302 Prof. E. Rutherford on Slow 



he finally succeeded in obtaining 3 milligrams of intensely 

 active material. 



Since the mineral contains about 50 per cent, of uranium, 

 the theoretical yield is about 2*1 milligrams. It is not likely, 

 however, that the total amount would be separated, so that 

 the three milligrams obtained probably contain some impurity. 

 The enormous activity of this substance so prepared has been 

 pointed out by Marckwald. A copper plate, which had 

 been coated w T ith about 1/100 of a milligram of the material 

 by dipping it in a solution of the active substance, lighted up 

 a zinc sulphide screen to a sufficient extent to be clearly 

 visible in a dark room at 15 metres distance. 



The results deduced from theoretical considerations are 

 thus in harmony with the experimental results. 



I have previously pointed out that there were strong reasons 

 for supposing that polonium and radio-tellurium contained 

 the same radioactive constituent. The most direct test of this 

 point is a comparison of their rates of decay. Mme. Curie 

 has given some results in this direction. A sample of polonium 

 nitrate lost half its activity in 11 months, and 95 per cent, in 

 33 months. A sample of the metal lost 67 per cent, in six 

 months. 



These results are not at all concordant. The sample of metal 

 loses half its activity somewhat faster than radium F, while the 

 nitrate at first loses it much more slowty. In addition, the 

 activity does not decrease according to an exponential law 

 with the time. The results indicate that the polonium nitrate 

 contained more than one constituent. I think it is not 

 improbable that this second constituent is radium D. The 

 presence of some of this substance, which gives rise to 

 radium F, would at first cause the a. ray activity to decrease 

 more slowly than the normal rate when only radium F is 

 present. 



I had in my possession a sample of polonium about three 

 years old. During that time it had lost the greater proportion 

 of its activity, but, on testing it, the activity was found to 

 have reached a small and nearly constant value. However, 

 from rough observations which I had made from time to time 

 in the interval, the activity decayed to half value in about six 

 months, but the observations were not sufficiently accurate to 

 more than indicate the probable period of the decay of the 

 activity. 



More accurate determinations of the decay of activity of 

 polonium are required before the point can be considered 

 definitely settled ; but I think there can be no reasonable 



