rori'Ki: 



463 



I.ntli of ( 'hathiim ' (1779-80), an impressive sub- 



J'ect, in \vliicli the portraits of tin- \-<-\* were rare- 

 ully studied from life, ami the still liner ' Death of 

 Miijin Pienon* (1783). Both are in the National 

 Gallery ; the former was engraved by liartoloz/.i, 

 the latter by Heath. In 1789-90 he executed the 

 immense ' Siege and Relief of Gibraltar,' now in 

 the Ciiildhall. Among his numerous other popular 

 works may l>e named ' The Surrender of Admiral 

 de Windt to Lord Duncan;' 'Charles I. demand- 

 ing tlio Surrender of the Five Members,' now in 

 I'M .s ton; 'Charles I. signing Stafford's Death- 

 warrant ; ' and ' The Assassination of Bucking- 

 ham.' Till the end of his life he was unwearied 

 in tlie pursuit of his art. In August 1815 he was 

 attacked by paralysis, and died on 9th September, 

 leaving a son, the future Lord Lyndhurst. 



Copley's historical subjects are more original, 

 spirited, and realistic than those of his friend and 

 countryman West, with whom he is commonly 

 classed; and they are distinguished by far richer 

 and finer colouring. His composition is simple and 

 effective, and his draftsmanship careful and accu- 

 rate. In religious and poetical subjects he was less 

 successful. His portraits, full or 'individuality, 

 excellent in modelling and colour, are in them- 

 selves enough to justify a great reputation ; and 

 in artistic qualities the finest of them may be 

 said to approach the works of Reynolds and 

 Gainsborough. See Lives by Perkins (1873) and 

 Mrs Amory (1882). 



Copper. This appears to have been the first 

 metal employed by man both in war and the peace- 

 ful arts. Like gold and silver, it is found native, 

 but, except in one or two districts, only to a small 

 extent. It can, however, be extracted from its 

 ores at a comparatively low heat, and it is not 

 altered by exposure to dry air ; although in moist 

 air, in the presence of carbonic acid, it soon takes 

 on a coating of the green carbonate of copper. 

 The use of copper by ancient nations is well known, 

 through tlie weapons and other objects of Bronze 

 (q.v.) that is, copper mixed with a small quantity 

 of tin, &c. which have been so largely collected by 

 archaeologists. Some prehistoric implements are, 

 however, of unalloyed copper. It was obtained by 

 the ancients from various places, but especially from 

 Cyprus whence the name. Copper has a charac- 

 teristic fine red colour and takes a brilliant polish. 

 It is nearly nine times heavier than water, its 

 specific gravity l>eing from 8 '8 to 8 '95. Next 

 to silver it is the best conductor of heat and 

 electricity, hence its many useful applications. Its 

 point of fusion lies between silver and- gold, but 

 unlike these metals, it absorbs oxygen when strongly 

 heated in the air, and scales ofulack oxide form 

 rapidly on its surface. Copper is moderately hard, 

 and is highly malleable, ductile, and tenacious, 

 although not so strong as iron. When held, in the 

 form or sheet or wire, in a flame, it communicates 

 to it a highly characteristic green colour. Whereas 

 steel is hardened by being heated to redness and 

 suddenly cooled in cold water, copper is softened by 

 the same process. Copper forms two important com- 

 pounds with oxygen cuprous and cupric oxides. 



Cuprous Oxide (red oxide, sub-oxide), Cu a O. 

 This is obtained by heating to redness the black 

 oxide with nearly its own weight of finely divided 

 copper in a well-covered crucible, to protect the 

 mixture from the oxidising action of the air. It is 

 got as a hydroxide by adding grape-sugar to a solu- 

 tion of sulphate of copper, and then caustic soda, 

 till a blue precipitate, which is first formed, is re- 

 dissolved. The solution, on being gently warmed. 

 deposits the hydroxide as a rich orange-yellow 

 powder. On continuing the heating till the liquid 

 has reached the l>oiling-point, and maintaining the 

 ebullition for some time, the powder changes into 



the red anhydrous oxide. TliU oxide in used in 

 colouring gloxH a fine ruby tint. It in not acted on 

 by air or moisture, and for this reason U produced 

 on copper surfaces a* a bronze to keep tlie metal 

 it -el i from becoming stained. The .-alt- of this 

 oxide are generally colourless, but they are liable 

 to absorb oxygen and pan* into the blue-coloured 

 cupric salts. Cuprous chloride is the most im- 

 portant salt, being used for almorbing carbonic 

 oxide in gas analysis. 



Cupric Oxide (copper monoxide, black oxide), 

 CuO, is the scale or rust of copper which peels off 

 the surface of the metal when heated. It is got for 

 chemical purposes by heating nitrate of copper to 

 redness in a crucible with occasional stirring, and 

 carefully avoiding any possible admission of coaly 

 matter. By the use or cupric oxide Liebig estab- 

 lished the method by which the composition of all 

 organic substances has been determined, as it 

 readily gives up its oxygen at a red heat to carlxm 

 and hydrogen, converting them, respectively, into 

 carbonic acid and water, from the weight of which 

 the composition of the organic body is calculated. 

 This oxide is used for staining glass, to which it 

 imparts a green colour ; and its solution in ammonia 

 has the remarkable property of dissolving cotton 

 fibre. The Hydroxide, Cu(OH) 2 , is obtained as a 

 blue precipitate by adding caustic soda to sulphate, 

 or otner salt, of copper, which, as in the case of 

 the cuprous oxide, becomes anhydrous on boiling, 

 the blue precipitate becoming black and granular. 

 The salts of cupric oxide are readily obtained by 

 dissolving it in the necessary acids ; for example, 

 in sulphuric acid for the sulphate, and in nitric acid 

 for the nitrate of copper. 



Cupric Sulphate ( sulphate of copper, blue vitriol ), 

 CuSO 4 , occurs native in veins of copper and iron 

 pyrites, and is manufactured on a large scale by 

 gently roasting native copper sulphide (copper 

 pyrites), when oxygen is absorbed from the air, the 

 anhydrous sulphate thus obtained being dissolved 

 in water, and from this solution the salt as found in 

 commerce crystallises out. The crystals are large, 

 transparent, and have a fine blue colour. They are 

 much used by the dyer and calico-printer, in electro- 

 plating, and in the preservation of organic materials. 



Cupric Nitrate, CufNC^J-j. The crystals of this- 

 salt are of an intense blue colour and 'deliquescent. 

 It is much used in calico-printing as an oxidising 

 agent. 



Cupric Cyanide, CuCy 2 , along with cyanide of 

 potassium, gives the solution from which copper is- 

 deposited on an iron surface. It is not, however, 

 necessary to prepare pure cupric cyanide, as the sul- 

 phate in excess of potassium cyanide serves the 

 purpose. 



Cupric Arsenite, CuHAsO 3 (Scheele's green), is a 

 well-Known green pigment, got by adding an alka- 

 line arseuite to cupric sulphate, and washing the 

 precipitate till free from sulphate, and drying. 

 This colour has been much useo for wall-papers, but 

 has been supposed to have insanitary effects. See 

 ARSENIC. 



Copper Acetate, Cu(C,H s O 2 ),, is got by adding 

 copper hydroxide, or carbonate, to acetic acid. It 

 forms dark blue prisms. If acetic acid is allowed 

 to act on metallic copper in the presence of air and 

 moisture, a basic acetate is slowly formed termed 

 verdigris ; this has less acetic acid than the previous 

 compound, and is much less soluble. It has a bluish- 

 green colour. Verdigris and arsenious acid boiled 

 together in water form the fine colour termed 

 emerald green an aceto-arsenite of copper. 



Copper Stearate is obtained by adding stearate of 

 soda to sulphate of copper in hot solutions. It is a 

 light bluish-green powder used for colouring candles. 



The. pigment, Britnsirick green, used in the arts, 

 is an oxychloride of copper. 



