27 
on the surface of the water evaporated. Upon adding water to the 
soil after having been dried, it is probable the materials deposited 
from previous evaporation would be more soluble than the other 
mineral constituents. In addition a certain amount of oxidation 
and other chemical changes in the organic matter might reasonably 
be expected to take place, which would have some effect on the 
solubility oi the mineral bases that tend to combine with the organic 
matter. 
The solution obtained upon shaking with water a soil previously 
dried should, in the light of these views, be of a greater concentration 
than that prepared from the air-dried soil. With the absence of soil 
films and a more or less altered condition of the colloids present the 
solvent would have more ready access to the soil particles during a 
short period in addition to coming into immediate contact with 
solids deposited on the surface of the particles. 
Why several of the mineral constituents of the soil should be so 
markedly more soluble when heated to 250° C. than at the other 
temperatures is a question not easily answered. The difference in 
physical effects were quite noticeable in that there was a greater 
aggregation of particles. Again, there was a more complete destruc- 
tion of organic matter effected at this temperature, and also it is not 
entirely impossible that drying at 100° C. for eight hours does not 
effect a complete elimination of the soil moisture and especially the 
water of chemical combination. It seems reasonable, then, that the 
effects of heating to 100° C. are simply magnified when heated to 
250° C. Added to this there is a more complete destruction of organic 
matter, the effect, both physical and chemical, being of the same 
general nature but more complete at the higher temperature. The 
destruction of organic constituents being more complete would neces- 
sarily increase the solubility of the mineral matter held in combination, 
as it is generally conceded that the organic constituents of the soil 
in its natural state are quite insoluble in water and acids, more 
especially in the former. There is also evidence of the existence of 
fatty or resinous organic matter which would materially affect the 
properties of the soil film. For the decomposition of such bodies it 
would be necessary to heat the soils considerably above 100° C. 
In addition to the above-mentioned effects of heat the relation 
between solid and solvent would naturally be affected by other factors. 
Among these is the absorption or "fixing power" of the soil. 1 It is 
reasonable to expect soils with widely varying physical and chemical 
properties, such as those used in this series, to differ greatly in 
absorptive power. Hence it is not at all unlikely that the lack of 
consistency in some of the results in the foregoing tables is due 
primarily to this factor. Not only is there lack of uniformity in 
i Richter (Landw. Vers. Stat., 47 (1896), p. 269) found that heating increased the absorptive power oi 
the soil for water. 
