Whether it be that the press and general public are growing more enlightened in matters of science, or that Professor Rontgen"s discovery appeals in a peculiar way to the popular imagination, it has certainly evoked a livelier and more sudden interest than either the telephone, microphone, or phonograph. I was present when Lord Kelvin first announced the invention of the telephone to a British audience, and showed the instrument itself, but the intelligence was received so apathetically that I suspect its importance was hardly realised. It fell to my own lot, a few years afterwards, to publish the first account of the phonograph in this country, and I remember that, between incredulity on the one hand, and perhaps lack of scientific interest on the other, a considerable time elapsed before the public at large were really impressed by the invention. Perhaps the uncanny and mysterious results of Rontgen"s discovery, which seem to link it with the "black arts," have something to do with the quickness of its reception by all manner of people.
Like most, if not all, discoveries and inventions, it is the outcome of work already done by other men. In the early days of electricity it was found that when an electric spark from a frictional machine was sent through a gla.s.s bulb from which the air had been sucked by an air pump, a cloudy light filled the bulb, which was therefore called an "electric egg". Hittorf and others improved on this effect by employing the spark from an induction coil and large tubes, highly exhausted of air, or containing a rare infusion of other gases, such as hydrogen. By this means beautiful glows of various colours, resembling the tender hues of the tropical sky, or the fleeting tints of the aurora borealis, were produced, and have become familiar to us in the well-known Geissler tubes.
Crookes, the celebrated English chemist, went still further, and by exhausting the bulbs with an improved Sprengel air-pump, obtained an extremely high vacuum, which gave remarkable effects (page 120). The diffused glow or cloudy light of the tube now shrank into a single stream, which joined the sparking points inserted through the ends of the tube as with a luminous thread A magnet held near the tube bent the streamer from its course; and there was a dark s.p.a.ce or gap in it near the negative point or cathode, from which proceeded invisible rays, having the property of impressing a photographic plate, and of rendering matter in general on which they impinged phosph.o.r.escent, and, in course of time, red-hot. Where they strike on the gla.s.s of the tube it is seen to glow with a green or bluish phosph.o.r.escence, and it will ultimately soften with heat.
These are the famous "cathode rays" of which we have recently heard so much. Apparently they cannot be produced except in a very high vacuum, where the pressure of the air is about 1-100th millionth of an atmosphere, or that which it is some 90 or 100 miles above the earth. Mr Crookes regards them as a stream of airy particles electrified by contact with the cathode or negative discharging point, and repelled from it in straight lines. The rarity of the air in the tube enables these particles to keep their line without being jostled by the other particles of air in the tube. A molecular bombardment from the cathode is, in his opinion, going on, and when the shots, that is to say, the molecules of air, strike the wall of the tube, or any other body within the tube, the shock gives rise to phosph.o.r.escence or fluorescence and to heat. This, in brief, is the celebrated hypothesis of "radiant matter," which has been supported in the United Kingdom by champions such as Lord Kelvin, Sir Gabriel Stokes, and Professor Fitzgerald, but questioned abroad by Goldstem, Jaumann, Wiedemann, Ebert, and others.
Lenard, a young Hungarian, pupil of the ill.u.s.trious Heinrich Hertz, was the first to inflict a serious blow on the hypothesis, by showing that the cathode rays could exist outside the tube in air at ordinary pressure. Hertz had found that a thin foil of aluminium was penetrated by the rays, and Lenard made a tube having a "window" of aluminium, through which the rays darted into the open air. Their path could be traced by the bluish phosph.o.r.escence which they excited in the air, and he succeeded in getting them to penetrate a thin metal box and take a photograph inside it. But if the rays are a stream of radiant matter which can only exist in a high vacuum, how can they survive in air at ordinary pressure? Lenard"s experiments certainly favour the hypothesis of their being waves in the luminiferous ether.
Professor Rontgen, of Wirzburg, profiting by Lenard"s results, accidentally discovered that the rays coming from a Crookes tube, through the gla.s.s itself, could photograph the bones in the living hand, coins inside a purse, and other objects covered up or hid in the dark. Some bodies, such as flesh, paper, wood, ebonite, or vulcanised fibre, thin sheets of metal, and so on, are more or less transparent, and others, such as bones, carbon, quartz, thick plates of metal, are more or less opaque to the rays. The human hand, for example, consisting of flesh and bones, allows the rays to pa.s.s easily through the flesh, but not through the bones.
Consequently, when it is interposed between the rays and a photographic plate, the skeleton inside is photographed on the plate. A lead pencil photographed in this way shows only the black lead, and a razor with a horn handle only the blade.
Thanks to the courtesy of Mr. A. A. Campbell Swinton, of the firm of Swinton & Stanton, the well-known electrical engineers, of Victoria Street, Westminster, a skilful experimentalist, who was the first to turn to the subject in England, I have witnessed the taking of these "shadow photographs," as they are called, somewhat erroneously, for "radiographs" or "cryptographs" would be a better word, and shall briefly describe his method. Rontgen employs an induction coil insulated in oil to excite the Crookes tube and yield the rays, but Mr. Swinton uses a "high frequency current,"
obtained from apparatus similar to that of Tesla, and shown in figure 100, namely, a high frequency induction coil insulated by means of oil and excited by the continuous discharge of twelve half-gallon Leyden jars charged by an alternating current at a pressure of 20,000 volts produced by an ordinary large induction coil sparking across its high pressure terminals.
A vacuum bulb connected between the discharge terminals of the high frequency coil, as shown in figure 101, was illuminated with a pink glow, which streamed from the negative to the positive pole--that is to say, the cathode to the anode, and the gla.s.s became luminous with bluish phosph.o.r.escence and greenish fluorescence. Immediately under the bulb was placed my naked hand resting on a photographic slide containing a sensitive bromide plate covered with a plate of vulcanised fibre. An exposure of five or ten minutes is sufficient to give a good picture of the bones, as will be seen from the frontispiece.
The term "shadow" photograph requires a word of explanation. The bones do not appear as flat shadows, but rounded like solid bodies, as though the active rays pa.s.sed through their substance.
According to Rontgen, these "x" rays, as he calls them, are not true cathode rays, partly because they are not deflected by a magnet, but cathode rays transformed by the gla.s.s of the tube; and they are probably not ultra-violet rays, because they are not refracted by water or reflected from surfaces. He thinks they are the missing "longitudinal" rays of light whose existence has been conjectured by Lord Kelvin and others--that is to say, waves in which the ether sways to and fro along the direction of the ray, as in the case of sound vibrations, and not from side to side across it as in ordinary light.
Be this as it may, his discovery has opened up a new field of research and invention. It has been found that the immediate source of the rays is the fluorescence and phosph.o.r.escence of the gla.s.s, and they are more effective when the fluorescence is greenish-yellow or canary colour. Certain salts--for example, the sulphates of zinc and of calcium, barium platino-cyanide, tungstate of calcium, and the double sulphate of uranyle and pota.s.sium--are more active than gla.s.s, and even emit the rays after exposure to ordinary light, if not also in the dark.
Salvioni of Perugia has invented a "cryptoscope," which enables us to see the hidden object without the aid of photography by allowing the rays to fall on a plate coated with one of these phosph.o.r.escent substances. Already the new method has been applied by doctors in examining malformations and diseases of the bones or internal organs, and in localising and extracting bullets, needles, or other foreign matters in the body. There is little doubt that it will be very useful as an adjunct to hospitals, especially in warfare, and, if the apparatus can be reduced in size, it will be employed by ordinary pract.i.tioners. It has also been used to photograph the skeleton of a mummy, and to detect true from artificial gems. However, one cannot now easily predict its future value, and applications will be found out one after another as time goes on.
CHAPTER X.
THE WIRELESS TELEGRAPH.
Magnetic waves generated in the ether (see pp. 53-95) by an electric current flowing in a conductor are not the only waves which can be set up in it by aid of electricity. A merely stationary or "static" charge of electricity on a body, say a bra.s.s ball, can also disturb the ether; and if the strength of the charge is varied, ether oscillations or waves are excited. A simple way of producing these "electric waves" in the ether is to vary the strength of charge by drawing sparks from the charged body. Of course this can be done according to the Morse code; and as the waves after travelling through the ether with the speed of light are capable of influencing conductors at a distance, it is easy to see that signals can be sent in this way. The first to do so in a practical manner was Signer Marconi, a young Italian hitherto unknown to fame. In carrying out his invention, Marconi made use of facts well known to theoretical electricians, one of whom, Dr, Oliver J. Lodge, had even sent signals with them in 1894; but it often happens in science as in literature that the recognised professors, the men who seem to have everything in their favour--knowledge, even talent--the men whom most people would expect to give us an original discovery or invention, are beaten by an outsider whom n.o.body heard of, who had neither learning, leisure, nor apparatus, but what he could pick up for himself.
Marconi produces his waves in the ether by electric sparks pa.s.sing between four bra.s.s b.a.l.l.s, a device of Professor Righi, following the cla.s.sical experiments of Heinrich Hertz. The b.a.l.l.s are electrified by connecting them to the well-known instrument called an induction coil, sometimes used by physicians to administer gentle shocks to invalids; and as the working of the coil is started and stopped by an ordinary telegraph key for interrupting the electric current, the sparking can be controlled according to the Morse code. In our diagram, which explains the apparatus, the four b.a.l.l.s are seen at D, the inner and larger pair being partly immersed in vaseline oil, the outer and smaller pair being connected to the secondary or induced circuit of the induction coil C, which is represented by a wavy line. The primary or inducing circuit of the coil is connected to a battery B through a telegraph signalling key K, so that when this key is opened and closed by the telegraphist according to the Morse code, the induction coil is excited for a longer or shorter time by the current from the battery, in agreement with the longer and shorter signals of the message. At the same time longer or shorter series of sparks corresponding to these signals pa.s.s across the gaps between the four b.a.l.l.s, and give rise to longer or shorter series of etheric waves represented by the dotted line. So much for the "Transmitter." But how does Marconi transform these invisible waves into visible or audible signals at the distant place? He does this by virtue of a property discovered by Mr. S. A. Varley as far back as 1866, and investigated by Mr. E. Branly in 1889.
They found that powder of metals, carbon, and other conductors, while offering a great resistance to the pa.s.sage of an electric current when in a loose state, coheres together when electric waves act upon it, and opposes much less resistance to the electric current. It follows that if a Morse telegraph instrument at the distant place be connected in circuit with a battery and some loose metal dust, it can be adjusted to work when the etheric waves pa.s.s through the dust, and only then. In the diagram R is this Morse "Receiver" joined in circuit with a battery B1; and a thin layer of nickel and silver dust, mixed with a trace of mercury, is placed between two cylindrical k.n.o.bs or "electrodes"
of silver fused into the gla.s.s tube d, which is exhausted of air like an electric glow lamp. Now, when the etheric waves proceeding from the transmitting station traverse the gla.s.s of the tube and act upon the metal dust, the current of the battery B1 works the Morse receiver, and marks the signals in ink on a strip of travelling paper. Inasmuch as the dust tends to stick together after a wave pa.s.ses through it, however, it requires to be shaken loose after each signal, and this is done by a small round hammer head seen on the right, which gives a slight tap to the tube. The hammer is worked by a small electromagnet E, connected to the Morse instrument, and another battery b in what is called a "relay" circuit; so that after the Morse instrument marks a signal, the hammer makes a tap on the tube. As this tap has a bell-like sound, the telegraphist can also read the signals of the message by his ear.
Two "self-induction bobbins," L Ll, a well-known device of electricians for opposing resistance to electric waves, are included in the circuit of the Morse instrument the better to confine the action of the waves to the powder in the tube.
Further, the tube d is connected to two metal conductors V Vl, which may be compared to resonators in music. They can be adjusted or attuned to the electric waves as a string or pipe is to sonorous waves. In this way the receiver can be made to work only when electric waves of a certain rate are pa.s.sing through the tube, just as a tuning-fork resounds to a certain note; it being understood that the length of the waves can be regulated by adjusting the b.a.l.l.s of the transmitter. As the etheric waves produced by the sparks, like ripples of water caused by dropping a stone into a pool, travel in all directions from the b.a.l.l.s, a single transmitter can work a number of receivers at different stations, provided these are "tuned" by adjusting the conductors V Vl to the length of the waves.
This indeed was the condition of affairs at the time when the young Italian transmitted messages from France to England in March, 1899, and it is a method that since has been found useful over limited distances. But to the inventor there seemed no reason why wireless telegraphy should be limited by any such distances.
Accordingly he immediately developed his method and his apparatus, having in mind the transmission of signals over considerable intervals. The first question that arose was the effect of the curvature of the Earth and whether the waves follow the surface of the Earth or were propagated in straight lines, which would require the erection of aerial towers and wires of considerable height. Then there was the question of the amount of power involved and whether generators or other devices could be used to furnish waves of sufficient intensity to traverse considerable distances.
Little by little progress was made and in January, 1901, wireless communication was established between the Isle of Wight and Lizard in Cornwall, a distance of 186 miles with towers less than 300 feet in height, so that it was demonstrated that the curvature of the Earth did not seriously affect the transmission of the waves, as towers at least a mile high would have been required in case the waves were so cut off. This was a source of considerable encouragement to Marconi, and his apparatus was further improved so that the resonance of the circuit and the variation of the capacity of the primary circuit of the oscillation transformer made for increased efficiency. The coherer was still retained and by the end of 1900 enough had been accomplished to warrant Marconi in arranging for trans-Atlantic experiments between Poldhu, Cornwall and the United States, stations being located on Cape Cod and in Newfoundland. The trans-Atlantic transmission of signals was quite a different matter from working over 100 miles or so in Great Britain. The single aerial wire was supplanted by a set of fifty almost vertical wires, supported at the top by a horizontal wire stretched between two masts 157 1/2 feet high and 52 1/2 feet apart, converging together at the lower end in the shape of a large fan. The capacity of the condenser was increased and instead of the battery a small generator was employed so that a spark 1 1/2 inches in length would be discharged between spheres 3 inches in diameter. At the end of the year 1901 temporary stations at Newfoundland were established and experiments were carried on with aerial wires raised in the air by means of kites. It was here realized that various refinements in the receiving apparatus were necessary, and instead of the coherer a telephone was inserted in the secondary circuit of the oscillation transformer, and with this device on February 12th the first signals to be transmitted across the Atlantic were heard. These early experiments were seriously affected by the fact that the antennae or aerial wires were constantly varying in height with the movement of the kites, and it was found that a permanent arrangement of receiving wires, independent of kites or balloons, was essential. Yet it was demonstrated at this time that the transmission of electric waves and their detection over distances of 2000 miles was distinctly possible.
A more systematic and thorough test occurred in February, 1902, when a receiving station was installed on the steamship Philadelphia, proceeding from Southampton to New York. The receiving aerial was rigged to the mainmast, the top of which was 197 feet above the level of the sea, and a syntonic receiver was employed, enabling the signals to be recorded on the tape of an ordinary Morse recorder. On this voyage readable messages were received from Poldhu up to a distance of 1551 miles, and test letters were received as far as 2099 miles. It was on this voyage that Marconi made the interesting discovery of the effect of sunlight on the propagation of electric waves over great distances. He found that the waves were absorbed during the daytime much more than at night and he eventually reached the conclusion that the ultraviolet light from the sun ionized the gaseous molecules of the air, and ionized air absorbs the energy of the electric waves, so that the fact was established that clear sunlight and blue skies, though transparent to light, serve as a fog to the powerful Hertzian waves of wireless telegraphy. For that reason the transmission of messages is carried on with greater facility on the sh.o.r.es of England and Newfoundland across the North Atlantic than in the clearer atmosphere of lower lat.i.tudes. But atmospheric conditions do not affect all forms of waves the same, and long waves with small amplitudes are far less subject to the effect of daylight than those of large amplitude and short wave length, and generators and circuits were arranged to produce the former. But the difficulty did not prove insuperable, as Marconi found that increasing the energy of the transmitting station during the daytime would more than make up for the loss of range.
The experiments begun at Newfoundland were transferred to Nova Scotia, and at Glace Bay in 1902 was established a station from which messages were transmitted and experimental work carried on until its work was temporarily interrupted by fire in 1909. Here four wooden lattice towers, each 210 feet in height, were built at the corner of a square 200 feet on a side, and a conical arrangement of 400 copper wires supported on stays between the tops of the towers and connected in the middle at the generating station was built. Additional machinery was installed and at the same time a station at Cape Cod for commercial work was built. In December, 1902, regular communication was established between Glace Bay and Poldhu, but it was only satisfactory from Canada to England as the apparatus at the Poldhu station was less powerful and efficient than that installed in Canada. The transmission of a message from President Roosevelt to King Edward marked the practical beginning of trans-Atlantic wireless telegraphy. By this time a new device for the detection of messages was employed, as the coherer we have described even in its improved forms was found to possess its limitations of sensitiveness and did not respond satisfactorily to long distance signals. A magnetic detector was devised by Marconi while other inventors had contrived electrolytic, mercurial, thermal, and other forms of detector, used for the most part with a telephone receiver in order to detect minute variations in the current caused by the reception of the electro-magnetic waves. With one of Marconi"s magnetic detectors signals from Cape Cod were read at Poldhu.
In 1903 wireless telegraphy had reached such a development that the transmission of news messages was attempted in March and April of that year. But the service was suspended, owing to defects which manifested themselves in the apparatus, and in the meantime a new station in Ireland was erected. But there was no cessation of the practical experiments carried on, and in 1903 the Cunard steamship Lucania received, during her entire voyage across from New York to Liverpool, news transmitted direct from sh.o.r.e to sh.o.r.e. In the meantime intercommunication between ships had been developed and the use of wireless in naval operations was recognized as a necessity.
Various improvements from time to time were made in the aerial wires, and in 1905 a number of horizontal wires were connected to an aerial of the inverted cone type previously used. The directional aerial with the horizontal wires was tried at Glace Bay, and adopted for all the long distance stations, affording considerable strengthening of the received signals at Poldhu stations. Likewise improvements in the apparatus were effected at both trans-Atlantic stations, consisting of the adoption of air condensers composed of insulated metallic plate suspended in the air, which were found much better than the condensers where gla.s.s was previously used to separate the plates. For producing the energy employed for transmitting the signals a high tension continuous current dynamo is used. An oscillatory current of high potential is produced in a circuit which consists of rapidly rotating disks in connection with the dynamo and suitable condensers.
The production of electric oscillations can be accomplished in several ways and waves of the desired frequency and amplitude produced. Thus in 1903 it was found by Poulsen, elaborating on a principle first discovered by Duddell, that an oscillatory current may be derived from an electric arc maintained under certain conditions and that undamped high frequency waves so produced were suitable for wireless telegraphy. This discovery was of importance, as it was found that the waves so generated were undamped, that is, capable of proceeding to their destination without loss of amplitude. On this account they were especially suitable for wireless telephony where they were early applied, as it was found possible so to arrange a circuit with an ordinary microphone transmitter that the amplitude of the waves would be varied in harmony with the vibrations of the human voice. These waves so modulated could be received by some form of sensitive wave detector at a distant station and reproduced in the form of sound with an ordinary telephone receiver. With undamped waves from the arc and from special forms of generators wireless telephony over distances as great as 200 miles has been accomplished and over shorter distances, especially at sea and for sea to sh.o.r.e, communication has found considerable application. It is, however, an art that is just at the beginning of its usefulness, standing in much the same relation to wireless telegraphy that the ordinary telephone does to the familiar system employing metallic conductors.
On the spark and arc systems various methods of wireless telegraphy have been developed and improved so that Marconi no longer has any monopoly of methods or instruments. Various companies and government officials have devised or modified systems so that to-day wireless is practically universal and is governed by an international convention to which leading nations of the world subscribe.
One of the recent features of wireless telegraphy of interest is the success of various directional devices. As we have seen, various schemes were tried by Marconi ranging from metallic reflectors used by Hertz in his early experiments with the electric waves to the more successful arrangement of aerial conductors. In Europe Bellini and Tosi have developed a method for obtaining directed aerial waves which promises to be of considerable utility, enabling them to be projected in a single direction just as a searchlight beam and thus restrict the number of points at which the signals could be intercepted and read.
Likewise an arrangement was perfected which enabled a station to determine the direction in which the waves were being projected and consequently the bearing of another vessel or lighthouse or other station. The fundamental principle was the arrangement of the antennae, two triangular systems being provided on the same mast, but in one the current is brought down in a perpendicular direction. The action depends upon the difference of the current in the two triangles.
Wireless telegraph apparatus is found installed in almost every seagoing pa.s.senger vessel of large size engaged in regular traffic, and as a means of safety as well as a convenience its usefulness has been demonstrated. Thus on the North Atlantic the largest liners are never out of touch with land on one side of the ocean or the other, and news is supplied for daily papers which are published on shipboard. Every ship in this part of the ocean equipped with the Marconi system, for example, is in communication on an average with four vessels supplied with instruments of the same system every twenty-four hours. In case of danger or disaster signals going out over the sea speedily can bring succour, as clearly was demonstrated in the case of the collision between the White Star steamship Republic and the steamship Florida on January 26, 1909. Here wireless danger messages were sent out as long as the Republic was afloat and its wireless apparatus working. These brought aid from various steamers in the vicinity and the pa.s.sengers were speedily transferred from the sinking Republic. On April 15, 1912, the White Star liner t.i.tanic, the largest ship afloat, sank off Newfoundland, after colliding with an iceberg.
Wireless SOS calls for help brought several steamships to the scene, and 703 persons from a total of 2,206, were rescued. On October 9, 1913, the Uranium liner Volturno caught fire in mid- ocean, and her wireless calls brought ten steamships to her aid, which, despite a heavy sea, rescued 532 persons from a total of 657. Again, on November 14, 1913, the Spanish steamship Balmes caught fire off Bermuda, and at her wireless call the Cunard liner Pannonia saved all of her pa.s.sengers--103. The t.i.tanic horror led the princ.i.p.al maritime nations to take immediate steps to perfect their wireless systems, and the installation of apparatus and operators soon became a prime requisite of the equipment of the world"s shipping. Wireless telegraphy has been developed to great efficiency in all the leading navies, and powerful plants are installed on all warships. The United States, Great Britain, and Germany, most noticeably, have established sh.o.r.e stations, by which they can "talk all around the world" from any ship or station. In operation secrecy is most important. For in the navy practically all important messages are sent in code or cipher under all conditions while in commercial work the tapping of land wires or the stealing of messages while illegal is physically possible for the evil disposed yet has never proved in practice a serious evil. The problem of interference, however, seems to have been fairly solved by the large systems though the activity of amateurs is often a serious disturbance for government and other stations.
Despite the progress of wireless telegraphy it has not yet supplanted the submarine cable and the land wire, and in conservative opinion it will be many years before it will do so.
In fact, since Marconi"s work there has been no diminution in the number or amount of cables laid and the business handled, nor is there prospect of such for years to come. While the cable has answered admirably for telegraphic purposes yet for telephony over considerable distances it has failed entirely so that wireless telephony over oceans starts with a more than favorable outlook.
But wireless telegraphy to a large extent has made its own field and here its work has been greatly successful. Thus when Peary"s message announcing his discovery of the North Pole came out of the Frozen North, it was by way of the wireless station on the distant Labrador coast that it reached an anxious and interested civilization. It is this same wireless that watches the progress of the fishing fleets at stations where commercial considerations would render impossible the maintenance of a submarine cable. It is the wireless telegraph that maintains communication in the interior of Alaska and between islands in the Pacific and elsewhere where conditions of development do not permit of the more expensive installation of submarine cable or climatic or other conditions render impossible overland lines. At sea its advantages are obvious. Everywhere the ether responds to the impulses of the crackling sparks, and even from the airship we soon may expect wireless messages as the few untrodden regions of our globe are explored.
CHAPTER XL
ELECTRO-CHEMISTRY AND ELECTRO-METALLURGY.
In no department of the application of electricity to practical work has there been a greater development than in electro- metallurgy and electro-chemistry. To-day there are vast industries depending upon electrical processes and the developments of a quarter of a century have been truly remarkable. Already more than one-half of the copper used in the arts is derived by electrolytic refining. The production of aluminum depends entirely on electricity, the electric furnace as a possible rival to the blast furnace for the production of iron and steel is being seriously considered, and many other metallurgical processes are being undertaken on a large scale. We have seen in our chapter on Electrolysis how a metal may be deposited from a solution of its salt and how this process could be used for deriving a pure metal or for plating or coating with the desired metal the surface of another metal or one covered with graphite. In the following pages it is intended to take up some of the more notable accomplishments in this field achieved by electricity, which have been developed to a state of commercial importance.
The electric arc not only supplies light, but heat of great intensity which the electrical engineer as well as the pure scientist has found so valuable for many practical operations. It is of course obvious that for most chemical operations, and especially in the field of metallurgy, heat is required for the separation of combinations of various elements, for their purification, as well as for the combination with other elements into alloys or compounds of direct utility. The usual method of generating heat is by the combustion of some fuel, such as coal, c.o.ke, gas or oil, and this has been utilized for hundreds of years in smelting metals and ores and in refining the material from a crude state. Now it may happen that a nation or region may be rich in metalliferous ores, but possess few, if any, coal deposits.
Accordingly the ore must be mined and transported considerable distances for treatment and the advantages of manufacturing industries are lost to the neighborhood of its original production. But if water power is available, as it is in many mountainous countries where various ores are found, then this power can be transformed into electricity which is available as power not only in various manufacturing operations, but for primary metallurgical work in smelting the ores and obtaining the metal therefrom. A striking instance of this is the kingdom of Sweden, which contains but little coal, yet is rich in minerals and in water power, so that its waterfalls have been picturesquely alluded to as the country"s "white coal." Likewise, at Niagara Falls a portion of the vast water power developed there has been used in the manufacture of aluminum, calcium carbide, carborundum, and other materials, while at other points in the United States and Canada, not to mention Europe, large industries where electricity is used for metallurgical or chemical work are carried on and the erection of new plants is contemplated.
The application of electricity to metallurgical and chemical work has been, in nearly all cases, the result of scientific research, and elaborate experimental laboratories are maintained by the various corporations interested in the present or future use of electrical processes. It is recognized by many of the older workers in this field that electrical developments are bound to come in the near future, and while they have not installed such appliances in their works yet they are keeping close watch of present developments, and in many cases experimental investigation and research is being carried on where electrical methods have not yet been introduced generally into the plant.
Prior to 1886 the refining of copper was the only electro- metallurgical industry and at that time it was carried on on a very limited scale. To-day the production of electrolytic copper as an industry is second in importance only to the actual production of that metal. From the small refinery started by James Elkington at Pembury in South Wales, a vast industry has developed in which there has been a change in the size of operations and in the details of methods rather than in the fundamental process. For a solution of copper sulphate is employed as the electrolyte, blocks of raw copper as the anodes, and thin sheets of pure copper as the cathodes. The pa.s.sage of the electric current, as we have seen on page 79, in the chapter on Electrolysis, is able to decompose the copper in the electrolyte and to precipitate chemically pure copper on the cathode, the copper of the solution being replenished from the raw material used as the anode by which the current is pa.s.sed into the bath. At this Welsh factory 250 tons yearly were produced, and small earthenware pots sufficed for the electrolyte. Thirty years later one American factory alone was able to produce at least 350 tons of electrolytic copper in twenty-four hours, and over 400,000 tons is the aggregate output of the refineries of the world, which is about 53 per cent, of the total raw copper production. Of this amount 85 per cent, comes from American refineries, whose output has more than doubled since 1900.
The chief reason for this increased output of electrolytic copper has been the great demand for its use in the electrical industries where not only a vast amount is consumed, but where copper of high purity, to give the maximum conductivity required by the electrical engineer, is demanded. When it is realized that every dynamo is wound with copper wire and that the same material is used for the trolley wire and for the distribution wires in electric lighting, it will be apparent how the demand for copper has increased in the last quarter of a century. Electrolytic methods not only supply a purer article and are economical to operate, especially if there is water power in the vicinity, but the copper ores contain varying amounts of silver and gold which can be recovered from the slimes obtained in the electrolytic process. Wherever possible machinery has been subst.i.tuted for hand labor, the raw copper anodes have been cast, and the charging and discharging of the vats is carried on by the most modern mechanical methods in which efficiency and economy are secured. On the chemical side of the process attempts have been made to improve the electrolyte, notably by the addition of a small amount of hydrochloric acid to prevent the loss of silver in the slimes, and this part of the work is watched with quite as much care as the other stages. Electric furnaces have also been constructed for smelting copper ores, but these have not found wide application, and the problem is one of the future. For the most part the copper electrically refined is produced in an ordinary smelter. The mints of the United States are now all equipped with electrolytic refining plants to produce the pure metal needed for coinage and they have proved most satisfactory and economical.
As the electrolytic production of copper is an industry of great present importance, so the production of iron and steel by electricity promises to be of the greatest future importance.
Electric furnaces for making steel are now maintained, and the industry has pa.s.sed beyond an experimental condition. But it has not reached the point where it is competing with the Bessemer or the open hearth process of the manufacture of steel, while for the smelting of iron ores the electric furnace has not yet been found practical from an economic standpoint. Before 1880 Sir William Siemens showed that an electric arc could be used to melt iron or steel in a crucible, and he patented an electric crucible furnace which was the first attempt to use electricity in iron and steel manufacture. He stated that the process would not be too costly and that it had a great future before it. This was an application of the intense heat of the arc, which supplies a higher temperature than any source known except that of the sun. This heat is used to melt the metal, in which condition various impurities can be removed and necessary ingredients added.
Siemens" furnace did not find extensive application, largely on account of the great metallurgical developments then taking place in the iron industry and the thorough knowledge of metallurgical processes as carried on, possessed by metallurgical engineers. But the idea by no means languished, and in 1899 Paul Heroult and other electro-metallurgists were active in developing a practical electric furnace for iron and steel work. The Swedish engineer, F.
A. Kjellin, was also active and as the result of the efforts of these and other workers, by 1909 electric furnaces were employed, not only in the manufacture of special steels whose composition and making were attended with special care, but for rails and structural material. There were reported to be between thirty and forty electric steel plants in various countries, and the outlook for the future was distinctly bright. The application of electro- metallurgy at this time was confined to the manufacture of steel, as the smelting of iron had not emerged from the experimental stage of its development, though extensive trials on a large scale of various furnaces have been undertaken in Europe and by the Canadian government at Sault Ste. Marie, where the Heroult furnace, soon to be described, was employed. Electro-metallurgy of steel, as in all utilization of electrical power, depends upon obtaining electricity at a reasonable cost, and then utilizing the heat of the arc or of the current in the most practical and economical form. One of the pioneer furnaces for this purpose which has seen considerable development and practical application is the Heroult furnace, which is a tilting furnace of the crucible type, whose operation depends upon both the heat of the arc and on the heat produced by the resistance of the molten material. In the Heroult process the impurities of the molten iron are washed out by treatment with suitable slags. The furnace consists of a crucible in the form of a closed shallow iron tank, thickly lined with dolomite and magn.a.z.ite brick, with a hearth of crushed dolomite. The electric current enters the crucible through two ma.s.sive electrodes of solid carbon, 70 inches in length and 14 inches in diameter, so mounted that they can be moved either vertically or horizontally by the electrician in charge. These electrodes are water-jacketed to reduce the rate of consumption.
The furnace contains an inlet for an air blast and openings in its covering for charging the material and for the escape of the gases. The actual process of steel-making consists of charging the crucible with steel sc.r.a.p, pig iron, iron ore, and lime of the proper quality and in the right proportions, placing this material on the hearth of the furnace. Combined arc and resistance heating is applied to raise the charge to the melting point. The current is of 120 volts or the same as that used in an ordinary incandescent lighting circuit, but is alternating and of 4,000 amperes. This is for a three-ton furnace. As the material melts the lime and silicates form a slag which fuses rapidly and covers the iron and steel in the crucible, so that the molten bath is protected from the action of the gases which are liberated and the oxygen in the atmosphere. The next step in the process is to lower the electrodes until they just touch beneath the surface of the molten slag so that subsequent heating is due not to the effect of the arc but to the resistance which the bath offers to the pa.s.sage of the current.
Air from an air blast is introduced into the crucible to oxidize the impurities of the metal, particularly the sulphur and the phosphorus which are carried into the slag and this is removed by the tilting of the furnace. Fresh quant.i.ties of lime, etc., are added, and the operation is repeated until a comparatively pure metal remains, when an alloy high in carbon is added and whatever other const.i.tuents are desired for the finished steel. The charge is then tipped into the casting ladle and the part of the electric furnace is finished. For three tons of steel eight to ten hours are required in the Heroult crucible furnace.
Furnaces of an altogether different type are those employing an alternating current, such as the Kjellin and Rochling furnaces, where the metal to be heated really forms the secondary circuit of a large and novel form of transformer which in principle is a.n.a.logous to the familiar transformer seen to step down the potential of alternating current as for house lighting. For such a transformer the primary coil is formed of heavy wire and the secondary circuit is the molten metal which is contained in an annular channel. The current obtained in the metal is of considerable intensity, but at lower potential than that in the primary coil, and roughly is equal to that of the primary multiplied by the number of turns in the coil. The condition is similar to that in the ordinary induction coil where the current from a battery at low potential flows around a coil of a few turns and is surrounded by a second coil with a large number of turns of fine wire in which current of small intensity but of high potential is generated. In the induction furnace the reverse takes place and the current flowing in the metal derived from that of the heavy coil in the primary is of great intensity. For this type of furnace molten metal is required and the furnace is never entirely emptied, so that its process is continuous. The temperature attained is not as high as in the arc furnace, so that the raw materials used have to be of a high degree of purity, and this has proved a restriction of the field of usefulness of this type of furnace in many cases. It, however, has been improved recently and two rings of molten metal employed instead of one so that a wide centre trough is obtained in which the metal is subjected to ordinary resistance heat by direct or alternating currents. This furnace permits of various metallurgical operations and the elimination of impurities as in the Heroult type.
A third type of furnace that is meeting with some extensive use is the Giroud, which, like the Heroult furnace, is based on the arc and resistance in principle, but in its construction has a number of different features. As the current pa.s.ses horizontally from the upper electrodes through the slag and molten metal in the furnace chamber to the base electrodes of the furnace, it permits of the easy regulation of the arcs and the use of lower electromotive force, while there is only one arc in the path of the current instead of two as in the Heroult type.