TUNGSTEN. 207 



precipitated. This is filtered from the solution, dried and reduced 

 to metal with carbon in graphite crucibles fired in gas-heated furnaces. 

 The powder so produced contains about 98' 5 per cent, of metallic 



tungsten. 



Ferro-tungsten is made by the reduction of wolfram or scheelite, 

 preferably the former, by means of carbon in the electric furnace. 

 The ores used must be practically free from sulphur and phosphorus. 

 The alloy produced requires refining, which is carried out in an 

 arc furnace by melting under a slag of ferric oxide, lime and fluor 

 spar. The ferric oxide reduces the carbon and silicon, the latter 

 combining with the lime to form silicate of lime. The fluor spar 

 is added as a flux. 



Other uses. 



Tungsten is used for making permanent magnets, for the valves (f 

 some makes of internal combustion engines, as contacts for spark 

 plugs, tremblers and voltage regulators, etc.. for targets and cathodes 

 of Roentgen ray tubes, as a constituent of stellite and other alloys, 

 as an alloy with aluminum in the mixture known as " partinium," 

 as an alloy in dental and surgical instruments, in gramophone needles, 

 and as a catalyser for the production of ammonia from atmospheric 

 nitrogen and hydrogen. Tungstic acid and sodium tungstate are 

 used in the production of colour resists for aniline black. The 

 sodium salts are also said to be used to saturate materials, with 

 the effect that if they catch fire they smoulder and do not blaze. 

 The meta-tungstate is employed for the manufacture of tungsten- 

 bronze. Tungstic acid is used in the preparation of magenta- 

 bronze and saffron-bronze. The high melting point of tungsten 

 combined with the toughness and fineness of the wire into which it 

 may be drawn and its behaviour under the action of an electric 

 current, make it the best material known for incandescent electric 

 lamp filaments and millions of these are now made annuallv 

 Unfortunately a comparatively minute amount of wolfram is com 

 sumed in this manner. 



TUNGSTEN MINERALS IN GENERAL. 

 Tungsten has never been found as a native metal but always in 

 combination with other elements. There are comparatively few 

 of these compounds. The better known tungsten minerals are 

 given in the following list : — 



Ferberite, iron tungstate, FeWO + . 



D 



