484. When bricklayers mix water with cement and lime, the resulting mortar boils and steams.

485. Green plants will not grow in the dark.

486. Parts of the body are constantly uniting with oxygen. This keeps the body warm.

487. Water will not always put out a kerosene fire.

488. Delicately colored fabrics should be hung in the shade to dry.

489. A match glows when you rub it in the dark.

490. Candy hardens when it cools.

SECTION 52. Explosions.

What makes a gun shoot?

What makes an automobile go?

Usually we think of explosions as harmful, and they often are, of course. Yet without them we could no longer run automobiles; gasoline launches would stop at once; motorcycles would no longer run; gasoline engines for pumping water or running machinery would not be of any use; and all aviation would immediately cease. Tunneling through mountains, building roads in rocky places, taking up tree stumps, and preparing hard ground for crops would all be made very much more difficult. War would have to be carried on much as it was during the Middle Ages; soldiers would use spears and bows and arrows; battleships would be almost useless in attacking; modern forts would be of little value; cannon, guns, rifles, howitzers, mortars, and revolvers would all be so much junk.



WHAT MAKES AN AUTOMOBILE GO. In all the above cases the explosions are caused by chemical action. When gasoline mixed with air is sprayed into the cylinder of an automobile, an electric spark makes the gasoline combine with the oxygen of the air; the gasoline suddenly burns and changes to steam and carbon dioxid. As you already know, when a liquid like gasoline turns to gases such as steam and carbon dioxid, the gases take much more room. But that is not all that happens. Much heat is released by the burning of the gasoline spray, and heat causes expansion. So the gases formed by the burning gasoline are still further expanded by the heat released by the burning. Therefore they need a great deal more room; but they are shut up in a small place in the top of a cylinder. The only thing to hold them up in this small space, however, is a piston (Fig. 180), and the suddenly expanding gases shove this piston down and escape. The piston is attached to the drive wheel of the automobile, and when the piston is pushed down it gives the automobile a push forward. If it were not for the expansion of a gas in the cylinder, this gas being confined to a small space, the piston would not be pushed down.

An explosion is simply the sudden pushing of a confined gas expanding on its way to freedom. The gasoline vapor and air were the confined gas. Their chemical combining made them expand; by pushing the piston out of its way the newly formed gas suddenly freed itself. This was an explosion, and it gave the automobile one forward push. But the automobile engine is so arranged that the piston goes up into the cylinder again, and is pulled down again, drawing a spray of gasoline and air into the cylinder after it. Then it goes up a second time, an electric spark explodes the gasoline, the piston is forced down violently once more, and so it goes on. There are several cylinders, of course, and the explosions take place within them one after the other so as to keep the automobile going steadily.

HOW A GUN SHOOTS. Pulling a trigger makes a gun shoot by causing an explosion. There is a spring on the hammer of a gun. This drives the hammer down suddenly when you release the spring by pulling the trigger. The hammer jars the chemicals in the cap and causes them to explode. The heat and flame then cause the oxygen in the gunpowder to combine with some of the other elements in the powder to make a gas. The gas requires more room than the powder and is further expanded by the heat released by the chemical change. The expanding gas frees itself by pushing the bullet out of its way. The bullet gets such a push through the exploding of the gunpowder that it may fly to a mark and pierce it.



There is a slight explosion even when you shoot an air gun. First you compress some air in the upper part of the barrel of the air gun; then you suddenly release it. The only thing in the way of the expanding air is the bullet; so the air pushes this out in front of it.

In Experiment 36, where you stoppered a test tube containing a little water and then held the tube over a flame until the cork flew out, you were causing an explosion. As the water changed to steam, the steam was an expanding gas. It was at first confined to the test tube by the cork. Then there was an explosion; the gas freed itself by blowing out the cork.

Steam boilers have safety valves to prevent explosions. These are valves so arranged that when the steam expands and presses hard enough to endanger the boiler, the steam will open the valves and escape instead of bursting the boiler to get free.

EXPLOSIVES. Dynamite, gunpowder, and most explosives are mixtures of solids or liquids that will combine easily and will form gases that expand greatly as a result of the combination. One of the essentials in explosives is some compound of oxygen (such as the manganese dioxid or potassium chlorate you used to make oxygen in Experiment 93) which will easily set its oxygen free. This oxygen combines very swiftly with something else in the explosive, releasing heat and forming a gas that takes much more room. In its effort to free itself, this expanding gas will blast rocks out of the way, shoot cannon balls, or do any similar work.

But if gunpowder does not have to push anything of much importance out of its way to expand, there is no explosion. That is why a firecracker merely fizzes when you break it in two and light the powder. The cardboard no longer confines the expanding gas; so there is nothing to burst or to push violently out of the way.

Useful explosions are generally caused by a chemical action which suddenly releases a great deal of heat and combines solid things into expanding gases. But the bursting of a steam boiler, or the "blow out" of an automobile tire, or the bursting of a potato in the oven, although not caused by chemical action, still are real explosions. An explosion is the sudden release of a confined gas.

APPLICATION 77. Explain how gasoline makes a motorcycle go, and why it goes "pop, pop, pop." Explain why a paper bag will burst with a bang, when you blow it up and then clap it between your hands; why a Fourth-of-July torpedo "goes off" when you throw it on the pavement.

INFERENCE EXERCISE

Explain the following:

491. The engine of an automobile is cooled by the water that passes over it from the radiator.

492. When you light a firecracker, the flame travels down the wick until it reaches the gunpowder, and then the firecracker bursts with a bang.

493. If you light a small pile of gunpowder in the open, as you do when you make a squib by breaking the firecracker in two, you merely have a blaze.

494. Air-filled tires make bicycles ride much more evenly than solid tires would.

495. When clay has once been baked into brick, you can never change it back to clay.

496. A photographic negative turns black all over if it is exposed to the light before it is "fixed."

497. The outside of a window shade fades.

498. A vacuum electric lamp globe feels hot instantly when turned on, but if turned off again at once, it immediately feels cold.

499. Coal gas is made by heating coal very hot in an air-tight chamber.

500. White straw turns yellow when it is long exposed to the sunlight.



CHAPTER ELEVEN

SOLUTION AND CHEMICAL ACTION

SECTION 53. Chemical change helped by solution.

Why does iron have to get wet to rust?

Is it good to drink water with your meals?

When iron rusts, it is really slowly burning (combining with oxygen). If your house is on fire, you throw water on it to stop the burning. Yet if you throw water on iron it rusts, or burns, better than if you leave it dry. What do you suppose is the reason for this?

The answer is not difficult. You know perfectly well that iron does not burn easily; we could not make fire grates and stoves out of iron if it did. But when iron is wet, a little of it dissolves in the water that wets it. There is also a little oxygen dissolved in the water, as we know from the fact that fish can breathe under the water. This dissolved oxygen can easily combine with the dissolved iron; the solution helps the chemical change to take place. The chemical change that results is oxidation,—the iron combining with oxygen,—which is a slow kind of burning; and in iron this is usually called rusting.[10] But when we pour water on burning wood, the wood stops burning, for there is not nearly enough oxygen dissolved in water to combine rapidly with burning wood; and the water shuts off the outside air from burning wood and therefore puts the fire out.

[Footnote 10: The rusting of iron is not quite as simple as this, as it probably undergoes two or three changes before finally combining with oxygen. But the solution helps all these changes.]

Another chemical change, greatly helped by solution, is the combining of the two things that baking powder is made of, and the setting free of the carbon dioxid (CO_2) that is in one of them. Try this experiment:

EXPERIMENT 104. Put half a teaspoonful of baking powder in the bottom of a cup and add a little water. What happens?

The chemical action which takes place in the baking powder and releases the gas in bubbles—the gas is carbon dioxid (CO_2)—will not take place while the baking powder is dry; but when it is dissolved, the chemical change takes place in the solution.

If you ate your food entirely dry, you would have a hard time digesting it; and this would be for the same reason that baking powder will not work without water. Perhaps you can drink too much water with a meal and dilute the digestive juices too much; certainly you should not use water to wash down your food and take the place of the saliva, for the saliva is important in the digestion of starch. But you need also partly to dissolve the food to have it digest well. Crackers and milk are usually more easily digested than are plain crackers, for the milk partly dissolves the crackers, and drinking one or two glasses of water with a meal hastens the digestion of the food.

APPLICATION 78. Explain why paint preserves wood; why iron will rust more quickly in a wet place than it will either under water or in a dry place; why silver salts must be dissolved in order to plate a spoon by electricity.

INFERENCE EXERCISE

Explain the following:

501. There is dew on the grass early in the morning.

502. Cold cream makes your hands and face soft.

503. Glowworms and fireflies can be seen on the darkest nights.

504. A lake looks gray on a cloudy day and blue on a clear day.

505. Dried fruit will keep much longer than fresh fruit.

506. If you scratch a varnished surface, you can rub the scratch out completely by using a cloth wet with alcohol.

507. Soda is usually dissolved in a little water before it is added to a sour-milk batter.

508. Iron rusts when it gets wet.

509. Peroxide is usually kept in brown bottles.

510. Dry lye may be kept in tin cans, but if the lye is moistened it will eat the can.

SECTION 54. Acids.

Why are lemons sour?

How do acids act?

Some acids are very powerful. There is one, called hydrofluoric acid, that will eat through glass and has to be kept in wax bottles; and all acids tend to eat or corrode metals. You saw what hydrochloric acid did to the zinc shavings when you wanted to make a balloon; or, to be more accurate, you saw what the zinc shavings did to the acid, for the hydrogen gas that bubbled off was driven out of the acid by the zinc. Then the zinc combined with the rest of the acid to form what chemists call a salt.

If we were to let the soft metal, sodium, act on hydrochloric acid, we should get hydrogen also; but the salt that formed would be regular table salt (NaCl). You cannot do this experiment, however, as the sodium does its work so violently that it is dangerous.

EXPERIMENT 105. To be done by the teacher before the class. If acid spatters on any one's skin or clothes, wash it of immediately with ammonia or a strong soda solution.

Drop a little candle grease on a piece of copper about 3/4 inch wide and 2 or 3 inches long. In the flame of a Bunsen burner, gently heat the end of the copper that has the candle grease (paraffin) on it, so that the paraffin will spread out all over the end. Let it harden. With a nail, draw a design in the paraffin on the copper, scratching through the thin coat of paraffin to the copper below. Pour a couple of drops of concentrated nitric acid on the paraffin-covered end of the piece of copper, and spread the acid with a match so that it can get down into the scratches. Let it stand by an open window for 5 or 10 minutes. Do not inhale the brown fumes that are given off. They are harmless in small amounts, but if breathed directly they are very irritating. Now wash off the acid by holding the copper under the hydrant, and scrape off the paraffin.



The nitric acid did to the copper in this experiment exactly what the hydrochloric acid did to the zinc shavings when you made the toy balloon. The copper drove the hydrogen out of the nitric acid and incidentally broke down some of the nitric acid to make the brown gas, and then the copper joined the rest of the nitric acid to make a salt called copper nitrate. This salt is green, and it dissolves in water. When you washed the copper, the green salt was washed away and a dent remained in the copper where the copper salt had been.

Here is a more practical experiment showing the action of acid on metal:

EXPERIMENT 106. Use two knives, one of bright steel and the other a silver-plated one. If the steel knife is not bright, scour it until it is. Drop a little lemon juice on each knife and let it stand for a few minutes, while the teacher does the next experiment. Then rinse both knives and examine them. What has the lemon juice done to the silver knife? to the steel one?

The lemon juice acts in this way because it is acid. Acids act on the taste nerves in the tongue and give the taste of sourness; everything sour is an acid. The black stuff formed on the steel knife by the lemon juice is an iron salt. The iron in the knife drove the hydrogen out of the lemon juice, but there was not enough for you to see it coming off; then the iron combined with the rest of the lemon juice to form an iron salt.

Whenever an acid acts on a metal, the metal drives off the hydrogen and forms a salt. The salt is not always good to eat; for instance, the salt that tin forms with acids is poisonous.

ACTION OF ACIDS ON OTHER SUBSTANCES. Acids do not act on metals only, however. Watch the next experiment to see what a strong acid will do to cloth.

EXPERIMENT 107. To be done by the teacher. Put a drop of concentrated nitric or sulfuric acid on a piece of colored wool cloth, or on a piece of colored silk. Let it stand for a few minutes, then rinse it thoroughly. Test the cloth where the acid has been to see whether or not it is as strong as the rest of the cloth. How has the acid affected the color?



ACTION OF ACIDS ON THE NERVES OF TASTE. Acids act on the taste nerves in the tongue and give the taste of sourness; everything sour is an acid. Lemon juice, sour milk, and sour fruits are all too weak acids to injure clothes or skin, but their sour taste is a result of the acid in them acting on the nerves of taste.

APPLICATION 79. A girl wanted to make lemonade. She did not know which of two knives to use, a steel-bladed one or a silver-plated one. Which should she have used?

APPLICATION 80. A woman was going to put up some tomatoes. She needed something large to cook them in. She had a shiny new tin dish pan, an older enamelware dish pan, a galvanized iron water pail, and an old-fashioned copper kettle. Which would have been best for her to use?

Make a list of as many acids as you can think of.

INFERENCE EXERCISE

Explain the following:

511. Sugar dissolves readily in hot coffee.

512. The sugar disappears, yet the coffee flavor remains and so does the sweetness of the sugar.

513. A tin spoon left overnight in apple sauce becomes black.

514. If one's clothes are on fire, rolling over on the ground is better than running.

515. Lemon juice bleaches straw hats.

516. Will-o'-the-wisps glow at night, deceiving travelers by their resemblance to moving lanterns.

517. Tomatoes should never be left in a tin can after it has been opened.

518. Boiled milk tastes different from ordinary milk.

519. Your hands become very cold after you have washed things in gasoline.

520. Wood decays more quickly when wet than when dry.

SECTION 55. Bases.

Why does strong soap make your face sting?

How is soap made?

"Contains no free alkali," "Will not injure the most delicate of fabrics," "99-44/100% pure,"—such phrases as these are used in advertising soaps. What is meant by 99-44/100% pure? What is free alkali? Why should any soap injure fabrics? What makes a soap "strong"?

The answer to all these questions is that there are some substances called bases, which are the opposites of acids, and some of which are as powerful as acids. Lye, ammonia, caustic soda, and baking and washing soda are common bases. The strong bases, like lye and caustic soda, are also called alkalies. If you want to see what a strong base—an alkali—will do to "the most delicate of fabrics," and to fabrics that are not so delicate, for that matter, try the following experiment:

EXPERIMENT 108. To be done by the teacher. If you get any alkali on your skin or clothes, wash it off immediately with vinegar or lemon juice.

Put half a teaspoonful of lye and a quarter of a cup of water into a beaker, a small pan, or an evaporating dish. Bring it to a gentle boil. Drop a small piece of woolen cloth and a small piece of silk cloth into it and let them boil gently for a couple of minutes. What happens to them? Try a piece of plain cotton cloth, and then a piece of cloth that is mixed wool and cotton or mixed silk and cotton. What happens to them? This is a very good test to determine whether any goods you buy are pure silk or wool, or whether there is a cotton thread mixed with them. Drop one end of a long hair into the hot lye solution. What happens to it? Drop a speck of meat or a piece of finger nail into it.

From this experiment you can readily see why lye will burn your skin and ruin your clothes. You can also see how it softens the food that sticks to the bottom of the cooking pan and makes the pan easy to clean. Lye is one of the strongest bases or alkalies in the world.



HOW SOAP IS MADE. When lye and grease are boiled together, they form soap. You cannot very well make soap in the laboratory now, as the measurements must be exact and you need a good deal of strong lye to make it in a quantity large enough to use. But the fact that soap is made with oil, fat, or grease boiled with lye, or caustic soda, which is almost the same thing, shows why a soap must be 99-44/100% pure, or something like that, if it is not to injure "the most delicate fabric." If a little too much lye is used there will be free alkali in the soap, and it will make your hands harsh and sore and spoil the clothes you are washing. A "pure" soap is one with no free alkali in it. A "strong" soap is one that does have some free alkali in it; there is a little too much lye for the oil or fat, so some lye is left uncombined when the soap is made. This free alkali cleans things well, but it injures hands and clothes.

When the drainpipe of a kitchen sink is stopped up, you can often clear it by sprinkling lye down it, and then adding boiling water. If you ever do this, stand well back so that no lye will spatter into your face; it sputters when the boiling water strikes it. The grease in the drainpipe combines with the lye when the hot water comes down; then the soap that is formed is carried down the pipe, partly dissolved by the hot water.

When you sponge a grease spot with ammonia, the same sort of chemical action takes place. The ammonia is a base; it combines with the grease to form soap, and this soap rinses out of the cloth.

THE LITMUS TEST. To tell what things are bases and what are acids, a piece of paper dyed with litmus is ordinarily used. Litmus is made from a plant (lichen). This paper is called litmus paper. Try the following experiment with litmus paper:

EXPERIMENT 109. Pour a few drops of ammonia, a base, into a cup. Into another cup pour a few drops of vinegar, an acid. Dip your litmus paper first into one, then into the other, and then back into the first. What color does the vinegar turn it? the ammonia? Try lemon juice; diluted hydrochloric acid; a very dilute lye solution.

This is called the litmus test. All ordinary acids, if not too strong, will turn litmus pink. All bases or alkalies will turn it blue. If it is already pink when you put it into an acid, it will stay pink, of course; if it is already blue when you put it into a base, it will stay blue. But if you put a piece of litmus paper into something that is neither an acid nor a base, like sugar or salt, it will still stay the same color. So, to test for a base, use a piece of litmus paper that is pink and see if it turns blue, or if you want to test for an acid, use blue litmus paper. Do this experiment:

EXPERIMENT 110. With pink and blue litmus paper, test the different substances named below to see which are acids and which are bases. Make a list of all the acids and another list for all the bases. Do not put down anything that is neither acid or base. You cannot be sure a thing is an acid unless it turns blue litmus pink. A piece of pink litmus would stay pink in an acid, but it would also stay pink in things that were neither acid nor base, like salt or water. In the same way you cannot be sure a thing is a base unless it turns pink litmus blue. Here is a list of things to try: 1, sugar; 2, orange; 3, dilute sulfuric acid; 4, baking soda in water; 5, alum in water; 6, washing soda in water; 7, ammonia; 8, dilute lye; 9, lemon juice; 10, vinegar; 11, washing powder in water; 12, sour milk; 13, cornstarch in water; 14, wet kitchen soap; 15, oil; 16, salt in water.

You may have to make the orange and sour milk test at home. You may take two pieces of litmus paper home with you and test anything else that you may care to. If you have a garden, try the soil in it. If it is acid it needs lime.

APPLICATION 81. A boy spilled some greasy soup on his best dark blue coat. Which of the following methods would have served to clean the coat? to sponge it (a) with cold water; (b) with water (hot) and ammonia; (c) with hot water and vinegar; (d) with concentrated nitric acid; to sprinkle lye on the spot and pour boiling water over it.

APPLICATION 82. A woman scorched the oatmeal she was cooking for breakfast. When she wanted to wash the pan, she found that the blackened cereal stuck fast to the bottom. Which of the following things would have served best to loosen the burned oatmeal from the pan: lye and hot water, ammonia, vinegar, salt water, lemon juice?

INFERENCE EXERCISE

Explain the following:

521. After clothes have been washed with washing soda or strong soap, they should be thoroughly rinsed. Otherwise they will be badly eaten as they dry.

522. Carbon will burn; oxygen will support combustion; yet carbon dioxid (CO_2), which is made of both these elements, will neither burn nor support combustion.

523. You can clean silver by putting it in hot soda solution in contact with aluminum.

524. When you stub your toe while walking, you tend to fall forward.

525. Electric lamps glow when you turn on the switch.

526. If you use much ammonia in washing clothes or cleaning, your hands become harsh and dry.

527. If a person swallows lye or caustic soda, he should immediately drink as much vegetable oil or animal oil as possible.

528. Water is made of hydrogen and oxygen; air is made of nitrogen and oxygen; yet while things will not burn in water, they will burn easily in air.

529. The backs of books that have been kept in cases for several years are not as bright colored as the side covers.

530. If you try to burn a book or magazine in a grate, only the outer pages and edges burn.

SECTION 56. Neutralization.

When you put soda in vinegar, what makes the vinegar less sour?

When we use sour milk for cooking, why does the food not taste sour?

One of the most interesting and important facts about acids and bases is that if they are put together in the right proportions they turn to salt and water. Strong hydrochloric acid (HCl), for instance, will attack the skin and clothes, as you know; if you should drink it, it would kill you. Caustic soda (NaOH), a kind of lye, is such a strong alkali that it would dissolve the skin of your mouth in the way that lye dissolved hair in Experiment 108. Yet if you put these two strongly poisonous chemicals together, they promptly turn to ordinary table salt (NaCl) and water (H_2O). Or, as the chemists write it:

NaOHHCl -> NaClH_2O.

You can make this happen yourself in the following experiment, using the acid and base dilute enough so that they will not hurt you:

EXPERIMENT 111. Although strong hydrochloric acid and strong caustic soda are dangerous, if they are diluted with enough water they are perfectly harmless. You will find two bottles, one labeled "caustic soda (NaOH) diluted for tasting," and the other labeled "hydrochloric acid (HCl) diluted for tasting." From one bottle take a little in the medicine dropper and let a drop fall on your tongue. Taste the contents of the other bottle in the same way. It is not usually safe to taste things in the laboratory. Taste only those things which are marked "for tasting."

Now put a teaspoonful of the same hydrochloric acid into a clean evaporating dish. Lay a piece of litmus paper in the bottom of the dish. With a medicine dropper gradually add the dilute caustic soda (NaOH), stirring as you add it. Watch the litmus paper. When the litmus paper begins to turn blue, add the dilute caustic soda drop by drop until the litmus paper stays blue when you stir the mixture. Now add a drop or two more of the acid until the litmus turns pink again. Taste the mixture.

Put the evaporating dish on the wire gauze over a Bunsen burner, and bring the liquid to a boil. Boil it gently until it begins to sputter. Then take the Bunsen burner in your hand and hold it under the dish for a couple of seconds; remove it for a few seconds, and then again hold it under the dish for a couple of seconds; remove it once more, and keep this up until the water has all evaporated and left dry white crystals and powder in the bottom of the dish. As soon as the dish is cool, taste the crystals and powder. What are they?

Is salt an acid or a base?

Whenever you put acids and bases together, you get some kind of salt and water. Thus the chlorine (Cl) of the hydrochloric acid (HCl) combines with the sodium (Na) of caustic soda (NaOH) to form ordinary table salt, sodium chloride (NaCl), while the hydrogen (H) of the hydrochloric acid (HCl) combines with the oxygen and hydrogen (OH) of the caustic soda (NaOH) to form water (H_2O). Chemists write this as follows:

NaOHHCl -> NaClH_2O.

WHY SOUR MILK PANCAKES ARE NOT SOUR. It is because bases neutralize acids that you put baking soda with sour milk when you make sour milk pancakes or muffins. The soda is a weak base. The sour milk is a weak acid. The soda neutralizes the acid, changing it into a kind of salt and plain water. Therefore the sour milk pancakes or muffins do not taste sour.

In the same way a little soda keeps tomatoes from curdling the milk when it is added to make cream of tomato soup. It is the acid in the tomatoes that curdles milk. If you neutralize the acid by adding a base, there is no acid left to curdle the milk; the acid and base turn to water and a kind of salt.

When you did an experiment with strong acid, you were advised to have some ammonia at hand to wash off any acid that might get on your skin or clothes. The ammonia, being a base, would immediately neutralize the acid and therefore keep it from doing any damage. Lye also would neutralize the acid, but if you used the least bit too much, the lye would do as much harm as the acid. That is why you should use a weak base, like ammonia or baking soda or washing soda, to neutralize any acid that spills on you. Then if you get too much on, it will not do any harm.

In the same way you were warned to have vinegar near at hand while you worked with lye. Strong nitric acid also would neutralize the lye, but if you happened to use a drop too much, the acid would be worse than the lye. Vinegar, of course, would not hurt you, no matter how much you put on.

Any acid will neutralize any base. But it would take a great deal of a weak acid to neutralize a strong base or alkali; you would have to use a great deal of vinegar to neutralize concentrated lye. In the same way it would take a great deal of a weak base to neutralize a strong acid; you would have to use a large amount of baking soda or ammonia to neutralize concentrated nitric acid.

APPLICATION 83. A woman was cleaning kettles with lye. Her little boy was playing near, and some lye splashed on his hand. She looked swiftly around and saw the following things: soap, oil, lemon, flour, peroxide, ammonia, iodine, baking soda, essence of peppermint. Which should she have put on the boy's hand?

APPLICATION 84. A teacher spilled some nitric acid on her apron. On the shelf there were: hydrochloric acid, vinegar, lye, caustic soda, baking soda, ammonia, salt, alcohol, kerosene, salad oil. Which should she have put on her apron?

APPLICATION 85. A boy had "sour stomach." His sister said, "Chew some gum." His aunt said, "Drink hot water with a little peppermint in it." His mother told him to take a little baking soda in water. His brother said, "Try some hot lemonade." Which advice should he have followed?

APPLICATION 86. Two women were bleaching a faded pair of curtains. The Javelle water which they had used was made of bleaching powder and washing soda. Before hanging the curtains out to dry, one of them said that she was afraid the Javelle water would become so strong as the water evaporated from the curtains that it would eat the curtains. They decided they had better rinse them out with something that would counteract the soda and lime in the Javelle water, and in the laundry and pantry they found: ammonia, blueing, starch, washing powder, soap, vinegar, and gasoline. Which of them, if any, would it have been well to put in the rinsing water?

INFERENCE EXERCISE

Explain the following:

531. Solid pieces of washing soda disappear in hot water.

532. Greasy clothes put into hot water with washing soda become clean.

533. If you hang these clothes up to dry without rinsing them, the soda will weaken the cloth.

534. Lemon juice in the rinsing water will prevent washing soda from injuring the clothes.

535. If you hang them in the sun, the color will fade.

536. A piece of soot blown against them will stick.

537. A drop of oil that may spatter against them will spread.

538. The clothes will be easier to iron if dampened.

539. The creases made in ironing the clothes will reappear even if you flatten the creases out with your hand.

540. After they have been worn, washed, and ironed a number of times, clothes are thinner than they were when they were new.

SECTION 57. Effervescence.

What makes baking powder bubble?

What makes the foam on soda water?

Did you ever make soda lemonade? It is easy to make and is rather good. Try making it at home. Here are the directions:

EXPERIMENT 112. Make a glass of ordinary lemonade (half a lemon, 1-1/2 teaspoonfuls of sugar; fill the glass with water). Pour half of this lemonade into another cup or glass. Into the remaining half glass stir half a teaspoonful of soda. Drink it while it fizzes. Does it taste sour?

When anything fizzes or bubbles up like this, we say that it _effervesces_. Effervescence is the bubbling up of a gas from a liquid. The gas that bubbled up from your lemonade was carbon dioxid (CO_2), and this is the gas that usually bubbles up out of things when they effervesce.

When you make bread, the yeast turns the sugar into carbon dioxid (CO_2) and alcohol. The carbon dioxid tries to bubble up out of the dough, and the bubbles make little holes all through the dough. This makes the bread light. When bread rises, it really is slowly effervescing.

HOW SODA WATER IS MADE. Certain firms make pure carbon dioxid (commercially known as _carbonic acid_ _gas_) and compress it in iron tanks. These iron tanks of carbon dioxid (CO_2) are shipped to soda-water fountains and soda-bottling works. Here the compressed carbon dioxid is dissolved in water under pressure,—this is called "charging" the water. When the charged water comes out of the faucet in the soda fountains, or out of the spout of a seltzer siphon, or out of a bottle of soda pop, the carbon dioxid that was dissolved in the water under pressure bubbles up and escapes,—the soda water effervesces.

Sometimes there is compressed carbon dioxid down in the ground. This dissolves in the underground water, and when the water bubbles up from the ground and the pressure is released, the carbon dioxid foams out of the water; it effervesces like the charged water at a soda fountain.

But the most useful and best-known effervescence is the kind you got when you stirred the baking soda in the lemonade. Baking soda is made of the same elements as caustic soda (NaOH), with carbon dioxid (CO2) combined with them. The formula for baking soda could be written NaOHCO2, but usually chemists put all of the O's together at the end and write it NaHCO3. Whenever baking soda is mixed with any kind of acid, the caustic soda part (NaOH) is used up in neutralizing the acid. This leaves the carbon dioxid (CO2) part free, so that it bubbles off and we have effervescence. Baking soda mixed with an acid always effervesces. That is why sour milk muffins and pancakes are light as well as not sour. The effervescing carbon dioxid makes bubbles all through the batter, while the caustic soda (NaOH) in the baking soda neutralizes the acid of the sour milk.



EFFERVESCENCE GENERALLY DUE TO THE FREEING OF CARBON DIOXID. Since baking soda is so much used in the home for neutralizing acids, people sometimes get the idea that whenever there is neutralization there is effervescence. Of course this is not true. Whenever you neutralize an acid with baking soda or washing soda, the carbon dioxid in the soda bubbles up and you have effervescence. But if you neutralize an acid with ammonia, lye, or plain caustic soda, there is not a bit of effervescence. Ammonia, lye, and plain caustic soda have no carbon dioxid in them to bubble out.

Baking powder is merely a mixture of baking soda and dry acid (cream of tartar or phosphates in the better baking powders, alum in the cheap ones). These dry acids cannot act on the soda until they go into solution. As long as the baking powder remains dry in the can, there is no effervescence. But when the baking powder is stirred into the moist biscuit dough or cake batter, the baking powder dissolves; so the acid in it can act on the baking soda and set free the carbon dioxid.

In most cases it is the freeing of carbon dioxid that constitutes effervescence, but the freeing of any gas from liquid is effervescence. When you made hydrogen by pouring hydrochloric acid (HCl) on zinc shavings, the acid effervesced,—the hydrogen gas was set free and it bubbled up.

Stirring or shaking helps effervescence, just as it does crystallization. As the little bubbles form, the stirring or shaking brings them together and lets them join to form big bubbles that pass quickly up through the liquid. That is why soda pop will foam so much if you shake it before you pour it, or if you stir it in your glass.

APPLICATION 87. Explain why we do not neutralize the acid in sour milk gingerbread with weak caustic soda instead of with baking soda; why soda water which is drawn with considerable force from the fine opening at a soda fountain makes so much more foam than does the same charged water if it is drawn from a large opening, from which it flows gently; why there is always baking soda and dry acid in baking powder.

APPLICATION 88. A woman wanted to make gingerbread. She had no baking powder and no sour milk, but she had sweet milk and all the other articles necessary for making gingerbread. She had also baking soda, caustic soda, lemons, oranges, vanilla, salad oil, vinegar, and lye. Was there any way in which she might have made the gingerbread light without spoiling it?

INFERENCE EXERCISE

Explain the following:

541. Harness is oiled to keep it flexible.

542. When you pour nitric acid on copper filings, there is a bubbling up of gas.

543. The flask or dish in which the action takes place becomes very hot.

544. The copper disappears and a clear green solution is left.

545. In making cream of tomato soup, soda is added to the tomatoes before the milk is, so that the milk will not curdle How does the soda prevent curdling?

546. The soda makes the soup froth up.

547. A wagon squeaks when an axle needs greasing.

548. Seidlitz powders are mixed in only half a glass of water.

549. The work of developing photographs is all done with a ruby light for illumination.

550. Coal slides forward off the shovel into a furnace when you stop the shovel at the furnace door.



CHAPTER TWELVE

ANALYSIS

SECTION 58. Analysis.

How can people tell what things are made of?

If it were not for chemical analysis, most of the big factories would have to shut down, much of our agricultural experimentation would stop, the Pure Food Law would be impossible to enforce, mining would be paralyzed, and the science of chemistry would almost vanish.

Analysis is finding out what things are made of. In order to make steel from ore, the ore has to be analyzed; and factories could not run very well without steel. In order to test soil, to test cow's milk, or to find the food value of different kinds of feed, analysis is essential. As to the Pure Food Law, how could the government find out that a firm was using artificial coloring matter or preservatives if there were no way of analyzing the food? In mining, the ore must be assayed; that is, it must be analyzed to show what part of it is gold, for instance, and what part consists of other minerals. Also, the analysis must show what these substances are, so that they can be treated properly. And the science of chemistry is largely the science of analyzing—finding out what things are made of and how they will act on each other.

The subject of chemical analysis is extremely important. But in this course it is impossible and unnecessary for you to learn to analyze everything; the main thing is for you to know what analysis is and to have a general notion of how a chemist analyzes things.



When you tested a number of substances with litmus paper to find out which of them were acids, you were really doing some work in chemical analysis. Chemists actually use litmus paper in this way to find out whether a substance is an acid or a base.

THE BORAX BEAD TEST. This is another chemical test, by which certain substances can be recognized:

EXPERIMENT 113. Make a loop of wire about a quarter of an inch across, using light-weight platinum wire (about No. 30). Seal the straight end of the wire into the end of a piece of glass tubing by melting the end of the tube around the wire.

Hold the loop of wire in the flame of a Bunsen burner for a few seconds, then dip the looped end in borax powder. Be careful not to get borax on the upper part of the wire or on the handle. Some of the borax will stick to the hot loop. Hold this in the flame until it melts into a glassy bead in the loop. You may have to dip it into the borax once or twice more to get a good-sized bead.

When the bead is all glassy, and while it is melted, touch it lightly to one small grain of one of the chemicals on the "jewel-making plate." This jewel-making plate is a plate with six small heaps of chemicals on it. They are: manganese dioxid, copper sulfate, cobalt chlorid, nickel salts, chrome alum, and silver nitrate. Put the bead back into the flame and let it melt until the color of the chemical has run all through it. Then while it is still melted, shake the bead out of the loop on to a clean plate. If it is dark colored and cloudy, try again, getting a still smaller grain of the chemical. You should get a bead that is transparent, but clearly colored, like an emerald, topaz, or sapphire.

Repeat with each of the six chemicals, so that you have a set of six different-colored beads.



This is a regular chemical test for certain elements when they are combined with oxygen. The cobalt will always change the borax bead to the blue you got; the chromium will make the bead emerald green or, in certain kinds of flame, ruby red; etc. If you wanted to know whether or not certain substances contained cobalt combined with oxygen, you could really find out by taking a grain on a borax bead and seeing if it turned blue.

THE HYDROCHLORIC ACID TEST FOR SILVER. The experiment in which you tested the action of light in effecting chemical change, and in which you made a white powder or precipitate in a silver nitrate solution by adding hydrochloric acid (page 327), is a regular chemical test to find out whether or not a thing has silver in it. If any silver is dissolved in nitric acid, you will get a precipitate (powder) when hydrochloric acid is added. Make the test in the following experiment:

EXPERIMENT 114. Use distilled water all through this experiment if possible. First wash two test tubes and an evaporating dish thoroughly, rinsing them several times. Into one test tube pour some nitric acid diluted 1 to 4. Heat this to boiling, then add a few drops of hydrochloric acid diluted 1 to 10. Does anything happen? Pour out this acid and rinse the dish thoroughly. Now put a piece of silver or anything partly made of silver into the bottom of the evaporating dish. Do not use anything for the appearance of which you care. Cover the silver with some of the dilute nitric acid, put the dish over the Bunsen burner on a wire gauze, and bring the acid to a gentle boil. As soon as it boils, take the dish off, pour some clean, cold water into it to stop the action, and pour the liquid off into the clean test tube. Add a few drops of the dilute hydrochloric acid to the liquid in the test tube. What happens? What does this show must have been in the liquid?

You can detect very small amounts of silver in a liquid by this test. It is a regular test in chemical analysis.

THE IODINE TEST FOR STARCH. A very simple test for starch, but one that is thoroughly reliable, is the following:

EXPERIMENT 115. Mix a little starch with water. Add a drop of iodine. What color does the starch turn? Repeat with sugar. You can tell what foods have starch in them by testing them with iodine. If they turn black, blue, or purple instead of brown, you may be sure there is starch in them. And if they do not turn black, blue, or purple, you can be equally sure that they have no starch in them. Some baking powders contain starch to keep them dry. Test the baking powder in the laboratory for starch. Often a little cornstarch is mixed with powdered sugar to keep it from lumping. Test the powdered sugar in the laboratory to see if it contains starch.

Test the following or any other ten foods to see if any of them are partly made of starch: salt, potatoes, milk, meat, sausage, butter, eggs, rice, oatmeal, cornmeal, onions.



THE LIMEWATER TEST FOR CARBON DIOXID. In crowded and badly ventilated rooms carbon dioxid in unusual amounts is in the air. It can be detected by the limewater test.

EXPERIMENT 116. Pour an inch or two of limewater into a glass. Does it turn milky? Pump ordinary air through it with a bicycle pump. Now blow air from your lungs through a glass tube into some fresh limewater until it turns milky. By this test you can always tell if carbon dioxid (CO_2) is present.



Carbon dioxid turns limewater milky as it combines with the lime in the limewater to make tiny particles (a precipitate) of limestone. If you pour seltzer water or soda pop into limewater, you get the same milkiness, for the bubbles of carbon dioxid in the charged water act as the carbon dioxid in your breath did. If you pumped enough air through the limewater you would produce some milkiness in it, for there is always some carbon dioxid in the air.

The purpose of these experiments is only to give you a general notion of how a chemist analyzes things,—by putting an unknown substance through a series of tests he can tell just what that substance contains; and by accurately weighing and measuring everything he puts in and everything he gets out, he can determine how much of each thing is present in the compound or mixture. To learn to do this accurately takes years of training. But the men who go through this training and analyze substances for us are among the most useful members of the human race.

INFERENCE EXERCISE

Explain the following:

551. A little soda used in canning an acid fruit will save sugar.

552. The fats you eat are mostly digested in the small intestine, where there is a large excess of alkali.

553. The dissolved food in the liquid part of the blood gets out of the blood vessels and in among the cells of the body, and it is finally taken into the cells through their walls.

554. Ammonia takes the color out of delicate fabrics.

555. Dishes in which cheese has been cooked can be cleaned quickly by boiling vinegar in them.

556. Prepared pancake flour contains baking powder. It keeps indefinitely when dry, but if the box gets wet, it spoils.

557. When water or milk is added to prepared pancake flour to make a batter, bubbles appear all through it.

558. When a roof leaks a little, a large spot appears on the ceiling.

559. Gasoline burns quietly enough in a stove, but if a spark gets into a can containing gasoline vapor, there is a violent explosion.

560. Turpentine will remove fresh paint.

GENERAL REVIEW INFERENCE EXERCISE

Explain the following:

561. We can remove fresh stains by pouring boiling water through them.

562. A ship can be more heavily laden in salt water than in fresh water.

563. Water flies off a wet dog when he shakes himself.

564. In cooking molasses candy, baking soda is often added to make it lighter.

565. An egg will not stand on end.

566. Women who carry bundles on their heads stand up very straight.

567. To get all crayon marks off a blackboard, the janitor uses vinegar in water.

568. Sunlight makes your skin darker.

569. Water puts out a fire.

570. You get a much worse shock from a live wire when your hands are wet than when they are dry.

571. Stone or brick buildings are cool in summer but warm in winter.

572. If you take the handle off a faucet, it is almost impossible to turn the valve with your fingers.

573. Sparks fly from a grindstone when you are sharpening a knife.

574. Violin strings are spoiled by getting wet.

575. The oxygen of the air gets into the blood from the lungs, although there are no holes from the blood vessels into the lungs.

576. You push a button or turn a key switch and an electric lamp lights.

577. A rubber comb, rubbed on a piece of wool cloth, will attract bits of paper to it.

578. People whose eyes no longer adjust themselves have to have "reading glasses" and "distance glasses" to see clearly.

579. When you look through a triangular glass prism, things appear to be where they are not.

580. Lye and hot water poured down a clogged kitchen drainpipe clear out the grease.

581. You can draw on rough paper with charcoal.

582. When little children get new shoes, the soles should be scratched and made rough.

583. You can get your face very clean by rubbing cold cream into it, then wiping the cold cream off on a towel or cloth.

584. Soft paper blurs writing when you use ink.

585. Water will flow over the side of a pan through a siphon, if the outer end of the siphon is lower than the surface of the water in the pan.

586. There is a loud noise when a gun is fired.

587. Colored cloths should be matched in daylight, not in artificial light.

588. Lamp chimneys are made of thin glass.

589. When you sweep oiled floors, no dust flies around the room.

590. The ocean is salty, while lakes are usually fresh.

591. A glass gauge on the side of a water tank shows how high the Water in the tank is.

592. You burn your hand when you touch a hot stove.

593. Pounding a piece of steel held horizontally over the earth and pointing north and south will make it become a magnet.

594. When only one side of a sponge is in water, the sponge gradually gets soft all over.

595. If we breathe on a cold mirror, a fine mist collects on it.

596. Butter is kept in cool places.

597. Water will boil more quickly in a covered pan than in an open one.

598. Mucilage, glue, and paste all become hard and dry after being spread out on a surface for a while.

599. You cannot see things clearly through a dusty window.

600. In making fire grates it is necessary to have the bars free to move a little.



APPENDIX

A. THE ELECTRICAL APPARATUS

For giving children a practical understanding of such laws of electricity as affect everybody, the following simple apparatus is invaluable. It is the electrical apparatus referred to several times in the text. The only part of it that is at all difficult to get is the nichrome resistance wire. There is a monopoly on this and each licensee has to agree not to sell it. It can be bought direct from the manufacturer by the school board if a statement accompanies the order to the effect that it is not to be used in any commercial devices, nor to be sold, but is for laboratory experimentation only. The manufacturers are Hoskins Manufacturing Company, Detroit, Michigan.

The following diagram will make the connections and parts of the electrical apparatus clear:



The flush switch (G) should be open at the bottom for inspection,—remove the back. The snap switch (E) should have cover removed so that pupils can see exactly how it works.

The fuse gap (D) consists either of two parts of an old knife switch, the knife removed, or of two brass binding posts. Across it a piece of 4-ampere fuse wire is always kept as a protection to the more expensive plug and cartridge fuses. Between the resistance wire (I, J, K) and the wall should be either slate or sheet asbestos, double thickness. Under the fuse gap the table should be protected by galvanized iron so that the melted bits of fuse wire can set nothing on fire when the fuse wire burns out.

B. CONSTRUCTION OF THE CIGAR-BOX TELEGRAPH

The "cigar-box telegraph" shown on page 381 is made as follows: An iron machine bolt (A) is wound with about three layers of No. 24 insulated copper magnet wire, the two ends of the wire (B, B) projecting. The threaded end of the bolt (C) is not wound. A nut (D) is screwed on the bolt as far down as the wire wrapping. The threaded end is then pushed up through the hole in the top of the cigar box as that stands on its edge. Another nut (E) is then screwed on to the bolt, holding it in position. The bolt can now be raised or lowered and tightened firmly in position by adjusting the two nuts (D and E), one above and one below the wood.

A screw eye (F), large enough to form a rest for the head of another machine bolt (G), is screwed into the back of the box about three fourths of an inch below the head of the suspended bolt (A). Two or three inches away, at a slightly higher level, another screw eye (H) is screwed into the back of the cigar box. This screw eye must have an opening large enough to permit an iron machine bolt (G) to pass through it easily. A nut (I) is screwed down on the threaded end of a machine bolt until about an inch of the bolt projects beyond the nut. This projecting part of the bolt is then passed through the screw eye (H) and another nut (J) screwed on to it to hold it in place. This nut must not be so tight as to prevent the free play of the bolt as its head rises and falls under the influence of the vertical bolt. The head of the horizontal bolt rests upon the screw eye which is immediately below the head of the suspended bolt. You therefore have the wrapped bolt hanging vertically from the top of the box, with its head just over the head of the horizontal bolt. There should be about one quarter inch of space between the heads of the two bolts. An electric current passing through the wires of the vertical bolt will therefore lift the head of the horizontal bolt, which will drop back on to the screw eye when the circuit is broken.



INDEX

An asterisk (*) indicates use of one or more illustrations in connection with reference to which appended.

Acetylene, carbon and hydrogen in, 315.

Acids, 351 ff.; action of, on metals, 351-353*; action of, on cloth, 354*; action of, on nerves of taste, 354-355; distinguished from bases by litmus test, 358-359; neutralization of, by bases, 360-364.

Action and reaction, law of, 77-81*.

Adhesion, 39, 41-44; cohesion, capillary attraction, and, 47.

Air, cooling of, on expanding, 95-96; liquid, 97; heat carried by, by convection, 118-119; absorption of light by, 169; sound produced by vibrations of, 174-181*; pitch due to rapidity of vibrations of, 186; water vapor in, 275-280*; a mixture and not a compound, 309; part taken by, in making automobile go, 344; limewater test for carbon dioxid in, 375.

Air pressure, 10 ff., 14*; height water is forced up by, in vacuum, 19; high and low, 20, 282; winds caused by, 20-21.

Air pump, 14*, 15.

Alcohol, boiling of, 112; distilling, 113*-114.

Alkali, 356; in soap, 357-358.

Alloys, definition of, 310.

Alternating current, defined, 211-212.

Alum crystals, experiment with, 265-266*.

Aluminum, an element, 299.

Alum in water, testing with litmus paper, 359.

Amber, electricity produced by rubbing with silk, 196.

Ammonia, example of a common base, 356; action of, in cleaning cloth, 358; litmus test of, 359; neutralization of acid by, 363.

Ampere, defined, 246.

Analysis, chemical, 370-376.

Aneroid barometer, 285*.

Arc, the electric, 233-240*.

Atoms, description of, 196; electrons and, 197; everything in the world made of, 310-311; in molecules, 311.

Aurora Borealis, cause of, 193.

Automobile, reason for cranking, 210; how made to go, 344-345.

Automobile races, overcoming of centrifugal force in, 75*.

Automobile tires, reason for wearing of, 80; blow-outs of, 348.

Baking powder, chemical change by solution shown by, 349-350; elements of which made, 367-368.

Baking soda, a common base, 356; testing with litmus paper, 359; neutralization of sour milk by, in cooking, 362; carbon dioxid in, 366-367.

Ball bearings, used to diminish friction, 54-55.

Balloon, expansion of, 17-18, 109*; reason for rising of, 26; filling of, with hydrogen, 301-304*.

Barometer, use of, 280-285*.

Bases, substances called, 355-358; litmus test for distinguishing from acids, 358-359; neutralization of, by acids, 360-364.

Batteries, electric, 203-205*; different kinds of, 205*-207*; general principle of all, 206.

Bell, electric battery for ringing, 204-205*; working of electric, 255*.

Bending of light (refraction), 136-141*.

Black, the absence of light, 164.

Bleaching, process of, 326-327.

Blow-out of tire, a real explosion, 348.

Blue-flame heaters, 319.

Blueness of sky, reason for, 169.

Blueprints, making of, 330-331.

Boiling and condensing, 107-115*.

Borax bead test, 371*-372*.

Brass, an alloy, 310.

Bread making, chemical action in, 365.

Breath, cause of visibility of, on cold days, 288, 289*.

Bronze, an alloy, 310.

Burning, explanation of, 308, 312-313.

Calcium chlorid, 114.

Camera, lens of, 143, 148; human eye as a small, 151*-153; explanation of, 327-332.

Capillary attraction, 36*-40; difference between adhesion, cohesion, and, 47.

Carbon, in electric battery, 203-206; resistance of, to electric current, 231; an element, 293, 299; one of chief elements in fuel, 315-316.

Carbon dioxid, in seltzer siphon, 17; produced by joining of carbon with oxygen, 315; combining of water and, by plants, 332-333; releasing of, in baking powder, 349-350; bubbling of, in effervescence, 365-366; in soda water, springs, and baking soda, 366-367; limewater test for, 375-376.

Carbonic acid gas, commercial name for pure carbon dioxid, 365-366.

Cat's hairs, static electricity in, 201.

Caustic soda, a common base, 356.

Center of weight, 30-33*.

Centrifugal force, 5, 72-74; law of, 74-75.

Charcoal, production of, 316.

Charging water with carbon dioxid, 366.

Chemical analysis, 370-376.

Chemical change, and energy, 293 ff.; burning (oxidation), 312-322; caused by heat, 323-325; caused by light, 326-335; caused by electricity, 335-339; energy released by, 340-341; helped by solution, 349-351.

Chemical equations, 297-299.

Chlorine, an element, 299.

Chlorophyll in plants, work of, 332.

Cigar-box telegraph, construction of, 249*, 380-381*.

Circuits, electric, 219-220*; breaking and making, 220-221; connecting in parallel, 221-223*; grounded, 225-229*; short, 240-245*.

Cloth, action of acids on, 354*; action of an alkali on, 356, 357*.

Clouds, how formed, 277-278.

Coal, carbon and hydrogen in, 315.

Cohesion, 39, 44*-49.

Cold, caused by expansion, 94; is the absence of heat, 95, 120.

Color, 161-172*.

Comb, electricity produced by rubbing, 197-198.

Compass, use of, 190-195*.

Complete electric circuits, 219-224*.

Compounds, how elements hide in, 300; definition of, 308-309; mixtures distinguished from, 309-310.

Concave mirrors, 154*, 155*, 157; magnification by, 157; in reflecting telescopes, 157.

Conduction, of heat, 116-118; of electricity, 213-218.

Conductors of electricity, good and poor, 213.

Conduits for electric wires, 237.

Conservation of energy, 57 ff.

Convection, carrying of heat by, 118-119.

Convex lens, 148-149*; in microscope, 155-157*; in telescope, 157.

Cooling from expansion, 94-96.

Coolness at night and in winter, 127-128.

Copper, a good conductor of electricity, 215; an element, 299; nickel plating of, 336-339*; etching of, with acid, 352*-353.

Copper nitrate, salt called, 353.

Cream, separating from milk, by centrifugal force, 75-76.

Crystals, formation of, 265-268.

Cylinder of engine, 344*.

Dead Sea, reason for salt in, 104-105*.

Decay, a kind of oxidation, 313.

Dew, 275; how formed, 287.

Dictaphone, working of, 175, 178, 179*.

Diffusion, 268-274; of light, 158-161.

Direct-current electricity, 211-212.

Distilling of liquids, 112-115*.

Doorbell, electric battery for ringing, 204-205.

"Down," meaning of word, 4.

Drainpipe, cleaning of, with lye, 358.

Dry-cell battery, 206*.

Dust, reason for clinging to walls, 43-44.

Dynamite, 343*; making of, 347.

Dynamo, how electric current is made to flow by, 207*-210*.

Earth, magnetism of, 190-195.

Easy circuit, a short circuit an, 244-245.

Echoes, explanation of, 183-185.

Effervescence, process of, 365; generally due to freeing of carbon dioxid, 367*-368; helped by stirring or shaking, 368.

Elasticity, 82-86; of form distinguished from elasticity of volume, 86-87.

Electrical apparatus, 216-217*, 222-223*; description of, 379-380.

Electric arc, the, 233*-240.

Electric battery, the, 203-206*.

Electricity, magnetism and, 190 ff.; static, 196-202; negative and positive charges of, 198*-200; action of, in thunderstorms, 200-201; flowing, 203 ff.; flowing of, in dynamo, 207-210; alternating and direct-current, 211-212; conduction of, 213*-218; chemical change caused by, 335-339.

Electric lamps, vacuums in, 12*, 317; incandescent, 125; gas-filled, 317.

Electric motors, 256*-257*.

Electrolysis apparatus, 294-295*.

Electromagnets, 247-257*.

Electrons, 193; description of, 197; number of, in negative and in positive charges, 198-200.

Elements, defined, 293; chemists' abbreviations of, 297-299; list of common, 299-300; hiding of, in compounds, 300-301.

Emulsion, defined, 261; difference between solution and, 263.

Energy released by chemical change, 340-341.

Engine, working of cylinder and piston of, 344*.

Ether, carrying of heat and light by, 124-125; light as waves of, 163-164.

Ether waves, 124-125, 163-164.

Evaporating dish, 101*.

Evaporation, 100-106*; part taken by, in formation of clouds, rain, and dew, 277.

Expansion, caused by heat, 88-93; cooling from, 94-96*.

Expansion ball and ring experiment, 91*-92.

Explosions, use of, 342* ff.; automobiles made to go by succession of, 344-345; cause of, 345; shooting of guns caused by, 345-346.

Explosives, manufacture of, 347.

Extension lights, 238.

Eye, lens of, 142; section of, 151*; working of, 151*-153.

Fading, process of, 326-327.

Filament of incandescent lamp, 125.

Fire engines, need of, to force water high, 9.

Fire extinguishers, action of, 317.

Fires, caused by electric arcs, 236; putting out of, by water, 317. See Burning.

Flames, formation of, 318.

Floating, sinking and, 23-28.

Focus of light, 142*-149*.

Fogs, cause of, 288.

Food, light necessary to production of, 332-333.

Force, overcoming of extra motion by, in lever, 63-64*; reason for, of steam, 110.

Forecasters, weather, 282-285.

Form, elasticity of, 86-87.

Freckles, cause of, 327.

Freezing and melting, 96-99.

Friction, 49-55*; electricity produced by, 197-198*.

Frost, 97, 275; explanation of, 287.

Fuel, chief elements in, 315-316.

Fulcrum of lever, 59-60*.

Fuse gap, the, 241*, 379*.

Fuses, short circuits and, 240-245.

Gas, cooling of, on expanding, 94-95; carbon and hydrogen in, 315; used for filling electric lamps, 317-318; will not burn until hot enough, 323-324; an explosion the sudden release of a confined, 348.

Gases, diffusion of, 269-271; as elements, 293-294.

Gas heaters, action of, 319, 321*, 322*.

Gasoline, evaporation of, 103; boiling of, 112; distilled from petroleum, 114; elements of, 315; action of, in making automobiles go, 344-345.

Geysers, cause of, 110.

Glass, a poor conductor of heat, 118; used as insulator of electricity, 215.

Glowworms, reason for glowing of, 341-342.

Gold, an element, 293, 299; plating of, 339.

Gravitation, defined, 3.

Gravity, 1; pull of, opposed to pull of adhesion, 42-43.

Grease, friction diminished by, 53-54; combined with lye to form soap, 357.

Great Salt Lake, reason for salt in, 104-105.

Greeks, early knowledge of electricity possessed by, 196.

Green color of water, reason for, 169-171*.

Grounded circuits, 225-229*.

Gun, shooting of, caused by explosion, 345-346.

Gunpowder, action of, in shooting of a gun, 345-346; how made, 347.

Hail, explanation of, 286.

Heat, a result of friction, 53; is the motion of molecules, 90; not caused by expansion, 94-95; cold is absence of, 95, 120; required to evaporate liquids, 102-103; conduction of, 116-118; carried by air, by convection, 118-119; radiation of, 122-128; of incandescent lamp, 125-126; brought to focus by convex lens, 149; chemical change caused by, 323-325.

Heaters, hot-water, 120*; electric, 230, 232; gas, 319, 321*, 322*.

Heat waves, cause of, 141.

Hydrochloric acid, getting hydrogen from, 301-304; testing for silver with, 373.

Hydrofluoric acid, 351.

Hydrogen, an element, 294, 299; in water, 295-296; experiments with, 301-304*; one of chief elements in fuel, 315-316; part taken by, in burning, 312-319.

Ice, slight friction of, 52*; action of molecules in, on freezing and melting, 96-97; reason for floating of, 98-99.

Incandescence, defined, 125.

Incandescent lamps, 125-126; number of electrons in, 197; working of, 229-232.

Inertia, 66-71; definition of, 70.

Insulators, of heat, 118; of electricity, 213; substances used as, 215.

Iodine, an element, 299; testing with, for starch, 373-374.

Iron, a good conductor of heat, 118; an element, 299.

Irons, electric, 229*, 230, 232.

Iron salt, formed by lemon juice on steel, 353.

Iron ships, reason for floating, 24*-26.

Kerosene, boiling of, 112; distilled from petroleum, 114; carbon and hydrogen in, 315.

Laughing gas, 309.

Lava in volcanoes, 110.

Lead, an element, 299.

Lead pencils, arc light from, 233*-234*.

Leaning Tower of Pisa, 29*-30.

Lemon juice, action of, on silver and on steel, 353; litmus test of, 359.

Lens, of eye, 142, 151*-153; of camera, 143, 149*, 328; convex, 148-149; concave, 149*; in telescope, 157.

Levers, 57-65*.

Light, radiation of, 122, 123*-128; reflection of, 129-135*; refraction of, 136*-141; focus of, 142-149*; brought to focus by convex lens, 149; diffusion of, 158-161*; color a kind of, 162; speed of, 182; chemical change caused by, 326-335; and manufacture of food in plants, 332-333.

Lightning, cause of, 200-201.

Limewater test for carbon dioxid, 375*-376.

Liquid air, 97, 112.

Liquids, absorption of, 36-40; diffusion in, 272.

Litmus paper, experiments with, 358-359.

Litmus test, the, 358-359.

Lye, a common base, 356; experiment with, 356; soap made from, 357; used for clearing out drainpipe, 358; neutralization of, by acids, 363.

Machinery, oiling of, to decrease friction, 53-54.

Magdeburg hemispheres, 15, 16*-17.

Magnetism, 190 ff.

Magneto, of automobile, 210, 211*; of old-fashioned telephone, 210-211.

Magnets, 190-195*.

Magnification, 150-157; by concave mirror, 157.

Magnifying glass, convex lens in, 149; operation of, 150-156*.

Manganese dioxid, an essential in explosives, 347.

Megaphone, working of, 184.

Melting, freezing and, 96-99.

Membrane, diffusion through a, 272.

Mercury, cohesion of, 47-48*; use of, in thermometer, 89*, 90-91; an element, 299.

Mercury-vapor lamps, 167-168*, 172.

Metals, good conductors of heat, 118; good conductors of electricity, 215; as elements, 310; plating of, 336-339*; action of acids on, 351-353.

Microscope, 88; working of, 155-157*.

Mirrors, concave, 154*, 155*, 157.

Mixtures, distinguished from compounds, 309-310.

Molecular attraction, 36 ff.

Molecules, pull of, on each other, 46-47; explanation of, 88-89; heat defined as the motion of, 90; action of, in evaporation, 102-103*; action of, in boiling water, 107; action of, in conduction of heat, 117; action of, in radiation of heat and light, 125; action of, in magnetizing, 194*-195; made up of atoms, 196, 310; mingling of, 259 ff.; action of, in formation of clouds, rain, and dew, 277.

Moon, cause of ring around, 131.

Morse telegraph code, 253.

Motion-picture machines, lenses of, 143, 148.

Motor, the electric, 255-257*.

Mountains, rainfall on, 286-287.

Musical instruments, pitch of, 185-187*, 188; vibrating devices of, 188.

Nail plug, the, 241*, 379*.

Needle, magnetizing of, 192*, 193*-195.

Negative charges of electricity, 198-200.

Neutralization of acids and bases, 360-364.

Niagara Falls, electricity generated by, 210.

Nickel, an element, 299.

Nickel-plating copper, process of, 336-339*.

Night, reason for coolness at, 127-128.

Nitric-acid, etching copper with, 352*-353; action of, on cloth, 354*.

Nitrogen, an element, 299; a non-burning gas, 308; used in electric lamps, 317.

Northern Lights, cause of, 193.

Ocean, why salt, 104-105.

Oil, reason for floating of, 26-27; decreasing of friction by, 53-54; softening due to, 290-292; carbon and hydrogen in crude, 315; why water will not put out burning, 317.

Oil heaters, action of, 319.

Orange, litmus test of, 359.

Osmosis, process called, 272-274.

Osmotic pressure, 272-273*.

Oxidation, 312-322.

Oxygen, an element, 293, 299; an element of water, 295-296; experiments in getting, from two solids, 305-308*; function of, in burning, 308; part taken by, in burning (oxidation), 312-313; released in manufacture of plant food, 333-335; a compound of, an essential in explosives, 347.

Pancakes, made from sour milk, 362.

Paper, carbon and hydrogen in, 315.

Paraffine, production of, 114.

Parallel circuits, 221-223*.

Peat, carbon and hydrogen in, 315.

Pencils, making arc light with, 233*-234*.

Periscope experiment, 134-135*.

Petroleum, gasoline and kerosene distilled from, 114.

Phonograph, working of, 177-178*.

Phosphorescence, cause of, 341-342.

Phosphorus, an element, 300; meaning of name, 341.

Photographs, process of making, 327-332*.

Pitch of sound, explanation of, 185-188*.

Plants, light and the manufacture of food in, 332-333; how oxygen is supplied by, 333-335.

Plating of metals, 336-339*.

Platinum, an element, 300.

Poles, positive and negative, 206-207.

Porcelain, used as insulator, 215.

Positive charges of electricity, 198-200.

Potassium, experiment with, 304.

Potassium chlorate, an essential in explosives, 347.

Precious stones, formation of, 263-264.

Prism, refraction of light by, 136-140*; separation of light into rainbow colors by, 162-163*.

Quicksilver. See Mercury.

Radiation of heat and light, 122*-128.

Radium, an element, 300.

Rain, 275; cause of, 278-280.

Rainbow, making a, on wall, 162*-163; how formed, 170-171.

Reading glasses, 144*; convex lens in, 150.

Red color of sky at sunset, reason for, 170.

Reflecting telescopes, 157.

Reflection of light, 129-135*.

Refraction of light, 136-141*.

Resistance, electrical, 229-232.

Retina of eye, 151*, 153.

Reverberation of sound, 183-185.

Ring around moon, cause of, 131.

Rock candy, how made, 267.

Rubber, used as insulator, 215.

Rusting of iron, 349.

Safety valves on steam boilers, 347.

Salt, reason for, in sea, 104-105*; a compound, 308; elements of, 310-311; formed by hydrochloric acid and zinc, 351; iron, formed by lemon juice on steel, 353; acids and bases turned to water and, by combining, 361-362.

Salt water, litmus test of, 359.

Samson cells, 204.

Scattering of light (diffusion), 158-161*.

Seesaw, example of a lever, 57-58*.

Seltzer siphon, working of, 17.

Ships, reason for floating, 24*-26.

Shock, electrical, 214-215.

Short circuits and fuses, 240-245.

Silver, an element, 300; plating of, 339; hydrochloric acid test for, 373.

Silver chlorid, formation of, 327.

Sinking and floating, 23-28*.

Siphon, 18*.

Sky, reason why blue, 169; why red at sunset, 170.

Smoke, consistency of, 318-319.

Snow, 275; formation of, 285-286.

Snowflakes, 97, 286*.

Soap, how made, 357-358.

Soda water, how made, 365-366.

Sodium, experiment with, 304.

Softening due to oil or water, 290-292.

Soil, litmus test of, 359.

Solution, defined, 261; difference between emulsion and, 263; a mixture and not a compound, 309; chemical change helped by, 349.

Sound, cause of, 174; rate of speed, 181-182; action of, in echoes, 183-185*; pitch of, 185-188.

Sour milk, litmus test of, 359; neutralization of, by baking soda, 362.

Sourness, taste of, caused by acids, 353, 354-355.

Spectroscope, use of the, 172.

Spectrum, the, 172.

Spring water, carbon dioxid in, 366.

Stability, 29-34.

Starch, iodine test for, 373-374.

Stars, twinkling of, 141; how to tell of what made, 171-172.

Static electricity, 196-202*.

Steam, reason for force exerted by, 110; geysers and volcanoes caused by, 110; real, not visible, 112 n.

Steel, generally an alloy, 310.

Stereopticons, lenses of, 148.

Storage battery, 206, 207*; action of electricity in, 339.

Stoves, electric, 230, 232.

Street car, electric motor of, 255-257.

Suction pump, 19*.

Sugar, making of, by plants, 332-333; litmus test of, 359.

Sulfur, an element, 300.

Sulfuric acid, action of, on cloth, 354; litmus test of, 359.

Sun, radiation of heat and light from the, 122-128; how to tell of what made, 171-172.

Sunbeams, explanation of, 131.

Sweat glands, function of, 291.

Tanning, process of, 327.

Telegraph apparatus, 247-252*, 380-381*.

Telegraph code, 253.

Telephone, working of, 253-255.

Telescopes, 156*, 157; how made, 157; reflecting, 157.

Temperature, finding the, by reading a thermometer, 90-91.

Thermometer, the, 89*-91*.

Thermos bottle, how made, 126-127*.

Thunder, cause of, 200-201.

Tin, an element, 300.

Tin salt, poisonous, 353.

Toasters, electric, 230, 232.

Tomatoes, use of soda to neutralize acid of, 362-363.

Tungsten, in incandescent lamps, 231.

Tuning-fork experiments, 181*, 186-187*.

Twinkling of stars, cause of, 141.

"Up," meaning of word, 4.

Vacuum, defined, 11; reason for, in electric lamp, 12*, 317; use of, in manufacture of thermos bottles, 126-127*; impossibility of producing sound in, 176-177.

Valves, safety, on boilers, 347.

Vaseline, production of, 114.

Vibrations, of air, 174-181*; pitch due to rapidity of, 186.

Vinegar, litmus test of, 359; neutralization of lye by, 363.

Violin, tuning of, 187.

Volcanoes, cause of, 110; explosions and, 346*.

Volume, elasticity of, 86-87.

Washing soda, a common base, 356; litmus test of, 359.

Water, seeks its own level, 6-10; gurgling of, when poured from bottle, 13; experiment with, to show centrifugal force, 73-74; used for making thermometer, 90*-92; expansion of, when frozen, 98; evaporation of, 100-106; action of, in geysers and volcanoes, 110; absorption of light by, 169-170; as conductor of electricity, 216; use of, for generating electricity, 256-257; softening due to, 290-292; elements of, 294-297; a compound and not a mixture, 308; formed by burning fuel, 316; why fire is put out by, but not burning oil, 317; combining of carbon dioxid and, by plants, 332-333; rusting of iron by, 349; acids and bases turned to salt and, by combining, 361-362.

Wear, a result of friction, 53.

Weather, forecasting of, 282-285.

Weight, center of, 30-33*.

Wet battery, 204-205*.

White, a combination of all colors, 162.

Winds, cause of, 20-21.

Winter, reason for cold in, 127-128.

Wiring for arc lamps, 236-239.

Wood, poor conductor of heat, 118; carbon and hydrogen in, 315.

Yardstick, experiment with, to show leverage, 59*-60.

Yeast, action of, in bread making, 365.

Yellow, in flames, 318.

Yerkes Observatory, telescope of, 156*.

Zinc, in electric battery, 203-206; an element, 300; used for driving hydrogen out of acid, 301, 304.

* * * * *

CONSERVATION SERIES



Conservation Reader

By HAROLD W. FAIRBANKS, Ph. D.

Lecturer, University of California; Geography Supervisor Berkeley Public Schools

A small book bringing out in a simple and interesting manner the principles of conservation of natural resources has long been wanted, or there has been little on the subject that could be placed in the hands of pupils. It is to answer this need that Fairbanks' CONSERVATION READER has been prepared.

The book touches upon every phase of conservation, but it deals at greatest length with saving the soil, the forests, and wild life. It is one of the author's main purposes to arouse a stronger sentiment for preserving what remains of the forests as well as for extending their areas. This is because proper forestation will lessen the danger of floods and of erosion of the soil, and it will encourage the return of the wild creatures that are of so much economic importance and add so much to the joy of life.

The matter is presented in an easy narrative style that is calculated to arouse the intelligent interest of children. The text is illustrated with photographs of wild animals, trees, landscapes, and rarely beautiful birds, printed in colors. The subject is timely and the treatment is happy throughout.

CONSERVATION READER should be used as a reader or as a book for regular study in every elementary school in the country.

Cloth, vi + 216 pages. Price $1.40.

WORLD BOOK COMPANY

YONKERS-ON-HUDSON, NEW YORK 2126 PRAIRIE AVENUE, CHICAGO



* * * * *

INDIAN LIFE AND INDIAN LORE

INDIAN DAYS OF THE LONG AGO

IN THE LAND OF THE HEAD-HUNTERS

TWO BOOKS FOR YOUNG PEOPLE BY

EDWARD S. CURTIS

Author of "The North American Indian"

In Indian Days of The Long Ago the author gives an intimate view of Indian life in the olden days, reveals the great diversity of language, dress, and habits among them, and shows how every important act of their lives was influenced by spiritual beliefs and practices.

The book tells the story of Kukusim, an Indian lad who is eagerly awaiting the time when he shall be a warrior. It is full of mythical lore and thrilling adventures, culminating in the mountain vigil, when Kukusim hears the spirit voices which mark the passing of his childhood. Illustrated with photographs by the author and drawings by F. N. Wilson.

* * * * *

Theodore Roosevelt once said that Mr. Curtis has caught glimpses, such as few white men ever catch, into the strange spiritual and mental life of the Indians. In In the Land of the Head-Hunters these glimpses are shared with his readers.

The story centers about Motana, the son of the great War Chief. The mountain vigil, the wooing and winning of Naida, the raid of Yaklus and his warriors, the rescue of the captured Naida, and the final victory, celebrated by ceremonial dances, are all described. The action is rapid and the story is told in the direct, simple style of the true epic. Illustrated with thirty full-page photographs by the author.

Price $1.60 each.

WORLD BOOK COMPANY

YONKERS-ON-HUDSON, NEW YORK 2126 PRAIRIE AVENUE, CHICAGO



* * * * *



INSECT ADVENTURES

By J. HENRI FABRE

Selected and Arranged for Young People by Louis Seymour Hasbrouck



A new supplementary reader in nature study for the intermediate grades. A book containing a vast amount of information relating to insect life—the life story of the spider, the fly, the bee, the wasp, and other insects—told by one who was at once a lover of nature, a great scientist, and a most entertaining writer. Maeterlinck calls Fabre the "insects' Homer," and declares that his work is as much a classic as the famous Greek epic, and deserves to be known and studied as a classic.

This is the first time that Fabre's writings have been made available for school use, and the book will prove a delight to school children wherever they are given the chance to read it. No live boy or girl could fail to be interested in nature subjects presented by so gifted a naturalist as Fabre in the form of such absorbing adventures.

The many quaint sketches with which the book has been illustrated by Elias Goldberg complete its charm.

A useful index is included.

Cloth. 300 pages. Price $1.48.

WORLD BOOK COMPANY

YONKERS-ON-HUDSON, NEW YORK 2126 PRAIRIE AVENUE, CHICAGO

* * * * *



NEW-WORLD SCIENCE SERIES

Edited by John W. Ritchie

TREES, STARS and BIRDS

A BOOK OF OUTDOOR SCIENCE

By EDWIN LINCOLN MOSELEY

Head of the Science Department, State Normal College of Northwestern Ohio

The usefulness of nature study in the schools has been seriously limited by the lack of a suitable textbook. It is to meet this need that Trees, Stars, and Birds is issued. The author is one of the most successful teachers of outdoor science in this country. He believes in field excursions, and his text is designed to help teachers and pupils in the inquiries that they will make for themselves.

The text deals with three phases of outdoor science that have a perennial interest, and it will make the benefit of the author's long and successful experience available to younger teachers.

The first section deals with trees, and the discussion of maples is typical: the student is reminded that he has eaten maple sugar; there is an interesting account of its production; the fact is brought out that the sugar is really made in the leaves. The stars and planets that all should know are told about simply and clearly. The birds commonly met with are considered, and their habits of feeding and nesting are described. Pertinent questions are scattered throughout each section.

The book is illustrated with 167 photographs, 69 drawings, 9 star maps, and with 16 color plates of 58 birds, from paintings by Louis Agassiz Fuertes.

It is well adapted for use in junior high schools, yet the presentation is simple enough for pupils in the sixth grade.

Cloth. viii + 404 + xvi pages. Price $1.80.

WORLD BOOK COMPANY

YONKERS-ON-HUDSON, NEW YORK 2126 PRAIRIE AVENUE, CHICAGO

* * * * *



NEW-WORLD SCIENCE SERIES

Edited by John W. Ritchie

SCIENCE for BEGINNERS

By DELOS FALL

Professor of Chemistry, Albion College

To supply the need for a course that will give the preparatory training which any scientific study demands, SCIENCE FOR BEGINNERS by Professor Delos Fall was made. The aim in this text is to win the interest of pupils, to give them conceptions of nature that are fundamental, and above all to ground them in the method of science.

The subject matter has to do with the earth sciences, and principally with physics and chemistry. In the development of each topic, every advantage that the pupils' experience and interest may afford is utilized. Exercises or experiments are interspersed throughout the work, and for these only the simplest materials are required. The studies are carried to those connecting principles which permit the organization of knowledge. The book is illustrated with a number of excellent photographs and over 200 drawings of more than usual merit.

The text is adapted for use in grades seven, eight, and nine, or in any classes that are about to take up their first work in science. It will prove helpful to the teachers and pupils who use it directly, and its influence will continue with classes as they advance. It will thoroughly ground pupils in those ideas that are prerequisite to any right work in science.

xi + 388 pages. Price $1.68

WORLD BOOK COMPANY

YONKERS-ON-HUDSON, NEW YORK 2126 PRAIRIE AVENUE, CHICAGO

* * * * *



NEW-WORLD SCIENCE SERIES

Edited by JOHN W. RITCHIE

The publication of books that "apply the world's knowledge to the world's needs" is the ideal of this house and it is intended that the different volumes of this series shall express this ideal in a very concrete way.

Completed

HUMAN PHYSIOLOGY. By John W. Ritchie, Professor of Biology, College of William and Mary. A text on physiology, hygiene, and sanitation for upper grammar or junior high schools. $1.60.

LABORATORY MANUAL FOR HUMAN PHYSIOLOGY. By Carl Hartman, University of Texas. A manual to accompany Ritchie's Human Physiology. BOUND IN PAPER AND CLOTH. 60 cents and $1.00.

SCIENCE FOR BEGINNERS. By Delos Fall, Albion College, Michigan. A beginning text in general science for intermediate schools and junior high schools. $1.68.

EXERCISE AND REVIEW BOOK IN BIOLOGY. By J. G. Blaisdell, Yonkers, N. Y., High School. A combined laboratory guide, notebook and review book for students' use. Written from the standpoint of efficiency and furnishing material for a year's work and to accompany any one of several high-school texts in general biology. BOUND IN STRONG PAPER. $1.20.

TREES, STARS, AND BIRDS. By E. L. Moseley, Ohio State Normal College, Bowling Green. A book of outdoor science for junior high schools and the upper grammar grades. $1.80.

PERSONAL HYGIENE AND HOME NURSING. By Louisa C. Lippitt, University of Wisconsin. A practical text for use with classes of young women in vocational and industrial high schools, colleges, and normal schools. $1.68.

SCIENCE OF PLANT LIFE. By E. N. Transeau, Ohio State University. A scientific and very practical text for high schools. $1.88.

ZOOeLOGY. By T. D. A. Cockerell, University of Colorado. A text for college use. $3.60.

EXPERIMENTAL ORGANIC CHEMISTRY. By A. P. West, University of the Philippines. A text for college use. $3.20.

COMMON SCIENCE. By Carleton W. Washburne, Superintendent of Schools, Winnetka, Illinois. Especially made for junior high schools. $1.68. Also Manual for above, 20 cents.

Other volumes are also in preparation.

WORLD BOOK COMPANY

YONKERS-ON-HUDSON, NEW YORK 2126 PRAIRIE AVENUE, CHICAGO

* * * * *



INDIAN LIFE AND INDIAN LORE

THE HERO OF THE LONGHOUSE

By MARY E. LAING

Illustrations from 27 paintings by David C. Lithgow

This story gives a portrayal of the noblest of Indians—Hiawatha. It follows established facts, and bares to the reader the heart of his race. It is a convincing tale.

The training of the Indian youth is shown; the career of the hero as a warrior is told; his great work for peace with the Five Tribes is described.

Besides the story, there is an account of the historical Hiawatha; also a complete Glossary giving definitions as well as pronunciations of the new Indian words. A map of the country of the Longhouse will enable the reader to follow the journeys of the Indian people.

The book is intended as a supplementary reader in schools, being adapted to the sixth grade or above. It will also be valuable in groups of the Wood-craft League, Camp-fire Girls, and Boy Scouts.

Cloth, xxvi + 329 pages. Price $1.60.

WORLD BOOK COMPANY

YONKERS-ON-HUDSON, NEW YORK 2126 PRAIRIE AVENUE, CHICAGO

* * * * *



REGISTERED TRADE MARK

CHEMCRAFT

THE CHEMICAL OUTFIT

Makes You an Amateur Chemist!

You can perform a great many useful and practical chemical experiments, have a lot of fun, and learn the principles of chemistry, if you have a CHEMCRAFT outfit. And an outfit now will help you in chemistry later on.

Each CHEMCRAFT outfit is a complete chemical laboratory containing many harmless chemicals, all needed apparatus, and a Manual of Instruction giving accurate information on the subject. CHEMCRAFT is real chemistry. These outfits are now used by many schools and are endorsed by professors and teachers. You can choose your outfit from

FIVE SIZES=NO. 0—75C. NO. 1—$1.50. NO. 2—$2.50. NO. 3—$5.00. NO. 4—$10.00

(West of Denver, Colo., 10% additional)

Sold by most toy stores and in any toy departments. If not obtainable near your home, any outfit will be delivered from the factory at the price listed. More complete descriptions will be sent Free to any boy or girl, or school authority, upon request.

THE PORTER CHEMICAL COMPANY

Porter Products Put Science at Your Service

HAGERSTOWN—MARYLAND

* * * * *



The Biggest Thing of its kind in the World

CALUMET BAKING POWDER

It may be interesting to know which is the largest city in China—the largest river in Africa—but it is MORE important to know about the industrial life of your country—because when most of you go out into the world you will become active figures in the making, buying and selling of things.

The Calumet Baking Powder factories, in Chicago and East St. Louis are the largest, most modern and sanitary plants of their kind on earth. More pounds of Calumet are sold than of any other brand of baking powder.

That is because Calumet is the best purest, most dependable baking powder made; makes the finest, most wholesome, tasty pies, cakes, biscuits, doughnuts, etc.

You will find the same rule applies to everything you do in life. If you do a thing better than any one else—your services will always be in demand and you will surely be a leader in your line of work. Calumet Baking Powder is sold at a moderate price—has more than the usual leavening strength—and NEVER fails.

A slip in pound can tells how to get the beautifully illustrated Calumet Cook Book.

* * * * *



VENUS PENCILS

The largest selling QUALITY pencil in the world



As soft as you wish; as hard as you please; but always smoother than you had dreamed. Any Venus Pencil you select glides over the paper with a restful freedom from friction.

17 BLACK DEGREES, 3 COPYING

For bold, heavy lines 6B-5B-4B-3B For writing sketching 2B-B-HB-F-H For clean fine lines 2H-3H-4H-5H-6H For delicate, thin lines 7H-8H-9H

PLAIN ENDS, PER DOZ. $1.00 RUBBER ENDS, PER DOZ. 1.20

VENUS ERASERS

12 SIZES



Of the same superb quality as the Venus Pencil

Send for free sample.

At all Stationers and Stores

American Lead Pencil Co. 220 Fifth Ave., N. Y. and London, Eng.

* * * * *

Transcriber's Notes:

page 238: changed "diagramed" to "diagrammed" (As there diagrammed, the electricity passes out...)

page 253: the Morse telegraph code is as in the original; this is not the modern International Morse code

Page 412, changed "conrcete" to "concrete" (... shall express this ideal in a very concrete way.)

General: variable spelling of iodin/iodine in the original has been preserved

General: spelling of dioxid and chlorid in the original has been preserved

THE END