COP 



COP 



a sisth of the mass: A little tin and lead 

 were found in some ; but in such small 

 proportion as to appear only an acci- 

 dental impurity. 



The alloys of copper and tin are ex- 

 tremely important in the arts, and cu- 

 rious as chemical mixtures. They form, 

 in different proportions, mixtures, which 

 have a distinct and appropriate use. Tin 

 added to copper makes it more fusible ; 

 much less liable to rust or corrosion by 

 common substances ; harder, denser, and 

 more sonorous. In these respects the 

 alloy has a real advantage over unmixed 

 copper; but this is in many cases more 

 than counterbalanced by the extreme 

 brittleness which even a moderate por- 

 tion of tin imparts, and which is a singu- 

 lar circumstance, considering how very 

 malleable both metals are before mix- 

 ture, and the remarkable softness and 

 ductility of tin. 



Copper, or sometimes copper with a 

 little zinc, alloyed with as much tin as 

 will make from about one-tenth to about 

 one fifth of the whole, forms an alloy, 

 which is the principal, and often the only 

 composition for bells, brass cannon (so 

 called,) bronze statues, and several 

 smaller purposes, and hence it is called 

 bronze, or bell-metal ; and it is excellent- 

 ly fitted for these purposes, by its hard- 

 ness, density, sonorousness, and fusibility, 

 whereby the minute parts of hollow 

 moulds may be readily filled before it 

 fixes in cooling. For cannon, a lower 

 portion of tin seems to be used. Bronze 

 cannon are much less liable to rust than 

 those of iron; but in large pieces of 

 ordnance, by very rapid firing, the touch- 

 hole is apt to melt down, and spoil the 

 piece : of which there is a remarkable 

 instance at the Tower of London, of a 

 mortar of the largest calibre thus spoiled 

 at the siege of Namur. On account of the 

 sonorousness of bronze, these cannon 

 give a much sharper report than those of 

 iron, which for a time impairs the hear- 

 ing of the people that work them. A 

 common alloy for bell-metal is about 80 

 of copper to 20 of tin ; or where copper, 

 brass, and tin are used, the copper is 

 from 70 to 80 per cent, including the por- 

 tion contained in the brass, and the re- 

 mainder is tin and zinc. The zinc cer- 

 tainly makes it more sonorous. Antimo- 

 ny is also often found in small quantity 

 in bell-metal. Some of the finer kinds 

 used for small articles contain also a little 

 silver, which much improves the sound. 

 When the tin is nearly one-third of the 

 alloy, it is then most beautifully white, 

 with a lustre almost like that of mercury, 



extremely hard, very close-grained, and 

 perfectly brittle. In this state it takes a 

 most beautiful polish, and is admirably 

 fitted for the reflection of light for all 

 optical purposes. It is then called specu- 

 lum metal, which, however, for the 

 extreme pe7-fection required in modern 

 astronomical instruments, is better mix- 

 ed with a very small proportion of other 

 metals, particularly arsenic, brass, and 

 silver.. 



When more tin is added than amounts 

 to half the weight of the copper, the 

 alloy begins to lose that splendid white- 

 ness, for which it is so valuable as a 

 mirror, and becomes more of a blue- 

 grey. As the tin increases, the texture 

 becomes rough-grained, and .as it were 

 rotten, and totally unfit for manufacture. 

 The speculum metal is therefore in 

 the highest proportion of alloy of tin 

 that copper will admit, for any useful 

 purpose. See Aikin's Dictionary of Che- 

 mistry. 



COPPERAS is the sulphate of iron, 

 and is commonly called green vitriol. If 

 sulphuric acid be diluted with water, and 

 be poured upon iron, much effervescence 

 will be seen : the metal will be dissolv- 

 ed, and the solution, when evaporated, 

 will exhibit the sulphate of iron, or com- 

 mon copperas, which is a neutral salt in a 

 very impure state. Copperas is the basis 

 of many dyes : it gives a fine black, 

 though it rather subjects the material to 

 decay, unless used with extreme caution, 

 the least excess occasioning the cloth, 

 &c. to rot very soon. It seems that wool 

 is more affected by it than felt, as is ob- 

 vious from the greater duration of hats 

 beyond what broad cloths, &c. exhibit 

 when dyed black. Ink owes its rich 

 blackness principally to the copperas it 

 contains; and our fine black leathers are 

 equally indebted to its powerful quali- 

 ties, which so firmly fix the colour on all 

 occasions. Many servants are in the 

 habit of cleansing their copper kitchen 

 utensils with green vitriol, which is ex- 

 tremely dangerous : the copperas is 

 highly corrosive, and disengages a very 

 large portion of the copper, which 

 cannot be always removed, even when 

 much pains are taken, the salt being 

 buried under projecting rims, rivets, &c. 

 We are apt to believe that many most 

 painful and dangerous complaints have 

 resulted from this, though probably they 

 may have been assigned to other suppos- 

 ed causes. 



Mi'. Murdoch, of Cornwall, obtained a 

 patent for extracting copperas from mun- 

 dic, and other ores containing sulphur, 



