The Nobel Prize in Chemistry 1943
George de Hevesy
In regard to de Hevesy's work, Professor A. Westgren, member of the Nobel Committee for Chemistry of the Royal Swedish Academy of Sciences, made the following statement*
When, in 1913, de Hevesy was working with
Rutherford in Manchester, this
young scientist had been commissioned to isolate radium D from
radioactive lead. His efforts were unsuccessful. It had in fact
become apparent that radioactive radium D differed so little from
inactive radium G, the last of the series of descendants of
radium, that all attempts to isolate them from each other seemed
destined to failure. The reason for this was at the same time
discovered. Radium D and radium G are isotopes and constitute
different species of lead. They differ in their atomic weight
whilst their atoms have the same nuclear charge. The shells of
their electrons, shells which determine their chemical
properties, are therefore more or less identical.
Although unsuccessful, de Hevesy's efforts were not wasted. They
gave him the idea for a new method of chemical research.
If it is impossible to isolate chemically a radioactive isotope
from an element of which it is part, it must be possible to use
this peculiarity to follow in its details the behaviour of this
element during chemical reactions and physical processes of
different kinds. The active atoms are recognized by their
radiation and, being faithful companions of the inactive atoms of
an element, they serve as markers for them. Since the intensity
of radiation can be determined with such precision that
imponderable quantities can be measured in this way, extremely
small quantities of a marker of this kind are sufficient.
By using radium D as a marker, de Hevesy determined the
solubility of highly insoluble lead compounds. He succeeded in
determining exactly the quantity of lead sulphide or of lead
chromate taken up under different conditions from solvents of
different types. He studied the exchangeability of lead atoms
into the dissolved substances and was able to confirm that it
corresponded to the behaviour of the lead atoms as ions. The
movements of the atoms in solid lead, i.e. the self-diffusion
which occurs in this metal, would be determined; it had
previously been impossible to measure this process. By
precipitating thorium B, a very active isotope of lead, on the
surface of a lead crystal and by following the reduction in
radiation intensity brought about by the changes in place of the
active atoms with the inactive lead atoms of the lower layer, and
hence with the penetrations which took place in the crystal, he
was able to measure the energy needed to liberate an atom from
the crystallised part of the lead, in other words the
dissociation energy of the crystal lattice. This energy was found
to be of the same order of magnitude as the heat of vaporisation
of lead. This latter research is particularly interesting from
the physico-chemical point of view.
The new method has also enabled biological processes to be
studied. Beans placed in solutions containing lead salts with a
mixture of active lead atoms absorbed a part of these salts but
the distribution of the metal was not the same in the root, the
stem and the leaves. Most of the lead, which does not favour
natural biological development but on the contrary acts as a
poison, stays in the root. Relatively more lead was extracted
from dilute than from more concentrated solutions. Absorption and
elimination of lead, bismuth and thallium salts by animal
organisms was studied in this way. A knowledge of the
distribution of bismuth compounds introduced into an animal
organism is valuable from the medical point of view, since some
of these compounds, as we know, are used therapeutically.
So long as natural radioactive elements only were used as
markers, use of the new method was inevitably very limited. In
fact the method could be applied only in the case of heavy metals
- lead, thorium, bismuth and thallium - and their compounds. The
situation was to be very different when Frédéric and Irène
Joliot-Curie, and Fermi succeeded in
producing radioactive isotopes from any element by bombarding it
with particles. This discovery was made some ten years ago and
the study of chemical processes by means of radioactive markers
has since then been carried to such a point that it is now widely
used in laboratories throughout the world. De Hevesy has remained
the prime mover in this new field of activity and much
first-class and important research has been carried out by him
and his co-workers.
Exceptionally valuable results have thus been obtained in
biology. An isotope of radioactive phosphorus, which can be
obtained by exposing sulphur to neutron radiation or ordinary
phosphorus to radiation from nuclei of heavy hydrogen, has mostly
been used. This radioactive phosphorus is sufficiently
long-lasting for tests of this nature. It has a half-life of
approximately 14.8 days. De Hevesy produced physiological
solutions of sodium phosphate containing this marker and injected
them into animals and humans. The distribution of the phosphorus
was determined at certain intervals. A study of blood samples
showed that the phosphorus thus introduced quickly left the
blood. In human blood the radio-phosphorus content had fallen
after only 2 hours to a mere 2% of its initial value. It diffuses
into the extra-cellular body fluid and gradually changes places
with the phosphorus atoms of the tissues, organs and skeleton.
After some time it can even be found, though in very small
quantities, in the enamel of the teeth. Exchanges small and slow
as they may be, therefore occur between the outer hard parts of
the teeth and the inner tissues of the bones and the lymph. Most
of the phosphorus introduced, finds its way into the skeleton,
muscles, liver and gastro-intestinal organs. Elimination of
phosphorus from living organisms has also been studied by this
method.
Phosphorus is an extremely important element in biological
processes. The knowledge of its functions in living organisms
which has been acquired thanks to the use of radioactive markers
is therefore of the very greatest interest. De Hevesy succeeded
in detecting where and at what speed the various organic
compounds of phosphorus are able to form and the paths which they
take in the animal organism. In order to form from a phosphate
which has been injected into the blood they must first penetrate
into the cells. Acid-soluble compounds of phosphorus form
rapidly, whereas phosphatides closely related to fatty substances
are slower-forming. These latter form mainly in the liver, whence
they are carried by the blood plasma to the places where they
will be consumed. De Hevesy showed that the phosphatides of the
chicken embryo are produced in the embryo itself and that they
cannot be extracted from the egg yolk.
De Hevesy also carried out several investigations with
radioactive sodium and potassium. He studied how physiological
saline containing radioactive sodium which was injected into a
human subject first spread into the blood and then slowly
penetrated into the cells; he also studied the manner in which it
is excreted. After 24 hours the blood corpuscles had lost
approximately half their sodium content.
In addition to the above-mentioned markers, several other active
isotopes, such as magnesium, sulphur, calcium, chlorine,
manganese, iron, copper and zinc, have been used for this type of
research. In the case of the lighter elements it has also been
possible to use inactive isotopes such as heavy hydrogen, with an
atomic weight of 2, nitrogen, with an atomic weight of 15, and
oxygen, with an atomic weight of 18. It is of course less easy to
determine the content of an inactive than of an active marker,
but this can be done by determinations of density or
mass-spectrographically. To determine the concentration of
deuterium, or heavy hydrogen, which is twice as heavy as ordinary
hydrogen, is a relatively easy matter. De Hevesy used deuterium
as marker in many tests. He then noticed that a person who has
drunk water containing heavy hydrogen excretes deuterium in the
urine after only 26 minutes. Frogs and fishes swimming in water
containing deuterium absorb it and, after about 4 hours, are in
equilibrium with the medium as far as the deuterium is concerned.
Heavy nitrogen and heavy oxygen have also been used in many
investigations.
* Talk given on the radio on 10th December, 1944, with amendments and additions. The Nobel Prize in Chemistry 1943 was announced on November 9, 1944.
From Nobel Lectures, Chemistry 1942-1962, Elsevier Publishing Company, Amsterdam, 1964
Copyright © The Nobel Foundation 1943
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