422 



AGRICULTURAL ANALYSIS 



It is seen from the above that the nitrate will give, by this 

 treatment, double the volume of nitrogen which it contains. In 

 practice, the two reactions may be secured in one operation by 

 warming the nitrate solution slowly with sulfuric and phos- 

 phorous acids and ammonium chlorid. The nitric acid, as it be- 

 comes free, gives a part of its oxygen to the phosphorous com- 

 pound, and the nitrous acid, in a nascent state, is at once reduced 

 by the ammonium chlorid. There are two sources of error which 

 must be guarded against in the work ; a portion of the nitrogen 

 may escape reduction to the elementary state, or some of the 

 nitrate may fail to be decomposed. These errors are easily 



Fig. 31. Gantter's Nitrogen Apparatus. 



avoided if the reaction be begun slowly, so that the evolution of 

 gas may be gradual. The temperatures at first should, therefore, 

 be kept as low as possible. The development of red fumes, show- 

 ing the presence of undecomposed nitrogen oxids, shows that 

 the results will be too low. It is necessary, also, to provide for 

 the absorption of the hydrochloric acid which is formed. The 

 reaction is very conveniently conducted in the apparatus shown 

 in Fig. 31. The decomposition takes place in the flask A, and 

 the mixed gases pass into the absorption bulb C. The delivery 

 tube is very much expanded, as shown in the figure, so that no 

 soda-lye can enter A during the cooling of the flask. The absorp- 



