108 THE RCLE OF NITROGEN IN PLANT-MKTABOLISM, iii., 



and run approximately parallel to the end. The latter part 

 of the curve consists of the protein or proteins most difficult 

 to precipitate by alcohol. 



With a concentration of 55% and upwards, of alcohol, the 

 gums present in the extract are precipitated with the protein, 

 and their influence on the percentage of nitrogen in the latter 

 part of the curve is noticeable. The two curves of precipitate 

 and nitrogen, however, run approximately parallel through- 

 out. 



As will be seen from the foregoing Tables, in addition to 

 the proteins existing in the saline extracts, there is a con- 

 siderable amount of nitrogenous compounds in a form other 

 than protein. 



( N in form of soluble proteins 40 % 



\N left ill residue of seeds 15 



N ill non-protein form 45 



% of the total N in the seeds ... 100- 



The following experimental studies are devoted to the eluci- 

 dation of the nature of this 45% of the nitrogen of the same 

 Acacia seeds. The solutions were prepared in different ways, 

 and the results are all stated in per cent, of the non-protein 

 nitrogen, taken as 100. 



(1) Fre/paration of the solution — Method («). The powdei-ed 

 seeds were extracted as completely as possible with cold 

 water. After filtering, the liquid was concentrated on ;:, 

 water-bath to about a litre ; the coagulated proteins were 

 removed, and the remaining proteins precipitated by tannic 

 acid. The latter reagent was removed from the solution by 

 lead acetate, the lead by sulphuric acid and hydrogen sul- 

 phide, and the excess of the latter by a current of air. 



Method (h). The seeds were extracted as completely as 

 possible by hot water, and the solutions filtered. The com- 

 bined fluids were concentrated, and poured into alcohol, 

 making a solution of 80% in strength. After standing over 

 night, the proteins were filtered off. The clear alcoholic fluid 



