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amount of silver in the copper, he alloys it fourfold ; for instance, if in threequarters of a centumpondium of copper there is less than the following proportions, i.e.: half a libra of silver, or half a libra and a sicilicus, or half a libra
and a semi-uncia, or half a libra and semi-uncia and a sicilicus, then rich
lead—that is, that from which the silver has not yet been separated—is
added, to the amount of half a centumpondium or a whole centumpondium, or
a whole and a half, in such a way that there may be in the copper-lead alloy
some one of the proportions of silver which I have just mentioned, which is
the first alloy. To this " first " alloy is added such a weight of de-silverized
lead or litharge as is required to make out of all of these a single liquation cake
that will contain approximately two centumpondia of lead; but as usually
from one hundred and thirty librae of litharge only one hundred librae of lead
are made, a greater proportion of litharge than of de-silverized lead is added
as a supplement. Since four cakes of this kind are placed at the same time
into the furnace in which the silver and lead is liquated from copper, there
will be in all the cakes three centumpondia of copper and eight centumpondia
of lead. When the lead has been liquated from the copper, it weighs six
centumpondia, in each centumpondium of which there is a quarter of a libra
and almost a sicilicus of silver. Only seven unciae of the silver remain in the
exhausted liquation cakes and in that copper-lead alloy which we call
" liquation thorns " ; they are not called by this name so much because they
have sharp points as because they are base. If in three-quarters of a centumpondium of copper there are less than seven uncia and a semi-uncia or a bes
of silver, then so much rich lead must be added as to make in the copper and
lead alloy one of the proportions of silver which I have already mentioned.
This is the " second " alloy. To this is again to be added as great a weight
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weighed 225 to 375lbs. This size was wonderfully persistent from Agricola down to modern
times; and was, no doubt, based on sound experience. If the cakes were too small, they
required proportionately more fuel and labour; whilst if too large, the copper began to melt
before the maximum lead was liquated. The ratio of the copper and lead was regulated by
the necessity of enough copper to leave a substantial sponge mass the shape of the original
cake, and not so large a proportion as to imprison the lead. That is, if the copper be in too
small proportion the cakes break down ; and if in too large, then insufficient lead liquates
out, and the extraction of silver decreases. Ercker (p. 106-9) insists on the equivalent of about
3 copper to 9.5 lead; Lohneys (p. 99), 3 copper to 9 or 10 lead. Schliiter (p. 479, etc.)
insists on a ration of 3 copper to about 11 lead. Kerl (Handbuch Der Metallurgischen Hiitten
kunde, 1855 ; Vol. III., p. 116) gives 3 copper to 6 to 7 parts lead. Agricola gives variable
amounts of 3 parts copper to from 8 to 12 parts lead. As to the ratio of silver in the copper,
or to the cakes, there does not, except the limit of payability, seem to have been any difficulty
on the minimum side. On the other hand, Ercker, Lohneys, Schliiter, and Karsten all
contend that if the silver ran above a certain proportion, the copper would retain considerable
silver. These authors give the outside ratio of silver permissible for good results in one
liquation at what would be equivalent to 45 to 65 ozs. per ton of cakes, or about 190 to 250 ozs.
per ton on the original copper. It will be seen, however, that Agricola's cakes greatly exceed
these values. A difficulty did arise when the copper ran low in silver, in that the liquated
lead was too poor to cupel, and in such case the lead was used over again, until it became rich
enough for this purpose. According to Karsten, copper containing less than an equivalent
of 80 to 90 ozs. per ton could not be liquated profitably, although the Upper Harz copper,
according to Kerl, containing the equivalent of about 50 ozs. per ton, was liquated at a profit.
In such a case the cakes would run only 12 to 14 ozs. per ton. It will be noticed that in the
eight cases given by Agricola the copper ran from 97 to over 580 ozs. per ton, and in the description of enrichment of copper " bottoms " the original copper runs 85 ozs., and " it cannot
be separated easily " ; as a result, it is raised to no ozs. per ton before treatment. In addition
to the following tabulation of the proportions here given by Agricola, the reader should refer to
footnotes 15 and 17, where four more combinations are tabulated. It will be observed from
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