Boilers are vessels in which fluids are boiled or heated, and are
almost of every form and size. Some boilers, such as those attached
to steam-engines, are more strictly called “steam generators,” as
they are constructed solely for the production of steam at the lowest
possible expense of time and fuel, and also to resist the pressure
which the steam exerts at high temperatures; these boilers are not
only used to produce the steam for the motion of engines, but are
extensively used in its production for heating evaporating-pans and
boilers (in the strict sense of the word), and also for warming and
ventilating buildings. They are more particularly noticed under the
head “Steam Engines.”
Boilers for all purposes were formerly made of metal (usually copper
or iron), and were exposed directly to the fire intended to heat
their contents, but since the properties of steam have been more
fully recognised, it is now very frequently employed for heating
boilers--especially where a heat at or below the boiling point of
water is required. There are great advantages arising from this
plan, one of which consists in doing away with the risk of the
materials in the boiler being burnt. Some boilers are now made of
wood, having steam-pipes running through them, and in those cases
in which the admixture of water is no detriment steam--in the form
of jets--is thrown directly into the fluid to be heated, which very
quickly raises it to the boiling point. Boilers of cast-iron, lined
with platinum or enamel, are also used for various purposes, as the
condensation of acid substances, &c., which would act on most metals.
Glass and glazed pans, too, can be used with a steam apparatus,
without any danger arising from breakage, which would frequently
occur if they were directly applied to the fire.