N. M. Comber 375 



creased. Experiments made by Sciiolleubergeri indicate, however, that 

 there is a limit to the increase in base absorbing power which is brought 

 about by acid extraction. Working with a Clyde clay he found the base 

 absorbing power increased with the concentration of the acid used up to 

 an acid concentration of about N/2-5, but greater concentrations of acid 

 failed to produce any further increase in the base absorbing power. 

 With a Miami clay loam Schollenberger found that extraction with iV/10 

 acid brought the soil to its maximum base absorbing power. 



The strong indication of these results is that the base absorbing power 

 of soils as measured by the ordinary "lime requirement" methods, is a 

 phenomenon exclusively confined to the colloidal surface of soil particles 

 and is not to any appreciable extent a simple and direct reaction with 

 the structural minerals forming the cores of the particles, as is suggested 

 by Sulhvan- and others. 



In further examination of the point, seven soils were taken at random 

 and samples of each, after passing the 1 mm. sieve were extracted for one 

 day under similar conditions with HCl of various concentrations. 35 gm. 

 soil and 100 c.c. acid were used for each extraction. The soils were filtered, 

 washed, and air dried. The "lime requirement"' was determined by the 

 Hutchinson-McLennan method. The figures are as follows and fully con- 

 firm Schollenberger's results. 



Table I. 

 "Lime Requirements" of soils after extraction with HCl of various 



concentrations. 

 {CaCOs per 100 of Soil.) 



Soil 



2. Attempts were made to carry out similar experiments with ortho- 

 clase felspar and with powdered granite, but the base absorbing powers 

 of these after acid extraction were so small that the attempt was 



1 Soil Science,, 1917, 3. ^ U.S. Oeol. Survey Bull. 1907, 312. 



