NITROGEN AND AMMONIA 231 



tube having a total capacity of about 250 /xl. for the diffusion process. 

 The sample was placed in the bottom of the tube and the ammonia 

 from it was allowed to diffuse into a drop of standard acid placed 

 in the upper part of the tube to form a seal across the lumen (Fig. 

 46). Conway and Byrne used a special diffusion cell (Fig. 41) re- 

 quiring considerably more of the liquids; hence it was not suitable 

 for the accurate measurement of much less than 14 jug. ammonia 

 nitrogen. The Linderstr0m-Lang and Holter method had a precision 

 of 0.005 fxg. nitrogen and it could be used for the determination of up 

 to about 28 /xg. The following year Gibbs and Kirk ( 1934) employed 

 a modified Conway-Byrne procedure, which they used for the esti- 

 mation of from 1.5-8.3 fig. ammonia nitrogen. Conway (1935b) 

 subsequently described a refinement of the diffusion cell method 

 which had an ultimate standard deviation of 0.02 /xg. ammonia 

 nitrogen. 



Levy (1936) developed a technique for the determination of total 

 nitrogen based on the direct Nesslerization of the acid-digested 

 sample. The complete treatment was carried out in the same vessel 

 and the final solution was transferred for colorimetry to a micro- 

 cuvette having a capacity of 0.2 ml. Levy's method was adapted for 

 quantities of nitrogen in the range 0.5-6.0 /xg. and the average devia- 

 tion observed was 0.03 jug. 



A titrimetric method for total nitrogen employing features of both 

 the Linderstr0m-Lang and Holter and the Conway techniques was 

 published by Needham and Boell ( 1939) . These investigators used 

 a single vessel with a special cap for all the operations, i.e., digestion, 

 diffusion, and titration. The method was adapted to 1-20 /xg. of 

 nitrogen and the standard deviation in control experiments was 0.3 

 fig. In order to refine the earlier colorimetric method of Borsook 

 (1935), Borsook and Dubnoff (1939) also borrowed features of the 

 Linderstr0m-Lang and Holter technique as well as the diffusion cell 

 of Conway and Byrne to develop a method for total nitrogen, am- 

 monia, and other nitrogenous compounds. The procedure of Borsook 

 and Dubnoff for 5-10 fig. total nitrogen involves acid digestion, 

 transfer of an aliquot to a diffusion cell, and finally electrometric 

 titration of the excess acid. The standard deviation was around 

 0.05 fxg. 



Levy and Palmer ( 1940) adapted the hypobromite method for am- 

 monia to the iodometric estimation of nitrogen without diffusion. 



