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: any sorting or grading of bulk material or loose articles fit to be handled like bulk material which results automatically from the construction of the apparatus and properties of the material, e.g. by a trap opening under an object of a certain minimum weight, by an aperture of graduated size; sorting of articles in so far as the same conditions apply, e.g. sorting of timber by passing it over successively longer openings; the articles may or may not be orientated for the purpose of sorting. SEPARATING SOLIDS FROM SOLIDS USING NETWORKS, GRATINGS, OR GRIDS SEPARATING SOLIDS FROM SOLIDS USING GAS CURRENTS , , , OTHER SEPARATING; COMBINATIONS ; This subclass covers sorting of materials or articles by hand or by devices actuated, manually or automatically, as a result of inspection or of detection or measurement of some feature of the material or articles. SORTING CHARACTERISED BY THE METHOD , , SORTING ACCORDING TO DESTINATION ,