An apparatus for testing a rheological property of a fluid with a particulate includes: (a) a receptacle having a cylindrical side wall enclosed by a bottom wall defining a cavity for receiving a fluid to be tested; (b) an axial support adapted to be positioned in the cavity of the receptacle, whereby relative rotational motion can be imparted to the receptacle and the axial support; (c) at least one inward projection extending inward from an inside surface of the receptacle; (d) at least one outward projection extending outward from the axial support; and (e) at least one projection for directing fluid flow that has at least one major surface angled or curved upward. A method of testing a rheological property of a fluid with a particulate includes: (a) placing a sample of the fluid and the particulate in the apparatus; (b) imparting relative rotational motion to the receptacle and the axial support; and (c) measuring the torque between the receptacle and the axial support. A method of fracturing a subterranean formation penetrated by a well includes: (a) placing a sample of a fracturing fluid and a particulate in the apparatus; (b) imparting relative rotational motion to the receptacle and the axial support; (c) measuring the torque between the receptacle and the axial support; (d) adjusting the conditions for mixing the fracturing fluid and the particulate in response to the measured torque; and (e) injecting the fluid and particulate into the well at a sufficient rate and pressure to fracture the formation.