33 
Table IX. — Phosphoric acid soluble in water. 
[Expressed in parts per million.] 
Percolates of 100 cc. each. 
Phosphate added. 
First 
100. 
Second 
and 
third 
100. 
Fourth 
100. 
Fifth 
100. 
Sixth 
100. 
Seventh 
100. 
Total. 
26 
28 
36 
36 
Trace. 
Trace. 
4 
4 
Trace. 
Trace. 
Trace. 
Trace. 
Trace. 
Trace. 
Trace. 
Trace. 
62 
54 
3 
16 
20 
70 
66 
4 
4 
4 
4 
Trace. 
4 
4 
4 
38 
66 
4 
4 
26 
26 
60 
60 
6 
4 
4 
4 
38 
27 
58 
58 
6 
10 
4 
4 
11 
29 
46 
48 
6 
21 
16 
16 
21 
9 
6 
4 
4 
138 
Do 
146 
286 
Do 
289 
Slag 
31 
Do 
24 
Phosphate rock 
4 
4 
24 
Do 
24 
Commercial sodium phosphate 
Do 
25 
25 
28 
•40 
60 
14 
16 
70 
95 
4 
14 
16 
10 
4 
48 
15 
8 
76 
70 
4 
22 
28 
22 
30 
29 
12 
16 
82 
76 
17 
7 
11 
18 
24 
9 
17 
21 
33 
82 
Disodium phosphate 
80 
D o . . . t ! 
75 
Monosodium phosphate 
130 
Do I " 
227 
Tripotassium phosphate 
54 
'Do .1 ...' 
61 
Monn^alHum phnsphato 
311 
Do ~....r 
100 
4 
428 
Check 
After 700 cubic centimeters had passed through, the soil was 
removed from the percolators and extracted with 1 per cent citric 
acid according to the Dyer method. The solubility in this solvent 
is given in Table X. 
|Table X. — Phosphoric acid soluble in 1 per cent citric acid. 
[Expressed in per cent of air-dry soil.] 
Phosphate added. 
Per cent. 
Phosphate added. 
Per cent. 
Acid phosphate 
0.210 
.204 
.182 
.192 
.138 
.151 
.204 
.202 
.212 
Commercial sodium phosphate 
0.180 
Do 
Disodium phosphate* r 
.154 
.242 
Do 
Do 
.198 
Slag 
Tripotassium phosphate 
.124 
Do 
'Do ". * 
.122 
Phosphate rock 
Monocalcium phosphate 
.222 
Do ... . 
Do 
.222 
Check 
.019 
The results clearly show the rapid fixation which takes place when 
soluble phosphates are added to the soil as well as the solubility of 
the phosphates after fixation. 
In view of these results, a further set of experiments was planned 
in order to study the comparative action of iron and aluminum phos- 
phates. If soluble phosphates revert to iron and aluminum phos- 
phates, it is desirable to study the solubility of the latter. This series 
was carried out in the same manner as the previous one except that 
separate samples were extracted and a larger quantity of soil — that 
