pressure, frequently produces a condition that is toxic both to the 
germination and the subsequent growth of plants. Usually the toxic 
condition is of short duration and the growth of crops seems to aid 
effectively in overcoming it. There are many phases of this question 
that are not fully understood. 
There are two characteristics of Hawaiian soils that give them 
special interest in this connection, (1) the peculiarities and the high 
proportion of the clay; (2) the inertness of the unplow r ed and unbroken 
sod lands. The former gives special interest to the question of heat- 
ing from the physical point of view, and the latter is of interest to the 
question because of its bearing on soil aeration. With but few excep- 
tions it is necessary to plow T the land, following with thorough tillage 
at frequent intervals for several months before planting. A field 
plowed for the first time, although the soil be thoroughly pulverized 
and reduced to a state of fine tilth, usually will not support plant 
growth satisfactorily. The farmers of Hawaii have found it neces- 
sary to aerate newly plowed lands for a period of several months 
before planting the first crop. It has been observed, however, that 
excellent growth of crops is obtained on the small spots where brush 
was burned and without the continued aeration above referred to. 
Heat, therefore, seems to accomplish in the soil effects similar to those 
brought about by aeration. The application of fertilizers produces 
no such effects. 
In connection with a general study of soil aeration the authors 
have, therefore, been led to a study of the effects of heat on these 
soils. The present paper deals with one phase of this question, the 
physico-chemical changes produced. In the first part are presented 
the data obtained with reference to the solubility of the inorganic 
constituents and in the second part are some data of a more or less 
empirical nature on the grosser effects of heat on soil nitrogen. 
THE EFFECTS OF HEAT ON THE SOLUBILITY OF INORGANIC 
CONSTITUENTS. 
While a considerable number of investigators have studied the 
question of the effect of heat upon the solubility of phosphoric acid, 
using various solvents, apparently few have gone beyond this and 
determined its effect upon the solubility of the remaining mineral 
constituents commonly occurring in soils. In fact, with few excep- 
tions, the entire stress has been laid upon the three elements generally 
considered to be of greatest plant-food value, namely, nitrogen, phos- 
phoric acid, and potash. 
In most instances the results of these earlier investigations have 
shown an increase in solubility of phosphoric acid, with increase in the 
temperature to which the soils have been heated. M. Xagaoka, 1 on 
> Bui. Col. Agr., Tokyo Imp. Univ., 6 (1904), No. 3, p. 263. 
