Abstract

A fused silica sphere, 96 mm in diameter, has been manufactured as a solid density standard. It will be used to measure the densities of liquids by the method of hydrostatic weighing. The volume of the sphere has been determined by making a large number of interferometric diameter measurements. The sphere was placed within an uncoated etalon, and the gaps between sphere and etalon were measured by observing the circular interference fringes formed by light reflected from each etalon plate and the adjacent sphere surface. A cadmium lamp provided illumination of limited coherence to avoid unwanted interference effects due to internally reflected light. The interference fringes were scanned by displacing the etalon with respect to the sphere so that the sum of the two gaps was obtained directly. This paper describes the experimental arrangement, including the method used to turn the sphere so that a large number of diameters could be measured under computer control. It also includes sample results and an estimate of the final accuracy of volume measurement which is expected to exceed that of previous measurements.

© 1985 Optical Society of America