Aaaaargh
Question: People鈥檚 hair is sometimes reported to have turned white overnight
as a result of shock. Can white hair be the result of shock and, if this is so,
how long might it take? What is the process involved?
Answer: White hair results from the loss of melanocytes when we age.
Melanocytes produce the pigment melanin, which gives hair and skin their colour.
Hair that is already grown is fairly immutable and only new growth can bring
about a change in colour. Hair strands have a life span of up to seven years so
a complete shift to white would take at least that long. I have never heard of
hair turning white overnight as a result of shock.
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Pedro Gonzalez
by e-mail, no address supplied
Micro madness
Question: A colleague of mine is in the habit of heating bottled water for
his tea in a mug in a microwave oven. When the water is up to temperature he
removes the mug.
On several occasions, the water has started to bubble violently after he has
added a tea bag. On one occasion, the boiling started when he was removing the
mug. It was so violent that it blew 90 per cent of the water from the
mug鈥攚hich is obviously quite dangerous. What is happening?
Answer: A portion of the water in the cup is becoming superheated鈥攖he
liquid temperature is actually slightly above the boiling point, where it would
normally form a gas. In this case, the boiling is hindered by a lack of
nucleation sites needed to form the bubbles.
This never occurs when boiling a kettle, for example, because the presence of
the rough surface of the element, as well as the convective stirring from rising
hot water, are sufficient to produce proper boiling. Turbulence in liquids is
known to provide enhanced nucleation in other cases: when you pour a cola drink,
for example.
In your colleague鈥檚 case, the addition of a tea bag (and, in the other case,
simple movement) sufficed to allow bubble formation. Even with a large
proportion of the water superheated, only a little will convert to steam, as the
amount of latent heat required for this phase change is very large. I imagine
that by keeping the cup still and microwaving for a long time, one could blow
the entire contents of the cup into the interior of the microwave as soon as you
introduced any nucleation sites. It is this sometimes explosive rate of steam
production that means you should take great care when using a microwave
oven.
Richard Barton
Guildford, Surrey
Wine into water
Question: No matter what colour of drink one consumes, when the liquid
finally leaves the body the colour has gone. What happens to it?
Answer: The liquid that leaves the body is almost unrelated, in chemical
composition, to the liquid consumed. Any substance, solid or liquid, that goes
down the oesophagus, passes through the digestive tract and, if not absorbed, is
incorporated into the faecal matter. Urine, in contrast, is created by the
kidneys from metabolic waste produced in the tissues and transported through the
bloodstream.
Any coloured compound that you drink either will or will not interact
biochemically with the body鈥檚 systems. If it does, this interaction (like any
other chemical reaction it might undergo) will tend to alter or eliminate its
colour. If it does not, the digestive system will usually decline to absorb it
and it will be excreted in the faeces which, you will have noticed, show
considerably more colour variation than the urine.
Stephen Gisselbrecht
Boston, Massachusetts
Answer: Coloured substances in food and drink are usually organic compounds
that the human body has an amazing ability to metabolise, turning them into
colourless carbon dioxide, water and urea. The toughest stuff is often taken
care of by the liver, which is a veritable waste incinerator. However, on the
very infrequent occasion when the intake of coloured substances exceeds what the
body can quickly metabolise, the colour is not necessarily removed as the liquid
leaves the body. This is well known to anyone who has indulged in large
quantities of borsch (Russian beetroot soup).
Hans Starnberg
Gothenburg, Sweden
Box of tricks
Question: On a recent visit to Edinburgh, we were in a pub which had an
instrument at the end of the bar approximately 30 centimetres in length and 3
centimetres wide. It appeared to be a black rectangular box, open on one side,
with a series of red lights inside.
When you moved your head swiftly, a brand name of vodka appeared to flash
along the surface of the bar although not all the letters could necessarily be
seen at once. How did the box produce this image, why could all the letters not
be seen simultaneously and why was the image only obtained when your head was
moved vigorously?
(continued)
Answer: The instrument with the row of lights is a display based on an
imaging method patented by Bill Bell in 1984 (US patent number 4 470 044,
鈥淢omentary Visual Image Apparatus鈥�), which was called the light stick.
Jerome Liss
Philadelphia, Pennsylvania
Title claims
Question: It is easier to read titles on book spines on my bookshelf if I
incline my head. Why?
(continued)
Answer: I am sure the answer from your correspondent is correct鈥攚e are
used to horizontal text and incline our heads to make reading spines easier. But
have you noticed something else?
When I was an engineering student many years ago, all my drawings had to be
produced in 鈥渇irst angle projection鈥�, whereby they could be read by someone
viewing from the bottom or the right-hand side鈥攖hat is, by standing
straight or tipping your head to the left.
Nowadays, for reasons neither clear nor published, book titles are produced
in 鈥渢hird angle projection鈥� which means you have to tip your head to the right
to read them. Can anyone explain why this happened? It doesn鈥檛 half make life
difficult when browsing.
Barry Linton
Reading, Berkshire
This week鈥檚 question
Question: This question was first asked on the news group sci.botany,
but nobody answered it. Are New 杏吧原创 readers able to help?
When a pepper is cut open there is a space inside, but there are no gaps in
the pepper where air could get through. What is the composition of gases in this
space and how did they get there? If a green pepper contains chloroplasts would
there be more oxygen and less carbon dioxide in a green pepper than in a red,
yellow or orange one?
Rosa Clements (aged 14)
Harrogate, North Yorkshire