Apparatus for vaporizing a particulate material, comprising a metering apparatus including: a reservoir; a housing having an internal volume and first and second openings for respectively receiving and discharging the particulate material; a rotatable shaft disposed in the internal volume, the shaft having a smooth surface and a circumferential groove for receiving particulate material from the reservoir and for discharging the particulate material; the rotatable shaft and the internal volume cooperating such that the particulate material is transported by the circumferential groove and not along the remainder of the rotatable shaft; a scraper disposed in relation to the second opening, having at its end substantially the same cross section as the groove in the rotating shaft, the scraper cooperating with the groove to dislodge particulate material retained therein, and in response to the shaft rotating, delivers metered amounts of particulate material through the second opening; to the flash evaporator.