Abstract: A method for producing a photographic emulsion is disclosed. The method includes the process of adding a dispersion of a substantially water-insoluble photographic additive to a photographic emulsion. The dispersion being prepared merely by mechanically grinding and dispersing the photographic additive in a form of fine grain having a size of 1.mu. or less in an aqueous system adjusted to a pH value of 6 to 8 and controlled to a temperature of 60.degree. to 80.degree. C. The additive is included in the photographic emulsion without the need of an organic solvent. The emulsion of the invention can be easily and quickly coated to form a uniform layer.

Abstract: A method and apparatus for converting gel-like substances from a gel state to a sol state in which the melting speed can be accurately controlled over a wide range and the apparatus can be easily cleaned. A grid-type heater constructed of rotatable parallel heating pipes is disposed at the bottom of a melting tank. Rotation of the pipes which simultaneously heating them imparts flowability to a heat transfer boundary formed on the side of the gel-like substance. The melting speed is controlled by controlling the speed of rotation of the pipes.

Abstract: Crude hydroquinone containing impurities is purified in a sublimation purification apparatus where the crude hydroquinone is introduced into a stirred and fluidized bed, a carrier gas which is inert to the hydroquinone is passed therethrough, and the temperature therein is kept at about 110.degree.-170.degree.C whereby crude hydroquinone is sublimed, and thereafter a mixed gas consisting of the sublimed vapor and the carrier gas is introduced into a condenser at a temperature at about 25.degree.-90.degree.C whereby the hydroquinone only is fractionally solidified. After the sublimation purification, hydroquinone of high purity can be collected.