The earth contains a large number of metals which are useful to man.Any carbon content above that percentage is present in 
the form of flaky graphite.A 
certain number of non-ferrous metals, including aliminium and zine, are also 
important, but even today the majority of our engineering products are of iron or 
steel.The process of smelting consists 
of heating the ore in a blast furnace with coke and limestone, and reducing it to
metal.These non-metallic 
constituents of cast-iron include carbon, silicon and sulphur, and the presence of 
these substances affects the behaviour of the metal.The non-metallic constituents 
of the ore combine with the limestone to form a liquid slag.We can melt this down again in another furnace - a capula - with more 
coke and limestone, and tap it out into a ladle or directly into moulds.Iron which contains a 
negligible quantity of carbon, for example wrought-iron, behaves differently 
from iron which contains a lot of carbon.Moreover, iron possesses magnetic properties, which have made the 
development of electrical power possible.The ore becomes molten, 
and it oxides combine with carbon from the coke.Steel contains no free graphite, and its carbon content 
ranges from almost nothing to 1 1/2 %.This is 
cast-iron.