THE PLASTIC WORLD

On the other hand, materials that we now know to be polymeric were already in wide domestic and industrial use many centuries ago. A trivial example is the use, since prehistoric times, of egg-white, blood plasma, and gelatin from bones in varnishes (even on cave paintings) and sizes. Rubber, which was known to the Mayan Indians of Mexico as early as the eleventh century, is 

Rubber, or elastic gum , came to Europe in the eighteenth century. Charles Marie de La Condamine had been despatched by the French Academy of Sciences to measure a part of the meridian passing through Peru. On his return in 1736 he reported that the local Indians were using the cured latex to make waterproof boots and pear-shaped bottles, which qected jets of liquid ( like a syringe ) when squeezed. The new substance excited much curiosity in Europe. It was the English savant, Joseph Priestley who discovered in about 1770 that blocks of the recovered latex could be used to rub out pencil marks (by scraping off the surface of the paper), whence the name India rubber for the material (since it was believed to come from the West Indies). 

Then in 1824 a resourceful Scottish chemist, Charles Mackintosh, found a good solvent— naphtha, one of the oily fractions derived from coal tar— for the latex. He also of course used the 

Over the ensuing years, many chemists tried to discover the chemical structure of rubber. It could be broken down by high temperature, and distillation would then yield an oil, which in turn gave rise to a liquid with a low boiling point. It turned out to be a pure substance, and was given the name isoprene with the formula 

Sir William Tilden, Professor of Chemistry at what is now Imperial College in London, who had done the work, also tried, with some success, to turn isoprene back into rubber. The methods available at the time (around 1900) to measure molecular weights all indicated that rubber must consist of very large molecules (even if the zealots of the colloid school clung to their own 

---