[110] Sir WILLIAM RAMSAY and FREDERICK SODDY: “Experiments in Radioactivity and the Production of Helium from Radium,” _Proceedings of the Royal Society of London_, vol. lxxii. (1903), pp. 204 _et seq._ [111] E. RUTHERFORD, F.R.S., and T. ROYDS, M.Sc.: “The Nature of the α-Particle from Radio-active Substances,” _Philosophical Magazine_ [6], vol. xvii. (1909), pp. 281 _et seq._ Nature of this Change. § =95.= Here, then, for the first time in the history of Chemistry, we have the undoubted formation of one chemical element from another, for, leaving out of the question the nature of the emanation, there can be no doubt that radium is a chemical element. This is a point which must be insisted upon, for it has been suggested that radium may be a compound of helium with some unknown element; or, perhaps, a compound of helium with lead, since it has been shown that lead is probably one of the end products of the decomposition of radium. The following considerations, however, show this view to be altogether untenable: (i.) All attempts to prepare compounds of helium with other elements have failed. (ii.) Radium possesses all the properties of a chemical element; it has a characteristic spectrum, and falls in that column in the Periodic Table with those elements which it resembles as to its chemical properties. (iii.) The quantity of heat liberated on the decomposition of the emanation is, as we have already indicated, out of all proportion to that obtained even in the most violent chemical reactions; and (iv.) one very important fact has been observed, namely, that the rate of decay of the emanation is unaffected by even extreme changes of temperature, whereas chemical actions are always affected in rate by changes of temperature. It will also be advisable, perhaps, to indicate some of the differences between helium and the emanation. The latter is a heavy gas, condensable to a liquid by liquid air (recently it has been solidified[112]); whereas helium is the lightest of all known gases with the exception of hydrogen and has been liquefied only by the most persistent effort.[113] The emanation, moreover, is radioactive, giving off α-particles, whereas helium does not possess this property. [112] By Ramsay. See _Proceedings of the Chemical Society_, vol. xxv. (1909), pp. 82 and 83. [113] By Professor Onnes. See _Chemical News_, vol. xcviii. p. 37 (July 24, 1908). Is this Change a true Transmutation?