MAGIC OF THE ELECTRIC FURNACE.

Otago Witness, Issue 2815, 26 February 1908, Page 79

MAGIC OF THE ELECTRIC FURNACE.

i CONQUERING THE NEW METALS i WITH HIGH TEMPERATURES. * (By Renb Bache.) The electric furnace has opened up a -whole world of new arts to exploration. l In particular the field of investigation thus I made accessible offered opportunities for '• experiment with various rare metals, , which, regarded hitherto ar mere curiosi- > ties of the laboratory, are now being ' turned to account for many important in- > dustrial uses. It is the electric fnra'ace, capable of ■ producing a temperature of 7200deg Fah- ; renheit, that has made practicable ths E reduction to metallic form of that elueire ' element tantalum. — so called, by very rea- ' son of i'he difficultiee which were en- > countered in trying to separate it from > its ores. But it"wae worth the troubl-, s for it 6olved the problem of - the electric i lamp, furnishing a satisfactory substitute for the carbon filament. The ordinary carbon incandescent lamp ' is not economical. It consumes a largo ■ amount of electrical energy, relatively to i the illumination afforded, and its profitably I life is short — only about 500 hours. After * that length of time it loses efficiency, ow- > ing to the blackening of the glass bulb through -dissipation, of the carbon flla- ' ment ; and if the lamp is used on a voit- '> age high enough to give a light approach- ■ ing whiteneffl, tts ufe is much snorter. 1 Accordingly, efforts have 'been made to [ construct, a lamp that would give a bettc L light with less consumption of electrical i energy, and this was finally accomplished by substituting osmium, and then tantalum, for carbon as a "material for the L luminous filament* Many tantalum lamps > are now in use. The light they give is 1 much whiter than that of the carbon lamp, ■ and more brilliant, because the metal can ' be raised to a higher temperature than tho k carbon filament.^ The higher the tem- > ' perature the brighter the light. It is ' steadier, too, because less sensitive t-> * | changes of current. The life of the lamp . is no longer than that of the carbon, but > ! there is a considerable saving of electrical I energy, the tantalum consuming only two 5 watts per candlepower, against three anl t a-half watts for the carbon lamp. [ — The Hardest Metal Known. — i A lump of tantalum heated to a red glow J can be beaten easily into a plate under 9 a steam hammer, and, after being thus , heated and hammered several times, it ' I acquires a hardness equal to that of th- 1 t j diamond. Attempts to bore a hoie s through such a sheet one-third of an inch thick "with a diamond drill running at 1. > rate of 5000 revolutions a minute for thre-s [- days resulted in -a penetration only one- * fourth of the way through, while the drvl * was much worn. A complete perforation ) could not be made. On account of its wonderful hardness » hopes are entertained that the metal may t be successfully employed jor dies, drills, 1 j bearings, and journals. It should mul- > tiply the efficiency of lathes and other cut1 j ting tools, greatly augmenting their «apa- * ; city to do work. Doubtless, many other 3 uses will be found for it, -one to whioh it is ! I already applied being the manufacture of I * , pens. These pens resist the chemical ' t action of ink and the atmosphere as we' 1 , - as gold pens, to which they are very > > superior in respect to elasticity and hardl "ness. It may be added that the principal - . supply of tantalum now comes from Wesl. tern Australia, but there is plenty of it in , the Black Hills of Soutb Dakota and in ] i North Carolina: „ j , 1 The" superior efficiency of the iantalu-»i ' >■] lamp, it will be understood, is attribut- j 9 able primarily to the extraordinarily hii*'i ; . ! melting point of the metal — 5200deg Fab- i i renheit. But although, in this respect, ' , it represented the first gain over the ca^- ' c bon light, it is by no means the best t t thing possible. Tungsten, another re9 ; fractory metal, has an even higher melting t point (5500deg), so that a filament mad' 3 i; of it can be burned at a corresponding^ s^ higher temperature without being deb ~ stroyed. Now, it '.happen*- curiously

enough, that an increase of only 200deg in the temperature of the filament nearly doubles the light. A comparatively slight increase in temperature augments the light by 15 per cent. Thus the tungsten lamp, worked ordinarily at 4100deg Fahrenheit (higher than is possible for carbon), is touch more brilliant than the lamp with the carbon filament. Tungsten incandescent lamps are now on the market at a reasonable price, and | are being introduced largely. Their light, I instead of yellow, is white and of a very j pleasing quality, but its ' extreme brightf ness renders a frosted or coloured globe desirable in living rooms or offices. With, an expenditure of one-third of the electrical energy they will give the same amount of illumination as carbon lamps, and they have been burned for as long as three thousand hours without perceptible loss of brilliancy. — Tungsten Cutting Tools) — Boulder County, in Colorado, is the only source in this country from which any considerable quantity of tungsten is now obtained. Its ores are -associated nvith granites, and one of them, called "scheelite" (calcium tungstate), occurs in promising quantities near the entrance of the Yellowstone Park, in- Montana, and five miles from Johannesburg, in the JvTojave Desert of California. This scheelite, when dissolved in a mineral acid, precipitates a yellow powder (tungstk oxide), which, when mixed with carbon and- -heated in a crucible, comes out in the form of metallic tungsten. The melting point of the stuff is so high that it cannot be fused,- and so it is mixed with iron to make an alloy, which is put into ! steel to harden the latter. When thus i used, it multiplies the efficiency of lathes 1 and other cutting tools by five — enabling '• them, that is to say, to do five times as ! much work before wearing out. ! Tungsten — wMch, by the way, looks somewhat like platinum, and takes a high ' polish — hae other Taluable uses, being employed largely in fireproofing ctoth for curtains, draperies, etc., and as a mordant in dyeing. In Chester County, Pennsylvania, the farmers ploughing the fields frequently pick up large crystals of a substance known ! as "rutile." It is an oxide of another | interesting metal, called titanium, and has a considerable market value, being utilised by .manufacturers- of dental . supplies for, colouring artificial teeth. Also, it is used to give to porcelain tile a soft and beautiful yellow tint. — Titanium. — Though generally spoken >f as one of the rare elements, titanium is, in reality, one of the most common. According to . the reckoning of Professor F. W. Clarke, Chemist-in-Chief of the United States Geological Survey, it forms nearly onehalf of 1 per cent, of the surface rocks of the globe, being much more plentiful than lead, zinc, or copper. It occurs in i many kinds of rocks, and is almost always found in clays in appreciable quantities. I The melting point of titanium is so high, however, that it cannot be obtained from its ores in a pure metallic form without the help of the electric furnace. Small quantities of it add greatly to the strength of cast iron, and likewise to the tensile j strength and elasticity of steel. Experiments are now 'being made with a view to : utilising it as a material for filaments in ! incandescent lamps, but the difficulty of 1 reducing it to a metal is so great that only partial success has thus far rewarded the* effort. Another rare and interesting metal, found associated with sandstones in Southwest Colorado, is vanadium. It is used like tungsten and titanium to augment the hardness and tensile strength of steel. Cutting tool* of vanadium steel mag be-

come almost red-hot without losing their temper.

In addition, it has been discovered recently tKafb vanadic acid affords an admirable and comparatively cheap substitute for true gold bronze. In the form of a fine light powder it is easily mixed with gums or varnishes, and" gives a handsome colour and durable lustee to objects to which it is applied. Both uranium and molybdenum are now used — their salts,, that is to say — in pottery making. The lattei gives a fine blue colour to glazes, and uranium salts are employed also in the' manufacture of iridescent glass. Uranium ores are very rare and hard' to find. Those of molybdenum are associated with old crystalline and metamorphic rocks in many- parts of the United States, but the problem of extracting the metal is most difficult. Its salts are utilised as a germicide, for fireproofing, and as a disinfectant. A new use for chromium has been, found in the manufacture of artificial rubies, which, produced in the electric furnace, are new appearing on the market. These synthetic gems, like the natural ones, are crystallised -corundum, and chromium (as in Nature) is employed to colour them. The metal-fQur principal supply of it comes from -Asiatic Turkey, though there are ' considerable deposits m Yancey County, North Carolina — is aleo utilised in making " chrome - brick," for building smelting furnaces and openhearth steel furnaces. But its most' imiportant \ise is in the production of chrome steel, which is now considered the most desirable thing for armour plates of warsMps. — Measuring High Temperatures. —

With the introduction >f these new arts, depending upon enormously Mgh temperatures, it has become necessary to devise means for accurately measuring such temperatures. For tMs purpose manufacturers of steel, porcelain, glass, etc., employ so-called pyrometers (the word, literally translated, meaning firemeasurers), which are in themselves very novel contrivances. Where heats so intense are concerned, it is not practicable to use mercury thermometers, of course, because the mercury would' vaporise. In(genious devices of other kinds must be utilised, some of them, called " optical pyrometers," determining the temperature by measurinnr the intensity of the light given out from the furnace.

It is of utmost importance that the pyro» meters shall be accurate, in ofder that the manufacturing processes ' in connection with which they are used may not go wrong. ,. For example, in a glass factory the sheets of glass, rolled red-hot, pass through a series of annealing ovens while their temperature is gradually lowered. If the ovens are not heated just right, the final product will be unfit for use. It is the same way with the hardening of armour plates; for unless the temperature is kept uniform, strains will be set up in the material, rendering it brittle.