Berzelius’s electro-chemical system, and the dualistic ideas associated with it, were of considerable service when applied to the inorganic branch of the science; but attempts to fit them to the facts of organic chemistry, which began to accumulate rapidly after the first quarter of the century, failed. Its inadequacy as a comprehensive generalisation became more and more manifest, and it eventually fell. In fact, it may be said to have received its death-blow by Davy’s discovery of the elementary nature of chlorine, and by the recognition of the fact that the acids do not necessarily contain oxygen. Davy and, later, Dulong made it obvious that, if any one element was to be regarded as the acidifying principle, it was hydrogen, and not oxygen; and, in a sense, this view ultimately prevailed in the recognition of the acids as salts of hydrogen. In France the study of electro-chemistry was undertaken by Gay Lussac and Thénard, largely owing to the action of the Emperor Napoleon, who furnished the funds for the construction of a powerful galvanic battery. The results were published, in 1811, under the title, _Recherches Physico-Chimiques, faites sur la Pile_, etc. Gay Lussac, whose name has already been mentioned as one of the discoverers of the Law of Combination of Gases, played a considerable part in the history of chemistry at this period. He was one of the earliest to appreciate the importance of Dalton’s generalisation, and to point out the significance of his own discovery in strengthening it. He was probably led, in the first instance, to the recognition of the law of gaseous combination by Berthollet’s work on the volumetric composition of ammonia gas, and by his own discovery—made in 1805, in conjunction with Humboldt, in the course of their analysis of atmospheric air—that one volume of oxygen combined with exactly two volumes of hydrogen to form water. The regularities thus indicated he found to be general: all gases which are capable of chemical union combine in simple proportions by volume, and the volume of the product, if a gas, always stands in some simple relation to the volumes of the constituents. =Joseph Louis Gay Lussac= was born in 1778, at Saint Leonard, studied chemistry in Paris, and was associated in chemical inquiry with Berthollet. As Eleve-Ingenieur in the École Nationale des Ponts et des Chaussées he began the experimental work in physics and chemistry upon which his fame rests. In 1804 he undertook, with Biot, a series of balloon ascents for the purpose of investigating the physics and chemistry of the upper regions of the atmosphere. In 1806 he became Professor of Chemistry at the École Polytechnique, and in 1832 Professor at the Jardin des Plantes. He was one of the chief assayers of the French Mint, and, as member of many commissions, exerted considerable influence in official circles. He died in 1850.