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Q: Glenbrook Infants School went to the seaside for our summer outing. We had a nice time, but please can you tell me why the sea is salty. My mum doesn’t know.

A: The sea is salty because the rivers that flow into it wash salts and other minerals out of the ground. The salts dissolve in the rivers and the rivers flow into the sea. As the Sun evaporates the water from the sea to make clouds, it leaves the salts and minerals behind, so the sea is saltier than rivers and lakes.

A: John Connolly is a brainy guy

Asking questions and wondering

why

The salty sea which is such fun

When splashing in the waves and Sun

Is not freshwater from the tap

Or from a bottle with a cap;

So he will learn that salt and sea

Mix just like sugar into tea

And that many other kinds of salt

Dissolve into this briny malt,

Sodium chloride, the salt of table

Has other friends within its stable

Potassium Ch, magnesium Ch, and iodide

All flow solvent with the tide.

So now dear John, you clever lad

Off you go – tell mum and dad!

This is probably the last time we will resort to rhyme to answer a question – Ed.

This week’s questions

Mussel fight: A colleague and I are disputing the existence of pearls in edible mussels (Mytilus edulis). On occasions when I have collected and eaten mussels in Scotland, I have sometimes found small, white pearl-like objects. My friend believes them to be something else, and says that mussels never contain pearls. Who is right and, if there are pearls, are they similar to the pearls found in oysters?

Elizabeth Boulter, London

Bright sparks: The tide was out one day as a friend and I were walking along a beach. As we walked on the littoral zone – the part of the beach between low and high tides – strange blue lights lit up around our feet as we stepped on the sand. The lights were similar to lightning and the harder we stepped on the ground the more intense the blue lights became. Nobody has been able to provide us with a satisfactory explanation and, no, we were not under the influence of any drugs. Just what was happening?

Suzanne Roman, Melbourne, Victoria

Cold spell: Why do people catch colds and flu more often in the winter? Are viruses transmitted more easily in damp air, is the resistance of the population reduced by the cold and lack of sunlight, or do the viruses simply take advantage of the greater time we spend indoors with each other?

Nigel McFarlane, Pulloxhill, Bedfordshire

Mix and match: When making cocoa drinks, the normal method is to mix the powder with a small amount of cold milk or water, before adding the rest of the hot or cold liquid to the required strength. Initially the cocoa powder is not wetted by the liquid and remains separate from it. But, after vigorous stirring, a critical state is reached when all the powder suddenly goes into suspension. The same is true of cornflour or blancmange. What causes this? Is temperature important. Is this behaviour related to mixing flour with a small amount of fat before liquid is added to make sauce?

Simon Cox, Subiaco, Western Australia

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