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Vol. 26, No. 3 
4. A large part of the experimental work was done on one soil, with 
supplementary work on other soils and materials. Calcium in the form 
of Ca(OH) 2 was added to soil in various amounts and the P H values and 
unadsorbed calcium determined. This was done both in the presence 
and absence of KC 1 . CaC 0 3 was also used in some experiments. 
5. The general effect of KC 1 was to increase the hydrogen-ion concen¬ 
tration except in soils which have a comparatively large amount of 
calcium. It reduced calcium adsorption from zero to one-half, more 
being adsorbed with the larger amount of Ca(OH) 2 added. 
6. The hydrogen-ion concentration was greater on the suspensions 
than on the extracts except where there was an excess of hydroxyl ions. 
Leaching a soil did not decrease the hydrogen-ion concentration nor the 
adsorptive power; the last of these, however, was decreased by ignition. 
The addition of CaC 0 3 and Ca(OH) 2 did not materially affect the P H 
values unless there was a long period of contact with the CaC 0 3 . The 
amount of calcium adsorbed from Ca(OH) 2 was not affected by the pres¬ 
ence of CaC 0 3 . The adsorptive power of soil was more closely related 
to the clay content than to the original hydrogen-ion concentration. 
7. Fuller’s earth had a higher hydrogen-ion concentration and a greater 
adsorptive power than soil. 
8. The hydrogen-ion concentration and adsorptive power of soil when 
treated with hydrochloric acid and washed was the same irrespective of 
the original calcium content of the soil. 
9. Addition of small amounts of 0.04N HC 1 increased the hydrogen-ion 
concentration proportionally to the amount added. Oxalic acid of the 
same concentration decreased the hydrogen-ion concentration with the 
smaller portions of acid, and increased it with the larger portion of acid. 
This increase was not as great as with equivalent amounts of HC 1 . The 
difference in the effect of the two acids is due to the formation of feebly 
ionized salts of a weak acid and strong base in the case of the oxalic 
acid. 
10. The fundamental cause of the acid condition of a mineral soil is 
found in the chemical changes which accompany weathering. The bases 
are removed and acid alumino-silicates accumulate. Since the removal 
of bases takes place gradually, readsorption would take place in a like 
manner. The harmful effect of these alumino-silicates is not necessarily 
due to the higher hydrogen-ion concentration, but more probably to 
the adsorption of calcium to such an extent that not enough is available 
for plant use. The amount of calcium adsorbed when definite amounts 
of a solution of Ca(OH) 2 is added to soil and the P H value produced can 
be measured by the methods described. 
LITERATURE CITED 
(1) Abbott, J. B., Conner, S. D., and Smalley, H. R. 
1913. SOIL ACIDITY, NITRIFICATION, AND THE TOXICITY OF SOLUBLE SALTS OF 
aluminum. Ind. Agr. Exp. Sta. Bui. 170, p. 329-374, 22 fig. 
(2) Ames, J. W., and SchollEnberger, C. J. 
1916. liming and lime requirement of soil. Ohio Agr. Exp. Sta. Bui. 306, 
p. 281-396, 5 fig. Bibliographical footnotes. 
(3) BemmELEN, J. M. van. 
1888. die absorptionsverbindungen und das absorptionsvermQgen der 
ACKERERDE. In Landw. Vers. Stat., Bd. 35, p. 69-136. Bibliograph¬ 
ical footnotes. 
(4) BoviE, W. T. 
1915. A DIRECT READING POTENTIOMETER FOR MEASURING AND RECORDING 
BOTH THE ACTUAL AND THE TOTAL REACTION OF SOLUTIONS. In Jour. 
Med. Research, v. 33, (n. s. v. 28), p. 295-322, illus. 
