270 
NATURE 
2 
[JANUARY 17, 1907 
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Production of Radium from Actinium. 
In a recent letter to this Journal (November 15, 1906) 
Dr. Boltwood has given an account of experiments which 
show that radium is continuously produced in a solution 
of actinium, and concludes that radium is a disintegration 
product of actinium, the latter occupying an intermediate 
position in the family of disintegration products between 
uranium and radium. The radium is produced from the 
actinium at about the theoretical rate, and he deduces in 
a simple way that the time for radium to be half trans- 
formed is about 3000 years. These results of Dr. Bolt- 
wood are of great interest, and mark an important stage 
in the search for the somewhat elusive parent of radium. 
It may be of interest to the readers of Nature to give 
a brief account of some experiments I have made on this 
subject, the results of which were communicated to the 
American Physical Society at New York on December 28, 
1906. In the Bakerian lecture of. 1904 (Phil. Trans., A, 
p- 169, 1904). I briefly described some experiments that 
had been commenced to see whether actinium produced 
radium. -Some of Giesel’s actinium was taken, dissolved 
in acid, and the greater part of the radium then present 
was removed -by precipitating barium in the solution. The 
amount of radium left. in the solution was determined by 
the emanation method, using an electroscope carefully 
calibrated by means of a standard radium solution. Over 
a period of three months no very certain evidence was 
obtained that the amount of radium had increased. The 
solution of actinium was then set aside in a closed vessel 
with the intention of testing it for the presence of radium 
‘at regular intervals. In-the meantime, the great danger of 
possible contamination, in testing solutions for radium in 
a laboratory where considerable quantities of radium were 
continually in use, was recognised, and. for this and other 
reasons the solution was not again tested. until two and 
and a half years had elapsed. 
When Dr. Boltwood informed me of the growth of 
radium in his actinium, I at once tested this solution for 
radium by the emanation method. A preliminary observ- 
ation showed that there had been a large increase in the 
quantity of radium in the solution in the interval since the 
early experiments. In the course of making an accurate 
determination, the solution was unfortunately contaminated 
with radium, prebably through the use of a lubricant on 
a stop-cock attached to the vessel. Under such conditions 
I could place no reliance on the final measurement. 
Happily, however, I had placed aside, at the time of pre- 
paring the original actinium solution, a sample of the 
actinium salt the radium content of which at that time 
had been accurately determined. This was now tested, 
and the amount of radium in it was found to have in- 
creased at least four times the initial value in the two 
and a half years’ interval, showing a rate of growth of 
radium in the actinium of much the same magnitude as 
that observed in the experiments recorded later. I think 
that my failure to observe an increase in the amount of 
radium in the actinium solution over a period of three 
months was due to the unsuitable chemical treatment used 
initially to remove the radium from the actinium. An 
excess of sulphuric acid must have remained in the solu- 
tion, and this would tend to precipitate the radium when 
formed as sulphate—a condition in which probably only 
a fraction of the emanation would be released. A con- 
siderable increase in the amount of radium might con- 
sequently only show a small increase in the amount of 
emanation carried away by aspirating air through the 
solution. 
Experiments were at once undertaken to remove the 
radium again from the contaminated solution by a simpler 
and better methed. This proved successful, and only a 
minute fraction of the radium was left. in the solution. 
The latter was then placed in a glass vessel, and the 
NO. 1942 VOL. 75] 
amount of radium in it determined weekly by boiling out 
the emanation, and then introducing it into a suitable 
emanation electroscope. A progressive increase in the 
amount of radium has been observed, amounting to 80 per 
cent. of the initial value over a period of five weeks. If 
this rate of growth continues at a constant, rate, the 
amount of radium in the solution at the end of a year 
should be more than eight times the initial value. _ The 
actinium used in this experiment was equivalent to about 
half a gram of an actinium preparation of activity about 
250 times uranium, and the rate of growth of radium 
observed corresponds to about 3x10-" gram of radium 
per year. 
There is one important point that suggests itself in 
considering the results as given by Dr. Boltwood. The 
growth of radium observed in his actinium solution possibly 
might arise, not from the actinium itself, but from another 
distinct substance, normally separated from the radio- 
active mineral with the actinium. In order to throw some 
light on this question, I compared the rate of production 
of radium observed in my actinium with the rate of pro- 
duction to be expected on the simple theory, supposing 
that the actinium is transformed directly into radium. 
Without going into details, it suffices to say that this can 
be done by comparing the a-ray activity of a known frac- 
tion of the actinium solution in the form of a very thin 
film with that of a thin film containing a known quantity 
of radium. In this way I calculated that the growth of 
radium observed agreed with the disintegration theory, if 
the period of half transformation of radium was about 
2600 years. The period so deduced is not very different 
from that determined bv Boltwood from quite distinct con- 
siderations. This is satisfactory so far as it goes, but 
such an agreement between the periods obtained by the 
two methods implies that the activity, due to the actinium 
in pitchblende, is about the same as that due to radium 
and its products. As a result of careful measurements, 
Boltwood, however, found that this is not the case, for 
the activity due to the actinium is only a small fraction of 
that due to radium. Further experiments are required to 
explain this anomaly. 
There is one other point on which I have made a number 
of experiments. If radium arises from actinium, it should 
be produced by the active deposit of actinium which con- 
tains the last products cf the actinium series, namely, 
actinium A and B. In order to test this, a platinum plate 
was made the negative electrode in a vessel containing 
a very active actinium preparation, and the active deposit 
was collected for a week or more. The platinum plate 
was then removed and immersed in a closed vessel con- 
taining dilute hydrochloric acid. After standing for a 
week, the accumulated emanation was boiled out, and the 
amou:: determined in an electroscope. Knowing the 
amount of the a-ray activity due to the active deposit on 
the platinum plate compared with the activity due’ to a 
thin film of radium, and also the time of exposure, it is 
a simple matter to calculate the growth of radium to be 
expected on the assumption that radium is half trans- 
formed in about 3000 years. Using a small platinum plate, 
the amount of radium observed was certainly not greater 
than one-tenth the theoretical amount, and, with a much 
larger plate, not more than one-fifth. In these experi- 
ments the greatest care was taken to avoid any possible 
radium contamination. The observations were made in the 
chemistry building which is free from radio-active material, 
and I was fortunate in having the use of the emanation 
electroscopes of low natural leak, set up by Mr. Eve, who 
kindly assisted me in these experiments. The plates and 
solutions employed were initially tested for the presence 
of radium, so that the growth of radium observed, though 
much smaller than the theoretical amount, was still quite 
definite. These experiments are being continued. The 
smallness of the amount of radium observed may either 
be due to the presence of another change between 
actinium B and radium, or, what is more probable, to 
the loss in an electric field of the radium. formed on the 
platinum plate. Such a possibility is suggested by the 
results of Meyer and Schweidler, who observed that there 
was always a small residual activity on substances, ex- 
posed for a long time in the presence of the actinium 
emanation, which gradually disappeared. 
