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The ultimate constitution of matter is a subject which has always exercised a powerful attraction upon the minds of men. Philosophical speculations of the essential unity of all matter and of the possibility of transforming the different kinds into one another have come down to us from the ancients. The modern science of Chemistry had its origin in the actual attempts at such transformation or transmutation made by the alchemists in the Middle Ages. These attempts centred around the transmutation of lead or other base metal into gold, and the alchemists believed that there existed, and spent their lives trying to discover, a “philosopher's stone” to which was ascribed the power to effect this transmutation in almost unlimited amount. The philosopher's stone was also credited with acting as a universal medicine, prolonging life and health indefinitely, or at least to periods rivalling those enjoyed by the Hebrew patriarchs of old. Whether these ideas were wholly the inventions of charlatans, or whether they were the distorted parrot-like repetition of the wisdom of a lost Atlantis, none can now say. But it may be remarked that sober modern science of to-day sees in the power to effect transmutation of the elements the power to prolong the physical welfare of the community for indefinite periods. Indeed, without some such
, discovery the phase of civilisation, ushered in by 1 Contributed to the Aberdeen University Review, February 1917.
science, must from its very nature be but transitory. We are spending improvidently in a year the physical means of life that would have sufficed our ancestors for a century, and the exhaustion of the available supplies of energy, upon which the present era of the world relies, is already no longer a remotely distant prospect.
So long as the world was supposed to be six days older than man, and man a creature of the last 6000 years, the idea that we were “the first that ever burst" into the silent sea of science was pardonable enough. Possibly we were not. Just as no one would feel qualified to write a history of this country from materials gleaned from the newspapers of the present century, so no one ought to be so bold as to attempt to write a history of the human race from such written records as now exist, the most ancient of which go back to a time when the race was quite inappreciably younger than it is to-day. Neither is there any very valid ground for the belief that the startling advance civilisation had made in the past hundred or so years is in any way the climax or natural culmination of the slow and by no means even continuous progress previously. It seems rather a sudden forward leap apparently unconnected with and certainly not culminating necessarily out of the periodic ebb and flow of human fortune of which history tells. It is the work of a mere handful of men. The mass probably are little more scientific to-day than they were two thousand years ago, and this being the case, the advance does not appear to be the inauguration of the millennium, nor, indeed, of any other prolonged period of stable régime. Nothing but the most sublime egoism, the unconscious constitutional disability of the natural man to conceive of a universe not revolving around himself, can make
it appear improbable that what occurred so suddenly and mysteriously in the past few centuries of recorded history may not have occurred before, not once but perhaps many times during the vastly longer period of which no record has yet been interpreted. It is only right to consider the possibility that the command exercised over Nature in the twentieth century may have been attained, possibly exceeded, previously.
However that may be, however slender may be the justification for such a view, and still more however fanciful it may seem to seek that justification in the rigmarole of alchemical charlatans of the Middle Ages, the fact remains that science to-day would ascribe to the problem of the ultimate constitution of matter, and the practical achievement of the problem of the transmutation of the elements, an importance and significance that cannot but be flattering to the instincts of the human mind over which these problems have for so long exerted a most powerful fascination.
Twenty years ago not a single valid fact was known to science about transmutation. To-day we may watch it going on, in the case of certain elements, spontaneously before our eyes, as it seems to have been going on, all unsuspected, from the beginning of time.
But till 1896 the universal experience of physical and chemical science was that the atoms of the chemical elements are the ultimate constituents out of which matter is built up and, in all processes then known and in every kind of change that matter undergoes, these remain unchanged and unchangeable. What did Clerk Maxwell say? The words of his British Association address at Bradford in 1873 have often been quoted, but they are so true, not only of the knowledge of his day,
but are still true of all processes known before the fateful year 1896, that they may be recalled again :“Natural causes, as we know, are at work which
w tend to modify, if they do not at length destroy, all the arrangements and dimensions of the earth and the whole solar system. But though in the course of ages catastrophes have occurred and may yet occur in the heavens, though ancient systems may be dissolved and new systems evolved out of their ruins, the molecules 1 out of which these systems are built — the foundation stones of the material universe-remain unbroken and unworn."
Modern chemistry has at hand incomparably more powerful methods of experiment than were known to the alchemist. But the foundation stones of the material universe still remained unbroken and unworn.
After having been attacked without success by the alchemist with fanatical fervour and devotion, after having eluded the utmost efforts of the chemist to change them, until at last he had accepted his defeat as the firm basis on which to build his science, the eighty or so elements, that had been discovered and recognised, possessed a reputation for permanence and unchangeability that was unique in the whole universe of reality. Thus far and no further into the analysis of matter experiment had penetrated. Beyond there was nothing but speculation and imagination, plenty of both, but not of much value in science, apart from experimental knowledge, and least of all, perhaps, in favour with the "sceptical chemist.” He knew the elements as a shepherd is supposed to know his flock, their properties, the
i Clerk Maxwell was a physicist. If he had been a modern chemist he would have used the word atoms where he uses molecules.
THE PERIODIC LAW
compounds they form in such wealth and variety, their spectra, and the relative weights of their atoms, down to the merest minutiæ and with an accuracy unsurpassed in quantitative science.
He discovered the most curious family resemblances between them, some being so similar in their whole character and so regular even in their differences that no discipline of the imagination could entirely suppress the private question, "What are they?” even though the memory of those early heresies about transmutation and the unity of matter made it bad form to romance about them. Lastly, he made, when he put out the elements in the order of the relative weights of their atoms-beginning with hydrogen, the lightest atom, and ending with uranium, the heaviest—a sweeping generalisation about them known as the Periodic Law. Essentially this is that nearly the whole of the properties of the elements are periodically recurring functions of their atomic weights. The tenth element in the list has a close family resemblance to the second, the eleventh to the third, the twelfth to the fourth, and so on to the seventeenth which is like the ninth. The eighteenth is like the second and tenth, the nineteenth like the third and eleventh. Hydrogen, the first element, stands alone and has no analogues. After the twenty-second element, titanium, a change in the nature of the periodicity occurs, which becomes more complex. Another very abrupt change occurs at the fifty-sixth element, barium, when the rare-earth elements commence. These, the next thirteen or fourteen elements, all resemble one another with extreme closeness, in direct contradiction to what occurs with the elements both before and after them in the list. At the seventy-third element, tantalum, the law departed from at the fifty-sixth element is reverted to again