one now pours sodium nitrite 

 solution (30 gms. NaNOo to 

 100 c.c. EbO) until D is full of solution and enough excess is 

 present to rise a little above the cock into A. It is convenient to 

 mark A for measuring off this amount also. The gas exit from D 

 is now closed at c, and, a being open, D is shaken for a few seconds. 

 The nitric oxide, which instantly collects, is let out at c, and the 

 shaking repeated. The second crop of nitric oxide which washes 



