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Dinner-table science A 1997 Christmas present to web site visitors Drinks Atmospheric pressure Young people have livelier minds than adults and can be relied upon to get quickly into the spirit of scientific investigation. Therefore locate a young person drinking a fizzy drink from a bottle with a straw. Suggest that they put their lips round the top of the bottle with the bent upper end of the straw sticking out of the corner of their mouth. Now ask them to suck. Swallowing streams of foam in this way, they will joyfully show off to their friends. You will observe this discovery communicating itself across the room purely through a process of imitation. The singing glass Take a wine glass with just a teaspoonful of wine at the bottom. Dip your fingertip in the wine and let it soak into the skin for one minute. Hold the glass firmly by its base, leaving the bowl of the glass free to vibrate. Slide your wet finger around the edge of the glass, maintaining a perfectly constant speed. Explain to your young disciples that it is almost impossible for human ears to determine the direction this awesomely loud ringing sound comes from, on account of its pure wave-form. Suggest quietly that they might therefore like to repeat this during the meal, under the table cloth. Drinking straw mayhem
Produce a small pair of scissors from your pocket, flatten the end of a drinking straw then cut it as shown. When other children hear the raucous and irreverent sound this makes when blown through hard, you will be surrounded by a clamouring crowd within seconds, all asking for one. As you obligingly whittle away, the rising crescendo of sound dictates that this experiment should be the last before the meal. Starters Eat a burning candle As people take their seats for dinner, you put an extra candle holder on the table, with a short stub of white candle in it. You light it. People are staring at you. Much is expected now, and you must oblige. You blow out the candle and eat it, having paused just a few seconds until the smoking wick stopped glowing. What people don't know and seldom notice is that the 'candle' was really a piece of banana. You carved a 'wick' from the oil-rich, combustible heart of an almond and charred it black with a match. Don't tell them this until after coffee. Chatter about the fat-loving eskimos who are said to have eaten candles presented to them by early explorers. Flashback 
You have people's undivided attention. You have proved that knowledge is power. Conversation stops entirely now, as you reach for one of the real, burning candles. With it you light a matchstick or a cocktail stick, then blow out the candle. You hold the burning cocktail stick in the creamy-white plume of thick smoke from the wick and move it closer until the last inch or two of smoke (and vaporised wax) suddenly flashes and the wick re-lights itself. Michael Faraday included this demo in his popular book, The Chemical History of a Candle. Blowing round corners Place a wine bottle in front of a burning candle. Blow hard against the side of the bottle. The air-flow follows the shape of the bottle and puts out the candle flame on the opposite side. Main course The amazing human magnet 
Take your dessert spoon and thoughtfully lick its convex under-surface. Bring it slowly towards your face while assuming an expression of intense concentration. When it is very close, snap it against your forehead as if it is being attracted by a magnet. Press it hard for a moment and let go. Raise your hands in the air dramatically. If you have practised this well enough, the way the handle rests against your nose provides just enough extra friction to stop the spoon from sliding off. It looks very impressive. Don't allow people to go home thinking you really have a magnetic head! Ordeal by fire Hold your hand out flat, palm down and with fingers spread apart. Float your hand slowly, steadily, horizontally through the centre of a candle flame, so that the middle joint of each finger in turn passes through the heat. Having practised beforehand, you will appear to do this remarkably slowly, even though each finger is only in the flame for a short time. When done well, there is a noticeable burst of sooty smoke after each (cool) finger crosses the flame and an impressive band of dark soot across all of them afterwards. You should perhaps think carefully about demonstrating this to children, but any show-off, macho adults who burn their hands will probably benefit from the lesson. Walking coin 
Near the edge of the table cloth, support any glass upside down on top of two, diametrically opposite, pound coins, with a penny or five pence coin in the middle. Explain that you will use the principle of inertia to make the smaller coin 'walk' out. Scratch the table cloth repeatedly with your fingernail and the coin will glide towards you, emerging from under the glass. As your fingernail moves across the tiny corrugations of the woven cloth, each 'bump' in it springs backwards faster than your finger dragged it forwards. While on the subject of inertia, you should suggest brightly that perhaps some volunteer might like to attempt the full-scale version of the jerked-tablecloth demonstration, later, when it is time to clear the table. Dessert and coffee Galaxy formation Here, astrophysics makes a rare dinner table appearance. Ask people to pour their milk into the centre of their stirred coffee, and to observe that the rotating coffee actually speeds up when the milk enters. As surface liquid is drawn horizontally towards the middle because of downward flow through the axis of rotation, its angular momentum is conserved and it speeds up just like a spinning ice skater who suddenly pulls in her extended arms. Any floating foam on the surface shows the shape of a spiral galaxy. Napkin chromatography Tearing your paper napkin into narrow strips, you can point out that this is only possible in one direction because the paper has a 'grain'. The fibres become aligned as wood pulp flows onto a faster-moving conveyor belt during paper manufacture. Dangling one end of a strip in your coffee, you show the rapid separation of dark coloration as the increasingly clear liquid climbs higher up the paper. Hopefully, this will prompt a general examination of tablecloth stains and further stimulating discussion. After-Eight aroma Ask each guest to hold their first small piece of minty chocolate in one hand and pinch their nostrils with the other. On the count of three, people start to suck their chocolate and notice that they cannot taste the mint particularly strongly. Then they let go of their noses and experience a sudden rush of flavour. Much of what we assume to be 'taste' actually involves our closely related sense of smell. The final salvo 
You really need to end with something extravagant and crazy. There is a special way of throwing wooden matches so they go screaming over people's heads, sounding exactly like the ricocheting bullets in all good cowboy films. You just spin the match very powerfully as you throw it, with an action somewhere between spinning a top and snapping your fingers. You'll either find this dead easy or never, ever, get the hang of it. Use safety matches and send them out, rapid-fire, in all directions. This has to be your last demo, simply because other people will want to try it themselves. If they don't, but merely stare at you silently, then you have seriously misjudged your audience. It's time to leave the table, anyway.
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