CHAMBERLIN— THE AGE OF THE EARTH. 267 



The present status of knowledge and opinion is summarized by 



the following quotations. 



Dr. Truog writes : ^^ 



The minerals or salts in soils consist largely of silicates. On weathering 

 the bases are removed from the silicates, leaving acid residues or acid silicates. 

 These acid silicates will react with salts like KCl and NaCl and remove the 

 base and leave HCl in solution. When soil is treated with equal molecular 

 strengths of these two solutions, the potassium is removed to a greater ex- 

 tent than the sodium. This is due to the fact that the potassium forms 

 more insoluble compounds with the acid silicates than the sodium. Further- 

 more, silicates which have not had their bases removed will also react with 

 these salts and exchange bases with them. For example, potassium chloride 

 will react with an insoluble sodium silicate in which reaction the potassium 

 replaces the sodium and the sodium is left in solution as soluble sodium 

 chloride. If an insoluble potassium silicate were treated with a solution of 

 sodium chloride some of the sodium would replace the potassium and some 

 potassium would thus go into solution as the soluble chloride. This, how- 

 ever, would not proceed to as great an extent as the previous reaction, since 

 the potassium forms a more insoluble silicate than sodium. In reading some 

 of the literature on this subject one may get the impression that sodium 

 is not retained by soil's like the potassium, but this is really not the case ; the 

 action is merely relative. The potassium is retained to a greater extent 

 simply because it forms more insoluble compounds with the soils. 



Dr. Milton Whitney-* writes : 



The investigations of this Bureau -^ show that the absorptive power of a 



Eichhorn, Pogg.-An., Vol. 125 (1854), p. 126. 

 Voelcker, Jour. Roy. Agri. Soc, 2d series. Vol'. I., pp. 289-316. 

 Kullenberg, Hoffman's " Jahres bericht der Agrikultur Chemie," Vol. 8 

 (1865), p. 15. 



Lemberg, Scitschr. deutsch. Geol. Gescll., Vol. 29 (1877), p. 483. 



23 E. Truog, Soil Chemist, Dept. of Soils of the College of Agriculture, 

 University of Wisconsin. Personal communication. 



24 Milton Whitney, Chief Bureau of Soils, U. S. Department of Agricul- 

 ture. Personal communication. 



25 These include numerous publications containing many analyses as well 

 as special discussions, but as in all agricultural publications, the constituents 

 that most concern plant life receive most attention and data relative to sodium 

 is incidental. The following may be cited : 



Cameron, F. K., and Bell', J. M., " The Mineral Constituents of the Soil 

 Solution," U. S. Dept. Agr., Bur. Soils, Bull. 30, 1905. 



Cameron, F. K., and Patten, H. E., " The Distribution of Solute between 

 Water and Soil," Jour, of Phys. Chem., Vol. II., pp. 581-93, 1907. 



Patten, H. E., " Some Surface Factors Affecting Distribution," Trans. 

 Amcr. Elcctrochem. Soc, Vol. 10, pp. 67-74, 1906. 



Patten, H. E., and Gallagher, F. E., " Absorption of Vapors and Gases 

 by Soils," U. S. Dept. Agr., Bur. Soils, Bull. 51, 1908. 



