THE DETERMINATION OP NITRATE AND AMMONIA 
IN NITROGENOUS MATERIALS 1 
By O. M. Shedd, Research Chemist , Kentucky Agricultural Experiment Station 3 
INTRODUCTION 
The estimation of nitrate and of ammonia in the presence of other soluble and 
easily decomposable nitrogenous compounds of organic origin is difficult. They 
are determined by colorimetric methods or by procedures involving either gravi¬ 
metric or volumetric features, and if present in large amounts the latter have 
proved more reliable. The present work consists mainly of a comparison of a 
recent Devarda alloy method devised by Strowd ( 6) s for the determination of 
nitrates in plants and a slight modification of same whereby the control deter¬ 
mination in the modified method was used to estimate the ammonical nitrogen 
present in some samples. The latter has been made an incidental study, how¬ 
ever, and the results obtained in this connection are included here, inasmuch 
as the procedure described may possibly be used for this determination on other 
materials. 
HISTORICAL REVIEW 
It has been recognized from the earliest work on the subject that the estima¬ 
tion of nitrate in the presence of organic nitrogenous materials presents difficulties. 
Some colorimetric methods such as those devised by Caron (#), and particularly 
the modified phenolsulphonic acid procedure of Chamot and coworkers ( 3 ), have 
been found very satisfactory under certain conditions, provided the amount of 
nitrate present is small and a clear solution of it can be obtained. Other methods 
are more satisfactory when larger amounts of nitrate are present and among them 
some form of reduction process is generally used. Gasometric methods involving 
either the Schlosing method or modifications (7, p. 456) have found favor with 
some workers. The “nitron” method (7, p. 451) has also been found to be 
applicable in certain cases. If no separation of the nitrate is to be made, but it 
is desired to include it with other forms of nitrogen that may be present, one of 
the improved salicyl-sulphonic acid procedures may be used (f, p. 7, 8). 
The methods that are most popular at present, however, involve some reduc¬ 
tion process whereby the nitrate is reduced to ammonia by nascent hydrogen 
generated by the action of an alkali or acid on one or more metals. The ammonia 
is afterwards distilled into an excess of standard acid and titrated. Briefly men¬ 
tioned, they are the ferrous sulphate-zinc-soda method, which is carried on in 
an alkaline solution and recommended for nitrogen in commercial nitrate; the 
zinc-iron method, also carried on in an alkaline solution; and the Ulsch-Street, 
or reduced iron method, in which the nitrate is reduced in an acid solution by 
the action of sulphuric acid on reduced iron. The above three methods have 
been adopted as official in fertilizer work by the Association of Official Agricul¬ 
tural Chemists ( 1 , p. 10). Some other methods which have been used are reduc¬ 
tion with aluminum in an alkaline solution according to Pozzi-Escot (5) and 
1 Received for publication April 1, 1924. Published by permission of the director of the Kentucky 
Agricultural Experiment Station. 
a The writer desires to thank Dr. A. M. Peter, head of the Department of Chemistry, for helpful criti¬ 
cisms during this investigation and in the preparation of the manuscript. 
* Reference is made by number (italic) to literature cited, p.538, 539. 
Journal of Agricultural Research, 
Washington, D. C. 
( 527 ) 
Vol. XXVIII, No. 6 
May 10, 1924 
Key No Ky.-16 
