850 On the Constant of Cranium X. 



from to 226 days, a value identical with that found for 

 the /3-rays. The rate of decay of the /3-rays of preparations 

 A, B, C, and D of the fourth separation was higher than the 

 normal value over the first ten days after preparation, the 

 value of X (day) -1 varying from 0*033 to O029. No such 

 initial abnormal decay was shown in the ^-ray measurements 

 conducted at the same time on these preparations. From 

 about the tenth day onwards the decay was quite normal. 

 Such a result had been sought for, as it has been shown by 

 one of us * that the apparent value of the radioactive constant 

 of uranium X (0*031 day) -1 might be composed, assuming a 

 double disintegration of uranium X into two bodies in the 

 proportion of 7 to 1, of two separate values, one of 0*027, and 

 another of 0*004. The abnormalities were not confirmed, 

 however, by a special experiment in which two different, 

 newly prepared uranium X preparations were compared with 

 another, known to be decaying normally, care being taken 

 to get all the preparations into the same physical state. 

 Measurements at intervals of 2 days for 16 days showed 

 that all three preparations decayed at the normal rate 

 (X, = 0*028 (day) -1 ). The abnormalities in the decay may be 

 due to the fact tliat the preparations had not come immediately 

 into equilibrium with the surrounding atmosphere with 

 regard to their physical state. Thus a preparation which 

 had been heated strongly in the course of mounting and 

 which therefore was very dry on the first day of measure- 

 ment, would tend to give diminishing values of X, until it 

 had assumed its state of physical equilibrium. This point 

 will be further examined. 



The electroscope used for /3-rays was tested to see whether 

 two radioactive preparations gave together the sum of the 

 leaks produced by each separately. If A and B denote 

 respectively the intensities of two radioactive preparations, 

 the activity of which could be measured either separately or 

 together, it w r as found that for the electroscope used, A and B 

 separately gave a greater effect than A-f-B together, if 

 A-f B was greater than 215 divisions per minute, a smaller 

 effect if A + B lay between 215 and 115, and exactly the 

 same effect if A-j-B varied from 115 down to the smallest 

 leak tried (1 division of the scale =0*023 mm.). To avoid 

 disturbances due to secondary rays from the radioactive 

 preparations themselves, when both were used together, one 

 of the sources was a 7-ray preparation placed in a definite 

 position at the side of the instrument, the other a /^-ray 

 preparation under the base. Between 115 and 215 the 

 * Soddy, Phil. Mag. [6] xviii. r- '42 (1909). 



