"for his work on the equation of state for gases and liquids"
Presentation Speech by the Rector General of National Antiquities, Professor 0. Montelius, President of the Royal Swedish Academy of Sciences
Your Majesty, Your Royal Highnesses, Ladies and Gentlemen,
The Academy of Sciences has resolved to award this year's Nobel Prize for
Physics to the world-famous Dutch physicist, Johannes Diderik van der Waals
for his studies of the physical state of liquids and gases.
As far back as in his inaugural dissertation "The relationship between
the liquid and the gaseous state". Van der Waals indicated the problem
to which he was to devote his life's work and which still claims his attention
today. In the dissertation to which I have referred he sought to account
for the discrepancies from the simple gas laws which occur at fairly high
pressures. He was led to the assumption that these discrepancies are partly
associated with the space occupied by the gas molecules themselves, and
partly with the attraction which the molecules exert on one another, owing
to which the pressure acting on the interior of the gas is greater than
the external pressure. These two factors become more and more pronounced
with increasing compression of the gas. At a sufficiently high pressure,
however, the gas becomes liquid, unless the temperature exceeds a certain
value, the critical temperature as it is termed. Van der Waals showed that
it is possible to apply the same considerations and calculations to liquids
as to gases. When the temperature of a liquid is raised to beyond the critical
temperature without the liquid being allowed to volatilize, it is in fact
converted continuously from the liquid to the gaseous form; and close to
the critical temperature it is impossible to distinguish whether it is liquid
or gas.
The force preventing the separation of the molecules in a liquid is their
mutual attraction, owing to which a high pressure prevails in the interior
of the liquid. Van der Waals calculated this pressure, the existence of
which had already been vaguely perceived by Laplace, for water. It amounts
to not less than about 10,000 atmospheres at normal temperature. In other
words the internal pressure, as it is called, of a drop of water would be
about ten times greater than the water pressure at the greatest depth of
the sea known to us.
However, this was not the most important result of Van der Waals' studies.
His calculations led him to consider that once we are acquainted with the
behaviour of a single type of gas and the corresponding liquid, e.g. that
of carbon dioxide, at all temperatures and pressures, we are able by simple
proportioning to calculate for any gas or liquid its state at any temperature
and pressure, provided that we know it at only one, i.e. the critical, temperature.
On the basis of this law of what are known as "corresponding states"
for various gases and liquids Van der Waals was able to provide a complete
description of the physical state of gases and, more important, of liquids
under varying external conditions. He showed how certain regularities can
be explained which had earlier been found by empirical means, and he devised
a number of new, previously unknown laws for the behaviour of liquids
It appeared, however, that not all liquids conformed precisely to the simple
laws formulated by Van der Waals. A protracted controversy arose around
these discrepancies which were ultimately found to be attributable to the
molecules in these liquids not all being of the same character; the older
Van der Waals laws apply only to liquids of uniform composition. Van der
Waals then extended his studies to mixtures of two or more types of molecules
and here too he managed to find the laws and these, of course, are more
complex than those which apply to substances composed of molecules of a
single type. Van der Waals is still occupied with working out the details
of this great investigation.
Nevertheless, he has successfully surmounted the difficulties that were
initially in his path.
Van der Waals' theory has also been brilliantly successful through its predictions
which made it possible to calculate the conditions for converting gases
to liquids. Two years ago Van der Waals' most prominent pupil, Kamerlingh
Onnes, in this way succeeded in compelling helium-the last previously uncondensed
gas - to assume the liquid state.
Yet Van der Waals' studies have been of the greatest importance not only
for pure research. Modern refrigeration engineering, which is nowadays such
a potent factor in our economy and industry, bases its vital methods mainly
on Van der Waals' theoretical studies.
Professor Van der Waals. The Royal Academy of Sciences has awarded you this
year's Nobel Prize for Physics in recognition of your pioneering studies
on the physical state of liquids and gases.
Hamurabi's and Moses' laws are old and of great importance. The laws of
Nature are older still and even more important. They apply not just to certain
regions on this Earth, but to the whole world. However, they are difficult
to interpret. You, Professor, have succeeded in deciphering a few paragraphs
of these laws. You will now receive the Nobel Prize, the highest reward
which our Academy can give you.
From Nobel Lectures, Physics 1901-1921.