Q.(a) What is tailing of mercury? How is it removed?

(a) Tailing is a purity test/defect of mercury caused by impurities; (b) Deacon's process makes chlorine by catalytic air-oxidation of HCl gas.

(a) Tailing of mercury:

When mercury containing traces of base metal impurities (like Zn, Pb, Sn) is poured across an inclined clean glass or porcelain surface, it does not roll freely as clean spherical globules the way pure mercury does. Instead, it leaves behind a thin streak or 'tail' of adhering metal on the surface — this phenomenon is called tailing of mercury, and is used as a simple test for the purity of mercury (pure mercury shows no tailing).

Removal: The impurities are removed by:

• squeezing the impure mercury through a chamois leather or fine cloth (removes solid particulate impurities),
• washing/agitating it with dilute nitric acid (which dissolves the base-metal impurities, since mercury itself is far less reactive), followed by washing with water and drying, or
• vacuum distillation, which leaves the less-volatile impurities behind.

(b) Deacon's method for manufacturing chlorine: …