Warm feeling
Question: For Christmas I was given a device for warming bottles of red wine. It is a plastic jacket filled with transparent gel which wraps around the bottle. When you press a stud on the jacket the gel gradually becomes opaque and warm. The opacity spreads out from the stud, taking about 30 seconds to cover the gel. To regenerate the jacket you immerse it in boiling water for 15 minutes until the gel is transparent again. How does it work?
Answer: The jacket of your wine heater contains a solution of sodium acetate trihydrate in water. This solution has two unusual properties that make it ideal for use in these 鈥渉eat packs鈥�.
First it has a very large heat of crystallisation, which means it gives out a significant amount of energy on solidifying鈥攈ence the temperature rise to around 50 掳C. Secondly, the solution exists as a metastable, supercooled liquid at room temperature. After the crystals have been dissolved, by boiling the heat pack for about 15 minutes, the liquid remains remarkably resistant to crystallisation, and can be cooled to below room temperature without solidifying.
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In fact, the only way to set off the crystallisation process at room temperature is to introduce a solid crystal of the same substance into the liquid. Nucleation occurs on this crystal, which is where the metal stud comes in. Tucked inside microscopic cracks on the stud鈥檚 surface are many tiny crystals that do not dissolve when the heat pack is boiled up. These crystals do not melt because temperature and pressure act a little strangely at the thin end of cracks and there simply isn鈥檛 sufficient crystal surface area available to the hot liquid to allow these crystals to melt. When the stud is depressed, it flips from being concave to convex, ejecting these tiny crystals into the surrounding liquid and starting the crystallisation. The stud and heat pack can be reused in this way many, many times.
In addition, sodium acetate trihydrate is entirely non-toxic and non-corrosive, so there鈥檚 no problem if the pack accidentally splits open, although it does smell a little of vinegar.
Tim Inman, Rachael Elder, Mansel
Rogerson and Silvana Cardoso
Department of Chemical Engineering
University of Cambridge
Size matters
Question: New 杏吧原创鈥檚 picture of Montserrat Caballe (10 November 2001, p 16) set me thinking. Why are opera singers often large? What benefit does it convey? Surely it鈥檚 no coincidence that they are all so well built.
Answer: It is important to define what 鈥渂ig鈥� actually means. Some opera singers are arguably overweight but many others, such as Placido Domingo and Russell Watson, have large frames but are not fat.
Then again, don鈥檛 forget that Jos茅 Carreras, a famous tenor, is only 170 centimetres tall and is extremely slight, yet he has one of the finest voices in opera.
Marcus Taylor
Oxford
Answer: The depth and ability of a person鈥檚 singing voice are qualities which take a lot of training and which must subsequently be practised repeatedly. Only then can a singer obtain the vocal control and power of a world-class opera performer. However, the ability to sing well at all is a largely predetermined characteristic that can be inherited. This boils down to the qualities of your larynx, better known as the voice box.
It is generally believed that the more fatty tissue surrounds the larynx, the better its resonance and the more aesthetically pleasing the note it produces. The amount of this fatty tissue varies from person to person. Therefore, in operatics, the majority of people would seem to be of larger proportions because this extra tissue surrounding their larynx boosts the quality of their singing voice. Furthermore, a person鈥檚 size also affects the power of their diaphragm and lungs and their corresponding ability to reach, hold and control notes.
Peter Galek
University of Durham
Answer: Opera singers need a powerful diaphragm to be able to project their voice above the sound of a big orchestra in a cavernous opera house, so a large chest cavity and good control of the lungs will provide a suitable mass to drive the diaphragm.
In the 18th and early 19th centuries, opera was an expanding medium. Successive generations sought larger and more dramatic effects, and larger audiences drawn in required bigger theatres.
This produced new technology for wind instruments and the reconstruction of older baroque string instruments. Of course, singers could not be re-engineered, so they developed vocal techniques to cope with this steady rise in volume, hence the advantage of a large chest.
Ian Gammie
Corda Music Publications
St Albans, Hertfordshire
This week鈥檚 questions
Chaaaaarge!: Your recent question on electric toothbrushes led to an argument among my friends. Opinion is divided on whether you should replace the toothbrush on its recharger after each use or whether you should empty its power source to the point where its performance is noticeably reduced. To prolong the battery鈥檚 life, is it better to recharge it constantly or first let it run down?
Christian Guksch
Hamburg, Germany
Ear for music: I am friends with two couples, all equally keen birdwatchers.
Both women can distinguish between different birdsongs but, although both like music, can鈥檛 tell one symphony from another. The two men have excellent memories for music but both have great difficulty in distinguishing birdsong. Are two different kinds of memory required, or are the sounds processed by different parts of the brain?
Anne Gerrish
Ely, Cambridgeshire
Flying doughnuts: Flying over German Bight at about 13,000 metres I saw a completely annular cloud.
It appeared unrelated to the other scattered clouds that were present and, for the two minutes I was able to watch it, it didn鈥檛 change its appearance. It must have been 3 or 4 kilometres across and 300 or 400 metres thick, though this varied around its circumference.
Could it have been natural and, if not, what could have caused it?
Chris Miller
High Wycombe, Buckinghamshire