Abstract: An apparatus for mixing a particulate material into a liquid includes a pair of variable volume receptacles interlinked by a communication passage. A combined volume of liquid and particulate material is received within the variable volumes, and the volume of the variable volumes is alternately reduced and to force the materials back and forth through the connection passage. The variable volumes may be formed from a rigid walled cylinder having a free floating piston therein, and the piston and inner diameter may have a tight, sealed gap therebetween. To load the piston into the cylinder without effecting the seals, a load apparatus may be used to depress the seals inwardly of the piston and align the piston in the cylinder.