CHEMICAL PHENOMENA IN LIFE 



negatively electric, but in acid medium they are 

 charged with positive electricity. Emulsion 

 colloids also show quite a different reaction to 

 small quantities of electrolytes. Emulsion colloids 

 are never precipitated by a small amount of 

 mineral salts. The electric properties of the ions 

 cannot alter the colloid state. 



Otherwise emulsion colloids in many respects 

 resemble real solutions. In the first place, the 

 diffusion of emulsion colloids is considerable 

 enough to be measured by means of the usual con- 

 trivances for studying diffusion phenomena. Such 

 experiments had already been made by Graham. 

 Later on, Pfeffer carried out experiments on 

 solutions of gum-arabic and glue, to show that 

 distinct osmotic pressure can be observed to be 

 exercised by such colloids. The osmotic pressure, 

 however, is very small as compared with the osmotic 

 effects of sugar solution or of inorganic salts. 

 Even the freezing-point of emulsion colloids is dis- 

 tinctly lower than the freezing-point of the pure 

 medium. Such sols show many transition charac- 

 teristics to true solutions. The density of sols is 

 distinctly different from the specific gravity of the 

 pure medium. The surface tension of sols also 

 differs regularly from the surface tension of the 

 pure medium. In many cases the surface tension 

 of water is lowered by dissolving colloids in it. 



Such characteristics are to be expected in the 

 emulsion colloids of protoplasm. Protoplasm, 

 32 



