190 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
chemical properties, but there is a move of one column to the right 
in the periodic table; a gam of one m the atomic number and no 
change in the atomic weight. 
A brief example of the whole scheme applicable to all radiants is 
given below: 
Column. 
IME V. | Wile | At. Wts. 
| 
| 
UrxX1—~ Ur X 2—>5 Ur 2 234.5 
90, 8 91, 8 92,4 
eee Url 238.5 
92,4 
In the case of these radiants Ur | ejects an @ particle and gives 
rise to UrX 1. The latter and Ur X 2, respectively, emit a f particle. 
It should be added that the short-lived product Ur X 2 or ‘‘bre- 
vium” was discovered by this theory, after it had been formulated 
from the known behavior of other radiants. 
It will be seen that Urantum 1 and 2 are in the same column and 
have the same atomic number, but that their atomic weights differ 
by 4. Such substances have chemical properties so identical that 
they are called inseparables, or nonseparables, or isotopes, for they 
occupy the same place in the periodic table. Thus the old trouble 
of finding places in the periodic table for the 30 or 40 radiant elements 
has suddenly vanished. They may be superposed even when their | 
atomic weights differ, if their atomic numbers are the same. The 
nuclear charges of isotopes must be identical, but the distribution of 
electrons may be different. Other examples of inseparables are lead, 
radium B, radium D, all 82; thorium and radiothorium; radium and 
mesothorium. 
It must be further noted that the results of radiochemistry appear 
to require the presence of negative electrons in the nucleus itself. 
The expulsion of a @ particle or one negative electron from the nucleus 
is equivalent to the gain of one positive electron, and involves a unit 
increase in the atomic number. 
14. The last advance is the most important and far-reaching. 
There has been long search for the positive electron, and in vain; yet 
it seems likely that it has been under our eyes all the time. Since the 
hydrogen atom never loses more than a single electron, is it not pos- 
sible, suggests Rutherford, that the nucleus of the hydrogen atom may 
be the positive electron ¢ 
é 
») 2 
The electromagnetic mass of an electron 1s 3 where ¢ is the charge 
a 
and a the radius. If the mass of the hydrogen nucleus is wholly elec- 
tromagnetic, then its radius must be smaller than that of the electron — 
