agent added is less than an optimum amount dispersion efficiency is reduced or that since the amount of dispersing agent added is excessively large agglomeration occurs due to bridging accordingly the dispersing agent must be added in an appropriate amount in consideration of the ph of the slurry the amount of dispersing agent suitable for addition must decrease as the ph of the slurry is reduced it is preferable that the amount of dispersing agent added be 2 2 3 0 wt based on the polishing particles when the ph of the slurry is 8 7 9 5 1 4 2 2 wt based on the polishing particles when the ph of the slurry is 8 0 8 7 and 0 6 1 4 wt based on the polishing particles when the ph of the slurry is 7 4 8 0 the preferable amount of dispersing agent is obtained when the conductivity is 300 900 u03bcs cm and more preferably it is obtained when the conductivity is 500 600 u03bcs cm next changes in the properties of slurry and micro scratches which were dependent on a stage at which the dispersing agent was added were examined 25 kg of highly pure cerium carbonate was charged in a container by about 800 g and calcined in a tunnel kiln at 700 u00b0 c for 4 hours to prepare ceria powders 9 to 11 during all of the calcination processes calcination.