294 Prof. E. Rutherford on Slow 



D on the plate had not been volatilized. It is seen that the 

 transformation periods, deduced from the recovery curve 

 (6 days), and from the decay curve (4*5 days), are somewhat 

 different. I do not think this difference in the periods can 

 be ascribed to experimental errors, but is more probably due 

 to an alteration of the rate of transformation of radium E, 

 resulting from the high temperature to which it has been sub- 

 jected. A similar effect of temperature on the rate of 

 transformation of radium C has been noted by Curie and 

 Danne. It is intended to continue these experiments in order 

 to settle definitely the cause of this difference in the period 

 obtained by the two methods. 



The period deduced from the recovery curve is more likely 

 to be the correct value under normal conditions. 



This method of separation is of interest, and shows in a 

 striking way how the difference in physical properties of the 

 products can be utilized to effect a partial or complete isola- 

 tion of a substance which is mixed with several others. 



The volatility of radium D, as weli as of radium F, has 

 also been noted in other experiments, for it has been found 

 that the a ray activity of a platinum plate after exposure to 

 a temperature of 1000° C. does not increase with time to the 

 same extent as that of a similar plate which has not been so 

 treated. Such a result is to be expected if a large part of the 

 parent matter radium D is removed by the heating. 



The experiment of heating the platinum plate was also 

 utilized to prove that radium E was the parent of the a ray 

 product radium F. The a ruy activity of the plate was 

 determined immediately after heating, and at subsequent 

 intervals. The increase of activity of the plate with time after 

 heating is shown in fig. 2. 



The activity rose far more rapidly during the first two 

 weeks than for equal intervals later. The slow period of 

 increase is due to the production of radium F from the radium 

 E, which is continuously produced from the fraction of radium 

 D which was not volatilized. The rapid initial increase of 

 the activity is at once explained if the excess of radium E 

 changes into F. 



We may then conclude that E is the parent of F, and that 

 the three products D, E, F are successive, for we have 

 previously shown that E is produced from D. 



In the previous paper it was calculated that radium D 

 should be half transformed in about 40 years. This result 

 still holds good, although it has been found that radium D 

 itself does not emit rays. About 40 days after removal, the 

 ft ray activity of radium E is constant, and the number of 



