ELECTRICAL FURNACES
_How the Hottest Heat is Produced--Making Diamonds_
No feats of discovery, not even the search for the North Pole or
Stanley's expeditions in the heart of Africa, present more points of
fascinating interest than the attempts now being made by scientists to
explore the extreme limits of temperature. We live in a very narrow zone
in what may be called the great world of heat. The cut on the opposite
page represents an imaginary thermometer showing a few of the important
temperature points between the depths of the coldest cold and the
heights of the hottest heat--a stretch of some 10,461 degrees. We exist
in a narrow space, as you will see, varying from 100° or a little more
above the zero point to a possible 50° below; that is, we can withstand
these narrow extremes of temperature. If some terrible world catastrophe
should raise the temperature of our summers or lower that of our winters
by a very few degrees, human life would perish off the earth.
But though we live in such narrow limits, science has found ways
of exploring the great heights of heat above us and of reaching and
measuring the depths of cold below us, with the result of making many
important and interesting discoveries.
I have written in the former "Boys' Book of Inventions" of that
wonderful product of science, liquid air--air submitted to such a degree
of cold that it ceases to be a gas and becomes a liquid. This change
occurs at a temperature 312° below zero. Professor John Dewar, of
England, who has made some of the most interesting of discoveries in
the region of great cold, not only reached a temperature low enough to
produce liquid air, but he succeeded in going on down until he could
freeze this marvellous liquid into a solid--a sort of air ice. Not
content even with this astonishing degree of cold, Professor Dewar
continued his experiments until he could reduce hydrogen--that very
light gas--to a liquid, at 440° below zero, and then, strange as it may
seem, he also froze liquid hydrogen into a solid. From his experiments
he finally concluded that the "absolute zero"--that is, the place where
there is no heat--was at a point 461° below zero. And he has been able
to produce a temperature, artificially, within a very few degrees of
this utmost limit of cold.
[Illustration:
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DEGREES | |
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10000 --+ +-- Conjectural heat
| | of the sun.
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7000 --+ +-- Highest heat
| | yet obtained
| | artificially.
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3500 --+ +-- Steel boils.
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212 --+ +-- Water boils.
0 --+=+-- Zero.
461 --+=+-- Prof. Dewar's
|=| absolute zero.
{===}
|
DEGREES |
|
0 --+-- Zero.
|
40 --+-- Mercury freezes.
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|
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202 --+-- Alcohol freezes.
|
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300 --+-- Oxygen boils.
312 --+-- Liquid air boils.
320 --+-- Nitrogen boils.
|
|
|
|
|
440 --+-- Hydrogen boils.
461 --+-- Prof. Dewar's
absolute zero.]
Think what this absolute zero means. Heat, we know, like electricity and
light, is a vibratory or wave motion in the ether. The greater the heat,
the faster the vibrations. We think of all the substances around us
as solids, liquids, and gases, but these are only comparative terms. A
change of temperature changes the solid into the liquid, or the gas
into the solid. Take water, for instance. In the ordinary temperature
of summer it is a liquid, in winter it is a hard crystalline substance
called ice; apply the heat of a stove and it becomes steam, a gas. So
with all other substances. Air to us is an invisible gas, but if the
earth should suddenly drop in temperature to 312° below zero all the air
would fall in liquid drops like rain and fill the valleys of the earth
with lakes and oceans. Still a little colder and these lakes and oceans
would freeze into solids. Similarly, steel seems to us a very hard and
solid substance, but apply enough heat and it boils like water, and
finally, if the heat be increased, it becomes a gas.
Imagine, if you can, a condition in which all substances are solids;
where the vibrations known as heat have been stilled to silence; where
nothing lives or moves; where, indeed, there is an awful nothingness;
and you can form an idea of the region of the coldest cold--in other
words, the region where heat does not exist. Our frozen moon gives
something of an idea of this condition, though probably, cold and barren
as it is, the moon is still a good many degrees in temperature above the
absolute zero.
Some of the methods of exploring these depths of cold are treated in the
chapter on liquid air already referred to. Our interest here centres
in the other extreme of temperature, where the heat vibrations are
inconceivably rapid; where nearly all substances known to man become
liquids and gases; where, in short, if the experimenter could go high
enough, he could reach the awful degree of heat of the burning sun
itself, estimated at over 10,000 degrees. It is in the work of exploring
these regions of great heat that such men as Moissan, Siemens, Faure,
and others have made such remarkable discoveries, reaching temperatures
as high as 7,000, or over twice the heat of boiling steel. Their
accomplishments seem the more wonderful when we consider that a
temperature of this degree burns up or vaporises every known substance.
How, then, could these men have made a furnace in which to produce this
heat? Iron in such a heat would burn like paper, and so would brick
and mortar. It seems inconceivable that even science should be able to
produce a degree of heat capable of consuming the tools and everything
else with which it is produced.
The heat vibrations at 7,000° are so intense that nickel and platinum,
the most refractory, the most unmeltable of metals, burn like so much
bee's-wax; the best fire-brick used in lining furnaces is consumed by
it like lumps of rosin, leaving no trace behind. It works, in short, the
most marvellous, the most incredible transformations in the substances
of the earth.
Indeed, we have to remember that the earth itself was created in a
condition of great heat--first a swirling, burning gas, something like
the sun of to-day, gradually cooling, contracting, rounding, until we
have our beautiful world, with its perfect balance of gases, liquids,
solids, its splendid life. A dying volcano here and there gives faint
evidence of the heat which once prevailed over all the earth.
It was in the time of great heat that the most beautiful and wonderful
things in the world were wrought. It was fierce heat that made the
diamond, the sapphire, and the ruby; it fashioned all of the most
beautiful forms of crystals and spars; and it ran the gold and silver
of the earth in veins, and tossed up mountains, and made hollows for the
seas. It is, in short, the temperature at which worlds were born.
More wonderful, if possible, than the miracles wrought by such heat is
the fact that men can now produce it artificially; and not only produce,
but confine and direct it, and make it do their daily service. One asks
himself, indeed, if this can really be; and it was under the impulse of
some such incredulity that I lately made a visit to Niagara Falls, where
the hottest furnaces in the world are operated. Here clay is melted in
vast quantities to form aluminium, a metal as precious a few years ago
as gold. Here lime and carbon, the most infusible of all the elements,
are joined by intense heat in the curious new compound, calcium carbide,
a bit of which dropped in water decomposes almost explosively, producing
the new illuminating gas, acetylene. Here, also, pure phosphorus and
the phosphates are made in large quantities; and here is made
carborundum--gem-crystals as hard as the diamond and as beautiful as the
ruby.
An extensive plant has also been built to produce the heat necessary to
make graphite such as is used in your lead-pencils, and for lubricants,
stove-blacking, and so on. Graphite has been mined from the earth for
thousands of years; it is pure carbon, first cousin to the diamond. Ten
years ago the possibility of its manufacture would have been scouted as
ridiculous; and yet in these wonderful furnaces, which repeat so nearly
the processes of creation, graphite is as easily made as soap.
The marvel-workers at Niagara Falls have not yet been able to make
diamonds--in quantities. The distinguished French chemist Moissan has
produced them in his laboratory furnaces--small ones, it is true, but
diamonds; and one day they may be shipped in peck boxes from the
great furnaces at Niagara Falls. This is no mere dream; the commercial
manufacture of diamonds has already had the serious consideration
of level-headed, far-seeing business men, and it may be accounted a
distinct probability. What revolution the achievement of it would work
in the diamond trade as now constituted and conducted no one can say.
These marvellous new things in science and invention have been made
possible by the chaining of Niagara to the wheels of industry. The power
of the falling water is transformed into electricity. Electricity and
heat are both vibratory motions of the ether; science has found that the
vibrations known as electricity can be changed into the vibrations known
as heat. Accordingly, a thousand horse-power from the mighty river is
conveyed as electricity over a copper wire, changed into heat and light
between the tips of carbon electrodes, and there works its wonders. In
principle the electrical furnace is identical with the electric light.
It is scarcely twenty years since the first electrical furnaces of
real practical utility were constructed; but if the electrical furnaces
to-day in operation at Niagara Falls alone were combined into one, they
would, as one scientist speculates, make a glow so bright that it could
be seen distinctly from the moon--a hint for the astronomers who are
seeking methods for communicating with the inhabitants of Mars. One
furnace has been built in which an amount of heat energy equivalent to
700 horse-power is produced in an arc cavity not larger than an ordinary
water tumbler.
On reaching Niagara Falls, I called on Mr. E. G. Acheson, whose name
stands with that of Moissan as a pioneer in the investigation of high
temperatures. Mr. Acheson is still a young man--not more than forty-five
at most--and clean-cut, clear-eyed, and genial, with something of the
studious air of a college professor. He is pre-eminently a self-made
man. At twenty-four he found a place in Edison's laboratory--"Edison's
college of inventions," he calls it--and, at twenty-five, he was one
of the seven pioneers in electricity who (in 1881-82) introduced the
incandescent lamp in Europe. He installed the first electric-light
plants in the cities of Milan, Genoa, Venice, and Amsterdam, and during
this time was one of Edison's representatives in Paris.
[Illustration: Mr. E. G. Acheson, One of the Pioneers in the
Investigation of High Temperatures.]
"I think the possibility of manufacturing genuine diamonds," he said to
me, "has dazzled more than one young experimenter. My first efforts in
this direction were made in 1880. It was before we had command of the
tremendous electric energy now furnished by the modern dynamo, and when
the highest heat attainable for practical purposes was obtained by
the oxy-hydrogen flame. Even this was at the service of only a few
experimenters, and certainly not at mine. My first experiments were made
in what I might term the 'wet way'; that is, by the process of chemical
decomposition by means of an electric current. Very interesting results
were obtained, which even now give promise of value; but the diamond did
not materialise.
"I did not take up the subject again until the dynamo had attained high
perfection and I was able to procure currents of great power. Calling in
the aid of the 6,500 degrees Fahrenheit or more of temperature produced
by these electric currents, I once more set myself to the solution of
the problem. I now had, however, two distinct objects in view: first,
the making of a diamond; and, second, the production of a hard substance
for abrasive purposes. My experiments in 1880 had resulted in producing
a substance of extreme hardness, hard enough, indeed, to scratch the
sapphire--the next hardest thing to the diamond--and I saw that such a
material, cheaply made, would have great value.
"My first experiment in this new series was of a kind that would have
been denounced as absurd by any of the old-school book-chemists, and had
I had a similar training, the probability is that I should not have made
such an investigation. But 'fools rush in where angels fear to tread,'
and the experiment was made."
This experiment by Mr. Acheson, extremely simple in execution, was
the first act in rolling the stone from the entrance to a veritable
Aladdin's cave, into which a multitude of experimenters have passed in
their search for nature's secrets; for, while the use of the electrical
furnace in the reduction of metals--in the breaking down of nature's
compounds--was not new, its use for synthetic chemistry--for the putting
together, the building up, the formation of compounds--was entirely
new. It has enabled the chemist not only to reproduce the compounds of
nature, but to go further and produce valuable compounds that are wholly
new and were heretofore unknown to man. Mr. Acheson conjectured that
carbon, if made to combine with clay, would produce an extremely hard
substance; and that, having been combined with the clay, if it should
in the cooling separate again from the clay, it would issue out of the
operation as diamond. He therefore mixed a little clay and coke
dust together, placed them in a crucible, inserted the ends of two
electric-light carbons into the mixture, and connected the carbons with
a dynamo. The fierce heat generated at the points of the carbons fused
the clay, and caused portions of the carbon to dissolve. After cooling,
a careful examination was made of the mass, and a few small purple
crystals were found. They sparkled with something of the brightness
of diamonds, and were so hard that they scratched glass. Mr. Acheson
decided at once that they could not be diamonds; but he thought they
might be rubies or sapphires. A little later, though, when he had made
similar crystals of a larger size, he found that they were harder than
rubies, even scratching the diamond itself. He showed them to a number
of expert jewellers, chemists, and geologists. They had so much the
appearance of natural gems that many experts to whom they were submitted
without explanation decided that they must certainly be of natural
production. Even so eminent an authority as Geikie, the Scotch
geologist, on being told, after he had examined them, that the crystals
were manufactured in America, responded testily: "These Americans! What
won't they claim next? Why, man, those crystals have been in the earth a
million years."
Mr. Acheson decided at first that his crystals were a combination of
carbon and aluminium, and gave them the name carborundum. He at once
set to work to manufacture them in large quantities for use in making
abrasive wheels, whetstones, and sandpaper, and for other purposes for
which emery and corundum were formerly used. He soon found by chemical
analysis, however, that carborundum was not composed of carbon and
aluminium, but of carbon and silica, or sand, and that he had, in fact,
created a new substance; so far as human knowledge now extends, no such
combination occurs anywhere in nature. And it was made possible only
by the electrical furnace, with its power of producing heat of untold
intensity.
[Illustration: The Furnace-Room, where Carborundum is Made.
"_A great, dingy brick building, open at the sides like a shed._"]
In order to get a clear understanding of the actual workings of
the electrical furnace, I visited the plant where Mr. Acheson makes
carborundum. The furnace-room is a great, dingy brick building, open at
the sides like a shed. It is located only a few hundred yards from the
banks of the Niagara River and well within the sound of the great falls.
Just below it, and nearer the city, stands the handsome building of
the Power Company, in which the mightiest dynamos in the world whir
ceaselessly, day and night, while the waters of Niagara churn in the
water-wheel pits below. Heavy copper wires carrying a current of 2,200
volts lead from the power-house to Mr. Acheson's furnaces, where the
electrical energy is transformed into heat.
There are ten furnaces in all, built loosely of fire-brick, and fitted
at each end with electrical connections. And strange they look to
one who is familiar with the ordinary fuel furnace, for they have no
chimneys, no doors, no drafts, no ash-pits, no blinding glow of heat
and light. The room in which they stand is comfortably cool. Each time
a furnace is charged it is built up anew; for the heat produced is so
fierce that it frequently melts the bricks together, and new ones must
be supplied. There were furnaces in many stages of development. One had
been in full blast for nearly thirty hours, and a weird sight it was.
The top gave one the instant impression of the seamy side of a volcano.
The heaped coke was cracked in every direction, and from out of the
crevices and depressions and from between the joints of the loosely
built brick walls gushed flames of pale green and blue, rising upward,
and burning now high, now low, but without noise beyond a certain low
humming. Within the furnace--which was oblong in shape, about the height
of a man, and sixteen feet long by six wide--there was a channel, or
core, of white-hot carbon in a nearly vaporised state. It represented
graphically in its seething activity what the burning surface of the sun
might be--and it was almost as hot. Yet the heat was scarcely manifest a
dozen feet from the furnace, and but for the blue flames rising from
the cracks in the envelope, or wall, one might have laid his hand almost
anywhere on the bricks without danger of burning it.
[Illustration: Taking Off a Crust of the Furnace at Night.
_The light is so intense that you cannot look at it without hurting the
eyes._]
In the best modern blast-furnaces, in which the coal is supplied with
special artificial draft to make it burn the more fiercely, the heat may
reach 3,000 degrees Fahrenheit. This is less than half of that produced
in the electrical furnace. In porcelain kilns, the potters, after hours
of firing, have been able to produce a cumulative temperature of as much
as 3,300 degrees Fahrenheit; and this, with the oxy-hydrogen flame (in
which hydrogen gas is spurred to greater heat by an excess of oxygen),
is the very extreme of heat obtainable by any artificial means except
by the electrical furnace. Thus the electrical furnace has fully doubled
the practical possibilities in the artificial production of heat.
Mr. Fitzgerald, the chemist of the Acheson Company, pointed out to me a
curious glassy cavity in one of the half-dismantled furnaces. "Here the
heat was only a fraction of that in the core," he said. But still
the fire-brick--and they were the most refractory produced in this
country--had been melted down like butter. The floors under the furnace
were all made of fire-brick, and yet the brick had run together until
they were one solid mass of glassy stone. "We once tried putting a
fire-brick in the centre of the core," said Mr. Fitzgerald, "just to
test the heat. Later, when we came to open the furnace, we couldn't find
a vestige of it. The fire had totally consumed it, actually driving it
all off in vapour."
Indeed, so hot is the core that there is really no accurate means of
measuring its temperature, although science has been enabled by various
curious devices to form a fairly correct estimate. The furnace has a
provoking way of burning up all of the thermometers and heat-measuring
devices which are applied to it. A number of years ago a clever German,
named Segar, invented a series of little cones composed of various
infusible earths like clay and feldspar. He so fashioned them that one
in the series would melt at 1,620 degrees Fahrenheit, another at 1,800
degrees, and so on up. If the cones are placed in a pottery kiln, the
potter can tell just what degree of temperature he has reached by the
melting of the cones one after another. But in Mr. Acheson's electrical
furnaces all the cones would burn up and disappear in two minutes. The
method employed for coming at the heat of the electrical furnace,
in some measure, is this: a thin filament of platinum is heated red
hot--1,800 degrees Fahrenheit--by a certain current of electricity. A
delicate thermometer is set three feet away, and the reading is taken.
Then, by a stronger current, the filament is made white hot--3,400
degrees Fahrenheit--and the thermometer moved away until it reads the
same as it read before. Two points in a distance-scale are thus
obtained as a basis of calculation. The thermometer is then tried by
an electrical furnace. To be kept at the same marking it must be placed
much farther away than in either of the other instances. A simple
computation of the comparative distances with relation to the two
well-ascertained temperatures gives approximately, at least, the
temperature of the electrical furnace. Some other methods are also
employed. None is regarded as perfectly exact; but they are near enough
to have yielded some very interesting and valuable statistics regarding
the power of various temperatures. For instance, it has been found
that aluminium becomes a limpid liquid at from 4,050 to 4,320 degrees
Fahrenheit, and that lime melts at from 4,940 to 5,400 degrees, and
magnesia at 4,680 degrees.
There are two kinds of electrical furnaces, as there are two kinds of
electric lights--arc and incandescent. Moissan has used the arc furnace
in all of his experiments, but Mr. Acheson's furnaces follow rather the
principle of the incandescent lamp. "The incandescent light," said
Mr. Fitzgerald, "is produced by the resistance of a platinum wire or a
carbon filament to the passage of a current of electricity. Both light
and heat are given off. In our furnace, the heat is produced by the
resistance of a solid cylinder or core of pulverised coke to the passage
of a strong current of electricity. When the core becomes white hot it
causes the materials surrounding it to unite chemically, producing the
carborundum crystals."
The materials used are of the commonest--pure white sand, coke, sawdust,
and salt. The sand and coke are mixed in the proportions of sixty to
forty, the sawdust is added to keep the mixture loose and open, and the
salt to assist the chemical combination of the ingredients. The furnace
is half filled with this mixture, and then the core of coke, twenty-one
inches in diameter, is carefully moulded in place. This core is sixteen
feet long, reaching the length of the furnace, and connecting at
each end with an immense carbon terminal, consisting of no fewer than
twenty-five rods of carbon, each four inches square and nearly three
feet long. These terminals carry the current into the core from huge
insulated copper bars connected from above. When the core is complete,
more of the carborundum mixture is shovelled in and tramped down until
the furnace is heaping full.
Everything is now ready for the electric current. The wires from the
Niagara Falls power-plant come through an adjoining building, where one
is confronted, upon entering, with this suggestive sign:
DANGER
2,200 Volts.
Tesla produces immensely higher voltages than this for laboratory
experiments, but there are few more powerful currents in use in this
country for practical purposes. Only about 2,000 volts are required for
executing criminals under the electric method employed in New York; 400
volts will run a trolley-car. It is hardly comfortable to know that a
single touch of one of the wires or switches in this room means almost
certain death. Mr. Fitzgerald gave me a vivid demonstration of the
terrific destructive force of the Niagara Falls current. He showed me
how the circuit was broken. For ordinary currents, the breaking of a
circuit simply means a twist of the wrist and the opening of a brass
switch. Here, however, the current is carried into a huge iron tank full
of salt water. The attendant, pulling on a rope, lifts an iron plate
from the tank. The moment it leaves the water, there follow a rumbling
crash like a thunder-clap, a blinding burst of flame, and thick clouds
of steam and spray. The sight and sound of it make you feel delicate
about interfering with a 2,200-volt current.
[Illustration: The Interior of a Furnace as it Appears after the
Carborundum has been Taken Out.]
This current is, indeed, too strong in voltage for the furnaces, and
it is cut down, by means of what were until recently the largest
transformers in the world, to about 100 volts, or one-fourth the
pressure used on the average trolley line. It is now, however, a current
of great intensity--7,500 ampères, as compared with the one-half ampère
used in an incandescent lamp; and it requires eight square inches of
copper and 400 square inches of carbon to carry it.
Within the furnace, when the current is turned on, a thousand
horse-power of energy is continuously transformed into heat. Think of
it! Is it any wonder that the temperature goes up? And this is continued
for thirty-six hours steadily, until 36,000 "horse-power hours" are used
up and 7,000 pounds of the crystals have been formed. Remembering that
36,000 horse-power hours, when converted into heat, will raise 72,000
gallons of water to the boiling point, or will bring 350 tons of iron up
to a red heat, one can at least have a sort of idea of the heat evolved
in a carborundum furnace.
When the coke core glows white, chemical action begins in the mixture
around it. The top of the furnace now slowly settles, and cracks in
long, irregular fissures, sending out a pungent gas which, when lighted,
burns lambent blue. This gas is carbon monoxide, and during the process
nearly six tons of it are thrown off and wasted. It seems, indeed, a
somewhat extravagant process, for fifty-six pounds of gas are produced
for every forty of carborundum.
"It is very distinctly a geological condition," said Mr. Fitzgerald;
"crystals are not only formed exactly as they are in the earth, but we
have our own little earthquakes and volcanoes." Not infrequently gas
collects, forming a miniature mountain, with a crater at its summit, and
blowing a magnificent fountain of flame, lava, and dense white vapour
high into the air, and roaring all the while in a most terrifying
manner. The workmen call it "blowing off."
[Illustration: Blowing Off.
"_Not infrequently gas collects, forming a miniature mountain, with a
crater at its summit, and blowing a magnificent fountain of flame, lava,
and dense white vapour high into the air, and roaring all the while in a
most terrifying manner._"]
At the end of thirty-six hours the current is cut off, and the furnace
is allowed to cool, the workmen pulling down the brick as rapidly as
they dare. At the centre of the furnace, surrounding the core, there
remains a solid mass of carborundum as large in diameter as a hogshead.
Portions of this mass are sometimes found to be composed of pure,
beautifully crystalline graphite. This in itself is a surprising
and significant product, and it has opened the way directly to
graphite-making on a large scale. An important and interesting feature
of the new graphite industry is the utilisation it has effected of
a product from the coke regions of Pennsylvania which was formerly
absolute waste.
To return to carborundum: when the furnace has been cooled and the walls
torn away, the core of carborundum is broken open, and the beautiful
purple and blue crystals are laid bare, still hot. The sand and the coke
have united in a compound nearly as hard as the diamond and even more
indestructible, being less inflammable and wholly indissoluble in even
the strongest acids. After being taken out, the crystals are crushed to
powder and combined in various forms convenient for the various uses for
which it is designed.
I asked Mr. Acheson if he could make diamonds in his furnaces.
"Possibly," he answered, "with certain modifications." Diamonds, as he
explained, are formed by great heat and great pressure. The great heat
is now easily obtained, but science has not yet learned nature's secret
of great pressure. Moissan's method of making diamonds is to dissolve
coke dust in molten iron, using a carbon crucible into which the
electrodes are inserted. When the whole mass is fluid, the crucible and
its contents are suddenly dashed into cold water or melted lead. This
instantaneous cooling of the iron produces enormous pressure, so that
the carbon is crystallised in the form of diamond.
But whatever it may or may not yet be able to do in the matter of
diamond-making, there can be no doubt that the possibilities of the
electrical furnace are beyond all present conjecture. With American
inventors busy in its further development, and with electricity as cheap
as the mighty power of Niagara can make it, there is no telling what
new and wonderful products, now perhaps wholly unthought-of by the human
race, it may become possible to manufacture, and manufacture cheaply.