oct. so. 1933 Soil Reaction in Relation to Calcium Adsorption 
95 
Table V.— Ph on suspensions and extracts of soil + Ca(OH) 29 also titrations and 
calcium content of extract and calcium adsorbed by soil 
Calcium added. 
Suspension. 
Extract. 
Titer 0.05N 
HC 1 . 
Calcium in 
extract. 
Calcium not 
adsorbed. 
Calcium 
adsorbed. 
Mgm. 
^H' 
P . 
Cc. 
Mgm. 
Mgm. 
Mgm. 
2-5 . 
6. 14 
8.06 
— O. I 
2.4 
O. O 
2*5 
50. 
7. 08 
8. 20 
—. I 
2-3 
. O 
5 *o 
8. 0. 
7 - 45 
8. 54 
. O 
2. O 
-•3 
8.0 
12. 0. 
7. 90 
8- 57 
•4 
2-3 
. 0 
12. 0 
16. 0. 
8. 13 
8. 88 
-4 
2.7 
-4 
15.6 
20. 0. 
8. 7I 
8. 91 
•5 
3-7 
1.4 
18.6 
28. 0. 
9 - 55 
9 - 38 
.6 
4.0 
i -7 
26. 3 
36. 0. 
IO. 46 
IO. 23 
.8 
4-7 
2.4 
33-6 
48. 0. 
II. 07 
II. OO 
1. 6 
8. 0 
5-7 
42.3 
60. 0. 
ii- 54 
II. 41 
3-5 
13. 0 
10. 7 
49-3 
80. 0. 
11.85 
II. 71 
12. 6 
23-3 
21. 0 
59 -° 
The figures for the smaller amounts of calcium added are the averages of 
several determinations. The P H values show that the hydrogen-ion con¬ 
centrations were higher in the suspensions than in the extracts until more 
than 16 mgm. of calcium had been added. Beyond 16 mgm. of calcium 
the P H values for suspensions and extracts were nearly equal. In these 
the OH-ion concentration was so large as to mask the influence of any 
substance dissolved from the soil. The P H values became equal in the 
suspension and the extracts when the adsorption of calcium ceased to be 
practically complete. This is shown in what follows. 
All of the extracts to which less than 16 mgm. of calcium were added 
contained nearly the same amounts of calcium. This calcium may be 
accounted for partly by the small amount of water-soluble calcium in the 
soil, and partly from the re-solution of adsorbed calcium. The water- 
soluble calcium from the soil was 1.3 mgm. In the presence of Ca(OH) 2 
this amount would be less. When Ca(OH) 2 comes in contact with soil in 
such a water suspension as was used in this experiment it probably forms 
an adsorption compound. This compound would be to some extent 
soluble in water ( 26 ) and would account for a larger part of the calcium 
in those extracts in which the adsorption was practically complete. Part 
of the calcium may have been present in a colloidal suspension, however, 
as shown by titration results; very little, if any, Could have been present 
as a carbonate. 
The average amount of calcium found in the extracts, when 16 or less 
mgm. were added as Ca(OH) 2 , was 2.3 mgm. The mgm. of the adsorbed 
calcium were obtained by subtracting 2.3 from the subsequent figures in 
the column. According to this calculation, adsorption can be considered 
complete until 16 or more mgm. of calcium were added and comparatively 
little remained unadsorbed until more than 36 mgm. were added. This 
shows the large adsorptive capacity of this soil for calcium when added in 
the form of Ca(OH) 2 . Since 4 mgm. represent the equivalent of 1 ton 
of CaC 0 3 per acre 7 inches deep, this soil requires the equivalent of be¬ 
tween 4 and 5 tons of CaCO per acre to produce a P H value in the suspen¬ 
sion corresponding to the color change of phenolphthalein. (See fig. 6.) 
