nized compounds are formed by the union together of two or more supposed elements; and no revelations concerning the nature of the latter can well disturb that established knowledge. However we may speculate, the experimentally-ascertained facts will remain unaltered. They may receive slightly different theoretical interpretations, without having their practical bearings changed in the least degree.
The prevalent view of the subject, that the elements are elementary, is held by philosophical chemists in a purely provisional way. We need a convenient working hypothesis, and these sixty-three substances are elements for aught we absolutely know to the contrary. As far as we are at present experimentally concerned, then, we call them elements, bearing always in mind the possibility that they may be compounds. They have never been decomposed; we have no means adequate to their analysis; not one of them can be obtained from materials in which it does not already exist. But all this evidence is only negative. How do we know but that some future discovery may render possible the decomposition of these supposed elements? Shall we assert positively that we have reached the ultimate analysis, and may never hope to go any farther? Obviously, so definite a statement would be unjustifiable, and no sane chemist would venture to make it. The uncertainty of the subject may well be illustrated by a reference to chemical history. At the beginning of the present century the alkalies and alkaline earths were thought to be elements. They were not decomposable by any means then known, so that the supposition was perfectly fair. A very few years passed away, the galvanic battery was brought into use, and presently it was found that each of these bodies was a compound, containing a metal united with oxygen. Perhaps a similar advance in our knowledge may demonstrate the possibility of decomposing many of the substances now regarded as elementary. Such a discovery might work in either one of three ways. It might largely increase the number of supposed elements, by dividing each one into two or more new bodies. It might reduce the number by proving that our elements were formed by the union, in various proportions, of only a very few simpler substances, Or it might demonstrate the unity of matter, just as recent science has demonstrated the unity of force, and give us only one true element underlying all material forms. Such a culmination of our knowledge would be grand, indeed!
The evidence, then, upon which we assert the elementary nature of the fifty metals and thirteen non-metals, is very incomplete. On this side of the question there is really no other important testimony, save that just cited. Arguing from our present inability to decompose certain bodies, we assume for convenience that they are indecomposable. Now let us see what there is in favor of the opposite view.
One of the first things learned by the student in chemistry is, that the so-called elements are readily classifiable into a few natural groups.