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 this subclass, the following term or expression is used with the meaning indicated: "mixing" covers stirring of a single material. DISSOLVING MIXING, DISPERSING, EMULSIFYING Processes Apparatus flow mixers with rotary action , other mixers , accessories EMULSIFYING OR DISPERSING AGENTS In this subclass, the following terms or expressions are used with the meanings indicated: "solid particles" includes such particles whether catalysts, reactants or inert in solid, semi-solid or pasty state; "fluidised particles" means finely divided solid particles lifted and agitated by a stream of fluid; "fluidised-bed technique" means fluid-solid contacting technique in which finely divided particles are lifted and agitated by a rising stream of fluid, said stream having such a speed as to form a lower dense phase (the "bed") and an upper dilute fluidised phase of "fluidised particles"; "processes conducted in the presence of solid particles" does not include processes wherein the only solid particles present are formed during the reaction. In this subclass, tradenames that are often found in scientific and patent literature have been used in order to define precisely the scope of the groups. CHEMICAL, PHYSICAL, OR PHYSICO-CHEMICAL PROCESSES OR APPARATUS , , , , , CHEMICAL PROCESSES INVOLVING A GAS , , , CHEMICAL PROCESSES INVOLVING A LIQUID , , , CATALYSTS containing elements or inorganic compounds , , Raney type Molecular sieves containing hydrides, coordination complexes or organic compounds Catalyst carriers in general Preparation Regeneration or reactivation of catalysts, in general SORBENT, FILTER AID COMPOSITIONS ION EXCHANGE PROCESSES COLLOID CHEMISTRY GRANULATION This subclass covers only laboratory apparatus which is either applicable solely to laboratory purposes or which, by reason of its simple construction and adaptability, is such as would not be suitable for industrial use.