Decoloration and the Ultramicroscopic Behaviour of Natural Blue and Violet Rock Salt

Abstract

THE absorption spectrum of blue rock salt from Stassfurt was determined photo-electrically in the natural state and after heating for a certain time at various temperatures. The spectrum shows the well-known high maximum at 653 mµ and the smaller one at 535 mµ. On increasing the time of heating, the first maximum begins to shift towards shorter wave-lengths; its intensity increases at first and then decreases. The second maximum does not alter its position; it decreases immediately and disappears sooner than the first. The violet salt from the Grimberg mine in the Werra valley behaves quite differently. It shows only one maximum, at 583 mµ, which is not displaced after heating, and begins to decrease immediately.