34 
is, 25 grams of soil to 250 cubic centimeters of solvent — was used. 
Additional solvents were used in order to make the experiment com- 
plete. The results are given in Table XL 
Table XI. — Solubility of phosphoric acid, added at the rate ofl percent, in red-clay soil. 
Fertilizer added. 
Acid phosphate 
Phosphate rock 
Sodium phosphate 
Tripotassium phosphate 
Ferrous phosphate 
Do 
Ferric phosphate 
Do 
Check 
Soluble 
in water. 
Per cent. 
0.00C9 
.0027 
.0848 
.0249 
Trace. 
Trace. 
Trace. 
Trace. 
Trace. 
Soluble 
in fifth- 
normal 
nitric 
acid. 
Per cent. 
0.297 
.251 
.353 
.217 
.496 
.464 
.346 
.319 
Trace. 
Soluble 
in l per 
cent cit- 
ric acid. 
Per cent. 
0.237 
.181 
.304 
.152 
.385 
.380 
.235 
.208 
.0025 
Soluble 
in 1 per 
cent so- 
dium hy- 
droxid. 
Per cent. 
0.222 
.077 
.632 
.442 
.720 
.528 
.494 
.360 
.052 
These results indicate that a large part of the soluble phosphates 
does revert to the iron and aluminum phosphates. 
SOLUBILITY OF PHOSPHATE NATURALLY OCCURRING IN HAWAIIAN 
SOILS. 
Table XII, showing the relatively small quantities of phosphoric acid 
dissolved out of Hawaiian soils by fifth-normal nitric acid, which is a 
solvent of calcium phosphate, and the larger quantities soluble in 1 
per cent sodium hydroxid, which is a solvent of iron and aluminum 
phosphates, indicates that the major part of the phosphates in these 
soils exists normally in combination with iron and aluminum. 
Table XII. — Solubility of phosphoric acid in various types of Hawaiian soils. 
[Expressed as per cent r 2 O f ,.] 
Soil Soil 
No. 1. No. 2. 
Soil 
No. 3. 
Soil 
No. 4. 
Soil 
No. 5. 
Soil 
No. 6. 
Soil 
No. 7. 
Soil 
No. 8. 
Soil 
No. 9. 
Soil 
No. 
10. 
Soil 
No. 
11. 
Hydrochloric acid (specific gravity 
1.115) 
0.677,0.28 
.152 -0036 
0.289 
.0033 
.0018 
.0615 
.710 
2.171 
0.427 
0.286 
.005 
.0003 
.279 
.460 
0.116 
.004 
.0004 
.052 
.240 
0.104 
.003 
.0003 
.055 
.450 
0.024 
0.234 
0.225 
.324 -008 
.004 
Fifth-normal nitric acid 
One per cent sodium hydroxid 
Total phosphoric acid as deter- 
mined by fusion with sodium 
.007 
.153 
1.060 
.0024 
.0363 
.670 
.015 
.222 
3.300 
.0005 
.298 
.440 
.0001 
.008 
.030 
.0013 
.008 
.400 
.0005 
.043 
.340 
Phosphoric acid in humus, per 
22.98 
1.49 
1.09 
3.48 
1.02 
4.93 
4.96 
7.96 
2.98 
3.83 
2.38 
3.93 
1.23 
3.50 
1.36 
3.78 
0.530 
1,690 
1.110 
0.930 
Humus in soil per cent. . 
1.630 
6.960 
In selecting the soils to be tested, several widely varying types were 
chosen. No. 1 is a sandy soil high in magnesia (8.74 per cent) and 
lime (1.84 per cent) and is the same as No. 1 in the pot experiments, 
which did not respond to phosphate fertilizers ; Nos. 2 and 3 are the 
