110 THE ROLE OF NITROGEN IN PLANT-METABOLISM, iii., 



slow evolution of ammonia begins ; it continues slowly, hour 

 after hour, and does not seem to come to a definite end in a 

 reasonable time. After twenty minutes boiling, about 1 cc. 

 of decinormal ammonia had collected ; and, after four hours, 

 5 cc. ; it was then distilling at the rate of 04 cc. per hour. 

 (In a control, it was found that the whole of the ammonia 

 from 0-6 gm. of ammonium chloride was distilled in less than 

 twenty minutes, at the same rate of boiling ; and required 

 over 100 cc. decinormal acid.) One must conclude from this, 

 that the ammonia does not all exist preformed in the solu- 

 tion, but is evolved from a substance which slowly decom- 

 poses by the action of magnesia, when boiled. 



(iii.) The original solution was next treated with phos- 

 photungstic acid, and the precipitate of basic compounds 

 assayed for nitrogen. A phosphotungstic precipitation was 

 also done on the solution, previously boiled with magnesia for 

 four hours. 



(iv.) The phosphotungstic filtrate from the former was dis- 

 tilled with magnesia, while a part was hydrolysed by boiling, 

 for two hours, in 107 HCl, then neutralised, and distilled 

 with magnesia. 



(v.) The phosphotungstic filtrate from No. i., was examined 

 for amino-groups by the sodium hypobromite method. The 

 phosphotungstic acid was removed as barium salt, and excess 

 of barium precipitated by carbon dioxide. The nitrogen 

 evolved by the hypobromite was measured in a eudiometer. 



The order of the experiments is indicated thus : — 



Magnesia distillation (ii.) — ^phosphotung.(iii.) — ^aod. hypobromite (v.) 



Phosphotungstic (iii.) -> |5''i'"f*'?" <':^ ^. ,.„ ,. 

 '^ 6 V / ^ y^hydrolyais and distillation. 



The percentage of nitrogen obtained in each of the above 

 determinations, is set out in the following table: — 



