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



(iii.) The above hydrolysis, with 8% HCl, was accom- 

 panied by a considerable blackening of the solution, due to 

 the formation of melanoidin. After the first hydrolysis, the 

 residue in the retort from the distillation was dissolved in 

 sulphuric acid, and allowed to stand. The black precipitate 

 was filtered oflf. It contained 4-8% of the nitrogen. 



(iv.) The solution, after these two distillations, was now 

 used for the estimation of amino-groups ; and, first, the 

 sodium hypobromite method was tried, with entirely negative 

 results. That is, after acid hydrolysis and distillation of the 

 ammonia formed, those substances are destroyed, which had 

 previously liberated nitrogen gas with this reagent. 



The nitrous acid method of Sachsse and Kormann was 

 then applied. 



The apparatus gave the theoretical yield of nitrogen from 

 a sample of pure asparagin. Portion of the solution, after 

 the first hydrolysis and distillation, was treated by the above 

 nitrous acid process, and gave, after all the necessary cor- 

 rections were made, 65-7% of the nitrogen. The solution, 

 after the second hydrolysis and distillation, yielded, in the 

 same way, 38-8% of the nitrogen. 



(v.) After the first hydrolysis and distillation, the solution 

 was treated with phosphotungstic acid for basic substances, 

 and the precipitate contained 141% of the nitrogen. 



The results obtained from this series of experiments may 



now be tabulated as under : — 



Table x. 



Total nitrogen in the protein-free solution 100 



(i.) Hydrolysed and distilled with magnesia 96 



(iii.) Melanoidin formed by above hj'drolysis 4'8 



(ii) Second hydrolysis, distilled with magnesia 8'0 



(iv.) Nitrogen evolved b}' sodium hypobromite nil 



Half nitrogen evolved by nitrous acid 38'8 



Undetermined N ... 388 



(i.) First hydrolysis and distillation with magnesia 96 



(v.) Precipitated by phosphotung. after hydrolysis and distilln. 14'1 



(i.) First hydrolysis and distilln. with magnesia 9'6 



(iv.) Half N evolved by nitrous acid after hydrol. and distilln. 65 '7 



