"The rubber-trees are abundant on both sides of the river for a long distance in either direction. How far inland they may be found is not definitely known. The scientific name of the tree is Siphonia elastica, or Siphonia cachucha, but there are several other trees that produce the gum which is so largely used in American and European industry. An incision is made in the side of the tree, and a cup made of leaves and clay is so placed as to catch the juice which flows from the cut. In a few hours the cup is filled, and a man comes around with a large jar in which the juice is collected.
"The liquid is about the consistency of milk, and contains from ten to twenty per cent. of gum. It is poured into shallow basins, very often into empty turtle-shells, and allowed to stand in the sun, by which a good deal of the liquid is evaporated. When it is about the thickness of ordinary cream it is poured into a turtle-shell, and an Indian sits down to convert the liquid into rubber.
INDIA-RUBBER MAKING ON THE MADEIRA.
"He has a small fire made of palm nuts, and over the fire is an inverted jar with a hole in the bottom, through which the smoke ascends. He dips a paddle into the cream, and then holds it over the hole in the jar until it is dried by the heat, which must always be gentle, through fear of spoiling the rubber. When the gum is hardened he dips the paddle again, and again dries it; he repeats the process until the desired thickness is secured.
"When the rubber is thick enough it is cut off and is ready for market. Instead of a paddle he sometimes uses a mould of clay; formerly they made moulds resembling the human foot, and thus fashioned the rubber shoes that were worn in America forty or fifty years ago. Fantastic figures were traced on the shoes with the end of a hot wire, and the mould was generally soaked in water till it fell to pieces, and the clay could be washed out. The modern processes of working rubber have driven these shoes from the market, and very few of them are made at present.
"A good day's work for one man is six pounds of rubber. Another way of hardening the gum is to place it in a kettle and suspend it over a small fire, taking care not to burn the material. When it is sufficiently reduced, and is still warm and plastic, it is shaped into balls or bricks, weighing several pounds each; the buyers prefer to have it dried on the paddle, as the natives occasionally commit frauds by putting sand or lumps of clay inside the masses while shaping them. The deception can only be detected by cutting carefully through the mass, and dividing it into small pieces. Frank suggests that the natives have probably heard of some of the tricks attributed to Connecticut Yankees, but I think he must be mistaken.
"The rubber of the Amazon valley is considered the best in the world, and the amount of the product is rapidly increasing. I am told it is not far from six thousand tons a year, and will be increased to ten thousand tons as soon as the means of transportation from Bolivia are made more practicable. This does not include the rubber sent from the northern part of the continent, from the country not drained by the Amazon.
"We call this substance 'India-rubber,' because it was first brought from the Indies, but, properly speaking, the name does not belong to it at the present day. The greater part of the rubber of commerce is from South America, which produces more than all other countries together."