An apparatus for dispersing gas in liquid mediums comprising a rigid adapter, a rigid tubular inner member secured to the adapter cooperating with a passage in said adapter to form a continuous conduit for gas, a terminal member for said rigid tubular inner member, a flexible, collapsible porous sleeve, having one permanently closed end and a peripheral dimension approximately equal to the peripheral dimension of a cross section of said tubular member, enclosing said tubular member and said terminal member and secured to the adapter to form an air chamber between the tubular member and the sleeve, said terminal member having means for passage of gas between the interior of the tubular member and the closed end of said sleeve and separate communication means connecting the closed end of said sleeve and the longitudinally extending space between the sleeve and said tubular member.