376 Boltwood — Ionium, a New Radio-active Element. 



nitrate and about live grams of the chlorides of inactive rare 

 earths from cerite. The rare earths were precipitated as 

 oxalates, after the removal of the hydrogen sulphide group, 

 and the thorium was separated from the other rare earths 

 (and the actinium) by repeated precipitation with sodium thio- 

 sulphate. In this way a few milligrams of a substance, con- 

 sisting chiefly of thorium oxide and haviug ah activity at least 

 1000 times that of an equal weight of uranium oxide, were 

 obtained. The radiations emitted by this material in the form 

 of a thin film were examined in the electroscope and were 

 compared with that emitted by a preparation of polonium on 

 bismuth having an approximately equal activity. It was 

 found that the new body gave out an a radiation which was 

 much more readily absorbed by air and aluminium than the a 

 radiation from polonium. The presence of a /3 radiation, pro- 

 ducing over ten per cent of the total ionization, was also noted. 

 The first measurements were thought to indicate a high absorp- 

 tion, but on comparing the results with those obtained by 

 Levin* for uranium X, it was found that the coefficient of 

 absorption for the /3 rays was the same in both cases. t That 

 this /3 radiation was due to uranium X was also evident from 

 the fact that it fell off exponentially with the time at a rate 

 corresponding to half-value in about 22 clays. 



An attempt was then made to determine the range of the a 

 particles in air by the scintillation method, and although the 

 difficulties were increased by the presence of a small propor- 

 tion of a particles of longer range emitted by the thorium 

 products in the material, it was easily ascertained that range in 

 air of the a particles from the new substance was certainly less 

 than three centimeters. No other radio-active element emit- 

 ting rays of so short a range had been previously identified. 

 From this and from the data obtained in the other experi- 

 ments it was evident that the material in hand contained a 

 new radio-active element and the name " ionium " was sug- 

 gested for this substance. 



Separation of Ionium. 



As a result of further experiments it was found that highly 



active preparations of ionium free from appreciable amounts of 



other radio-active substances could be obtained in the following 



manner : A quantity of carnotite^: was treated with hydrochloric 



* Phys. Zeit., viii, 585, 1907. 



f Levin's measurements give the value 17 - 0(cm) -1 for the coefficient of 

 absorption for thicknesses of ahimininm between - 0136 and 0"180 cm . For 

 the same thicknesses I obtained the same value for the coefficient of absorp- 

 tion of the 8 rays from my preparation. 



X The carnotite used in these and the earlier experiments was kindly sent 

 to me by Mr. William Zowe of Uranium, Colo. I have recently obtained 

 some very excellent material of the same sort from Mr. B. J. Manning of 

 Paradox, Colo. 



