A hopper is closed at its lower end by a scraper which is provided with two opposite edges that laterally delimit an elongated discharge opening, a motorized rotating shaft extends parallel to the elongated discharge opening in a scraping relationship with the opposite edges, and is provided with a plurality of blind receptacles that are adapted to receive doses of salt which is loaded into the hopper, and after passing the first edge in relation to the direction of rotation of the shaft, the salt is discharged by gravity.