The phenomenon of precipitation of colloidal solution by the addition of excess of electrolyte is called coagulation or flocculation.
Peptization or deflocculation is the process for the formation of colloid from precipitate by adding electrolyte. So,peptization is the reversal of coagulation.
Tyndall effect is the phenomenon in which light beam is scattered when passing through medium of small suspended particles.
Dialysis is the purification of colloidal solution by separating colloidal particles from dissolved ions,otherwise these ions can cause coagulation.