Abstract: An electrode E.sub.1 having the design function of an ion source is placed in a gas stream and emits by corona discharge effect ions which are collected on two electrodes E.sub.2 and E.sub.3. These electrodes consist of grids placed at right angles to the direction of the gas stream on each side of the electrode E.sub.1 at approximately equal distances from this latter. The device comprises electronic means for amplifying the currents collected at the electrodes E.sub.2 and E.sub.3 as well as for calculating the difference and the sum of the currents collected at the electrodes after amplification.

Abstract: A sulfur dioxide containing gas is purified by successive contact with an ammonia solution and then a dilute ammonium sulfite solution; the latter solution is regenerated by electrodialysis while the ammonia solution, after SO.sub.2 absorption, is vaporized in order to recover ammonia and sulfur dioxide.