Oct. ao, 1933 
Soil Reaction in Relation to Calcium Adsorption 
119 
calcium to potassium was 1 to 30 about half as much calcium was ad¬ 
sorbed as in the absence of KC 1 , and considerable was adsorbed even 
with a wider ratio. This indicates that the adsorptive power of these 
alumino-silicates for calcium is greater than for potassium. 
CONCLUDING STATEMENT 
The process of weathering removes by degrees the bases in soils, and 
hence alumino-silicates are present with varying amounts of bases. The 
definite composition of many supposed minerals is questioned (38). If 
definite calcium aluminates exist, an equilibrium must have been reached 
(38). In the absence of such an equilibrium a heterogeneous mixture 
is present. If the removal is gradual, and substances are present with 
varying amounts of bases, the recombination would also be gradual. 
These may be purely chemical combinations, but, if so, the quantitative 
relationship is as would be expected by the adsorption law. This has 
been shown in Experiments 5 to 18. The amount of calcium adsorbed 
bears a certain relation to the amount added. The total amount ad¬ 
sorbed increases according to the amount added. When relatively small 
amounts are added, all is adsorbed. When larger amounts are added 
the greater part is adsorbed. Adsorption is further emphasized by the 
fact that the amount of clay has a greater effect on the amount of cal¬ 
cium adsorbed than the intitial hydrogen-ion concentration (Experi¬ 
ments 19 and 22). 
Many problems have been suggested by the present investigation. 
There are a number of factors which affect the electrometric measure¬ 
ments on soils. The hydrogen electrode does not give as satisfactory 
results with soils as it does with many other materials. The phenomenon 
of poisoning the electrode that exists with other materials is worse with 
soil. There is great need of standardizing the electrometric method for 
soils. vSeveral of the experiments should be repeated on a more extensive 
scale; particularly those on the effect of organic acids on soils; leaching; 
ignition; and the acid treatment. More knowledge is needed concerning 
tie solubility of the acid-forming substance in soil. The adsorption of 
the hydroxyl ions, only incidentally touched upon, needs further inves¬ 
tigation. 
SUMMARY 
1. Acidity or alkalinity of aqueous solutions is expressed by the sym¬ 
bol P H and some number which denotes the degree of the hydrogen-ion 
or the hydroxyl-ion concentration. The ion in excess determines whether 
the solution is acid or alkaline. This general concept is applied to water 
solutions and water suspensions of soil. The hydrogen-ion concentra¬ 
tion in soil was measured with the hydrogen electrode. When used 
with soil this method presents many difficulties; these, however, are not 
necessarily insurmountable. 
2. Since surface plays an important part, and phenomena of hetero¬ 
geneity are manifest, the term adsorption rather than absorption is used 
to describe the combination of soil and Ca(OH) 2 . Quantitatively, the 
combination obeys the adsorption law. 
3. Successful use of the hydrogen electrode with soils depends on 
effective methods and efficient apparatus. A special apparatus was 
devised by which it is possible to carry on six electrode measurements 
at the same time with the minimum attention of the operator. 
