VII] CONTINUOUS PRODUCTION OF RADIO-ACTIVE MATTER 193 
with sulphuric acid and ignition to a white heat. The oxide so 
obtained was spread on a plate, but no change of its activity was 
observed with time, showing that in this case the rate of produc- 
tion was independent of molecular state. This,method, which is 
limited in the case of thorium, may be applied generally to the 
uranium compounds where the results are not complicated by the 
presence of an emanation. 
No differences have yet been observed in the recovery curves 
of different thorium compounds after the removal of Th X. For 
example, the rate of recovery is the same whether the precipitated 
hydroxide is converted into the oxide or into the sulphate. 
127. Disintegration hypothesis. In the discussion of the 
changes in radio-active bodies, only the active products Ur X 
and Th X have been considered. It will, however, be shown later 
that these two products are only examples of many other types of 
active matter which are produced by the radio-elements, and that 
each of these types of active matter has definite chemical as well 
as radio-active properties, which distinguish it, not only from the 
other active products, but also from the substance from which it 
is produced. 
The full investigation of these changes will be shown to verify 
in every particular the hypothesis that radio-activity is the ac- 
companiment of chemical changes of a special kind occurring in 
matter, and that the constant activity of the radio-elements is 
due to an equilibrium process, in which the rate of production of 
fresh active matter balances the rate of change of that already 
formed. 
The nature of the process taking place in the radio-elements, 
in order to give rise to the production at a constant rate of new 
kinds of active matter, will now be considered. Since in thorium 
or uranium compounds there is a continuous production of radio- 
active matter, which differs in chemical properties from the parent 
substance, some kind of change must be taking place in the radio- 
element. This change, by which new matter is produced, is very 
different in character from the molecular changes dealt with in 
chemistry, for no chemical change is known which proceeds at the 
same rate at the temperatures corresponding to a red heat and 
Iie Teck. as 
