Chemical Element. In the present state of science this term admits of no very precise definition. In general the word element is applied to any substance which has as yet never been decomposed into constituents or transmuted into any other substance, and which differs in some essential property from every other known body. Several elements indeed occur under two or more allotropic conditions, in which states they exhibit different properties. These modifications are however mutually convertible into each other, and are regarded as mere varieties of one and the same substance. As now used, the term element does not possess in any degree the absolute signification at one time attached to it, none of the elements now admitted being regarded as proved to be primary principles of matter, although it is not impossible that some of them may be such. Provisionally, all substances which have hitherto resisted every method of analysis that has been applied to them - all, in short, which cannot be proved to be compound - are called elements. The number is increasing, some having been discovered by means of the spectrum analysis : caesium and rubidinum by Bun-sen and Kirchhoff in 1860, thallium by Crookes in 1861, and indium by Reich and Richter in 1863. There are now 64 admitted in the list.
Whether the number will continue to increase, or whether it may be diminished by the discovery that some of them are different conditions of the same substance, of course cannot be foretold. Some of these so-called elements are exceedingly rare, and have been seen but by few persons besides their discoverers. Two have been proposed which are not included in the list, dianium and norium, their existence being uncertain, and their properties not well known. The great mass of the matter of which the world is composed consists of about 30 elements, the remaining 34 being comparatively rare. - For a complete catalogue of the elements, see Equivalent.