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112 classified as rich, of which each one hundred librae contains more than three librae of silver. This quality comprises rudis silver, whether silver glance or ruby silver, or whether white, or black, or grey, or purple, or yellow, or brilliancy, does not justify a more narrow rendering than “ironstone.” Agricola (De Nat. Fos., Book V.) gives elaborate descriptions of various iron ores, but the descriptions under any special name would cover many actual minerals. The subject of pyrites is a most con- fused one; the term originates from the Greek word for fire, and referred in Greek and Roman times to almost any stone that would strike sparks. By Agricola it was a generic term in somewhat the same sense that it is still used in mineralogy, as, for instance, iron pyrite, copper pyrite, etc. So much was this the case later on, that Henckel, the leading mineralogist of the 18th Century, entitled his large volume Pyritologia, and in it embraces practically all the sulphide minerals then known. The term marcasite, of mediæval Arabic origin, seems to have had some vogue prior and subsequent to Agricola. He, however, puts it on one side as merely a synonym for pyrite, nor can it be satisfactorily defined in much better terms. Agricola apparently did not recognise the iron base of pyrites, for he says (De Nat. Fos., p. 366): “Sometimes, however, pyrites do not contain any gold, silver, copper, or lead, and yet it is not a pure stone, but a compound, and consists of stone and a substance which is somewhat metallic, which is a species of its own.” Many varieties were known to him and described, partly by their other metal association, but chiefly by their colour. . The minerals embraced under this term by the old mineralogists form one of the most difficult chapters in the history of mineralogy. These complexities reached their height with Agricola, for at this time various new minerals classed under this heading had come under debate. All these minerals were later found to be forms of zinc, cobalt, or arsenic, and some of these minerals were in use long prior to Agricola. From Greek and Roman times down to long after Agricola, brass was made by cementing zinc ore with copper. Aristotle and Strabo mention an earth used to colour copper, but give no details. It is difficult to say what zinc mineral the cadmium of Dioscorides (v. 46) and Pliny (, 2), really was. It was possibly only furnace calamine, or perhaps blende, for it was associated with copper. They amply describe cadmia produced in copper furnaces, and pompholyx (zinc oxide). It was apparently not until Theophilus (1150) that the term calamina appears for that mineral. Precisely when the term “zinc,” and a knowledge of the metal, first appeared in Europe is a matter of some doubt; it has been attributed to Paracelsus, a contemporary of Agricola (see note on p. ), but we do not believe that author's work in question was printed until long after. The quotations from Agricola given below, in which zincum is mentioned in an obscure way, do not appear in the first editions of these works, but only in the revised edition of 1559. In other words, Agricola himself only learned of a substance under this name a short period before his death in 1555. The metal was imported into Europe from China prior to this time. He however does describe actual metallic zinc under the term conterfei, and mentions its occurrence in the cracks of furnace walls. (See also notes on p. ).

The word cobalt (German kobelt) is from the Greek word cobalos, “mime,” and its German form was the term for gnomes and goblins. It appears that the German miners, finding a material (Agricola's “corrosive material”) which injured their hands and feet, con- nected it with the goblins, or used the term as an epithet, and finally it became established for certain minerals (see note 21, p., on this subject). The first written appearance of the term in connection with minerals, appears in Agricola's Bermannus (1530). The first practical use of cobalt was in the form of zaffre or cobalt blue. There seems to be no mention of the substance by the Greek or Roman writers, although analyses of old colourings show some traces of cobalt, but whether accidental or not is undetermined. The first mention we know of, was by Biringuccio in 1540 (De La Pirotechnica, Book, Chap.. ), who did not connect it with the minerals then called cobalt or cadmia. “Zaffera is another mineral substance, like a metal of middle weight, which will not melt alone, but accompanied by vitreous substances it melts into an azure colour so that those who colour glass, or paint vases or glazed earthenware, make use of it. Not only does it serve for the above- mentioned operations, but if one uses too great a quantity of it, it will be black and all other colours, according to the quantity used.” Agricola, although he does not use the word zaffre, does refer to a substance of this kind, and in any event also missed the relation between zaffre and cobalt, as he seems to think (De Nat. Fos., p. 347) that zaffre came from bismuth, a belief that existed until long after his time. The cobalt of the Erzgebirge was of course, intimately associated with this mineral. He says, “the slag of bismuth, mixed together with metalliferous substances, which when melted make a kind of glass, will tint glass and earthenware vessels blue.” Zaffre is the roasted mineral ground with sand, while smalt, a term used more frequently, is the fused mixture with sand.

The following are the substances mentioned by Agricola, which, we believe, relate to cobalt and zinc minerals, some of them arsenical compounds. Other arsenical minerals we give above.