A unit for treating or reacting particulate solid material, in particular for ageing comminuted alkali cellulose (see Group IV (a)) comprises a longitudinally extending tank having an inlet and an outlet opening and longitudinally extending advancing means rotatable about a longitudinal axis (e.g. one or more screw conveyers rotatable about an offset axis) for advancing the material from the inlet to the outlet opening, the advancing means being also bodily rotatable about an axis other than its own axis of rotation, whereby the material is agitated during its advancement, and means for effecting the rotation about the two axes at independently adjustable rates. As shown in Figs. 3 and 4, each of a pair of interconnecting units 10, 11 includes a cylindrical tank 12 having a feed end 13 and a discharge end 14. The cylindrical shell 16 of each tank is provided with two or more jackets 27 through which a heat exchange medium is circulated. Each of the tanks 12 has an inlet opening 30 and a discharge opening 34, the discharge opening of the upper tank being directly connected to the inlet opening of the lower tank. A tubular stub shaft 41, to the outer end of which is keyed a sprocket wheel 43, is rotatably supported by a radial bearing 40 at the drive end of each of the tanks. The shaft 41 terminates at its inner end in a gear-wheel 42 disposed within the tank 12. A <PICT:0830985/III/1> <PICT:0830985/III/2> tubular main shaft 44 passes through the stub shaft along the longitudinal axis of each tank 12 and through the bush 40 at the opposite end of each tank 12. A sprocket wheel 46 is keyed to the free drive end of each of the shafts 44, and these sprockets are coupled to each other by a chain 48, while the sprockets 43 are coupled to each other by the chain 47. Keyed to the lower shaft 44 is a sprocket 49 which is driven by an adjustable variable-speed motor 52 through a chain 51. The chain 47 is driven by another adjustable variable-speed motor drive 53. The shafts 41, 44 may thus be independently driven at any desired speed. Located within each of the tanks 12 adjacent to the drive end thereof is a narrow cylindrical gear housing 56 including a circular rear wall 57 having an opening allowing the stub shaft 41 to pass through rotatably. The circular front wall 59 of the gear housing 56 is keyed to the shaft 44, whereby the gear-box 56 rotates with the shaft 44. The shafts 74 of a pair of longitudinally extending screw conveyers 73 are rotatably engaged by bushes 63 in the front wall of the gear-box 56 and bushes 69 in the disc-shaped support member 65 keyed to the shaft 44 adjacent to the rear end wall 14 of the tank 12. Also carried by the shaft 44 and keyed thereto is a circular partition 70 having a pair of large circular openings coaxial with the screw conveyers 73, permitting egress of the forwarded material to the outlet 34. At the drive ends of each of the shafts 74 in the gear-box 56 is keyed a spur gear 76 which engages the drive gear 42. Thus if the gear 42 is rotated with the stub shaft 41 by sprocket 43 clockwise at a lower angular speed than the gear-box 56, the screw conveyers 73 in the upper unit 10 will be rotated clockwise about their own axes and, as the pitch of the upper screw conveyers is right-handed, the material will be advanced from left to right in the upper unit 10. The pitch of the screw conveyers 73 in the lower unit 11 is left-handed, so that clockwise rotation of these conveyers advances the material from right to left in the lower unit. A number of pairs of longitudinally spaced hollow arms 78, 79 project radially from the main shaft 44 between the screw conveyers 73 and communicate with the hollow interior of the shaft. The ends of each pair of arms 78, 79 support and communicate with a hollow scraper or paddle element 80 having a tapered leading edge 81, disposed close to the inner wall of the tank 12, and a rounded trailing edge 82. The paddle element 82 may extend linearly or along a portion of a helical path. Mounted at the free ends of each of the shafts 44 is a conventional rotating fluid coupling 83 (shown on the right-hand end of the shafts only) through which a heat exchange medium may be introduced and flow through the hollow arms 78, 79 and hollow paddle 80, partitions 77 within the hollow main shaft 44 preventing the heat exchange medium from flowing direct from one end of the shaft to the other. The units 10, 11 may be arranged and spaced in end-to-end relationship, 10 being a heating unit and 11 a cooling unit of greater capacity than unit 10. A belt-type conveyer may extend from below the discharge conduit underneath unit 10 to above the feed conduit above unit 11 and may be totally enclosed in a heat-insulated housing. Alternatively, the material discharged from the unit 10 may be pneumatically conveyed to a cyclone separator mounted above one end of a horizontal endless belt conveyer mounted above the unit 11 in a heat-insulated housing. The cyclone separator discharges the heated material on to one end of the conveyer belt which conveys the material to the inlet hopper of the unit 11. The portion of the conveyer housing nearer the inlet hopper may be a precooling chamber in which a stream of cool air is directed over the material transported by the conveyer. By means of the apparatus described particulate solid materials may be treated in a uniform manner.ALSO:<PICT:0830985/IV (a)/1> <PICT:0830985/IV (a)/2> A unit for ageing comminuted alkali cellulose comprises a longitudinally extending tank having an inlet and an outlet opening and longitudinally extending advancing means rotatable about a longitudinal axis (e.g. one or more screw conveyers rotatable about an offset axis) for advancing the alkali cellulose from the inlet to the outlet opening, the advancing means being also bodily rotatable about an axis other than its own axis of rotation, whereby the alkali cellulose is agitated during its advancement, and means for effecting the rotation about the two axes at independently adjustable rates. As shown in Figs. 3 and 4, each of a pair of interconnecting units 10, 11 includes a cylindrical tank 12 having a feed end 13 and a discharge end 14. The cylindrical shell 16 of each tank is provided with two or more jackets 27 through which a heat-exchange medium is circulated. Each of the tanks 12 has an inlet opening 30 and a discharge opening 34, the discharge opening of the upper tank being directly connected to the inlet opening of the lower tank. A tubular stub shaft 41, to the outer end of which is keyed a sprocket wheel 43, is rotatably supported by a radial bearing 40 at the drive end of each of the tanks. The shaft 41 terminates at its inner end in a gearwheel 42 disposed within the tank 12. A tubular main shaft 44 passes through the stub shaft along the longitudinal axis of each tank 12 and through the bush 40 at the opposite end of each tank 12. A sprocket wheel 46 is keyed to the free drive end of each of the shafts 44, and these sprockets are coupled to each other by a chain 48, while the sprockets 43 are coupled to each other by the chain 47. Keyed to the lower shaft 44 is a sprocket 49 which is driven by an adjustable variable speed motor drive 52 through a chain 51. The chain 47 is driven by another adjustable variable speed motor drive 53. The shafts 41, 44 may thus be independently driven at any desired speed. Located within each of the tanks 12 adjacent to the drive end thereof is a narrow cylindrical gear housing 56 including a circular rear wall 57 having an opening allowing the stub shaft 41 to pass through rotatably. The circular front wall 59 of the gear housing 56 is keyed to the shaft 44, whereby the gear-box 56 rotates with the shaft 44. The shafts 74 of a pair of longitudinally extending screw conveyers 73 are rotatably engaged by bushes 63 in the front wall of the gear-box 56 and bushes 69 in the discshaped support member 65 keyed to the shaft 44 adjacent to the rear end wall 14 of the tank 12. Also carried by the shaft 44 and keyed thereto is a circular partition 70 having a pair of large circular openings coaxial with the screw conveyers 73, permitting egress of the forwarded alkali cellulose to the outlet 34. At the drive ends of each of the shafts 74 in the gear-box 56 is keyed a spur gear 76 which engages the drive gear 42. Thus, if the gear 42 is rotated with the stub shaft 41 by sprocket 43 clockwise at a lower angular speed than the gear-box 56, the screw conveyers 73 in the upper unit 10 will be rotated clockwise about their own axes and, as the pitch of the upper screw conveyers is right-handed, the alkali cellulose will be advanced from left to right in the upper unit 10. The pitch of the screw conveyers 73 in the lower unit 11 is lefthanded, so that clockwise rotation of these conveyers advances the alkali cellulose from right to left in the lower unit. A number of pairs of longitudinally spaced hollow arms 78, 79 project radially from the main shaft 44 between the screw conveyers 73 and communicate with the hollow interior of the shaft. The ends of each pair of arms 78, 79 support and communicate with a hollow scraper or paddle element 80 having a tapered leading edge 81, disposed close to the inner wall of the tank 12, and a rounded trailing edge 82. The paddle element 82 may extend linearly or along a portion of a helical path. Mounted at the free ends of each of the shafts 44 is a conventional rotating fluid coupling 83 (shown on the right-hand end of the shafts only) through which a heat-exchange medium may be introduced and flow through the hollow arms 78, 79 and hollow paddle 80, partitions 77 within the hollow main shaft 44 preventing the heat-exchange medium from flowing direct from one end of the shaft to the other. The units 10, 11 may be arranged and spaced in end-to-end relationship, 10 being a heating unit and 11