462 
NAT ORE 
[Marcu 17, 1904 
be obvious even with this rough test, but it certainly would 
not be sufficiently marked in nine months. We may there- 
fore take it as settled that there is absolutely no evidence 
at the present time for supposing that radio-tellurium 
possesses a more constant radio-activity than polonium. If 
only this point has been made clear this correspondence may 
be considered to have justified itself. 
According to Prof. Marckwald the idea associated with 
the term polonium is an extremely variable and_ in- 
determinate one. It seems to me that this is to put a wrong 
valuation on the work of its discoverer. Madame Curie gave 
the name to the hypothetical constituent of the bismuth 
separated from Joachimsthal pitchblende which caused its 
radio-activity. The radio-activity in question is distinct 
from that of any known radio-active substance, for it com- 
prises only the emission of the a or non-penetrating type of 
radiation. Moreover, it slowly decays with time, and 
diminishes to half the initial value in about a year. Madame 
Curie has always been careful to point out that she has not 
succeeded in separating polonium from bismuth, or in 
obtaining any spectroscopic or other more direct proof of its 
existence. The name polonium applies to the body causing 
this particular kind of radio-activity. Hundreds of workers, 
I suppose, have obtained from the Société de Produits 
‘Chimique de Paris specimens of polonium prepared by 
Madame Curie’s method, and have satisfied themselves by 
their own observations as to the character of its radio- 
activity. Now Prof. Marckwald has never claimed that he 
has isolated his body radio-tellurium, although he has been 
more fortunate than Madame Curie in effecting its con- 
centration. Hence the name radio-tellurium applies also to 
the hypothetical constituent causing the radio-activity rather 
than to the preparation itself. Many, no doubt, have 
obtained also specimens of radio-tellurium from the firm of 
Dr. Sthamer, of Hamburg, and have compared its properties 
with those of polonium. 
The meaning applied by Prof. Marckwald to the word 
polonium may be illustrated by these sentences quoted from 
his letter. ‘‘ Shortly after the discovery of polonium Giesel 
found that this substance quickly lost its radio-activity. ...”’ 
““ Giesel’s polonium emitted @ and B rays and lost its activity 
within a few weeks.’’ ‘‘ In this (Giesel’s polonium) I have 
found traces of radio-tellurium, and I have shown that after 
the removal of the latter the remaining substance shows 
strong 6 and diminished a radiation.” 
The question at issue is therefore a very simple one. Is 
Prof. Marckwald justified in applying Madame Curie’s 
name to Prof. Giesel’s preparation? ‘‘ Giesel’s polonium,”’ 
according to Prof. Marckwald’s statement, is a mixture of 
two radio-active constituents :—(1) radio-tellurium, (2) a 
constituent giving B as well as a rays. The latter, since 
it can neither have been polonium nor radio-tellurium, need 
not be further considered in the present discussion. It may 
be something new and interesting, but, on the other hand, 
there is nothing to show that it was not merely a trace of 
radium present as an impurity. In either case it does not 
concern us, and two bodies only, Madame Curie’s polonium 
and Prof. Marckwald’s radio-tellurium, need be further 
considered. Both are obtained from the same variety of 
pitchblende, both are distinguished from all the other radio- 
elements by the fact that they only give a rays, and both 
possess at least a considerable fraction of their initial 
activity after the lapse of one year. Now Prof. 
Marckwald used the same* raw material as Madame 
Curie, namely, the bismuth extracted from the Joachimsthal 
pitchblende. Since he states that his method separated all 
the active constituent we may feel certain (1) that radio- 
1 The point raised in the footnote to Prof. Marckwald’s letter is, I take 
it, aside issue. He brings forward no evidence thatthe bismuth separated 
from the pitchblende by sulphuretted hydrogen (Curie) is different in its 
radio-active properties from that separated by himself as oxychloride, nor 
any reason for supposing that the active constituent in the two cases might 
be expected to be different. It is true that his bismuth contained a minute 
proportion of ordinary inactive tellurium, which was probably almost or 
quite absent in Madame Curie’s preparation. This fact he made use of as 
the basis of his elegant method of concentrating the active constituent, and 
he seems to have at first confused the difference of behaviour of the two raw 
materials to differences in the chemical nature of the active constituents 
But his own 
rather than to the fertuitous presence of a trace of tellurium. 
later experiments (Ber? hte, 1903, p. 3) show that when the tellurinm is 
removed from the solution his methods of precipitating the active con- 
stituent completely fail, but again work perfecily if a few tenths of a 
milligram of ordinary telluric acid in aqueous solution are added. 
NO. 1794, VOL. 69 | 
tellurium must certainly contain polonium; (2) that as it 
gives no B rays it contains none other of the known radio- 
active elements ; (3) that as the radio-active properties of the 
two preparations are indistinguishable the active con- 
stituent of Prof. Marckwald’s preparation is the same as 
that of Madame Curie’s preparation, and therefore by every 
recognised canon should be termed polonium. 
Prof. Marckwald’s work has shown that there are present 
on a maximum estimate 4 milligrams of the active con- 
stituent in two tons of pitchblende, or in 8 kilograms of the 
bismuth salt separated from it. Hence what possible bear- 
ing can such a small trace of substance have upon the 
analytical reactions of the relatively vast bulk of the raw 
material? In laying stress on these reactions he frequently 
seems to apply the term polonium to Madame Curie’s pre- 
paration rather than to its radio-active constituent. 
The same criticism might be applied to the following 
sentence, to be found in his most recent communication 
(Berichte, 1903, p. 2665). ‘‘ Whether this Curie’s polonium 
does not perhaps contain also some radio-tellurium is a 
question which must be left to the discoverers of polonium.” 
With regard to the view expressed that polonium is merely 
radio-active bismuth, or inducedly active bismuth, in sup- 
port of which an opinion once expressed by Madame Curie 
is quoted, the answer, of course, is that Prof. Marckwald’s 
own subsequent work has shown otherwise. By the experi- 
ment of depositing on a stick of pure bismuth the whole of 
the polonium present in a solution, he makes it evident that 
the latter cannot be bismuth. Those who are acquainted 
with the work of Rutherford in 1900 on “‘ induced ”’ activity 
know that the whole conception of radio-active induction 
has been built up on a simple misconception of the pheno- 
mena it is designed to explain. The conception had its 
origin in the belief that the rays from a radio-active sub- 
stance could excite radio-activity in otherwise inactive 
matter, which was not in accordance with the facts known 
at the time it was put forward. 
Giesel repeated the identical experiment of Prof. Marck- 
wald with a solution of pure radium, and found that a stick 
of bismuth after immersion becomes permanently (?) active 
and then only emits a rays, and Prof. Marckwald, in spite 
of his own work, concludes that there exists with certainty 
an inducedly active bismuth giving only a rays, which might 
with accuracy be termed polonium. He, however, omitted 
to state that Giesel obtained the identical result if a stick 
of platinum or palladium were immersed in the radium solu- 
tion. Hence it might be argued that there exist an inducedly 
active platinum and an inducedly active palladium, both of 
which might with accuracy be termed polonium. The 
alchemists considered that they had turned iron into copper 
by means of a solution of blue vitriol, until it was pointed out 
that the latter substance contains copper. It has never been 
shown that any of the effects of the so-called ‘* radio-active 
induction ’’ are really due to the conversion of an inactive 
element into radio-active matter. From the existing 
evidence to the contrary, it would seem more reasonable to 
suppose that they admit of a similar interpretation to that 
now adopted to explain the cuprification of iron. 
FREDERICK Soppy. 
Dependence of the Ionisation, produced by Rontgen 
Rays, upon the Type of the Rays. 
Mr. Eves, in his letter in Nature of March ro (p. 436), 
shows that the relative amount of ionisation produced by 
R6éntgen rays in different gases depends upon the “ hard- 
ness ’’ or penetrating power of the rays. I have lately 
been investigating this question of the dependence of the 
relative ionisation upon the type of rays, and an abstract 
of a preliminary paper on the subject appeared in a report 
of the proceedings of the Cambridge Philosophical Society in 
the number of Nature issued on February 18 (p. 383). These 
experiments, along with later ones, show that the relative 
ionisation in different gases depends upon the type of rays 
used. I used a balance method, balancing the ionisation 
in each gas against that in air. The pressure of the gas 
in the Réntgen ray bulb was varied, thereby varying the 
““hardness ’’ of the rays, and it was found that in the case 
of gases in which the ionisation is greater than in air the 
ionisation in these gases decreases relatively to that in air 
