wall of the chips is active by placing the impregnation step early in the pulp manufacturing process a long time is provided for diffusion of the impregnation liquid into the fiber wall the chemical solution having insufficient time for affecting the fiber wall of the chips during their transport to the refiner usually is regarded as a process loss at a subsequent bleaching operation for example it may be considered advantageous that the excess impregnation chemicals be removed because they normally consume bleaching chemicals it may also be considered advantageous that the chemicals which during the impregnation step have not diffused into the fiber walls of the chips be removed by washing the chips when the chip washer is arranged for use after the impregnation part of the impregnation chemicals is transferred from the chips to the washing liquid the staying time in the chip washer being short most of the chemicals transferred come from surface water on the chips or from lumen liquid at the ends of the chips according to laboratory investigations about 15 percent of the sulphite is transferred while washing in clean water at the temperature and time occurring in a chip washer see fig4 the greatest part can be considered excess chemicals when the impregnation washing system approaches equilibrium the chemical content in the washing.