theory. The illustrious Boyle, who does not seem to have been aware of the doctrine of Beccher and Stahl, although it was promulgated before his death, performed a very remarkable experiment, which, had he subjected to mature reflection, might have led to the discovery of oxygen gas, and to an overthrow of the phlogistic theory. Having fused some tin in an open glass vessel, and retained it for some time at the melting temperature, he allowed it to cool, and weighed the result, which was now found to be heavier than the original tin. This experiment is merely cited by Boyle with the view of proving the materiality of heat, and, as interpreted by him, is, in so far, inconsistent with the phlogistic theory, that, according to Boyle, the calx or oxide of tin was not tin minus something, i. e., the imaginary phlogiston, but plus something,-i. e., heat, or the matter of heat. * * In reference to this experiment of Boyle, Professor Johnstone has made the following pertinent remark :-"How much the progress of science depends on the mode in which phenomena are interpreted by the first observers, is strikingly illustrated in the case of certain experiments of Robert Boyle. He observed that, when copper, lead, iron, and tin, were heated to redness in the air, a portion of calx was formed, and there was a constant and decided increase of weight (Experiments to make fire and flame ponderable. London, 1673). This experiment he repeated with lead and tin in glass vessels, hermetically sealed, and found still an increase of weight; but observed further, that when the sealed neck of the retort was broken off, the external air rushed in with a noise' (Additional experiments, No. V., and a discovery of the perviousness of glass Very soon after the time of Stahl, the gain of weight acquired by substances after combustion had become a phenomenon so generally known, that such as advocated the phlogistic theory were obliged to devise some other explanation for the phenomenon. Accordingly, the hypothesis was assumed, that phlogiston, in itself, possessed the quality of levity; hence, that its presence must confer the property of lightness; indeed, the phlogistic theory was held with extraordinary pertinacity, until the discovery of oxygen by Priestley rendered its further acceptation untenable. In the year 1774, Dr. Priestley, being at Paris, demonstrated to Lavoisier that oxygen gas could be extracted from red oxide of mercury, a demonstration which caused Lavoisier to become a powerful advocate to ponderable parts of flame,-Exp. iii.). From this he reasoned correctly, that in calcination, the metal lost nothing by drying up, as was generally supposed, or that if it did, 'by this operation it gained more weight than it lost.'-Coroll. ii. But this increase of weight he attributed to the fixation of heat, stating it as 'plain that igneous particles were trajected through the glass,' and that 'enough of them to be manifestly ponderable did permanently adhere.' Had he weighed the sealed retort before he broke it open, he must have concluded that the metal had increased in weight at the expense of the enclosed air. He stood, in fact, at the very brink of the pneumatic chemistry of Priestley; he had in his hand the key to the great discovery of Lavoisier. How nearly were those philosophers anticipated by a whole century, and the long interregnum of phlogiston prevented! On what small oversights do great events in the history of science, as of nations, depend!”—Johnstone, Trans. Brit. Ass. vol. 7, p. 163. of the anti-phlogistic doctrine. In 1785, Barthollet also adopted the new view. Fourcroy and Guyton de Morveau then joined the ranks, and, from this time forward, the anti-phlogistic theory continued to advance in public estimation. Its universal adoption may be said to close the second great epoch of chemical progress. III. THIRD CHEMICAL EPOCH-DISCOVERIES AND GENERALISA TION OF LAVOISIER-NEW CHEMICAL NOMENCLATURE No sooner was the phlogistic theory overthrown, than Lavoisier and his associates began to furnish that nomenclature of chemical bodies which, in all its essential particulars, still remains, although inconsistent with many facts at this time known. The nature and outline of this nomenclature are so well known as to render unnecessary any remarks on the subject. The nomenclature is one of great simplicity and beauty, but affords a striking instance of the disadvantage resulting from the adoption of theories as the ground-work of systematic arrangements. By a too hasty generalisation of a limited number of facts, the substance oxygen was assumed to be the universal former of acids, and hence its name. This assumption of the universal acidifying quality of oxygen, is a fault which lies at the basis of Lavoisier's nomenclature, and prejudices its structure. The greater number of acids, it is true, contain oxygen, but many are without it-and even those which contain it cannot logically be said to manifest the quality of acidity on account of any one special element in their composition. The theory of Lavoisier affords, when contemplated in all its bearings, study for the psychologist no less than the chemist; characterising well that extraordinary period when a whole nation, convulsed to its very depths, shook off the trammels of political feudalism and scientific precedent, obliterating, with one fell swoop, theories, ordinances, institutions-daring to elevate human reason into a false infallibility. The nomenclature of Lavoisier may be designated as simple, beautiful, and arrogant. Not contented with reducing to classification members and species then known, it provided also for the classification of whole genera yet to be discovered, on the assumption of their conforming to the limited number of facts then known. This is its greatest fault. It is now time to advert to that interesting reduction of chemical phenomena to the form of mathematical expression which constitutes the science of stochiometry, and in which England, by the agency of Dalton, has appeared so honourably. There can scarcely be a more interesting matter of contemplation to the philosopher, than the one involved in a comparison of inductive results with dawning speculations on similar subjects of imaginative writers. Wide, even to infinity, as may appear at a first glance the space dividing imaginative speculations from induced facts, yet alliances have been frequently seen to exist where they might least have been expected. |