July 21, 1923 
Oxygen-Supplying Power of the Soil 
137 
In operation, the outlet tube from the absorbing cylinder is joined by 
lead tubing to the inlet tube of the indicator bottle, and the outlet of 
the latter is connected to the intake of an ordinary bottle aspirator. 
The outlet of the aspirator is joined to the inlet of a series of large scrub¬ 
ber bottles partly filled with alkaline pyrogallol, and the outlet of this 
series is connected by lead tubing to the inlet tube of the absorbing 
cylinder. The gas system is thus completely closed. All tubing except¬ 
ing the connections to the absorbing cylinder is of glass, with rubber 
connections. 
The aspirator consists of two 8-liter bottles, each closed by a sealed-in 
rubber stopper bearing two tubes, one of which reaches to the bottom of 
the bottle, while the other reaches only through the stopper. The two 
long tubes are joined together by a 2-meter length of rubber tubing. 
Each of the short aspirator tubes is connected by a Y and a 2-way cock 
to the closed circulatory system, so that either one of the short aspirator 
tubes may be operated as inlet to the aspirator while the other is oper¬ 
ated as outlet. One bottle stands about 1.5 meter above the other, ths 
upper one having been initially filled with water and the siphon started 
through the long tube. Water flows out of the upper bottle and enters 
at the bottom of the lower one. Gas is gradually removed from the 
lower and transferred through the circulatory system to the upper, the 
two-way cocks being properly set so that the gas circulates in the direc¬ 
tion indicated above. When the upper one is nearly empty the positions 
of the two bottles are reversed and the two-way cocks are both reversed, 
so that circulation continues in the right direction. The rate of gas 
movement through the system is maintained practically uniform by 
adjusting the relative heights of the two aspirator bottles. A nearly 
closed cock was introduced into the circulatory system, adjusted to give 
the required rate of gas movement. The rate of movement was deter¬ 
mined from time to time by counting the number of bubbles entering 
the indicator bottle per minute. 
A safety bottle arranged like the indicator bottle was inserted in the 
system so that the circulating gas traversed it just before entering the 
absorbing cylinder, and another was inserted in the gas stream imme¬ 
diately beyond the indicator bottle. The alkaline pyrogallol solution in 
these safety bottles did not become colored, thus indicating that the gas 
entering the cylinder was without oxygen, and that no oxygen from the 
cylinder escaped being collected in the indicator bottle. 
The apparatus was furnished with a somewhat complicated system of 
tubes, cocks, extra containers, etc., and with a Chapman filter pump to 
furnish suction when needed in this auxiliary system. By means of this 
system the two stock solutions—of aqueous pyrogallol and aqueous 
potassium hydroxid—were prepared and brought together with proper 
dilution, the indicator bottle and the safety bottles could at any time be 
emptied, rinsed and refilled with fresh indicator solution, and other 
necessary operations could be performed, all without the entrance of 
oxygen into the system at any place excepting via the absorbing cylinder. 
The apparatus just described in its essentials was used as follows: The 
absorbing cylinder is placed in the exposure for which the oxygen- 
supplying power is to be determined, and the gas stream is started and 
allowed to continue for several hours, to establish dynamic equilibrium. 
A fresh charge of indicator solution is placed in the indicator bottle (the 
bottle is thoroughly rinsed several times with new indicator solution, 
after the old solution has been withdrawn, the old solution and the rinsing 
