45 AGRICULTURAL ANALYSIS 



ammonia in the sample having been previously determined. The 

 increase in ammonia is due to nitrates or nitrites reduced by the 

 couple. 



IODOMETRIC ESTIMATION OF NITRIC ACID IN 

 NITRATES 



391. Method of De Eoninck and Nihoul. This process is 

 applicable only in the absence of organic bodies and other reduc- 

 ing agents. 



The principle on which it rests, as applied by McGowan, is 

 as follows 73 



When a fairly concentrated solution of a nitrate is warmed 

 with an excess of pure, strong hydrochloric acid, the nitrate is 

 completely decomposed, and the production of nitrosyl chlorid 

 and chlorin is quantitative. The reaction, as shown by Tilden, 

 is represented by the following equation : 74 



HNO 3 +3HCl=NOCl-fCl 2 +2H 2 O. 



One molecule of nitric acid thus yields two atoms of chlorin 

 and one molecule of nitrosyl chlorid capable of setting free three 

 atoms of iodin. The iodin can be estimated in the usual man- 

 ner by titration with sodium thiosulfate. The nitrosyl chlorid is 

 decomposed by the potassium iodid, nitric oxid escaping. 



The apparatus employed is shown in Fig. 35. 



A is a small, round-bottomed flask, into the neck of which a 

 glass stopper x is accurately ground. The capacity of the bulb 

 is about 46 cubic centimeters^ and the length of the neck, from x 

 to y, 90 millimeters. The first condenser is a simple tube, slightly 

 enlarged at the foot into two small bulbs. 75 The length from a 

 to b is 300 millimeters, from b to c 180 millimeters, and from e 

 to / 30 millimeters. The capacity of the bulb B is 25 cubic centi- 

 meters, and the total capacity of the two bulbs and tube, up to 

 the top -of C, 41 cubic centimeters. This condenser is immersed 

 up to the level of c, in a beaker of water. D is a geissler bulb 

 apparatus, E is a calcium tube, filled with broken glass, which acts 

 as a tower and g is a small funnel, attached by rubber and clip 



n Journal of the Chemical Society, 1891, 59 : 530. 



74 Journal of the Chemical Society, 1874, 27 : 630; 1875, 28 : 514. 



76 Sutton, Volumetric Analysis, gth Edition, 1907 : 77. 



