=Best Select Copper= for alloy manufacture. And, in addition, Lake Copper and some Converter Bars. A number of unrefined metallic products met with in practice include:— _Converter Bars._—The product from the Bessemer operation on copper mattes. Most converter metal is subsequently electrolytically refined, but several varieties of Australian and American copper are put on the market direct in this form. Being produced from fairly pure ores, which carry but little silver and gold, the converter metal may be sufficiently pure to render electrolytic refining unnecessary, and too low in gold and silver values to make such an operation profitable. _Cathode Copper_ is the product from the electrolytic refinery, and is usually remelted, brought up to pitch, and cast into ingots previous to use. _Black Copper_ is produced by the smelting of oxide ores, and is subsequently refined. _Cement Copper_ is produced by wet processes, usually by precipitation from copper-bearing solutions by means of iron, the product being a rather impure reddish-brown spongy mass. Many varieties contain arsenic. It requires melting and subsequent refining to adapt it for service. _Blister Copper_ was the name given to the crude metal from the older type of furnace operations. Such copper contained large quantities of gas, particularly SO_{2}, which, tending to escape at the moment of solidification in the mould, gave a blistered appearance to the surface. It contained 96 to 98 per cent. of metallic copper, and was subsequently refined. The term is generally applied still to all crude copper exhibiting similar features. _Chili Bar_ is an impure copper imported from Chili for refining. The composition varies, the metal usually containing 96 to 98 per cent. of copper, with indefinite quantities, sometimes small, of undesirable impurities. Appended is a series of representative analyses of various copper products, compiled from different sources. The composition of such material as tough pitch copper and the various cruder varieties is, however, subject to very great variation. =The Sources of Copper.=—Copper ores usually consist of various minerals of copper mixed with those of many other metals, and accompanied by very varied gangue, according to the locality in which they are found. They are best classified under three groups:— (1) _Native Ores._ (2) _Sulphide Ores._ (3) _Oxide Ores._ The most important points to be noted with regard to the distribution of these different classes are that— (1) Native ores are localised in their occurrence, being chiefly confined to the Lake Superior district. TABLE IV.—ANALYSES OF VARIOUS COMMERCIAL COPPERS.