Tina Peters, an analytic chemist, is standing in her white lab coat before a class of eight and nine-year-olds holding up a plastic crate full of ping-pong balls. Only they are not ping-pong balls, she tells them, they are molecules, and when they are tightly packed together like this it means they are a solid.
"Look at the poster." She points at the wall where she has pinned up some simple diagrams of solids, liquids and gases. "If they were a bit looser in the box and able to move about" - she shakes and stirs the box around - "they'd be a liquid. And if they were all spread out and wide apart like this" - and she suddenly throws the balls all over the children crowded at her feet - "they'd be a gas." Squeals of delighted horror. Liam Evans, aged eight, says it is "good fun" to have a scientist in the class because "you do all kinds of things, like make a volcano and see how it works, that you don't normally do".
Sandwich junior school, in Kent, has borrowed Tina Peters for a morning from Pfizer, the drug company whose UK headquarters is just up the road. Pfizer has an active education outreach programme, and part of this is its Link Scientist Scheme, which hooks up practising scientists with local primary schools in a project designed to introduce young children to the delights of science.
Tina Peters saw the scheme advertised in the canteen at work and got involved because: "I love kids. I've got two of my own, aged seven and nine, so I'm used to the age group, and I remember how science was taught to me at school as fun."
Earlier that morning she helped the children make modelling dough volcanoes filled with baking powder, which fizz when vinegar is dropped on them, and talked about acids and alkalines and the carbon dioxide which is released in the bubbles. Later on, after the excitement of the molecule explosion has quietened down, she puts on rubber gloves and sets a small polystyrene container on a table. The silence as she lifts the lid is almost tangible. She takes out a small, milky, smoking stick of something.
This, she tells them, is frozen carbon dioxide and the reason it is smoking is that, as it warms up, it is going straight from being a solid to a gas. She puts some sticks of it in a couple of rubber gloves, which she ties up and leaves on the table, where they slowly blow up until they look like udders. To help explain why this happens, she puts some more sticks in a bowl and as they start to vanish she teases out of the children the word "evaporate" and then encourages them to think about whether carbon dioxide is heavier or lighter than air.
She lights a candle in a bowl and talks about the oxygen it needs to burn, then tips the carbon dioxide from the other bowl into the candle bowl, where the flame immediately goes out. As she talks, she gently introduces the concepts of scientific theories, experimentation and proof. "Shall we do that again? Maybe it only went out because that particular match was a bit silly."
Her class management skills are excellent. "Sometimes it helps to go into mum mode and just say 'sit down, be quiet'," she says. The audience eats out of her hand and some of the children later say they are already thinking abou a future in science.
"I'd like to go round the world and find things and be famous for what I find out," says nine-year-old Amelia Able. "I'd like to find out more about rocks, and things like that."
Class teacher Susan Croney, herself a science graduate and science co-ordinator for the school, says the scheme is wonderful. "I don't have access to a lab, so I couldn't hope to do the things they come and do. Look at how much the children loved seeing that frozen carbon dioxide. This is very much about providing equipment and giving children that proper scientific feel."
Link Scientists are attached to individual schools - all within about 10 miles of Pfizer - and normally go in once or twice a term, after working out with the teacher what activities will fit in with part of the science curriculum the pupils are currently doing. They might be biologists, chemists or environmentalists, but all get some introductory training and can share classroom ideas and experiences through a new website.
The benefit is not all one way. John Adams, academic liaison manager for Pfizer, points out that while most volunteers join the scheme saying they want to give something back, they all tend to learn something, too. "Look at this morning. Tina will have learned more about time management, communication and negotiating skills, and planning and executing a mini-project."
Not everyone is suited to the scheme, but briefing and training sessions tend to weed out those it would not suit. In fact, it has suited some all too well. Two scientists involved in the scheme have left to train as teachers. Maddy Forster, a Bath University student on a six-month placement working with John Adams to administer the scheme, has so enjoyed her time in local classrooms she has also decided to switch tracks and train as a primary teacher.
Pfizer runs education support schemes which amount to about pound;1.5 million a year in time and resources. It supports secondary science teachers, hosts visits to the plant, lends scientific equipment to schools and backs science teaching awards and projects. It also allows employees up to five days a year to undertake voluntary activities provided they are linked in some way with their jobs and inevitably many of these days are spent in education.
"We might not spend as much money as some of the bigger companies in the UK, but in terms of getting real, live scientists out and about and involved in the local community I would think we lead the field," says John Adams.
For Tina Peters, packing up at the end of her morning in school, the goal is more modest. "If I can pass on that 'wow factor' to just one child I'll feel I've done something worthwhile."
It is obvious she has succeeded. "I loved everything. Especially blowing up the gloves with carbon dioxide," says Nathan Shaw.
"And when she threw the ping-pong balls to show solids going to gas!" adds Ashley Groombridge. "All those mol- mol- molten things."
Teachers can e-mail John Adams, academic liaison manager, about Pfizer's Link Scientist scheme: John_C_Adams@sandwich.pfizer.com Teachers can also contact their local Education Business Partnerships (or call EBP's national line: 01753 502370) to find out about similar schemes. Useful website: Medical Research Council: www.mrc.ac.ukschools