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SynopsisWhen small wood (or cellulose) samples are vacuum-dried a t room temperature, their h a 1 weight is found to vary according to their previous sorption history. The weight variations, of up to I%, are shown to be due to strongly retained water. A minimum weight is obtained reproducibly ( f 0.01%) only when the wood is dried rapidly from the wetted state. When wood thus dried is exposed to water vapor and redried, water is retained even after drying for long periods or a t higher temperatures (65°C.) and is removed only by again wetting and redrying the wood. The quantity of water retained is greatest after exposure to relative vapor pressures of approximately 0.5 and increases linearly with the square root of time of exposure up to at least 1000 hr. As some of these phenomena have been reported for the wool-water system also, it is possible that other poIymers, particularly those which swell in water, may behave similarly. The significance of these resulta for the experimental determination of moisture content and the study of water sorption is discussed.