UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



AGRICULTURAL SCIENCES 



Vol. 1, No. 2, pp. 21-37 October 15, 1912 



STUDIES ON THE PHENOLDISULPHONIC 



ACID METHOD FOR DETERMINING 



NITRATES IN SOILS 



BY 

 C. B. LIPMAN AXD L. T. SHARP 



Despite the fact that some careful research has been carried 

 out on the colorimetric method for determining nitrates, many 

 factors concerned with it have not been studied, and the some- 

 what uncertain nature of the method makes it imperative to con- 

 trol, so far as possible, every factor which may interfere with 

 the accurate analysis of nitrate-containing material. These 

 statements apply particularly to the analysis of soils for nitrates 

 and the authors therefore deem the subjoined data, derived from 

 a thorough investigation, deserving of the attention of every soil 

 chemist. 



Among the interfering factors in the phenoldisulphonic acid 

 method which have been either studied inadequately or not at 

 all, are the effects of salts, the effects of agents employed to pre- 

 cipitate the clay and organic matter, and the effects of decolor- 

 izing agents. Cognizance must be taken of all of these factors 

 by the chemist in the determination of nitrates and in the ar- 

 rangement and interpretation of results. The importance of salt 

 effects and their significance in this connection are emphasized 

 by the fact that many soils, and particularly those of arid and 

 semiarid regions, may frequently be found to a greater or less 

 degree impregnated with one or more of the so-called "alkali 

 salts," together with which, it often happens indeed, consider- 



