This metal occurs sparsely in many iron ores, and passes into the slag and the pig-iron in the smelting; but it is found much more abundantly in molybdenite (molybdenum sulphide) and in wulfenite (lead-molybdenum oxide), and is met with as a native trioxide (molybdic ochre). Metallic molybdenum is prepared by heating the trioxide or a chloride to redness in a current of hydrogen; the trioxide is not easily reduced, and the product requires to be afterwards heated in a current of anhydrous hydrochloric acid. The pure metal dissolves rapidly in hot concentrated sulphuric acid, in nitric acid, and in aqua-regia, but is insoluble in dilute sulphuric and hydrochloric acids and in hydrofluoric; it oxidizes only when heated in contact with the air, and is in-fusible in the highest heat of a blast furnace; it has a sp. gr. of 8.6, and a silvery colour.