Simply scientific

Press, 8 January 1980, Page 10

Simply scientific

’ Here are some simple science experiments to try out during the holidays. You will find most of the materials you need around the house. For instance, among your souvenirs from the Christmas celebrations you may have a balloon and a piece of candle. Nearly everything is wrapped in plastic these days, even garments returned from the dry cleaners, and one of those bags would be fine for the “desert” experiment. Air Expands When Heated. You will need a balloon, a glass bottle and a fairly shallow pan of water to try this experiment. What to do — Stretch the mouthpiece of the balloon over the mouth of the empty bottle and stand it in the pan of cold water. Place the pan on the stove over moderate heat.

What should happen — the balloon should begin to inflate as it does when blown up by mouth. Because — the air par-

tides'in the bottle begin to move further apart with ’ the effect of the heat, and the air expands causing greater pressure which escapes into the balloon. Remove the bottle from the heat and the balloon will" be seen to shrink to its former shape. Metal conducts heat You will need — a metal kitchen sieve and a candle. What to do — Hold the metal sieve in the candle flame. ‘ What should happen — the flame does not pass through the wire mesh, although the sieve will be seen to turn red if you hold it over the flame for any length of time. Because — the metal in the sieve conducts so much heat away that the candle wax vapour cannot burn above the mesh. This is- why fireguards are made from a similar metal material. How to get Water in the Desert You will need — A quantity of sand, a large sheet of plastic, a beakertype container, a moder-

ately heavy stone, ice plant or other type of moisture-conserving plant that grows plentifully. This is not essential but it is a plant of the desert environment, and will add reality to the experiment.

What to do — Make a fairly deep V-shaped hole in the sand. Cut up the cactus plant and put the pieces in the sides. Place the beaker at the bottom. Spread the plastic over the hole. Press it into the shape of the hole, very close to the sides, but not quite touching. Weight the plastic at the bottom with the stone placed over the mouth of the beaker. Secure the plastic firmly on each side o f the hole at the surface.

What should happen — small drops of . moisture will form on the underside - of the plastic. As they become larger they will flow down into the beaker. Because — The sun will heat the sand covered by - the plastic. The moisture' • in the sand will evaporate until the enclosed air is saturated and small drops of moisture will be deposited on the cooler plastic. ;