A mixer apparatus for use with a vessel centered about a longitudinal axis is disclosed. The mixer has a blade which: defines a central head axis; has a first end and a second end. The second end defines an inside blade diameter "ID" and the first end defines an outer blade diameter "OD". The blade is positioned within and coaxial to the vessel. A scotch yoke, operatively connected to the blade by a shaft, effects reciprocating longitudinal movement of the blade through a stroke "S", with a duration "T" for each cycle, wherein 1750.36OD²/ID²S/T250 when OD, ID and S are expressed in inches, and T is expressed in minutes.