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and derived from the same source as, benzin; carbon tetrachlorid, a non-inflammable coal tar product; organic acids, as citric acid, which is obtained from lemons, and oxalic acid, which is made chiefly from wood by heating sawdust and shavings with caustic potash or soda. Ammonia will dissolve the oxids of copper and nickel and is therefore often added to polishes used for cleaning these metals. Kerosene or coal oil, a distillate of petroleum, will dissolve several of the metal oxids, especially that of iron, therefore it is much used to remove rust from iron; it will also dissolve the lime soap formed, as shown in Chapter XV., when soap is put into hard water. Oxalic acid is another oxid solvent and both it and kerosene act also, to some extent, by reduction-i. e., uniting with oxygen and thus taking it away from another substance.

Alkalies and Soaps

Reason for use.-Fat is the most common constituent of soiling matter and thus one of the most necessary procedures in general cleaning is to render the fat soluble in water so that it can be washed away. Alkalies do this by saponification and soap has the same, but less pronounced, effect as the alkalies, because, when it is dissolved in water, some of its alkaline constituent is set free. Soap and soap powders are more frequently used than the free alkalies for their action is sufficiently strong for ordinary purposes and they have not the harmful effect upon many substances that the stronger detergents have. Alkalies, however, are necessary for some purposes, as shown in the preceding chapter.

Nature and source of the alkalies most frequently used for cleaning. The alkalies in most common use as detergents are: Ammonia, borax, sodium and potassium compounds.

Ammonia.-Ammonia water (NH4OH) can be made by, under special conditions, running ammonia gas (NH3) into water, but its common source is the ammoniacal liquor which is produced during the destructive distillation of coal in the making of gas.

Borax.-Borax is a compound of sodium, oxygen, and boron-a non-metallic element that resembles silicon. Borax deposits occur in various parts of the world, principally in the deserts. Borax is much used, not only for cleaning, but also in many industries. It is too expensive to use for general laundry work and scouring, but it is used for cleaning material that would be injured by the stronger alkalies.

Potassium and sodium carbonates.-The soft, light-weight, silver-white, metal elements, potassium and sodium, are never found free in nature, but their compounds are numerous and common. The compounds that are of special interest in connection. with the study of detergents are the carbonates and hydroxids.

Potash or potassium carbonate has been in use since early in the middle ages, when it was discovered that after wood was burned, certain soluble salts were found in the ashes which, if boiled in pots with water until the latter evaporated, left a solid residue that had cleaning properties. This residue was called pot-ashes. Later, it became known as potash, lye, and potassium carbonate. Some of the potash used to-day is made in the old way, but its more common sources are the refuse left in making beet sugar,

Derivation of the term hydroxid. The hydroxids received their name because the elements which form them do so by their interaction with water. For example, if the element sodium is dropped on water, some of the latter will be decomposed and the metal will at once unite with the oxygen and half of the hydrogen, and the other part of the hydrogen will escape in gaseous form. The reaction takes place so quickly that sufficient heat is caused to melt the metal, but, if the remaining water is evaporated, the sodium hydroxid formed by the interaction will remain as a white solid. The reaction that occurs

is as follows: Na+H2O= NaOH+H.

Characteristics of hydroxids.-All true hydroxids contain the hydroxyl radical (OH) and the majority of them consist of a metal in combination with this radical. When bases are dissolved in water, they dissociate into two kinds of ions one of which is always the hydroxyl ion and the other the metal element, as described in Chapter VII. Bases have a soapy feeling, a brackish taste, and an alkaline reaction. They destroy tissues by abstracting their water, dissolving their albumin, and saponifying the fat. They destroy bacteria by the same means.

The action of alkalies upon albumin and fat makes them valuable for cleansing agents, but, as will be seen in Chapter XVI., they, like acids, cannot be used for cleaning all kinds of substances, and when strong basic solutions are used on absorbent material, their action must be neutralized by the use of an acid.

Neutralization

Experiment 19. Object: To study neutralization. Articles required: An iron stand or tripod, a

Soaps. Soaps are made by causing the interaction of a fat with an alkali. When this is done, the fat separates into its component parts-i.e., fatty acids and glycerin—and the acids unite with the alkali, thereby forming the soap. This interaction may be produced (1) by what is known as the cold process, in which the fat is combined with either sodium or potassium hydroxid and either churned or subjected to heavy pressure; (2) by boiling the fat with a strong solution of either sodium or potassium hydroxid. Soap made by this process is in solution in the water and glycerin, but it may be salted out by the addition of sodium chlorid to the solution, soap being insoluble in salt solutions. After the soap is removed, the glycerin can be freed from foreign substances. This is, in fact, the usual source of glycerin. Soap made by the cold process retains the glycerin in combination. Toilet soaps are often made in this

way.

Reasons for differences in soaps.-The various differences in soaps depend chiefly upon (1) which alkali is used; (2) the nature of the fat used; (3) the addition of extra substances to the soap; (4) faulty manufacture of the soap.

Hard and soft soap.-Soaps made with sodium hydroxid are much harder than those made with potassium and are classed as hard soaps, while those made with potassium are called soft soaps.

Fats of soap.-All kinds of fat are used for soap and various oils, e.g., fish oil, olive oil, cocoanut oil, and castor oil. Although, as stated in the preceding paragraph, soaps made with soda are harder than those containing potassium, the kind of fat used. and the amount of water left in the soap cause con

siderable variation in the degree of hardness of even the soda soaps; e. g., soaps made with olive and similar oils are softer and lather more easily than those for which tallow is used.

Substances frequently added to soap. Various substances, some of which are harmless and others very objectionable, are often added to soap.

Some of the additions that, under ordinary circumstances, are harmless are perfumes; medicinal substances as tar and salicylic acid; emollientsas glycerin, almond oil, and oatmeal; disinfectants -as carbolic; such detergents as borax, kerosene, and naphtha. These detergents increase the cleansing value of soap for laundry purposes and, if not present in excess, do not injure fabrics. Other detergents sometimes added to soap are sodium and potassium carbonate and rosin (the resinous substance that remains after the distillation of oil of turpentine from the fresh pitch of pine wood; it is known also as colophony). The presence of these substances in soap that is used for rough cleaning is not a disadvantage, but, as will be seen in the experiments in Chapter XVII., even dilute alkaline solutions will injure silk and wool and they will also destroy paint and varnish, and solutions that are at all concentrated will injure some of the metals. Rosin, if present in more than very small amounts, will leave yellow spots on fabrics. For these reasons and, also, because sodium carbonate and potash are cheaper than even cheap soaps, it is generally considered better to buy pure soaps and, when required, add a stronger detergent to the water, or, for scrubbing, to use a scouring powder.

Fillers. By fillers are meant cheap substances with little or no detergent properties that are added

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