414 AGRICULTURAL ANALYSIS 



nitric oxid by the action of mercury in the presence of sulfuric 

 acid. The operation as at first described is conducted in a glass 

 jar eight inches long by one and a half inches in diameter, filled 

 with mercury and inverted in a trough containing the same liquid. 

 The nitrate to be examined, in a solid form, is passed into the 

 tube, together with three cubic centimeters of water and five of 

 sulfuric acid. With occasional shaking, two hours are allowed 

 for the disengagement of the gas, which is then measured. 



359. Warington's Modification. A graduated shaking-tube is 

 employed, which allows the nitrate solution and oil of vitriol to 

 be brought to a definite volume. 47 The nitrate solution, with rins- 

 ings, is always two cubic centimeters, and enough sulfuric acid 

 is added to increase the volume to five cubic centimeters. The 

 sulfuric acid should give no gas when shaken with distilled water. 

 Any gas given off in the apparatus before shaking is not expelled 

 but is included in the final result. The persistent froth some- 

 times noticed where some kinds of organic matter are present, 

 is reduced by the addition of a few drops of hot water through 

 the stop-cock of the apparatus. The nitric oxid is finally meas- 

 ured in Frankland's modification of Regnault's apparatus. 



This method, accurate for pure nitrates, unfortunately fails in 

 the presence of any considerable amount of organic matter. 



According to Warington's observations, the presence of chlo- 

 rids is no hindrance to the accurate determination of both nitric 

 and nitrous acids by the mercury method. This simplifies the 

 operation as carried on by Frankland, who directs that any chlorin 

 present be removed before the determination of the nitric acid is 

 commenced. 



360. Noyes' Method. In the analyses made by Noyes for 

 the National Board of Health, the Crum-Frankland method was 

 employed. 48 The apparatus used was essentially that which is 

 now known as Lunge's nitrometer, and it will be described in 

 the next paragraph. No correction is made by Noyes for the 

 tension of aqueous vapor in the measurement of the nitric oxid 

 because of the moderate dilution of the sulfuric acid by the liquid 



47 Journal of the Chemical Society, 1879, 35 : 376. 



48 Report of the National Board of Health, 1882 : 281. 



