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

264 LIFE OF GEORGE STEPHENSON. [chap. xxii.
The fitting of the copper tubes in the boiler of the " Rocket
so as to prevent leakage, was a work of some difficulty. They
were manufactured by a Newcastle coppersmith, and soldered to
brass screws, which were screwed into the boiler ends, standing
out in great knobs. When the tubes were thus fitted, and the
boiler was filled with water, hydraulic pressure was applied;
but the water squirted out at every joint, and the factory floor
was soon flooded. Robert went home in despair; and in the
first moment of grief, he wrote to his father that the whole thing
was a failure. By return of post came a letter from his father,
telling him that despair was not to be thought of—that he must
" try again ; " and he suggested a mode of overcoming the diffi-
culty, which, singularly enough, his son had already anticipated
and proceeded to adopt. It was, to bore clean holes in the boiler
ends, fit in the smooth copper tubes as tightly as possible, solder
up, and then raise the steam. This plan succeeded perfectly,
the expansion of the copper tubes completely filling up all in-
terstices, and producing a perfectly water-tight boiler, capable of
withstanding extreme internal pressure.
The mode of employing the steam blast for the purpose of
increasing the draught in the chimney, was also the subject of
numerous experiments. The increased effect obtained by con-
tracting the orifice of the blast-pipe had by this time been
ascertained, although doubts were expressed whether the greater
draught thus secured was not counterbalanced in some degree by
the negative pressure upon the piston. A series of experiments
was made with blast-pipes of different diameters; and their
efficiency was tested by the amount of vacuum that was produced
in the smoke-box. The degree of rarefaction was determined
by a glass tube fixed to the bottom of the smoke-box, and de-
scending into a bucket of water, the tube being open at both
ends. As the rarefaction took place, the water would of course
rise in the tube ;. and the height to which it rose above the
surface of the water in the bucket, was made the measure of the
amount of rarefaction. These experiments proved that a con-
siderable increase of draught was obtained by the contraction of
the orifice ; accordingly, the two blast-pipes opening from the
cylinders into either side of the " Rocket " chimney, and turned
"