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The round hole In the sides of these furnaces gives anopportunity of introducing the nose of a pair of doublebellows; so that one pot singly, or two combined togetheras in the foregoing article, may be readily converted intoa blast furnace; in which cafe all the other aperturesbeneath the grate must be closed while the bellowsacts, to prevent the air forced in by it from escaping. Itis of great advantage, in sundry operations, to be thusable, at certain periods, to suddenly animate the fire.

One pot inverted over the other, with the iron hoopplaced between them, make a furnace for cupellation,calcination under a muffle, and the other purposes ofwhat is called the astay furnace ; as also for experimentsof enamelling, of baking colours on earthen ware andglass, 6cc. The chimney, or a part of it, is occasionallyset upon the top for raising the fire when it proves toolanguid.

In want of the muffle made for operations in the assayfurnace, its office may be supplied by a common cruciblelaid upon its side, with a bed of loam in it to form a flatsurface for the cupels or other vessels to stand on. Thelargest of the three grates is set upon the lower pot, whichit wholly covers; and the iron hoop, which of coursebears upon the rim of the grate, is placed with its doorlowermost. The muffle, or its substitute, is laid upon aflip of brick on the grate, with its mouth fronting theopening in the hoop, through which the cupels, &c. areintroduced. In processes which require frequent inspectionof the subject-matters, and the admission of heated air;the plate, on which the door of this aperture is rivetted,is let down to an horizontal situation, and some pieces oflighted charcoal, with sufficient interstices between themfor the cavity of the muffle to be seen, are laid upon the

plate,