By measuring the static pressure drop in a glass bubble column, the gas hold-up of oxygen and hygrogen in several electrolyte solutions was determined. A homogeneous bubble flow regime existed up to a gas through-put of some 4 cm/s in the bubble column. It was found that the gas hold-up is mainly determined by the impediment to coalescence. The velocity of bubbles in different solutions was measured with an ultrasonic doppler velocimeter. The velocity measurements indicated that coalescence already occurs at low gas through-put. A strong dependence of the bubble velocity on the electrolyte concentration was observed. When the velocity of the bubbles drops, the concentrations are close to values confirmed by other authors to be the critical concentrations for coalescence. By studying the hydrodynamics in the bubble column at a gas through-put less than 4 cm/s a zone with circulation flow was detected above the gas sparger. Over this zone there was homogeneous bubble flow.