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Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format. New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address. THE LAST WORD Hard tea fallin’ I live in an area with hard water and have noticed that drinking tea without milk stains my cups. Why is that? And why, if I add lemon, does it solve the problem? n Tea contains catechins: mildly acidic, tannic substances with insoluble calcium salts. In hard water, which often contains calcium ions, these form a scum in black tea. You can prevent scum forming by adding citric acid such as that found in lemons. This removes calcium ions by forming covalent, soluble calcium citrate. Interestingly, donated blood is also prevented from clotting by adding sodium citrate as the resulting reaction removes free calcium ions to form calcium citrate. Removing these ions prevents the activation of thrombin – an enzyme that catalyses the formation of fibrin, allowing blood to clot. Catechins also combine with proteins in milk; this removes them from solution and so prevents scum. This reaction of tannin and protein is the basis for tanning leather. Luce Gilmore Cambridge, UK The term catechins is commonly used to refer to the related family of flavonoids – Ed n Tea contains considerable quantities of polyphenolic flavonoids, the substances we refer to as tannins. These make a major contribution to tea’s flavour, particularly its astringency, as well as its colour. The structures of many of these flavonoids, particularly one called epigallocatechin gallate, include an aromatic ring with three hydroxyl groups attached to neighbouring carbon atoms in what is called a gallate group. At the fairly neutral pH of brewed tea, many gallate hydroxyl groups ionise and in turn react readily with proteins in the mouth lining (hence the astringency) and with silicates in the glaze lining a cup (hence the brown stain). Drinkers add lemon or milk to reduce astringency. The lemon juice also lowers the pH, returning the gallate hydroxyl groups to the un-ionised state that no longer attaches to mouth proteins, or glaze. Milk proteins mop up the reactive hydroxyl groups with the same end results. Tom Coultate Leighton Buzzard, Bedfordshire, UK The writer is the author of Food: The Chemistry of its Components (the fifth edition was published by RSC Paperbacks in 2010) – Ed Die another day James Bond must have had thousands of bullets aimed at him over the course of his career. He must be the most shot-at fictional film hero of all time. Can anybody calculate the odds of him not having taken a fatal hit over the past five decades? Surely they are astronomical. (Continued) n An earlier correspondent noted that James Bond had survived at least 4662 gunshots. This figure may not be too far-fetched. A study of soldiers’ small arms peacetime hit rates found them to be about 60 per cent. This figure would lead one to expect that the 6462 rounds fired by British marines at the start of the Falklands war 30 years ago would have produced more Argentinian casualties than the two confirmed deaths and two confirmed wounded. This apparently low figure can be explained by the fact that many shots are fired to keep the enemy’s head down and to stop the enemy from firing back. James Bond, continue the good work. Your chances of surviving to an old age are as good as ever! Ted Lovesey Stoke Gabriel, Devon, UK This week’s questions CONCERTINA CARS I was driving down the motorway the other day when the traffic suddenly came to a standstill. After 10 slow minutes of being mostly stationary, the traffic started moving again and was back up to full speed almost immediately. There was no visible reason for the standstill, no accident or junction in sight, and it was slightly later than morning rush hour. Can anyone tell me why traffic bunches up like this for no apparent reason? Edith Harris London, UK STRIKE ACTION If I am swimming in an outdoor pool surrounded by tall trees, and a tropical thunderstorm breaks out, am I at an increased risk of being struck by lightning in the pool? And will it harm me? Simon Hare Siem Reap, Cambodia FREE FALLING I was travelling down from the 10th floor of my office building in the lift when I bent over to fasten my shoelace. I was suddenly dizzy and disoriented and had to kneel down to stop myself falling over. I never have any difficulties travelling in lifts, but presumably this was in some way caused by the fact that I was descending. I tried it again a week later with much the same effect. Why does bending over in a descending lift make me dizzy? Richard Martens Brussels, Belgium TURNING TO MUSH? When I start to fry mushrooms in oil they quickly absorb all the liquid, making the pan quite dry. But after a couple of minutes they suddenly start to release it all again. What’s going on? Francis Keynes Dover, Kent, UK “You can prevent scum forming in tea by adding citric acid such as that found in lemons” Last words past and present, plus questions, at last-word.com Eureka! answers (see page 34) 1 4 2 3 5 No right answer Attach box to wall using drawing pin Move the pennies at the corners Note
