28 SODDY, Evolution of Matter by Radio-active Elements. 



■quantity is best expressed in terms of the time required 

 to produce it. It can be shown that the equiHbrium 

 quantity of any transition-form of matter is that quantity 

 produced in the period of the average life of the metabolon. 

 Thus the quantity of emanation stored up by a radium 

 compound when the maximum value is reached is that 

 ■quantity which would be produced in 5 "3 days of steady 

 production. (The actual quantity present after this 

 interval is of course smaller on account of the change it 

 •continually undergoes). The data obtained by Sir William 

 Ramsay and myself show that the equilibrium quantity 

 ■of the emanation from 60 milligrams of radium bromide 

 •occupies a volume between '03 and '04 cubic millimetre 

 at normal temperature and pressure. The actual weight 

 of radium in the compound employed is not accurately 

 known, but it may be assumed without probably incurring 

 serious error to be about one half of the total weight of 

 the compound. The maximum amount of emanation 

 stored up by one gram of radium (element) therefore 

 occupies a volume of about a cubic millimetre. 



One gram of hydrogen occupies the volume of 11 "2 

 litres, and if its molecule were monatomic would occupy 

 22"4 litres. One gram of radium if it could be obtained 

 in the form of a monatomic gas would therefore occupy 

 a volume of 22"4-^225=0'i litre. It seems likely that 

 the molecule of the emanation is, like argon, monatomic, 

 since it shows no powers of chemical combination. With 

 a density of 80, the atomic weight of the emanation would 

 therefore be 160, and there is not room for more than one 

 atom to be produced, from each atom of radium. In a 

 cubic millimetre of emanation there are one one-hundred- 

 thousandth of the number of atoms present in a gram of 

 radium. If one atom of radium produces one atom of 

 emanation, it follows that one one-hundred-thousandth 



