PROTEINS 157 



excess, otherwise they exert a protective action. Hydrophile negative 

 inorganic hydrosols, e.g., silicic acid, differ from positive hydrosols 

 only by the presence of H and OH ions which act oppositely to those 

 in the positive hydrosols. 



Only a small fraction of the albumin is precipitated by hydrophobe 

 inorganic colloids; but the greater portion, and at times all the albu- 

 min, is precipitated by hydrophile hydrosols. 



Albumins appear to react with proteins of pronounced basic (histone) 

 or acid character (U. FRIEDEMANN and H. FRIEDENTHAL*) just as do 

 inorganic hydrophile hydrosols. 



Albumin, Heavy Metals and Salts of Heavy Metals. 



On shaking salt-free albumin solutions with metallic iron, cobalt, 

 copper, lead, nickel or aluminium, portions of these metals go into 

 solution and are bound by albumin in a hitherto unrecognized 

 "masked" form, according to BENEDICENTI and REVELLO-ALVES. 



Electrolyte-free albumin yields no precipitate with zinc, copper, 

 mercury or lead salts. In the presence of salts, however, albumin 

 forms with salts of the heavy metals precipitates whose chemical com- 

 position is not constant, but depends on the concentration of the 

 components at the time of precipitation. By precipitating albumin 

 with solutions of heavy metal salts of varying concentrations we 

 get "irregular series," which frequently show two zones of precipi- 

 tation: one with very dilute solutions of the metal salt (one ten 

 thousandth normal and under) and another with high concentration; 

 between these there is always a zone with no precipitation. The 

 precipitation zone with great dilutions of the metal salt is due accord- 

 ing to H. BECHHOLD* to metal hydroxid split off hydrolytically, 

 which precipitates with albumin, forming an insoluble heavy metal- 

 albumin compound. The resolution of this precipitate at somewhat 

 greater concentration of metal salt results from ionization. W. 

 PAULI and HECKER have shown by very convincing experiments 

 upon the action of FeCl 3 on albumin that a soluble ferric ion-albumin 

 complex occurs somewhat in accordance with the following scheme 

 [zFe(OH) 3 - protein] + 0FeCl 3 = [zFe(OH) 3 - protein] 0Fe + 3 gCl. 



Upon addition of more FeCl 3 , just as when acid is added to acid 

 albumin, partial neutralization occurs and there is further precipi- 

 tation. Ur0 2 Cl 2 behaves like FeCl 3 , as do also, to a certain extent, 

 AgN0 3 , ZnSO 4 and Pb(N0 3 ) 2 . On the other hand, the precipitate 

 disappears with higher concentration of CuCl 2 and HgCl 2 , and, abso- 

 lutely no precipitate is formed with electrolyte-free albumin and the 

 chlorides of Fe", Co", Mn", Cd". 



