Boltwood — Note on a New Radio- Active Element. 371 



that the rate of production of radium in solutions of the parent 

 is not affected appreciably by the presence of radio-actinium 

 and its products. Continued observations of the growth of 

 radium in my original solution indicate that the rate of produc- 

 tion of radium has been constant, within the limits of experi- 

 mental error, for a period of over 500 clays. Using one of my 

 own preparations, I have been unable to repeat the separation 

 of the radium parent from actinium by the ammonium sulphide 

 treatment which Rutherford has described. With pure, freshly- 

 prepared ammonium sulphide no separation could be detected. 

 The radium parent can, however, be quite completely separated 

 fro n actinium by precipitation with sodium thiosulphate, under 

 the conditions usual for the precipitation of thorium. As am- 

 monium sulphide readily changes into ammonium thiosulphate, 

 it would appear probable that the separation noticed by Ruth- 

 erford was due to the latter compound. 



An interesting and important relation has been observed be- 

 tween the growth of radium and the activity of the substances 

 other than thorium in my solutions containing the radium 

 parent. This proportionality is most striking in those solutions 

 containing the more completely, purified salts. More significant 

 still is the fact that this radio-active constituent does not appear 

 to possess any of the characteristic properties af the recognized 

 radio-active elements. Less than half a gram of thorium oxide 

 containing an amount of this new body having an activity 

 about equal to that of five grams of uranium did not produce 

 sufficient actinium emanation to permit its detection in a sensi- 

 tive electroscope, although under the conditions of experiment 

 the thorium emanation evolved could be detected and measured 

 without difficulty. . 



That the active substance is not actinium was also demon- 

 strated by the fact that from a solution over five months old, 

 containing about 3 grams of thorium and a quantity of the new 

 substance with an activity equal to that of about 35 grams of 

 uranium, no active substances other than thorium products could 

 be separated by precipitation of the earths with ammonia, by the 

 formation of finely divided sulphur from sodium thiosulphate 

 or by the precipitation of considerable quantities of barium 

 sulphate in the solution. The first process should have sepa- 

 rated actinium X and the last two should have separated radio- 

 actinium had these products been present. 



The behavior of the oxides obtained by strongly igniting the 

 hydroxides precipitated by ammonia from a solution similar to 

 the above is also significant. The activities of these oxides 

 remain nearly constant for long periods, showing only a slight 

 initial rise corresponding to the formation of thorium X in the 

 thorium present. No rise corresponding to the formation of 



