Tungsten (W = 184), is a metallic element, which occurs chiefly in the minerals wolfram and scheelite. The metal, which may be obtained by the reduction of the oxide in hydrogen, is of an iron-grey colour, hard, and fusible with difficulty. It is unalterable in air, except in a very finely-divided state. Heated in chlorine, it gives rise to solid, volatile chlorides of considerable chemical interest. It forms two oxides, WO2 and WO3. The last gives rise to a large number of complicated salts, the tungstates. Of these the normal sodic tungstate, Na2WO42H2O, is the most important, being used largely as a mordant in calico-printing and dyeing, and also for rendering cotton, etc., fabrics fire-proof. The metal when present to a small extent in steel communicates to it great hardness and increases its power of retaining magnetism.