Respirometer for small samples with automatic registration

The respiration chamber containing the sample is a small glass test tube with a closure of KOH solution. During registration the gas volume is kept constant by adjusting the pressure through a feedback mechanism: a microscope projects the picture of the meniscus of KOH onto a photodiode connected to a pen recorder with a vertically moving pen. A levelling bulb with water mounted on the pen transmits the pressure adjustments to the KOH solution through a water filled tubing. The accuracy is +/-0.1 mm water column (1 Pa) and the minimum air volume is 10 nl, so that an oxygen consumption down to 1 pl can be seen.