G. D. Hubbard — Colloids in Geologic Problems. 101 



F. W. Clarke in his "Data of Geochemistry," p. 533, 

 accepts psilomelane, and some other less known man- 

 ganese ores as colloidal complexes. In this connection 

 he also mentions lampadite, a cupriferous hydrate of 

 manganese. The copper may be present simply by 

 adsorption. 



The silicate nickel ores have always been a confusing 

 group, but an interpretation involving colloidal sub- 

 stances seems to simplify the matter. It will be remem- 

 bered that these ores are hydrous magnesium nickel sili- 

 cates. The non-metalliferous foundation seems to have 

 accumulated first as a gel, 12 and subsequently to have 

 adsorbed some nickel compound, perhaps nickel silicate, 

 and a magnesium compound, and thus a mixture of two 

 substances occurs whose proportions may vary greatly 

 within short distances. 



Coagulation or Flocculation of Sediments. — It has long 

 been known that even the finest sediments which come out 

 to the sea in the waters of our great rivers fall to the 

 bottom long before they get far into the sea, and that 

 the main body of the ocean is made of comparatively 

 clear water. This speedy precipitation of sediments has 

 also been ascribed to the saltiness of the sea, but the con- 

 nection had not been worked out until recent studies in 

 colloids and their relations to electrolytes. 



An electrolyte is a salt, or in some. cases a base or an 

 acid, in water solution through which electric current 

 flows. Salts are generally better electrolytes than acids. 

 The theory is that the electrolyte is ionized, e.g., sodium 

 chloride becomes Na + and CI" in solution, magnesium 

 chloride becomes Mg ++ and 2 CI" in solution. The higher 

 the valence of the base part of the salt (the positive ion), 

 the more powerful the electrolyte, as a coagulant of nega- 

 tively charged suspensions, and the power seems to bear 

 no definite relation to the valence. Aluminum chloride, 

 for example, is hundreds of times more potent than 

 sodium chloride. The charge on the electrolyte and on 

 the colloid must be of opposite sign. The aluminum ion 

 of A1 2 (S0 4 ) 3 has a positive charge, and aluminum is 

 trivalent in the sulphate. Since most colloids are nega- 

 tive, aluminum sulphate is one of the most effective floc- 

 culators. 



12 Kruseh, P., loc. cit. 



