DISSOCIATION, or DISASSOCIATION, a word belonging to the nomenclature of chemistry, first adopted by Henry St. Clair Deville to express the influence of heat in the decomposition of compound bodies. In a paper presented to the French institute, 1857, he says that "by selecting a proper compound and heating it sufficiently, the dis tance between the molecules can be increased to such extent that they will separate into their elementary conditions." He holds that water may be thus dissociated into its constituent elements at the temperature of melted silver. Deville placed a tube of porous porcelain within a tube of glass, and provided each with a separate outlet. He passed hydrogen through the inner tube, and carbonic acid through the annular space; both the gases passed through the pores of the septum, and a combustible gas issued from the carbonic acid tube. Thus far the experiment was not new. He now placed the tubes in a furnace heated to between 1000° and 1300° C., and substituted steam fOr the hydrogen of the inner tube. Part of the steam was decomposed, the hydrogen passing through the porous matter to the outer tube, and a corresponding portion of carbonic acid entering the inner tube by the same route. Some hydroden was lost by
combining with oxygen of the carbonic acid, yieldino. CO From the inner tube came steam, carbonic acid, and oxygen, from which the oxygen was easily isolated; from the outer tube came steam, carbonic acid, carbonic oxide, and hydrogen, from which the hydrogen was also isolated. If the carbonic acid of the process were derived from the furnace which furnished the heat, and the steam were generated by the same heat, there results from the heating of water in this apparatus a certain quan tity of separated oxygen and hydrogen, which might be used for the production of light and heat. By a modification of this process, sulphurous acid was separated, at 1200° C., into sulphur and anhydrous sulphuric acid; hydrochloric acid into hydrogen and chlo rine; carbonic oxide into carbon and carbonic acid; and carbonic acid into carbonic oxide and oxygen. The economic value of this discovery is yet a problem. Lamy has applied it to the preparation of a pyrometer for showing high temperatures.