The element of surprise

Water, the liquid that should be a gas, is one of the most investigated yet least understood substances, says John Emsley

Water has fascinated scientists down the ages. The ancient Greek philosopher Thales thought that water was an element, and it was regarded as such until 1774, when Henry Cavendish, of Clapham, showed that it was a compound of hydrogen and oxygen. Since then it has become one of the most investigated of all chemicals, but it is still the least understood.

This month Which? magazine reported on bottled mineral waters, of which the British now buy 500 million litres a year, often paying more per litre for it than for petrol. This is odd, because most of us get cleaner and purer water from our kitchen tap, and it is a thousand times cheaper. Indeed some companies fill their bottles with tap water, and recently famous spas in France were caught using tap water to supplement their natural springs.

The annual report of the UK's Drinking Water Inspectorate shows that tap water quality is improving. Each year analysts check more than three million water samples: 99 per cent pass strict regulations governing, among other things, the levels of disease pathogens, dissolved lead, nitrates and pesticide residues. Claims by environmentalists that our tap water is a "cocktail of toxic chemicals" are simplistic nonsense.

WRc, at Marlow, Buckinghamshire, is Europe's leading water research organisation. It employs 500 people and has an annual turnover of pounds 20m. (It was previously known as the Water Research Centre, before a staff buy-out.) Dr Tony Dobbs is WRc's environmental business manager. He says that talk of increasing amounts of dangerous chemicals in water is founded on scientific ignorance. "Because water is such a good solvent, and because of remarkable advances in analytical technology, it is not surprising that we can now detect minute traces of almost anything," says Dobbs.

WRc scientists are gathering data on the quality of freshwater supplies for the European Environment Agency. Even natural spring waters contain traces of toxic materials. For example, interest is focusing on arsenic, a known carcinogen. There are relatively high levels of it in some areas and in some bottled waters. Drinking water should have fewer than 10 parts per billion of arsenic, according to the World Health Organisation.

Nothing could be simpler than a water molecule, consisting as it does of two hydrogen atoms attached to an oxygen in a V-shaped arrangement, and yet nothing is as complex in its behaviour. For example, H2O should be a gas, like hydrogen sulphide (H2S), but it is a liquid. Moreover, when it freezes at 0C its solid form, ice, floats instead of sinking. Recently, chemists have been finding water doing even stranger things.

Although water boils at 100C, this is only strictly true at sea level. At the top of Mount Everest it boils at about 75C because of the reduced air pressure. If we increase the pressure we can increase the boiling point up to 374C, but to do so requires a pressure of 220 times atmospheric. Above this, water becomes a so-called supercritical fluid, in which it behaves both like a gas and a liquid.

As such it will dissolve almost anything, even oils, and when it does, the volume of fluid can suddenly shrink to a half or less. This happens because supercritical water tends to pack tightly around other molecules. More strangely still, organic materials will flame and burn in it. Treatment with supercritical water has been suggested as an alternative to incineration for disposing of sewage sludge, which is converted to a crystal clear, odourless, germ-free solution.

When oxygen gas is pumped into supercritical water it becomes a powerful oxidising agent, able to break down some of the most persistent toxic wastes. American researchers at the Los Alamos National Laboratory in New Mexico are developing this as a way of disposing of unwanted rocket fuels, explosives and chemical weapons.

Dr Anthony Clifford of Leeds University is Britain's leading researcher into supercritical water. His group is studying the speed with which chemicals react in it. He finds that some reactions go 100 times faster than under ordinary conditions. The trouble with supercritical water is that it is capable of slowly corroding almost any metal, even gold, and the problem faced by researchers is to find a material for pressure vessels that will resist it.

The corrosive properties of water have caused enormous economic problems for the nuclear power industry. Welds inside pressurised water reactors have failed because the water has eaten away at tiny cracks, requiring huge components to be taken out and replaced, sometimes only a few years after the reactor had started operating.

Ultrasound, the frequency of which is too high for humans to hear, does remarkable things to water, creating tiny bubbles in which extremely high temperatures and pressures exist for a fraction of a second when the bubbles collapse. Under such conditions a water molecule in the bubble will cleave one of its hydrogen atoms to form the highly reactive hydroxyl (OH radical). This will then react with any other molecule it meets, and in this way dangerous or intractable materials in the water can be got rid of.

Sonochemistry, as it is called, can even eliminate the ozone-depleting chlorofluorocarbons (CFCs), which are difficult to dispose of because they were designed to be nonflammable and chemically uncreative, which is why they were widely used for 40 years in aerosols, insulation foams and cooling units. A group of Japanese chemists at Osaka University, headed by Yoshio Nagata, have demonstrated that CFCs, currently being collected from old fridges and air-conditioning units for disposal, can be converted to simple chemicals such as carbon dioxide and hydrochloric acid simply by blasting them with soundwaves in water at 20C.

Dr John Emsley is science writer in residence at Imperial College, London.

Start your day with The Independent, sign up for daily news emails
PROMOTED VIDEO
ebooks
ebooksA year of political gossip, levity and intrigue from the sharpest pen in Westminster
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Account Manager

£20000 - £35000 per annum: Recruitment Genius: This full service social media ...

Recruitment Genius: Data Analyst - Online Marketing

£24000 - £35000 per annum: Recruitment Genius: We are 'Changemakers in retail'...

Austen Lloyd: Senior Residential Conveyancer

Very Competitive: Austen Lloyd: Senior Conveyancer - South West We are see...

Austen Lloyd: Residential / Commercial Property Solicitor

Excellent Salary: Austen Lloyd: DORSET MARKET TOWN - SENIOR PROPERTY SOLICITOR...

Day In a Page

Isis in Iraq: Yazidi girls killing themselves to escape rape and imprisonment by militants

'Jilan killed herself in the bathroom. She cut her wrists and hanged herself'

Yazidi girls killing themselves to escape rape and imprisonment
Ed Balls interview: 'If I think about the deficit when I'm playing the piano, it all goes wrong'

Ed Balls interview

'If I think about the deficit when I'm playing the piano, it all goes wrong'
He's behind you, dude!

US stars in UK panto

From David Hasselhoff to Jerry Hall
Grace Dent's Christmas Quiz: What are you – a festive curmudgeon or top of the tree?

Grace Dent's Christmas Quiz

What are you – a festive curmudgeon or top of the tree?
Nasa planning to build cloud cities in airships above Venus

Nasa planning to build cloud cities in airships above Venus

Planet’s surface is inhospitable to humans but 30 miles above it is almost perfect
Surrounded by high-rise flats is a little house filled with Lebanon’s history - clocks, rifles, frogmen’s uniforms and colonial helmets

Clocks, rifles, swords, frogmen’s uniforms

Surrounded by high-rise flats is a little house filled with Lebanon’s history
Return to Gaza: Four months on, the wounds left by Israel's bombardment have not yet healed

Four months after the bombardment, Gaza’s wounds are yet to heal

Kim Sengupta is reunited with a man whose plight mirrors the suffering of the Palestinian people
Gastric surgery: Is it really the answer to the UK's obesity epidemic?

Is gastric surgery really the answer to the UK's obesity epidemic?

Critics argue that it’s crazy to operate on healthy people just to stop them eating
Homeless Veterans appeal: Christmas charity auction Part 2 - now LIVE

Homeless Veterans appeal: Christmas charity auction

Bid on original art, or trips of a lifetime to Africa or the 'Corrie' set, and help Homeless Veterans
Pantomime rings the changes to welcome autistic theatre-goers

Autism-friendly theatre

Pantomime leads the pack in quest to welcome all
The week Hollywood got scared and had to grow up a bit

The week Hollywood got scared and had to grow up a bit

Sony suffered a chorus of disapproval after it withdrew 'The Interview', but it's not too late for it to take a stand, says Joan Smith
From Widow Twankey to Mother Goose, how do the men who play panto dames get themselves ready for the performance of a lifetime?

Panto dames: before and after

From Widow Twankey to Mother Goose, how do the men who play panto dames get themselves ready for the performance of a lifetime?
Thirties murder mystery novel is surprise runaway Christmas hit

Thirties murder mystery novel is surprise runaway Christmas hit

Booksellers say readers are turning away from dark modern thrillers and back to the golden age of crime writing
Anne-Marie Huby: 'Charities deserve the best,' says founder of JustGiving

Anne-Marie Huby: 'Charities deserve the best'

Ten million of us have used the JustGiving website to donate to good causes. Its co-founder says that being dynamic is as important as being kind
The botanist who hunts for giant trees at Kew Gardens

The man who hunts giants

A Kew Gardens botanist has found 25 new large tree species - and he's sure there are more out there