18 
The results in the above tables can be compared with those of the 
previous series only relatively, due to the fact that the solution in 
this case was so much more concentrated. They indicate the prac- 
tical impossibility of saturating Hawaiian soils with phosphoric acid 
or adding an excess in a practical way. It will be noted that this 
type of soil is able to absorb nearly 4 per cent of its weight of phos- 
phoric acid (P0 4 ) in the fresh soil and nearly 3 per cent in the air-dry 
soil from the potassium salt;, also, that from the calcium salt the 
soil absorbed nearly 6 per cent of its own weight of phosphoric acid 
in the fresh soil and 5.5 per cent in the air-dry soil. It is difficult 
to explain the higher absorptive power of the fresh soil over the air 
dry, but it is probably due to the physical properties, and is related 
to the soil films. 
This soil is composed of very fine particles, exposing relatively 
enormous surface to the action of the soil solution or any added salt 
solution. In the fresh soils of this type these particles are in a high 
state of deflocculation and the effect of drying in the air tends to 
flocculate them to a great extent, thereby reducing the area of the 
exposed surface. Drying would also tend to modify the film sur- 
rounding each particle. Even with only 50 grams of soil it was 
found impossible, due to the strong deflocculating action of the 
phosphate salts, to make the percolations in tubes, but funnels had 
to be used. The samples previously dried in the air percolated 
more slowly than the fresh soils. This is probably due to the fact 
that the soil swelled more in the tube after the addition of the solu- 
tion, thus packing more closely and closing up the pore spaces. 
There was apparently very little difference between the absorbing 
power of the soil and subsoil, but considerable variation between 
the fresh and air-dry soils. The rate of fixation in the early part of 
the experiment was considerably faster in the latter than in the 
former, and hence the air-dry soils were more quickly saturated by 
the salts. Another interesting fact is the difference in the absorp- 
tive power of this type of soil for phosphoric acid in the two forms. 
The data are sufficient to justify the statement that this difference 
is due to the reversion of the calcium salt, although due also in great 
part to the state of the iron and aluminum compounds which exist 
in this type of soil. The absorption from the potash salt was more 
complete at the first application, but thereafter decreased quite 
rapidly and regularly. It should also be noted that at the outset 
the air-dry soil absorbed the potash salt more completely than the 
fresh soil. This is thought to be due to the partial elimination of 
the film surrounding the soil particles, thus allowing the solution to 
penetrate more thoroughly. 
