422 



Mr. G. N. Antonoff on tin 



The curve for hard rays gives a half period of 23*5 days. 

 The curve for the uncovered preparation seems to give a 

 slightly lower period of about 23' days, but the difference 

 is within the limits of experimental error. 



To obtain the recovery curve of uranium, the UrX was 

 completely separated from uranium by boiling the solution 

 of uranium nitrate with a large quantity of ferric oxide. 

 The ferric oxide was filtered off and the above process 

 repeated several times. The uranium nitrate was converted 

 into oxide, which was spread on a tray and placed under a 

 /3 ray electroscope. Its activity was measured for several 

 months. The initial value soon after the separation was 

 found to be O05 div. per minute. The constant maximum 

 value after several months was found to be 9*2 divs. per 

 minute. The half value was reached after about 23*5 days, 



Fig. 2. 



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y \ 



y 























y 



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t, 



y 



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 / 



























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corresponding to the half period found from the decay of 

 UrX. Curve 1 in fig. 2 shows on a large scale the initial 

 part of the theoretical curve calculated from the equation 

 I/I = 1— e~ Kt , where I is the maximum activity and I is the 

 activity at any time t } taking for \ the value corresponding 



