Heavy water is nothing but d2o it is normally found in water but only in small proportion it is separeted by girdler sulfide process and electrolysis
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Heavy Water ( Preparation - Electrolytic cell Method )Heavy Water:

Heavy water is also called as deuterium oxide or 2H2or D2O. The oxide of hydrogen is called heavy water.Heavy water was discovered by Urey in 1932.Heavy water occurs naturally, although it is much less common than regular water.Preparation of heavy water :
             The main source of heavy water is the ordinary water from which it is isolated. Generally it is prepared by prolonged electrolysis or fractional distillation.

Prolonged Electrolysis Of Ordinary Water:
            This method is involved in multistage electrolysis of ordinary water containing alkali. ( eg. NaOH ). The cylindrical vessels made of steel which act as cathode. The cylindrical sheet of nickel which act as anode with a number of holes punched in it. The electrolysis carried out in different stages. In these stage large number of electrolytic cells are used.