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 (CO₂) 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 (CO₂)—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 (CO₂), 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 (H₂O). Or, as the chemists write it:

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 (H₂O). Chemists write this as follows:

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 (CO₂), 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 (CO₂) 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 (CO₂) 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.