Abstract: This process consists in placing liquid DMSO with a low water content in contact with an ion exchange resin in --SO.sub.3 H form, and then in separating the liquid from the resin.The DMSO thus obtained has a content of iron cation tracer element of less than or equal to 1 ppb and a content of Na cation tracer element of less than or equal to 2 ppb.

Abstract: Process for removing hydrogen sulfide at low concentration in a gas containing water vapor. The gas is cooled to a temperature below the dew point of water, which condenses and separates the water. The dry gas is scrubbed free of hydrogen sulfide by an H.sub.2 S-absorbent solvent forming a purified gas. The purified gas is contacted and rehydrated with heated water so that the water content as water vapor corresponds to a mass flow rate of water substantially equal to the mass flow rate of the water present in the H.sub.2 S-containing gas before cooling. The condensed water circulates in a closed circuit to contact and rehydrate the purified gas, and then is cooled to the appropriate temperature for cooling the H.sub.2 S-containing gas. An apparatus, appropriate for carrying out the process is disclosed.