NITROGEN AND AMMONIA 233 



inetliud for the colorimetric determination of ammonia, which had 

 been used earlier by Van Slyke and Hiller ( 1933) and Borsook 

 (1935). By the reaction of ammonia with phenol and hypochlorite 

 in alkaline solution an intense blue product is formed, which is be- 

 lieved to be indophenol or a closely related compound. The method 

 has been applied to 1.5 ml. ammonia solution containing 0.5-6.0 ixg. 

 nitrogen. Larger or smaller volumes may be used to extend the range 

 of the method. 



Boell (1945) employed a method for the estimation of 1-50 /xg. 

 tutal nitrogen which utilized a digestion similar to that of Levy 

 ( 1936) , transfer of an aliquot of the digest to a diffusion unit made 

 up of ordinary laboratory glassware rather than the special cells of 

 Conway and Byrne, and titration with a simplified microburette. 

 The standard deviation was about 0.1 [xg. nitrogen. 



The method of Linderstr0m-Lang and Holter (1933b) for am- 

 monia has been adapted to the determination of total nitrogen and 

 subjected to exhaustive critical trial and investigation in the Carls- 

 berg Laboratory. Changes have been introduced as dictated by 

 experience and a description of the procedure used in 1939 was 

 given in a publication of Bottelier, Holter, and Linderstr0m-Lang 

 (1943). A final summary of the method after further improvements, 

 with a full treatment of each step, was the subject of a paper by 

 Briiel, Holter, Linderstr0m-Lang, and Rozits (1946). In principle, 

 the final method consists merely of the digestion of the sample, 

 transfer of the digest to the bottom of a paraffin-coated tube, and 

 titrimetric measurement of the ammonia in a manner similar to 

 that originally employed by Linderstr0m-Lang and Holter but with 

 improvements in certain of the details. 



The preceding survey indicates that various procedures may be 

 used for every step in the nitrogen determination. The choice of 

 method may depend to some degree on the prejudices and prefer- 

 ences of the experimenter, but the method of Briiel et al. ( 1946) is 

 recommended as the most foolproof and reliable. 



Titrimetric Methods. The Levy and Palmer (1940) method 

 has the great advantage of employing a simple small tube for all of 

 the chemical steps, and the diffusion process is avoided altogether. 

 Certainly the digestion of the sample can be performed in a small 

 tube regardless of the ensuing procedure. If an ammonia diffusion is 

 to be employed, it is simpler to use small tubes for it rather than 



