The penetration of aqueous sulphite solutions into differently shaped blocks of spruce wood has been investigated, the effect of the shape and type of wood, and of the presence of imprisoned air being determined. Measurements of the rates of diffusion of the constituents of calcium bisulphite solutions into pre-soaked blocks of wood showed that "free" sulphur dioxide diffused more readily than calcium bisulphite. Adsorption of sulphur dioxide and calcium bisulphite solutions by spruce wood was measured at 30° and 50 °C., and the influence of this factor on penetration was determined. The effect of penetration on delignification indicated the necessity of a satisfactory distribution of the lime salt at a low temperature to avoid localization of the lime during the pulping process.