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CORNING GLASS WORKS P  Y  R  E  X T.M. REG. U.S. PAT. OFF. POWER LINE INSULATORS PAT. MAY 27, 1919 TRANSMISSION and distribution insulators should be made only from material possessing unusual electrical, thermal and mechanical properties. PYREX insulators manufactured by Corning Glass Works have these essential qualities. Homogeneous Formed by the complete fusion of its constituents, the most important of which are the oxides of silicon, boron and alkali. It is non-porous. An unusually high permanent dielectric strength The design of various types of PYREX insulators is such that puncture strength exceeds A.I.E.E. Standard specifications. PYREX insulators have high electrical resistance The chemical stability of the material prevents the surface from being hygroscopic. The result is quick drying and low surface conductivity. The volume resistance is extremely high. PYREX insulators are transparent to solar heat The increase but slightly in temperature when exposed to the sun. Stresses due to temperature variations within the insulator itself are a minimum. PYREX insulators resist power arcs Tests prove that these insulators maintain satisfactory line insulation when subjected to an arc of 1800 amperes for two seconds. Low dielectric loss Low linear coefficient of thermal expansion 0.0000032 per degree Centigrade rise or fall in temperature is the value obtained for this constant. Few substances occur in Nature with an expansion as low as this. Chemically stable Tests demonstrate the extraordinary resistance of PYREX insulators to solution by water, acids and alkalies. The exceptional service rendered by PYREX products in the chemical laboratories of the world bears out this statement. PYREX insulators are easily inspected for internal defects The transparency of PYREX insulators permits them to be inspected visually for internal defects. This inspection may be made in the factory, during installation, or in service. This advantage, combined with thorough electrical tests, insures sound insulators. NOTE.--All electrical characteristics determined by Purdue University Laboratory, Lafayette, Indiana, and Electrical Testing Laboratories, New York City, in accordance with A.I.E.E. insulator test specifications.