486 A. B. BEAUMONT 
marized by Cameron and Gallagher (1908), Lyon and Bizzell (1910), 
Kelley and McGeorge (1913), and Klein (1915). 
Cameron and Gallagher show a variation in the volume of soils with 
repeated wetting and drying, depending on the previous condition of the 
soil. Finally a condition of natural packing is reached, at which the 
expansion on wetting is equal to the contraction on drying. 
Lyon and Bizzell found, along with other investigators, that the effect 
of steam sterilization was to increase the soluble matter of both organic 
and inorganic constituents. This increase was particularly marked in the 
case of organic matter. 
Kelley and McGeorge studied the water and acid extracts of different 
soils that had been air-dried and others that had been dried at higher 
temperatures. They found that on an average the solubility of the 
constituents increased with the temperature of drying. Iron was an 
exception. The high solubility of the soils used in aquatic agriculture is, 
according to these investigators, decreased by drying. They say the 
subject is very complex, and among the many factors involved are floccu- 
lation of colloids, oxidation, deoxidation, decomposition, dehydration, and 
the attending physical alterations of the soil film. 
Klein’s work is divided into two parts. In experiment 1, the effect of 
partial drying of soils on total water-soluble salts, nitrates, potassium, 
calcium, and acid-soluble phosphorus, and on the growth of plants, is 
studied. In experiment 2, the effect of complete air-drying on the pro- 
duction of carbon dioxide and nitrates is studied. In this experiment the 
soils were repeatedly wetted and dried, three dryings being the maximum. 
Klein arrived at the following conclusions, among others: 
In experiment 1: (1) Drying the soil previous to planting has a bene- 
ficial effect on plant growth. (2) The water-soluble matter is increased 
by drying in a soil low in organic matter, but is decreased in a soil high 
in organic matter. (3) Drying the soil has but little effect on the avail- 
able potassium, calcium, and phosphorus of the soil. 
In experiment 2: (1) Bacterial activity, as measured by carbon-dioxide 
production, is increased by a previous drying of the soil. (2) Previous 
drying increases the soil nitrification, reaching a maximum with three 
dryings. The author thinks that the physical effects of drying are 
important in this connection, and that the flocculation of the colloidal 
material is very important. 
