576 Prof. Rutherford and Mr. Soddy 



practically all of the emanation comes off very suddenly at a 

 temperature not much more than one degree above that at 

 which only 2 per cent, has volatilized. The general indication 

 o£ all the experiments, considered together, is to show that 

 the condensed emanation possesses a true vapour-pressure, 

 and that the emanation commences to volatilize slowly two 

 or three degrees below the temperature of rapid volatilization 

 even when the process occurs in a stationary atmosphere. 

 The emanations therefore possess the usual properties possessed 

 by ordinary gaseous matter, in so far as the phenomena of 

 volatilization and condensation are concerned. It was shown 

 in a recent paper that they also possess the property possessed 

 by oases of being occluded by solids under certain conditions. 

 These new properties, taken in conjunction with the earlier dis- 

 covered diffusion phenomena, characteristic of the radioactive 

 emanations, leave no doubt that the latter must consist of 

 matter in the gaseous state. 



McGill University, Montreal, 

 March 9, 1903. 



LX. Radioactive Change. By 1 ^. Rutherford, M.A., D.Sc> 

 Macdonald Professor of Physics, McGill University, and 

 F. Soddy, M.A. (Oxon.). 



Contents. 



I. The Products of Radioactive Change, and their Specific Material 



Nature. 

 II. The Synchronism between the Change and the Radiation. 



III. The Material Nature of the Radiations. 



IV. The Law of Radioactive Change. 

 V. The Conservation of Radioactivity. 



VI. The Relation of Radioactive Change to Chemical Change. 

 VII. The Energy of Radioactive Change and the Internal Energy of 

 the Chemical Atom. 



§ 1. The Products of Radioactive Change and their 

 Specific Material Nature. 



IX previous papers it has been shown that the radioactivity 

 of the elements radium, thorium, and uranium is main- 

 tained by the continuous production of new kinds of matter 

 which possess temporary activity. In some cases the new 

 product exhibits well-defined chemical differences from the 

 element producing it, and can be separated by chemical 

 processes. Examples of this are to be found in the removal 

 of thorium X from thorium and uranium X from uranium. 

 In other cases the new products are gaseous in character, and 



* Communicated bv the Authors. 



