If no difficulty, as yet unforeseen, bars the way, Mr Barff's plan for rendering iron impenetrable by rust promises to be of the highest practical importance. Iron is by far the most useful of metals, but it has an unfortunate propensity when exposed to water or moist air for attracting oxygen, and this oxygen eats into its substance, and forms the familiar compound known as rust. The consequence is that iron when exposed to the air, especially in so damp a climate as ours, has to be coated with paint, varnish, or tin. But even this coating does not afford entire protection; the slightest flaw in the armour lets in the enemy oxygen, who often does his work all the more surely because concealed from view. A vessel made of iron and coated with some other substance, may look sound to the eye, and yet be a mere mass of crumbling rust. Mr Barff's remedy for this state of things seems to be after the doctrine of the homoeopathists, that like is cured by like. If a small degree of moisture affects iron with two distinct species of oxide or rust, what will exposure to a very excessive degree of moisture do? Well, it appears that if iron is placed in a hot chamber and exposed to the action of superheated steam, a new kind of oxide, called the magnetic or black oxide, forms on its surface. Not only does this benevolent species of black rust refuse to penetrate any further into the metal, but it forms an impervious coating against all other influences; and articles thus prepared have been exposed out of doors for weeks this winter without a particle of rust appearing on them. If careful experiments shew that iron is lessened neither in strength nor in durability by this process, its use will be greatly increased, as for several purposes it will take the place of other and more costly metals.—The Graphic.