General Science

by Bertha May Clark

Most fats contain a substance of an acid nature, and are decomposed by the action of bases such as caustic soda and caustic potash. The acid component of the grease partially neutralizes the base, and a new substance is formed, namely, soap.

With the advance of civilization the labor of soap making passed from the home to the factory, very much as bread making has done in our own day. Different varieties of soaps appeared, of which the hard soap was the most popular, owing to the ease with which it could be transported. Within the last few years liquid soaps have come into favor, especially in schools, railroad stations, and other public places, where a cake of soap would be handled by many persons. By means of a simple device (Fig. 157), the soap escapes from a receptacle when needed. The mass of the soap does not come in contact with the skin, and hence the spread of contagious skin diseases is lessened.

FIG. 157.—Liquid soap container.

Commercial soaps are made from a great variety of substances, such as tallow, lard, castor oil, coconut oil, olive oil, etc.; or in cheaper soaps, from rosin, cottonseed oil, and waste grease. The fats which go to waste in our garbage could be made a source of income, not only to the housewife, but to the city. In Columbus, Ohio, garbage is used as a source of revenue; the grease from the garbage being sold for soap making, and the tankage (Section 188) for fertilizer.

206. Why Soap Cleans. The natural oil of the skin catches and retains dust and dirt, and makes a greasy film over the body. This cannot be removed by water alone, but if soap is used and a generous lather is applied to the skin, the dirt is "cut" and passes from the body into the water. Soap affects a grease film and water very much as the white of an egg affects oil and water. These two liquids alone do not mix, the oil remaining separate on the surface of the water; but if a small quantity of white of egg is added, an emulsion is formed, the oil separating into minute droplets which spread through the water. In the same way, soap acts on a grease film, separating it into minute droplets which leave the skin and spread through the water, carrying with them the dust and dirt particles. The warmer the water, the better will be the emulsion, and hence the more effective the removal of dirt and grease. This explanation holds true for the removal of grease from any surface, whether of the body, clothing, furniture, or dishes.

207. Washing Powders. Sometimes soap refuses to form a lather and instead cakes and floats as a scum on the top of the water; this is not the fault of the soap but of the water. As water seeps through the soil or flows over the land, it absorbs and retains various soil constituents which modify its character and, in some cases, render it almost useless for household purposes. Most of us are familiar with the rain barrel of the country house, and know that the housewife prefers rain water for laundry and general work. Rain water, coming as it does from the clouds, is free from the chemicals gathered by ground water, and is hence practically pure. While foreign substances do not necessarily injure water for drinking purposes (Section 69), they are often of such a nature as to prevent soap from forming an emulsion, and hence from doing its work. Under such circumstances the water is said to be hard, and soap used with it is wasted. Even if water is only moderately hard, much soap is lost. The substances which make water hard are calcium and magnesium salts. When soap is put into water containing one or both of these, it combines with the salts to form sticky insoluble scum. It is therefore not free to form an emulsion and to remove grease. As a cleansing agent it is valueless. The average city supply contains so little hardness that it is satisfactory for toilet purposes; but in the laundry, where there is need for the full effect of the soap, and where the slightest loss would aggregate a great deal in the course of time, something must be done to counteract the hardness. The addition of soda, or sodium carbonate to the water will usually produce the desired effect. Washing soda combines with calcium and magnesium and prevents them from uniting with soap. The soap is thus free to form an emulsion, just as in ordinary water. Washing powders are sometimes used instead of washing soda. Most washing powders contain, in addition to a softening agent, some alkali, and hence a double good is obtained from their use; they not only soften the water and allow the soap to form an emulsion, but they also, through their alkali content, cut the grease and themselves act as cleansers. In some cities where the water is very hard, as in Columbus, Ohio, it is softened and filtered at public expense, before it leaves the reservoirs. But even under these circumstances, a moderate use of washing powder is general in laundry work.

If washing powder is put on clothes dry, or is thrown into a crowded tub, it will eat the clothes before it has a chance to dissolve in the water. The only safe method is to dissolve the powder before the clothes are put into the tub. The trouble with our public laundries is that many of them are careless about this very fact, and do not take time to dissolve the powder before mixing it with the clothes.

The strongest washing powder is soda, and this cheap form is as good as any of the more expensive preparations sold under fancy names. Borax is a milder powder and is desirable for finer work.

One of the most disagreeable consequences of the use of hard water for bathing is the unavoidable scum which forms on the sides of bathtub and washbowl. The removal of the caked grease is difficult, and if soap alone is used, the cleaning of the tub requires both patience and hard scrubbing. The labor can be greatly lessened by moistening the scrubbing cloth with turpentine and applying it to the greasy film, which immediately dissolves and thus can be easily removed. The presence of the scum can be largely avoided by adding a small amount of liquid ammonia to the bath water. But many persons object to this; hence it is well to have some other easy method of removing the objectionable matter.