Abstract: Optically clear silicone compositions comprising 100 parts by weight of at least one polydiorganosiloxane and 15 to 120 parts by weight of a hydrophobic reinforcing silica filler wherein substantially all of the surface-treated silica filler particles are sufficiently small in their largest dimensions such that a uniform 2.54 mm thickness of the composition possesses a haze value of less than 4% and a luminous transmittance value of at least 85% according to ASTM D1003-61. The refractive index of the polydiorganosiloxane does not have to be matched with that of the silica filler to obtain optically clear compositions. The haze value of certain of such compositions does not increase by more than 1% per 2.54 mm thickness when the composition is heated from 23.degree..+-.2.degree. C. to 100.degree..+-.5.degree. C. Optionally, curing agents and other additives can be present in the compositions. Optically clear cured elastomers useful as lenses or tubing can be prepared from such elastomers.

Abstract: Combustion chamber arrangements for divided chamber (prechamber) type diesel engines characterized by relatively low emissions of HC, CO and NO.sub.x, relatively low noise and physical stress and good fuel economy and power output and having (1) canted valves in the heads and forming therewith lateral wedge-shaped valve recesses, (2) cooperating wedge recesses in the pistons forming disc or pancake-like valve pockets in conjunction with the cylinder head recesses and (3) in-head prechambers closed by flame cups having wide connecting passages in their floors and side outlets for connection through channels with the edges of the valve pockets.