The methods used for preparing thin sheets of silver chloride, silve r bromide, binary and ternary mixed crystals of silver halides, and mixed crystals of silver bromide with silver sulphide and other metallic bromides are described in detail. The results of expriments on the chemical sensitization of these materials are presented. The conclusion has been reached that, as far as the formation and development of the latent image is concerned, there is no significant increase in the sensitivity of the mixed crystals compared with that of strained crystals of pure silver bromide. Experiments with antifogging agents, antiplumming agents, development accelerators and dye sensitizers and supersensitizers are briefly described , The causes of low intensity reciprocity failure in the formation of the surface and internal latent images in the thin sheets are discussed in detail and methods which may be used to diminish low intensity failure in the formation of the surface latent image are outlined.