the ozone reaction agent embodiment the fibrous materials and circulating medium enter defibrator 1 are mixed and comminuted and travel along process line 9 to reaction zone 2 in this case hydrogen peroxide reaction agent is a liquid and is allowed to react with the fibrous materials for several hours after a sufficient retention time has passed the fibrous materials and liquid h 2 o 2 are discharged via process line 16 while the resulting circulating gas is transmitted through the system to be recycled when hydrogen peroxide is the reaction agent air is used as the carrier gas the air absorbs hydrogen peroxide vapors while in reaction zone 2 and the vaporized hydrogen peroxide is recycled with the circulating gas the use of hydrogen peroxide vapors in the defibrator enhances the brightness gain in the bleaching process thus circulating gas exits reaction zone 2 and is passed to defibrator 1 via process lines 11 13 13a 37 25 27 and 29 all of the vapors from reaction zone 2 are recycled to defibrator 1 so gas discharge zone 3 is not utilized unless a buildup of gases occur in the system in this case gas discharge zone 3 would merely purge the excess gases since they are nontoxic and thus treatment is unnecessary before release to the atmosphere thermal treatment of the recycled gas is not required because hydrogen peroxide does not decompose as rapidly as ozone however if cooling were desired in defibrator 1 the circulating gas could be routed through heat exchanger 4 before returning to defibrator 1 in order to obtain an optimum adjustment.