116 the role of nitrogen in plant-metabolism, iii., 



Discussion of Results. 

 i. The Proteins. 



Soluhdit [/. — The seeds of Acacia i^ijcnantha contain 4-5% 

 of nitrogen, partly in the form of protein, and partly as 

 other nitrogenous compounds. Table i. shows that, of the 

 total nitrogen, over 70% can be extracted from the seeds by 

 water, and 13% by sodium chloride. By extracting as com- 

 pletely as possible with 10% salt solution, and treating with 

 a 5% tannic acid solution, the proteins precipitated corres- 

 pond to 40% of the nitrogen, and the filtrate contains 45% 

 nitrogen as non-protein compounds. The solubility of the 

 proteins in salt-solution is greatly increased by nearly neu- 

 tralising to phenolphthalein. In Table ii., are given the 

 relative amounts of protein extracted by sodium chloride 

 from 1 to 10%, alone, and with alkali added till nearly 

 neutral. 



Alone. Witli 01 % alkali. 



Sodium chloride 1% 5 8 



10% 8 10 



Sodium hydroxide 01% 8 



The same amount is extracted by 01% alkali as by 10% 

 salt. 



An extract of the seeds in 10% salt-solution filtered clear, 

 slowly becomes acid to litmus, and deposits protein on stand- 

 ing. According to Osborne, an insoluble salt is formed of the 

 basic proteins with the free acid of the extract. 



Action of various ]}reci'pifaiifs. — From a 10% salt-extract, 

 the following reagents precipitate the proteins in decreasing 

 amounts, in the order given, and in the following relative 

 proportions : — 



Tannic acid 14" % of the total N 



'rrichloracetic acid 1 1 "5 



Heat coagulation 10" 



Carbon dioxide 9" 



Sodium chloride saturation 2" 



A 5% tannic acid solution was added to the 10% salt-extract 

 till no further precipitation took place, avoiding excess. The 



