Chemical Properties of Silver

At the ordinary temperature silver is stable towards moisture and atmospheric oxygen, but at 200° C. an invisible, superficial layer of oxide is produced, detected by its power of reacting with ozone at ordinary temperature. It reacts with sulphur and compounds of sulphur to form silver sulphide. In absence of air, hydrogen sulphide and the sulphides of the alkali-metals do not affect silver, but addition of oxygen or hydrogen peroxide induces instantaneous blackening.

Pure silver is dissolved by pure sulphuric acid at the boiling-point, provided the concentration of the acid is not less than 77.5 per cent., and in presence of impurities the metal is attacked also by the dilute acid:

2Ag + 2H₂SO₄ = Ag₂SO₄ + SO₂ + 2H₂O.

Nitric acid reacts energetically at ordinary temperatures, with formation of the nitrate and of the oxides of nitrogen. The behaviour of the metal with hydrochloric acid is similar to that of lead. The action of concentrated sulphuric acid and of nitric acid finds application in the separation of alloys of gold and silver. The corrosive effect of acids is accelerated by the presence of an oxidizer.

The metal is scarcely attacked by fused alkalies, and only slowly by the halogens. In contact with air or hydrogen peroxide it is readily dissolved by potassium cyanide. It is converted by mercury into an amalgam.

At ordinary temperatures and 200 atmospheres hydrogen expels the metal from solutions of its salts. It is precipitated.from its salts by the action of phosphorous acid and of sodium hypophosphite.