Plate LXXVIII. AAAA, fig. 1, is a front elevation of an assay furnace; aa a view of one of the two iron rollers on which the furnace rests, and by means of which it is moved forward or backward; b the ash-pit; c c are the ash-pit dampers, which are moved in a horizontal direction towards each other for regulating the draught of the furnace; d the door or opening by which the cupels and assays are introduced into the muffle; e a movable funnel or chimney, by which the draught of the furnace is increased.