The gas being analyzed for CO₂ and the air are brought into rotary motion in the gas and air chambers, 1 and 2, by fans 3 and 4 which are driven in opposite directions by electric motor 7. Shafts A and D of the gas and air impellers, 5 and 6, are not linked to the fan shafts, but are linked together by four-bar rocker arm linkwork ABCD. Mounted on shaft D of air impeller 6 is hand a. The pressure produced by the fans in the gas and air chambers is transmitted to the impellers which tend to rotate in opposite directions. Since the specific mass of the CO₂ in the gas being analyzed is greater than that of air, the torque in the gas chamber is greater than that in the air chamber, and the hand of the instrument is deflected in one direction. The deflection of the hand corresponds to the content of CO₂ in the analyzed gas. The instrument is zeroed by passing air through both chambers.
$3934$LHP,M$