73 



silver, as it contains less copper and more nickel. Composition : copper, 

 40.4; nickel, 81.6; zinc, 25.4; iron, 9.6. 



There are also several varieties of bronze — 1st, that which is 

 employed in making coins generally contains from 89 to 93 per cent, 

 of copper, and 7 to 11 per cent, of tin. The same alloy is employed 

 in the manufacture of statuary and large castings. 2d, the alloy for 

 gun metal, whose composition is very closely allied to the one just 

 described. 3d, the alloy employed for making gongs and cymbals, 

 being composed of 78 per cent, of copper, 9'2 per cent, of tin. 4th, 

 bell metal, containing 77 per cent, of copper, 21 per cent, of tin, and 

 2 per cent, of autimouy. 5th, telescope and speculum metal ; this is 

 au alloy which possesses a steel white colour, is exceedingly hard and 

 brittle, may be very highly polished, and contains 66.6 per cent, of 

 copper and 33.4 per cent, of tin. 



On the subject of liquid tests and assaying its ores, the following 

 observations were made : — 



With hydrosulphuric acid and sulphide of ammonium solutions of 

 copper pi'oduce a black precipitate of sulphide of copper ; with the 

 caustic alkalies, they produce a blue precipitate of hydrated oxide of 

 copper, which loses its water on boiling, and becomes black. 



Ammonia produces at first a blue precipitate of oxide ; but on the 

 addition of an excess, this precipitate is dissolved, forming a liquid of 

 a beautiful azure blue colour. Cyanide of potassium produces a 

 yellowish green precipitate of cyanide of copper, which dissolves in 

 excess of cyanide of potassium. 



Ferrocyanide of potassium produces, in exceedingly dilute solutions 

 of copper, a purple red precipitate of ferrocyanide of copper. 



Salts of copper may also be detected by heating them on charcoal, 

 with carbonate of soda, before the blowpipe, when the smallest traces of 

 this metal may be detected with the greatest facility. 



In order to determine the per centage of copper in the dry way, in an 

 ore composed of iron and copper pyrites, the following process is 

 usually adopted : 200 grains are placed in an earthen crucible, in the 

 fire of an ordinary assay furnace, and roasted until all the sulphur has 

 passed off in the form of sulphurous acid. This requires about two 

 hours, the mass being constantly stirred in order to prevent the ore 

 from sticking to the sides of the crucible, and to obtain an uniform 

 amount of heat. After no more vapours are preceptible, the crucible 

 may be removed from the fire and allowed to cool ; a small piece of 

 carljonate of ammonia (about 90 grains) is added and the crucible is 

 replaced in the fire, covered by a smaller one inverted. The addition 

 of tills salt is for the .purpose of driving off the last traces of sulphurous 



