52 University of California Publications in Agricultural Sciences [Vol. 1 



and salts found in soils, form insoluble compounds with the 

 "nitron" (1.4-diphenyl-3.5 endanilodihydrotryazol) as well as 

 does the nitrate radicle. The sterilization of soils also appears 

 to liberate substances which interfere with the crystallization of 

 the "nitron" nitrate.' The occurrence of soluble organic matter 

 invariably present in the soil solutions tends, in many cases, to 

 vitiate completely the results.* The calcium oxid. which we use 

 to coagulate the clay before filtration, comes down as the car- 

 bonate in the filtrate, thus making a gravimetric determination 

 impracticable. (Lime has been shown to effect the least loss of 

 nitrates of any of the common coagulants.) The trouble and 

 cost of procuring the reagent also militated against the use of 

 this method. The Schulze-Tiemann,^ Schlosing- Wagner,® and 

 similar methods which depend upon the liberation and subse- 

 quent measurement of the nitric oxide from the nitrates did not 

 appear feasible because of the errors introduced through atmos- 

 pheric conditions, the expense of apparatus for a large number 

 of determinations, and the length of time necessary for the 

 operations involved. 



Thus all but the reduction methods were eliminated. In 

 1890 the Agricultural Experiment Station' at Halle, Germany, 

 perfected a reduction method for the determination of nitrogen 

 in nitrates. They used zinc dust, iron filings, and a solution 

 (sp. gr. 1.3) of sodium hydrate. The presence of chlorides and 

 sulfates did not impair the accuracy of the determination. Sev- 

 eral modifications of this reduction process are now used. In 

 the modified Ulsch^ method sulfuric acid and reduced iron are 

 employed to liberate the nascent hydrogen, an excess of mag- 

 nesium oxid being added just before distillation. In the Devarda® 

 method an alkali, an alloy of aluminum, copper and zinc, and 

 ethvl alcohol are all used to effect the reduction. M. E. Pozzi- 



3 J. Litzendorflf, Ztsclir. Aiigew. Chem. 20 (1907), 51. pp. 2209-13. 



4 Mich. Exp. Sta. Eep. for 1911, pp. 178-181. 



5 Bohm. Ztschr. Zuckerind. 2.5 (1900). p. 356, abs. in Chem. Centrbl. 

 (1901), I, 22, p. 1216. 



eKonig's Untersuch. Landw. Stoffe, p. 151. 



"> Experiment Station Eecord, vol. V, pp. 464-465. 



8 New Jersey Exp. Sta. Rep. for 1892, pp. 188-193. 



9 Analyst, 35 (1910), 412, p. 307. 



