factory and unsafe, and discarded.

Another feature in the design of the Babcock & Wilcox boiler tending
toward added safety is its manner of suspension. This has been indicated
in the previous chapter and is of such nature that all of the pressure
parts are free to expand or contract under variations of temperature
without in any way interfering with any part of the boiler setting. The
sectional nature of the boiler allows a flexibility under varying
temperature changes that practically obviates internal strain.

In boilers utilizing water-leg construction, on the other hand, the
construction is rigid, giving rise to serious internal strains and the
method of support ordinarily made necessary by the boiler design is not
only unmechanical but frequently dangerous, due to the fact that proper
provision is not made for expansion and contraction under temperature
variations.

Boilers utilizing water-leg construction are not ordinarily provided
with mud drums. This is a serious defect in that it allows impurities
and sediment to collect in a portion of the boiler not easily inspected,
and corrosion may result.

Economy--That the water-tube boiler as a class lends itself more readily
than does the fire-tube boiler to a variation in the relation of grate
surface, heating surface and combustion space has been already pointed
out. In economy again, the construction made possible by the use of
headers in Babcock & Wilcox boilers appears as a distinct advantage.
Because of this construction, there is a flexibility possible, in an
unlimited variety of heights and widths that will satisfactorily meet
the special requirements of the fuel to be burned in individual cases.

An extended experience in the design of furnaces best suited for a wide
variety of fuels has made The Babcock & Wilcox Co. leaders in the field
of economy. Furnaces have been built and are in successful operation for
burning anthracite and bituminous coals, lignite, crude oil, gas-house
tar, wood, sawdust and shavings, bagasse, tan bark, natural gas, blast
furnace gas, by-product coke oven gas and for the utilization of waste
heat from commercial processes. The great number of Babcock & Wilcox
boilers now in satisfactory operation under such a wide range of fuel
conditions constitutes an unimpeachable testimonial to the ability to
meet all of the many conditions of service.

The limitations in the draft area of fire-tube boilers as affecting
economy have been