Front Page Titles (by Subject) 4. Homogeneity. - Money and the Mechanism of Exchange
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4. Homogeneity. - 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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All portions of specimens of the substance used as money should be homogeneous, that is, of the same quality, so that equal weights will have exactly the same value. In order that we may correctly count in terms of any unit, the units must be equal and similar, so that twice two will always make four. If we were to count in precious stones, it would seldom happen that four stones would be just twice as valuable as two stones. Even the precious metals, as found in the native state, are not perfectly homogeneous, being mixed together in almost all proportions; but this produces little inconvenience, because the assayer readily determines the quantity of each pure metal present in any ingot. In the processes of refining and coining, the metals are afterwards reduced to almost exactly uniform degrees of fineness, so that equal weights are then of exactly equal value.