Write the principle behind the following methods of refining: (i) Hydraulic washing (ii) Vapour-phase refining

Hydraulic washing : It is a type of gravity separation when water is used as a medium. Gravity separation is a process of concentration of ore in which gangue is separated from desired metal ore on the basis of their gravity.
Vapour-phase refining is the process of refining metal by converting it into its volatile compound and then decomposing it to obtain a pure metal. To carry out this process,

1. the metal should form a volatile compound with an available reagent, and
2. the volatile compound should be easily decomposed so that the metal can be easily recovered.
   Nickel, zirconium and titanium are refined using this method.