Name the phenomenon/process involved
i) mixing of hydrated ferric oxide (`+ve` sol) and arsenious sulphide (`-ve` sol)
ii) An impure sol is purified by removing dissolved particles using suitable membrane
iii) Movement of dispersion medium is observed in an electric field. 

Explanation

i) mixing of hydrated ferric oxide (`+ve` sol) and arsenious sulphide (`-ve` sol) is known as Mutual Cougulation.
ii) An impure sol is purified by removing dissolved particles using suitable membrane is called as dialysis
iii) Movement of dispersion medium is observed in an electric field is called electro osmosis.