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The men who told the world four years ago that they had discovered cold fusion will next week publish the most detailed account yet of their experiments. The two chemists, Martin Fleischmann and Stanley Pons, who now work in the laboratories of a French company, IMRA Europe, say the paper shows conclusively that their test-tube experiments generate energy as intense as that found in nuclear reactors.

But scientists who have attempted to replicate their work say the new data show that the chemists are not generating energy. They say if the two have discovered anything, it is no more than a minor chemical phenomenon of no practical use.

Fusion is the process by which the Sun generates its energy. In March 1989, Fleischmann and Pons created a sensation by announcing that they had harnessed fusion in a test tube. Since then, researchers at the United Kingdom Atomic Energy Authority, the US Department of Energy and Japan’s National Laboratory for High Energy Physics have tried and failed to find evidence of cold fusion. Teams in France, Japan, the US and Russia continue to claim success, but their work has not been widely replicated. As a result, most scientists believe cold fusion does not exist.

The new paper describes how Fleischmann and Pons measure energy when an electric current is passed between electrodes of palladium in ‘heavy water’ – in which the hydrogen is replaced by the isotope deuterium. Each deuterium nucleus, or deuteron, contains a neutron as well as the normal proton. The paper will resurrect two arguments: is fusion taking place, and are the cells really generating more energy than is pumped into them?

In 1989, Fleischmann and Pons suggested that the large amounts of heat they detected were caused by deuterons ‘fusing’ inside the metal electrodes. But, since then, even experiments which seem to have succeeded in generating energy have failed to find evidence of fusion. Not enough of the products of fusion – neutrons and tritium nuclei (hydrogen nucleii with two neutrons) – are generated.

‘The fusion ashes – neutrons, tritium and so on – are not there in sufficient amounts,’ says Jean-Pierre Vigier, editor of Physics Letters A, in which the paper is published. ‘It is not fusion.’

The two chemists use a graph to display some of their findings (see Below). They say the rise in power generation on the right side of the graph is evidence of fusion. But David Williams, who led the UKAEA’s experiments, points out that the power generated by this increase is less than that produced by the process dominating the left side, which is due to the absorption of deuterium ions into the palladium electrodes – a known chemical process. ‘It might be an intriguing chemical phenomenon, but fusion? No,’ he says. ‘This paper shows it is a much smaller effect than was at first suggested.’

Vigier has not allowed Fleischmann and Pons to use the word ‘fusion’ in their paper. But even Fleischmann is now more circumspect about whether fusion is taking place. ‘I do not know,’ he says. ‘I am very cautious.’ He does not rule out some new form of fusion, but thinks it may only be part of the story.

This explanation makes the case even less believable, says Douglas Morrison, a physicist at CERN, the European centre for particle physics near Geneva, who writes a sceptical newsletter on cold fusion. ‘Originally they claimed one miracle,’ says Morrison. ‘Now it is many.’

In the experiment, as current is passed between the electrodes, the cell gains and loses energy through four known processes. Electrolysis of heavy water generates heat; heavy water which turns to gas uses up energy; some energy is radiated from the cell into the surroundings; and energy is both gained and lost through conduction. By estimating how these processes should affect the temperature and comparing this with the measured temperature, Fleischmann and Pons deduce the excess power being generated by their experiment. They find extra power of up to 2 watts per cubic centimetre of palladium in the electrodes.

But Williams estimates that this power can be accounted for by just a small discrepancy in the measured temperature, or estimates of what it should be. Fleischman and Pons expect the temperature to rise by about 40 degreeC. But Williams says withou the extra power the two are claiming, the temperature rise would be only 1 or 2 degree less – well within the margin of error for the experiment. ‘It is very sensitive to experimental error,’ he says.

‘It is natural to hope that Fleischman and Pons are not completely wrong,’ says Morrison. ‘But the more careful the experiment, the smaller the effect which has been found. And the really careful experiments find absolutely nothing.’