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 Cast iron occupies a less space in a fluid, than in a solid form. Hence its fitness for castings. This fact depends on crystalline form which the iron takes on cooling.
228. Nickel is perfectly malleable and may be forged when hot, and hammered into plates when cold. Its colour is white, and intermediate between those of silver and tin. It admits of being finely polished, and has a lustre between steel and platina. Its ductility is such, as it may be drawn into very fine wire It cannot easily be soldered on account of the oxide which forms on its surface when heated. It is one of the most infusible of the metals. Like iron, it is magnetic. By long exposure to a red heat it is converted into a dark brown oxide which is still magnetic. Its specific gravity about 9At a sufficiently high heat its oxides are reducible without addition ; nor is it more tarnished by a strong heat than gold, silver, or platina. It ranks therefore among the noble or perfect metals.
229. The principle ore of this metal is a sulphuret. It comes from various parts of Germany, where it is found with cobalt.
OA.?. 1. It is a curious circumstance, that nickel has been found alloyed with iron in all the specimens of stones which have fallen from the atmosphere, where these have been analyzed.
2. Nickel is employed in China in making white copper, which is a very beautiful compound. It has also been proposed to make use of this metal in combination with steel, for the purpose of making surgical instruments, as such an alloy is not liable to oxidize.
The properties of tin must be examined in the state of grain-tin, or block-tin ; what is commonly known by the name of tin being nothing more than iron plates with a thin covering of this metal.
232. Tin has a silvery white colour, which is very little altered by exposure to air. It is ductile and very malleable, being easily rolled, or hammered into thin plates. Next to lead it is the softest and least elastic of all elastic metals. Its specific gravity is a little more than 7- It is easily fuzed, and bends with a peculiar crackling noise.

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