Injector for a flotation device

In a flotation apparatus comprising a flotation device for separating constituents by flotation and comprising an injector having a flow channel with an inlet end and an outlet end, means for introducing a liquid into said flow channel, and means for introducing a gas into said flow channel, both said liquid introducing means and said gas introducing means disposed upstream of said flow channel with respect to a direction of fluid flow through the channel, said flow channel having a variable cross sectional area with respect to the direction of fluid flow through the injector, said injector connected to means for introducing a mixture of gas and liquid from said injector into the flotation device, the improvement comprising repeated narrowings and widenings of the flow channel in the direction of fluid flow and wherein the flow channel is defined by first and second opposing injector plates, said flow channel being substantially narrow, each said plate having elongate projections defining a plurality of ridges, with adjacent ridges oriented with respect to one another ranging from being parallel to deviating at most 8.degree. with respect to one another, the elongate projections of the first plate crossing in superposed relationship the elongate projections of the second plate.