THE COLLOIDAL PROPERTIES OF SOIL 155 



as absorption was only a substitution, the greater the amount 

 of replaceable base the greater would be the absorption of 

 ammonia. The method was applied to a number of soils and 

 gave results in fair agreement with their agricultural history. 

 It was somewhat modified by Kellner, 1 who measured the 

 quantities of potassium and calcium displaced and found that 

 they agreed exactly with the amounts taken up by plants in 

 pot culture. The method was still furthur improved by 

 Ramann : a 5 per cent solution of ammonium nitrate is 

 allowed to percolate through the soil and the displaced potas- 

 sium and calcium are estimated. 2 A detailed study has 

 been made by Prianischnikow (229^). 



Van Bemmelen (200) began by accepting Way's chemical 

 hypothesis, and showed that soils with a high power of ab- 

 sorption usually contained a large quantity of easily decom- 

 posable silicates (iQtf): Way's double silicates would pre- 

 sumably be of this nature. Further, absorption of bases 

 always involved displacement of other bases from the soil, a 

 strong indication of chemical change. Later on, however, he 

 made extensive studies of absorption by simple gels : silica, 

 alumina, ferric hydroxide, tin hydroxide, etc., and found it 

 closely to resemble absorption by soils : other studies of 

 colloids were made and in each case the similarity to soil 

 phenomena was so close as to leave no doubt that soil was 

 essentially a colloid and soil absorption simply a manifesta- 

 tion of the colloidal properties. 



This new idea was soon found to explain many of the old 

 discrepancies. Chemists had several times attempted to bring 

 the phenomena of absorption equilibrium into line with those 

 of chemical equilibrium, but the equations would not fit except 

 for a narrow range of concentrations. Boedecker in i859 3 

 had fitted an expression to Henneberg and Stohmann's results 

 for ammonia absorbed and calcium displaced in the interaction 



[ J O. Kellner, Landw. Versuchs-Stat., 1886, 33, 349. 



2 Recorded by J. A. Hanley in Nature, 1914, 93, 598. See also Kullenberg, 

 Jahresber. Agric. Ghent., 1865, 8, 15. 



3 Journ. f. Landw., 1859, 48. 



) 



