BOOK XI. 535 



When he has compressed the bellows, he introduces this bar as quickly as 

 possible into the crucible through the pipe between the two nozzles, and 

 takes out samples two, three, or four times, until he finds that the copper is 

 perfectly refined. If the copper is good it adheres easily to the bar, and 

 two samples suffice ; if it is not good, then many are required. It is 

 necessary to smelt it in the crucible until the copper adhering to the bar is 

 seen to be of a brassy colour, and if the upper as well as the lower part of 

 the thin layer of copper may be easily broken, it signifies that the copper 

 is perfectly melted ; he places the point of the bar on a small iron anvil, 

 and chips off the thin layer of copper from it with a hammer. ^^ 



If the copper is not good, the master draws off the " slags " twice, or 

 three times if necessary- — the first time when some of the cakes have been 

 melted, the second when all have melted, the third time when the copper has 

 been heated for some time. If the copper was of good quahty, the "slags" 

 are not drawn off before the operation is finished, but at the time they are to be 

 drawn off, he depresses the bar over both bellows, and places over both a 

 stick, a cubit long and a palm wide, half cut away at the upper part, so that it 

 may pass under the iron pin fixed at the back in the perforated wood. This 

 he does Hkewise when the copper has been completely melted. Then the 

 assistant removes the iron plate with the tongs ; these tongs are four feet 

 three palms long, their jaws are about a foot in length, and their straight part 

 measures two palmfe and three digits, and the curved a palm and a digit. 

 The same assistant, with the iron shovel, throws and heaps up the larger 

 pieces of charcoal into that part of the hearth which is against the little wall 

 which protects the other wall from injury by fire, and partly extinguishes 

 them by pouring water over them. The master, with a hazel stick inserted 



*^This description of refining copper in an open hearth by oxidation with a blast and 

 " poling " — the gaarmachen of the Germans — is so accurate, and the process is so little changed 

 in some parts of Saxony, that it might have been written in the 20th century instead of 

 the i6th. The best account of the old practice in Saxony after Agricola is to be found in 

 Schliiter's Hi'dte Werken (Braunschweig, 1738, Chap, cxviii.). The process has largely been 

 displaced by electrolytic methods, but is still in use in most refineries as a step in electrolytic 

 work. It may be unnecessary to repeat that the process is one of subjecting the molten mass 

 of impure metal to a strong and continuous blast, and as a result, not only are the impurities 

 to a considerable extent directly oxidized and taken off as a slag, but also a consider- 

 able amount of copper is turned into cuprous oxide. This cuprous oxide mostly melts and 

 diffuses through the metallic copper, and readily parting with its oxygen to the impurities 

 further facilitates their complete oxidation. The blast is continued until the impurities are 

 practically eliminated, and at this stage the molten metal contains a great deal of dissolved 

 cuprous oxide, which must be reduced. This is done by introducing a billet of green wood 

 (" poling "), the dry distillation of which generates large quantities of gases, which reduce the 

 oxide. The state of the metal is even to-day in some localities tested by dipping into it the 

 point of an iron rod ; if it be at the proper state the adhering copper has a net-like appearance, 

 should be easily loosened from the rod by dipping in water, is of a reddish-copper colour 

 and should be quite pliable ; if the metal is not yet refined, the sample is thick, smooth, and 

 detachable with difficulty ; if over-refined, it is thick and brittle. By allowing water to run 

 on to the surface of the molten metal, thin cakes are successively formed and taken off. These 

 cakes were the article known to commerce over several centuries as " rosetta copper." The 

 first few cakes are discarded as containing impurities or slag, and if the metal be of good 

 quality the cakes are thin and of a red colour. Their colour and thinness, therefore, become a 

 criterion of purity. The cover of charcoal or charcoal dust maintained upon the surface of 

 the metal tended to retard oxidation, but prevented volatilization and helped to secure the 

 impurities as a slag instead. Karsten (Archiv., 1st series, p. 46) gives several analyses of the 



