Transformation Products of Radium. 641 
Explanation of the Results. 
We have seen that the a ray activity zncreases if the B ray 
product is present, but remains sensibly constant or changes 
very slowly if the 2 ray product is removed from the 9 ray 
product by the action of a bismuth plate. The # ray activity 
remains sensibly constant independently of whether the 2 
ray product is present or not.’ These results show that the 
8 ray product is the parent of the a ray product. The 
amount of residual activity from the radium emanation 
depends on the amount of emanation present and the time ot 
exposure to the emanation. These results show that the 
active deposit of slow decay is a decomposition product of 
the emanation, and, since the first three transition products 
of the emanation, viz. radium A, radium B, and radium C, 
have been carefully analysed and shown to be consecutive, it 
is natural to suppose that the matter of slow rate of change 
is a product of the last rapid change in radium C. 
Following the nomenclature suggested, radium © gives 
rise to the 8 ray product, which will be called radium D, 
while radium D changes into the 2 ray product, which will 
be called radium E. The product radium D gives out only 
8 rays. The transition products of the disintegration of 
radium are shown diagrammatically in fig. 2. 
Fig. 2. 
Ae 
NS” = e 2. 
cs y Ry % @ af 
So 
RACIUM RAD. EM. RAD. A RAO.B FRAD.C RAD.D RADE 
A ee Ne ee 
ACTIVE DEPOSIT ACTIVE DEPOSIT 
OF OF . 
RAPID CHANGE SLOW CHANGE 
No further changes have so far been observed. The active 
solution of radium D and E was tested to see if an emanation 
were present. A trace of the radium emanation was always 
observed, but this was probably due to a slight trace of 
‘radium carried over into the emanation vessel. This point is, 
however, under further investigation. 
Theory of two Successive Changes. 
Tn all cases of radioactive change that have been examined, 
the amount of unchanged matter N; present at any time ¢ is 
