538 Boltivood — Production of Radium by Actinium. 



cipitation with oxalic acid. I have found from a number of 

 other experiments that practically all of the actinium contained 

 in a mineral can be separated in this manner. 



The oxalates obtained from the second precipitation were 

 converted into chlorides, and the dilute solution of the chlor- 

 ides was sealed up in a glass bulb. About two months later, 

 on the twenty-fifth of April last, the gases and emanation col- 

 lected in the bulb were boiled out and, after standing for some 

 time, were introduced into a standardized electroscope. The 

 quantity of radium emanation present corresponded to the 

 presence of 5*7 XlO -9 gram of radium in the actinium solu- 

 tion. The bulb was again sealed and allowed to stand undis- 

 turbed until November 4th, when the emanations and gases 

 were again boiled out and tested. The amount of radium 

 emanation then found corresponded to 14*2 Xl0~ 9 gram of 

 radium, indicating that during the interval of 193 days there 

 had been formed in the solution a quantity of radium equal to 

 8'5xl0 -9 gram. This is equivalent to the production of 

 about 1*6 XlO -8 gram of radium in one year. The amount of 

 radium in equilibrium with 200 grams of uranium (the approx- 

 imate amount of uranium in the mineral used) is 7*6 XlO -5 

 gram.* Assuming that the total amount of actinium present 

 in the mineral was separated by the treatment described, the 

 value of X for radium can be calculated from the above num- 

 bers and is given as 2 , lXlO~ 4 (y ear )" 1 - The period required 

 for the decay of the activity of radium to one-half its initial 

 value is thus indicated as about 3300 years, and this is of the 

 same order of magnitude as the most recent estimate made by 

 Rutherford.f 



Strong evidence has therefore been obtained in support of 

 the assumption that actinium is the intermediate disintegra- 

 tion product between uranium and radium. 



The entire series of operations from the start will be repeated 

 with special precautions in order that a more accurate value 

 for the various constants can be obtained. 



New Haven, Conn., Nov. 5, 1906. 



"* Rutherford and Boltwood, this Journal, xxii, 1, 1906. 

 f 2600 years, Phil. Mag. (6), xii, 367, 1906. 



