The Nobel Prize in Chemistry 1926
The Svedberg
Presentation Speech by Professor H.G. Söderbaum, Secretary of the Royal Swedish Academy of Sciences, on December 10, 1926
Your Majesty, Your Royal Highnesses, Ladies
and Gentlemen.
The Academy of Sciences has decided to award the Nobel Prize in
Chemistry for 1926 to The Svedberg, Professor of Physical
Chemistry at the University of Uppsala, for his work on
disperse systems.
Almost a hundred years ago, or more accurately in 1827, the
English botanist Robert Brown discovered with the aid of an
ordinary microscope that small parts of plants, e.g. pollen
seeds, which are slurried in a liquid, are in a state of
continuous, though fairly slow movement in different directions.
A more detailed study of this phenomenon during the last few
decades has led to extremely interesting results. By means of the
ultramicroscope it has been possible to observe a similar, only
much livelier movement with very much smaller particles of a
colloidal nature. As we have recently heard, Einstein evolved a
theory for this so-called Brownian movement which was then
developed to a high degree by the now late Smoluchowski.
According to these scientists, the movement arises through the
impacts of the molecules of the liquid against the particles
slurried in the liquid, provided that the latter are sufficiently
small. Taking a crude analogy: if a fly or a gnat flies against
an elephant, the elephant will not noticeably alter its position,
but this can occur if the fly or gnat collides only with a
bee.
The theory in question has been confirmed convincingly by
experimental investigations of several colloid scientists among
whom especially two of today's prize-winners, Perrin and Svedberg,
have occupied and still occupy a leading position. Should it now
be true that the movement of particles suspended in a liquid,
which we can actually observe with the aid of our extremely
highly magnifying instruments, can be explained only as a result
of the movement of molecules beyond the limits of direct human
vision, then this provides visual evidence for the real existence
of molecules and consequently also for that of atoms, evidence
which is all the more remarkable as not so long ago an
influential school of scientists declared these particles of
matter to be unreal fictions representing an obsolete viewpoint
of science.
It is known that the opposition conducted by the colloid
scientists so successfully against this so-called energetic view
has been continued by others who have gone much farther in that
according to this view not only what we call matter, but also
electricity occurs solely as particles of a definite size - the
so-called electrons - and even that energy at all is regarded as
bound to larger or smaller multiples of a smallest unit, the
so-called elementary quantum.
If one has once become convinced of the existence of atoms and
molecules, the question as to their real size is naturally - this
hardly needs stressing - a question of the very greatest
interest. Whereas it was formerly possible to calculate this size
only roughly from the properties of gases and in connection with
the theory applying to them, the position was now, as happens so
often in the history of science, that almost simultaneously
several new and considerably more precise methods for determining
the natural constant in question appeared. Among these methods
those based on colloid-chemical phenomena occupy a special
position through their vividness and persuasive power, even
though they may be for the time being slightly superseded by
other methods in regard to accuracy. Also in this field Svedberg
and the school of eminent scientists trained by him, Swedes as
well as nationals from more or less distant countries, have
achieved extremely valuable results. This has been done in
several ways, among others, by determining the speed at which
colloidal particles migrate by themselves, or diffuse in a
liquid, or by measuring the distribution of such particles in a
column of liquid, the latter according to a method proposed
originally by Perrin.
In accordance with the theory for the movement of gas and liquid
molecules which, as just indicated, has also been applied to
colloidal particles, it is assumed that the mean value of the
momentum of molecules or particles has a definite magnitude at
each temperature, but that the speeds of the individual particles
can vary within wide limits. If we now consider a very small
volume fraction, the result is that, as Smoluchowski has
calculated in detail, the number of particles present
simultaneously within this volume can change from one moment to
another. Svedberg and his collaborators have been able to confirm
this extremely interesting conclusion that a "few-molecular"
system having definite limits within a large volume of a material
with a definite mean temperature may contain a varying number of
particles, partly by counting the colloidal particles,
partly in the case of solutions of radioactive substances
by counting the number of so-called scintillations, i.e. light
flashes, which radioactive particles produce when they impinge
upon a screen coated with zinc sulphide.
With the last investigation, however, we have gone beyond the
field of actual colloid chemistry, although the solution of a
radioactive substance, e.g. polonium chloride, can naturally be
called a disperse system, though more accurately it is
molecular-disperse because the substance dissolved in the solvent
occurs here as molecules, not as molecular aggregates, as is the
case in a colloidal solution.
During the last few years Svedberg has completed an extremely
ingenious invention, the so-called ultracentrifuge, which enables
highly interesting investigations to be made also on such
molecular-disperse systems. We know that when a slurry, an
emulsion, is put into a rapidly rotating motion, its heavier
constituents are thrown outwards in the direction of the
periphery of the motion. This happens in the most used of all
centrifuges, the milk separator, where the skimmed milk is
pressed outwards whilst the lighter fat particles, the cream,
accumulate inwards and can therefore be separated. Similarly in a
solution, when centrifuging is sufficiently rapid, the molecules
of the dissolved substance must accumulate outwards if they are
considerably heavier than the molecules of the solvent. After
overcoming exceptional experimental difficulties Svedberg
succeeded in demonstrating this with the aid of an apparatus
which allows the enormous speed of rotation of 40,000 revolutions
per minute, and in which through a highly refined arrangement the
progressive distribution of the particles within the extremely
rapidly whirling solution can be observed and recorded
photographically. The molecular weight of the dissolved material
can be calculated from this distribution. This has already been
done for certain proteins essential for organic life and for
other substances allied to them. For example, the molecular
weight of the red colouring agent of the blood, haemoglobin, has
been determined as approximately 67,000 which assumes that there
are in the region of 10,000 atoms in such a molecule.
In view of the fact that this year not less than three Nobel
Prizes have been awarded for work in the field of colloid
research, some people may ask whether this field really has a
corresponding importance "for mankind".
By way of answer the following few remarks may be made.
Inorganic chemistry has revealed more and more cases where only a
colloid-chemical approach was able to clarify the observed
phenomena.
For physical chemistry colloids form a rich and rewarding field
of research.
In organic chemistry we meet the perhaps most important colloids,
the proteins and the polymeric carbohydrates, which cannot be
studied without the aid of colloid research.
As all living matter is built up largely from organic colloids,
the importance of colloid research for physiology and the medical
sciences is obvious.
Finally, colloids play an important part in the various branches
of chemical industry, such as in dyeing and tanning, in the
cellulose, nitrocellulose, celluloid and textile industry, in
rubber manufacture, in the pottery and cement industry, in the
photographic industry, etc.
Professor Svedberg. With a feeling of
sincere pleasure and justified pride the Academy of Sciences
again sees itself able to recruit from the ranks of its own
members the corps d'élite of researchers which has
been set up by Alfred Nobel's legacy.
You have been able to accept on a previous occasion the assurance
of the Academy on this together with its sincere
congratulations.
In this festive hour we would now only add to this the hope that
it may be made possible for you to carry out in your own country
the important investigations which have already borne such fine
fruit to the honour of Swedish research and which appear to be
not less full of promise for the future.
From Nobel Lectures, Chemistry 1922-1941, Elsevier Publishing Company, Amsterdam, 1966
Copyright © The Nobel Foundation 1926
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