the same law as the emanation lost its activity. Ramsay and Collie found that the emanation had a new and definite spectrum similar in some respects to that of the argon group of gases.
There can thus be no doubt that the emanation is a transition substance with remarkable properties. Chemically it behaves like an inert gas and has a definite spectrum and is condensed by cold. But, on the other hand, the gas is not permanent, but disappears, and is changed into other types of matter. It emits during its changes about one million times as much energy as is emitted during any known chemical change.
From the similarity of the behavior of the emanation of thorium and actinium to that of radium, we may safely conclude that these also are new gases which have only a limited life and change into other substances.
The non-volatile products of the radioactive bodies can be dissolved in strong acids and show definite chemical behavior in solution. They can be partially separated by electrolysis and by suitable chemical methods. They can be volatilized by the action of high temperature and their differences in this respect can be utilized to effect in many cases a partial separation of successive products. There can be little doubt that each of these radioactive products is a transition substance possessing, while it lasts, some definite chemical and physical properties which serve to distinguish it from other products and from the parent element.
