CHAPTER XXXIX

MORE EXPERIMENTS

TIPS AND DODGES FOR THE WINTER EVENINGS

THE REFRACTORY CORK

A VERY interesting and amusing experiment may be performed with a bottle and a cork.

Take a cork of a diameter less than the internal diameter of the neck of the bottle you propose using, and ask a friend to make it enter the bottle by blowing upon it.

At first sight this seems a very easy task, and your friend at once proceeds to blow strongly upon the cork. This, however, instead of making the cork enter the bottle, causes it to fly out.

Again your friend tries to overcome the troublesome cork, on the next occasion by blowing very gently, but again it flies out (Fig. 1).

The explanation of this is as follows:--

In blowing upon the cork, a certain amount of air at the same time enters the bottle, the air in which becomes so compressed that it rapidly ejects the cork. There are, however, three ways in which the refractory cork may be overcome.

Since you know that by blowing on the cork it is at once ejected, try to achieve success by performing the contrary action--that is, by withdrawing some of the air from the bottle.

Indeed, the experiment will prove to you that, by so doing, you create in the bottle a partial vacuum, and as soon as your mouth leaves the neck of the bottle air enters it owing to atmospheric pressure. This incoming current of air pulls with it the cork, which at once slides into the aperture.

The same result may also be achieved by first warming the bottle, when, owing to the expansion of the air, a part of it is expelled. Directly the air inside the bottle cools, a vacuum is created, and a current of air from without enters. If you add to this current of air by blowing air from your mouth, you will find this quite sufficient to cause the cork to enter the bottle. Then, again, having a straw or a pipe-stem handy, all you have to do is to blow through the tube, directing the air exactly on the base of the cork, which will once again enter the aperture.

Whichever of these means is adopted, you must always take the precaution of seeing that the bottle is perfectly dry. It should be wiped every time. The moisture formed in the neck is sufficient to prevent the cork from gliding along the glass.

THE FLYING COIN

You may be inclined to think that special apparatus is necessary to make a coin fly from the bottom of a glass, but here is shown a very simple method by which the trick may be performed at any moment in your home.

First procure a liqueur glass of conical shape, having in its largest part a diameter not much greater than that of a silver dollar. At the bottom of this glass place a quarter, and above it, near the top of the glass, a silver dollar, the latter forming a kind of cover (A, Fig. 2). Now declare to your friends that, without touching the dollar, you will make the quarter jump from the glass.

This at first seems to them an impossibility, but all you have to do is to blow very strongly on the edge of the dollar. This will make the larger coin turn about on its own diameter into a vertical position, whilst the compressed air under the quarter causes the latter to fly out of the glass, after which the dollar returns to its original horizontal position.

A CIGARETTE-SMOKING LAMP-GLASS

This is a very striking experiment, and is quite easy to perform. The apparatus is also quite simple, and may be easily obtained. It consists of a lamp-chimney, a cork, a cigarette, together with two little valves.

Tightly cork up one end of the lamp-chimney with a large cork, thus hermetically sealing it. In this cork bore two holes, one following the line of the cork’s axis and having exactly the same diameter as the cigarette: the other being oblique with respect to this axis, and having a much smaller diameter (Fig. 3).

It is now necessary to make the valves. This is done by cutting from a glove two round pieces of the skin or leather, which, by means of pins, may be fixed over the holes, one being above the little hole on the top of the cork, the other over the large hole on the under side of the cork.

The first valve allows the smoke to escape, at the same time preventing the entrance of any external air, whilst the lower valve allows the smoke from the cigarette to enter the glass tube, but will not allow it to escape by the same hole.

Having thus made the valves, next plunge the tube in the water as far as the cork, and place the cigarette in the hole made for it. After having lit it, proceed to make the lamp-chimney smoke it.

In order that it may inhale the smoke, slowly raise the glass. By so doing a vacuum is produced between the surface of the water and the bottom of the cork. To destroy this vacuum, air must enter from without, and the only means of its entrance is through the cigarette, as the valve on the top of the cork remains tightly closed. In passing through the cigarette this current of air greatly assists combustion, and the smoke formed will pass with the air into the lamp-chimney.

If now the glass be lowered again, the air which is compressed by so doing closes the central valve, whilst that above the oblique tube is opened. From this valve the smoke will ascend in clouds (Fig. 4).

In this way the glass may be made to smoke the whole cigarette.

WATER SWINGING

Nearly every one has seen, at the circus or elsewhere, an acrobat executing giddy circular movements with a glass of water, and doubtless has wondered how it is that none of the liquid is spilt. This is due to the action of centrifugal force.

Having placed the glass full of water on the table, it is only a matter of taking it properly with the hand, holding it at arm’s length, and, with the arm thus extended, describing a complete circle, after which it may be placed upon the table without the loss of a single drop.

To insure the success of the experiment, particular attention must be paid to the manner in which the glass is held. Instead of taking it as you would when drinking, hold it with the hand reversed, the palm being turned upwards, as shown in Fig. 5.

Without hesitation throw the arm in the air, and swing it, not too quickly, but without shaking it, in the direction of the arrows in the diagram (Fig. 6).

After one complete revolution the glass should be as shown by Fig. 7; whilst in this position it may be placed on the table. At first it is advisable to practice this experiment with water, but, as more skill is acquired, other liquids, such as milk or wine, may be used as occasion permits.

A NOVEL MIRROR

A simple method of illuminating the back of the mouth and throat, especially when throat trouble is suspected, may often be found extremely useful. Here is a means of supplying, at a moment’s notice, an extemporized illuminant of this kind.

Take a well-cleaned spoon, and hold it against a candle flame, when you form an excellent mirror, which will permit you to concentrate the rays of light and produce at the back of the throat enough illumination for the making of a careful examination (Fig. 8).

A silver spoon, moreover, allows you to study the curious properties of curved mirrors. Holding the hollow part of the spoon before your face, notice that the head is at the bottom; turn the spoon round, and you have the bulging part a convex mirror, which will show an image, very long and narrow. If you approach this face in the spoon little by little, you will see the nose attain the most amusing proportions.

A DISAPPEARING COIN

If you look at an object which has been placed in water, owing to the phenomenon of refraction, the article appears in a different position from that in which it really is.

It is due to this phenomenon, therefore, that a stick, when half plunged into water, seems to be bent or broken.

A very interesting experiment based on this principle is the following:--

Take a bowl full of water, and at the bottom place a coin. Next request one of your friends to lower his head until his eye, the edge of the bowl, and the near edge of the cent, appear to be in the same line.

As a matter of fact, it is not the coin itself that your friend can see, but only the image created by refraction.

Now, keeping your friend in the same position, inform him that you intend to make the coin disappear from his view.

To do this, remove some of the water from the bowl, which may be accomplished by means of a small syringe (Fig. 9).

Directly you lower the level of the water, your friend will no longer be able to see the image of the coin, which will be hidden by the side of the bowl. If, however, the extracted water be replaced, the image of the coin immediately reappears.

ELECTRIFIED PAPER

Very few people realize that paper can be electrified at a moment’s notice, no special apparatus for the purpose being required.

Take a piece of light paper, which should have been well dried, and rub it briskly with a clothes brush, silk handkerchief, or even the open hand.

After a little time the paper, becoming electrified, will adhere to your face, your hands, or your clothes, as easily as if it were attached by means of gum.

Nor is this property confined to thin paper. Thick paper, when dried, will act in the same manner. For instance, take a postcard, dry it, and rub it, and you will notice that, as is the case with sealing-wax, glass, sulphur, &c., the card has the power of attracting light bodies, such as small pieces of cork.

The following interesting experiment may be carried out with an electrified postcard and a walking-stick.

Balance the walking-stick over the back of a chair, and announce that you can make the stick fall without touching it, without blowing it, or without interfering with the chair. This is easily possible by utilizing the electrified postcard.

First rub it on the sleeve of your coat. Now hold it near one end of the stick, and you will notice that the latter follows it as iron follows a magnet (Fig. 10), until the moment when the equilibrium being destroyed, the stick falls to the ground.

Of course the experiment may be varied by using any other suitable article in place of the stick, as for instance a fishing-rod.

ELECTRIFIED BALLOONS

From the last experiment it may have been gathered that if a piece of paper is dried and rubbed with a silk handkerchief or the dry hand it will adhere to the face, arms, or clothing.

It may not be so widely known, however, that if toy balloons be filled with air, and then stroked for a short time with a piece of fur, they will act in the same way as the electrified paper.

It is rather amusing to see these balloons, after being treated thus, placed against the wall or ceiling, where they will stick as if they were glued there.

Having entertained your friends in this manner, you may, by way of a little change, take two of these toy balloons, and, after having electrified them, suspend them from the same point by means of two silken threads.

You will be surprised to find that the balloons now repel each other in the same manner as pith balls do (Fig. 11).

EXPLODING FLOUR

Flour will create an explosion!

Take a large handful of flour, and leave it for some time near the fire, in order that every trace of dampness may be expelled.

Whilst the flour is drying take a large tin box (a cracker tin will do admirably), and near the bottom make a small hole.

Through this hole pass the end of a piece of india-rubber tubing, and place the handful of dry flour in front of it.

At the other end of the box place a short piece of candle, and after lighting it, cover the box with the lid, taking care that it is not too firmly fixed.

If you now blow down the tube with your mouth, or better still, with a pair of bellows an explosion at once takes place, as a result of which the lid will be blown off (Fig. 12).

If flour be not available the experiment may be performed with equal success by using fine dust, such as may be found on the backs of pictures, or collected from any elevated parts of the room.

THE APPARENTLY IMPOSSIBLE

Have you ever had tea on the top of a mountain? If so, you will agree that your cup of tea could by no means be termed excellent.

Now, why is it that a cup of tea made on a mountain-top is much inferior to one made at a lower level? If the fault lay in the tea, the defect could be easily remedied, but such is not the case, for it depends upon the fact that water on the top of a mountain boils at a lower temperature than water at the sea-level.

In order to make a good cup of tea, the water must boil at a temperature very near 100° C., and it is at this temperature that the water is generally boiled in your homes.

Why is it, then, that water boils at different temperatures at different altitudes? It is because, as the altitude is increased, so the atmospheric pressure becomes less.

At sea-level, atmospheric pressure is equal to about 15 lbs. to the square inch, but at the top of a mountain it is much less. The greater the atmospheric pressure the more heat is required before the bubbles of vapor formed within the water can break at the surface.

After this explanation, perhaps the subjoined experiment will be attempted with additional interest.

Take a flask, to which should be fitted a good cork or india-rubber stopper, and in it boil some water, taking care of course to remove the stopper beforehand.

After some minutes the steam from the boiling water will have expelled all the air from the flask. Now remove the source of heat, at the same time quickly inserting the stopper.

If the flask is allowed to stand for a minute or two, the temperature of the water will fall considerably below 100° C.

Next inform your friends that, without applying any extra heat, you will cause the water in the flask to boil vigorously again. This seems to them impossible, especially when you tell them that you are going to do it by means of cold water. Quickly turn the glass upside down, and squeeze a sponge soaked in cold water on its upturned under-surface. Immediately the liquid inside will begin to boil, as if extra heat had been applied (Fig. 13).

But how are you to explain this apparently extraordinary phenomenon?

Well, directly the cold water comes in contact with the flask it causes the steam contained therein to condense, and, as no air can enter, thanks to the well-fitting cork, the pressure on the surface of the warm water is now considerably less than it was before.

Directly the pressure is lessened the vapor bubbles contained within the warm water are able to rise to the surface, and the water is seen to boil merrily.

MAKING COAL GAS

Here is a very simple way of obtaining coal gas.

Procure an ordinary long clay tobacco pipe, the bowl of which should be filled with very small pieces of coal. Carefully cover the top with soft clay, and put the bowl in the fire, with the long stem protruding through the bars. Now watch this end of the pipe very closely and see what happens.

Very soon you will notice a light-colored smoke issuing from the mouthpiece, but after a time this smoke disappears. But what happens if you hold a lighted match to the mouthpiece of the pipe? Immediately a bright yellow flame appears (Fig. 14).

The gas now burning is the same gas as is burnt in your house, although this latter, of course, is much purer.

If now you take the pipe from the fire, allow it to cool and then break it, you will be surprised to find that its contents have changed in appearance, for, in place of the coal, you will see what looks like a cinder. This is the coke. Thus you have manufactured gas from coal, at the same time producing coke.

EXPERIMENTS WITH CARBONIC ACID GAS

In a previous chapter, when describing how to make a miniature cannon, it was explained that the “gunpowder” with which the “shell” was fired is in reality carbonic acid gas.

It may not be amiss to show how to generate it, in order that you may discover for yourselves some of its properties.

There are several ways of obtaining carbonic acid gas, but most of these are of a complicated nature. The following, however, is an extremely simple method.

Take a 6-oz. or 8-oz. flask, and fit it with a cork with a hole, in which may be fitted a piece of glass tubing.

This tubing should be bent twice at right angles, as shown in Fig. 15, and the longer end should be allowed to dip into a large glass.

Into the flask pour a little lemonade, soda water or ginger ale, and after replacing the cork or tube, heat the flask by means of a gas-burner or spirit lamp.

You will notice that bubbles of gas are given off, and, as this gas is considerably heavier than air, it will, after being forced up the tube, displace the air in the glass, and gradually fill it. To test whether the glass is full, hold a match in the top. If the match is extinguished, the glass which is full may be removed. In this way several glasses can be filled, care being taken to cover each with a glass plate or cardboard disc to prevent diffusion.

From this experiment you will have discovered the three main properties of this gas (commonly known as carbon dioxide)--that it is colorless, is considerably heavier than air, and will not support combustion. Its high density affords another interesting experiment, which consists of pouring the gas from one glass to another (Fig. 16).

Take two glasses, one full of air and the other containing the carbonic acid gas, and into each plunge a lighted match. The match of course will burn in the glass containing air, whilst it will be immediately extinguished when it comes in contact with the carbon dioxide. You have thus clearly shown which glass contains air and which contains the gas. Now take the glass containing the gas and pour its contents into the other glass, in exactly the same way as you would pour in water. Again test with a lighted match and you will find that the gas has passed from one glass to another, thus proving that it is much heavier than air.

Next take two glasses, one containing air and the other carbonic acid gas, and, by means of a clay pipe, blow a soap bubble into each, carefully watching the different manners in which they behave. That dropped into the glass containing air will sink to the bottom, where, coming in contact with the glass, it will burst. The other bubble, however, as soon as it reaches the gas in the glass, rebounds owing to the high density of the carbon dioxide, but after a time, when it has settled down, it will float motionless on the surface (Fig. 17).

Before you finish experimenting you should know how to detect the presence of carbon dioxide. Take a little lime water, which may be obtained from any druggist, and pour it into a glass containing carbon dioxide. Shake the glass, and carefully observe the change which takes place. The lime water, which was previously colorless, has assumed a certain milkiness, and if allowed to stand the white powder causing this milkiness will settle at the bottom of the glass. This powder proves to be calcium carbonate, or chalk, which is always formed when lime water comes in contact with carbon dioxide, so that you have here a means of detecting the presence of carbon dioxide. Breathe into a little lime water and you will learn, from the milky appearance it at once assumes, that the air we exhale contains a certain quantity of this interesting gas.