And for my next trick...

5th September 2003 at 01:00
Anyone seen liquid air? Invite a professor into your class and sit back for a rattling good demonstration. Chris Fautley reports from an Eastbourne primary

Why would a professor walk into school with a bunch of carnations, a frying pan and a packet of balloons? Answer: to add a sparkling new dimension to primary school science - as 120 children from Langney Primary Years 5 and 6 in Eastbourne will concur.

The professor is Andrew Lloyd from the School of Pharmacy and Biomolecular Sciences at the University of Brighton. He is at Langney to reinforce what the children have already learned about solids, liquids and gases - using plenty of visual impact. The idea, says Andrew, is to demonstrate the magic of science and how it contributes to the world around us.

After briefly recapping on molecular structure with the help of Year 5 "atoms", Andrew picks up a flask of liquid nitrogen from the table before him. "How many of you have seen liquid air?" With a liquefaction point of around - 173 LESS THAN C none of us can say we have - until Andrew dons a pair of elbow-length gloves and removes the flask lid. A collar of vapour hovers around its rim as he tips out a small quantity. The sound resembles myriad tiny ball bearings rattling as they hit the floor. One hundred and twenty pairs of eyes pop from their heads as it disperses in a cloud of vapour.

"How many of you have tried putting flowers in the freezer?" Andrew enquires, dipping a carnation into the nitrogen.

"Why is it bubbling?" he asks. Because the nitrogen is warming up, we deduce. He extracts the flower and strikes it on the table. It shatters into dozens of pieces, as if made of fine bone china. He dips a few more and passes them round the audience.

Even though the nitrogen "rattles" when spilled, it really is liquid, Andrew assures us. Thus it should occupy more space when it turns to gas.

He demonstrates by pouring a little into a test tube, over which he stretches a balloon. Magically, it inflates.

Andrew also reveals how materials change when cooled. He takes a length of rubber seal and demonstrates its elasticity before dipping it in the nitrogen. You can hear a pin drop as we watch, goggle-eyed. He removes the seal and snaps it in half.

Next, he pours a soup of nitrogen into a frying pan, cracks an egg, and "cooks" it. Although it is frozen, it looks for all the world like a fried egg.

"How do you follow that?" I wonder. With carbon dioxide, it transpires.

Andrew has brought a small supply which, this being science with a difference, is frozen. He pours some into two cylinders containing red and purple pH (acidity indicator) solutions. The purple solution turns clear, then effervesces; to a hall-full of collective gasps, the red solution turns clear, then yellow, and bubbles violently. The solutions, he explains, are slightly alkaline, but when the carbon dioxide is added, they turn more acidic - hence the spectacular effects.

Meanwhile, Andrew tips a few globules of carbon dioxide into some balloons.

He hands them to teachers who shake them to help the carbon dioxide melt: as it does, it gasifies and expands. The balloons self-inflate. Knotting them, he holds them up and drops them. They plummet to earth - proof that carbon dioxide is heavier than air.

"I always like to finish off with this. It makes a nice mess," Andrew enthuses as 45 minutes of spell-binding experiments draw to a conclusion.

And so he adds carbon dioxide to a beaker of dilute washing-up liquid, producing a crescendo of carbon dioxide bubbles - or a fire extinguisher.

To prove it, he dips a lighted taper into them; it is instantly extinguished.

Nina Sparrowhawk, Langney's science co-ordinator, found the presentation particularly relevant to liquids, solids and gases, and materials and their properties. Follow-up work would include Year 6 students creating posters, leaflets and guides as an introduction to the topic to help next year's Year 5 students; this would clarify their understanding by recording it in a way that works for other children. Yet the sad fact is that it is becoming increasingly difficult to bring science like this into the classroom. The result, Andrew explains, is that fewer pupils see its magic and excitement.

He says it is important for children to relate the experiments to the world around them - hence references to fire extinguishers and liquid air. "To be quite honest, teaching solids, liquids and gases is quite a bland subject to teach when you're limited to looking at water, effectively. This adds an extra dimension to it and allows the children to have a better appreciation.

"Hopefully, one or two of these children will develop their curiosity for science and have an enthusiasm for it when they go to secondary school," he continues. "That may be carried through and one day, because of this, they will become scientists or engineers."


Andrew Lloyd believes universities have a role to play in working with schools to help stimulate children to want to become scientists and engineers. But it is a two-way process. "We rely on science co-ordinators coming to us and saying, 'We want you to help us deliver this,'" he says.

He recommends contacting SETPOINT co-ordinators who should have links with universities. Tel: 020 7636 7705 or free call 0800 14 64 15 Alternatively, try the education department at The Royal Society of Chemistry, Burlington House, Piccadilly, London W1J 0BA. Tel: 020 7437 8656.

Add fizz to your science lessons with two experiments:

DIY pH indicator

Boil a handful of red cabbage.

Allow to cool.

Discard the cabbage; save the lavender-coloured water.

Add vinegar: the water turns red.

Alternatively, add baking powder and it turns blueturquoise.

Fire extinguisher: junior version

Take a small quantity of vinegar and add baking powder.

The resultant foam contains carbon dioxide.

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