The most considerable iron mines at present existing are those in Great Britain and France. After iron ore is dug out of the earth, it is crushed or broken into small pieces, by machinery. It is next washed, to detach the grosser particles of earth which adhere to it. This operation ended, it is roasted in kilns, formed for the purpose, by which the sulphur, and some other substances that are capable of being separated by heat, are detached. It is then thrown into a furnace, mixed with a certain portion of limestone and charcoal, to be melted. Near the bottom of the furnace there is a tap─hole, through which the liquid metal is discharged into furrows made in a bed of sand. The larger masses, or those which flow into the main furrow, are called _sows_; the smaller ones are denominated _pigs_ of iron; and the general name of the metal in this state is _cast iron_. With us iron is employed in three states, of cast iron, wrought iron, and steel. _Cast iron_ is distinguishable, by its properties of being, in general, so hard as to resist both the hammer and the file; being extremely brittle, and for the most part, of a dark grey or blackish colour. A great number of useful and important articles are formed of cast iron, such as grates, chimney backs, pots, boilers, pipes, and cannon shot. These are made by casting ladles full of the liquid metal into moulds that are shaped, for the purpose, in sifted sand. _Wrought iron._ The process of converting cast iron into wrought or malleable iron, is called _blooming_. The cast iron is thrown into the furnace, and kept melted by the flame of combustibles which is made to play upon its surface. Here it is suffered to continue for about two hours, a workman constantly stirring it, until, notwithstanding the continuance of the heat, it gradually acquires consistency, and congeals. It is then taken out, while hot, and violently beaten with a large hammer worked by machinery. In this state it is formed into bars for sale. The value of iron is beyond all estimate, and infinitely greater than even that of gold. By means of this metal the earth has been cultivated and subdued. Without it houses, cities, and ships, could not have been built; and few arts could have been practised. It forms also the machinery by which the most useful and important mechanical powers are generated and applied.