Iron stands first in usefulness of all the metals, for railways, bridges, ships, and a thousand other purposes; it can be both cast and wrought, having that peculiar property, the capability of being “welded,” that is to say, of softening while hot to such an extent that when two pieces are made white hot and laid together, a few blows of the hammer will cause them to unite into one piece, and it is by means of this most useful quality that large masses of wrought iron are produced, such, for instance, as anchors and cranks for steam-boats. This property of welding, and the abundance of the ores of iron, render it one of the most useful materials supplied by nature for the various purposes of manufacture. In combination with carbon it forms that hardly less useful article known by the name of steel. Cast Iron has scarcely any of the metallic lustre, and is only fitted for solid work; it is brittle, like steel, without its elasticity, and is too soft and too porous to be made into any of the numerous tools and instruments for which steel is so eminently suitable. Cast iron contains many impurities, the chief of which are carbon, sulphur, and silica, got from the coke whilst being smelted in contact with it, and from the fluxes used in the process; it is coarse in grain, and much more fusible than wrought iron, which is iron in a nearly pure state and can be fused only by the very highest heat capable of being produced. Cast iron is converted into wrought or malleable iron by being re-melted and stirred for a long time in contact with the air, this process is called “puddling,” its object is to get rid of all the impurities (chiefly carbon and sulphur) which, by being brought into contact with the air at a high temperature, are said to be burnt out, that is to say, they combine with oxygen and form carbonic and sulphurous acids. After puddling, the iron is rolled or hammered out, folded up, and again extended, and as a general rule it may be said, the more this is continued the purer and softer is the iron. COPPER. Illustration: NATIVE COPPER. Copper is a reddish-coloured heavy metal, much used for sheathing the under part of ships, for making boilers, &c. It is about eight-and-a-half times heavier than water, and is too valuable to be used for many purposes where either iron, tinned iron, or zinc are applied, but for which purposes its great durability would fit it, as it is easily rolled out or beaten into plates, and is not quickly acted on by the weather. It is used as coin in pence, halfpence, and farthings; all vessels for cooking purposes, when made of copper, are tinned inside to prevent the food becoming poisonous from verdigris, which is the rust of copper, and is very injurious. Copper is found chiefly combined with sulphur, forming “native sulphuret of copper.” Copper melts at a full red heat. LEAD. Illustration: SULPHURET OF LEAD.