268 CHAMBERLIN— THE AGE OF THE EARTH. 



soil resides almost wholly in the ultra clay or the colloidal material in the soil. 

 This ultra clay is mainly a hydrous silicate of alumina and iron, with hydrated 

 oxides of iron and probably alumina and absorbed calcium, magnesium, so- 

 dium and potassium. It is of a colloidal nature, and can be separated from 

 the soil in the form of minute droplets in dilute colloidal solutions which form 

 into colloidal aggregates when the concentration is somewhat over one gram 

 per 1000 c.c. 



The chemical' analysis of the soil colloids which we have separated shows 

 considerable amounts of lime, potash, soda and other material which we be- 

 lieve to be absorbed in colloidal condition. We believe there is a distribution 

 between the amount so absorbed and the concentration of the non-colloidal 

 part of the solution. We believe also that the absorption of any one of these 

 constituents such as potassium will be influenced by the presence of other salts 

 such as sodium or calcium. Under all stable conditions there will be an equi- 

 librium between the amount absorbed and the concentration of the surround- 

 ing liquid. Sodium chloride lowers the absorption of potassium chloride and 

 calcium salts lower the absorption of potassium chloride. In general' soils and 

 the colloids obtained therefrom absorb the basic ions much more readily than 

 they absorb the acid ions. 



According to Clarke the earth's crust contains 3.28 per cent, of Na^O and 

 2.96 per cent, of KjO. Thirty soils and the colloids obtained from the same 

 collected by this Bureau contained in the soil 1.59 per cent, of K2O and 1.45 

 per cent, in the colloids. The soils contained on the average 0.77 per cent, of 

 NaaO and 0.29 per cent, in the colloids. These figures show very clearly the 

 greater power possessed by the soil colloids to absorb and to hold back potash 

 than they have for sodium. 



A diffusion experiment with a soil colloid lasting over two months in 

 which large volumes of distilled water were allowed to act showed a loss of 

 25 per cent, of total K;0 and over 95 per cent, of the total Na^O. 



There is no question that the soil colloids are able to absorb NaCl. This 

 is shown by the ancient experiments of making sea water drinkable by filter- 

 ing through soil filters. 



Data and references examined show that under conditions of leaching by 

 rain water where equilibrium conditions are changed potassium is largely re- 

 tained by the soil but sodium is largely leached out. 



In the presence of much NaCl, as is found in sea water, ocean shore de- 

 posits would undoubtedly absorb considerable NaCl up to the point where the 

 colloids were in equilibrium with the sea water. If the material were then 

 formed into a shale and elevated to land areas the induration would presum- 

 ably destroy the colloidal properties leaving the NaCl free from its colloidal 

 entanglements and with the change of the solvent from sea water to rain 



Patten, H. E., and Waggaman, W. H., " Absorption by Soils," U. S. Dept. 

 Agr., Bur. Soils, Bull. 52, 1908. 



Schreiner, Oswald, and Failyer, G. H., " The Absorption of Phosphates 

 and Potassium by Soils," U. S. Dept. Agr., Bur. Soils, Bull. 32, 1906. 



Parker, E. G., " Selective Adsorption by Soils," Jour, of Agr. Research, 

 Dept. Agr., Vol. I., No. 3 (Dec. 10, 1913). 



