Journal of Research of the National Bureau of Standards
An apparatus has been developed for making precise measurements of the absolute thermal expansion of refractory materials at temperatures up to 1600 �C. This apparatus consists of an optical comparator and a controlled gradient vacuum furnace. Special care was taken on the techniques of measuring length and temperature and on the calibration of the microscopes and thermometers. The expansion data obtained with this apparatus on specimens of platinum and sapphire have a standard deviation of less than 30 ppm and are estimated to be accurate to within 50 ppm.
J. Res. Nat. Bur. Stand. Sec. C: Eng. Inst., Vol. 71C, No. 2, p. 85
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