The Nobel Prize
in Chemistry 1925The Nobel Prize
in Chemistry 1925Presentation Speech by Pr Nobel fetish abducted Chemistry in Prize ofessor H.G. Söderbaum, Secretary of the Royal Swedish Academy of Sciences, on December 10, 1926*
Your Majesty, Your Royal Highnesses, Ladies and Gentlemen.
Around the middle of the 19th century the English scientist Graham put forward
a new principle of subdividing matter by classifying all substances into one
of the two great classes: crystalloids and colloids. A crystalloid, e.g. common
salt, is characterized in that it passes in the dissolved state readily through
membranes such as parchment paper or collodion films and also that it exhibits
a rapid free diffusion. A colloid, on the other hand, e.g. glue, is unable to
pass through such membranes and diffuses extremely slowly, in contrast to the
crystalloid. In passing it may be mentioned that the name colloid originates
precisely from kolla, the Greek word for glue.
Other examples of colloids well known to everyone are proteins, starch, rubber,
water glass, etc.
It was very soon found that sometimes one and the same substance can occur in
one case as a crystalloid and in another case as a colloid. For instance, gold
with mercury produce a crystalloidal solution, whilst gold in an aqueous solution
exists only in the colloidal state. It is consequently more correct to differentiate
between crystalloidal and colloidal states rather than between crystalloidal
and colloidal substances. When it then became a question of forming an
opinion of the reason for these different states, several people, e.g. the American
scientist Lea, had recourse to the concept of allotropy which existed previously
in chemistry, and was illustrated by the typical example of phosphorus with
its two so-called allotropic modifications, the yellow and the red. Others again
imagined the difference to be that the colloidal Nobel Шкаф Chemistry Prize in ШРС Chemistry in полностью подиум Nobel Prize деревянный акустический solutions were not uniform
throughout, not homogeneous as the crystalloidal ones, but that they contained
particles, molecule aggregates, of a size which exceeded by many times the size
of the molecules in a crystalloidal solution. But which of the two interpretations
was the correct one?
This difficult problem was brought a decisive step nearer to its solution by
the invention of the ultramicroscope at the beginning of the 20th century.
The idea originated from Zsigmondy and was developed in detail by him in cooperation
with Siedentopf, an able optician with the firm of Zeiss. The principle of this
instrument is briefly that the intensely illuminated object, the solution to
be examined, is observed by means of a microscope from the side, i.e. vertically
to the axis of the incident light beam. In this way it is possible to differentiate
between particles of such small size that they could not be observed under an
ordinary microscope, just as the dust particles suspended in the air in our
rooms, which are invisible under ordinary conditions, sometimes become visible
when the sun's rays shine through the window in a definite direction in relation
to the observer. With the ultramicroscope, and especially the improved type
which is called the immersion ultramicroscope, progress has been such that particles
with a diameter of down to 8 mm are recognized with
arc-light illumination, and down to 4 mm when using the sun as the light source.
Zsigmondy now found that various gold colloids prepared by him contained delimited
particles under the ultramicroscope although they had appeared completely homogeneous
under an ordinary microscope. He further showed by a systematic study of the
gold colloids that they can be produced in a varying distribution of fineness,
onwards from colloids the particles of which are invisible even in the ultramicroscope,
up to ones whose particles lie at the limit of visibility in the microscope.
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up from small, ultramicroscopic silver particles. He finally showed that the
examination of other colloids also gave similar results. This proved the correctness
of the particle hypothesis, and the heterogeneous nature of colloidal solutions
was established. It has also been possible to determine quantitatively the size
of the particles. The procedure is to delimit optically a small volume of the
colloid to be examined, after which the number of particles in it is counted.
If the mass concentration of the colloid is known, it is easy to obtain the
mass of the particles, and from this - assuming, for example, a spherical shape
and normal specific gravity - the size can be calculated.
As mentioned, there are colloids which are so fine-grained that their particles
cannot be distinguished even in the ultramicroscope. However, Zsigmondy has
made also these accessible to scientific observation by the invention of the
so-called nucleus method. This was also first applied to gold, the classical
metal of colloid research, and it is carried out by introducing the fine-grained
gold colloid into a reducing solution from which metallic gold is slowly precipitated.
This now settles on the invisible, colloidal gold particles so that they - the
so-called gold nuclei - gradually increase in size, and finally become visible
in the ultramicroscope. In this way gold particles with a diameter of down to
1 1/2 mm have been measured, and it has become possible to determine
the particle size - thus, the degree of heterogeneity - in the case of all gold
colloids. It was possible to apply the method later to a large number of other
metals, and it has proved to be of the greatest importance for a whole number
of investigations which had the object of establishing general principles for
colloids, indeed it may seem doubtful whether these investigations could have
been at all possible without Zsigmondy's nucleus method.
It is a generally known fact that when a colloidal solution, for example one
of protein, is treated with certain substances such as salts or acids - in short,
electrolytes - it coagulates or "solidifies to a jelly", i.e. it passes into
a semi-solid form or a so-called gel. Corresponding, although not completely
similar, conditions also arise in regard to colloidal metals, the reason being
that the primary particles join together to form large aggregates, i.e. they
increase in size whilst diminishing in number.
Zsigmondy's work has quite simply been pioneering as regards the explanation
of the mechanism of the coagulation phenomenon and also as regards the study
of the structure of gels. It has been found that coagulation progresses extremely
slowly at a low concentration of the electrolyte, whilst with increasing concentration
the rate of coagulation gradually increases up to a certain stage - at the so-called
threshold value - when it rapidly reaches a limiting value which then no longer
increases further or changes when the concentration is further increased. Within
the rapid coagulation, as Zsigmondy found, the coagulation time is independent
not only of the concentration of the electrolyte but also of its nature, whilst
on the other hand, the threshold value and the rate within the range of slow
coagulation are characteristic for each individual electrolyte.
Based on these facts, Zsigmondy expressed several important fundamental ideas
for explaining the coagulation mechanism which were later formulated more accurately
and developed to a mathematical theory of coagulation by Smoluchowski. In turn,
Zsigmondy and his pupils have been able to verify experimentally this theory
in its various details whereby its great general validity has been proved in
a brilliant manner.
The brief review given here of some of the most important work of Zsigmondy
is necessarily highly incomplete, if not to say fragmentary, but should surely
suffice to show how it pioneered the way and opened up new regions in a field
of research which had so far been difficult of access, a field which must be
recognized as having the very greatest importance for human knowledge. Let us
only remember in this connection that all manifestations of organic life are
finally bound to the colloidal media of the protoplasm.
This by way of motivation for the decision of the Academy of Sciences to award
the Chemistry Nobel Prize for 1925 to Dr. Richard Zsigmondy, Professor of Chemistry
at the University of Göttingen, for proving the heterogeneous nature of
colloidal solutions and for the methods used which have laid the foundation
of modern colloid chemistry.
 
Professor Zsigmondy. When the Royal Swedish Academy of Sciences
after mature consideration decided to award you the Nobel Prize in Chemistry
for the year 1925, it did this in the firm conviction that it would only be
making itself the executor of the unanimous verdict of the entire scientific
world.
Convinced that the significance of your pioneering work which is generally recognized
today, will in future times stand possibly in an even clearer light, the Academy
allows itself to offer you its sincere congratulations on the well-deserved
reward the external insignia of which you are now about to receive.
* The Nobel Prize in Chemistry 1925 was announced on November 11, 1926.
From Nobel Lectures, Chemistry 1922-1941, Elsevier Publishing Company, Amsterdam, 1966