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.
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.
A hypothetical colloid
made of dimcod molecules.
should act between the carbon-carbon double bonds,
making dimcod molecules clump together to form colloids.
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.
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.
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.
William Henry Perkin - a biographical sketch, part of Chemical Achievers from the Chemical Heritage Foundation.
2. Morris, Peter J. T. Polymer Pioneers. Philadelphia: The Beckman Center for the History of Chemistry, 1986. Press, 1998.