The following notes are meant to assist in the use of this part of the classification scheme; they must not be read as modifying in any way the elaborations. In this sub-section, the separation of different materials, e.g. of different matter, size, or state, is predominantly found in the following subclasses: , , , , . The classifying characteristics of these subclasses are: the physical state of the matter to be separated; the principle of the process used; particular kinds of apparatus. The first of these characteristics involves six different aspects, assembled in three groups: liquid/liquid or liquid/gas and gas/gas; solid/liquid or solid/gas; solid/solid. These subclasses are to be used according to the following general rules: is the most general class as far as separation other than solids from solids is concerned. Apparatus for separating solids from solids are covered by when the process concerned is regarded as the equivalent of "washing" in the sense of the mining art, even if such apparatus is a pneumatic one, especially pneumatic tables or jigs. Screens per se are not covered by this subclass but are classified in , even if they are being used in a wet process. All other apparatus for the separation of solids from solids according to dry methods are classified in . If the separation takes place as a result of the detection or measurement of some feature of the material or articles to be sorted it is classified in . It should also be noted that the separation of isotopes of the same chemical element is covered by , whatever process or apparatus is employed. LIQUID/LIQUID, LIQUID/GAS OR GAS/GAS SEPARATION Method General operations by centrifugal force, using centrifuges or free-vortex apparatus using magnetic or electrostatic effect Apparatus General operations by centrifugal force, using centrifuges or free-vortex apparatus , using magnetic or electrostatic effect SOLID/LIQUID OR SOLID/GAS SEPARATION Method General operations by centrifugal force using centrifuges or free-vortex apparatus using magnetic or electrostatic effect Apparatus General operations by centrifugal force using centrifuges or free-vortex apparatus , using magnetic or electrostatic effect SOLID/SOLID SEPARATION Method Dry methods material in bulk Individual sorting Screening, sifting, pneumatic sorting using pneumatic tables or jigs by magnetic or electrostatic effect by centrifugal force using centrifuges or free-vortex apparatus Wet methods General operations flotation, differential sedimentation screening Combinations Dry methods - wet methods Apparatus Dry methods material in bulk Individual sorting Screening, sifting, pneumatic sorting using pneumatic tables or jigs by magnetic or electrostatic effect by centrifugal force using centrifuges or free-vortex apparatus , Wet methods General operations flotation, differential sedimentation screening Combinations Dry methods - wet methods In this class, the following terms or expressions are used with the meanings indicated: "other fluent materials" includes semiliquids, pastes, melts, solutions, dispersions, suspensions, particulate materials, gases or vapours; "particulate materials" includes powders, granules, short fibres or chips; "coating" means the materials applied. The coating may be a liquid having become solid after drying, e.g. paint. This subclass covers particularly apparatus for the release or projection of drops or droplets into the atmosphere or into a chamber to form a mist or the like. For this purpose, the materials to be projected may be suspended in a stream of gas or vapour. Attention is drawn to the Note following the title of class . APPARATUS CHARACTERISED BY THEIR STRUCTURE , , APPARATUS FOR DISCHARGE OF FLUIDS FROM TWO OR MORE SOURCES ELECTROSTATIC OR ELECTRIC APPARATUS APPARATUS CHARACTERISED BY MANIPULATION THEREOF , OTHER APPARATUS OUTLETS OR OTHER DETAILS , DELIVERY CONTROL This subclass covers apparatus or hand tools, in general, for applying liquids or other fluent materials to a surface or a part thereof, by any mechanical or physical method, in particular apparatus for obtaining a uniform distribution of liquids or other fluent materials on a surface. Attention is drawn to the Note following the title of class . APPARATUS CHARACTERISED BY THE MEANS USED , , , APPARATUS FOR SPECIAL WORK OR MATERIALS , HAND TOOLS DETAILS OR ACCESSORIES , , , , This subclass covers: processes for applying liquids or other fluent materials to a surface or part of a surface, in general, by any mechanical or physical method and particularly processes producing a uniform distribution of liquids or other fluent materials on a surface; pretreatment of surfaces to which liquids or other fluent materials are to be applied; after-treatment of applied coatings. Attention is drawn to the Note following the title of class . PROCESSES CHARACTERISED BY means used special result obtained surfaces to be treated PRETREATMENT OF SURFACES; AFTER-TREATMENT OF COATINGS