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 (CO2) is present.
Fig. 189. The limewater test shows that there is carbon dioxid in the air.
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.