x] RADIO-ACTIVE PROCESSES 337 
of X is 44 x 10-4, and on the maximum estimate 1°76 x 10~-> when 
1 year is taken as the unit of time. The total heat emission from 
1 gram of radium during its life thus les between 2 x 10° and 
5 x 10” gram-calories. The minimum estimate is probably nearer 
the truth than the maximum. The heat emitted in the union of 
hydrogen and oxygen to form 1 gram of water is about 4 x 10° 
gram-calories, and in this reaction more heat is given out for 
equal weights than in any other chemical reaction known. It is 
thus seen that the total energy emitted from 1 gram of radium 
during its changes is about one million times greater than that in- 
volved in any known molecular change. That matter is able, under 
special conditions, to emit an enormous amount of energy, 1s well 
exemplified by the case of the radium emanation. The total heat 
emission from the emanation released from 1 gram of radium, 
and from the secondary products, corresponds to about 10 
gram-calories, and this amount of heat is given out as a conse- 
quence of changes in a minute volume of gas. Taking the 
estimate that the volume of the emanation is 3 x 10-4 cubic 
centimetres at standard pressure and temperature, and its atomic 
weight about 200, it can be calculated that 1 gram of emanation 
gives out during its life about 10° gram-calories. Quite inde- 
pendently of any theory, a result of the same order of magnitude 
can be deduced from the experiments. 
Since the other radio-elements only differ from radium in the 
slowness of their change, the total heat emission from uranium 
and thorium must be of a similar high order of magnitude. There 
is thus reason to believe that an enormous store of latent energy 
is resident in the atoms of the radio-elements. This store of 
energy could not have been recognized if the atoms were not 
undergoing a slow process of disintegration. The energy emitted 
in radio-active changes may thus be supposed to be derived from 
the internal energy of the atoms. The emission of this energy 
does not disobey the law of the conservation of energy, for it is 
only necessary to suppose that, when the radio-active changes 
have ceased, the energy stored up in the atoms of the final 
products is less than that in the original atoms of the radio- 
elements. The difference between the energy originally possessed 
by the matter, which has undergone the change, and the final 
R. B.-A. 22 
