3i8 BOTANICAL GAZETTE [November 



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+++N03-+4H+-»3Fe++++NOgas+2H30. Therefore i mol. 

 NO gas gives an equivalent of 62 gm. of NO3, or i cc. of 



gas = = 2.77 mg. NO3. 



^ 22400 ' ' <=> ^ 



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 o. 5 per cent KNO3 is 11 .078 cc. 



The deterrnination of nitrates in the samples was made by 



taking an aliquot of the soluble fractions (Fi and F2). 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 CO2 



and neutralize the hydrochloric acid (HCl 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 KMn04 in Hemple pipette 



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



volume from 'temperature and barometric pressure, for example: 



I II 



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 3.53 3-59 



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



Volume at standard condition 3 . 23 327 



