of large diameter and proportionate
length from being started at the ends, even when secured by ferules; but
the brass tubes commonly employed are so small as to be susceptible of
sufficient compression endways by the adhesion due to the ferules to
compensate for the expansion, whereby they are prevented from starting at
the ends. In some, of the early marine boilers fitted with brass tubes, a
galvanic action at the ends of the tubes was found to take place, and the
iron of the tube plates was wasted away in consequence, with rapidity; but
further experience proved the injury to be attributable chiefly to
imperfect fitting, whereby a leakage was caused that induced oxidation, and
when, the tubes were well fitted any injurious action at the ends of the
tubes was found to cease.

386. _Q._--What is the best mode of constructing the chimney and the parts
in connection therewith?

_A._--In sea-going steamers the funnel plates are usually about nine feet
long and 3/16ths thick; and where different flues or boilers have their
debouch in the same chimney, it is expedient to run division plates up the
chimney for a considerable distance, to keep the draughts distinct. The
dampers should not be in the chimney but at the end of the boiler flue, so
that they may be available for use if the funnel by accident be carried
away. The waste steam pipe should be of the same height as the funnel, so
as to carry the waste steam clear of it, for if the waste steam strikes the
funnel it will wear the iron into holes; and the waste steam pipes should
be made at the bottom with a faucet joint, to prevent the working of the
funnel, when the vessel rolls, from breaking the pipe at the neck. There
should be two hoops round the funnel, for the attachment of the funnel
shrouds, instead of one, so that the funnel may not be carried overboard if
one hoop breaks, or if the funnel breaks at the upper hoop from the
corrosive action of the waste steam, as sometimes happens. The deck over
the steam chest should be formed of an iron plate supported by angle iron
beams, and there should be a high angle iron cooming round the hole in the
deck through which the chimney ascends, to prevent any water upon the deck
from leaking down upon the boiler. Around the lower part of the funnel
there should be a sheet iron casing to prevent any inconvenient dispersion
of heat in that situation, and another short piece of casing, of a somewhat
larger diameter, and riveted