Abstract: Hot briquetting apparatus for ferrous or non-ferrous particles has a furnace having upper and lower chambers. The particles are supplied to the lower chamber and leave the lower chamber through a discharge tube to enter a briquetting press. A passage is performed between the lower and upper chambers and sensing means sense the constituents of the gases in that passage. Control means control the air-to-fuel ratio of a zone of the lower chamber. The control means are connected to the output of the sensing means so as to maintain the atmosphere within the zone as a reducing atmosphere, the whole of the lower chamber being a reducing atmosphere.