ration of their stays, and such an explosion might be almost as
disastrous as that of a shell boiler. The headers in a Babcock & Wilcox
boiler are practically free from any danger of explosion. Were such an
explosion to occur, it would still be localized to a much larger extent
than in the case of a water-leg boiler and the header construction thus
almost absolutely localizes any danger from such a cause.

Staybolts are admittedly an undesirable element of construction in any
boiler. They are wholly objectionable and the only reason for the
presence of staybolts in a boiler is to enable a cheaper form of
construction to be used than if they were eliminated.

In boilers utilizing in their design flat-stayed surfaces, or staybolt
construction under pressure, corrosion and wear and tear in service
tends to weaken some single part subject to continual strain, the result
being an increased strain on other parts greatly in excess of that for
which an allowance can be made by any reasonable factor of safety. Where
the construction is such that the weakening of a single part will
produce a marked decrease in the safety and reliability of the whole, it
follows of necessity, that there will be a corresponding decrease in the
working pressure which may be safely carried.

In water-leg boilers, the use of such flat-stayed surfaces under
pressure presents difficulties that are practically unsurmountable. Such
surfaces exposed to the heat of the fire are subject to unequal
expansion, distortion, leakage and corrosion, or in general, to many of
the objections that have already been advanced against the fire-tube
boilers in the consideration of water-tube boilers as a class in
comparison with fire-tube boilers.

[Illustration: McAlpin Hotel, New York City, Operating 2360 Horse Power
of Babcock & Wilcox Boilers]

Aside from the difficulties that may arise in actual service due to the
failure of staybolts, or in general, due to the use of flat-stayed
surfaces, constructional features are encountered in the actual
manufacture of such boilers that make it difficult if not impossible to
produce a first-class mechanical job. It is practically impossible in
the building of such a boiler to so design and place the staybolts that
all will be under equal strain. Such unequal strains, resulting from
constructional difficulties, will be greatly multiplied when such a
boiler is placed in service. Much of the riveting in boilers of this
design