The Significance of “Allotropy.”
§ 102. A very suggestive argument for the transmutation of the metals was put forward by Professor Henry M. Howe, LL.D., in a paper entitled “Allotropy or Transmutation?” read before the British Association (Section B), Sheffield Meeting, 1910. Certain substances are known which, although differing in their physical properties very markedly, behave chemically as if they were one and the same element, giving rise to the same series of compounds. Such substances, of which we may mention diamond, graphite and charcoal (e.g., lampblack)—all of which are known chemically as “carbon”—or, to take another example, yellow phosphorus (a yellow, waxy, highly inflammable solid) and red phosphorus (a difficultly-inflammable, dark red substance, probably possessing a minutely crystalline structure), are, moreover, convertible one into the other.[127] It has been customary to refer to such substances as different forms or allotropic modifications of the same element, and not to regard them as being different elements. As Professor Howe says, “If after defining ‘elements’ as substances hitherto indivisible, and different elements as those which differ in at least some one property, and after asserting that the elements cannot be transmuted into each other, we are confronted with the change from diamond into lampblack, and with the facts, first, that each is clearly indivisible hitherto and hence an element, and, second, that they differ in every property, we try to escape in a circle by saying that they are not different elements because they do change into each other. In short, we limit the name ‘element’ to indivisible substances which cannot be transmuted into each other, and we define those which do transmute as ipso facto one element, and then we say that the elements cannot be transmuted. Is not this very like saying that, if you call a calf’s tail a leg, then a calf has five legs? And if it is just to reply that calling a tail a leg does not make it a leg, is it not equally just to reply that calling two transmutable elements one element does not make them so?
[127] Diamond is transformed into graphite when heated by a powerful electric current between carbon poles, and both diamond and graphite can be indirectly converted into charcoal. The artificial production of the diamond, however, is a more difficult process; but the late Professor Moissan succeeded in effecting it, so far as very small diamonds are concerned, by dissolving charcoal in molten iron or silver and allowing it to crystallise from the solution under high pressure. Graphite was also obtained. Red phosphorus is produced from yellow phosphorus by heating the latter in absence of air. The temperature 240-250° C. is the most suitable; at higher temperatures the reverse change sets in, red phosphorus being converted into yellow phosphorus.
“Is it philosophical to point to the fact that two such transmutable elements yield but a single line of derivatives as proof that they are one element? Is not this rather proof of the readiness, indeed irresistibleness, of their transmutation? Does not this simply mean that the derivativeless element, whenever it enters into combination, inevitably transmutes into its mate which has derivatives?”[128]
[128] Professor Henry M. Howe, LL.D.: “Allotropy or Transmutation.” (See The Chemical News, vol. cii. pp. 153 and 154, September 23, 1910.)
According to the atomic theory the differences between what are termed “allotropic modifications” are generally ascribed to differences in the number and arrangement of the atoms constituting the molecules of such “modifications,” and not to any differences in the atoms themselves. But we cannot argue that two such “allotropic modifications” or elements which are transmutable into one another are one and the same element, because they possess the same atomic weight, and different elements are distinguished by different atomic weights; for the reason that, in the determination of atomic weights, derivatives of such bodies are employed; hence, the value obtained is the atomic weight of the element which forms derivatives, from which that of its derivativeless mate may differ considerably for all we know to the contrary, if we do, indeed, regard the atomic weights of the elements as having any meaning beyond expressing the inertia-ratios in which they combine one with another.
If we wish to distinguish between two such “allotropic modifications” apart from any theoretical views concerning the nature and constitution of matter, we can say that such “modifications” are different because equal weights of them contain, or are equivalent to, different quantities of energy,[129] since the change of one “form” to another takes place only with the evolution or absorption (as the case may be) of heat.[130] But, according to modern views regarding the nature of matter, this is the sole fundamental difference between two different elements—such are different because equal weights of them contain or are equivalent to different quantities of energy. The so-called “allotropic modifications of an element,” therefore, are just as much different elements as any other different elements, and the change from one “modification” to another is a true transmutation of the elements; the only distinction being that what are called “allotropic modifications of the same element” differ only slightly in respect of the energy they contain, and hence are comparatively easy to convert one into the other, whereas different elements (so called) differ very greatly from one another in this respect, whence it is to be concluded that the transmutation of one such element into another will only be attained by the utilisation of energy in a very highly concentrated form, such as is evolved simultaneously with the spontaneous decomposition of the radium emanation.
[129] For a defence of the view that chemical substances may be regarded as energy-complexes, and that this view is equally as valid as the older notion of a chemical substance as an inertia-complex, i.e., as something made up entirely of different units or atoms each characterised by the possession of a definite and constant weight at a fixed point on the earth’s surface, see an article by the present writer, entitled “The Claims of Thermochemistry,” Knowledge and Scientific News, vol. vii. (New Series), pp. 227 et seq. (July, 1910).
[130] In some cases the heat change accompanying the transformation of an element into an “allotropic modification” can be measured directly. More frequently, however, it is calculated as the difference between the quantities of heat obtained when the two “forms” are converted into one and the same compound.