the stratified bulk material filter according to fig1 - 3 comprises a housing 1 provided with a crude gas inlet and a purified gas outlet , and which is subdivided by a partition 2 into a crude gas space and a purified gas space 3 . preferably several , e . g . four , vertical bulk material layers 4 , 5 , 6 and 7 are situated in the crude gas space , and are enflanked at opposite sides by gas permeable delimitations which for example consist of perforated surfaces or strips of material 8 and 9 which are installed one above the other with an inward and downward inclination from the outside of the layers . it is also possible to install the perforated strips of material adjacently one above another in a plane or to replace the delimitations 8 at the flow arrival side by horizontal areal members or horizontal branches of angular sections , as indicated in fig5 . fig6 shows the application of plane delimiting surfaces provided with perforations . the material strips or surfaces 8 form the flow arrival side of the bulk material layers , whereas the surfaces or strips of material 9 form the flow departure side of the purified crude or flue gas . the delimitation forming the flow departure side may also consist of spaced solid sheet metal strips which force the bulk material to form a slope by oblique positioning and at the same time allow of a gas throughflow . according to the example , pairs of adjacent bulk material layers , 4 , 5 and 6 , 7 are associated to form respective purified gas flow departure spaces 10 , 11 . the crude or flue gas is distributed within the housing 1 and flows through the bulk material layers in the direction of the pecked arrows of fig1 and 3 and then flows as purified gas to the outside via the flow departure spaces 10 and 11 and the purified gas space 3 , the flow for example being caused by a suction fan . the bulk material layers 4 to 7 which are supplied with bulk material from above from a stock via a conveyor screw 12 or the like , are closed off at the bottom or supported by an extraction device , for example comprising a fixed upper grid 13 and a movable bottom grid 14 which latter covers the passages of the upper grid 13 in the inoperative position . the displacement of the bottom grid for removal of bulk material is caused via a crank drive for example . according to the invention , the strips 8 or surfaces forming the flow arrival sides of the bulk material layers are provided with a perforation or opening of which the dimensions are larger than the diameter of the bulk material grains and bulk material slopes may be formed at the openings . the delimitations 9 at the flow departure side are so formed that no bulk material passes into the flow departure spaces 10 and 11 with the bulk material layers closed off at the bottom , or rather in the case of incorporation of bottom extraction grids , very little bulk material only passes -- e . g . in the form of grains of too small a size -- into the flow departure spaces 10 and li , which are then in comnunication at the bottom with the grid . if the perforations of the strips 8 or surfaces at the flow arrival side of the bulk material layers have a greater diameter than the bulk material grains , no bulk material emerges sideways without a complementary deliberate action , since the grains form a slope at or within the perforations . to renew the bulk material which is charged with particles or noxious gases or deactivated , at the flow arrival side and to allow for egress of bulk material against the direction of flow arrival of the crude or flue gas , the bulk material grains are energized into a movement whereby they emerge laterally through the perforations and drop downwards . to accomplish this , a counterflow flushing operation or counterflow compressed gas flushing operation , is performed briefly and cyclically , e . g . in 0 . 1 to 1 second . to this end , a distributor pipe 17 which may be supplied with compressed gas from a source 15 via an openable valve 16 and has outlet slots directed at nozzles 18 which for their part are directed into the purified gas flow departure spaces 10 and 11 , projects into the purified gas space 3 . as soon as the bulk material is excessively charged with particles at the flow arrival side 8 , the resistance of the filter being increased thereby , or as soon as the bulk material at the flow arrival side has been deactivated by combining with noxious gases , the valve 16 is opened and a compressed gas surge is applied in counterflow to the crude or flue gas on the bulk material of the two adjacent bulk material layers , which causes the slope - forming grains to be set in motion before or within the perforations at the flow arrival side 8 and thereby to emerge sideways out of the layers through the perforations of greater diameter or out of the bulk material slopes , and to drop down whilst fresh bulk material drops down from above in replenishment into the bulk material layers . so that a displacement of the grains may occur at the flow arrival side during the counterflow surge in any event , e . g . in the case of the deposition and incorporation of highly adhesive particles , the bottom grid 14 of the supporting grids 13 , 14 may for example be set in motion briefly and simultaneously with the pulse , so that bulk material is removed at the bottom and the bulk material layer is thereby placed in motion from the top towards the bottom . the compaction of the grains is loosened thereby and the lateral extraction of grains by the flushing gas pulse is intensified . instead of the compressed gas counterflow flushing operation by means of the embodiment described , a different flushing gas flow may also be generated , e . g . as described in the german patent application no . p 33 41 065 . 8 - 23 . it may be advantageous in special cases to form the separating surfaces at the flow arrival side so that bulk material grains cannot pass through the perforations for which reason their dimensions are then kept smaller than the diameter of the grains . in this case , the extraction of bulk material then occurs exclusively via a bottom extraction grid , the periodic counterflow flushing action being retained as an important complement . this combination is advantageous , for example if for special reasons the layer of bulk material is to be replaced practically in toto in one operation from time to time , to resolve problems posed regarding adsorption of noxious gases . if , in this connection , the crude gas is also charged with particles apart from noxious gases , these are preferentially deposited on or in the flow arrival section and generate an undesirable rise in flow resistance . it is consequently necessary during the dwell period of the bulk material to remove the particles towards the side and finally to cause these to drop into the collector space 1a , by means of the counterflow flushing action , advantageously coupled by a simultaneous and consequently very brief removal of extremely small grains at the bottom . so that the particles merging laterally from the delimitations 8 have enough time to drop into the bottom collector space 1a in the case of a necessary and extensive separation of particles , the bulk material filter is divided advantageously into chambers -- advantageously at least in the region of the purified gas space 3 , so that for example one pair of bulk material layers 4 , 5 and 6 , 7 is allocated to each chamber . the division into chambers is denoted by the dash - dotted line 19 in fig3 . a separation of the chamber against being acted upon by crude or flue gas will then be retained during and after the counterflow gas flushing action performed in a chamber , until the laterally emerging particles have dropped in free fall downwards into the collector space 1a . a redeposition of cleaned - off particles before reaching the collector space 1a after completion of a brief counterflow action is thereby prevented whilst the invention and many of its attendant advantages will be understood from the foregoing description , it will be apparent that various changes may be made in the form , construction and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing all of its material advantages , the form hereinbefore described merely being a preferred embodiment .