oct. 20,1923 Soil Reaction in Relation to Calcium Adsorption 
93 
salts such as NaCl and BaCl 2 as well as KC 1 increased the hydrogen-ion 
concentration of certain soil suspensions. What happens may be pic¬ 
tured as follows: 
KC 1 K+ + C 1 - 
HOH ^ OH-+H+ 
The increase in hydrogen-ion concentration is due to the greater ad¬ 
sorptive capacity of soil for the K + and OH - * ions. According to 
Parker (36) molecular adsorption of KOH may also take place. 
It will be shown in a subsequent experiment that the amount of cal¬ 
cium made soluble in a 0.5N KC 1 solution is very nearly the same as in 
0.5N HC 1 solution. The above equations show that it is simply a reac¬ 
tion of calcium with chlorinions whether the solution is made with 
HC 1 or KC 1 . 
EXPERIMENT 3 .—SOIL -f CALCIUM CARBONATE 4 
Precipitated CaC 0 3 was added in definite amounts to io gm. of soil. 
Two groups of mixtures were prepared. One group was placed in 
125-cc. wide-mouthed glass-stoppered bottles, sealed, and let stand for 
6 weeks, with occasional shaking. On this group the P H values were 
determined on the suspensions only. The other group was given the 
usual 24 hours contact and the P H values were determined on both the 
suspensions and the extracts. The results are presented in Table III. 
Table III.— Ph on water suspensions and extracts of soils to which CaC 0 3 had been added 
Calcium added. 
Oswego silt loam. 
Bates very fine sandy loam. 
6 weeks. 
24 hours. 
6 weeks. 
24 hours. 
Suspension. 
Suspension. 
Extract. 
Suspension. 
Suspension. 
Extract. 
Mom. 
Ph 
Ph 
Ph 
Ph 
Ph 
Ph 
2 -5 . 
7. 46 
6. 00 
6.31 
7 - 79 
5- 66 
6. 24 
5 -o. 
7 - 93 
7 - 05 
6. 64 
8. 10 
6. 30 
7 - 59 
10. 0. 
8. 10 
7 - 83 
8. 34 
8. 10 
7 - 79 
8. 23 
20. O. 
8.13 
7 - 93 
8. 42 
8. 40 
8. 30 
8. 10 
40. O. 
8.37 
8.13 
8.93 
8. 40 
8.37 
8. 91 
Calcium added in the form of CaC 0 3 will change the hydrogen-ion 
concentration of a soil suspension, and the amount of change up to a 
certain point is proportional to the quantity of CaC 0 3 added. In a 
supplementary experiment it was found that the P H for suspensions 
prepared from soils to which increasing quantities of CaC 0 3 were added 
would approach a maximum of about 8.50, and remain at this figure 
regardless of the quantity of CaC 0 3 added, up to 20 tons equivalent per 
acre. When the same amount of CaC 0 3 is added to soil, a long-time 
contact produces a greater hydroxyl-ion concentration than a short 
time. The acid-producing substance in soil liberates its hydrogen ions 
very slowly. It has been shown by Hagar (75) and Mclntire (j2, 
p. 41-45,) that CaC 0 3 undergoes profound changes in soil. 
4 As water was used in all of the experiments in such amounts as to make the proportion of soil and liquid 
1:10, the presence of this substance is to be understood. 
