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