Photographic dry plates that can be developed in water contain one of the developing agents in a film of gum on the hack of the plate. On placing the plate in a specified quantity of water containing the alkali, the gum dissolves, liberates the reducing agent, and development commences. The process is recommended for the use of tourists, so as To avoid the necessity for carrying developing materials; but it is doubtful whether it possesses any advantages, as an accelerator and a restrainer and a glass measure must he carried. Tabloids are just as convenient, and probably more reliable, as the plates do not keep well; the plates are prepared as follows. Dissolve 100 gr. of pyro and 15 gr. of salicylic acid in 2 dr. of water ami add 1 dr. of alcohol. Dissolve 150 gr. of gum arabic in 3 dr. of water. Mix the two, and brush over the back of the plates. About 1/2 dr. should lie used for each quarter-plate. Allow to dry spontaneously. Expose as usual, and develop by immersion in water containing two to three drops of strongest liquor ammonia, .880 per ounce.