=Cleansing agents.=——Water is the great cleanser, and if it is not available in abundance and used freely, the washing is a failure. All other agents are merely aids to the water or substitutes for it. In primitive outdoor methods, still largely used in some countries, the flowing water is the only agent, and yet the result is fairly good. We aid the process by the use of soap or washing powders or ammonia. The air and sun are also purifiers, and clothing should be exposed to their action for drying whenever possible. There is a sweetness in air and sun-dried clothing that no artificial drier seems to give. Probably there takes place some oxidation of impurities present in very small amount and, moreover, any bacteria still clinging to the fabric may be killed by the sun’s rays. Heat is a purifier, oily substances being more readily removed by hot water and soap than by cold; and the boiling temperature of water renders bacteria and organic matter harmless. Some mechanical action that forces water through the fabric is necessary, and the method of accomplishing this is one of the important problems in laundering. We seek a method that will be thorough, that will not injure the fabric, and that will economize the muscular energy of the worker. Beating, pounding, and rubbing are the old methods, the use of a machine the new, and that is the best machine that meets all the requirements of the properly conducted washing process as described below. The _water_ should be soft and clean. Rain water is a perfectly soft water and excellent for laundering if the cistern is kept clean, and free from the dust of the roof. Lake, river, and well water are sometimes soft. Strainers may be used on the faucets if at any time the water from these sources becomes muddy. (See Chapter V for discussion of soft and hard water.) Hard water prevents the soap from lathering, and this must be counteracted for laundering. _Temporary hardness_ is removed by boiling. _Permanent hardness_ is not affected by boiling and can be overcome only by the addition of some substance like ammonia, borax, or soda. Only enough of these should be used to allow the soap to do its work, since they may injure fabric and the skin of the worker. _Soap_ is the most useful of the cleansing agents added to water. It may have been accidentally made in the first place by some housewife who put a greasy pot to soak with a solution of lye made from the ashes of her hearth fire. Heat and alkali break up the fat into two parts, glycerin and a fatty acid. The fatty acid combines with the alkali, giving soap, and the glycerin remains free. Both animal and vegetable fats are used, and different forms of alkali, usually potash or caustic soda, the former for soft, the latter for hard, soap.