CH. X] OF PROTEIDS. 255 



similar conditions. Since it is not common to find any 

 considerable quantities of these substances in vegetable 

 tissues under normal circumstances the colorimetric 

 method will generally suffice. 



Estimation of Proteids in alkaline solution. 



[As the other nitrogenous substances have been ex- 

 tracted by the previous treatment with water, all the 

 nitrogen in this solution may be taken to be in the form 

 of proteids.] 



Evaporate to dryness a portion of the alkaline solution, 

 weigh the residue and determine the nitrogen, in the whole 

 or a weighed portion of it, by Kjeldahl's method. 



For a full account of all necessary details of manipula- 

 tion and precautions desirable see Sutton, Volumetric 

 Analysis, 5th ed. pp. 68 70. 



Nitrogen found x 6'3 = Proteids. 

 or Ammonia x 5'2 = Proteids. 



Or 



Add so much of the solution as will contain not more 

 than 5 10 milligrams of proteids to 500 c.c. of pure 

 distilled water, free from ammonia, in a large retort, and 

 distil after addition of 50 c.c. of alkaline permanganate 

 solution. 



Determine the ammonia in the distillate byNesslerising. 



For a full account of the details of the process see 

 Wanklyn, Water-analysis (Triibner and Co.), or Sutton, 

 Volumetric Analysis, pp. 389 and 397. 



[The second 50 c.c. of distillate should be Nesslerised 

 first and if it is found to contain much ammonia, the first 



