Abstract: The disclosed treatment is for the removal of hydrogen halide constituents of an exhaust gas by means of a dry scrubbing agent to which the gas binds. The agent is sprayed into the gas in finely divided form just prior to flow of the gas through a register located at the entrance to a filter chamber. The agent is thus distributed evenly over the input of the filter and performs its binding function primarily while on the filter. The agent may be sprayed as a finely divided solid or as a fluid which rapidly dries to leave a coating of finely divided agent on the filter.Also disclosed is an apparatus for practicing the method, including a nozzle casing with a plurality of spray nozzles located in the gas passageway at the input side of a register at the entrance to the filter chamber housing an electrical filter.