On the purification and testing of Selenion

In 1895 I was enabled by a Royal Society grant to obtain about 100 lbs. weight of selenion of about 99·5-per-cent. selenion content. The grant was applied for to enable me to extend to selenion the investigations already made on purified sulphur. For the purpose of the investigation it was necessary to purify the selenion beyond the standard usual for material to be used in atomic weight investigations. This proved in the event to be impossible on account of the comparatively slight volatility of selenion dioxide, and the impossibility of preventing its formation in the course of the electric measurements I proposed to carry out. Meanwhile, I had prepared a great deal of very pure selenion, and began to investigate its properties—other than those of conduction, for which absolute purity is essential. The method of purification adopted was essentially that of Ekman and Petterson.