289,800. Stern, H. von. May 2, 1927, [Convention date]. Developing apparatus for the gaseous development of photographic prints comprises an endless conveyer sheet F passing over rollers G and in gas-tight contact with a plate C preferably arched, which is provided with holes band is arranged over a chamber A filled with developing gas. The prints are fed in at H and are carried by the sheet F over the perforated plate C, whereafter they are delivered at J down a guide 0 into a chamber R from which air is continuously exhausted in order to remove gas still adhering to the prints. The gas may be obtained by evaporation from liquid in a trough B, or may be introduced into the chamber A from a gas cylinder, and may be heated by a hot pipe passing through the chamber. A motor beneath the chamber R drives the rollers G and the exhaust pump V.