1. A furnace ( 10 ) comprising: a generally cylindrical furnace body ( 12 ) having a closed ( 13 ) end and open ( 14 ) end, a frame ( 15 ) pivoted to a ground member ( 16 a, 16 b ), said frame ( 15 ) supporting the furnace body ( 12 ) for rotation at various angles in a reclined position from (α) the open end ( 14 ) and in an inclined angle (β) towards the open end ( 14 ), a burner ( 30 ) to heat the furnace and a hinged door ( 19 ), arranged to close the open end ( 14 ) of the furnace ( 10 ).