Rubber

a substance found in the milky juice of a thousand species of plants. Fifty species are of commercial importance. Rubber is found in small quantities in the milkweed, in dogbane, and in the milky sap of many northern plants; but the rubber of commerce is obtained chiefly from Brazil, Central America, Africa, and Farther India. It became known first as an American product. Columbus found the natives of Haiti playing with a ball "made of the gum of a tree," that was lighter and bounced better than any known at home. It was reported that the Indians of Mexico made a shoe of a gum which they taught the Spaniards to use as a wax to render their canvas cloaks waterproof. Pieces of this were first used in England to rub out pencil or India ink marks; hence the name, India rubber, given by artists.

The greater part of our supply comes from the giant forest trees of Brazil. The trees are tapped somewhat after the fashion of maple trees, and the gum is collected in tin or clay cups. The collector hardens and colors his rubber by drying and smoking it in a fire built in a small pit for the purpose. He first pours the contents of a cup on the blade of a stick shaped like a paddle. This he holds and turns in the heat and smoke until it is hardened. He then pours on more rubber and repeats the process until the ball of rubber is too heavy to handle to advantage. He then passes a knife under the edge of the rubber around the blade of the paddle, and slips the mass off. The best rubber comes down the Amazon to Para, the greatest rubber market in the world. Rubber is the chief export of the Congo Valley also.

In its natural state, rubber loses its elasticity when cold and softens by heat; that is, a rubber shoe made of natural rubber would be brittle in very cold weather and doughy in very warm weather. Comparatively little use could be made of natural rubber. In 1844 Mr. Charles Goodyear (1800-1860), took out a patent for vulcanizing rubber, as the process is called. He found that by shredding and washing rubber free from impurity and then heating it with sulphur, he not only increased its elasticity, but rendered it more nearly proof against changes of heat and cold. In all, Mr. Goodyear's patents cover sixty processes and devices. This is really the beginning of the application of rubber to hundreds of purposes from the waterproofing of a mackintosh to the making of a rubber valve. The immense amount of rubber goods produced in this country alone is evidence that rubber must be adulterated in every possible way to supply the demand. Brazil, which ships nearly half of the world's supply sells only 43,000,000 pounds annually.

Of late the city of London has put rubber to a new use. In searching for a pavement material that will obviate the noise of stone and the slipperiness of asphalt, a trial was made of rubber. A few squares, railway yards, and hotel courts have been paved with a combination of rubber at a cost of $32.70 per square yard. The promoters of this pavement claim that at an expense of from $30 to $40 per square yard an ideal durable noiseless pavement can be laid.

The demand for rubber has led to the cultivation of rubber-producing plants. The most prominent is the para rubber tree, spoken of sometimes as the hevea and also as the Brazilian rubber tree. Plantations have been established in the West Indies and in the moist, hot, fertile East Indian countries along the equator that market at Singapore. The plants are raised from the seeds. The seedlings are potted in bamboo joints. When about a foot high they are removed from the nursery to the plantation. The trees grow very rapidly, gaining from eight to fifteen feet in height yearly. At six years of age they are large enough to tap. The plantations are yet too young to ascertain the life of the tree, but some of the planted trees have yielded rubber for thirty-five years. Parent trees in the Amazon Valley have been tapped for eighty years. The usual method of tapping is a vertical incision with slanting incisions leading into it, something like the ribs of a leaf. A cup is placed at the lower end of the central incision to catch the milky flow. By freshening the incisions daily the flow of rubber may be kept up the year around, but it is customary to allow a tree to rest a few months that the incisions may heal.

The second rubber plant of importance is the Central American rubber tree. It is related to the bread fruit. It is cultivated in plantations in the northern part of South America and in Central America. Methods of cultivation are much like those employed in rearing the para tree. The Panama rubber requires, however, a little cooler climate than the para rubber. The yield of the Panama rubber is greater, but the quality is not so good. A third rubber tree, a relative of the tapioca plant, is quite unlike the two already mentioned. It is a drought-resisting plant, and does best in a sandy region where a season of early rainfall is followed by a season of dry weather. Other rubber plants are cultivated in the Malay region, in Trinidad, and in West Africa, respectively, but their cultivation is not extensive. Plantations of the so-called guayule plant have been established recently in Mexico and western Texas. It is a rubber-producing shrub, native to the dry, desert plateaus of northern Mexico. The shrub attains a height of three or four feet in two years. It is then cut off near the ground and the rubber is extracted from the woody portion of the shrub. An acre is expected to yield about two tons of shrub and about fifty dollars' worth of rubber.

The world rubber crop (1909) is worth about $100,000,000. About $28,000,000 worth a year is imported into the United States. A good quality of rubber is worth about $1.75 a pound.

See Gutta Percha; Milkweed

Working up against the heavy currents of these tributary rivers, the rubber collector hugs the shore and poles and paddles and pulls his craft--anything to get there with his outfit.

There's the invariable yellow dog. The senora and the dark kids and the baby are there. One or two shotguns, 100 years out of date, cotton hammocks, two dinted zinc trunks, several pails, miscellany that could not be interpreted north of the Panama ditch, and particularly a green parrot, sitting dejectedly somewhere on some kind of a perch. This is the outfit.

Whatever of food supplies brought from Brazilian civilization has been advanced him on credit by the merchant to whom he is to sell later the crude rubber for which he and his lares and penates are in search.

But, whether the rubber collector thus equipped goes up in his boat or pays the freight for himself, family, and equipment, he must leave the steamer somewhere at the mouth of a swift tributary if he has chosen that route, and then it is a case of taking to the woods.

It is the simple life there. The rubber collector himself has the bulk of the clothing, protecting him from saw edged grass, thorns, and thickets, to say nothing of the poisonous animal life that may menace him. He leaves his thatched roof tree with his frowsy wife and dark, naked children, and with a big knife, a shotgun, a galvanized pail, and a number of "nested" tin boxes akin to cake tins takes to the habitat of the rubber trees which have been assigned to him.

With the big knife he "taps" the first giant tree of the botanical Hevea Braziliensis class, starts the white sap running and, with a bit of stift clay, fastens the pan to the tree to receive it.

If he is working briskly--making allowance for the word brisk in such a climate--he is ready to turn back with his pail within an hour or so to that first tree, empty the tin box into the pail, replace it, and follow on down the line of his tappings. He should have a pail full of the sap when the day is done and he lugs it home by main strength--a strength built upon the regulation jerked beef, black beans, and yellow tapioca.

At home he builds his fire, ladles out sap from the pail, holds it over the heat and smoke of the fire until it begins to harden, then pours it into a heated iron pot. Ladle after ladle is treated this way until, when the sap pail is emptied and the pot is cooled, he dumps out an ovoid lump of rubber not unlike a football in shape and sometimes larger and sometimes smaller than the regulation pigskin of the universities. And this is the crude rubber of our commerce, of which we need a pound a year for every man, woman, and child in the nation.--Andrew Moore, in Worker's Magazine.