Ship!!!

Place a half-dollar or 10 new pence on the table and on one side of the coin a small cork disk. How can you move the cork to the exact centre of the coin without touching it!

Pour water on to the coin - drop wise, so that it does not spill over - to form a water mountain over the surface. At first the force of gravity holds the cork on the edge of the slightly curved water surface. If you now pour on more water, the pressure of the water on the edge increases, while it remains constant on the top. So the cork moves up the hill to the middle, which is the region of lowest pressure.

Mountain Of Water

Fill a dry glass just full with tap water, without any overflowing. Slide coins carefully into the glass, one after the other, and notice how the water curves above the glass.

It is surprising how many coins you can put in without the water spilling over. The water mountain is supported by surface tension, as though it is covered by a fine skin. Finally, you can even shake the contents of a salt cellar slowly into the glass. The salt dissolves without the water pouring out.

Water knots

An empty two-lb. can is pierced five times just above the lower edge with a thin nail. The first hole should be just over an inch from the fifth. Place the tin under a running tap, and a jet will flow from each hole. If you move your finger over the holes, the jets will join together. The water particles are attracted to one another and produce a force acting into the interior of the liquid, the surface tension. It is also this force which holds a water droplet together. In our experiment the force is particularly clear, and it diverts the jets into a sideways are and knots them.

String of pearls

Let a fine jet of water pour on a finger held about two inches under the tap. If you look carefully, you will see a strange wave-like pattern in the water. If you bring your finger closer to the tap, the waves become continuously more ball-shaped, until the water jet resembles a string of pearls. It is so strongly obstructed by the finger that because of its surface tension - the force that holds the water particles together - it separates into round droplets. If you take your finger further away from the tap, the falling speed of the water becomes greater, and the drop formation is less clear.

Ice hook

Who can hook an ice cube from a bowl of water with a match? A trick makes it quite easy: place the match on the ice cube and scatter some salt over it. In no time the match is frozen solid, and you can lift it together with the ice cube from the dish.

Salt water does not freeze as easily as ordinary water, and scattering salt on ice makes it melt. The salt grains on the ice cube also do this. However, when a substance melts, heat is consumed at the same time. This heat is taken from the moisture under the match, where no salt fell, in this case - and it freezes.

Cutting Through Ice

Place an ice cube on the cork of a bottle. Fix two objects of equal weight on a piece of wire, hang the wire over the ice and place the whole lot out of doors in frosty weather. After a certain time the wire will have cut through the ice without dividing it.

This trick of nature is explained by the fact that ice melts when it is subjected to pressure. Water is formed where the wire is resting, while it immediately freezes again above it. Skating is only made possible by slight melting of the ice under the moving surface, which reduces the friction.

Iceberg

Place a cube of ice in a tumbler and fill it to the brim with water. The ice cube floats and partly projects from the surface. Will the water overflow when the ice cube melts!

The water increases its volume by one-eleventh when it freezes. The ice is therefore lighter than water, floats on the water surface and projects above it. It loses its increased volume when it melts and exactly fills the space, which the ice cube took up in the water. Icebergs, which are a danger to navigation, are therefore especially harmful because one only sees their tips above the water.

Column of ice

Place an ink bottle filled to the brim with water in the freezing compartment of a refrigerator. Soon a column of ice will stick up out of the bottle.

Water behaves oddly: when warm water-cools it contracts, but if the temperature falls below 40C, it suddenly begins to expand again. At 0 C it begins to freeze, and in doing so increases its volume by one-eleventh. This is the reason why the ice sticks out of the bottle. If you had closed it, it would have cracked. Think about burst water pipes in winter and frost cracks on roads, in which water collected under the asphalt freezes.

Producing cold

With a rubber band fix a wad of cotton wool over the mercury bulb of a room thermometer. Note the temperature, damp the cotton wool with eau-de-cologne, and whirl the thermometer round on a string for a time. The temperature drops considerably. The alcohol in the eau-de-cologne evaporates quickly and so uses up heat. The draught caused by whirling the thermometer round accelerates the process and the heat consumption rises. In a refrigerator a chemical liquid evaporates in a container. The large amount of heat needed for this is taken from the food compartment.

Where Is The Wind Coming From?

Moisten your finger and hold it straight up in the air. You will notice at once that one side of the finger is cold. This is the direction from which the wind is coming. Heat is used up when a liquid vaporizes or evaporates. The wind accelerates the evaporation of the moisture on the finger and you will notice even with a weak air current the greater heat loss on the side facing the wind. Anybody who keeps on a wet bathing costume after a swim will shiver even in the heat. The water takes heat from the body as it evaporates.

Steam boat

Break off the head of a match and drop some glue on to the end. If you place the match in a dish of water it moves jerkily forward.

The glue contains a solvent, which evaporates to give a vapour. It puffs out from the drop in invisible little clouds, giving the match a small push each time.

Eventually so much of the solvent has escaped that the glue becomes solid. In a dried drop of glue you can still see the residual solvent vapour as small bubbles.

Bath game with a coin

Stretch a strip of cellophane (not plastic foil), 1 inch wide, tightly over a soup plate and fasten the ends with adhesive tape. Lay on the middle of the strip an average-sized coin and pour water into the dish up to about 3-inch under the coin.

The coin sinks slowly and reaches the water after several minutes.

The water vaporises, the cellophane absorbs the water particles from the air and expands until it reaches the water. But strangely enough it soon begins to tighten again, and the coin rises again slowly to its original position.

Water from the Desert

We still read in the newspapers of people dying of thirst in the desert, but many of them could help themselves in this emergency. An experiment on a small scale in a sandbox will show you how to do it. Dig a fairly deep hole and place a beaker in the middle. Spread a suitably sized piece of transparent plastic foil over the edge of the hole and lay a small stone in its centre so that it dips down to the beaker in the shape of a funnel. The edges are fixed firmly into the sand. Soon, especially in sunshine, small drops of water form on the underside of the foil. They become larger and larger and finally flow into the beaker. The effect of the sun is to heat the ground strongly under the foil. The moisture held in the sand evaporates until the enclosed air is so saturated that small drops of water are deposited on the cooler foil. Even desert sand contains some moisture. If you also place cut up cactus plants into the hole, you will obtain enough water to survive.

Hygrometer

Coat a strip of writing paper two inches long with glue and roll it onto a sewing needle. Stick a strip of shiny photographic paper about 3 inch wide and one foot long onto its end so that its shiny surface faces the glue-covered side of the writing paper. The filmstrip is rolled round the needle like a clock spring. Punch a small hole through the middle of the bottom and lid of a furniture polish tin, and also air holes in the bottom. File off the metal projections formed. Push the needle through the central holes and stick the end of the filmstrip firmly to the side of the tin.

Fix a paper pointer in front of the needle with a cork disk, and a bead behind it. The gelatin layer of the photographic film expands - in contrast to the paper layer - with increased air humidity, causing it to wind up sharply, and move the pointer to the right. When the humidity of the air falls, the pointer returns to the left.

Weather station

Fix a dry pinecone on to a small piece of wood with sealing wax or glue. Stick a pin into one of the central scales and place a straw over it. Put the cone out-of- doors, protected from the rain. The straw moves according to the state of the weather. Fix up a scale.

This simple hygrometer was built by nature. The pinecone closes when it is going to rain, to protect the seeds from damp. The outside of the scales absorbs the moisture in the air, swells up and bends - a process which you can also observe with a piece of paper which is wet on one side.

Rain In The Room

Rain after sultry days makes the inside of the windowpane suddenly sweat. You can distinguish the tiny water droplets through a magnifying glass. Where do they come from?

After it has been raining the air outside cools sharply because the water evaporates and thus uses heat. The warm air in the room, which is saturated with water vapor, especially from cooking, cools down only slowly on the windowpane. But cold air cannot hold so much moisture as warm air, and therefore loses some of it on to the pane. It forms water droplets - exactly as when it is raining out-of- doors and moist, warm air meets cold air.

Hovercraft

Place a tin lid on a hot plate and heat it well (take care!). If you then let a few drops of water fall on the lid, you will observe a small natural phenomenon. The drops are suspended in the air like hovercraft and whiz hissing to-and-fro for a while.

On contact with the heated metal the water drops begin to evaporate at once on the underside. Since the steam escapes with great pressure, it lifts the drops into the air. So much heat is removed from the drops by the formation of steam that they do not even boil.

Jet boat

Bore a hole from the inside through the screw top of an aluminium pill tube about four inches long, and pour some water into the tube. Fix the tube in an empty sardine can into which you have fixed three candle stumps and place the can in water. If you light the candles the water soon boils, and the jet of steam escaping from the back drives the boat.

Steam is formed in the boat’s boiler when the water boils. Because it expands sharply, it escapes at high pressure through the nozzle and causes a recoil. Do the experiment in calm weather!

Paper saucepan

Do you believe that you can boil water in a paper cup over a naked flame or in the embers of a fire!

Push a knitting needle through the rim of a paper cup containing some water, hang it between two upright bottles and light a candle under the cup.

After a little while the water boils - but the cup is not even scorched.

The water removes the heat transferred to the paper and begins to boil at a temperature of 212F or 100C.

The water does not get any hotter, so the paper does not reach the temperature, which is necessary for it to burn.

Fire Under Water

Warm the base of a candle stump and stick it in a bowl. Fill the bowl with cold water up to the rim of the candle. If you light the wick it burns until it is under the surface of the water. Then the candle flame hollows out a deep funnel. An extremely thin wail of wax remains standing round the flame and stops the water from extinguishing it. The water takes so much heat from the candle that its outer layer does not reach its melting point, and the wax there cannot evaporate and burn.