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.