60 ELISHA MITCHELL SCIENTIFIC JOURNAL 



In this manner we obtained from the four first mentioned 

 minerals, brog-gerite, cleveite, • euxenite and samarskite, some 

 strong- and some very strong- active Thorium preparations, far 

 surpassing- the activity of the usual Thorium compounds. 

 The assumption of the presence of Actinium therein was ten- 

 able, so we tried then, like Mr. and Mrs. Curie with Radium, 

 to separate the Actinium by means of fractionation. And to 

 all appearance we succeeded in this way, for we could accum- 

 ulate the activity in one part of the fractions. It happened 

 by fractional precipitation with Potassium sulphate, Sodium 

 thiosulphate, Potassium chromate, Hydrogen dioxide, and 

 fractional solution in Ammonium carbonate. 



Our work was suspended during- the vacation in 1901. On 

 resumption of the investigations our previously very strong-ly 

 active preparations had lost nearly all their activity upon the 

 photographic plate and the electroscope. Thus it was shown 

 that the Thorium could not possibly contain a primarily active 

 body. For these, as for instance Radium and Actinium, 

 behave quite differently. Immediately after their separation 

 they show a certain quantity of radioactivity, which increases 

 within a few weeks to a maximum, and then remains constant 

 during- several years, at least according- to our measuring- 

 methods. But Thorium behaved quite differently. Its activ- 

 ity rather diminished, and then indeed it reserved constantly 

 a very little activity. The /?-, or photographic action fell 

 down to an insignificant amount, whereas the a-radiation 

 assumed about the value of the weak Uranium radiation. 



As therefore Thorium evidently is not a primarily radio- 

 active body, the further question was to be decided: where 

 does the activity of the Thorium compounds come from? The 

 investigation of the other minerals gave us the key to this 

 problem. The four first mentioned minerals contain a great 

 deal of Uranium in comparison with the amount of Thorium 

 present. We found furthermore: the more Uranium and the 

 less Thorium a mineral contains, the more active is the Tho- 

 rium obtained from it. 



