no 
Journal of Agricultural Research 
Vol. » 6 , No. 3 
EXPERIMENT 21.—THE H-ION CONCENTRATION OP SUSPENSIONS OP SOIL IN WATER 
AND IN A SOLUTION OP POTASSIUM CHLORID AND THE CALCIUM CONTENT OP HYDRO¬ 
CHLORIC ACID SOLUTIONS 
In several preceding experiments it has been shown that the presence 
of KC 1 materially changes the P H value of both soil suspensions and soil 
extracts. One of the difficulties encountered in making electrometric 
measurements on a soil suspension or extract is the possible diffusion of 
KC1 from the contact tube. This is enhanced by the necessity of constant 
agitation of the electrode vessel and the long time required for making 
some of the measurements. It was desired to learn how serious a factor 
this is with different soils of varying calcium content. 
Twenty-four soils with accompanying subsoils, taken in the soil survey 
from various parts of Kansas, were selected for this experiment. These 
soils had been analyzed for total calcium as well as other nutrients, and 
the resulting data as well as physical texture, as far as that is revealed by 
soil type, formed the basis of selection. The calcium soluble in cold 
0.5N HC 1 was determined by digesting the soil at room temperature for 
24 hours. The P H values were determined both on the water suspensions 
and on the suspensions in the 0.5N KC 1 solution. Before taking the final 
voltmeter reading the rubber tube connecting the KC 1 solution reservoir 
and the capillary tube was opened slightly by pressing the pinchcock, so 
as to make fresh contact. This would introduce a small amount of KC 1 
into the soil suspensions. Preliminary experiments had shown that the 
concentration of the KC 1 solution used as a solvent could be varied con¬ 
siderably without affecting the P H values. The small quantity intro¬ 
duced by the manipulation just described would then have no effect on the 
suspension in which 0.5N KC 1 was used, but it might materially affect 
the water suspensions. It had been noticed several times in the preceding 
experiments that some of the soil colloidal matter would diffuse into the 
capillary KC 1 connecting tube. Just how much this influenced the read¬ 
ing was not known. When a KC 1 solution forms a part of the electrical 
connection with the calomel cell it is impossible to prevent some KC 1 en¬ 
tering the electrode vessel. If the system is so arranged that KC 1 forms 
part of the mixture in the electrode vessel the small quantity of KC 1 
entering from this source may safely be ignored. The P H values and the 
data on acid soluble calcium are given in Table XXI. 
Table XXI.— Hydrogen-ion concentration and calcium content of soil and subsoil 
Surface. 
Subsoil. 
County. 
Soil type. 
Cal¬ 
cium 
in HC 1 
solu¬ 
tion. 
HsO 
sus¬ 
pen¬ 
sion. 
KC 1 
sus¬ 
pen¬ 
sion. 
Cal¬ 
cium 
in HC 1 
solu¬ 
tion. 
H2O 
sus¬ 
pen¬ 
sion. 
KC 1 
sus¬ 
pen¬ 
sion. 
Allen . 
Oswego fine sandy 
Mgm. 
15 - I 
Pn- 
4. 82 
Ph- 
4. 82 
Mgm. 
21. I 
Ph- 
5. 22 
Ph- 
5. 22 
.do. 
loam. 
Oswego clay. 
Neosho silt loam.... 
34-8 
I 7 - 3 
5. 02 
5 * °9 
4. 82 
5.06 
50.4 
36-4 
5 * 77 
5- 66 
5 - 53 
5 * 33 
.do. 
Montgomery... 
Osage loam. 
Crawford loam. 
26. I 
18. 4 
5-09 
5 -i 2 
K. 06 
4. 82 
28. 2 
25.O 
5-43 
5.80 
5 * 56 
5. 60 
Allen. 
Summit silt loam . . . 
35 - 1 
5.16 
5.06 
189. 6 
7. 46 
7 - 93 
Brown . 
Marshall silt loam . . . 
31* 3 
5. 26 
5. 40 
37-3 
5 * 33 
5 * °9 
Allen. 
Summit silt loam . . . 
18. 0 
5 - 33 
5*46 
16. 7 
4. 65 
4: 72 
Riley . 
Oswego silt loam .... 
33 -o 
5 * 39 
5 * 33 
74.0 
7.16 
7. 72 
