Agricola, Georgius
,
De re metallica
,
1912/1950
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[Figure 311]
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[Figure 312]
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BOOK VII.
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<
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>Since the Sixth Book has described the iron tools,
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the vessels and the machines used in mines, this
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Book will describe the methods of assaying
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1
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ores;
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because it is desirable to first test them in order
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that the material mined may be advantageously
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smelted, or that the dross may be purged away and
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the metal made pure. </
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>Although writers have men
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tioned such tests, yet none of them have set down the
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directions for performing them, wherefore it is no
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wonder that those who come later have written nothing on the subject.
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<
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>By tests of this kind miners can determine with certainty whether
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ores contain any metal in them or not; or if it has already been
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indicated that the ore contains one or more metals, the tests show whether
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it is much or little; the miners also ascertain by such tests the method by
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which the metal can be separated from that part of the ore devoid of it;
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and further, by these tests, they determine that part in which there is much
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metal from that part in which there is little. </
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>Unless these tests have been
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carefully applied before the metals are melted out, the ore cannot be smelted
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without great loss to the owners, for the parts which do not easily melt in the
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fire carry the metals off with them or consume them. </
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<
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>In the last case, they pass
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off with the fumes; in the other case they are mixed with the slag and furnace
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accretions, and in such event the owners lose the labour which they have spent
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in preparing the furnaces and the crucibles, and further, it is necessary for them
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to incur fresh expenditure for fluxes and other things. </
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<
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>Metals, when they have
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been melted out, are usually assayed in order that we may ascertain what pro
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portion of silver is in a
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centumpondium
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of copper or lead, or what quantity of
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gold is in one
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libra
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of silver; and, on the other hand, what proportion of copper
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or lead is contained in a
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centumpondium
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of silver, or what quantity of silver is
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contained in one
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libra
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of gold. </
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<
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>And from this we can calculate whether it
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will be worth while to separate the precious metals from the base metals, or
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not. </
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<
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>Further, a test of this kind shows whether coins are good or are
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debased; and readily detects silver, if the coiners have mixed more than is
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lawful with the gold; or copper, if the coiners have alloyed with the gold or
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silver more of it than is allowable. </
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<
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>I will explain all these methods with the
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utmost care that I can.</
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