Arrangement for exposing a substance to a chemically active gaseous plasma

Apparatus which directs gas through an electric field between electrodes (4, 4') within a chamber (3) causing the generation of chemically active gaseous plasma. The chemically active gaseous plasma then being transferred into a vessel (8) which contains a substance to be exposed to the said plasma. The above chamber may operate at a pressure in excess of 50 millibar. An electrode (4') may include a passage (5) which links the chamber (3) to the vessel (8). The link between the chamber (3) and the vessel (8) may include a cooling arrangement (fig. 3, not shown).