To improve a cube lead-melting furniture from which the slag comes out with the lead and blocks up the hole, the temperature of the furnace should be raised gradually and air allowed to enter the furnace to oxidise the sulphur contained in the coke. The front of the furnace should be luted with clay, and a tap hole made to remove the slag above the lead. If this cannot readily be done, add a shovelful of lime to stiffen the slag. The temperature can then be raised and more lime thrown in, if necessary, when the slag can be removed in lumps. A comparatively low temperature is required for rich slags and a high temperature for poor slags.