Oct. 20, 1923 Soil Reaction in Relation to Calcium Adsorption 
99 
The P H values on both suspensions and extracts showed an increase 
in hydrogen-ion concentration corresponding to the increased amounts of 
HC 1 added. Where the smaller amounts of HC 1 were added, the hydro¬ 
gen-ion concentrations were greater in the suspensions than in the ex¬ 
tracts. The same relationship between suspensions and extracts was 
found in the preceding experiments when small amounts of Ca(OH) 3 
were added to soil. This was thought to be due to the relative insolu¬ 
bility of the acid-producing substance in soil. With HC 1 the added 
acid is soluble, and in the dilution used is completely ionized, yet the 
same differences in P H were found between the suspensions and the 
extracts. This can be accounted for by the additive influence of the 
acid-forming substance in the soil suspension. The titration figures 
show that a portion of the HC 1 is neutralized or adsorbed by the soil, 
and the amount so used corresponds to the adsorptive capacity of the 
soil. The two soils which adsorbed the greatest amount of calcium 
(Experiment 19) also neutralized the greatest amount of HC 1 . Perhaps 
the greater portion, though not all, of the HC 1 was neutralized in dis¬ 
solving calcium from the soil. The amount of calcium obtained in the 
extracts was proportional to the calcium content of the soil. 
The main point shown in this experiment is that while the addition 
of small amounts of a highly ionized acid like HC 1 results in an increase 
• in the hydrogen-ion concentration of the suspensions and the extracts, 
yet the influence of the acid-forming substance in the soil is also shown. 
EXPERIMENT 10 .—SOILS+OXALIC ACID 
This experiment was performed in the same manner as No. 9, except 
that 0.04N oxalic acid was used. The data obtained are presented in 
Table X. 
There was a notable difference in the P H values obtained with the 
use of oxalic acid as compared with HC1. The addition of the three 
smaller portions of oxalic acid produced a decrease in the hydrogen-ion 
concentration, while the two larger portions caused an increase. This 
means that the addition of a small amount of oxalic acid produces an 
actual increase in the hydroxyl-ion concentration. The hydrogen-ion 
concentration produced by 50 cc. of 0.04N oxalic acid is not as great as 
that produced by the same amount of 0.04N HC 1 (Experiment 9). This 
is due simply to the smaller ionization of oxalic acid, and also to the 
formation of insoluble oxalates. 
The titration figures show the expected gradual increase as the 
amount of acid added to the soil increased, and the figures for oxalic 
acid are larger than they are for HC 1 . Owing to the smaller solubility 
of calcium in oxalic acid, the amount of calcium obtained was less when 
oxalic acid was used than with HC 1 . 
60374—23 - 2 
