Abstract
Gas exchange in the 7-10 mμl. air film enclosed between a cover slip and the end of a capillary tube closed by a thin collodion membrane is measured by the external pressure required to restore the membrane to its constant volume position parallel to the slip. Membrane displacement is observed by two-beam reflexion monochromatic interferometry. The membrane separates each chamber from a common manifold leading through a central spherical joint to a conventional Warburg manometer. Rotation about the joint brings each chamber successively under the microscope. No membrane calibration is required. The capillaries are embedded vertically in an aluminium block for temperature uniformity. Preliminary results show a sensitivity of 1-10 μμl.