22 RADIO-ACTIVE SUBSTANCES [CH. 
06 gramme of active substance was obtained in this way. The 
activity of the matter obtained did not decay appreciably during 
nine months. A full chemical examination of this active matter has 
not yet been made, but Marckwald considers that the substance is 
more allied in chemical properties to tellurium than to bismuth. 
The radiations from Marckwald’s substance are similar to those 
of polonium, for no penetrating rays are present. The radiations 
are very intense. They have a marked photographic action, and 
cause many substances, like zinc oxide and the diamond, to 
phosphoresce brightly. The strong luminosity of the diamond. 
under these rays can be utilized to distinguish the diamond from 
imitations, for glass is only slightly phosphorescent in comparison. 
The identity of Marckwald’s preparation with the polonium of 
the Curies has not yet been settled, but from the method of pro- 
duction and the nature of the radiations, there can be little doubt 
that the two substances probably contain the same active constituent. 
Marckwald, on the other hand, states that his preparations have 
preserved their activity unchanged, while the polonium of the 
Curies undoubtedly loses its activity in the course of a few years. 
If Marckwald’s preparation retains its activity unchanged for a 
long period, it 1s strong evidence in support of the presence of 
a new radio-element. If the activity decays, the radio-tellurium 
probably consists of the admixture with the tellurium of a small 
quantity of active matter, produced from one of the radio-elements 
present in pitchblende. A possible origin of polonium is discussed — 
in section 188. 
20. Other products from radio-active minerals. Besides 
the very active substances radium and possibly polonium, it seems 
extremely probable that other radio-active elements of great activity 
exist In minute quantity in the radio-active minerals. Although 
many active products have been obtamed by treatment of uranium 
residues from pitchblende and other minerals rich in uranium and 
thorium, none of these products have so far been sufficiently purified 
to obtain a definite spectrum as in the case of radium. 
Actinium. Debierne' has obtained from pitchblende a very 
active substance which he named actinium. This active substance 
1 C, R.129, p. 593, 1899; 130, p. 906, 1900. 
