XCIII. Experiments on the reduction of crystals of silver bromide

Crystals of silver bromide in the form of thin sheets with plane parallel surfaces have been reduced to metallic silver by a variety of methods. Before reduction, they were treated with bromine to destroy all traces of chemical fog on the surfaces and they were not again exposed to actinic light to form either a surface or an internal latent image. Reduction by photographic developers was initiated at a limited number of centres on the surface and resulted in the production of masses of silver with one of the following characteristic forms : (1) compact masses of coherent micro- crystals of silver occupying cavities bounded by (111) surfaces of the silver bromide crystal; (2) rigid projections based upon such masses and consisting of agglomerates of micro-crystals of somewhat smaller dimensions ; and (3) loosely tangled bundles of micro-crystals linked by ribbon- like filaments of silver. The conditions under which silver is produced in these different forms are outlined. A series of model experiments is described which provides evidence on the mechanisms of reduction. The complexity of the problem is emphasized.