Abstract: A longitudinally extending housing with end closures forms a closed mixing chamber within the housing. A mixer that has a fluid material inlet at each end thereof with longitudinally spaced, opposed ends forming fluid material outlets and a central peripheral discharge from the mixer between the end outlets is supported on a rotatable shaft that extends through one of the end closures to position the mixer in the mixing chamber. Housing inlet means comprising a pair of conduits communicate fluid to the closed mixing chamber for discharging it thereinto adjacent, but spaced from the end fluid inlets of the mixer, and housing outlet means is aligned with the mixer to receive the central discharge therefrom. The diameter of the mixer is about one-half the diameter of the closed mixing chamber, and the length of the mixer is about one-third the longitudinal extent of the closed mixing chamber. The mixer is positioned substantially equidistant from the sides and ends of the mixing chamber.