LOCOMOTIVE ENGINE.
415
and lose about 6-| lbs. in the time they are in use. The cost of both the brass and of the
copper tubes is about £l each, and this makes the expense of repairing an engine very
considerable when a complete set of new tubes is required. The tubes being fixed
firmly into both ends of the boiler, serve to support and strengthen them; but for an
additional support to the upper part, six wrought iron rods, o o, (Plates XC. and XCII.,)
are placed above the internal fire-box, by the side of each other and longitudinally in
the boiler; and the ends are attached by a pin to a piece of wrought iron, called T
iron, riveted on to the end plate of the boiler and to the back plate of the fire-box.
The Smoke-box F F, is 4 feet wide, like the fire-box, and 2 feet long, and is
closed on all sides ; the back of it is formed by the wrought iron plate n, half an
inch thick, closing the end of the boiler to which it is attached by means of a piece
of angle iron riveted to both, like the similar joint at the fire-box. The rest of the
smoke-box is made of quarter inch iron plate, the front and back plates being
bent in round the edge, and the other plates riveted to them as in the fire-box,
except the front plate, which is fixed by screw bolts and nuts, because it is required
occasionally to take it off.
Upon the smoke-box is fixed the chimney G, (Plates LXXXIX., XC. and XCII.);
it is 15 inches in diameter, and is made of one eighth inch iron plates, riveted
together and bound round by hoops, as shewn in the section; the top is made funnel-
shaped to give more free egress to the hot air, and the bottom has a piece of plate
riveted to it, forming a flanch all round, by means of which the chimney is bolted
down upon the smoke-box.
In the lower part of the smoke-box are fixed the two cylinders H H, where the
steam is used and motion produced; these will be described afterwards. The steam,
when it has been used in the cylinder and has performed its work, is no longer wanted,
and is let out into the air by the pipe p, (Plates XC. and XCII.)
The tubes open into the upper part of the smoke-box, and the hot air passes from
them up the chimney; no smoke is produced, except at first lighting the fire, as the
fuel used is coke, which does not cause any smoke in burning, but only a light dust.
The height of the chimney is obliged to be small, as it can never exceed 14 feet
height from the rails ; so that the draught produced by it is not at all sufficient to urge
the fire to the intense degree of ignition that is necessary to produce steam at the
pressure and in the quantity that is required, and some other more powerful means
has, therefore, to be adopted to produce the draught. This is done by making the
waste steam issue through the pipe^jt?, (Plates XC., XCI., and XCII.,) called the
blast pipe, which is directed up into the centre of the chimney, and is gradually con
tracted throughout its length to make the steam rush out with more force; this
pipe is made of copper one eighth of an inch thick, and is 3§ inches in diameter