nents is not the only cause of the differences which distinguish compounds, but that the proportions in which these elements are united, and perhaps also the mode of their union, are other causes of these differences.
"Thus the whole doctrine of the pretended elements, or of the principles of things, or of their components, or of the compositions of different orders of compounds, is now reduced to conceptions as simple as they are precise. There are no hypotheses or useless distinctions or erroneous abstractions in the present ideas of chemists, and the obscurity which formerly reigned in this part of the science has wholly disappeared, and at the same time we have got rid of a source of vague and endless discussions. We have no longer to dwell in the schools on useless questions about a primitive matter and its relations; on whether there are four, three, two, or only a single element; on the pretended relations of the elements among themselves; on their transformation, or on the change of one into another. All these dreams of a sham speculative philosophy have vanished before the facts discovered by the experimental method; and the five propositions enunciated above, as simple as they are true, are data on which we can now securely build."
Turning, now, to Lavoisier's own "Traité élémentaire de Chimie," which must be regarded as the "Principia" of chemical science, we find, for the first time in the history of the subject, a list of twenty-five definite substances distinguished as elementary on the sole basis that they had as yet never been analyzed. This list is given in the first column of the table which we reproduce in translation on the following page, on account of its very great historical interest. Still, there is even here an obvious survival of Aristotle and the phlogiston theory, both in what the list includes and in what it omits. The first name on the list is caloric, and three of the other elements are the muriatic, fluoric, and boracic radicals, which, though not yet isolated, appear to Lavoisier so distinctly typified and foreshadowed that he does not hesitate to name them in this list. These radicals, it must be noticed, were radicals which, united to oxygen, would form respectively hydrochloric, hydrofluoric, and boracic acid, so that in the last case only were Lavoisier's expectations realized in the form which he expected. Indeed, the radical of muriatic acid, chlorine, was then a well-known substance, having been discovered by Scheele in 1774, but so little did it answer to the expected radical that it was regarded by Lavoisier as an oxide, and named by him "acide muriatique oxygéné," and under this name appears in this very table (translated oxidized muriatic acid). What we know as chlorine gas was classed by Lavoisier as the fourth degree of oxidation of his assumed muriatic radical, while muriatic acid itself was the
