The emision of corrosive vapours by wood. Hot-water-extracted O-acetylated hemicelluloses from sweet chestnut (Castnaea sativa) and wych elm (Ulmus glabrau) and a discussion of O-acetyl-group changes occurring in these woods during incubation at 48 degrees and 100 per cent relative humidity.

1. O-Acetylated polysaccharides were obtained from green wood of both sweet chestnut and wych elm by treatment of the residue remaining after dimethyl sulphoxide extraction with water at 98 degrees . This gives a mixture of polysaccharides containing xylose, galactose, glucose and uronic acids. Analysis of these and their fractionated products suggest that only xylans in green sweet chestnut and green wych elm are O-acetylated. 2. The isolated O-acetylated xylans are not representative of the total O-acetylated xylans occurring in sweet chestnut and wych elm. 3. Application of the method developed by Bouveng for the location of O-acetyl groups to all four O-acetylated xylans obtained in this series of investigations by dimethyl sulphoxide extraction showed that those from sweet chestnut and wych elm, under the same conditions of incubation, lost: 74.2 and 43.4% of acetyl groups respectively, at C-2; 58.0 and 28.5% of acetyl groups respectively at C-3; 41.8 and 82.2% of acetyl groups respectively at C-2 and C-3. 4. A consideration of electronic and steric factors indicates that there does not appear to be a purely chemical reason for the difference in loss of O-acetyl groups between sweet chestnut and wych elm. It is suggested that the location of O-acetylated xylans in the wood cell walls and the presence of extractive may play some part in this difference.