TRANSACTIONS OF SECTION B. 447 
plete scheme showing the passage of the radio-elements through the periodic table. 
His scheme was in certain respects imperfect, and it was followed almost imme- 
diately by another by K. Fajans,* who put forward the complete law in its present 
form, and made important and accurate deductions as to the positions occupied by 
the still unplaced members. Soddy independently arrived at a complete scheme 
similar to that of Fajans,° but which in one respect possibly went somewhat 
further in regard to the generalisation that all elements falling into the same 
place in the periodic table are not merely similar in chemical properties, but are 
chemically identical, non-separable by chemical methods, and probably spectro- 
scopically indistinguishable. From this the definite prediction was made that 
radium-C,, thorium-D', and actinium-) would prove’to be non-separable from 
thallium, and radium A from polonium, which Fleck has since established, 
whilst all the end-products would be non-separable from lead. The scheme, 
altered slightly to bring it up to date (July 1913), is shown in the accompanying 
plate. 
In all three schemes a new member was indicated in the V A family, as the 
product of uranium X. This has since been discovered by Fajans and Beer,® 
and confirmed by Fleck.” It proves to be a very short-lived substance of period 
of average life 1°7 minutes, and is called Uranium X,. Its parent, Uranium X,, 
with period 35°5 days, gives only the soft (8) rays, whereas the hard f-rays of 
Uranium X come from this new product. 
This missing member being short-lived disproves the suggestion (Soddy) that 
it might be a very long-lived and therefore well-defined element (Eka-tantalum), 
disintegrating dually and producing, in addition to Uranium II. by a f-ray 
change, actinium by a still undetected a-ray change. This being disproved, the 
only other possibility to consider as to the still unknown source of actinium is 
that it is produced in a f-ray or rayless change from radium. On account of the 
uncertainty of the origin of actinium, and therefore of the atomic weight both 
of itself and of all its products, the actinium series is shown separately beneath 
the others in the plate. 
The chemical analysis of matter is thus not an ultimate one. It has appeared 
ultimate hitherto, on account of the impossibility of distinguishing between ele- 
ments which are chemically identical and non-separable unless these are in the 
process of change the one into the other. But in that part of the Periodic Table in 
which the evolution of the elements is still proceeding, each place is seen to be 
occupied not by one element, but on the average, for the places occupied at all, by 
no less than four, the atomic weights of which vary over as much as eight units. 
It is impossible to believe that the same may not be true for the rest of the table, 
and that each known element may be a group of non-separable elements occupy- 
ing the same place, the atomic weight not being a real constant, but a mean 
value, of much less fundamental interest than has been hitherto supposed. 
Although these advances show that matter is even more complex than chemical 
analysis alone has been able to reveal, they indicate at the same time that the 
problem of atomic constitution may be more simple than has been supposed 
from the lack of simple numerical relations between the atomic weights. 
(i) The Chemistry of the Radio-Klements. 
By Avexanver FirEcK, B.Sc. 
Since last year’s meeting at Dundee, when the chemistry of three short-lived 
radio-elements was described, the study has been continued, and the chemical 
nature of eleven additional radio-elements has been worked out experimentally. 
In each of these cases, with the one exception of Uranium-X,, the chemistry of 
the substance may be summed up by saying that it has properties identical in 
all respects with those of some already known element. In general the experi- 
mental methods were divided into two parts: First, determining what element 
the short-lived radio-element most resembled, and, second, determining, usually 
“ Phys. Zett., February 15, 1913, 14, 131 and 136. 
° Chem. News, February 28, 1913, 107, 97. 
* Naturwissenschaften, April 4, 1913. ’ Phil. Mag. 
