The Locomotive - Lighthouse Survival Blog

54 THE LOCOMOTIVE. [April,
Castle, Pa., exploded on February 35tli. The brick-work and roof of the boiler-))ou.se-
were torn to pieces and hurled in all directions. No person was injured.
(65.)— The boiler in Egbert Naylor's large mill near Leatherwood, Ky., exploded
on February 25th. Washington Hudson, the fireman, was blown 100 feet away, and is-
likely to die from his injuries.
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(66.) — On February 28th a boiler exploded in Marthaville, Ont. James Duncan
and his engineer were killed, and a man named [McKensie fatally injured.
Leidenfpost's Phenomenon.
Elsewhere in this issue we have acknowledged the receipt of a paper on this subject
by the distinguished Italian engineer, Alfredo Gilardi. The phenomenon leferred to is
commonly known as the " spheroidal state" of w-ater, and many boiler explosions have
been attributed to it. In our own experience with boilers we have never found it neces-
sary to invoke any such cause to account for explosions, for, as a general rule, they can
be exjilained in much more obvious and probable ways. Engineer Gilardi's essay on the
subject is of considerable interest, and a translation of it is given below :
" It is known that when a liquid at the ordinary temperature is poured upon a red-
hot plate of metal, instead of wetting the plate and evaporating rapidly, it assumes a
spheroidal form. The mass evaporates slowly at the surface, and is so mobile as toremind
one forcibly of a drop of quicksilver; and after a certain interval it flashes sud-
denly into vajior. This behavior is due to the fact that between the liquid drop and the
hot metallic plate an atmosphei-e of saturated steam is»formed, which has a pressure suf-
ficient to sustain the weight of the drop and prevent it from coming into direct contact
with the metal. As the metal below the dro]) gradually cools there comes a time when
the tension of the film of steam is no longer sufficient to support the liquid spheroid,
which immediately comes in contact with the plate, and is immediately converted into
vapor, transforming the heat-energy it receives into mechanical energy.
" It was formerly taught and maintained by the majority of persons that when the
liquid mass and the surface at high temperature are large, and are contained in a hermet-
ically sealed enclosure (for instance a steam boiler), the rise in pressure may be so great
as to exceed the tensile strength of the material of which the receptacle itself is made,
and bring about an explosion. And how many boiler explosions have been erroneously
attributed to this cause
" The object of the present paper is to demonstrate tjiat, even if we admit the i)ossi-
bility of Leidenfrost's phenomenon occurring in a boiler, we should have, as the necessary
result of it, a diminution of the pressure; and hence, that not one steam boiler explosion
can be ascribed to this cause.
" It will be convenient to make various hypotheses and study them separately. We
shall first assume the boiler to be fed with cold water, which comes in contact with a
plate at a temperature of 800° Centigrade [1472° Fall.], and that the spheroidal state is
not produced. In this case the water will quickly absorb the excess of heat contained in
the plate, and a corresponding production of steam will occur; the pressure in the boiler
will rise, and, if it becomes great enough, the safety-valve will open and the excess of
steam be discharged through it.
"If we next assume the spheroidal state to occur, the water will evaporate slowdy
until the temperature of the plate has fallen to 200° or 300° Centigrade [say -iWP to 600*