44 AGRICULTURAL ANALYSIS 



After the flask is connected with the distilling apparatus, it is 

 gently warmed and the reduction is ended in about 20 minutes. 

 The ammonia which is formed is distilled into E, containing the 

 standard acid S, requiring about 20 minutes more. The com- 

 parative results given, show that the devarda method is equally 

 accurate as any of the other methods mentioned, giving prac- 

 tically theoretical results. 



In so far, however, as speed of an analysis is concerned, the 

 first place is awarded to the lunge nitrometer method, with which 

 a complete analysis can be made in from 30 to 40 minutes. In 

 the second rank, so far as speed is concerned, the devarda method 

 is recommended. All the methods give accurate results. 



380. Method of Sievert. Two grams of potassium or sodium 

 nitrate are dissolved, and the solution made up to 1000 cubic cen- 

 timeters. 62 Fifty cubic centimeters of the solution are placed in 

 a 600 cubic centimeter flask and diluted with 50 cubic centimeters 

 of water, and from 1 8 to 20 grams of caustic alkali added. After 

 the alkali is dissolved, 75 cubic centimeters of 96 per cent, alcohol 

 are added and a few pieces of bone-black to prevent foaming. 

 From 10 to 15 grams of zinc or iron dust are added to the flask 

 which is closed and connected with a U-tube holding about 200 

 cubic centimeters, which contains about 10 cubic centimeters of 

 normal sulfuric acid. This U-tube is kept cool by being immersed 

 in water. The whole mixture is allowed to stand for three 

 or four hours and the alcohol is distilled slowly, the ammo- 

 nia formed by the reduction of the nitrates being carried over with 

 it. The distillation lasts for about two hours. The contents 

 of the U-tube are carefully rinsed into a dish and the excess of 

 sulfuric acid titrated with one-fourth normal soda-lye. 



For soil extracts and substances containing unknown quan- 

 tities of nitric acid, a preliminary test will indicate approxi- 

 mately the amount thereof, and this will be an indication for 

 the quantity to be used in the analysis. 



The method of Stutzer differs from the foregoing in the em- 

 ployment of aluminum dust instead of iron or zinc. 63 The reducing 



61 Liebig's Annalen der Chemie, 1862, 125 : 293. 

 65 Zeitschrift fur angewandte Chemie, 1890, 3 : 695. 



