The life of George Stephenson, railway engineer - Lighthouse ...

260 LIFE OF GEORGE STEPHENSON. [ciiAr. xxii.
Though the adoption of the steam blast greatly quickened
combustion and contributed to the rapid production of high-
pressure steam, the limited amount of heating surface presented
to the fire was still felt to be an obstacle to the complete success
of the locomotive engine. Mr. Stephenson endeavoured to
overcome this by lengthening the boilers and increasing the sur-
face presented by the flue tubes. He also further endeavoured
to meet the difficulty by doubling the flue, the last engine which
he constructed for the Stockton and Darlington Railway, pre-
vious to the building of the " Rocket," being constructed with a
double tube, which thus presented a considerably greater surface
to the fire. The " Lancashire Witch,'' built by him for the
Bolton and Leigh Railway, and employed in the completion of
the Liverpool and Manchester Railway embankments, was also
constructed with a double tube, each of which contained a fire
and passed longitudinally through the boiler. But this arrangement
necessarily led to a considerable increase in the weight of
these engines, which amounted to about twelve tons each ; and
as six tons was the limit allowed for engines admitted to the
Liverpool competition, it was clear that the time was come
when the Killingworth engine must undergo a further important
modification.
For many years previous to this period, ingenious mechanics
had been engaged in attempting to solve the problem of the best
and most economical boiler for the production of high-pressure
steam. As early as 1803, Mr. Woolf patented a tubular boilerj
which was extensively employed at the Cornish mines, and was
found greatly to facilitate the production of steam, by the exten-
sion of the heating surface. This boiler consisted of eight tubes
placed horizontally in the centre of the longitudinal furnace
and they were so arranged that the whole current of the flame
passed over them before it escaped into the chimney. Mr.
"Woolf stated the object of the arrangement to be, that " the
tubes composing the boiler should be so combined and arranged,
and the furnace so constructed, as to make the fire, the flame,
and the heated air to act around, over, and among the tubes,
embracing the largest possible quantity of their surface." In
this arrangement the steam and water were within the tubes.
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