CHAPTER XVIII

ACIDS AND ALKALIES

174. Do We Use Science in the Home? - Have you ever thought how strange it is that men have learned to gather and to prepare so many different substances and to use each of them for some special purpose? Just think what a collection of substances there is in a druggist's shop. The modern housewife has not nearly so many as the druggist, yet she has a long list. Here are some of them: baking soda, washing soda, chloride of lime, lye, bluing, borax, starch, cream of tartar, salt, ammonia water, vinegar, sugar, flour, lard, baking powder, soap, ink, to say nothing of milk, butter, and our other foods. It is out of these materials that our meals are made ready for the table, our laundry work is done, our letters are written, our stains are erased. Can you name any other household substances?

175. Where Are Acids Found? As you know very well, we use vinegar to make certain articles of food sour, or "acid." This is true of beets, pickles, and salads. The chemist says that vinegar is sour because it contains an acid: acetic (pronounced ǎ-sēt'ĭc) acid. Most acids have a sour taste.

Vinegar is the result of a fermentation, or change caused by a ferment (Fig. 102). Ferments are found in small organisms that exist in nature and in some way or

other get into our fruit juices and other food materials. In the fall you may have seen how a cider press extracts the juice of apples and so makes "sweet cider." If we try to keep sweet cider very long, it bubbles and becomes "hard." The bubbling is due to the escape of carbon dioxide; the "hardness" is due to alcohol. The reason

for this is that the sugar of the apple juice is changed into alcohol and carbon dioxide. Yeast cells which are in the air fall into the juice and cause this change Shavings (cf. §201).

When the hard cider is allowed Vinegar to stand longer, a mold called "mother" begins to grow in it; this changes the alcohol to acetic and we then have cider vineGrape juice is changed in the same way, first into wine,

FIG. 102. We make vin

egar by letting the air oxidize

acid

fermented fruit juices, so that
their alcohol is changed to gar.

acetic acid.

which contains alcohol and carbon dioxide, then into wine vinegar, which contains acetic acid.

Milk sours because one particular kind of ferment gets into milk and changes the sugar of milk into lactic acid. This acid causes the milk to become curdy and to taste sour. The same acid is present in dill pickles and sauerkraut.

Many fruits, such as tomatoes, cherries, and green apples, and some plant stems, such as rhubarb and sour grass, are strongly acid. Lemons, oranges, and grapefruit contain citric acid; grape juice contains tartaric acid.

All of the acids we have named are compounds of carbon, hydrogen, and oxygen. There is also another very important acid which con

tains sulphur, hydrogen, and oxygen; this is sulphuric acid, or vitriol. Hydrochloric acid is another very important acid. Its old name is muriatic” acid. It contains hydrogen united with chlorine. Chlorine, you remember, is present in salt.

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176. What Makes a Compound an Acid? - In telling what acids are like, we can say, first, that they are sour. If acids are strong enough, they will "eat" the skin and clothing upon which they fall. Metals are also "eaten," or etched,” by acids. We have already learned that in making hydrogen (cf. § 114) zinc

is used up, or eaten, by the acid, and disappears. Are copper and lead used for cooking vessels? They cannot be, because the acids in foods act upon the metals and

FIG. 103.

The metal is

cause poisonous compounds of eaten out, or etched wherever

copper and lead to be formed.

it is exposed to the action of the acid.

Have you ever seen copper which has been etched so that it shows a beautiful design, as in Fig. 103? The design is made by covering all the copper, except where the lines are to be, with asphalt paint. Then the copper is put into nitric acid; the acid eats it wherever it is not covered. When the copper is removed from the acid, the asphalt is scraped off and there is a design on the copper.

Acids also act with marble, limestone, or soda. When an acid is mixed with marble, carbon dioxide is given off (cf. § 38). This causes a great deal of bubbling, or effervescence. Bones, which contain much limestone, lose their stiffening (largely limestone) by being placed in an acid. Why can a dog eat bones? Can it be that

the acid in the dog's stomach is strong enough to destroy the hard part of the bone?

177. What are Bases Like? Have you ever tried to wash a greasy pan with water alone? If you have, you know how hard it is to remove the grease, because it doesn't mix with the water. But if you put into the greasy pan some lye, or other washing powder, and add warm water to it, you find that the grease is easily washed off. It seems to dissolve and disappear. The lye and washing powder belong to the class of substances we call bases. We say they "cut" grease.

The chemist says lye is sodium hydroxide, to show it is composed of the elements sodium, hydrogen, and oxygen. Potash lye is called potassium hydroxide. What elements does it contain? Do you know what ammonia water is? It is a very strong-smelling liquid that acts in many ways like lye. You put some into water that you use for washing windows or glassware, because it removes grease and makes the glass bright and clean. Like lye it is a base.

There is another very common base; it is lime. Have you ever seen masons making mortar? They put lumps of a white solid (lime) into the vats of water, and the lime unites so vigorously with the water that the water becomes almost boiling hot. The product is slaked lime. Masons mix sand with the slaked lime and produce mortar. Lime will destroy animal substances, so men are able to use it for taking hair off from hides. Its solution, limewater, can be added to milk to sweeten it, if it has become slightly sour. Limewater mixed with

olive oil is used to heal burns.