Montana labor news., 1937-07-08
EMPLOYERS BAND TOGETHER TO DEFEAT
ORGANIZATION Of THE WORKING MEN
Smoke and Fume
(Ieansed by Super
Sound Wave Process

Dense clouds of fumes threatening
the greenery and freshness of a
countryside, subdued at the Shrek
of a whistlel Columns of choking
smoke darkening the skies of tenn
ing cities cleansed at the command
of a sound wavel Precious particles
of gold, silver, lead, copper and zinc,
bound skyward from the smelter
stack, knocked out of the fume and
collected as valuable by-productsl
Fragments of unburned coal and ash,
belched from factory chimneys, bent
on soiling the housewives linen or
smirching the surface of fresh paint,
diverted from its malignant course
at the behest of a "super-sonic
wave that may be of such high pitch
that you can't even hear it.
Such is the promise of a device
invented by H.. W. St. Clair, metal
lurgist, U. S. Bureau of Mines, which
will be demonstrated in the North
Interior Building Washington, D. c.,
Saturday, February 10, at 10 a. m.
The device should be of real aid in
solving the smelter-fume problem,
which has for years been the source
of expensive litigation due to suits
brought by property owners charg-
ing damage to vegetation, live stock,
and water supplies. The device
should also be of value in helping
to curb the smoke nuisance in large
cities, which has been responsible for
injury to property and health run
ming into many millions of dollars
annually.
1t has long been known that, when
sound waves are passed through a
tube containing a fine powder, the
powder will be concentrated at
points that are free from Migratory
motion. 1t has also been known that
waves of extremely high frequency
affected the diffusion of solid or
liquid particles in a gas. However,
as the Bureau of Mines points out, no
practical application has previously
been made of this knowledge.
The st. Clair method merely
passes the smoke or fume through
a tube in which standing sound
waves are established. These stand
ing waves r produced by so adj
justing the length of the tube that
waves reflected from the upper end
are in phase with the original sound
waves set up at the lower end.
In order that the process may
work at its best, the wave-length
used must be approximately equal
to the diameter of the tube. For a
tube Of practicable diameter, this
means that the frequencies used will
vary from 3 to 20 ~kilocycles per Sec
ond. A person of acute hearing can
detect wave of frequencies up to
about 5 k~ilocycles; those of greater
frequency are above the auditory
range and hence are sometimes
called 'super-sopic."
To generate sound waves of this
frequency, several types of equip
ment may be used. Mr.. st. Clair
has used what is technically known
as the magnetic strictive method, but
for purposes of popular demonstra-
ton, an acoustic generator is used.
This, in fact, is merely a shrill
whistle. The sound waves produced
by the whistle are reflected in phase
with the original waves from the top
of the tube and cause the solid
particles to fall out of the gas stream.
The action is similar to the effect
produced by drawing the bow of a
violin over a metal plate on which
dust particles r deposited, when
the vibrations cause the particles to
arrange themselves in groups.
The Bureau of Mines for many
years past has been interested in the
problem of smelter fumes. AS long
ago as 1929 it began work on the
possibility of settling smoke by
means of acoustic waves.
The installation of the process that
has now been devised should be
comparatively inexpensive, as it
uwtilizes simple sound waves instead
of the more elaborate processes en-
ployed in other fume-treatment
methods, and is therefore adaptable
to the smaller plants.
Patents covering the new process
will be applied for by members of
the staff of the Bureau of Mines for
the benefit of the public.
The process will be demonstrated
at the annual meeting of the Ameri-
can Institute of Mining and Metal
lurgical Engineers in New York next
week, the demonstration in Wash
ington being a preview for officials
of the Department of the Interior.