
330 RADIO-ACTIVE PROCESSES 
first, when the quantity of emanation in the tube was at its 
maximum. In addition, the diffusion experiments, already dis- 
cussed, point to the conclusion that the emanation is of high 
molecular weight. There can thus be no doubt that the helium is 
derived from the emanation of radium in consequence of changes 
of some kind occurring in it. 
In order to explain the presence of helium in radium on ordi- 
nary chemical lines, it has been suggested that radium is not 
a true element, but a molecular compound of helium with some 
substance known or unknown. The helium compound gradually 
breaks down, giving rise to the helium observed. It is at once 
obvious that this postulated helium compound is of an entirely 
different character to any other compound previously observed 
in chemistry. Weight for weight, it emits during its change an 
amount of energy at least one million times greater than any 
molecular compound known (see section 205). In addition, it must 
be supposed that the rate of breaking up of the hehum compound 
is independent of great ranges of temperature—a result never 
before observed in any molecular change. The helium compound 
in its breaking up must give rise to the peculiar radiations and 
also pass through the successive radio-active changes observed in 
radium. 
In order to explain the production of helium and radio-activity 
on this view, a unique kind of molecule must thus be postulated— 
a molecule, in fact, which is endowed with every single property 
which on the disintegration theory is ascribed to the atom of the 
radio-elements. On the other hand, radium as far as it has been 
examined, has fulfilled every test required for an element. It has 
a well-marked and characteristic spectrum, and there 1s no reason 
to suppose that it is not an element in the ordinarily accepted 
sense of the term. 
On the theory that the radio-elements are undergoing atomic 
disintegration, the helium must either be considered to exist 
within the radium atom, or else to be formed from its constituent 
corpuscles during the process of disintegration. The theory that 
the heavy atoms are all built up of some simple fundamental 
unit of matter or protyle has been advanced at various times by 
many prominent chemists and physicists. Prout’s hypothesis, 

