A method of deducing the chemical distribution of oxymethylene groups in cotton treated with (a) formaldehyde in the presence of acid and (b) methylene chloride in the presence of alkali by comparing their relative rates of acid hydrolysis with those of a series of model compounds is described. Aqueous-acid and acid-bake formaldehyde processes form oymetlylene cross-links between secondary hydroxyl groups in different anhydroglucose units as well as some polyoxymethylene links, whereas methylene chloride produces, in addition, links between primary, hydroxyl positions. The influence of hydrogen bonding and the proximity of acetyl groups on the acid-stability of the oxymethylene link is discussed and several new compounds are reported. A comparison of the mechanical properties of the chemically modified cotton fabrics suggests that cross-linking is the major cause of loss in strength and that the physical position of the links within the cellulose structure is more important than their exact chemical nature.