Sainte-Claire Deville began his experimental work in 1841 with investigations on oil of turpentine and balsam of tolu, in the course of which he discovered the hydro-carbon toluene. But he soon abandoned organic chemistry, and his most important work was in inorganic and thermal chemistry. In 1850 he discovered anhydrous nitric acid, a substance interesting not only in itself but as the first obtained of an important group, the so-called “anhydrides” of the monobasic acids. In 1855 he succeeded in obtaining aluminium in mass. This metal, of which clay is the hydrated silicate, is of course one of the most abundant of metals, but was not obtained in the metallic state until Wohler in 1827 decomposed its chloride by means of potassium. The aluminium thus prepared was in the form of a fine powder, and, although the isolation of the metal was of great theoretical importance, there did not seem much prospect of a practical application of the discovery. In 1845 Wohler returned to the subject and by using large quantities of material obtained small globules of an obviously metallic character. Deville, who knew only Wohler’s paper of 1827, set to work to prepare aluminium, not for the sake of the metal itself, but with the view of procuring by the action of aluminium on chloride of aluminium a lower chloride from which a series of new compounds corresponding to the ferrous salts might be obtained. He did not succeed in this, but he did succeed in producing globules of aluminium of considerable size. This led him to perfect the process, and ultimately he devised a method by which aluminium could be prepared on a large scale. The first use to which he put the metal was to make a medal with the name of Wohler and the date 1827. In connexion with the preparation of aluminium may be mentioned Deville’s investigations, partly with Wohler, into the allotropic forms of silicon and boron.

Along with Debray, Deville studied the platinum metals; their object was on the one hand to prepare the six metals in a state of purity and on the other to obtain a suitable metal for the standard metre. In the course of these investigations large quantities of platinum and of the alloys of platinum and iridium were fused and cast, and the methods used for obtaining the necessary high temperatures were applied to the fusion of other refractory metals, such as cobalt, nickel, chromium, and manganese.

Along with Troost, Deville devised a method for determining the density of vapours at very high temperatures and applied it to the cases of sulphur, selenium, tellurium, zinc, cadmium, and many other substances boiling at temperatures up to 1400° C. The interesting and important results have been already described (see Chemistry and Molecule). Deville made a large number of ingenious experiments on the artificial production of minerals. Among these may be specially mentioned the formation of apatite and isoinorphous minerals and of crystallized oxides. Deville and Caron found that when the vapour of a metallic fluoride acts on fused boracic acid the fluorine and the oxygen change places, a metallic oxide remains in crystals, while the gaseous fluoride of boron escapes. In this way they prepared corundum (crystallized oxide of aluminium) and sapphire, ruby and emerald; coloured forms of corundum were obtained by mixing small quantities of fluoride of chromium with the fluoride of aluminium. Another method discovered by Deville for the preparation of crystallized oxides is of great interest. When an amorphous oxide—such as amorphous ferric oxide—is heated to redness and exposed to a slow current of hydrochloric acid gas, it gradually changes into a crystalline oxide of the same composition. In this way Deville obtained haematite, tinstone, periclase, and other crystalline oxides. This conversion of an amorphous into a crystalline substance without change of composition, by the action of a gas (in this case hydrochloric acid) which itself undergoes no change, is one of those mysterious processes which used to be referred to a “catalytic force” or called “actions by contact”; like many such actions, this has been shown by Deville to belong to the same class of phenomena as dissociation.

This leads us to Deville’s greatest contribution to general chemistry. Many chemical actions have been long known which take place either in the one or the other sense according to certain conditions. For instance, if a tube containing metallic iron is heated to redness and steam passed through it, water is decomposed, black oxide of iron is formed, and hydrogen escapes. If, on the other hand, the tube is filled with black oxide of iron and hydrogen passed through, the oxide is reduced and water is formed. Both of these opposite changes occur at the very same temperature. Again, a solution of sulph-hydrate of potassium is completely decomposed by passing a current of carbonic acid gas through it for a sufficient time, sulphuretted hydrogen being given off and bicarbonate remaining in solution. But exactly the opposite happens if we begin with bicarbonate and pass sulphuretted hydrogen gas through it: carbonic acid gas escapes and the solution ultimately contains nothing but sulph-hydrate. An imperfect, unsatisfactory explanation of some of the phenomena of which these are examples was given by Berthollet; it remained for Deville to give a general theory and show their relation to such physical phenomena as hydrate of potassium, and of sulphuretted hydrogen on solution of bicarbonate of potassium. Equilibrium results when the pressures of the gases are in a certain ratio; if the equilibrium is disturbed chemical action takes place in the direction which tends to restore the equilibrium by reproducing the ratio of pressures.

The apparatus devised by Deville for detecting and measuring dissociation illustrates his remarkable ingenuity. We shall instance only one example in addition to those already mentioned.

One of the great difficulties in observing dissociation depends on its reversible character. A compound may indeed decompose when raised to a high temperature; but, if, as we cool it again, reunion occurs, it is not easy to prove that any chemical change took place, One of the ways in which Deville got over this difficulty was by the use of his “hot and cold tube.” Inside a porcelain tube he placed a metal tube of smaller diameter, so that their axes coincided, leaving an annular space between them. This annular space was closed at both ends, but, by means of side tubes near the ends, could be filled with any gas, or a current of gas could be passed through it. The porcelain tube was raised to a high temperature by being placed in a furnace, while the internal metal tube was kept cold by running water through it. By this means he proved the dissociation of carbonic acid gas, carbonic oxide, and sulphurous acid gas,—the carbon or sulphur being deposited on the outer wall of the cold internal tube, and thus kept at a temperature below that at which recombination could take place.

Deville’s observations on dissociation and his generalizations from them have a very direct bearing on the kinetic theory of gases, and it is a fact of interest in the history of science that Deville did not recognize the validity of that theory, Our estimate of the ingenuity, skill, and patience shown in his experimental work, and of the genius and sound judgment which directed his theoretical conclusions, is perhaps raised when we recollect that he was neither led in the first nor biassed in the second by ideas derived from the kinetic theory, and his hostile or at least neutral attitude towards it gives perhaps greater value to the evidence that his work has contributed to its soundness.

Deville’s works were published in the Annales de Chimie et de Physique and in the Comptes Rendus. He further published a volume, entitled De l'Aluminium; ses Propriétés, &c., Paris, 1859, and the lecture On Dissociation already referred to.