Abstract: Procedure and apparatus for the continuous analysis of the chloride ion content of overhead waters downstream of a hydrocarbon distillation column for more effectively preventing hydrochloric acid corrosion of downstream equipment while avoiding over-neutralizing the overhead waters to the detriment of the hydrocarbon product. This procedure comprises the following operations, in the order given or in a different order:Drawing from the overhead waters a stream of water for analysis;removing from the sample so drawn the hydrocarbons as well as the suspended matter;blowing nitrogen into the sample to sweep away the hydrogen sulfide ans the residual hydrocarbons;oxidizing the S.sup.2- or HS.sup.- sulfide ions to sulfate ions;acidifying the sample;finally, measuring by ionometry, and more particularly by means of a combined electrode, the content of chloride ions present.