to the method of Kalapathy, Proctor & Shultz (2000). The wheat husk obtained from a flour factory is burnt in open air with a hand-lighter. Semi-burnt wheat husk is burnt again in an incineration furnace (Protherm, Turkey) at 600°C for 5 hours because it is known that ashes with high silica content are obtained at temperatures lower than 400°C (Kamath and Proctor, 1998). Ozgul-Yucel et al. (2004) also demonstrated that rice husk ash has an amorphous structure when burnt at 600°C. Thus, 600°C is chosen as the burning temperature. 100 gm of ash is placed into a 2 L flask, 600 millilitres of 1 M sodium hydroxide solution was added, and the flask is capped with a watch glass. The mixture is boiled for 1 hour with constant stirring using a magnetic stirring bar. Then the mixture is filtered under vacuum, and the upper carbon residues are washed with 50 mL of hot water to separate clear sodium silicate solution from carbon residues (Ozgul-Yucel et al. 2004). The silicate solution is preserved in a plastic bottle until used. Determination of silica content of the sodium silicate solution is achieved by lowering the pH of the solution from 12 to 7 to precipitate silica. After filtration, silica solution is double washed with 100 mL of water, dried at 110°C for 12 hours, and weighed (Kamath and Proctor, 1998).