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Spice attack
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THE LAST WORD Air spray I wanted to chill a mug of water so placed it in the freezer, but then forgot about it and it froze solid. When I removed the block of ice from the mug it contained the most amazing thistle-like pattern of what seemed like canals of air (see photo). None of these canals extended to any outside surfaces. What happened?
■ The simple answer is that because you live in Somerset West, South Africa, you should ask your neighbour Jon Richfield, who
answers so many of the questions on this page. Just in case Jon can’t help, I’ll venture an opinion. In the freezer the water is cooled from the outside in. So the first crystals of pure ice form around the outside of the mass of water. As these ice crystals grow inwards, the air dissolved in the water becomes
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.
In this case, the front advanced trapped and its concentration smoothly along the curves increases. Initially it remains described by the long bubbles. The dissolved, because cold liquids original spherical bubbles caught can hold more dissolved gas than in place by the growing crystals hot ones. This is why the outer acted as nuclei into which the rest layer is almost free of air bubbles. of the gas collected as it escaped However, the concentration of from solution. Being surrounded dissolved air eventually exceeds the ability of the water to retain it by ice in every direction except in solution, so air bubbles begin to perpendicular to the ice surface, the bubbles formed tubes whose form and get trapped in the ice as the crystals grow inwards, forming shapes traced the advance of the crystal-water interface. the patterns observed. The lines It’s common to see such bubble all curve downwards because growth, but the lovely symmetry water on the verge of freezing is less dense than slightly warmer water, and so rises. Thus the water “The lovely symmetry requires still water and freezes from the top down, suitable temperature meaning that the water at the gradients and solutes” bottom (which is also somewhat insulated from the cold air in the and consistent bubble structure freezer) is the last to freeze. shown in the photograph require Simon Iveson still water and suitable solutes, Department of Chemical temperature gradients and crystal Engineering forms. To sculpt such bouquets in University of Newcastle various forms, and possibly in Callaghan, New South Wales, other media, should make for Australia satisfying science experiments and art projects. And, of course, Jon did provide an Jon Richfield answer – Ed Somerset West, South Africa ■ If the container is smooth, the outer layer is bubble-free because Spice attack solutes in the water, gases in The Last Word has told us why garlic particular, are unsaturated when freezing starts. Bubbles form only makes your breath and body smell, after some ice has formed, forcing but I want to know why the spice methi, or fresh fenugreek, has a enough gas to supersaturate the similar, possibly stronger, effect. surrounding water. Initially, tiny spherical bubbles appear on the advancing surface. What happens ■ Depending on their biochemical nature, volatile next depends on the path of the components of foods or their ice front and the form of the metabolic products enter the growing crystals.
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.
Do Polar Bears Get Lonely? Our latest collection ight serious enquiry, brilliant insight and the hilariously unexpected cted Available from booksellers m/ and at www.newscientist.com/ polarbears
blood and exit via lungs, urine, sweat, saliva or sebum, more than most people notice. As a result, families or communities with distinctive cuisines have distinct body scents. There are many examples beyond obvious ones such as asparagus and onion-like foods. Stewed mutton and beef give a recognisable odour to one’s urine. No doubt any self-respecting dog could identify other meats. Many nitrogen compounds are particularly likely to be excreted in urine or sweat. I rather like the yeasty smell of thiamine, but my wife hates it, as does a friend who once had to have daily thiamine injections. His skin would reek before the doctor even finished the injection. Some people can even guess which cheese you have eaten in the last few days; presumably the smell gets into your sebum. Fenugreek contains a range of sulphur and nitrogen-rich aroma molecules that the body modifies and excretes in breath and sweat, but the main burnt-sugar smell comes from the lactone sotolon, whose smell we can detect even in minute concentrations. Antony David Watford, Hertfordshire, UK
This week’s question RISE AND FALL
Why are the largest tide ranges in the world – of up to 16 metres – found in the Bay of Fundy, on Canada’s Atlantic coast? Peter Buckley Toronto, Canada
THE LAST WORD Air spray I wanted to chill a mug of water so placed it in the freezer, but then forgot about it and it froze solid. When I removed the block of ice from the mug it contained the most amazing thistle-like pattern of what seemed like canals of air (see photo). None of these canals extended to any outside surfaces. What happened?
■ The simple answer is that because you live in Somerset West, South Africa, you should ask your neighbour Jon Richfield, who
answers so many of the questions on this page. Just in case Jon can’t help, I’ll venture an opinion. In the freezer the water is cooled from the outside in. So the first crystals of pure ice form around the outside of the mass of water. As these ice crystals grow inwards, the air dissolved in the water becomes
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.
In this case, the front advanced trapped and its concentration smoothly along the curves increases. Initially it remains described by the long bubbles. The dissolved, because cold liquids original spherical bubbles caught can hold more dissolved gas than in place by the growing crystals hot ones. This is why the outer acted as nuclei into which the rest layer is almost free of air bubbles. of the gas collected as it escaped However, the concentration of from solution. Being surrounded dissolved air eventually exceeds the ability of the water to retain it by ice in every direction except in solution, so air bubbles begin to perpendicular to the ice surface, the bubbles formed tubes whose form and get trapped in the ice as the crystals grow inwards, forming shapes traced the advance of the crystal-water interface. the patterns observed. The lines It’s common to see such bubble all curve downwards because growth, but the lovely symmetry water on the verge of freezing is less dense than slightly warmer water, and so rises. Thus the water “The lovely symmetry requires still water and freezes from the top down, suitable temperature meaning that the water at the gradients and solutes” bottom (which is also somewhat insulated from the cold air in the and consistent bubble structure freezer) is the last to freeze. shown in the photograph require Simon Iveson still water and suitable solutes, Department of Chemical temperature gradients and crystal Engineering forms. To sculpt such bouquets in University of Newcastle various forms, and possibly in Callaghan, New South Wales, other media, should make for Australia satisfying science experiments and art projects. And, of course, Jon did provide an Jon Richfield answer – Ed Somerset West, South Africa ■ If the container is smooth, the outer layer is bubble-free because Spice attack solutes in the water, gases in The Last Word has told us why garlic particular, are unsaturated when freezing starts. Bubbles form only makes your breath and body smell, after some ice has formed, forcing but I want to know why the spice methi, or fresh fenugreek, has a enough gas to supersaturate the similar, possibly stronger, effect. surrounding water. Initially, tiny spherical bubbles appear on the advancing surface. What happens ■ Depending on their biochemical nature, volatile next depends on the path of the components of foods or their ice front and the form of the metabolic products enter the growing crystals.
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.
Do Polar Bears Get Lonely? Our latest collection ight serious enquiry, brilliant insight and the hilariously unexpected cted Available from booksellers m/ and at www.newscientist.com/ polarbears
blood and exit via lungs, urine, sweat, saliva or sebum, more than most people notice. As a result, families or communities with distinctive cuisines have distinct body scents. There are many examples beyond obvious ones such as asparagus and onion-like foods. Stewed mutton and beef give a recognisable odour to one’s urine. No doubt any self-respecting dog could identify other meats. Many nitrogen compounds are particularly likely to be excreted in urine or sweat. I rather like the yeasty smell of thiamine, but my wife hates it, as does a friend who once had to have daily thiamine injections. His skin would reek before the doctor even finished the injection. Some people can even guess which cheese you have eaten in the last few days; presumably the smell gets into your sebum. Fenugreek contains a range of sulphur and nitrogen-rich aroma molecules that the body modifies and excretes in breath and sweat, but the main burnt-sugar smell comes from the lactone sotolon, whose smell we can detect even in minute concentrations. Antony David Watford, Hertfordshire, UK
This week’s question RISE AND FALL
Why are the largest tide ranges in the world – of up to 16 metres – found in the Bay of Fundy, on Canada’s Atlantic coast? Peter Buckley Toronto, Canada