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Swirled, not stirred
THE LAST WORD What a gas When I turn off a gas ring on my cooker the flame reduces as you might expect, but then it sometimes extinguishes with a small explosive popping sound. Why does it do that?
n When gas is mixed with air it can burn smoothly or it can explode. The gas is fed to the gas ring by a small venturi mechanism, which uses incoming gas to draw in air for combustion. This is adjusted to give a blue cone-shaped flame which indicates complete combustion. For obvious safety reasons, the flame is not allowed to flow backwards into the cooker. There are two ways to control the flame. The first is by the outward velocity of the gas, which is higher than the speed at which the flame can grow. This is because the gas is travelling so fast at the point it emerges from the very small hole in the ring – the smaller the hole
Last words past and present, plus questions, at last-word.com
cooling effect of the metal is no longer enough to prevent the flame moving inwards. But once the flame front gets inside the gas ring any remaining gas quickly burns off and a small pop is heard. The same pop, on a much larger scale, can destroy a building filled with a similar mixture of gas and air. When you turn off the cooker gas and air are in an explosive ratio, albeit, in this case, not one that should cause any damage. Bill Jackson Toronto, Ontario, Canada
Scraping the bottom Why does the bottle of red wine vinegar I buy from my supermarket start off without sediment and then acquire it after a couple of months?
the faster it travels. The second factor blocking the flame is the cold metal of the cooker, which can cool the gas below its ignition temperature. Both of these effects keep the flame outside the gas ring on the cooker. When the flame is turned off, the gas velocity falls to zero and the flame front advances part of the way back into the system. The
n This could be due to a combination of things. Wines contain tartrates formed from the tartaric acid naturally present in grapes. These are the source of the glass-like crystals which often settle at the bottom of a bottle of wine. Tartrates become less soluble as the temperature drops, so these crystals form in wine stored at a lower temperature after bottling than that in the vats used to age the wine. The same should be true of wine vinegar because it is only the alcohol which is soured. The constituents responsible for the flavour of the wine, including tartrates, remain in the aqueous part of the vinegar or wine
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.
“For obvious safety reasons gas stove flames are not allowed to flow back into the cooker’s system”
throughout the fermentation and ageing process. It may also be the case that some yeasts and bacteria used to ferment the alcohol remain in suspension only to settle out when the wine vinegar is left standing. Terence Hollingworth Blagnac, France n As a chemist, I know that red wine contains polyphenolic compounds that are only slightly soluble and, given time, these slowly change composition to give insoluble compounds. This process can happen in the presence or absence of oxygen but is faster with it. The polyphenolics are oxygenated molecules anyway, which makes them heavier than water, hence the sediment. Colin Cook Basildon, Essex, UK
Jersey of many colours When I look at an electric light bulb through the fabric of my maroon, acrylic school jumper, why does it seem to have a rainbow halo around it?
n The threads in the acrylic jersey are acting in a similar way to raindrops or ice particles in the sky when we see a rainbow. Light from the electric bulb is refracted when it passes through the translucent threads of the jumper and is separated into its constituent colours just as light splits when it passes
through a prism. The rainbow effect is more noticeable towards the edge of the acrylic threads because these are the thinnest, most transparent parts of the jumper and refraction occurs more obviously and favourably here. You probably won’t get the same effect if you view the light bulb through the fibres of a woollen or cotton garment. These are not manufactured fabrics and do not have the same translucent, light-separating properties as acrylic. Francis Keigh Liverpool, UK
This week’s questions Swirled, not stirred
Why shake or stir vodka martinis at all? Both methods mean there is far more collision between liquid and ice, which makes the martini very dilute. I just hold the cocktail shaker gently and loosely spin it in a circular motion to swirl drink and ice together. Assuming there is a flaw in my method, what is it? Liam Case Aylesbury, Buckinghamshire, UK Write or wrong?
Why do we all have different styles of handwriting? In fact it is so individual that you can identify people such as friends and colleagues purely from their handwriting. Colin Mascord Sydney, Australia
Why are orangutans orange? A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans
n When gas is mixed with air it can burn smoothly or it can explode. The gas is fed to the gas ring by a small venturi mechanism, which uses incoming gas to draw in air for combustion. This is adjusted to give a blue cone-shaped flame which indicates complete combustion. For obvious safety reasons, the flame is not allowed to flow backwards into the cooker. There are two ways to control the flame. The first is by the outward velocity of the gas, which is higher than the speed at which the flame can grow. This is because the gas is travelling so fast at the point it emerges from the very small hole in the ring – the smaller the hole
Last words past and present, plus questions, at last-word.com
cooling effect of the metal is no longer enough to prevent the flame moving inwards. But once the flame front gets inside the gas ring any remaining gas quickly burns off and a small pop is heard. The same pop, on a much larger scale, can destroy a building filled with a similar mixture of gas and air. When you turn off the cooker gas and air are in an explosive ratio, albeit, in this case, not one that should cause any damage. Bill Jackson Toronto, Ontario, Canada
Scraping the bottom Why does the bottle of red wine vinegar I buy from my supermarket start off without sediment and then acquire it after a couple of months?
the faster it travels. The second factor blocking the flame is the cold metal of the cooker, which can cool the gas below its ignition temperature. Both of these effects keep the flame outside the gas ring on the cooker. When the flame is turned off, the gas velocity falls to zero and the flame front advances part of the way back into the system. The
n This could be due to a combination of things. Wines contain tartrates formed from the tartaric acid naturally present in grapes. These are the source of the glass-like crystals which often settle at the bottom of a bottle of wine. Tartrates become less soluble as the temperature drops, so these crystals form in wine stored at a lower temperature after bottling than that in the vats used to age the wine. The same should be true of wine vinegar because it is only the alcohol which is soured. The constituents responsible for the flavour of the wine, including tartrates, remain in the aqueous part of the vinegar or wine
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.
“For obvious safety reasons gas stove flames are not allowed to flow back into the cooker’s system”
throughout the fermentation and ageing process. It may also be the case that some yeasts and bacteria used to ferment the alcohol remain in suspension only to settle out when the wine vinegar is left standing. Terence Hollingworth Blagnac, France n As a chemist, I know that red wine contains polyphenolic compounds that are only slightly soluble and, given time, these slowly change composition to give insoluble compounds. This process can happen in the presence or absence of oxygen but is faster with it. The polyphenolics are oxygenated molecules anyway, which makes them heavier than water, hence the sediment. Colin Cook Basildon, Essex, UK
Jersey of many colours When I look at an electric light bulb through the fabric of my maroon, acrylic school jumper, why does it seem to have a rainbow halo around it?
n The threads in the acrylic jersey are acting in a similar way to raindrops or ice particles in the sky when we see a rainbow. Light from the electric bulb is refracted when it passes through the translucent threads of the jumper and is separated into its constituent colours just as light splits when it passes
through a prism. The rainbow effect is more noticeable towards the edge of the acrylic threads because these are the thinnest, most transparent parts of the jumper and refraction occurs more obviously and favourably here. You probably won’t get the same effect if you view the light bulb through the fibres of a woollen or cotton garment. These are not manufactured fabrics and do not have the same translucent, light-separating properties as acrylic. Francis Keigh Liverpool, UK
This week’s questions Swirled, not stirred
Why shake or stir vodka martinis at all? Both methods mean there is far more collision between liquid and ice, which makes the martini very dilute. I just hold the cocktail shaker gently and loosely spin it in a circular motion to swirl drink and ice together. Assuming there is a flaw in my method, what is it? Liam Case Aylesbury, Buckinghamshire, UK Write or wrong?
Why do we all have different styles of handwriting? In fact it is so individual that you can identify people such as friends and colleagues purely from their handwriting. Colin Mascord Sydney, Australia
Why are orangutans orange? A new collection: the usual insight, ingenuity and wit – this time with full colour photographs Available from booksellers and at newscientist.com/orangutans