Radioactive Properties of Uranium. 53 



reached, as well as the form of the curve, was dependent 

 upon many factors. In different experiments, the relative 

 values of the activity at the minimum point and the rates of 

 decay were dependent upon the thickness of the plate o£ 

 crystals, and upon the concentration of the solution from 

 which the crystals were obtained. 



In consequence, it would be difficult to suppose the 

 existence of some other product. 



The supposition of Meyer and Schweidler * that the 

 phenomena are produced by some changes in absorbing- 

 power of the plates of crystals cannot explain the observed 

 fact, when we take into consideration that the activity 

 measured by a rays does not exhibit the same behaviour. 

 The experiments of Meyer and Schweidler showed that the 

 a activity remained practically constant. The writer made 

 also experiments which completely confirmed this fact. And 

 every change in absorbing power of the plates would be, 

 of course, first of all shown by variation of a activity. 

 Since these results can neither be explained by the existence 

 of a new product nor by a change in absorbing power, there 

 remained the possibility that the process of crystallization 

 alone influences the ft activity of uranium nitrate. In order 

 to show whether this was really the case, the following 

 experiments were undertaken. 



The hot solution of uranium nitrate containing only the 

 water of crystallization w r as put under the electroscope. 

 After about two minutes the disturbance of the gold leaf, 

 produced by the neighbourhood of the hot body, ceased, and 

 it was then possible to investigate the effect due to the 

 process of crystallization by measurements of the activity. 

 The experiments showed that at the moment when the 

 crystallization started, the /3 activity commenced to increase 

 very rapidly, reaching the maximum when the crystallization 

 was finished. 



The following is an example of the experimental results 

 obtained. 25 grams of uranium nitrate were dissolved in 

 some water and evaporated in a flat glass dish on a water- 

 bath until it lost all the excess of water. The dish containing 

 this hot solution of uranium nitrate in water of crystallization 

 was then put under the electroscope. After three minutes 

 the activity could be measured with accuracy. The results 

 are shown in Table III., where T is the time in minutes 

 from the moment when the solution was taken off the 

 water-bath. 



* Meyer and Schweidler, he. cit. p. 1075. 



