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 This subclass covers: evaporation, distillation, crystallisation, filtration, dust precipitation, gas cleaning, absorption, adsorption; similar processes which are not concerned with, or limited to, separation (except in the case of absorption or adsorption). In this subclass, the terms or expressions are used with the meaning indicated: "filtration" and analogous terms include straining solids from fluids; "filter medium" is a porous material or porous arrangement of material used to filter solids from fluids; "filtering element" is a section of filter medium in addition to parts to which the medium is demountably or permanently fixed, including other sections of medium, end caps, peripheral frames or edge strips, but excluding housings; "filter housing" is the fluid-constraining impervious vessel, whether open or closed, which contains, or is adapted to contain, one or more filtering elements or filter media; "filter chamber" is the space within a housing, where filtering elements or filter media are located. Partitions may divide a single housing into a plurality of chambers; "filtering apparatus" consists of filtering elements combined with housings, cleaning arrangements, motor or the like parts, which are characteristic of the particular type of apparatus. Ancillary devices such as pumps or valves are considered part of a filtering apparatus when inside the apparatus. Ancillary devices performing similar or different unit operation such as comminutors, mixers or non-filtering separators, whether or not inside the apparatus, are not considered part of a filtering apparatus. The term does not extend to apparatus, e.g. washing machines, of which the filter forms only a part. For apparatus used in drying or evaporation, class takes precedence over this subclass. Group takes precedence over the other groups of this subclass and over other subclasses in class . EVAPORATION; DISTILLATION; SUBLIMATION ; ; ; COLD TRAPS, COLD BAFFLES CRYSTALLISATION SOLVENT EXTRACTION TREATING LIQUIDS: DISPLACEMENT, ADSORPTION, SEPARATION, DEGASIFICATION, CHROMATOGRAPHY , , , TREATING GASES OR VAPOURS: SEPARATION, RECOVERING, CHEMICAL OR BIOLOGICAL PURIFICATION OF WASTE GASES SEPARATION OF SUSPENDED PARTICLES FROM LIQUIDS By sedimentation By filtration processes gravity filters; filters formed from filtering elements, pressure or suction filters ; , cartridge filters filters with mobile filtering elements filtering devices filter circuits or combinations By other processes SEPARATION OF DISPERSED PARTICLES FROM GASES OR VAPOURS Pretreatment of the gas or vapour By gravity, inertia, centrifugal force; by filtration; by a combination of devices ; ; By other methods , FILTERING MATERIALS , SEPARATION OF ISOTOPES ABSORPTION, ADSORPTION, CHROMATOGRAPHY; OTHER SEPARATING METHODS , , , ; SEPARATION USING SEMI-PERMEABLE MEMBRANES; DIALYSIS, OSMOSIS, ULTRAFILTRATION In order that group may provide a basis for a complete search with respect to chromatography in general, all subject matter of general interest is classified in this group even if it is classified primarily in the application-oriented groups, for example dairy products , treatment of blood e.g. , optically active organic compounds or peptides . If the subject matter classified in this group also contains relevant information covered by other subgroups of group , it is also classified in the other appropriate subgroups of group . If the subject matter classified in this group also contains relevant information covered by other subgroups of group , it is also classified in the other appropriate subgroups of group . Processes using enzymes or micro-organisms in order to: liberate, separate or purify a pre-existing compound or composition, or to treat textiles or clean solid surfaces of materials are further classified in subclass . Group takes precedence over groups . In groups , in the absence of an indication to the contrary, classification is made in the last appropriate place (in respect of group , see also Note (1) following that group). In this group, the following term is used with the meaning indicated: "properties" covers those of a mechanical, physical or chemical nature. Manufacturing processes, if considered of interest, are also classified in group . In this group, if the material is a composition it is classified according to the constituent present in highest proportion. This constituent is classified according to the last place rule (see Note before group ). If there is more than one constituent present in equal highest proportions, then each of these constituents is classified according to the last place rule. Manufacturing processes, if considered of interest, are also classified in group . In this group the following term is used with the meaning indicated: "rubber" covers: natural or conjugated diene rubber; rubber in general (for specific rubber, see the group provided for such macromolecular compound).