157 
An APPARATUS FOR AERATING CULTURE SOLUTIONS. 
PAUL WEATHERW AX. 
A number of experiments on various phases of plant physiology, in each 
of which it was necessary to secure a constant stream of «ir continuing for 
several days, has led to the construction of a very efficient piece of ap- 
paratus for that purpose. The apparatus used by Prof. D. M. Mottier sev- 
eral years ago for aerating artificial cultures of algse was modified by F. L. 
Pickett and used in a series of experiments on desiccation; ald the writer 
has made some further changes in the construction of the apparatus shown 
in the figure and described below. This is now being used very success- 
fully in the aeration of culture solutions. 
The princple employed is that of the Sprengel mercury pump (water 
being used as a liquid in this case) by which bubbles of air are entangled 
in a stream of liquid which flows into a closed vessel. The only thing that 
remains to be done is to separate the air and the liquid, which are under 
slight pressure, and convey them from the reservoir by separate tubes. 
The first problem is that of getting a stream of water that will flow 
uniformly. An attachment to a water pipe is usually sutticient for this. 
If this is not satisfactory, however, a siphon may be arranged to give a 
uniform flow. D, in the figure, is an ordinary battery jar provided with 
a siphon, B, which has an adjustable stopcock. A, which taps a water 
pipe and has an adjustable stopcock, supplies the jar with water a little 
faster than it is taken out by the siphon, B. Another siphon, C, removes 
the excess and keeps the water always at the same level, determined by 
its outer end, thus assuring an even flow, which should be just fast enough 
to cause the water to fall as a succession of drops. 
The funnel, E, made by fitting a stopper into the end of a short piece 
of glass tubing about 1 cm. in diameter, has the end of the slender tube, F, 
extending 2 or 3 mm. above the cork. By means of this arrangement the 
water dropping into the funnel is caused to descend through the tube as 
a series of drops separated by spaces filled with air. Thus, if no escape 
is allowed, the reservoir, K, is filled with water and air under a pressure 
