1,154,205. Electrostatic precipitators. GOURDINE SYSTEMS, Inc. 5 Aug., 1966 [5 Aug., 1965], No. 35149/66. Heading B2J. Apparatus for precipitating particles contained in a gas stream comprises a conduit 10, Fig. 1, defining a flow path with upstream and intermediate and downstream portions 14, 23 a corona electrode 20 and an attractor electrode 18 to produce a radial space charge field in the fluid in the downstream portion. An axial ion-repelling field is produced in the intermediate portion by a dielectric nozzle 14. The radial space charge field causes particles to be driven to the boundary of the flow path in the downstream portion so that the particles are precipitated' from the fluid. The inner wall of the particle collecting section 23 has an earthed conductive liner 24. In operation, H.T. is applied across the electrodes 18, 20, and the charges on the ions and particles collected at the inner wall 24 are conducted to ground. The nozzle portion may include a stack of annular sections 36 Fig. 2 including particle traps 38 to prevent precipitated particles shorting out the section. In another embodiment precipitators leave via an annular opening 40, Fig. 3. Precipitators may be arranged in parallel stages, the corona electrodes being thin wire, and the attractor electrodes conductive strips, and particles may be dislodged from plates, which form a conduit wall, by rapping or vibrating. An aerosol may be injected into the working fluid to prevent "ion slip" (a condition where fluid velocity is greater than ion velocity). The aerosol liquid may be continuously recycled by a pump and an annular collecting reservoir.