Abstract: Apparatus for measuring the electrostatic properties of materials, particularly powder, in which a first fixed plate has a series of openings lying along the circumference of the circle the center of which lies on the axis of a rotor mounted adjacent the plate with its axis perpendicular to the plate, the motor carrying an electrode and probe spaced apart from one another in such positions that the electrode and the probe separately pass over each opening when the rotor rotates. The electrode is charged and means are provided for detecting the charge on the probe to detect the charge on the material. In order to hold the powdered material in the openings a second fixed plate is mounted under the first fixed plate and has cavities therein in register with the openings in the first fixed plate, each cavity having a porous element at the bottom, and suction is applied below the porous element to hold the powder in place.