Acid test
Question: How does putting a few drops of vinegar into water that is being
used for boiling eggs prevent the eggs cracking?
Answer: Adding salt and vinegar to the water in which eggs are boiled does
not prevent eggshells from cracking. Shells crack either because they are
dropped into the saucepan too roughly, or because the air in the air sac at the
broad end of the egg expands rapidly because of the sudden heat increase.
The first of these causes can be avoided by lowering the egg gently into the
water on a spoon, the second by piercing the shell at the broad end with a
needle before cooking the egg, thus allowing the expanding air to escape without
the combined danger of cracking the shell. I suppose cracks could also occur
when eggs are boiled very rapidly and they constantly collide with the saucepan
base in the turbulent water, but eggs should be simmered anyway to avoid tough,
rubbery whites.
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The purpose of adding salt and vinegar to the water is to make the egg white
coagulate more quickly when the shell does crack, so that less escapes into the
water.
Rene Thomson
Ashfield, New South Wales
We don鈥檛 believe the explanations below answer the original question. But
they do describe a great party trick and how it works. If you put only a few
drops of vinegar into the water in which you boil an egg, the solution will be
too dilute and the egg鈥檚 exposure to it too short to affect the shell
蝉颈驳苍颈蹿颈肠补苍迟濒测鈥抬诲
Answer: A trick I learnt some years ago demonstrates how flexible an eggshell
can become when soaked in vinegar overnight. Presumably, it is this reduction in
brittleness that prevents the shell cracking when vinegar is added to the water
in which an egg is boiled.
First, soak a fresh egg overnight in vinegar, ensuring that it is fully
immersed in the liquid. Then choose a bottle with a neck that is narrower than
the diameter of the the egg鈥攁bout two-thirds of the diameter of the egg
seems to work best.
You need to be extremely careful with the next step, which involves dropping
a piece of burning paper in to the bottle and then placing the damp egg on the
top of the bottle. The experiment works best if the pointed side is facing down
into the bottle opening. Children who wish to do this experiment should be
supervised by an adult.
As the air cools, the reduction in air pressure will draw the egg into the
bottle. If you then rinse out the bottle and egg with fresh water, the egg shell
will be restored to its original shape and hardness. You now possess a
conversation piece that will baffle anybody who does not know about this trick.
How did a solid egg get into the bottle?
Ian Docherty
Bracknell, Berkshire
Answer: Soak an egg in pure vinegar for 24 hours and it will become rubbery
and flexible as a water-filled balloon. Try it, it really is quite amazing!
The shell of an egg has the same composition as bone. It has a mineral
component (hydroxyapatite) and an organic component (the protein collagen). The
mineral component makes the shell hard but fragile, while the flexible collagen
acts like a glue that maintains the integrity of the whole structure. Acids such
as vinegar dissolve the calcium-based mineral component, which is alkaline,
leaving the flexible collagen intact. Hence you get a rubbery eggshell.
Pedro Gonzalez
London
Spot luck
Question: Does eating sweet things really cause spots?
Answer: This is a widely held myth but I think it serves a purpose for
parents. They can tell their children that if they eat sweets they will get
spots鈥攅ven though it isn鈥檛 true, parents find it useful to perpetuate the
myth.
Spots or acne are caused by the over sensitivity of the skin to the male
hormone testosterone. This causes increased oil production in the skin and a
growth change in the follicular keratinocytes. The result may be a partial
blockage of a pore, either at its opening or inside it. The accumulation of oil
leads to the proliferation of the bacterium Propionibacterium acnes,
which in turn causes inflammation and the red, pussy spot that is the hallmark
of acne.
Extensive studies in the US have examined the relationship between diet and
acne, including one controlled trial where some patients ate large quantities of
chocolate and other foods while others avoided such foods. The number of spots
that developed on each person was counted. There was no significant evidence
that sweets, chocolates, fried or fatty food had any impact on acne.
As with any medical condition, there were always exceptions to the rule. I
certainly have patients who tell me that if they even look at a sweet, they will
develop another spot. Obviously we take such claims seriously, and we do tell
these patients to avoid sweets. However, in about 95 per cent of people who
suffer from acne, it is certain that diet really plays no part at all.
Tony Chu
Dermatology Department
Imperial College, London
This week鈥檚 questions
Barely audible: I鈥檝e heard that the levels of noise in some busy restaurants
are now so high that they exceed industrial safety levels. Is this true? If so,
why? Is it a result of the current vogue, in Britain at least, for minimalist
furniture and bare floors that reflect sound? And are some kinds of noise more
damaging than others?
Charlotte Jemm
Berkhamsted, Hertfordshire
Lean view: Why do aeroplanes have such small windows, and why are they
positioned so low in the fuselage that most people have to bend down in order to
see other aeroplanes on the tarmac?
Timothy Kouloumpas
New York
Green wax: Over a candlelit dinner one evening, we wondered what
mass-produced candles are made of, and how smokeless candles are produced. This
led to the central question of our ponderings鈥攁re candles environmentally
friendly?
Janet Lock and Rob Rushmer
Chesterfield, Derbyshire
Network nightmare: How does a mobile phone network keep track of where every
individual鈥檚 phone is, so that an incoming call can be directed to the right
one?
Alistair Scott
Gland, Switzerland