Abstract: A chuck assembly is adapted to be mounted on the positioning assembly of a microscopic test device for effecting precise repeatable vertical movement of the object under test with negligible incidental movement of any other type. A triangular member fixed with respect to the positioning assembly is received in a circular recess in the upper surface of a housing. An annular projection on the bottom of the triangular member is disposed in an annular cavity in the housing, with a sealing gasket therebetween. The bottom of the cavity is coupled to an associated source of compressed air. A thin flat flexible metal disc overlies the triangular member and is fixed thereto centrally thereof, the periphery of the disc being fixedly clamped between the housing and a retaining ring. A top plate is secured to the housing.

Abstract: Collecting electrodes extend vertically in dust-collecting electrostatic precipitators, which are horizontally traversed by gas. Each collecting electrode comprises a plurality of profiled sheet metal strips which are suspended from the roof structure and are hooked into each other at their vertical longitudinal edges. The collecting electrodes also comprise at least one lower transverse connector. Two adjacent collecting electrodes define a gas passage which contains centrally disposed corona electrodes. Each sheet metal strip is substantially W-shaped in cross-section defining shallow dust-collecting pockets and comprises portions which are inclined alternately in opposite directions with respect to the direction of gas flow and portions which are parallel to the direction of gas flow and disposed between the inclined portions. The edge portions extend also parallel to the direction of gas flow and are reversely bent through 180.degree.

Abstract: A heat exchanger for the cooling of a gas, especially a gas containing SO.sub.2, comprises a tube bundle whose tubes, composed of lead, bridge a pair of tube sheets and can be provided with internal longitudinal ribs. According to the disclosure, the extruded cylindrical tubes are reshaped by indentations in a direction transverse to the longitudinal axis. The indentations may be annular or staggered.