Oct. 20, 1923 
Soil Reaction in Relation to Calcium Adsorption 
117 
(Experiment 13) a P H value indicating a higher hydrogen-ion concen¬ 
tration than that found in many acid soils. The adsorptive power for 
calcium was also greater. The silicates present in such materials as 
fuller’s earth and kaolin are relatively insoluble and very feebly ionized. 
Rice and Osugi (jp) found that the catalytic effect of the hydrogen ion 
from some silicates as indicated by the inversion of cane sugar was nil 
when KC 1 was absent, but considerable when this salt was present. 
The greater hydrogen-ion concentration produced by adding a neutral 
salt like KC 1 to an alumino-silicate is due to the adsorption of potassium 
(36 ), thus increasing the number of hydrogen ions. When a soil is 
suspended in water and agitated, some bases readily go into solution, 
as is well known by the analysis of the water extracts. Some of the 
hydrogen ions in a water suspension can be accounted for by the re¬ 
adsorption and consequent rearrangement of bases. 
ADSORPTION VERSUS CHEMICAL/ COMBINATION 
Whether the changes which occur when a hydroxid such as Ca(OH) 2 is 
added to soil shall be considered purely a chemical reaction or more in 
the nature of an adsorption phenomenon has been the subject of con¬ 
siderable study (j, J7, 18, ig y 43). Recent ideas ( 16 , 27) concerning the 
relationship between molecules, such as occur in the formation of crystals, 
and the phenomena of adsorption would point to the conclusion that 
there is no sharp dividing line between a purely chemical union of ele¬ 
ments or compounds and adsorption. If it is true that chemical com¬ 
pounds form when Ca(OH) 2 is added to soil, then from the experimental 
data here presented there must be an indefinite number of such com¬ 
pounds, all with different formulas. It is simpler to assume ordinary 
adsorption as an explanation. 
THE PROCESS OP ADSORPTION 
The process of adsorption was demonstrated in the experiment of 
Linder and Picton (28 ), who showed that when As 2 S 3 is precipitated from 
colloidal solution by BaCl 2 a certain amount of the barium is carried 
down and a corresponding amount of HC 1 produced. Parker (36) found 
that when an acid soil is shaken with a solution of KC 1 the potassium is 
displaced by aluminum and other bases in nearly equivalent amounts, 
the chlorin remaining unchanged. However, when NaOH was also 
added together with the KOI his data showed that just as much potas¬ 
sium was absorbed, but no calcium liberated. The following equations 
illustrate what takes place: 
KC 1 ^K + -C 1 
HOH^OH+H + 
KOH (adsorbed) + HC 1 
In soils of relatively low calcium content the solubility of this element 
(Experiment 23) in 0.5 N KC 1 was the same as in 0.5 N HC 1 . The above 
equations show that in reality HC 1 is the dissolving agent. If a base 
like NaOH is present, NaCl is formed and no calcium is dissolved. 
