Improvements in furnaces and like combustion appliances

694,352. Controlling combustion of solid fuel. C.U.R.A. PATENTS, Ltd. Jan. 3, 1950 [Oct. 7, 1948], No. 26189/49. Class 51(i) In a combustion appliance of the type wherein air under pressure is directed as a jet on to the free surface of a bed of fuel and combustion gases emerge from said free surface such as is disclosed, for instance, in Specification 579,324, the arched refractory roof 14 has shaped bricks 24 and 25 defining an air inlet slit 18 from which air supplied through an equalizing chamber 19 by a fan 21 is discharged at an angle of about 45 degrees to the vertical on to the surface 17 of the fuel bed. The size of the air slit may be corrected by the insertion of shaped obstructing elements 36. When it is desired to provide control of the heat release and of the composition of combustion gases as in the aforementioned Specification an adjustable control member is provided in the air supply slit in the form of a refractory tongue 45, Fig. 5, secured to a spindle 48 mounted with an externally screw-threaded sleeve 49 provided with an operating handle 50 and engaged with a bush 51 fixed to the top of a housing 52. When the air supply is cut off, the tongue 45 is retracted by disengaging the sleeve 49 from the bush 51, raising the spindle 48 until a hole 53 lies just above said bush 51 and inserting therein a retaining pin. Specifications 587,823 and 694,351 also are referred to.