When in 1900 Ernest Rutherford and Frederick Soddy, working at McGill University in Montreal, figured that thorium was spontaneously turning into argon by radioactive decay, Soddy exclaimed ‘This is transmutation!’ To which Rutherford thundered back, ‘For Mike’s sake Soddy, don’t call it transmutation. They’ll have our heads off as alchemists.’
For what could be worse than to be associated with that discredited and disreputable pseudoscience, according to which metals could be transmuted one to another by chemical manipulation, and thereby the knowledgeable adept could make gold from other metals? It was one of the revelations of nuclear chemistry, initiated by the work of Henri Becquerel and Marie and Pierre Curie on radioactivity in the 1890s, that chemical elements really could be interconverted, the composition of their atomic nuclei being altered by the emission of alpha or beta particles. This hardly seemed comparable, however, to the claims of alchemists to have transmuted other elements to gold by ‘sublimation, putrefaction, fixation, coagulation’ in the laboratory.
Or was it? A largely forgotten episode in the 1920s involving some scientists at the heart of the revolution in atomic theory shows that the dreams of alchemy had not dissipated even that late in the day.
The controversy began with experiments conducted in 1924 by chemist and photography expert Adolf Miethe and his colleague Hans Stammreich at the Technical University Berlin. They found that black deposits collected from a mercury lamp, in which an electrical discharge was passed through mercury vapour, contained gold.1 Although gold was known to be a trace impurity in commercially available mercury, the German researchers had purified their mercury by distillation. What they had seen, they said, was the ‘formation of gold from mercury’ by chemical means.
This rather extraordinary claim was backed up the following year by the Japanese physicist Hantaro Nagaoka at Tokyo Imperial University, previously known for having postulated a model of the atom in which a central mass was orbited by electrons like Saturn and its rings – a partial inspiration for Rutherford’s ‘solar-system’ atom. Nagaoka reported passing an electrical discharge of 600,000 volts between a tungsten and a mercury electrode immersed in oil, and finding a ‘black pasty mass’ in which he claimed to have found gold.2 In similar experiments he said that mercury had transformed into silver. Despite Rutherford’s warning to Soddy, Nagaoka was prepared to use that dread word: transmutation.
Needless to say, no conventional chemical process can explain these results. With their focus on mercury, gold and silver, they sound unnervingly alchemical. But in a weird way, the advent of modern atomic theory seemed to make the scientific world more receptive to such things than would have been the case only a few decades earlier – for radioactivity, and particularly Rutherford’s work, had shattered the immutability of the atom. ‘Claims to have effected the “great work” of transmutation have been made at frequent intervals since alchemy fell into disrepute’, said a 1926 commentary in Nature on the ‘transmutation controversy’3 – but ‘modern research into the constitution of the atom gave them a rational basis of possibility such as was never dreamed of by the medieval alchemist.’
Thus Soddy proposed that a mercury nucleus might be transmuted by absorbing an electron in a kind of reverse beta decay4 – only for Francis Aston, the discoverer of isotopes, to counter that no known mercury isotopes have a mass close enough to gold.5 Fritz Haber weighed in, repeating the experiments of Miethe and Nagaoka and at first announcing to the German Chemical Society in 1926 that he had confirmed them – only to retract the claim when further analysis showed the tiny amounts of gold to be contamination, in one case from the spectacles of an assistant.6 (This, note, is the Haber who concocted a scheme for extracting trace amounts of gold from sea water to pay off Germany’s war reparations bill.)
Other efforts at replication also failed, but the matter was never fully resolved. The claims look now to have all the hallmarks of what in 1953 Irving Langmuir called ‘pathological science’. They recall more than anything the episode of ‘cold fusion’ in 1989,7 whereby another chemical process – electrolysis – allegedly transformed deuterium to helium by nuclear fusion. There too the claims proved impossible to reproduce reliably, relied partly on detection of trace amounts of material, and defied conventional explanation.
