Abstract: A vessel for a molten substance for modifying the properties of objects of glass and similar materials, comprises an inner vessel and an outer vessel with an annular space defined therebetween, an elastic tongue connecting the inner vessel and the outer vessel, means in said space for guiding a heating gas including fins mounted on the inside of the outer vessel which also support the inner vessel and an upright web between the inner vessel and the outer vessel reinforcing the combined vessel structure and separating the hot gas guiding system into discrete sections on opposite sides of the web.

Abstract: For the continuous melting of salts to be used for modifying the properties of objects of glass or similar materials, an apparatus is provided with inner and outer vessels, an annular chamber between the vessels for containing a heat exchange fluid, ribs on the outer walls of the inner vessel for guiding the heat exchange fluid and assisting heat exchange from the heat exchange fluid to the inner vessel, means for transferring heat to the heat exchange fluid, means for circulating the heat exchange fluid through the chamber, means for admitting the salt to the inner vessel, the inner vessel having an upper portion of a semi-circular profile defining a radiant heating surface for radiating heat downwardly onto the salt and having a lower portion of approximately triangular to parabolic profile defining a conduction heating surface for transferring heat to the salt by conduction, the upper surface to be formed by the salt charged to the inner vessel defining a melting surface and the ratio of the area of the ra