Note 22 — Chapter VIII · BOILER AND ITS APPENDAGES.—FURNACE.

He uses a slightly inclined grate, at the back or lower end of which is the flue, and at the front or higher end, the hopper for admitting the coals. In the bottom or narrow end of the hopper is a moveable shelf, worked by the engine. Upon drawing back this shelf, a small quantity of fuel is allowed to descend upon a fixed shelf under it; and upon the return of the moveable shelf, this fuel is protruded forward upon the grate. Every alternate bar of the grate is fixed, but the intermediate ones are connected with levers, by which they are moved alternately up and down.[22] The effect is, that the coals upon the bars are continually stirred, and gradually advanced by their own weight from the front of the grate, where they fall from the hopper, to the back, where they are deposited in the ash-pit. By the shape and construction of the bars, the air is conducted upwards between them, and rushes through the burning fuel, so as to act in the manner of a blowpipe, and the entire surface of the fire presents a sheet of flame.