Image caption A droplet containing the soap is attracted to the magnet at left

An international team of scientists has demonstrated the first soap that responds to magnets.

This means the soap and the materials that it dissolves can be removed easily by applying a magnetic field.

Experts say that with further development, it could find applications in cleaning up oil spills and waste water.

Details of the new soap, which contains iron atoms, are reported in the chemistry journal Angewandte Chemie.

It is similar to ordinary soap, but the atoms of iron help form tiny particles that are easily removed magnetically.

"If you'd have said about 10 years ago to a chemist: 'Let's have some soap that responds to magnets', they'd have looked at you with a very blank face," said co-author Julian Eastoe of the University of Bristol.

He told BBC News: "We were interested to see, if you went back to the chemical drawing board with the tool-kit of modern synthetic chemistry, if you could...design one."

Iron clad

Soap is made of long molecules with ends that behave differently: One end of the molecule is attracted to water and the other is repelled by it.

The "detergent" action of soap comes from its ability to attach to oily, grimy surfaces, with the "water-hating" end breaking up molecules at that surface. The soap molecules then gather up into droplets in which all the "water-loving" ends face outward.

Prof Eastoe and his team started with detergent molecules that he said were "very similar to what you'd find in your kitchen or bathroom" - one of which can be found in mouthwash.

Image caption The soap could make for a far easier means of gathering oil from spills

The team found a way to simply add iron atoms into the molecules. The droplets that the soap formed were attracted to a magnet, just as iron filings would be.

But single iron atoms would not behave as tiny individual magnets, so some other process had to be at work. To get a look at what was going on in the chemical process required a view at the molecular level.

So the team sent their samples to the Institute Laue Langevin (ILL) in Grenoble, France, where an intense beam of the sub-atomic particles known as neutrons shed light on the matter.

They saw that the iron particles were clumping neatly together into iron nanoparticles, tiny clumps of iron that could in fact respond to a magnetic field.

Prof Eastoe said the research was still at the laboratory stages but was already the subject of discussion.

"The research at the University of Bristol in this field is about how we can take the ordinary and give it extraordinary properties by chemical design," he said.

"We have uncovered the principle by which you can generate this kind of material and now it's back to the drawing board to make it better."