Describes a new technique, for studying thermally-induced chemical changes in cellulose, consisting of a carbon dioxide laser for heating, an infrared thermometer and an optical reflectance spectrometer. Presents the results obtained from a single sample of linen cloth (spun from untreated flax, washed in water with saponaria and handwoven in a 3:1 herringbone twill pattern) along five isotherms between 200 and 290 degrees C. The results are discussed in terms of first-order chemical rate theory and a four-step model. Activation energies, Arrhenius constants and reflectivities of the chromophoric states are derived from the measurements. Tables, diagrams, 3 references.