Electrolytic refining method is used when very pure gold is required. The impure gold is made the anode while a thin sheet of pure gold acts as the cathode. The electrolyte consists of a solution of auric chloride (AuCl3) acidified with 10-12% HCl. On passing current pure gold gets deposited on the cathode.
Fineness of gold
Gold content of an alloy of gold is termed its fineness and is generally expressed in carats. Pure gold is 24 carats. Ornaments available these days are made of 18 carat gold, which is an alloy containing 18 parts by weight of gold alloyed with 6 parts by weight of another metal generally copper.
i) It is used in coinage, jewellery and ornamental vessels.
ii) Gold leaf is used for decorations, lettering and in medicine as tonic.
iii) “Purple of cassius” which is a combination of gold with colloidal stannic hydroxide is used for making ruby red glass and high class pottery.