C 8 ]

cases be charcoal, and of which the consumption is inthese kinds of furnaces inconsiderable, is put in at thetop, and is supplied with air through all or any of theapertures beneath the grate: by more or less closing oropening these apertures, the fire is diminished or increased.

This open furnace, besides its use for keeping fuelready lighted to be employed in others, affords the con-veniency of nealing metals when grown hard or rigidby hammering or rolling ; of setting any small vesseloccasionally upon the coals, as a crucible or iron ladle forthe melting of the more fusible metals, and serves formany other like purposes that occur in practice.

By introducing into the open furnace an iron pot, emptyor containing sand; it becomes a furnace for a capellavacua as it is called, or a sand furnace; in which the onlyvariation from the preceding is, that the mouth of thefurnace being occupied by the iron pot, the fuel is put inthrough the fire-place door or the aperture above thegrate.

An iron ladle, with its handle cut short, serves extremelywell for the capella or sand pot. It is supported over thefire by means of a flat iron ring, into which the ladle isinserted so as to bear against the ring by its upper widepart. It is necessary to have several of these rings, ofdifferent internal diameters for receiving ladles and othervessels of different sizes, but all of them wide enoughexternally to rest upon the top of the furnace. Between thefurnace and the ring are inserted, at equal distances, threeiron supporters, about a quarter of an inch thick, an inchlong, and equal in breadth to the thickness of the sides ofthe furnace. Through the space thus procured beneaththe ring, the burnt air passes off; and being permittedto issue freely on all sides, the heat is distributed,

and