Nov. 22, 191S 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 sufiicient 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. i). 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 



