[ 3 *]

Explanation os Plate III.

T H E three furnaces in this plate are different kindsof blast furnaces; with holes bored in the sides forreceiving the nose of the. bellows.

The uppermost consists of a pot of the size marked 80,fitted into one of ioo; with a portion of another of iooinverted over it for a dome. So much of the bottom of thislast is sawed off as to procure a sufficient aperture ; and somuch is sawed from the mouth, that the remainder may beof a proper width to fit upon the mouth of the lesser pot.A round flip, sawed from the bottom, serves both for agrate and for a support to the crucible (page 18). A sectionof this grate is shewn in the furnace, and a plan of it onthe right hand.

The right side furnace at the bottom of the plate is forfusion without a grate or among the fuel. The pot is ofthe largest size, and its height may be occasionally enlargedby the ring cut off from the dome of the foregoing furnace.To the sloping canal in its bottom is fitted the lower partof another pot. See page 21.

The lowermost furnace on the left hand is that describedin page 27, in which streams of air are impelled from dif-ferent parts of the fuel upon the crucible in the middle.The lower pot is that which serves for the blast furnacein the upper part of the plate ; and the perforated pot is ofthe size 90, with its bottom rounded, and a part of the topcut off for the greater convenience of inspecting or takingout the crucible. The circular plane over it is an iron plate,with a hole in the middle, which serves as a cover for thepot; and over this is a transverse section of the perforatedpot and crucible, to ihew the direction of the streams of air.