Blown away by science of bubbles and bugs

THERE'S a bit of the showman about Carl Palmer. "What we're going to do," he says, brandishing an empty and inoffensive-looking Fanta can in one fist, "is try to crush this can using just the difference in volume between gas and liquid!"

You can almost hear the drum roll. For a moment I'm tempted to tell him it would be easier just to squeeze the can, or else tread it underfoot. But his enthusiasm is so infectious it's hard not to get drawn along.

Still, the drum roll turns out to be rather a long one. The art of cooking is all in the preparation, they say. And so, it seems, is the art of doing a chemistry demonstration.

First, Carl has to pour a little boiling water into his can. Then he stands it on a hot plate, to heat the water even more and fill the can with steam. "If you then seal it and put it in cold water," he explains excitedly, "the steam shrinks in volume and it should crush the can." We look at him sceptically. "We've had several rounds of applause already," he assures us nervously.

His can, unfortunately, takes several minutes to 'cook' and build up a head of steam. However, Carl, a PhD student in the chemistry department at York University, reveals considerable showbiz flair and turns to another experiment he has prepared earlier: nails in a jar. There's one jam jar filled with cold water, and in it floats a sealed tube with a few nails in. The weight of the nails just balances the buoyancy given by the trapped air, so the nails in their tube float.

"Put that in hot water," Carl says, "and it sinks!" He demonstrates, transferring the nails with a triumphant flourish to a jar of heated water - and sure enough they do sink. Why? Cold water is denser than hot water, he explains, so it provides more buoyancy.

He steals a quick glance at the Fanta can, but it is still not quite ready so he seizes on several pieces of 'dry ice' (carbon monoxide) he just happens to have with him. They roll out on to a work-top, frizzing into gas as they warm up.

The thing about dry ice, he says, is that at room temperature it doesn't have a liquid form, and so goes straight from solid to gas - hence those amazing special effects you can get. If you artificially raise the pressure, however, to about five times that of normal, you do get a liquid form. "I've done it!" he says triumphantly. And what does it look like? His face falls. He has never actually seen any, he admits, because you need such a high pressure to get the liquid form, it can only be made in a sealed container.

Time for a quick exit - and luckily the Fanta can comes to his rescue. It's ready, steam curling lazily out of the top. He slaps some sticky tape over the opening to seal it, takes a deep breath, then plunges it into a bowl of cold water.

"Whup!" goes the can, instantly collapsing in on itself as the heated steam inside condenses back into water (which takes up less space than steam) and sucks the metal walls in on themselves. It's a dramatic moment - and just as he had predicted, Carl gets a round of applause.

It may all have an air of the Great Egg Race or Blue Peter about it - but there's no denying the sheer sense of fun Carl manages to generate about processes we'd normally take for granted.

His stand is just one of many in the Discovery Days exhibition at the Guildhall. The exhibition is the opening event of this year's York Festival of Discovery which coincides with National Science Week - and it aims to bring the fun of science to life for kids and their parents. One thing's for sure: if your kids have ever dismissed science as boring, a visit here will put them right.

One of Carl's colleagues is enthusiastically blowing bubbles - then showing how, if you're really careful, you can blow a bubble inside a bubble on a wet tabletop to create an iridescent, many-layered dome. The kids love it. Nearby, chemistry lecturer Dr Anne Hodgson is standing inside a cut-out tyre filled with soap solution. Colleagues gently lift a giant ring from the soap and draw it up the outside of her body until she's virtually encased in a giant bubble.

It's a property of the molecules which make up detergents that allows you to make soap bubbles, she explains. Each molecule is a bit like a tadpole: a large head, with a long, wriggly tail. The head of the molecule is attracted to water: the tail hates it. The 'skin' of a soap bubble is actually made of a thin layer of water sandwiched between two layers of soap bubbles, each with their heads in towards the water and their tails sticking out. The bubble can go on expanding until it stretches so far that the water drains away out of its sandwich - when the bubble bursts.

It's not just the wonders of chemistry that are on show in the Guildhall, either.

On the other side of the great hall, a team from the Centre for Novel Agricultural Products are showing children the wonders of the very small. There's a spider's leg seen through the lens of a microscope, magnified to huge, hairy bulk, and tipped with a vicious-looking claw.

Then there is a section of snail's tongue, looking under the microscope like nothing more than a giant honeycomb. It's made of chitin, the hard, organic material insects' bodies are made of, explains Dr Alex Brabbs, and each little piece is a file the snail uses to rasp away at plants when feeding.

Most popular of all with the kids, however, is the bed bug - magnified 60 times through the microscope's lens into a bulky, hairy, looming monster with barrel shoulders and fearsome jaws. It invariably has the kids screaming 'that lives in my bed!', Dr Brabbs grins - but they love it.

"It's the wow! factor," she says. "It opens up a new world that they haven't seen before."

Visit the Guildhall over the next couple of days, and you'll experience plenty more of the wow factor - finding out how designer suits could be made from crops, discovering the science behind chocolate and learning why sticky things are sticky.

If you're anything like me it won't be just your kids who leave feeling a new world has opened up to them.

Discovery Days is open to the public from 4-5.30pm tonight and from 10am to 4pm tomorrow.

Other events in this year's Festival of Discovery include a hands-on workshop exploring the mysteries of DNA at the National Centre for Early Music on Monday to Wednesday next week, and a series of public lectures on everything from how York Minster was built to the technology that underlies the great bridges of York.

To find out more, call Science City York on 01904 554428 or visit www.sciencecityyork.org.uk/discovery

Updated: 10:16 Friday, March 07, 2003