OF OASES UNDER THE BECQ.UEREL RAYS. 
509 
substance only about 10 per cent, of the ionisation is due to deflectable rays. The 
conducti\dty ratio to be measured did not differ in any case more than about 30 per 
cent, for the two kinds of rays. Thus the error due to the presence of deflectable 
rays is only of the order of 3 per cent., an amount not well outside the errors of 
exjDeriment. 
(2.) A preparation containing the other radio-active constituent of pitchblende, 
polonium. This body I obtained as follows :— 
Pitchblende was dissolved in dilute nitric acid. The filtered liquid was treated 
with sulphuretted hydrogen. The precipitate was found to contain antimony, 
arsenic, copper, and bismuth, the polonium being associated with the last. To remove 
antimony and arsenic, the precipitate was digested with ammonium sulphide. The 
liquid was filtered off, and the remaining precipitate, containing copper and bismuth, 
with polonium, wms dissolved in nitric acid, and excess of ammonia added. The 
resulting precipitate, consisting of bismuth and polonium hydroxide, was tested for 
radio-activity, and found to be fairly active. Some of it was fused with an excess of 
potassium cyanide with a view to reducing it to the metallic state. The contents of 
the crucible, digested with watej-, and filtered, gave a black insolulfie jjowder, not a 
coherent button of metal as had been anticipated. This black powder presumably 
consisted of the reduced metal. It was many times more active than the original 
oxidised product, and was accordingly used in the experiments.* 
(3.) Another specimen of polonium was used which I owe to the kindness of Sir 
William Crookes. I have no exact account of the metliod of preparation, but Sir 
W. Crookes tells me that it was, in outline, the same as that described by Curie 
(‘Comptes Piendus,’ vol. 127, p. 175). This substance was considerably more 
powerful than the polonium which I prepared. 
(4) Ordinary uranium compounds, as met with in commerce, have a feeble radio¬ 
activity. Indeed, it was in these that Becquerel first detected the effect. Sir W. 
Crookes has shown (‘ Proc. Boy. Soc.,’ vol. G6, p. 409) that the activity is due, not to 
the uranium itself, liut to a powerlully radiating body accompanying it in small 
quantities, and probably distinct from both radium and polonium. He has shown 
{loc. cit.) that if ordinary commercial crystallised uranium nitrate be dissolved in 
(3ther, the resulting li(|uid divides into two layers—the one consisting mainly of an 
a(|ueous, the other of an ethereal, solution of uranium nitrate. The water, of course, 
is supplied hy the water of crystallisation of the salt. The solid obtained by 
evaporating the aqueous solution is distinctly more powerfully radio-active than that 
from the ethereal one. In my experiments a product was used which had been 
several times concentrated in this way. 
* Tlie improvement in the polonium due to treatment with potassium cyanide at a red heat was so 
marked, that it does not seem possible to explain it by the greater concentration of the material when in 
the metallic condition. The observation is of some interest, and I hope to investigate the matter further; 
but it bears only indirectly on the subject of the present paper. 
