PURPOSE: To deodorize a substance to be adsorbed on calcium silicate sol prepared by directly reacting synthetic wollastonite with acids and to prevent the generation of foreign matter such as gel and bacteria by adding a small amount of H2O2 to the sol when the sol is diluted.

CONSTITUTION: To 100pts.wt. synthetic wollastonite are added 5W200pts.wt. inorg. acid and/or org. acid, and they are well mixed to prepare calcium silicate sol. About 500 times as much water of 6.14pH as the sol is added to the sol, and hydrogen peroxide is added to the resulting aqueous soln. by about 1/200 of the amount of the soln. to prevent the generation of foreign matter from the calcium silicate sol. The preparation of calcium silicate sol and gel from synthetic wollastonite is disclosed by Japan Patent Publication No. Sho 55-23764 (examined).