32 SODDY, Evolution of Matter by Radio-active Elements. 



emanation in hours, and is therefore about 10,000 calories. 

 The volume as we have seen is a cubic millimetre. The 

 energy emitted by a cubic centimetre of emanation during 

 its complete change is therefore 10^ calories. This is a 

 purely experimental result, and is independent of all hypo- 

 thesis. The energy liberated on explosion by a cubic 

 centimetre of hydrogen and oxygen in the proportion 

 required to form water, is about two calories. The energy 

 of the disintegration of the radium emanation is thus 

 five million times greater than the energy of explosion 

 of an equal volume of hydrogen and oxygen. This 

 furnishes perhaps the most convincing proof of the argu- 

 ment that the energy of radio-activity cannot possibly be 

 derived from the outside, or indeed from any other source 

 than from the internal energy of the atom. 



The above concludes the list of experimental advances 

 that have been made since the inception of the theory of 

 atomic disintegration. A few outstanding consequences 

 and predictions remain to be experimentally verified, and 

 some of these merit a brief consideration. It will be 

 convenient to review the two main lines along which our 

 knowledge of atomic disintegration has advanced. The 

 transition-forms are recognised by their rapid rate of 

 change, or more strictly by the large energy effects, 

 relative to the actual quantity involved, which accompany 

 the change. The ultimate products may be studied 

 because they continuously accumulate, and if sufficient 

 time is allowed or sufficient material is employed, will 

 attain to quantities great enough to allow of direct 

 recognition. The question arises as to whether a simple 

 rigid line of demarcation between the two classes is 

 allowable. In the table (p. 17) the known metabolons 

 were arranged in the order of their average lives. The 

 average lives in the case of uranium and thorium are 



