Part 42 (1/2)

Some say that in the furnace there are certain ma.s.ses of stone which, being smelted, become soldered together, and that the copper fuses around it, the ma.s.s not becoming liquid unless it is transferred to another furnace. It thus forms a sort of knot, as it were, in the metal.”

Pliny is a good deal confused over the copper alloys, failing to recognise _aurichalc.u.m_ as the same product as that made by mixing _cadmia_ and molten copper. Further, there is always the difficulty in translation arising from the fact that the Latin _aes_ was indiscriminately copper, bra.s.s, and bronze. He does not, except in one instance (x.x.xIV., 2), directly describe the mixture of _cadmia_ and copper. ”Next to Livian (copper) this kind (_corduban_, from Spain) most readily absorbs _cadmia_, and becomes almost as excellent as _aurichalc.u.m_ for making _sesterces_.” As to bronze, there is no very definite statement; but the _argentatium_ given in the quotation above from x.x.xIV, 20, is stated in x.x.xIV, 48, to be a mixture of tin and lead.

The Romans carried on most extensive copper mining in various parts of their empire; these activities extended from Egypt through Cyprus, Central Europe, the Spanish Peninsula, and Britain. The activity of such works is abundantly evidenced in the mines, but very little remains upon the surface to indicate the equipment; thus, while mining methods are clear enough, the metallurgy receives little help from these sources. At Rio Tinto there still remain enormous slag heaps from the Romans, and the Phoenician miners before them. Professor W. A. Carlyle informs us that the ore worked must have been almost exclusively sulphides, as only negligible quant.i.ties of carbonates exist in the deposits; they probably mixed basic and siliceous ores. There is some evidence of roasting, and the slags run from .2 to .6%. They must have run down mattes, but as to how they ultimately arrived at metallic copper there is no evidence to show.

The special processes for separating other metals from copper by liquation and matting, or of refining by poling, etc., are none of them clearly indicated in records or remains until we reach the 12th century.

Here we find very adequate descriptions of copper smelting and refining by the Monk Theophilus (see Appendix B). We reproduce two paragraphs of interest from Hendrie's excellent translation (p. 305 and 313): ”Copper is engendered in the earth. When a vein of which is found, it is acquired with the greatest labour by digging and breaking. It is a stone of a green colour and most hard, and naturally mixed with lead. This stone, dug up in abundance, is placed upon a pile and burned after the manner of chalk, nor does it change colour, but yet loses its hardness, so that it can be broken up. Then, being bruised small, it is placed in the furnace; coals and the bellows being applied, it is incessantly forged by day and night. This should be done carefully and with caution; that is, at first coals are placed in, then small pieces of stone are distributed over them, and again coals, and then stone anew, and it is thus arranged until it is sufficient for the size of the furnace. And when the stone has commenced to liquefy, the lead flows out through some small cavities, and the copper remains within. (313) Of the purification of copper. Take an iron dish of the size you wish, and line it inside and out with clay strongly beaten and mixed, and it is carefully dried.

Then place it before a forge upon the coals, so that when the bellows act upon it the wind may issue partly within and partly above it, and not below it. And very small coals being placed round it, place copper in it equally, and add over it a heap of coals. When, by blowing a long time, this has become melted, uncover it and cast immediately fine ashes of coals over it, and stir it with a thin and dry piece of wood as if mixing it, and you will directly see the burnt lead adhere to these ashes like a glue. Which being cast out again superpose coals, and blowing for a long time, as at first, again uncover it, and then do as you did before. You do this until at length, by cooking it, you can withdraw the lead entirely. Then pour it over the mould which you have prepared for this, and you will thus prove if it be pure. Hold it with pincers, glowing as it is, before it has become cold, and strike it with a large hammer strongly over the anvil, and if it be broken or split you must liquefy it anew as before.”

The next writer of importance was Biringuccio, who was contemporaneous with Agricola, but whose book precedes _De Re Metallica_ by 15 years.

That author (III, 2) is the first to describe particularly the furnace used in Saxony and the roasting prior to smelting, and the first to mention fluxes in detail. He, however, describes nothing of matte smelting; in copper refining he gives the whole process of poling, but omits the pole. It is not until we reach _De Re Metallica_ that we find adequate descriptions of the copper minerals, roasting, matte smelting, liquation, and refining, with a wealth of detail which eliminates the necessity for a large amount of conjecture regarding technical methods of the time.

[43] _Cadmia metallica fossilis_ (see note on p. 112). This was undoubtedly the complex cobalt-a.r.s.enic-zinc minerals found in Saxony. In the German translation, however, this is given as _Kalmey_, calamine, which is unlikely from the a.s.sociation with pyrites.

[44] The Roman _modius_ (_modulus_?) held about 550 cubic inches, the English peck holding 535 cubic inches. Then, perhaps, his seven _moduli_ would be roughly, 1 bushel 3 pecks, and 18 vessels full would be about 31 bushels--say, roughly, 5,400 lbs. of ore.

[45] Exhausted liquation cakes (_panes aerei fathiscentes_). This is the copper sponge resulting from the first liquation of lead, and still contains a considerable amount of lead. The liquation process is discussed in great detail in Book XI.

[46] The method of this paragraph involves two main objectives--first, the gradual enrichment of matte to blister copper; and, second, the creation of large cakes of copper-lead-silver alloy of suitable size and ratio of metals for liquation. This latter process is described in detail in Book XI. The following groupings show the circuit of the various products, the ”lbs.” being Roman _librae_:--

CHARGE. PRODUCTS.

{ Crude ore 5,400 lbs. } Primary matte (1) 600 lbs.

{ Lead slags 3 cartloads } 1st { Schist 1 cartload } Silver-copper alloy (A) 50 ”

{ Flux 20 lbs. } { Concentrates from } Slags (B) { slags & accretions Small quant.i.ty }

{ Primary matte (1) 1,800 lbs. } Secondary matte (2) 1,800 lbs.

{ Hearth-lead & litharge 1,200 ” } { Lead ore 300 ” } Silver-copper-lead 2nd { Rich hard cakes (A_{4}) 500 ” } alloy (liquation { Liquated cakes 200 ” } cakes) (A_{2}) 1,200 ”

{ Slags (B) } { Concentrates from } Slags (B_{2}) { accretions }

{ Secondary matte (2) 1,800 lbs. } Tertiary matte (3) 1,300 lbs.

{ Hearth-lead & litharge 1,200 ” } Silver-copper-lead { Lead ore 300 ” } alloy (liquation 3rd { Rich hard cakes (A_{4}) 500 ” } cakes) (A_{3}) 1,100 ”

{ Slags (B_{2}) } Slags (B_{3}) { Concentrates from } { accretions }

{ Tertiary matte (3) 11 cartloads } Quaternary hard cakes { Poor hard cakes (A_{5}) 3 ” } matte (4) 2,000 lbs.

4th { Slags (B_{3}) } Rich hard cakes of { Concentrates from } matte (A_{4}) 1,500 ”

{ accretions }

{ Roasted quartz } Poor hard cakes of 5th { Matte (4) (three } matte (A_{5}) 1,500 lbs.

{ times roasted) 11 cartloads } Final cakes of matte (5)

6th Final matte three times roasted is smelted to blister copper.

The following would be a rough approximation of the value of the various products:--

(1.) Primary matte = 158 ounces troy per short ton.

(2.) Secondary matte = 85 ” ” ”

(3.) Tertiary matte = 60 ” ” ”

(4.) Quaternary matte = Indeterminate.

A. Copper-silver alloy = 388 ounces Troy per short ton.

A_{2} Copper-silver-lead alloy = 145 ” ” ”