CHEMICAL CHARACTER 135 



THE CHEMICAL CHARACTER OF THE RADIO- 

 ELEMENTS. 



The simple connection between the sequence of 

 radioactive changes and the chemical character of 

 the products has effected an enormous simplifica- 

 tion, not only in the theory, but also in the practice 

 of radio-chemistry. The series extends over twelve 

 places, two, namely those in the families of the 

 halogens and the alkali metals, being- entirely 

 skipped. In the ten occupied places are forty- three 

 distinct types of matter, but only ten chemical 

 elements. Seven of these ten, thallium, lead, bis- 

 muth, emanation, radium, thorium, and uranium, 

 can now in every respect be considered, both 

 chemically and spectroscopically, thoroughly well 

 known. These seven places accommodate all but 

 nine of the known radio-elements, and these nine, 

 the isotopes of polonium, actinium, and ekatan- 

 talum respectively, are the only members the 

 chemistry and physics of which cannot be referred 

 to well-known elements obtainable in sufficient 

 quantity for ordinary chemical and spectroscopic 

 examination. 



Of these three, polonium, although the element 

 of which at present the chemistry is best known, 

 is likely to remain the most difficult to bring into 

 line with the others, for, although a vast amount 

 of exact information has been obtained as to its 

 reactions, it would seem to remain hopeless ever 

 to obtain it in anything but infinitesimal amount 

 owing to its relatively very short period. 



The chemistry of actinium has been enormously 

 simplified by the discovery that mesothorium-2 is 

 isotopic with it, for the latter may be used as an 

 indicator to show in what way the actinium distri- 

 butes itself after any chemical treatment. Owing 



