Front Page Titles (by Subject) Iron. - Money and the Mechanism of Exchange
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Iron. - William Stanley Jevons, Money and the Mechanism of Exchange 
Money and the Mechanism of Exchange (New York: D. Appleton and Co. 1876).
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Proceeding to consider briefly each of the more important metals, the statements of Aristotle, Pollux, and other writers prove that iron was extensively employed as money in early times. Not a single specimen of such money is now known to exist, but this is easily accounted for by the rapidity with which the metal rusts. In the absence of specimens, we do not know the form and size of the money, but it is probable that it consisted of small bars, ingots, or spikes, somewhat similar to the small bars of iron which are still used in trading with the natives of Central Africa. Iron money is still, or was not long since, used in Japan for small values; but its issue from the mint has been discontinued.
The use of pure iron coins in civilized countries at the present day is out of the question, both because of the cheapness of the metal, and because the coins would soon lose the sharpness of their impressions by rusting, and become dirty and easily counterfeited. But it is quite possible that iron or steel might still be alloyed with other metals for the coining of pence.