Washing experiments were performed in which liquid flows were directed perpendicularly and made to penetrate artificially soiled cotton fabrics. Two such cotton fabrics were used : one soiled with carbon black and palmitic acid, and the other with tris (8-quinolinolato) iron (III) (ferric oxynate) and hardened beef tallow liquid paraffin. Detergent concentration ranged from 0.1 to 0.4% and the flow velocity from 0.1 to 1.2 m/s. Detergency increased with increasing velocity but tended to saturate in the high velocity range. Washing periods exceeding 10 seconds did not increase the detergency.
Washing under the present experimental conditions was analysed theoretically; the relation between the degree of reflection and number of soil particles can be expressed by a simple equation, and assuming the soil particles to be removed by drag caused by Stoke's flow, detersive efficiency can be expressed as a function of velocity. Such a function would include parameters of soil particle adhesion force, the corresponding radii being decided by the structure of textile fabric, liquid viscosity and soil particle diameter. For given parameter values, the analytical results were found to agree well with the present experimental data.