400 PRINCIPLES OF CHEMISTRY. 



stand in the middle of those large periods (for example, K, Ca, Sc, Tf, 

 V, Or, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br) which start with 

 the true metals of the alkalis that is to say, the analogy and difference 

 "between potassium and copper are of the same nature as that between 

 chromium and selenium, or vanadium and arsenic. 



Copper is one of the few metals which have long been known in a 

 metallic form. The Greeks and Romans imported copper chiefly from 

 the island of Cyprus whence its Latin name, cuprum. It was known 

 to the ancients before iron, and was used, especially when alloyed with 

 other metals, for arms and domestic utensils. That copper was known 

 to the ancients will be understood from the fact that it occurs, although 

 rarely, in a native state, and is easily extracted from its other natural 

 compounds. Among the latter are the oxygen compounds of copper. 

 When ignited with charcoal, they easily give up theii oxygen to 

 it, and yield metallic copper j hydrogen also easily takes up the 

 oxygen from copper oxide when heated. Copper occurs in a native 

 fctate, sometimes -in association with other ores, in many parts of the 

 Urals angl in Sweden, and in considerable masses in America, espe- 

 cially in the neighbourhood of the great American lakes ; and also in, 

 Chili, Japan, and China, The oxygen compounds of copper are also of 

 somewhat common occurrence in certain localities ; in this respect 

 certain deposits of the Urals are especially famous. The geological 

 period of the Urals (Permian) is characterised by a considerable dis- 

 tribution of copper ores. Copper is met with in the form of cuprous 

 oxide, or suboxide of copper, Cu 2 0, and is then known as red copper 

 ore, because it forms red masses which not unf requently are crystallised 

 in the Tegular system. It is found much more rarely in thevstate of 

 cupric oxide, CuO, and is then called black copper ore. The mosf 

 common of the oxygenised compounds of copper are the basic carbonates 

 corresponding with the oxides. That these compounds are undoubtedly 

 of aqueous origin, is apparent, not only from the fact that specimens 

 are frequently found of a gradual transition from the metallic, sul- 

 phuretted, and oxidised copper into its various carbonates, but also from 

 the presence of water in their composition, and from the laminar, 

 reniform. structure which many of them present. In this respect mala- 

 chite is particularly well known ; it is used as a green paint and also 

 for ornaments, owing to the diversity of the shades of colour presented 

 by tho different layers of deposited malachite. The composition of 

 malachite corresponds with "the basic carbonate containing one molecule 

 of cupric carbonate to one of hydroxide : CuCO 3 ,CuH 2 02.' I n this 

 'form- the copper frequently occurs in admixture with yarious sedi- 

 .mentary rocks, forming large strata, which confirms the abuebus origin 



