ELECTRICAL DEPOSITION OF SMOKE
A good deal of scientific work is being done in the way of clearing away
fog and smoke; and this, through time, may have some practical results in
removing a great source of annoyance, illness, and danger in large towns.
Sir Oliver Lodge and Dr. Aitken have been throwing light upon the
deposition of smoke in the air by means of electricity.
If an electric discharge be passed through a jar containing the smoke from
burnt magnesium wire, tobacco, brown paper, and other substances, the dust
will be deposited so as to make the air clear. Brush discharge, or
anything that electrifies the air itself, is the most expeditious.
If water be forced upwards through a vertical tube (with a nozzle
one-twentieth of an inch in diameter), it will fall to the ground in a
fine rain; but, if a piece of rubbed (electrified) sealing-wax be held a
yard distant from the place where the jet breaks into drops, they at once
fall in large spots as in a thunder-shower. If paper be put on the ground
during the experiment, the sound of pattering will be observed to be
quite different. If a kite be flown into a cloud, and made to give off
electricity for some time, that cloud will begin to condense into rain.
Experiments with Lord Kelvin's recorder show that variations in the
electrical state of the atmosphere precede a change of weather. Then, with
a very large voltaic battery, a tremendous quantity of electricity could
be poured into the atmosphere, and its electrical condition could be
certainly disturbed. If this could be made practically available, how
useful it would be to farmers when the crops were suffering from excessive
drought! It might be more powerfully available than the imagined
condensation of a cloud into rain by the reverberation caused by the
firing of a range of cannon.
But what is the practical benefit of this information? If electricity
deposits smoke, it might be made available in many ways. The fumes from
chemical works might be condensed; and the air in large cities, otherwise
polluted, might be purified and rendered innocuous. The smoke of chimneys
in manufacturing works might be prevented from entering the atmosphere at
all. In flour-mills and coal-mines the fine dust is dangerously explosive.
In lead, copper, and arsenic works, it is both poisonous and valuable.
Lead smelters labour under this difficulty of condensing the fume which
escapes along with the smoke from red-lead smelting furnaces; and it was
considered that an electrical process of condensation might be made
serviceable for the purpose. At Bagillt, the method used for collecting or
condensing the lead fume is a large flue two miles long; much is retained
in this flue, but still a visible cloud of white-lead fume continually
escapes from the top of the chimney. There is a difficulty in the way of
depositing fumes in the flue by means of a sufficient discharge of
electricity, viz. the violent draught which is liable to exist there, and
which would mechanically blow away any deposited dust.
But Dr. Aitken suggests that regenerators might be used along with the
electricity. The warm fumes might be taken to a cold depositor, where (by
the ordinary law of cold surfaces attracting warm dust-particles) the
impurities would be removed, and, when purified, the air would again be
taken through a hot regenerator before being sent up the chimney. By a
succession of these chambers, with the assistance of electric currents,
the air, impregnated with the most deleterious particles, or valuable
dust, could be rendered innocuous.
The sewage of our towns must be cleaned of its deleterious parts before
being run into the streams which give drink to the lower animals, because
an Act of Parliament enforces the process. Why, then, ought we not to have
similar compulsion for making the smoke from chemical and other noxious
works quite harmless before being thrown into the air which contains the
oxygen necessary for the life of human beings?
There seems to be a good field before electricians to catch the smoke on
the wing and deposit its dust on a large scale. This seems to be a matter
beyond our reach at present, except in the scientist's laboratory; but
certainly it is a "consummation devoutly to be wished."