30 
experiments were ground to as nearly the same degree of fineness 
as possible. This applies more especially to the insoluble phosphates. 
(7) Basic slag is more effective as a source of phosphoric acid than 
phosphate rock, bone meal, or reverted phosphate. 
(8) In field conditions there is not such an abundant supply of 
water as was used in the pots, hence the soluble phosphates should be 
relatively more effective under field trials. 
(9) Lime applied with phosphates temporarily assists the plants in 
assimilating phosphoric acid, but it soon loses its effectiveness unless 
present in excessive amounts. 
SOLUBILITY OF DIFFERENT PHOSPHATES IN HAWAIIAN SOILS. 
The chemical analyses of Hawaiian soils by solution in hydro- 
chloric acid of specific gravity 1.115 or by fusion with sodium carbon- 
ate, with scarcely a single exception, show a far greater amount of 
phosphoric acid in the soil than would be required for plant growth. 
Hawaiian soils are largely a product of the disintegration of basaltic 
lava and contain abnormally high percentages of iron and aluminum. 
Likewise, they contain high percentages of phosphoric acid, but in 
spite of this fact, plants suffer from the lack of phosphoric acid, 
especially in the red-clay type of soil. 
In the work herewith presented, fifth-normal nitric acid, 1 per cent 
citric acid, 1 per cent sodium hydroxid, hydrochloric acid (specific 
gravity 1.115), water, and finally fusion with sodium carbonate were 
used in determining the solubility and combinations of the phosphates. 
While the voluminous literature regarding the action of these reagents 
as means of determining the availability of phosphoric acid is very 
contradictory, in general it may be said that fifth-normal nitric acid 
acts primarily as a solvent for calcium phosphate, while 1 per cent 
sodium hydroxid dissolves the iron and aluminum phosphates. 
In the experiments here reported, the soils were treated with the 
solvents as follows : Digested with hydrochloric acid (specific gravity 
1.115) according to the official method; digested with 1 per cent citric 
acid for 3 days with occasional shaking, the proportion of soil to 
acid being 1 to 10; digested with fifth-normal nitric acid for 5 
hours at 40° C. in the same proportion; digested with 1 per cent 
sodium hydroxid for 5 hours in boiling water in the same propor- 
tion, and finally digested with water for 1 week with frequent 
shaking. 
SOLUBILITY OF PHOSPHORIC ACID IN POTTED SOIL. 
Following the removal of the first crop of millet on the red-clay soil 
(Experiment I), samples of soil were taken from all of the pots for 
analysis. Distilled water, 1 per cent citric acid, and fifth-normal 
