De Re Metallica Part 51

Amount of 211.8 lbs. 211.8 lbs. 211.8 lbs. 211.8 lbs.

argentiferous copper

Amount of lead 564.8 " 635.4 " 776.6 " 847.2 "

Weight of each cake 193.5 " 211.5 " 247.1 " 264.75 "

Average value of 56 ozs. 62 ozs. 64 ozs. 66 ozs.

charge 3dwts. 4dwts. 4dwts. 7dwts.

Per cent. of copper 27.2% 25% 21.4% 20%

Average value of 207 ozs. 251 ozs. 299 ozs. 332 ozs.

original copper 4dwts. 3dwts. 15dwts. 3dwts.

per ton

Weight of 423.6 lbs. 494.2 lbs. 635.4 lbs. 706 lbs.

argentiferous lead liquated out

Average value of 79 ozs. 79 ozs. 79 ozs. 85 ozs.

liquated lead per ton

Weight of residues 353 lbs. 353 lbs. 353 lbs. 353 lbs.

(residual copper and thorns)

Average value of 34 ozs. 34 ozs. 34 ozs. 34 ozs. to residues per ton 38 ozs.

Extraction of 76.5% 73.4% 79% 85.3% silver into the argentiferous lead

[11] See p. 356.

[12] An a.n.a.lysis of this "slag" by Karsten (_Archiv_. 1st Series IX, p.

24) showed 63.2% lead oxide, 5.1% cuprous oxide, 20.1% silica (from the fuel and furnace linings), together with some iron alumina, etc. The _pompholyx_ and _spodos_ were largely zinc oxide (see note, p. 394).

[13] This description of a _centumpondium_ which weighed either 133-1/3 _librae_, or 146-3/4 _librae_, adds confusion to an already much mixed subject (see Appendix C.). a.s.suming the German _pfundt_ to weigh 7,219 troy grains, and the Roman _libra_ 4,946 grains, then a _centner_ would weigh 145.95 _librae_, which checks up fairly well with the second case; but under what circ.u.mstances a _centner_ can weigh 133-1/3 _librae_ we are unable to record. At first sight it might appear from this statement that where Agricola uses the word _centumpondium_ he means the German _centner_. On the other hand, in the previous five or six pages the expressions one-third, five-sixths, ten-twelfths of a _libra_ are used, which are even divisions of the Roman 12 _unciae_ to one _libra_, and are used where they manifestly mean divisions of 12 units. If Agricola had in mind the German scale, and were using the _libra_ for a _pfundt_ of 16 _untzen_, these divisions would amount to fractions, and would not total the _sicilicus_ and _drachma_ quant.i.ties given, nor would they total any of the possibly synonymous divisions of the German _untzen_ (see also page 254).

[14] If we a.s.sume Roman weights, the charge in the first case can be tabulated as follows, and for convenience will be called the fifth charge:--

5TH CHARGE (3 cakes).

Amount of copper 211.8 lbs.

Amount of lead 635.4 lbs.

Weight of each cake 282.4 lbs.

Average value of charge 218 ozs. 18 dwts.

Per cent. of copper 25% Average value of original copper per ton 583 ozs. 6 dwts. 16 grs.

Weight of argentiferous lead liquated out 494.2 lbs.

Average value of liquated lead per ton 352 ozs. 8 dwts.

Weight of residues 353 lbs.

Average value of residues per ton 20 ozs. (about).

Extraction of silver into the argentiferous lead 94%

The results given in the second case where the copper contains 2 _librae_ and a _bes_ per _centumpondium_ do not tie together at all, for each liquation cake should contain 3 _librae_ 9-1/2 _unciae_, instead of 1-1/2 _librae_ and 1/2 _uncia_ of silver.

[15] In this enrichment of copper by the "settling" of the silver in the molten ma.s.s the original copper ran, in the two cases given, 60 ozs. 15 dwts. and 85 ozs. 1 dwt. per ton. The whole charge weighed 2,685 lbs., and contained in the second case 114 ozs. Troy, omitting fractions. On melting, 1,060 lbs. were drawn off as "tops," containing 24 ozs. of silver, or running 45 ozs. per ton, and there remained 1,625 lbs. of "bottoms," containing 90 ozs. of silver, or averaging 110 ozs. per ton.

It will be noticed later on in the description of making liquation cakes from these copper bottoms, that the author alters the value from one-third _librae_, a _semi-uncia_ and a _drachma_ per _centumpondium_ to one-third of a _libra_, _i.e._, from 110 ozs. to 97 ozs. 4 dwts. per ton. In the Glossary this furnace is described as a _spleisofen_, _i.e._, a refining hearth.

[16] The latter part of this paragraph presents great difficulties. The term "refining furnace" is given in the Latin as the "second furnace,"

an expression usually applied to the cupellation furnace. The whole question of refining is exhaustively discussed on pages 530 to 539.

Exactly what material is meant by the term red (_rubrum_), yellow (_fulvum_) and _caldarium_ copper is somewhat uncertain. They are given in the German text simply as _rot_, _geel_, and _lebeter kupfer_, and apparently all were "coa.r.s.e" copper of different characters destined for the refinery. The author states in _De Natura Fossilium_ (p. 334): "Copper has a red colour peculiar to itself; this colour in smelted copper is considered the most excellent. It, however, varies. In some it is red, as in the copper smelted at Neusohl.... Other copper is prepared in the smelters where silver is separated from copper, which is called yellow copper (_luteum_), and is _regulare_. In the same place a dark yellow copper is made which is called _caldarium_, taking its name among the Germans from a caldron.... _Regulare_ differs from _caldarium_ in that the former is not only fusible, but also malleable; while the latter is, indeed, fusible, but is not ductile, for it breaks when struck with the hammer." Later on in _De Re Metallica_ (p. 542) he describes yellow copper as made from "baser" liquation thorns and from exhausted liquation cakes made from thorns. These products were necessarily impure, as they contained, among other things, the concentrates from furnace accretions. Therefore, there was ample source for zinc, a.r.s.enic or other metallics which would lighten the colour.

_Caldarium_ copper is described by Pliny (see note, p. 404), and was, no doubt, "coa.r.s.e" copper, and apparently Agricola adopted this term from that source, as we have found it used nowhere else. On page 542 the author describes making _caldarium_ copper from a mixture of yellow copper and a peculiar _cadmia_, which he describes as the "slags" from refining copper. These "slags," which are the result of oxidation and poling, would contain almost any of the metallic impurities of the original ore, antimony, lead, a.r.s.enic, zinc, cobalt, etc. Coming from these two sources the _caldarium_ must have been, indeed, impure.

[17] The liquation of these low-grade copper "bottoms" required that the liquated lead should be re-used again to make up fresh liquation cakes, in order that it might eventually become rich enough to warrant cupellation. In the following table the "poor" silver-lead is designated (A) the "medium" (B) and the "rich" (C). The three charges here given are designated sixth, seventh, and eighth for purposes of reference. It will be seen that the data is insufficient to complete the ninth and tenth. Moreover, while the author gives directions for making four cakes, he says the charge consists of five, and it has, therefore, been necessary to reduce the volume of products given to this basis.

6TH CHARGE. 7TH CHARGE. 8TH CHARGE.

Amount of copper 176.5 lbs. 176.5 lbs. 176.5 lbs.

bottoms

Amount of lead 282.4 lbs. 564.8 lbs. 635.4 lbs.

(slags) of (A) of (B)

Amount of 494.2 lbs. 211.8 lbs. 141.2 lbs. (A) de-silverized lead

Weight of each cake 238.3 lbs. 238.3 lbs. 238.3 lbs.

Average value of 22 ozs. 35 ozs. 50 ozs.

charge per ton 5dwts. 15dwts. 5dwts.

Per cent. of copper 18.5% 18.5% 18.5%

Average value per 97 ozs. 97 ozs. 97 ozs.

ton original copper 4dwts. 4dwts. 4dwts.

Average value per 90 ozs. 28 ozs. 28 ozs.

ton of 2dwts. (slags) 5dwts. (A) 5dwts. (A)

Average value per 3 ozs. 3 ozs. 42 ozs.

ton of 1dwt. (lead) 1dwt. (lead) 10dwts. (B)

Weight of liquated 550.6 lbs.

lead

Average value of 28 ozs. 42 ozs. 63 ozs.

the liquated lead 5dwts. (A) 10dwts. (B) 16dwts. (C) per ton

Weight of exhausted 225.9 lbs.

liquation cakes

Average value of 12 ozs.

the exhausted 3dwts.