_ Via nitrate, in a quartz vessel. 
FEBRUARY 15, 1917] 
NATURE 
469 
LETTERS TO THE EDITOR. 
{The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of NaTurE. No notice is 
taken of anonymous communications.] 
The Atomic Weight of ‘‘ Thorium’’ Lead. 
In continuation of preliminary work published by 
Mr. H. Hyman and myself (Trans. Chem. Soc., 1914, 
¢v., 1402) I gave an account in Nature, February 4, 
1915, p. 615, of the preparation of 80 grams of lead 
from Ceylon thorite and of the determination of its 
density in comparison with that of ordinary lead, 
which proved the thorite lead to be 0-26 per cent. 
denser. Taking the new international figure, 207-20, 
for the atomic weight of common lead, that for the 
thorite lead would be 207-74 on the assumption that 
the atomic volume of isotopic elements is constant. 
This lead and the comparison sample were each 
distilled in three fractions, and the atomic weights of 
the two middle fractions were determined from the 
ratio, Pb: PbCl,, by converting the metal into chloride, 
Only single deter- 
minations were done, which gave the values 207-694 
-and 207-199 respectively, which are in the ratio of 
100:24 to 100. 
This result, which indicated clearly that the atomic 
volume of isotopic elements is constant, was com- 
_municated in a lecture to the Royal Institution, 
May 15, 1915, and to Section A of the British Associa- 
tion at Birminghaim, 1915. 
Since then Prof. T. W. Richards and Mr. Wads- 
worth at Harvard have shown that the density of lead 
derived from uranium minerals is less than that of 
common lead, but, as in the case of thorium lead, the 
atomic volume is constant. Varieties of lead of 
atomic weight from 206-08 to 207-18 varied in density 
from 11-273 to 11-337. The latter values refer to 
common lead. 
Dr. R. W. Lawson, at present interned in Vienna 
but allowed full liberty to continue his investigations 
at the Radium Institut under Prof. Stefan Meyer, 
communicated to me in July last year the desire of 
the investigators in that institute to examine inde- 
pendently the atomic weight of some of my thorite 
lead, and I accordingly sent him the first fraction of 
the distilled lead, weighing some 12 grams. He has 
now written to me, and it is a pleasant duty first to 
mention that he speaks in the warmest terms of the 
utmost kindness and consideration shown him by the 
staff of the institute and of the courtesy and con- 
sideration of the police and other authorities during 
his internment. He reports that Prof. Hénigschmid 
has made four determinations of the atomic weight of 
my lead, according to the method of gravimetric 
titration and the relation of chloride to silver, and 
four by gravimetric analysis, whereby the weights of 
the chloride and silver chloride were determined. The 
complete mean of the eight results was 207-77+0-014, 
which is in excellent agreement with my own figure, 
207-74, found indirectly from the density, and shows 
that my single atomic-weight determination, 207-694, 
was not seriously in error. 
It is especially gratifying to have the conclusion 
that the atomic weight of thorium lead is higher than 
that of common lead confirmed by an investigator of 
the training and experience of Prof. Hénigschmid. 
For, although the converse proposition that the atomic 
weight of lead from uranium minerals is lower than 
that of ordinary lead has, since the publication of 
the first paper by Mr. Hyman and myself on thorite 
lead, been thoroughly and conclusively established by 
the work of many investigators at Harvard, in Vienna, 
NO. 2468, VoL. 98] 
and in Paris, several of them famous for their atomic- 
weight determinations, doubt has lingered with regard 
to our results for the very much more difficult case of 
thorium lead. In the first place, no one but myself 
has been able to obtain a suitable material by which 
to test the question, and I, of course, can claim no 
previous experience of atomic-weight work. In the 
second place, there has been an unfortunate confusion 
between my material, Ceylon thorite, and thorianite, 
a totally distinct mixed thorium and uranium Ceylon 
mineral. Lastly, there has been the widespread view, due 
to Holmes and Lawson, Fajans, and others, mainly 
derived from geological evidence, that thorium-E, the 
isotope of lead resulting from the ultimate change of 
thorium, was not sufficiently stable to accumulate over 
geological periods of time. This confirmation from 
Vienna thus clears up many controversial matters, and 
we now know of varieties of lead differing from 206-08 
to 207-77 in atomic weight, and from 11-273 to 11-376 
in density, the ‘atomic volume in all cases examined 
being constant. 
According to analyses by Miss A. F, R. Hitchins 
and myself, the 20 kilos of selected thorite worked 
upon contained 0-4 per cent. of lead, 57 per cent. of 
thorium, 1-03 per cent. of uranium, and o-5 c.c. of 
helium per gram. Taking the ratio of the period of 
thorium to that of uranium as 3-2, and assuming that 
the whole of the lead is of radioactive origin and is 
stable, 94:5 per cent. is derived from thorium, and 
5-5 per cent. from uranium. If 206-0 is the true 
atomic weight of uranium lead, Prof. Hénigschmid’s 
value, 207-77, for thorite lead gives the figure 207-87 
for the atomic weight of thorium lead, whilst his 
figure, 232-12, for the atomic weight of thorium gives 
a total loss of 0-25 unit of mass in the six a- and 
four B-ray changes suffered by the thorium atom. 
From these data and from Silberstein’s and his own 
theories of mutual electromagnetic mass, perhaps Prof. 
Nicholson may be able to give us further information 
as to the constitution of the nucleus of the thorium 
atom. FREDERICK SODDY. 
Marischal College, Aberdeen, February 1. 
The Bursting of Bubbles. 
PRESUMABLY all bubbles when they burst on the sur- 
face of a liquid commence to do so at the top and 
thus give rise to gaseous vortices. In the ordinary 
way these are not apparent, but recently we have 
accidentally discovered a neat way of making them 
easily visible. The method consists in creating the 
bubbles by sparking with a Ruhmkorff coil between 
two wires beneath the surface of some resin oil and 
thus gasifying the latter. As the bubbles are full of 
smoke, when they burst the vortex effect is clearly 
indicated by the formation of beautiful little smoke 
rings. The size of the bubbles and of the rings de- 
pends upon the viscosity of the oil, greater viscosity 
causing bubbles and rings to become larger. This can 
easily be shown by cooling or warming the oil. 
A. A. CAMPBELL SWINTON. 
Evetyn BEALE. 
66 Victoria Street, Londor, S.W. 
February 6. 
A Plea for a Scientific Quadruple Entente. 
Tue letter of Prof. Eugenio Rignano in Nature of 
January 25 may have recalled to some a discussion 
on literature which took place in Section D at the 
British Association meeting at Manchester in 1915, a 
discussion which was introduced almost precisely 
from the same point of view as that now given by 
Prof. Rignano. It is the fact that Germany, by wel- 
coming and publishing papers in French, Italian, and 
English, as well as in German, and by printing the 
material practically as fast as it arrived, had gained 
