Use of the Centrifuge in Determining the Density of Small Crystals

Abstract

THE accurate measurement of crystal density has recently acquired increased importance, since it is necessary to know this quantity in order to use X-ray methods for determining the molecular weights of unknown chemical substances. But the usual crystallographic methods of density measurement, using the specific gravity bottle or flotation of the crystals under gravity in liquids of known density, cannot easily be made to give accurate results where only small quantities of very finely crystalline material are available. We have therefore recently applied the centrifuge in the second of these two methods to hasten the settling of floating crystals, just as the centrifuge is used by biologists in the measurement of the densities of living cells.