Vicki Carr, age 11, of San Diego, Cal if. for her question:
How is rubber made.?
More than half the rubber we buy this year will be synthetic, or man‑made. The chemists have countless recipes for making substitute rubber and, for some purposes, these synthetic rubbers are better than natural rubber. Butyl, a synthetic, is as good or better than natural rubber for making inner tubes.
Natural rubber is composed of the common elements carbon and hydrogen. Nature, however, strings atoms of these elements into highly complex molecules. Our chemists have plenty of hydrogen and carbon with which to experiment, but so far they have been unable to duplicate Nature's recipe for making rubber molecules. The job was so hard that the scientists gave it up. Our man‑made substitute rubbers are made from such raw materials as alcohol, butane and acetylene.
A number of different plants make the milky sap called latex from which natural rubber is made. The ordinary potted rubber plant will ooze a little of this latex when its stem is cut. Only one plant, however‑, can produce enough latex to be of commercial use. It is the hevea tree, originally a native of Brazil. Hevea plantations now flourish in Indonesia, Indo‑China, Siam, Ceylon, Burma and Borneo. The tall, slender trees like a wet, tropical climate. They can be grown within 15 degrees of the equator where 75 inches of rain falls throughout the year.
A rubber tree is large enough to yield latex when it is six years old. The milky latex flows in spiral tubes under the outer bark. The tree is tapped when a slanting groove is cut half‑way around the trunk. Some of the latex tubes are broken and the milky fluid flows down the slanting cut into a pail. Atop grade hevea tree will yield 30 pounds of latex a year for 25 years.
The latex is collected and mixed with water. Acid is added and, after several hours] a rubbery scum jells on top of the watery mixture. This scum is the crude rubber from which all natural rubber products are made. It is lifted up and run through rollers which squeeze out the surplus water. Some of the crude rubber will be rolled several times and come out in large sheets of pale crepe rubber. The sheets will be dried in the air for two or three weeks. Then they will be baled and shipped to a factory where rubber products are made.
Most of the crude rubber is rolled into ribbed. sheets and dried in smoke filled air. After a week in a dry smoke house the sheets are ready for baling. All sorts of processes await the pale crepe and the amber‑colored smoked rubber at the factory, depending upon what products will be made from them.