NOV. 22, 1915 
Improved Respiration Calorimeter 
305 
variations in the pressure of the air in the chamber unless provision were 
made for corresponding fluctuations in the capacity of the system. 
This is accomplished by attaching a flexible diaphragm of thin rubber 
or a sensitive spirometer to a small tube opening into the chamber, 
which serves as a tension equalizer, keeping the air of the chamber 
always at the barometric pressure of that of the laboratory (PI. XXX). 
AIR-PURIFYING SYSTEM 
The circulation of air is maintained by a rotary air pump, which has a 
capacity of close to one-fourth of a liter per revolution and is driven at 
a rate of about 250 revolutions per minute, so that the air is forced 
through the purifying system at a rate of 60 to 70 liters per minute. 
An electric motor of one-eighth horsepower is sufficient to run the pump 
and to move the air through the absorbers (PI. XXXII, fig. 2). 
All piping in the air-circulating system is brass pipe of the so-called 
half-inch size, which has an internal diameter of 15 mm. The apertures 
of the air passages in the purifying devices are also of this size. This 
has been found sufficient to conduct the air at the desired rate without 
undue resistance, the pressure in the section of pipe between the com¬ 
pressor and the first water absorber, where it is higher than in any other 
part of the system, being less than 40 mm. of mercury. 
The motor, the rotary air pump, and the absorbers for water vapor 
and carbon dioxid are assembled on a suitable-sized stand or table, with 
three shelves, called the “absorber table” (PI. XXXIV, fig. 1). The 
motor and pump are on the lower shelf, and on the middle shelf are the 
purifying devices in a series or train; first, the absorbers for water vapor, 
and next, the absorbers for carbon dioxid. The air pipe from the respira¬ 
tion chamber passes to the pump and then to the inlet end of the absorber 
train. From the outlet end of the train the air pipe returns to the 
chamber, the ingoing and outgoing pipe passing through the walls in 
two apertures close together. Inside the walls the pipes extend to oppo¬ 
site ends of the chamber, the end of the ingoing pipe being near the top 
of the chamber, and that of the outgoing pipe near the bottom. 
Two absorber trains are set up in parallel and are used in alternate 
periods, the air pipe at each end of the trains being branched for this 
purpose. There is a valve in the piping at each end of each train, and 
the change from one train to the other involves merely closing the valves 
for one train and opening those for the other. When ordinary wheel 
valves are used, as shown in the illustration, the motor is stopped for 
the few seconds necessary to make the change; but the valves at each 
end of the purifying system may be replaced by a suitable 3-way cock 
or air trap at the point where the air line branches at each end of the 
train, and the two cocks may be actuated by the same shaft, so that the 
air current can be shunted from one train to the other with a single 
motion from either end of the absorber table and while the air pump is 
