From: CLXXII: An apparatus for the graphical recording of oxygen consumption and carbon dioxide output, especially adapted for clinical work. By H.C. Hagedorn.  Biochemical Journal, 1924, page 1304.

“Figure 2 shows the apparatus in a convenient form which has been in use for about two years with complete satisfaction. The gas meters and spirometers are arranged in a common water-bath, the spirometers recording on a common drum, most conveniently with ink of different colours. The water-bath is fitted with an overflow tube to secure constant water level; it contains about 100 kg. water, and the expired air is led through a pipe of considerable length which is immersed in the bath to cool the air to the temperature of the bath before it enters the gas meter. From the service pipe to the spirometer (B) there is a wide pipe to secure that every change in air pressure caused by the respiration is taken up promptly by the spirometer (B), so that there can be an absolutely constant in the gas meter I.

“The accuracy of the results largely depends on the care with which the spirometers are balanced; every change in the air pressure in one of the spirometers will affect the water level in the corresponding gas meter and so disturb its accuracy.  The spirometers are therefore arranged on special bearings and balanced with a double set of counterbalances, a large one for gross and a small one for fine adjustment. The counterbalances are adjustable horizontally and vertically, thus allowing convenient compensation for buoyancy of the spirometer.”