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



As was shown on a previous page, colloidal material 

 increases the tensile strength of shales, and it has been 

 shown to do the same for clays. Other colloidal ^ sub- 

 stances have also been used to increase the plasticity. 

 Humus, for example, an organic colloid, produces bene- 

 ficial results in lean clays. Clays in a cool, moist place 

 improve in plasticity even within a few weeks. It is 

 believed that the development of organic matter in the 

 clay by the growth of bacteria, or even protozoa, is 

 responsible for the improvement, for the protoplasm of 

 these minute organisms is itself a colloid. 



If plasticity of clays should be found to be dependent 

 upon the inorganic colloids in them, it might be pertinent 

 to ask if clays and shales laid in the sea would be more 

 plastic than those laid in fresh water, where the finest or 

 colloidal material had difficulty in being precipitated. 



Ries is has shown that the fineness of the material, the 

 thinness of the plates in the shale, and the colloids, are 

 each in themselves inefficient to fully explain plasticity. 

 His theory suggests that plasticity may be due to cohesion 

 and adhesion factors which depend on the constitution of 

 the molecule, but not on the chemical composition. It 

 might be said that he does not seem to be fully satisfied 

 with his explanation, for he adds that "practical work 

 to improve the plasticity of clays may well follow lines 

 already started, such as the addition of colloids, and 

 weathering, which may mean the addition of colloidal 

 material by bacterial growth. ' ' 



One can never understand the raw materials and their 

 relations to the finished products in cements, brick and 

 terra-cotta, pottery, porcelain, enamels, and glass, until 

 he has dipped rather seriously into the study of colloids 

 from the geologic side. Weathering is a colloid-pro- 

 ducing process, as well as a maker of most of the soils and 

 the salts of the sea. Since macadam, brick, cement, and 

 asphalt roads all start with materials whose vital proper- 

 ties are connected with the colloidal state of matter and 

 the geologic processes that produce these materials, the 

 road industry has real need of a colloid geologist. 



Colloids in Soils. Perhaps this topic will take us as 

 far into questions of physiography as the last has into 

 metallurgical and industrial processes, but in the last 



ls Kies, H.,.Geol. Survey, W. Va., vol. 3, pp. 46-54, 1905. 



