Destination Great Britain:
Early Clues
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We're in Great Britain, and the year is 1906. Right now there are many ideas about just what the
chemical structure of rubber is. Most rubber science is being done in Germany. But we're
interested in a British scientist named Samuel Pickles. Pickles had been a student of William
Perkin, the great chemist who learned how to make dyes from coal tar. More importantly, he
is not comfortable with the theories German scientists are proposing concerning rubber.
Scientists have figured out that natural rubber is a hydrocarbon (that is, it is made of only
hydrogen atoms and carbon atoms), that it contains carbon-carbon double bonds, and that it has
an empirical formula of
C5H8.
This doesn't mean that each rubber molecule has five carbon atoms and eight hydrogen atoms. It
just means that the ratio of carbon atoms to hydrogen atoms is 5:8. The real molecular
formula could be C10H16,
or C50H80, or any formula
that had a 5:8 carbon:hydrogen ratio.
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1,5-dimethyl-1,5-cyclooctadiene.
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Scientists also know that by heating natural rubber they can obtain an oily liquid, which would
later be known as
1,5-dimethyl-1,5-cyclooctadiene. Catchy name, for sure, but we're going to call it
dimcod from here on out. Dimcod has the same empirical formula as natural rubber, and a
molecular formula of C10H16.
A German scientist named Carl Dietrich Harries has a theory that he put together between 1902
and 1905. He could see that natural rubber and dimcod aren't very much like each other. The
rubber acts like it was made of molecules with very high molecular weights. Normal molecular
weight tests like vapor pressure osmometry and solution freezing point depression had given
unusually high numbers (as high as 100,000!) for lots of natural materials like rubber, starch,
cellulose, and proteins. So Harries is now proposing that dimcod molecules
are clumping together in giant blobs. These blobs are held together by intermolecular forces
acting between the carbon-carbon double bonds in the dimcod molecule, according to Harries.
He was proposing that rubber is not made from molecules with very high molecular weights, but
from small molecules loosely bound together so that they act like big giant molecules. These
clumps became known as colloids.
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A hypothetical colloid
made of dimcod molecules.
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According to Harries, attractive forces (shown in black)
should act between the carbon-carbon double bonds,
making dimcod molecules clump together to form colloids.
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Across the English Channel Pickles is taking this all in. He wonders about work that John
Hall Gladstone had done. Gladstone reduced the double bonds in a sample of
natural rubber, yet it still behaved like it was made of giant molecules.
Gladstone brominated natural rubber, reducing the double bonds to single bonds.
<
If Harries'
theory is right, reducing the double bonds would have turned the rubber into an oily liquid.
(Remember, Harries claims that forces between the double bonds hold his colloids together.)
Also, other scientists have shown that
cyclooctadiene cannot be made into rubber, another blow to the theory Harries is promoting.
Pickles has his own theory that rubber was made from larger ring like molecules, maybe with a
formula of
C40H64. His idea is better
at explaining the way rubber
behaves, and even Harries was starting to come around to his point of view. But an even
better theory is on the horizon, being
put forth by a very enthusiastic and often very unpopular fellow named Hermann Staudinger.
Meanwhile...
While Pickles ponders the problems with the colloid theory, this is going on in the
rest of the world:
1903: W.E.B. Du Bois publishes his book The Souls of Black Folk, which
examines racial division and injustice in the United States.
1905: In Switzerland, Albert Einstein publishes his theories of relativity.
1906: Mohandas Gandhi, while living in South Africa, begins a resistance movement among
the country's Indian immigrants against the government's racial policies.
For more information, at other websites...
Molecular Giants - part of Polymers and People: An Informal History
from the Chemical Heritage Foundation.
William Henry Perkin - a biographical sketch, part of Chemical
Achievers from the Chemical Heritage Foundation.
Bibliography
1. Furukawa, Yasu. Inventing Polymer Science. Philadelphia: University of Pennsylvania
Press, 1998.
2. Morris, Peter J. T. Polymer Pioneers. Philadelphia: The Beckman Center for the
History of Chemistry, 1986.
Press, 1998.
3. Britannica.com.
Work done by:
Polymer Science Learning Center
and
the Chemical Heritage Foundation
