DETERMINATION OF ALIPHATIC AMINO GROUPS 107 



with ether or a roll of filter paper before it receives the amino 

 solution. 



3. Absorption of Nitric Oxide and Measurement of Nitrogen. 

 The reaction being completed, all the gas in D is displaced into F 

 by liquid from A and the mixture of nitrogen and nitric oxide is 

 driven from F into the absorption pipette (the solution in the 

 absorption pipette is 40 gms. KMnCU and 25 gms. KOH in a liter). 

 The driving rod is then connected with the pipette by lifting the 

 hook from the shoulder of d and placing the other hook, on the 

 opposite side of the driving rod, over the horizontal lower tube of 

 the pipette. The latter is then shaken by the motor for a minute, 

 which, with any but almost completely exhausted permanganate 

 solutions, completes the absorption of nitric oxide. The pure 

 nitrogen is then measured in F. During the above operations a 

 is left open, to permit displacement of liquid from D as nitric 

 oxide forms in D. 



Blank determinations, performed as above except that 10 c.c. 

 of distilled water replaces the solution of amino substances, must 

 be performed on every fresh lot of nitrite used. Nitrite giving a 

 much larger correction than 0.3 to 0.4 c.c. should be rejected. 



The room temperature and the barometric pressure must be 

 noted. The calculation of the weight of nitrogen gas correspond- 

 ing to the volume obtained is most readily made with the aid of 

 the tables (see page 108) devised for this purpose. 



The Van Slyke Micro-apparatus. In later work Van Slyke 

 has used to a large extent an apparatus which differs from the one 

 described above only in being considerably smaller. More accurate 

 measurements can be made with this and smaller amounts of amino 

 nitrogen determined. In using this only 10 c.c. of nitrite solution 

 and 2.5 c.c. of acetic acid are required for an analysis. One-fifth 

 the amount of substance may be analyzed with the same degree of 

 accuracy as with the larger apparatus. Practically the only alter- 

 ation from the mode of operation already detailed above, is in 

 the speeds at which the deaminizing bulb and the Hempel pipette 

 are shaken. During the first stage of the analysis the deaminizing 

 bulb should be shaken by the motor at a very high rate of speed, 

 about as fast as the eye can follow or an unnecessary amount of 

 time is lost in freeing the apparatus from air. This stage is also 

 much accelerated by warming the nitrite solution to 30 before 

 it is used, in case a low room temperature has reduced the tern- 



