Thomas Alva Edison in a fringed muffler, Mrs. Edison, four servants, a dozen laboratory assistants and five carloads of laboratory gear & raw materials, all rolled southward last week from New Jersey toward Fort Myers, Fla. Through the press rolled headlines. For Inventor Edison, having celebrated the golden jubilee of his electric light bulb, had signalized his annual winter hegira by an announcement that sounded fraught with gold.
Packed in his five carloads of laboratory material were tons of stalks of a common, ubiquitous weed: goldenrod. Goldenrod, announced Inventor Edison, seemed a likely U. S. weed from which to produce the object of his major research in the past two years: Rubber.*
Chief Laboratory Assistant Frederick Ott is the sturdy mechanician who for 43 years has supervised experiments on Inventor Edison's ideas. The man who has for 19 years tried to keep the ideas from public garbling is a precise, British-born lawyer named William Henry Meadowcroft, 76. Last week Secretary Meadowcroft was exasperated by reports that he had predicted 16¢ per lb.: the present low price of real rubber, as the price of golden-rod rubber.† Neither Inventor Edison nor anyone in his organization could guess yet at manufacturing costs or how many acres of goldenrod would produce a ton of rubber.
The extensibility of rubber is usually confused with its elasticity. Rubber is one of the most inelastic of substances. An absolutely elastic substance is one which returns to its original size and shape after stretching. Rubber does not do that. Pull a piece of rubber, release it, measure it. It is deformed. Old rubbers are bigger than new ones. Steel is far more elastic than rubber, but of course much less stretchable. Glass is probably more elastic than steel. Quartz is an almost perfect elastic. Hence its use in nice measuring instruments such as telescopes.
The inelasticity of rubber is useful—in motor car tires, bumpers, airplane shock absorber cords—because it absorbs considerable of the energy which stretches it and transforms that absorbed energy into heat. That is why a continually flexing, moving tire is hot. Pull (not slide) a rubber band between closed lips. The lips can feel the heat. Pull (not slide) a piece of steel similarly (a machine is necessary), the steel will cool off.
Rubber is a complex hydrocarbon. Fundamental in its composition is isoprene. The organic chemist can make isoprene from such common stuffs as turpentine, petroleum, starch, coal tar or acetylene. News of goldenrod as a likely rubber source gave the casual daily press opportunity to picture farmers sneezing as they harvested the autumn-gorgeous weed. But goldenrod pollen is one of the lesser causes of hayfever. Ragweed, more widespread, is the chief cause in the U. S.
*There may be other rubber weeds. Mr. Edison has found traces of rubber in 1,200 U. S. plants, of 16,000 he has examined.
†Cheapest (English) artificial rubber, made from hydrocarbons, costs 75¢ per Ib.