In the turquoise there is nothing that can recommend it to notice except the agreeable softness of its colour, which is particularly distinguishable by candle-light; this alone has rendered it so fashionable as an ornament in female dress, for rings, ear-drops, and brooches, that the demand for it is at present greater than the supply. Imitations of turquoise are easily made in paste, and not unfrequently imposed upon the ignorant purchaser; but in these, though the colour is correctly given, there is a glassy lustre much higher than that of the real stone.
Of late years a spurious kind of turquoise has also found its way into Europe, which is much softer than the genuine kind; has more of a green than a blue cast, and is by no means capable of so good a polish.
233. IRON is a well-known metal, of livid greyish colour, hard and elastic, and capable of receiving a high polish. Its weight is nearly eight times as great as that of water.
It is seldom found in a truly native state, but occurs, abundantly, in almost every country of the world, in a state of oxide ([21]), and mineralized with sulphuric ([24]), carbonic ([26]), and other acids.
Iron is found in plants, in several kinds of coloured stones, and even in the blood of animals.
Of all the metals there are none which, in the whole, are so useful, or are so copiously and variously dispersed as iron. Its uses were ascertained at a very early period of the world. Moses speaks of furnaces for iron, and of the ores from which it was extracted, and tells us that swords, knives, axes, and instruments for cutting stones, were, in his time, all made of this metal.
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.