July 2i, 1923 
Oxygen-Supplying Power of the Soil 
139 
the cylinder had the power to absorb oxygen from the air at the rate of 
about 0.015 cc. in 40 minutes, or about 0.0225 cc. per hour. 
? The cylinder was next placed horizontally in the soil box on top of a layer 
of loosely sifted soil 8 cm. deep, after which more soil was loosely sifted 
into the box until the layer above the cylinder was 7.5 cm. deep. In placing 
the cylinder in the soil the lead tubes were bent so that they extended 
into the soil to the required depth and then, before reaching the absorb¬ 
ing cylinder, extended twice around it in the form of a horizontal ellipse 
lying about half way between the cylinder and the box wall. This pre¬ 
caution was taken so as to avoid possible direct movement of air from 
the atmosphere to the cylinder along the tube surfaces. 
Within three hours of the time the cylinder was placed in the soil its rate 
of delivery of oxygen to the indicator solution showed a noticeable 
decrease, and during the next two days this decrease continued. At the 
end of that period the time required for the color change was 80 min¬ 
utes; that is, the cylinder was absorbing at the rate of about 0.0112 cc. 
of oxygen per hour. 
The cylinder was itself able to take up oxygen at the rate of about 0.02 
cc. of oxygen per hour—as shown by the air test—and 8 cm. of very 
loosely packed moist soil could supply oxygen to the cylinder only about 
half as rapidly as the cylinder could have taken it up if the soil could 
have supplied it. 
The cylinder was allowed to remain for 40 days in the soil, without 
disturbance, to allow some settling. The box was covered and no water 
was added during this period. Twenty-four determinations were then 
made during the next 71 hours, with color-change periods of from 68 
to 83 minutes, the average being 75.8 minutes. This indicates an oxygen- 
supplying power of about 0.0119 cc. per hour. Eight cm. of loosely 
sifted soil was then added to the box, thus bringing the cylinder to a 
depth of about 16 cm. below the soil surface. A lengthening of the 
color-change period was evident after 3 hours, and the period lengthened 
gradually during the next 3 days, as shown by numerous readings taken 
at intervals. During the succeeding 2 days several series of readings 
were taken—16 in all—with color change periods of from 84 to 116 
minutes, the average being 94 minutes. This indicates an oxygen- 
supplying power, at this depth, of about 0.0096 cc. per hour. 
Water was next added to the soil, corresponding to 6 cm. of rainfall, 
which very nearly saturated the soil. This wetting produced shrinkage 
in the soil so that the soil surface came to be only 13.5 cm. above the 
cylinder. A marked increase in the length of the color-change period 
was shown after 8 hours. Five determinations during the next 18 hours 
gave periods of from 150 to 179 minutes with an average of 164 minutes, 
indicating an oxygen-supplying power of about 0.0055 cc. P er hour. 
The soil was next packed firmly, lowering the surface about 2.5 cm. 
but without disturbing the tubes or cylinder. A determination made 
directly after packing gave a color-change period of 240 minutes, and 
another determination immediately thereafter gave a period of 5,050 
minutes. The last-named period indicates an oxygen-supplying power 
of only about 0.0002 cc. per hour. 
For the particular cylinder used, it appears that, while the oxygen- 
supplying power at a depth of 8 cm. in loose moist soil was about 0.0119 
cc. per hour, the corresponding power at a depth of 13.5 cm. of firmly 
packed, nearly saturated soil, was only about 1.5 per cent as great. 
Changing the exposure of the absorbing cylinder from a depth of 8 cm. 
