'Dr Slare Experiments made on the Mineral Kobalt in Order to the discovering the Nature of Zaffer' Details about the specimens of minerals (Cobalt and 'minera Argenti'), which had been sent to Slare by the physician to the Duke of Zell Details of the method used by the Germans to disguise the nature of 'zaffera' Read to the Royal Society on 15 July 1685 15 July 1685