4 6 



Scientific Proceedings (36). 



29 (439) 



A method for the determination of amino nitrogen and its 



applications. 



By DONALD D. VAN SLYKE. 



[From the Rockefeller Institute for Medical Research.'] 

 It has long been known that aliphatic amines react with nitrous 

 acid according to the equation RNH 2 + HN0 2 =ROH+ H 2 0 + N 2 , 

 and several methods have been devised for estimating amino groups 

 by measuring the nitrogen gas evolved by this reaction. 1 None 

 of them has been sufficiently simple or accurate to attain general 

 use, however. The method proposed requires but little apparatus, 

 but a few minutes for completion, and is as accurate as a Dumas 

 or Kjeldahl determination. The reaction is carried out in a bottle 

 with a capacity of about 35 cubic centimeters, fitted with a three 

 hole No. 4 rubber stopper. Through the stopper pass : (1) the 

 stem of a 10 c.c. burette; (2) the thick-walled capillary inlet from 

 a cylindrical dropping funnel of 25 c.c. capacity; the capillary is 

 of 2 mm. internal diameter and reaches nearly to the bottom of 

 the bottle ; (3) an outlet tube for gas. This is a capillary 25 to 

 30 cm. high, 1 mm. internal, 5 to 6 mm. external diameter. The 

 lower end is flush with the bottom of the stopper, the upper end is 

 bent in a semi-circle to meet the inlet of a gas burette. The tube 

 has a stopcock near the middle. 2 



The amino solution for analysis is placed in the burette, and 

 a few cubic centimeters of water in the dropping funnel. Into the 

 bottle are poured 27 c.c. of a 10 to 3 solution of sodium nitrite 

 followed by 7 c.c. of glacial acetic acid. The stopper is placed in 

 position and the slight air volume left in the bottle displaced by 

 water from the dropping funnel. The outlet tube is then closed, 

 whereupon the nitric oxide gas formed by decomposition of the 

 nitrous acid fills the upper part of the bottle, forcing the solution 

 back into the funnel. When from 5 to 10 c.c. of gas are thus 

 gathered, which requires but a few seconds, the outlet is opened 

 and the gas driven out again, washing out the remaining traces of 



1 Hans Meyer : Anleitung zur quant. Best, organischen Atomgruppen, p. 81. 

 Fischer and Koelker, Annalend. Chem., 1905, cccxl, 177. 



2 The apparatus can be obtained from Eimer and Amend, New York. 



