Abstract: Finely divided precipitated silica for use as a delustering agent with high structure and a______________________________________ BET surface (DIN 66 132) of 150 to 350 m.sup.2 /g Stamping density (DIN 53 194) between 60 and 120 g/l DBP absorption number between 3.0 and 4.0 ml/g Particle size distribution at least 70% from 1 to 6 .mu.m ______________________________________ can be prepared by heating a mixture of water and sodium silicate under agitation to a temperature of 70.degree. to 80.degree. C., adding concentrated sulfuric acid into this mixture until half of the alkali present has been neutralized, shearing the reaction mixture and optionally raising the temperature at the same time to 86.degree..+-.5.degree. C. Concentrated sulfuric acid is added after a period of 30 to 120 minutes at a rather high rate until the pH of the silica suspension produced is 3.0 to 3.5.

Abstract: The invention is directed to the modification of synthetic, silicatic fillers with water insoluble sulfur containing organosilicon compounds. For this purpose, the fillers are converted into an aqueous suspension and treated with the organosilicon compounds, optionally in the presence of an emulsifier. The thus modified filler in vulcanized rubber mixtures results in a clear improvement in the industrial properties of the rubber.

Abstract: The invention is directed to the modification of natural oxidic or silicate fillers with water insoluble sulfur containing organosilicon compounds. For this purpose, the fillers are converted into an aqueous suspension and treated with the organosilicon compounds, in a given case in the presence of an emulsifier.

Abstract: Pyrogenically produced silica after separation of the hydrogen halide is mixed with nitrogen and conveyed into a cyclone. After separation of the gases, which are returned into the cooling stretch of the production apparatus, the silica is first mixed with organohalosilane and nitrogen and subsequently with steam and nitrogen. Subsequently the hydrophobization reaction is carried out in known manner in a fluidized bed reactor. The reaction waste gases are returned into the cyclone.