1. This property has previously been observed at high temperatures but not at room temperature (as here) by G. W. Luckey of ihe Kodak Research Laboratories at Rochester in sheets of silver bromide, prepared by F. Urbach, lo which cupric bromide had been added (Private communication). The fused cuprous bromide used for our experiments was prepared by distilling pure cuprous bromide in a high vacuum and it was a clear colourless material. Hydrogen bromide was used as a protective gas during all the operations involving the fused material so that oxidation of cuprous to cupric bromide is unlikely to have occurred.
2. James, The Theory of the Photographic Process. Macmillan, New York, 1954, p.677.
3. Lowe, Jones, and Roberts, Fundamental Mechanisms of Photographic Sensitivity. Butterworth, London, 1951, p.112.
4. Mitchell, J. Phot. Sci.1, 110, 1953.