Particulate silica is prepared by feeding a gas mixture of an organohalosilane
gas, a flammable gas capable of generating water vapor when burned, and a free
oxygen-containing gas to a reaction chamber through a multiple-tube burner, whereby
the organohalosilane is subjected to flame hydrolysis and oxidation reaction. The
amount of the flammable gas fed is 0.5-9 mol per mol of the organohalosilane and
such that the amount of water vapor resulting from combustion of the flammable
gas is 1-6 times the stoichiometric amount, and the gas mixture is fed to the center
tube of the burner such that it may have a linear velocity at the outlet of 50-120
m/sec, calculated in the standard state. The resulting silica has a surface area
of 100-400 m2/g and a narrow particle size distribution of primary particles
and ensures the transparency of silicone rubber filled therewith.