48 Dr. T. Godlewski on some 



rays, recovered its activity according to a complementary 

 curve *. 



The only difference between my experiments and those of 

 Meyer and Schweidler was that my uranium nitrate was 

 deprived even of its water of crystallization by evaporation, 

 while in the experiments of the above named authors the 

 uranium nitrate was crystallized from the solution. This 

 proves that the rapid decay of activity occurs only when 

 uranium nitrate is crystallized, but it does not occur when it 

 was obtained from the solution by evaporation which had 

 been carried so far that the water of crystallization was 

 driven off. 



This fact being established, the subsequent experiments were 

 made in the same manner as the experiments of Meyer and 

 Schweidler. 



After separation of the ether solution, the aqueous solution 

 containing an excess of UrX was concentrated on the water- 

 bath, and was then left for a short time at the temperature of 

 the room. The great part of the uranium nitrate crystallized 

 at the bottom of the dish forming a compact plate, on the 

 surface of which the rest of the solution remained. This 

 mother liquor was poured off into another dish and was kept 

 on the water-bath until the solution lost all except the water 

 of crystallization. The solution after it was taken off the 

 water-bath crystallized at the temperature of the room, forming 

 a compact dry plate. 



The whole process of preparation and measurement was 

 repeated many times. Table I. gives one of the series of 

 experiments. T denotes the time in days from separation to 

 measurement. The ft activity is expressed as the ratio of the 

 activity of the investigated product to the ft activity of a 

 standard amount of uranium oxide taken as 1000. The ft 

 activity is expressed in the same units throughout this 

 paper. 



These results are graphically represented in fig. ], 

 where the ordinates give the activity, in the same units as 

 before, the abscissa? the time in days after separation. 

 Curve I gives the activity of the ether portion, curve II that 

 of the first plate of crystal, curve II L the activity of the 

 plate of crystal obtained from the mother liquor. 



* I omit the detailed numbers obtained in tlr^se measurements because 

 the results are completely normal ; and further, during- the time when 

 these mvesligations were being made Meyer and Schweidler published a 

 short paper ( Wiericr Sitzungsber. Dec. 1904} in which they showed that 

 when a very small amount of water was present in the solution, the decay 

 of activity of UrX was quite regular. 



