Lecture 1 — 15 — Survey 



of how this can be done practically I shall not have 

 time to explain. Dr. Kelley has described in detail 

 the experimental reclamation of an area of black 

 alkali soil in the San Joaquin Valley of California. 

 The point to be stressed is that researches on base 

 exchange made the objective to be attained specific, 

 and they also provided chemical tools for determining, 

 from time to time, the effect of any given soil treat- 

 ment. The significance of researches on alkali soils 

 for the welfare of arid regions is not easily exag- 

 gerated. (See plates 3, U wnd\ 5). 



The acid soil condition and the black alkali soil 

 condition might seem to be entirely different phe- 

 nomena. Considered from the point of view of base 

 exchange, a fundamental unity is apparent. This is 

 illustrated by citing a simple experiment made a long 

 time ago by several of my colleagues, which was at 

 the time enlightening. A markedly acid soil from a 

 humid region was leached for some time with a sodium 

 chloride solution and then with pure water. The acid 

 soil became alkaline. Hydrogen ions of the original 

 colloid had been displaced by sodium ions. While the 

 soil was not converted into a typical black alkali soil 

 in all respects, it did acquire some of the character- 

 istics of the latter. 



Enough has been said to show why the study of 

 base exchange has been one of the strong trends in 

 plant nutrition and soil science for two decades. An- 

 other trend in the study of soil colloids has appeared 

 in recent years. Until this recent period the clay 

 colloids were envisaged as merely amorphous bodies 

 characterized by great development of surface and 

 certain chemical properties of a weak colloidal acid. 

 Some years ago Hendricks and Fry (1930) and Kel- 

 ley, DoRE and Brown (1931) began to make an ap- 

 plication of the X-ray diffraction method to clay col- 

 loids. These investigators established that the clay 

 colloids are capable of giving X-ray patterns betoken- 

 ing regular arrangement of atoms in crystal lattices. 



