BOOK XI.

535

When he has compressed the bellows, he introduces this bar as quickly aspossible into the crucible through the pipe between the two nozzles, andtakes out samples two, three, or four times, until he finds that the copper isperfectly refined. If the copper is good it adheres easily to the bar, andtwo samples suffice ; if it is not good, then many are required. It isnecessary to smelt it in the crucible until the copper adhering to the bar isseen to be of a brassy colour, and if the upper as well as the lower part ofthe thin layer of copper may be easily broken, it signifies that the copperis 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 . 25

If the copper is not good, the master draws off the “ slags ” twice, orthree times if necessary—the first time when some of the cakes have beenmelted, the second when all have melted, the third time when the copper hasbeen heated for some time. If the copper was of good quality, the “ slags ”are not drawn off before the operation is finished, but at the time they are to bedrawn off, he depresses the bar over both bellows, and places over both astick, a cubit long and a palm wide, half cut away at the upper part, so that itmay pass under the iron pin fixed at the back in the perforated wood. Thishe does likewise when the copper has been completely melted. Then theassistant removes the iron plate with the tongs ; these tongs are four feetthree palms long, their jaws are about a foot in length, and their straight partmeasures two palms and three digits, and the curved a palm and a digit.The same assistant, with the iron shovel, throws and heaps up the largerpieces of charcoal into that part of the hearth which is against the little wallwhich protects the other wall from injury by fire, and partly extinguishesthem by pouring water over them. The master, with a hazel stick inserted

as 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 changedin some parts of Saxony, that it might have been written in the 20th century instead ofthe 16th. The best account of the old practice in Saxony after Agricola is to be found inSchliiter’s Htitte Werken (Braunschweig, 1738, Chap. cxvm.). The process has largely beendisplaced by electrolytic methods, but is still in use in most refineries as a step in electrolyticwork. It may be unnecessary to repeat that the process is one of subjecting the molten massof impure metal to a strong and continuous blast, and as a result, not only are the impuritiesto 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 anddiffuses through the metallic copper, and readily parting with its oxygen to the impuritiesfurther facilitates their complete oxidation. The blast is continued until the impurities arepractically eliminated, and at this stage the molten metal contains a great deal of dissolvedcuprous 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 theoxide. The state of the metal is even to-day in some localities tested by dipping into it thepoint 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 colourand should be quite pliable ; if the metal is not yet refined, the sample is thick, smooth, anddetachable with difficulty ; if over-refined, it is thick and brittle. By allowing water to runon to the surface of the molten metal, thin cakes are successively formed and taken off. Thesecakes were the article known to commerce over several centuries as “ rosetta copper.” Thefirst few cakes are discarded as containing impurities or slag, and if the metal be of goodquality the cakes are thin and of a red colour. Their colour and thinness, therefore, become acriterion of purity. The cover of charcoal or charcoal dust maintained upon the surface ofthe metal tended to retard oxidation, but prevented volatilization and helped to secure theimpurities as a slag instead. Karsten ( Archiv ., 1st series, p. 46) gives several analyses of the