124 
Journal of Agricultural Research 
Vol. VII* No. 3 
there will be a definite concentration of H and OH ions, while with the 
addition of acid the reaction of H + + 0 H“ = H 3 0 occurs and equilibrium 
is restored by the solution of more calcium carbonate. 
Soil acidity should not be set apart and considered as a phenomenon 
unrelated to the ordinary concepts of acidity. The use of such terms 
as “apparent acidity,” “real acidity/' “adsorption acidity” has led to a 
confusion of ideas, and, hence, should be discarded. With this in view, 
it seems desirable to emphasize the generally neglected point of view 
that the equilibria resulting in the production of H ions are in their 
essential nature the same for soil solutions as for other -simpler chemical 
systems. 
The methods now in vogue for estimating the lime requirement (soil 
acidity) have often proved to be unsatisfactory and in any case do not 
measure the intensity of acidity—that is, the H-ion concentration. In 
order to secure reliable data upon these points, the method of determining 
the H-ion concentration by means of a hydrogen electrode was used. 
Some preliminary experiments led to the adoption of a modification of 
Hildebrand's (17) apparatus, which will be described in detail later. 
Few similar measurements with soils have been previously recorded. 
The work of Saidel (29) was limited to a few alkaline soil extracts 
whose reaction had been changed by boiling. For reasons discussed 
later, data obtained on soil extracts are not convincing. Fischer (12) 
also made a few hydrogen-ion determinations with soil. In a more 
noteworthy investigation, Gillespie (13) has measured the H-ion concen¬ 
tration of 22 soils in water suspensions. The investigations reported in 
this paper were begun before the appearance of Gillespie’s article. The 
present authors have extended the work into various other phases, such 
as titration with bases as a meafis of adjusting the soil reaction and of 
studying the general phenomena grouped under the term “adsorption.” 
Moreover, various factors affecting the H-ion concentration of soil 
suspensions were also considered. 
VARIOUS POINTS INVESTIGATED 
In the course of these investigations several related questions were 
studied, in addition to the determinations of the H-ion concentration in 
various soil suspensions and in soil extracts. Experiments were under¬ 
taken in order to obtain further evidence regarding the influence of 
varying proportions of soil to water, grinding the soil, heating it at vari¬ 
ous temperatures, and of the addition of salts on the H-ion concentration. 
Consideration has also been given to the relation of HCO/, CO/, and 
C 0 2 to soil reaction as measured by the electrometric method. Experi¬ 
mental data have likewise been secured with respect to the lime require¬ 
ment of soils and the so-called “adsorption of bases.” Finally, the 
apparatus and methods of procedure are described. 
