furnace 39 s charging hole 14 and the pedestal travel to reduce risk of damage to these elevator parts in the event the crucible 17 breaks and spills its molten content such breakage is potential even though the crucible 17 is made of alumina and is of small size being only 3 34 high and 11 2 34 in diameter to provide a total volume of only 4 5 cubic inches this elevator tray moves the pedestal 15 between a down position as shown in fig1 and 2 where the crucible 17 can be positioned on or removed from the pedestal top and an up position shown approaching by fig3 where the crucible is carried by the pedestal via the elevator tray upwardly into the heating space 4 the pedestal is designed to close the charging hole 14 when in its up position the shell top is formed with internal recessed upper and lower annular shelves 28 and 29 respectively of larger and smaller diameters a small disk 30 rests on the lower shelf and a larger disk 31 rests on the upper shelf and in the larger hole both disks cooperatively form a shank hole 32 of smaller diameter than the access hole 9 formed in the furnace top and the closure plug 10 has a shank 10a of reduced diameter which slidably fits in the shank hole 32 the plug forming a shoulder 10b resting on the large disk 31 both disks are made of a fibrous refractory of greater density and greater strength than the fibrous material from which the shell and its top and bottom are made these disks hold the plug 10.