298 
NALORLE 
[JANUARY 28, 1904 
ores, and to the enterprise of the Chinin-Fabrik, of 
Brunswick, many during the past year have had the 
opportunity of satisfying themselves by experiment 
that the marvellous properties attributed to radium 
have not been exaggerated. 
Considering the short time that has elapsed since 
the discovery, and the difficulty experienced in the past 
in obtaining the element, our knowledge of its proper- 
ties at the present time is surprisingly complete. 
Attention will here be mainly directed to outstanding 
features which need further inquiry. In the first 
place, in spite of the many years of painstaking labour 
devoted to the determination by Mme. Curie, doubt 
still lingers as to the atomic weight of the new 
element. The case is a remarkable one, and has never 
arisen before in the determination of an atomic weight. 
On the one hand we have Mme. Curie’s experimental 
value 225, and on the other an indirect value, 257.8, 
arrived at by Runge and Precht from spectroscopic 
data. Each of these determinations rests upon 
evidence which cannot be lightly set aside, and the 
discrepancy still remains to be explained. We have 
the authority of M. Demargay for the purity of the 
preparations employed by Mme. Curie, for the former 
states that the spectroscopic trace of barium present 
could have had no effect on the atomic weight deter- 
mination. 
In ordinary circumstances the value 225 would prob- 
ably be accepted as trustworthy to a unit in either 
direction. Runge and Precht’s result, on the other 
hand, cannot be ascribed to chance relationships 
between the lines in the spectrum, possessing no real 
physical significance. For they succeeded in sorting 
the lines into related series, the lines in each series 
being resolved in the same way in a magnetic field. 
The series for radium are strictly analogous to those 
previously recognised in the spectra of the other 
alkaline-earth elements, and the connection between 
the atomic weight of the element and the distance 
apart of the lines in the series, which is the same for 
the different series of the same elements, holds very 
exactly for the cases of magnesium, calcium, barium 
and strontium. For radium, however, the number 
257-8 is indicated. The evidence drawn from the 
chemical nature of radium and from the character of 
its spectrum agrees, however, in making the new 
element a member of the alkaline-earth family, and 
the experimental number is the only one which admits 
of this classification in the periodic table. The higher 
value, if it allows of the element being placed in the 
group of divalent metals at all, would make radium 
analogous to mercury and cadmium, so that it seems 
as if the experimental number should be accepted and 
the spectroscopic value regarded as abnormal for some 
unknown reason. The question is of considerable 
importance, and it is to be hoped that new experi- 
mental determinations will soon be available. 
An explanation of the property of radio-activity was 
put forward by Prof. Rutherford and the writer about 
a year and a half ago as a result of the discovery of 
thorium X and of the behaviour which the thorium 
from which it is separated exhibits. This has since 
been developed and extended to afford a working 
hypothesis applicable to every detail of the pheno- 
menon. The radio-elements are regarded as slowly | 
disintegrating, a definite proportion of the total | 
changing in the case of each element in the unit of 
time, the change being marked by the expulsion of 
rays. On account of the fact that the disintegration 
proceeds per saltum through several stages, and once 
started proceeds from stage to stage comparatively | 
rapidly, the infinitesimal amounts of the transition- | 
forms of matter can be detected and studied on | 
account of the rays they emit in passage to the next | 
NO. 1787, VOL. 69] 
succeeding stage. On this view thorium X, the 
uranium X of Crookes, the emanations of radium and 
thorium, and the active matter resulting from the 
further change of the latter, which gives rise to the 
phenomenon of ‘‘ induced ’’ or “‘ excited ’’ activity, are 
all transition-forms in the per saltum disintegration of 
the parent elements into more stable systems. The 
emanations are perhaps the most remarkable of these 
forms, as they are gaseous, and in consequence have 
been the most narrowly studied since the original dis- 
covery of the thorium emanation by Rutherford in 
1899. The energy given out is, on this view, derived 
from the store of internal energy of the changing 
atom, and is, for any given mass of matter changing, 
enormous compared with that involved in any pre- 
viously known change. It is in consequence of this 
fact that the excessively minute changes which produce 
radio-activity can be detected and investigated. 
With regard to the nature of the radiations, the 
advances made by Rutherford in our knowledge of the 
nature of the a rays are among the most important. 
The B rays are known from the work of J. J. Thomson 
and Becquerel to consist of high velocity kathode rays, 
or negatively charged particles of mass about one- 
thousandth of the hydrogen atom projected with a 
velocity approaching that of light. The y rays are in 
all probability X rays of high penetrating power which 
accompany the production of the 8 rays. Rutherford 
was the first to recognise that these two types are 
relatively unimportant, and that the a rays represent 
at least 99 per cent. of the total energy radiated. The 
analysis of the rays from a radio-element into its 
several parts, the greater part usually coming from the 
various transition-forms, which can be removed by 
chemical means, and only a small part from the parent 
element itself, has borne out this conclusion. For 
in the majority of cases known a@ rays are alone ex- 
pelled in the disintegration. The discovery of the 
magnetic and electric deviability of the a ray of 
radium to an extent about one thousand times less, 
and in the direction opposite to that suffered by 
the 8 ray in similar circumstances, enabled Ruther- 
ford to settle the question as to their nature by show- 
ing them to consist of projected particles carrying a 
positive charge, about one thousand times the mass 
of the kathode ray particle and therefore comparable 
in size to the hydrogen atom, travelling with a velocity 
about one-tenth that of light. 
This discovery has two bearings. On the one hand 
it confirms in a remarkable manner the view of the 
nature of electricity adopted by J. J. Thomson as the 
result of his investigations of the conduction of 
electricity through gases, that the negative charge can 
be dissociated from the atom, whereas the positive 
charge is always associated with a particle of atomic 
dimensions. On the other, it provided at once a 
mental picture of the precise change suffered by the 
atom of a radio-element, which the discovery of 
thorium X and the investigation of its behaviour had 
established. To take the case of radium as an ex- 
ample. The a@ particle expelled is an integral part of 
the heavy radium atom, which after disintegration 
forms a new and lighter atom, viz. that of the eman- 
ation. This suffers a second disintegration, expelling 
more @ particles and changing into the matter which 
causes the ‘‘ excited activity.’’ Owing to the average 
life of the emanation atom being short—only 5-79 days 
-—its energy is liberated so rapidly that a correspond- 
ingly small quantity can be detected. The energy 
manifestations from the emanation are very surprising, 
although it is not present in sufficient quantity to be 
detected by ordinary means. 
An interesting feature at the present time arises 
from the fact that since the a rays given out by a 
