Apparatus for metering and vaporizing a particulate material, comprising: (a) a metering device for metering particulate material including: (i) a reservoir for receiving particulate material; (ii) a housing having an internal volume and having first and second openings for respectively receiving the particulate material from the reservoir and for discharging the particulate material; (iii) a rotatable shaft disposed in the internal volume, the shaft having a smooth surface and a circumferential groove aligned with the first and second openings for receiving particulate material from the reservoir and for discharging the particulate material; (iv) means disposed in the reservoir for delivery and cooperating with the rotating shaft for fluidizing the particulate material and transporting the particulate material from the reservoir into the circumferential groove; (v) 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; (vi) means disposed in relation to the second opening for scraping, and cooperating with the groove to dislodge particulate material retained therein and fluidize the scraped particulate material, and in response to the shaft rotating, deliver metered amounts of particulate material through the second opening in the form of single particulate grains, or small aggregates of particulate grains, or both; and (b) a flash evaporator that receives and flash vaporizes the metered particulate material; wherein the scraping and fluidizing means comprises an oscillating scraper having at its end substantially the same cross section as the groove in the rotating shaft. (a) a metering device for metering particulate material including: (i) a reservoir for receiving particulate material; (ii) a housing having an internal volume and having first and second openings for respectively receiving the particulate material from the reservoir and for discharging the particulate material; (iii) a rotatable shaft disposed in the internal volume, the shaft having a smooth surface and a circumferential groove aligned with the first and second openings for receiving particulate material from the reservoir and for discharging the particulate material; (iv) means disposed in the reservoir for delivery and cooperating with the rotating shaft for fluidizing the particulate material and transporting the particulate material from the reservoir into the circumferential groove; (v) 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; (vi) means disposed in relation to the second opening for scraping, and cooperating with the groove to dislodge particulate material retained therein and fluidize the scraped particulate material, and in response to the shaft rotating, deliver metered amounts of particulate material through the second opening in the form of single particulate grains, or small aggregates of particulate grains, or both; and (i) a reservoir for receiving particulate material; (ii) a housing having an internal volume and having first and second openings for respectively receiving the particulate material from the reservoir and for discharging the particulate material; (iii) a rotatable shaft disposed in the internal volume, the shaft having a smooth surface and a circumferential groove aligned with the first and second openings for receiving particulate material from the reservoir and for discharging the particulate material; (iv) means disposed in the reservoir for delivery and cooperating with the rotating shaft for fluidizing the particulate material and transporting the particulate material from the reservoir into the circumferential groove; (v) 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; (vi) means disposed in relation to the second opening for scraping, and cooperating with the groove to dislodge particulate material retained therein and fluidize the scraped particulate material, and in response to the shaft rotating, deliver metered amounts of particulate material through the second opening in the form of single particulate grains, or small aggregates of particulate grains, or both; and (b) a flash evaporator that receives and flash vaporizes the metered particulate material; wherein the scraping and fluidizing means comprises an oscillating scraper having at its end substantially the same cross section as the groove in the rotating shaft.