Abstract: Particles are extracted automatically from a duct through which they are transported in a current of gas. The method of applicable for the determination of ash content and volatile content of solid fuels and for unburned materials in ash. The particles are deposited on a crucible (10) that is constantly inside a temperature controlled electric oven (9) The apparatus has a duct (16) that, penetrating the oven (9), terminates in the form of a dome at the height of the upper part of the crucible (10). The sample accesses the oven (9) by gravity through the duct (16) and is deposited in the crucible (10) where it is heated. This crucible (10) is supported on a rod (11) that penetrates the lower part of the oven and rests on an analytical balance (14). After heating, the sample is aspirated by the vertical duct (16) to enable the start of a new cycle.