396 AGRICULTURAL ANALYSIS 



centimeters of pure hydrogen, which are allowed to pass over 

 into the receiving flask by releasing the clamp in the same way 

 as for the nitric oxid. The hydrogen being introduced in succes- 

 sive portions, finally carries all the nitric oxid into the flask with- 

 out allowing any of the potash to enter. 



The flask containing the nitric oxid is now connected with a 

 reservoir of oxygen. The oxygen is allowed to enter, bubble by 

 bubble, meanwhile cooling the flask by immersion in water. The 

 transformation of nitric oxid into nitric acid is not entirely com- 

 plete until after 24 hours. It is necessary, therefore, to wait so 

 long after the introduction of the oxygen before determining 

 the amount of nitric acid produced. 



The contents of the flask are placed in a titration-jar, the flask 

 being washed two or three times and a few drops of tincture of 

 litmus being added. The nitric acid is then determined by a 

 standard solution of calcium hydroxid or some other standard 

 alkali. From the titration the content of nitric acid is calcu- 

 lated. 



The French committee further suggests that this method may 

 be modified in the way of making it more rapid by collecting 

 the nitric acid in a graduated tube filled with mercury and con- 

 taining some potash. The volume of the gas is determined and 

 the pressure of the barometer together with the temperature are 

 observed ; then the usual calculations are made to reduce the vol- 

 ume to zero and to a pressure of 760 millimeters of mercury. 

 Each cubic centimeter of nitric oxid thus measured corresponds 

 to 2.417 milligrams of nitric acid. The presence of organic mat- 

 ter does not interfere with the determination of nitric acid by 

 either of the methods given above. 



348. Method of the French Sugar Chemists. The nitrogen 

 in Chile saltpeter is estimated by the French chemists according 

 to the method of Schloesing. In order to avoid the trouble of 

 calculating the results from the volume of nitric oxid obtained, 

 a determination is first made with a pure salt, sodium or potassium 

 nitrate. The volume of gas obtained is read directly without 

 correction and used for direct comparison, which is made as 

 follows : 



