After reciting the above facts he explains why he has ventured to take up a subject on which Gay Lussac was still engaged. The explanation was no doubt necessary; he had evidently not forgotten Gay Lussac’s intrusion into his own field of work on the occasion of the discovery of the metals of the alkalis. He first draws attention to the peculiarities of the combination of the new substance with silver; this, he shows, is markedly different from silver chloride. He then forms this compound synthetically; forms also the combination with potassium by direct union, and describes its properties; studies the action of chlorine on the new substance, and notes the formation of the yellow solid chloride and the mode of its decomposition by water; prepares a number of metallic compounds; studies the action of the new substance on phosphorus, the nature of the product, and its mode of decomposition by water, with formation of the white crystalline phosphonium iodide and hydriodic acid gas. By acting on this gas with potassium he shows that it yields half its volume of hydrogen and forms the same product as by the direct union of the alkali metal with the new substance. He further finds that this gas is formed when the new substance and hydrogen are passed through a heated tube; it has a very strong attraction for water, which dissolves it to a large extent, and the concentrated solution rapidly becomes tawny. When the new substance is treated with potash solution it forms the same product as by its direct union with potassium, together with a salt precisely similar to potassium hyper-oxymuriate, and which, like that salt, is decomposed when heated, with evolution of oxygen. He shows that the new substance is expelled from its compounds when these are heated with chlorine. He studies the nature of the black fulminating compound discovered by Desormes and Clement by acting on the new substance with solution of ammonia, and concludes that it is analogous to the detonating oil of Dulong. He attempts to determine the combining proportion of the new substance, on the assumption that its compounds are analogous to those of chlorine, but he has to admit that his experiments have been made upon quantities too small to afford exact results. Nevertheless they prove that the value is much higher than those of the simple inflammable bodies, and higher even than those of most of the metals. He further shows that the combination with hydrogen must be one of the heaviest elastic fluids existing.