The Utilization of Solid Objects as Reference Standards in Density Measurements

NBS has measured the densities of four single crystal silicon objects to a standard deviation of 0.26 ppm with a systematic error of 0.7 ppm. These objects will be used as working standards to which density work in the United States will be referred. A redundant hydrostatic comparison test involving two standards at a time has been devised, the use of which facilitates the efficient propagation of the density information contained in these crystals into other objects which may be used as standards by other laboratories. This article describes a method of employing this redundant comparison procedure.