Oct. 16, 19x6 
Acidity and Adsorption in Soils 
127 
On the other hand, certain of the soils gave an H-ion concentration as 
high as 0.2 X io -3 , which indicates considerable intensity of acidity. 
Any ultimate conclusions regarding soil fertility must presuppose a 
knowledge of the composition of the soil solution. At present our 
methods do not enable us to study the soil solution itself, and conse¬ 
quently all deductions in regard to it must be purely inferential. In 
order to approximate the conditions existing in the soil solution, the 
ratio of water to soil in several cases was reduced as far as the method 
would permit. An inspection of the data indicates comparatively insig¬ 
nificant changes in the H-ion concentrations when widely varying pro¬ 
portions of water to soil are used. Most of these small fluctuations can 
be ascribed to the limitations of the apparatus. Hence, it is reasonable 
to assume that the H-ion concentrations of the soil suspensions approxi¬ 
mate those of the soil solutions. This argument is theoretically sound, 
since in all the larger proportions of soil employed it is probable that the 
solution is saturated with respect to the acid-forming constituents. 
RELATION OF HCOI, C 07 , AND C 0 2 TO SOIL REACTIONS 
At present it has been found impracticable to simulate exactly the 
CO s equilibria existing under field conditions. In the case of several 
acid soils the partial saturation of the soil suspensions with C 0 3 gas did 
not alter the reaction appreciably. Hence, it is quite possible that the 
C 0 3 content of the soil solution may not materially modify the above 
conclusions regarding the magnitude of the H-ion concentration in acid 
soils. In other words, the soil acids, whether organic acids or acid sili¬ 
cates, are the chief factors determining the reaction. 
On the contrary, the reaction of alkaline soils depends in large measure 
upon the equilibria between C 0 3 gaseous, C0 2 dissolved, C0 3 ion, and 
HC 0 3 ion. 1 From these considerations it might be predicted that the 
reaction of most alkaline soils is the resultant of the equilibria existing 
between HC 0 3 , C 0 3 , Ca ions and dissolved C 0 2 in contact with the C 0 3 
of the soil atmosphere. From the work of Cameron and Bell (6) and 
Johnson (19) it seems proper to infer that HCOJ in this class of soils 
largely determines the reaction. 
The application of the electrometric method to solutions or suspen¬ 
sions whose reaction depends upon the HC 0 3 ion requires great precau¬ 
tion to prevent the decomposition of HCOJ, with a loss of C0 2 . This 
reaction is slow, but there will be a gradual increase in the alkalinity of 
the solution as a result of the production of CO s ions. In the present 
work the shaking method by Gillespie (13) was employed and the decom¬ 
position of HCOJ largely avoided, although the results may tend to be 
slightly high. 
1 For a detailed discussion of this matter the reader is referred to Cameron and Bell (6) and to 
Johnson (19). 
