Silver has been known since the ancient times. Slag dumps in Asia Minor and on islands in the Aegean Sea indicate that man had learned to separate silver from lead as early as 3000 B.C.
Silver occurs native and in ores (argentite (Ag2S) and horn silver (AgCl2)); lead, lead-zinc, copper, gold and copper-nickel ores are principal sources. It is also recovered during electrolytic refining of copper.
Silver metal in its pure state has a brilliant white metallic lustre. It is a little harder than gold and is very ductile and malleable. It is classified with the precious metals. Silver is stable in pure air and water, but tarnishes when exposed to ozone, hydrogen sulphide, or air containing sulphur because of the formation of a silver sulphide.
It has the highest electrical and heat conductivity of all metals and the lowest contact resistance. Cold working will reduce this conductivity. When heated above its boiling point, silver boils off as a green vapour.
Silver is soluble in nitric acid and in hot sulphuric acid.
Silver has three commercial types:
• Fine silver which is greater than 99.9% pure
• Coin silver (a silver alloy) with 90% silver and 10% copper
• Silver powder that comes in several forms such as amorphous powder, dendritic crystals, atomised powder, silver-clad powder, silver flake and nickel-coated silver powder.
Silver salts are poisonous due to the anions present.