gems, zircon, Ceylon, Sri Lanka, chemistry

Early chemical analysis of zircon from Ceylon (Sri Lanka). Wiegleb notes that the stones, also called hyacinths, occur in white, grey, pale-yellow and reddish varieties and are distinguished by their considerable density and hardness. Four drachms of differently colored zircons were repeatedly ignited, quenched, finely powdered, and subjected to a series of chemical treatments involving fixed alkali and acids. Wiegleb separated the material into what he identified as silica (Kieselerde), bitter earth or magnesia (Bittersalzerde), lime (Kalkerde), and iron. His final accounting of the four drachms gave 3 drachms 30 grains of silica, 8 grains of magnesia, 6½ grains of lime, and 6 grains of iron, together with a loss of 4 grains during ignition and 5½ grains during the analysis. Most significantly, the substance subsequently recognized as zirconia was not distinguished as a separate earth; the principal constituent was identified by Wiegleb as silica. The paper thus provides an important example of the difficulties encountered in the chemical characterization of zircon immediately before Klaproth’s identification of the new earth zirconia in 1789.