Abstract: A method and apparatus for measuring the concentration of solid particles in a gaseous phase which consists in passing a solid particles laden gas through at least one fluidized bed of balls having a diameter greater than that of the largest particles of said gas in order that said balls are not carried away by the ascending air stream. During their passage through the fluidized bed, these particles collide with the balls of the fluidized bed giving rise to a triboelectrification phenomenon and the electric current collected by the metallic walls of the container in which the fluidized bed is provided, is measured by a suitable electric or electronic control system upon separation of particles from the balls.