VEGETABLE PROTEINS 101 



5. The Compounds of Fibrin with Inorganic Acids and Bases. 



— Employing methods similar to those utilized by Van Slyke and 

 Bosworth in the investigation of the compounds of casein with in- 

 organic bases, Bosworth has investigated the combining-capacity 

 of fibrin for inorganic bases and acids (6). He finds that at neu- 

 trality to phenolphthalein one gram of fibrin neutralizes 61.4 X 

 10-5 equivalents of NaOH or 61.6 X 10"^ equivalents of Ca(0H)2. 

 Fibrin, therefore, neutralizes bases, in the presence of excess of the 

 base, in equivalent-molecular proportions. At "saturation," i.e., 

 when the proportion of base is only just sufficient to hold the pro- 

 tein in solution, fibrin combines with 15.2 X 10"^ equivalents of 

 NaOH, and the precipitate produced on addition of HCl to this 

 solution is free from sodium. In other words no insoluble salts of 

 sodium are formed. The case is quite otherwise with calcium 

 which forms with fibrin an insoluble salt (soluble, however, in 

 5 per cent NaCl solution), containing 30 X lO'^ equivalents of the 

 base, and a soluble salt containing 45 X 10"^ equivalents of the 

 base. The proportion of 1:2:3 encountered in these various 

 compounds is irresistible evidence of the existence of definite 

 stoichiometrical relations between fibrin and the bases with which 

 it combines. 



The sulphur-content of fibrin would indicate a minimal com- 

 bining- weight of 6751. The proportion of base in the "saturated " 

 compound of fibrin with NaOH would indicate a combining-weight 

 of 6667. 



Calcium and barium fibrinates yield a precipitate of fibrin on the 

 passage of CO2 through them (6) (17), sodium, potassium and 

 ammonium fibrinates do not. Fibrin does not decompose CaCOs, 

 however, as casein does on trituration with this salt in the presence 

 of water. 



Fibrin forms a compound with hj^drochloric acid, which is just 

 soluble in water, containing 15 X 10"^ equivalents of the acid. 



6. The Compounds of the Vegetable Proteins with Inorganic 

 Acids and Bases. — These have been investigated by T. B. 

 Osborne (29) (30) (31) (32), who has found evidence of combina- 

 tion between inorganic acids and the following vegetable proteins: 

 Edestin, legumin, excelsin, amandin, corylin, phaseolin, gliadin, 

 hordein and zein. He finds that when edestin, deposited from 

 salt-solutions, is suspended in water and made neutral to phenol- 

 phthalein, edestin itself remains undissolved, while the added 

 alkaU carries into solution its equivalent of the acid or acids which 



