Abstract: Photographic emulsions comprise silver halide grains which are generally produced by reacting an aqueous silver salt solution, and an aqueous halide solution in an aqueous gelatin solution in a reaction vessel. However, it may often be difficult to control the formation of the grains to produce consistent and reproducible emulsions. Described herein is an improved nucleation device for mixing photographic emulsions. The device has three inlets through which the silver salt solution, the halide solution and the gelatin are introduced into the device. The inlets are respectively connected to tube member and passages, the tube member and passages being concentrically disposed about an axis. Solutions from the tube member and passage impinge on a rotating rotor in a first mixing zone. Solution from passage mixes with the mixture from the first mixing zone at a second mixing zone spaced therefrom.