Good soaps are nearly neutral substances because the alkali has been neutralized by the fatty acid. The coarser grades may contain more or less free alkali. All soaps are slightly decomposed when dissolved in water. The freed fatty acid produces the milkiness seen when a cake of soap is placed in perfectly pure water.

The cleaning action of soaps consists chiefly in forming emulsions with oily or greasy substances. Cream is an example of a very perfect emulsion. Its fat is in the shape of very finely divided globules and because of the whey which surrounds them, the cream can be mixed with a very large quantity of water and show no sign of greasiness. When the whey is separated as in churning, the globules of fat come together and butter is formed. An emulsion is not a true solution, for the particles of fat can be separated by proper means from the liquid.

The soap makes an emulsion with the oily or greasy substances holding the dirt, so that both may be washed away by the water. A certain proportion of free alkali in soap helps the action, but it has a corrosive effect on many materials. Soap will form emulsions with many other materials besides fats and oils; so while water is a very general solvent, soap and water will take up many additional substances.

The housekeeper may be familiar with two kinds of soap: hard soaps and soft soaps. Caustic soda makes the hard soaps and caustic potash makes the soft soaps.

Caustic potash is derived from wood ashes and a few generations ago soft soap was the only laundry soap used. Wood ashes were plenty when wood fires were universal. Soda-ash was at that time derived from sea weeds, and therefore uncommon inland. Early in the century a French manufacturer, Leblanc, discovered a process of making soda-ash from sodium chloride or common salt. This quite reversed the condition of the two alkalis, for now soda-ash is much more common, and the manufacture of soap on a large scale really began then. Soda-ash is now the cheapest form of alkali. Caustic soda is made from soda-ash.

Kinds of Soap

The terms, soda-ash, and pot-ash have been used; these substances in chemical terms are respectively the carbonate of sodium and the carbonate of potassium. They are chemical compounds made up of carbonic acid and two metals - sodium and potassium. When the carbon dioxide, which we have seen is formed by the combustion of carbon, is added to water, carbonic acid results. This is a very weak acid and when it is combined with the very strongly alkaline elements, sodium or potassium, the result is an alkaline substance. Soda-ash and potash (sometimes called pearl-ash) are called alkalis, but they are not nearly so powerful as the hydrates of sodium and potassium which are commonly called caustic soda and caustic potash.

When soda-ash, which is a white powder, is dissolved in hot water and the solution is cooled, crystals of the common washing soda are formed. This substance is also called "sal soda" and "soda crystals." The crystals contain about 65 per cent of water and when exposed to the air, lose some of this water and crumble to the white powder, soda-ash. The powder is, therefore, stronger than the original crystals.

Washing soda should never be used in a solid form, but should be dissolved in a separate dish, and the solution used with judgment. A satisfactory amount is about two ounces of the dry soda to a large tub of water, and well dissolved before the clothes are put in. Nearly all of the "washing compounds" on the market depend upon the washing soda for their efficiency, and sometimes they contain nothing else.

Borax is a useful alkali, milder than washing soda, but effective as a cleaner, disinfectant, and bleacher. It is more expensive than either of the others described, and because of its weaker alkaline action, more of it must be used to produce a given result. It is much less irritating to the skin and less injurious to fabrics than soda, so for some uses its additional cost may be justified. Caustic potash or "lye" is too strong an alkali to use on fabrics, but is valuable to put down the kitchen sink drain to free it from grease. The soap made in the drain will be washed out by water. Solid washing soda may be used for the same purpose.

In the laundry the composition of water is important. Water for domestic use is either hard or soft, according as it contains a greater or less quantity of certain soluble salts - usually compounds of lime or magnesia, which have been taken up by the water while passing through the soil.

When the hardness is caused by calcium carbonate (carbonate of lime) it is called "temporary" hardness, because it may be overcome by boiling. The excess of carbon dioxide is driven off and the carbonate of lime separates out. The same separation is accomplished by the addition of sal soda, borax, or ammonia.

When the hardness is due to the sulphates and chlorides of magnesia or lime, it cannot be removed by boiling. It is then known as "permanent" hardness. Public water supplies are sometimes softened before delivery to the consumer by the addition of slaked lime, which absorbs the carbon dioxide, and the previously dissolved carbonate separates out.

Soft water is needed in laundry work both for cleanness and economy, and water not naturally soft should be softened by boiling or by the addition of the before mentioned substances.

When soap is added to the hard water, it is decomposed by the water, and the new compound formed by the union of the lime and magnesia with the fatty acid of the soap is insoluble, and therefore settles upon any article with which it comes in contact. Until all the lime has been taken out, there will be no action between the soap and the dirt. Therefore, large quantities of soap must be wasted. It has been estimated that each grain of carbonate of lime per gallon causes an increased expenditure of two ounces of soap per 100 gallons, and that the increased expense for soap in a household of five persons where such hard water is used might amount to five or ten dollars yearly.

This "lime soap," although insoluble in water, will dissolve readily in kerosene or naphtha, for which reason, kerosene will be found very effective for cleaning bowls or the bath tub when the surface has become coated from the use of hard water and soap.

Hard waters produce certain undesirable effects in cooking processes. The cooking of beans and similar vegetables should soften the cellulose and break up the compact grains of starch. It is difficult to cook vegetables in hard water, for the legumin of the vegetable forms an insoluble compound with the lime or magnesia of the water, and the cellulose is softened with great difficulty. Hard water does not readily extract the flavor from tea and coffee, and therefore much more of either must be used to get the desired strength.

During this discussion of cleansing agents, let us hope that the breakfast dishes have been soaking in water, after having carefully scraped or "scrapped" so as to save soap in washing and to keep the water as clean as possible. Plenty of hot water and soap with clean, dry towels is the secret of quick and easy work. If the hard water is used, it may be softened for the soap is doing no good unless there is a strong suds.

To save the appearance of the hands, use a good white soap, free from alkali, and soften the water with borax.

Glass, silver ware, china and kitchen ware take their turn. All should be rinsed in hot water to remove the soap and heat the dishes so that they will drain nearly dry and thus make wiping easy. In the dish washing machine used in large hotels and restaurants, the dishes are simply washed with soapy water and rinsed in very hot water while in such a position that they drain perfectly. They dry completely and require no wiping. Fig. 16.

Restaurants.

Experiment. Wash a plate and dip it in very hot water, then place it so that all parts will drain. Observe if it dries completely. See if you can wash the dishes in this manner with very little wiping and if time would thus be saved.