Abstract: An apparatus (10) for analyzing material in particulate form is disclosed. The apparatus (10) comprises a vertically elongate housing (12) having an open upper end (26) and a restricted outlet at the lower end. A probe (28) directs light through a transparent cover (22), provided in one wall of the housing (12), and collects light reflected from particulate material in the housing (12). A slide valve (24), which includes a U-shaped section (30) and a T-shaped section (34) with a hole (32) therebetween, partially closes the outlet of the housing (12). Movement of the slide valve (24) by means of a knob (56), rod (36) and coil spring (44) allows for adjustment of the flow rate of the material through the apparatus (10), as well as for clearing blockages which may occur at the exit of the apparatus (10).