10. Ghostly noise

Fill a wineglass to overflowing with dried peas, pour in water up to the brim, and place the glass on a metal lid. The pea heap becomes slowly higher and then a clatter of falling peas begins, which goes on for hours.

This is again an osmotic process. Water penetrates into the pea cells through the skin and dissolves the nutrients in them. The pressure thus formed makes the peas swell. In the same way the water necessary for life penetrates the walls of all plant cells, stretching them. If the plant obtains no more water, its cells become flabby and it wilts.



11. Rain in a jar

Place a green twig in a glass of water in sunlight. Pour a layer of oil on to the surface of the water and invert a large jar over the lot. After a short time, drops of water collect on the walls of the jar. Since the oil is impermeable, the water must come from the leaves. In fact the water which the plant absorbs is given off into the air through tiny pores in the epidermis of the leaf. Air saturated with moisture and warmed by the sun
deposits drops like fine rain on the cool glass.



12. Zig-zag growth

Lay pre-germinated seeds on a sheet of blotting paper between two panes of glass, pull rubber bands around the panes and place in a water container in a window. Turn the glass panes with the shoots onto a different edge every two days. The roots always grow downwards and the stem grows upwards.

Plants have characteristic tendencies. Their roots strive towards the middle of the earth and the shoots go in the opposite direction. On slopes the roots of trees do not grow at right angles to the surface into the ground, but in the direction of the middle of the earth.



13.Leaf skeleton

Place a leaf on blotting paper and tap it carefully with a clothes brush, without pressing too hard or moving sideways. The leaf is perforated until only the skeleton remains, and you can see the fine network of ribs and
veins.

The juicy cell tissue is driven out by the bristles and sucked up by the blotting paper. The ribs and veins consist of the firmer and slightly lignified ( Cell walls strengthened and thickened ) framework and resist the brush.



14. Two Coloured Flower

Dilute red and green fountain pen inks with water and fill two glass tubes each with one colour. Split the stem of a flower with white petals, e.g. a dahlia, rose or carnation, and place one end in each tube. The fine veins of the plant soon become coloured, and after several hours the flower is half-red and half blue.

The coloured liquid rises through the hair-fine channels by which, the water and food are transported. The dye is stored in the petals while most of the water is again given off.



Chemistry

15. Colour magic

Cut a red cabbage leaf into small pieces and soak in a cup of boiling water. After half an hour pour the violet-coloured cabbage water into a glass. You can now use it for crazy colour magic. Place three glasses on the table, all apparently containing pure water. In fact only the first glass contains water, in the second is white vinegar and in the third water mixed with bicarbonate of soda. When you pour a little cabbage water into each glass, the first liquid remains violet, the second turns red
and the third green. The violet cabbage dye has the property of turning red in acid liquids and green in alkaline. In neutral water it does not change colour. In chemistry one can find out whether a liquid is acid or alkaline by using similar detecting liquids (indicators).



16. Violet becomes red

If you ever come across an anthill in the woods, you can there and then do a small chemical experiment. Hold a violet flower, e.g. a bluebell, firmly over the ants. The insects feel threatened and spray a sharp smelling liquid over the flower.

The places hit turn red. The ants make a corrosive protective liquid in their hindquarters. You notice it if an ant nips you, though it is generally quite harmless. Since the flower turns red where the drops fall, you know
that they are acid. The acid is called formic acid.



17. Invisible ink

If you ever want to write a secret message on paper, simply use vinegar, lemon, or onion juice, as the invisible ink. Write with it as usual on white writing paper. After it dries the writing is invisible. The person who receives the letter must know that the paper has to be held over a candle flame: the writing turns brown and is clearly visible.

Vinegar, and lemon or onion juice, cause a chemical change in the paper to a sub- stance’ similar to cellophane. Because its ignition temperature is lower than that of the paper, the parts written on singe.



18. Bleached rose

A piece of sulfur is ignited in a jam jar. Since a pungent vapor is produced, you should do the experiment out-of-doors. Hold a red rose in the jar. The color of the flower becomes visibly paler until it is white.

When sulfur is burned, sulfur dioxide is formed. As well as its germicidal action in sterilization, the gas has a bleaching effect, and the dye of the flower is destroyed by it. Sulfur dioxide also destroys the chlorophyll of plants, which explains their poor growth in industrial areas, where the gas
pollutes the air.



19. Transfer pictures

Photos and drawings from newspapers can be copied easily. Mix two spoonfuls of water one spoonful of turpentine and one spoonful of liquid detergent and dab this liquid with a sponge on the newspaper page.

Lay a piece of writing paper on top, and after vigorous rubbing with a spoon the picture is clearly transferred to the paper.

Turpentine and liquid detergent when mixed form an emulsion, which penetrates between the dye and oil particles of the dry printing ink and make it liquid again. Only newspaper printing ink can be dissolved, though.



20. Sugar fire



Place a piece of cube sugar on a tin lid and try to set it alight.

You will not succeed. However, if you dab a corner of the cube with a trace of cigarette ash and hold a burning match there, the sugar begins to burn with a blue flame until it is completely gone.

Cigarette ash and sugar cannot be separately ignited, but the ash initiates the combustion of the sugar. We call a substance, which brings about a chemical reaction, without itself being changed a catalyst.



21. Jet of flame

Light a candle, let it burn for a while, and blow it out again. White smoke rises from the wick. If you hold a burning match in the smoke, a jet of flame shoots down to the wick, and it re-lights.

After the flame is blown out the steam is still so hot that it continues to evaporate and produce a vapor. But as this is combustible, it can be re-lighted at once by a naked flame. The experiment shows that solid substances first become gaseous at the surface before they will burn in a supply of oxygen.



22. Gas pipe

Roll a thin piece of tin foil round a pencil to make a tube about four inches long, and hold it with one end in the middle of a candle flame. If you hold a burning match at the other end of the tube, a second flame will be lit there.

Like all solid and liquid fuels, searing produces combustible gases when heated, and these accumulate inside a flame. They burn, with the oxygen of the air, in the outer layer and tip of the flame. The unburnt searing vapor in the middle can be drawn off, like town gas from the gas works.



23. Gas balance

Fix two plastic bags to the ends of a piece of wooden beading about 18 inches long and let it swing like a balance on a drawing pin. Pour some bicarbonate of soda and some vinegar into a glass. It begins to froth, because a gas is escaping. If you tilt the glass over one of the bags, the
balance falls.

The gas, which is given off during the chemical reaction, is carbon dioxide. It is heavier than air, so it can be poured into the bag and weighed. If you were to fill a balloon with the gas it would never rise, and for this purpose other gases are used, which are lighter than air.



24. Fire extinguisher

Light a candle stump in an empty glass, and mix in another glass - as in the previous experiment - a teaspoonful of bicarbonate of soda with some vinegar and let it froth. If you tilt the glass over the candle, the flame goes out.

The carbon dioxide formed in the chemical reaction in the top glass displaces the air needed for the flame, because it is heavier, and because it is non-combustible the flame is smothered. Many fire extinguishers work in the same way: the sprayed foam consists of bubbles filled with carbon dioxide. It surrounds the flame and blocks the supply of oxygen.