648 
Journal of Agricultural Research vd. xxvii. No. 9 
Table XV.— Reacting values of the constituents of certain underground waters, the com¬ 
position of which is given in Table XII in parts per million 
Sample Na 
j r Ca. 
| 
r Mg. 
r HCOs. 
r Cl. 
r SO4. 
r NOa. 
r Acids. 
1. .. . 
1 
6. 69 
10. 13 
5 - 39 
3 - 99 
27. 70 
2 o -35 
i 3 - 47 
1. 97 
2. 30 
I - 3 1 
14 - 13 
12. 00 
44. 60 
15. 70 
4. 08 
2. 67 
3 - 8 7 
0 4 - 57 
8. 26 
9. 00 
7. 08 
18. 10 
14 - 13 
3 - 24 
8. 79 
. 3 - 95 
4 - 5 1 
2. 26 
4 - 39 
5 - 3 ° 
2. 64 
39 - 95 
122. 50 
s6. 20 
7 1 * I 5 
26. 57 
22. 41 
9 - 75 
53-31 
134 . 7 1 
69. 71 
80. 49 
2. 
0.31 
3. 
4 . ... 
K . 
6. 
7. ! 
7 ! 
a Includes 1.6 r CO5. 
Table XVI.— Composition of certain underground waters stated as percentages of the 
sum of the reacting values of the acids from Table XV 
Sample No. 
Total 
soilds. 
Percentage of reacting value. 
r Ca. 
1 
r Mg. 
rCa+ 
r Mg. 
r HCOs. 
r Cl. 
rSO-t. 
r NO3. 
1. 
0. 161 
25. 2 
7-4 
32. 6 
15-3 
68. 2 
16. 5 
2. 
• 145 
45- 2 
10. 3 
55- 5 
11 . 9 
63. 1 
23. 6 
1. 4 
3. 
•053 
55-3 
13-3 
68.6 
39- 7 
33-2 
27. 1 
4 . 
•357 
7- 5 
26. 5 
34- 0 
08.6 
16. 5 
74- 9 
5. 
• 9*4 
20. 6 
8.9 
29 - 5 
6. 1 
2. 9 
91. 0 
6 . 
• 540 
29. 2 
64. 0 
93-2 
12. 9 
6.5 
80.6 
7. 
.586 
16. 7 
J 9- 5 
36. 2 
8.8 
2. 8 
88.4 
a Includes 3.0 per cent r CO3. 
THE SOLUBILITY OF SOIL CONSTITUENTS 
In dealing with irrigated soils which often contain appreciable quanti¬ 
ties of material that is readily soluble in water it is possible to recognize 
four classes of substances, as follows: 
(1) Soluble material, which may be defined as material that is soluble to an extent 
greater than can be satisfied by the quantity of water in the soil, e. g., the salts of the 
strong acids with the four principal basic elements and also the carbonates and bicar¬ 
bonates of the alkali bases. A possible exception in this series is calcium sulphate. 
(2) Slightly soluble material, which may be defined as material that is so little soluble 
that the soil solution is ordinarily saturated with respect to it, e. g., the carbonates of 
the earthy bases, calcium, and magnesium, and sometimes calcium sulphate. 
(3) Replaceable material, which includes the bases, both earthy and alkaline, that 
are combined with the soil material in such a way that they may pass into solution only 
if the solution contains an excess of some other base with which the combined bases 
may exchange, e. g., a soil may be rich in combined calcium and may yield only a 
trace of this element to treatment to pure water, but when treated with a solution of 
sodium chlorid it may yield an abundance of calcium. 
(4) Insoluble material, which includes the great bulk of the soil. This consists 
largely of silica either as pure quartz or more commonly as double silicates or com¬ 
pounds of alumina and silica together with one or another of the common earthy or 
alkaline bases. Some of the double or complex silicates also contain iron and may 
contain more than one of the bases. 
This classification of the soil material, while admittedly an arbitrary 
one, is useful in that it makes it possible to arrive at a better understanding 
of the changes that occur in the soil solution as a result of irrigation and 
leaching and of the reactions that take place between the solution and the 
