318 BOTANICAL GAZETTE [novembeb 



ANALYSES 



Nitrogen compounds 

 Nitrates. — The nitrates were determined by the Schlosing- 

 Wagner method (14) as modified by Koch for use in his laboratory. 

 The modification consists essentially in the use of an inverted 

 burette instead of a tube sealed at one end, and of the Van Slyke 

 apparatus (only volumetric tube and Hemple pipette), to measure 

 the true volume of nitric oxide. The principle of the method is: 

 3Fe ++ +N0 3 -+4H+-^3Fe +++ +NOgas+2H 2 0. Therefore 1 mol. 

 NO gas gives an equivalent of 62 gm. of N0 3 , or 1 cc. of 



62 



gas= = 2 -ll m S- N0 3 . 



G 22400 " ° J 



In order to determine the accuracy of this method, a known 

 solution of KNO3 (0.5 per cent) was used. Four consecutive 

 determinations with 10 cc. of the known solution were made. 

 The average volume of nitric oxide gas for each 10 cc. solution, 

 calculated to standard condition, was 11. 12 cc. The theoretical 

 volume for 10 cc. of 0.5 per cent KN0 3 is n .078 cc. 



The determination of nitrates in the samples was made by 

 taking an aliquot of the soluble fractions (F 1 and F 2 ). The nitric 

 oxide gas driven over was caught in an inverted burette which had 

 previously been filled with 40 per cent NaOH to absorb the C0 2 

 and neutralize the hydrochloric acid (HO gas will come over when 

 the hydrochloric acid concentration reaches 20 per cent in the 

 boiling flask). The burette containing the nitric oxide gas was set 

 aside and allowed to cool to room temperature; then the nitric 

 oxide gas was transferred to the Van Slyke apparatus. The 

 total volume and the volume of unabsorbed gas were recorded. 

 The absorbed volume by the alkaline KMn0 4 in Hemple pipette 

 is that of nitric oxide. This volume was then calculated to standard 

 volume from temperature and barometric pressure, for example: 



1 11 



Aliquot in cc. used 25.0 25.0 



Total volume of gas (nitric oxide+air) 4 80 4 . 85 



Volume of unabsorbed gas (air) 1.27 1 . 26 



Volume of (absorbed) nitric oxide 3 . 5,3 3 . 59 



Barometric pressure = 746 . 9 ; temperature 20 . 5 C. 



Volume at standard condition 3.23 3 . 27 



