55 and an upward extending outer rim 56 which rim has at each of its ends a vertical flange 57 which may be bored to receive a loose fitting cross pin 58 the flanges 57 may be either bent inward from the ends of the outer rim 56 or upward from the horizontal base strips 55 and may be drilled at their mid points to accept joining pins 58 when assembled within the tank and a hinged pair of semi circular screens 52 opened and placed thereon the rack 50 may rest on two studs or bolts 65 which project inward from the tank inner wall at 90 u00b0 intervals into each lower support rack 50 is placed a circular full diameter filter which may be a simple open cell plastic foam pad 60 whose thickness is at least one inch preferably about two inches in it is poured a fill whose depth may vary for example from one fourth to one half of the tank depth of an h 2 s reactant oxide intermixed with and retained on inert carrier material such material pre mixed is obtainable from gas sweetener associates inc st louis mo under the trademark 34 sulfaclean 34 this pre mixed material has a composition substantially like that shown in u s pat no 5 320 992 except for the omission of sodium sulfite the approximate percentages of its ingredients are ______________________________________ingredient ______________________________________calcined montmorillonite 60reactive iron oxide composed of a 22crystalline phase of fe sub 3 o sub 4 togetherwith an amorphous fe sub 2 o.