25 
50 per cent. This table discloses the high concentration of soluble 
plant food in these soils under the reducing conditions. While the 
mineral constituents tend to increase in solubility with increase in 
heat with relation to the air-dry samples, a maximum solubility is 
obtained from the wet samples in the case of the iron, manganese, 
lime, magnesia, phosphoric acid, and bicarbonates, and in one of 
the samples a maximum solubility is obtained for the remaining 
constituents, silica, alumina, and potash. Therefore, these results 
indicate that the effect of drying and heating the soils used in aquatic 
agriculture does not increase the solubility of the mineral constitu- 
ents over and above the solubility in the wet state but rather brings 
about a decrease in all constituents except sulphates. 
The concentration of the extracts from these soils in the wet state 
does not necessarily indicate that the mineral constituents, with the 
exception of iron, are actually more soluble than those of dry-land 
soils. Neither should we conclude that the abnormal concentra- 
tion is wholly due to more complete diffusion coupled with greater 
solubility induced by the environment to which these soils are sub- 
jected. The amount of water always present in these soils is far in 
excess of that occurring in dry-land soils, and since there necessarily 
must be a tendency toward constancy in concentration regardless 
of the amount of solvent present, in time the absolute amounts of 
solids going into solution would be considerably greater in submerged 
•soils. The moisture content of these two soils when received at the 
laboratory was about 50 per cent, whereas the dry-land soils contain 
very much less moisture. The water extracts obtained by the 
methods employed, therefore, would necessarily contain greater 
absolute amounts of substances already in solution in the soil water. 
Hence the concentration of the nutrient solution occurring in sub- 
merged soils need not necessarily be greater than that of dry-land 
soils. 
DISCUSSION. 
The foregoing results show that an increase in solubility of the 
mineral constituents of various types of Hawaiian soils is effected 
by heating. The samples represent most of the normal and abnormal 
types of the islands. That there are both chemical and physical 
factors concerned in the phenomena at hand must be admitted at 
the outset. It is believed, however, that the most important set 
of factors affecting the solubility of inorganic soil constituents are 
of a physical nature. 
Undoubtedly the means by which the physical factors act is through 
the soil moisture in its relation to the physical properties of the soil. 
The conditions conducive to the formation of a colloidal state and the 
subsequent relation of heat to the destruction of this colloid are two 
of the most important of these factors. 
