on Radioactive Change. 585 



of some of the effects that have been attributed to radioactive 

 induction would lead to new disintegration products of the 

 known radio-elements being recognized. 



Other Results. — -A number of cases remain for consideration, 

 where, by working with very large quantities of material, 

 there have been separated from minerals possible new radio- 

 elements, i. e. substances possessing apparently permanent 

 radioactivity with chemical properties different from those 

 of the three known radio-elements. In most of these cases, 

 unfortunately, the real criteria that are of value, viz., the 

 nature of the radiations and the presence or absence of 

 distinctive emanations, have not been investigated. The 

 chemical properties are of less service, for even if a new 

 element were present, it is not at all necessary that it should 

 be in sufficient quantity to be detected by chemical or 

 spectroscopic analysis. Thus the raolio-lead described by 

 Hoffmann and Strauss and by Giesel cannot be regarded as 

 a new element until it is shown that it has permanent activity 

 of a distinctive character. 



In this connexion the question whether polonium (radio- 

 bismuth) is a new element is of great interest. The 

 polonium discovered by Mine. Curie is not a permanent 

 radioactive substance, its activity decaying slowly with the 

 time. On the view put forward in these papers, polonium 

 must be regarded as a disintegration product of one of the 

 radio-elements present in pitchblende. Recently, however, 

 Marckwald (Ber. der D. Ghem. Gesel. 1902, pp. 2285 & 

 4239), by the electrolvsis of pitchblende solutions, has ob- 

 tained an intensely radioactive substance very analogous to 

 the polonium of Curie. But he states that the activity 

 of his preparation does not decay with time, and this, if 

 confirmed, is sufficient to warrant the conclusion that he is 

 not dealing with the same substance as Mine. Curie. On the 

 other hand, both preparations give only a rays, and in this 

 they are quite distinct from the other radio-elements. Marck- 

 wald has succeeded in separating his substance from bismuth, 

 thus showing it to possess different chemical properties, and 

 in his latest paper states that the bismuth-free product is 

 indistinguishable chemically from tellurium. If the per- 

 manence of the radioactivity is established, the existence of 

 a new radio-element must be inferred. 



If elements heavier than uranium exist it is probable that 

 they will be radioactive. The extreme delicacy of radio- 

 activity as a means of chemical analysis would enable such 

 elements to be recognized even if present in infinitesimal 

 quantity. It is therefore to be expected that the number of 



