In recent years, the slow but steady depletion of finite resources of metals has engendered some concern. The Club of Rome, for example, has predicted that supplies of metals could be used up within 100 years. This prediction can be regarded as unnecessarily pessimistic. If we look at ail possible reserves, although not cur-rently economically usable, we see that our resources are, indeed, semi-infinite. However, it makes sense to design for minimum waste and to re-cycle as much waste as possible since, in the long term, the rubbish tip will be a more readily accessible store of metals than, say, the sea.
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