Argument from Prout’s Law.—The bearing of the hypothesis of Prout in relation to the evolution of the elements is first considered by Mr. Crookes. If that hypothesis were demonstrated it would show that the accepted elements are not co-equal, but have been formed by a process of expansion or evolution. According to this hypothesis the atomic weights of the elements are multiples by a series of whole numbers of the atomic weight of hydrogen. It is true that accurate determinations of the atomic weights of different elements do not by any means harmonise with the values which Prout’s Law requires; nevertheless the agreement in so many cases is so close that one can scarcely regard the coincidence as accidental.
The atomic weights have been recalculated with extreme care by Professor F. W. Clarke, of Cincinnati, and he says that “none of the seeming exceptions are inexplicable. In short, admitting half-multiples as legitimate, it is more probable that the few apparent exceptions are due to undetected constant errors than that the great number of close agreements should be merely accidental.” In reference to this suggestion of Professor Clarke, Mr. Crookes thinks that it places the matter upon an entirely new basis. For, suppose the unit atom to be not hydrogen, but some element of still lower atomic weight, say helium, an element supposed by many authorities to exist in the sun and other stellar bodies—an element whose spectrum consists of a single ray, and whose vapour possesses no absorbent power, which indicates a remarkable simplicity of molecular constitution. Granting that helium exists, all analogy points, says Mr. Crookes, to its atomic weight being below that of hydrogen; and here, then, we have the very element with atomic weight half that of hydrogen required by Professor Clarke as the basis of Prout’s Law.
Argument from the earth’s crust.—The probable compound nature of the chemical elements, Mr. Crookes thinks, is better shown by a consideration of certain peculiarities in their occurrence in the earth’s crust. “We do not,” he says, “find them evenly distributed throughout the globe. Nor are they associated in accordance with their specific gravities: the lighter elements placed on or near the surface, and the heavier ones following serially deeper and deeper. Neither can we trace any distinct relation between local climate and mineral distribution. And by no means can we say that elements are always or chiefly associated in nature in the order of their so-called chemical affinities: those which have a strong tendency to form with each other definite chemical combinations being found together, whilst those which have little or no such tendency exist apart. We certainly find calcium as carbonate and sulphate, sodium as chloride, silver and lead as sulphides; but why do we find certain groups of elements, with little affinity for each other, yet existing in juxtaposition or commixture?”
As instances of such grouping he mentions nickel and cobalt; the two groups of platinum metals; and the so-called “rare earths,” existing in gadolinite, samarskite, &c. Why, then, are these elements so closely associated? What agency has brought them together? It cannot be considered that nickel and cobalt have been deposited in admixture by organic agency; nor yet the groups of iridium, osmium, and platinum; ruthenium, rhodium, and palladium.
These features, Mr. Crookes thinks, seem to point to their formation severally from some common material placed in conditions in each case nearly identical.
Argument from the compound radicals.—A strong argument in favour of the compound nature of the elements, Mr. Crookes thinks, is derived from a consideration of their analogy to the compound radicals, or pseudo-elements as they might be called. It may be fairly held that if a body known to be compound is found behaving as an element, this fact lends plausibility to the supposition that the elements are not absolutely simple. From a comparison of the physical properties of inorganic with those of organic compounds, Dr. Carnelley concluded that the elements, as a whole, are analogous to the hydrocarbon radicals. This conclusion, if true, he added, should lead to the further inference that the so-called elements are not truly elementary, but are made up of at least two absolute elements, which he named provisionally A and B.
In Dr. Carnelley’s scheme all the chemical elements save hydrogen are supposed to be composed of two simpler elements, A = 12 and B = 2. Of these he regards A as a tetrad identical with carbon, and B as a monad of negative weight; perhaps the ethereal fluid of space. His three primary elements are, therefore, carbon, hydrogen, and the ether.
Argument from polymerisation.—The polymeristic theory of the genesis of the chemical elements propounded by Dr. Mills falls next to be considered.
It has been suggested by Dr. E. J. Mills that the pristine matter was once in an intensely heated condition, and that it has reached its present state by a process of free cooling, and that the elements, as we now have them, are the result of successive polymerisations. Chemical substances in cooling naturally increase in density, and we sometimes observe that as the density increases there are critical points corresponding to the formation of new and well-defined substances. The bodies thus formed are known as polymers. From a study of the classification of the elements Mr. Mills is of opinion that the only known polymers of the primitive matter are arsenic, antimony, and perhaps erbium and osmium.
Argument from the Periodic Law.—Lastly a scheme of the origin of the elements, suggested to Mr. Crookes by consideration of Professor Reynolds’s method of illustrating the periodic law of Newlands, is discussed.