TRANSMUTATION OF THE ELEMENTS. The transmutation of one metallic element into another was one of the chief objects of the earliest chemists, or alchemists, while to-day, under the influence of modern views on the constitution of matter, transmutation has again been attempted in various ways. Between the ancient and the modern tradition, however, there is a complete break, both as regard purpose and method. The alchemist was mainly interested to produce, from base metals, gold and silver in large quantities, on account of their intrinsic worth; the man of science of to-day has striven to effect the transformation because of the important light which such a process, however small the quantities involved and what ever the elements concerned, would throw on atomic theory. For ALCHEMY see that heading. The present article is concerned with Transmutation in Modern Times.
The discovery of radioactivity brought the question of the transmutation of the elements under the serious attention of men of science, and the development of the modern theory of the atom, leading up to Rutherford's experiments on the disruption of the nucleus, seemed to indicate a possibility of producing artificial transmutation. The various attempts which have been made along different lines have not led to any convincing success.
Radioactive Transmutations and Transmutation Pro duced by Alpha Particles.—The theory of radioactive trans formation, put forward in 1902 by Rutherford and Soddy, as sociated the emission of a- and j3-rays with actual changes in the chemical and physical nature of the atoms emitting the rays, and asserted that in radioactive processes we actually have one element gradually transmuted into another, the number of atoms changing in unit time being a definite fraction X of the number of atoms present. The value of X is characteristic of the kind of atom in question. It is now definitely established that for each a-particle emitted by a given radioactive element one atom of that element is transformed into an atom of an element whose atomic weight is less by 4, while its atomic number is less by 2, the unit of mass being one-sixteenth the mass of an oxygen atom, while, in the case ofg-transformations, the atom does not change its mass appreciably, but its atomic number increases by 1. (See
RADIOACTIVITY, ISOTOPES, NUCLEUS.) The change in properties attending this spontaneous transmutation is in many cases very striking. Thus radium is an element very much resembling barium; it is a metallic solid at ordinary temperatures, which readily forms halogen compounds. Radium emits a-particles and changes to a gas, the so-called radium emanation, or radon, which is, chemically speaking, extremely inert. This gas in its turn emits a-particles and changes to a solid.
Although, generally speaking, the radioactive elements are obtainable only in very small quantities, often unweighable, their electrical properties are so remarkable and so characteristic that their identification is certain, while in some cases, notably with radium and its product radium emanation, the quantities are sufficient to enable the physical and chemical properties to be obtained by ordinary means. For instance, the spectra of the two elements are radically different: the metallic nature of radium can be seen by inspection of the purified metal: the density of the gaseous emanation has been found by delicate weighings, and the vapour pressure of the liquefied gas measured. There is, then, no doubt that in radioactivity we are witnessing a transformation of the elements, but this transformation is outside our control. We cannot by heat or cold hurry it or delay it; the rate at which it takes place is uninfluenced by pressure, by chemical combination, or any other agent at our disposal in the laboratory.
In the case of radioactive substances we cannot, then, be said to be effecting a transmutation of the elements, but merely to be observing one staged by nature. However, the great energy of the radiations from radioactive substances, and the marked chemical effects which they can produce at once suggest them as weapons with which to attempt the transmutation of elements normally stable. The a-rays in particular represent so marked a localization of energy that they would appear most likely to be effective in this respect.