In order to analyse quantitatively the washing behavior of liquid flow to fabrics, it is studied to obtain the liquid drag coefficient of fabrics by using a falling method in which a specimen falls freely in a still liquid. A theoretical treatment of fabrics falling freely in a still liquid has shown that the liquid drag coefficient of fabrics is proportional to the falling time squared, the error of the estimated liquid drag coefficient of fabric being twice the error of falling time. The treatment has also shown that a fabric falls at the terminal velocity after travelling 10 cm from the beginning of its falling. The experiment in which fabrics were let to fall freely in a still liquid shows that the drag coefficient of fabrics is 1-3 for water, irrespective of the kind of fabrics, if the falling velocity is 1-30 cm/s, the fabric surface area vertical to the direction of falling being 1-25cm2, water temperature beings18°C. The experiment has also shown that for an aqueous solution of detergent, the drag coefficient is slightly higher.
This study aims to make clear the relationship between washing ability of detergents for clothings and the number of wash-wear cycles. In the washing test, naturally soiled neck-collar cloths have been laundered under the conditions of home laundering with soap or syndets. Experiments have revealed that although soaps, as compared with syndets, show the high detergency in the first laundering, soaps decrease their detergency with increasing unmber of wash-wear cycles. The amount of Ca-soap deposited on neck-collar cloths has increased with increasing the number of wash-wear cycles. The amount of soils deposited and remained on neck-collar cloths has also increased with increasing the, amount of deposited Ca-soap. Thus, the lowered detergency of soaps in the wash-wear cycles can be explained by the amount of Ca-soap deposited on the neck-collar cloth which has remarkable effect on the soil deposition and washing ability of detergents. As differences in soil removal have been recognized between the result of first laundering and wash-wear cycle test, a wash-wear cycle test is important to get the detergency agreed well the test result of consumer test.