VA“e ee 
ri Lei’ 
oe 
216 RADIO-ACTIVE EMANATIONS [CH. 
It is evident that the physical properties of the thoria are 
much altered by intense ignition. The compound changes in 
colour from white to pink ; it becomes denser and also far less readily 
soluble in acids. In order to see if the emanating power could be 
regenerated by a cyclic chemical process, the de-emanated thoria 
was dissolved, precipitated as hydroxide and again converted into 
oxide. At the same time a specimen of the ordinary oxide was 
subjected to an exactly parallel process. The emanating power of 
both these compounds was the same and was from two to three 
times greater than that of ordinary thoria. 
Thus de-emanation does not permanently deste the power 
of thorium of giving out an emanation, but merely produces an 
alteration of the amount of the emanation which escapes from the 
compound. 
143. Rate of production of the emanation. The eman- 
ating power of thorium compounds, then, is a very variable quantity, 
much affected by moisture, heat, and solution. Speaking generally, 
increased temperatures and solution greatly increase the emanating 
power of both thorium and radium. 
The wide differences between the emanating powers of these 
substances in the solid state and in solution poimted to the conclu- 
sion that the differences were probably due to the rate of escape of 
the emanation into the surrounding gas, and not to a variation of 
the rate of reaction which gave rise to the emanation. It is 
obvious that a very slight retardation in the rate of escape of the 
thorium emanation from the compound into the gas, will, on account 
of the rapid decay of activity of the emanation, produce great 
changes in emanating power. The regeneration of the emanating 
power of de-emanated thoria and radium by solution and chemical 
treatment made it evident that the original power of thorium and 
radium of producing the emanation still persisted in an unaltered 
degree. 
The question whether the emanation was produced at the same 
rate in emanating as in non-emanating compounds can be put to a 
sharp quantitative test. If the rate of production of emanation 
goes on at the same rate in the sold compound, where very 
little escapes, as in the solution, where probably all escapes, the 
