The Nobel Prize
in Chemistry 1926The Nobel Prize
in Chemistry 1926Presentation 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