xi] RADIO-ACTIVE PROCESSES 313 
The case of the radium emanation however is different. It 
can be shown (section 162) that probably the emanation exists in 
greater proportion in radium than radium does in pitchblende. 
Yet radium was detected in pitchblende by the property of radiat- 
ing which it possesses, and has been isolated from it and found to 
be an element of well-marked chemical and physical properties. 
It has been estimated that 1 gram of radium in a state of radio- 
active equilibrium probably contains a volume of about 0°3 cubic 
millimetre of the emanation, measured at standard pressure and 
temperature. From a kilogram of radium 0°3 cubic centimetre 
would be produced. When larger quantities of radium are available 
for experiments, there can thus be little doubt that a sufficient 
amount of the radium emanation will be obtained to examine 
chemically. In fact, as will be shown in section 201, even with 
the small quantities of radium now available, some very important 
spectroscopic evidence has already been obtained, in regard to the 
processes occurring in the emanation. 
[Volume of the E’manation’. 
Sir Wiliam Ramsay and Mr Soddy have kindly placed at my . 
disposal some preliminary results of a recent investigation by them 
on the volume of the emanation released from radium. In these 
experiments, 60 milligrams of pure radium bromide were used, in 
which the emanation had been allowed to collect for 8 days. This 
emanation, freed as far as possible from all other gases, was forced 
into a capillary tube in which its volume was measured. The 
following table shows the results obtained. 
Initial volume 07124 cubic millimetre. 
Volume after 1 day 0°027 _,, ig 
” oy) 3 days 0-011 ” ” 
pb) 9) 6 9? 00063 oP) 9 
”? oP) 9 9 00041 oP) ” 
by) ? 12 99 0-001 1 9 ” 
Final volume 0:0004 _,, 5 
The volume of the gas obtained shrank rapidly during the first 
day, then more slowly, and after the third day decreased approxi- 
mately according to an exponential law with the time, decreasing 
1 Added Feb. 1, 1904. 
