BY JAMES M. PETRIE. 



103 



A second extract was obtained as before, with 10% sodium 

 chloride solution, and further precipitations made for com- 

 parison : 



(a) Coagulation on boiling, (b) tannic acid ppt., as before, 



((•) Trichloracetic acid added to the extract, which was 

 then heated to boiling point, and filtered hot. The filtrate 

 was then allowed to cool, whereupon it became cloudy, and 

 deposited a further precipitate. On boiling once more, this 

 deposit redissolved, and was again obtained on cooling. The 

 nitrogen in each was estimated separately. 



(d) Saturation with sodium chloride till the protein was 

 salted out ; after remaining some time with excess of salt 

 still visible, it was separated by the centrifuge, and its 

 nitrogen estimated, (e) Phosphotungstic acid was added to 

 the filtrate from the tannic acid precipitation, after acidifying 

 with sulphuric acid. In the protein-free filtrate, phospho- 

 tungstic acid precipitates the basic nitrogen compounds,— 

 cholin, histidin, arginin, &c., if present. 



The results are given in the following table : — 



Table iv. 



Taking tannic acid, which yields the maximum protein- 

 precipitate as a standard, it is seen that the protein coagulated 

 by boiling is in both experiments considerably less, in fact 

 only about 75% of the tannic acid precipitate. This shows 

 how imperfectly plant-proteins are coagulated, even on boil- 



