306 Journal of Agricultural Research voi. v, no. 8 
still running. By actuating the shaft electrically the change can be 
made by the observer at a distance, or a clock can be used to close the 
electric circuit at any given time and thus make the change automatically. 
While the air is passing through one train the other is disconnected, 
the absorbers weighed, the absorbent renewed if necessary, and the train 
again connected in position. The absorbers are joined together by cou¬ 
plings which are attached to the inlet and outlet tubes by stout, flexible 
rubber tubing. Rubber washers between the halves of each coupling 
make a tight joint. A similar coupling connects each end of the train 
with the air pipe. When the whole train is in position it is tested for 
tightness, with the air in the system at a pressure of about i meter of 
water, which is considerably more than the highest pressure in any part 
of the train in service. 
Removing Water Vapor from the Air 
In the purifying system the air passes first through sulphuric acid, which 
removes all water vapor from it. The acid container, which is in effect 
a modified gas-washing bottle of moderately large capacity (PI. XXXIII, 
fig. i), was devised in connection with these investigations. A strong 
glass bottle about 2^ liters in capacity (about 24 cm. in height and 12 
cm. in diameter), with a wide mouth, is fitted with a special ground- 
glass stopper, in the top of which are sealed an entrance and an exit 
tube, each 15 mm. in internal diameter. The entrance tube, which is 
in the middle of the stopper, extends to very near the bottom of the 
bottle, and terminates in a bulb about 4.5 cm. in diameter, which has 
several holes about 4 mm. in diameter in the sides and bottom, the total 
area of the holes being about equal to that of the cross section of the 
tube. Surrounding the bulb is a bell of about 7.5 cm. diameter, attached 
to the tube at a point a little above that at which the bulb is attached. 
The bell is completely open at the bottom, and has a row of holes about 
7 mm. in diameter around the side at a level just above the top of the 
bulb. 
When charged, the bottle is filled with acid to a level a little above the 
row of holes in the bell, about 750 c. c. of acid being sufficient for this 
purpose. The air escaping through the holes in the bulb and in the bell 
is broken into bubbles, which in passing through the acid are deprived 
of moisture. The passage of the air through the acid keeps it vigorously 
stirred, acid coming up through the bottom of the bell to replace that 
forced out through the holes at the sides. To prevent globules of acid 
from being spattered or carried by the air into the exit tube, the bottom 
of the stopper, which is about 6 cm. below the top, is nearly closed, an 
annular space about 8 mm. across being left around the tube that pro¬ 
jects to the bottom of the bottle to provide for the exit of air. Into the 
space thus formed in the interior of the stopper are placed lumps of 
