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



A quantity of the finely powdered seeds was first extracted 

 with distilled water, until very little more was dissolved. The 

 extract was filtered clear, and the insoluble residue then 

 further extracted as completely as possible with a 10% 

 solution of sodium chloride. The residue obtained after 

 filtration was next treated with alcohol of 80% strength, the 

 alcoholic extract was filtered, and the residue then examined. 



A considerable amovmt of nitrogen still remained in the 

 insoluble residue of seedmeal after all these solvents had 

 been used. The nature of this nitrogen is still unknown, al- 

 though it most likely occurs in the form of protein also. The 

 fact that, when the residue is dried and ground still finer, 

 more protein is extracted, shows that some cells had resisted 

 disintegration and still enclosed part of the protein. There 

 is no doubt that tannins take an important part by com- 

 bining with the protein, and forming an insoluble compound, 

 for tannins are found in considerable quantities in the skins 

 of Acacia seeds. Part of the nitrogen in the residue can be 

 removed as protein by dilute alkalies and acids ; but it is 

 known, however, that these solvents alter the chemical nature 

 of the proteins by combining with them, and that the 

 original protein cannot again be restored. These reagents 

 were, therefore, not applied in this case. 



The distilled water and salt-extracts were each measured. 

 One portion of each was used for the estimation of the total 

 amount of nitrogen, and in another portion the proteins were 

 precipitated by tannic acid ; the tannic precipitates were 

 dropped into a flask, and the nitrogen determined by 

 Kjeldahl's method as protein-nitrogen. The results of these 

 determinations are stated in the following table: — 



Table i. — Acacia Seeds. 



Water driven ofiF at 100°C 11-58% 



Ash 3-34 



Organic constituents (by difference) 8508 



100 000 



