TABLES FOR CALCULATING RESULTS 337 



Hence, 38.26 milligrams of nitrogen correspond to 7.65 per 

 cent., when half a gram of substance is taken for the combustion. 



295. Aqueous Tension in Solutions of Potassium Hydroxid. 

 Even in strong solutions of potassium hydroxid the tension of 

 aqueous vapor is not destroyed, but is reduced to a minimum, 

 which is negligible in the calculation of the percentage by weight 

 of the nitrogen in a sample of fertilizer. When dilute solutions 

 of a caustic alkali are used, however, the neglect of the tension of 

 the aqueous vapor may cause an error of some magnitude. In 

 such cases the strength of the solution should be known and cor- 

 rection made according to the preceding table. 86 



296. Use of Volumetric Method. For practical purposes it 

 may be said, that the volumetric determination of nitrogen in 

 fertilizer analysis has gone entirely out of use. For control and 

 comparison it is still occasionally practiced, but it has had to give 

 way to the more speedy and fully as accurate processes of moist 

 combustion with sulfuric acid, which have come into general use 

 in the last two decades. The student and analyst, however, should 

 not fail to master its details and become skilled in its use. There 

 are certain nitrogenous substances, such as the alkaloids, which are 

 quite refractory when subjected to moist combustion. While 

 such bodies may not occur in fertilizers, except in rare cases 

 such as nicotine in tobacco waste, it is well to have at hand 

 a means of accurately determining their nitrogen content. 



297. Tables for Calculating Results. Where many analy- 

 ses are to be made by the copper oxid process, it has proved con- 

 venient to shorten the work of calculating analyses by taking 

 the data given in computation tables. 87 Before using these 

 tables it must be known whether they are calculated on the sup- 

 position that the gas is measured in a moist state, partly moist, or 

 wholly dry. Where the nitrogen is collected over water, a table 

 must be used in which allowance has been made for the tension 

 of aqueous vapor. In case a saturated solution of a caustic 

 alkali be used in the azotometer, it is customary to take no 

 account of the tension and the table employed must be con- 



M Landolt and Bornstein, Physikalisch-chetnische Tabellen, 2nd Edi- 

 tion, 1894 : 68. 



87 Battle and Dancy, Conversion Tables, 1885 : 34. 



