[Illustration: 1. Tapping Axe. 2. Tin Cup to Catch the Rubber Milk. 3.
The Beginning of a Rubber “Biscuit.” 4. A Palm Nut.]
[Illustration: Making Balls of Crude Rubber.]
[Illustration: Tapping the Trees in Japan.]
[Illustration: How the Rubber Looks when it comes to Market.]
[Illustration: Carrying Balls of Crude Rubber to Native Market.]
Pictures herewith by courtesy of The B. F. Goodrich Company, Ltd.
What Is Wild Rubber?
~WHERE RUBBER COMES FROM~
The first class, or wild rubbers, are collected from trees which have
grown wild and where no cultivation processes whatsoever have been
used. These rubber-producing trees, shrubs, etc., are found mostly in
Northern South America, Central America, Mexico, Central Africa and
Borneo.
The finest rubber in the world is Fine Para, and is gathered in the
Amazon regions of South America. This rubber has been gathered in
practically the same way for over a century. The natives go out into
the forests and, selecting a rubber tree, cut “V”-shaped grooves in the
bark with a special knife made for the purpose, these grooves being
cut in herring-bone fashion diagonally around the tree, with one main
groove cut vertically down the center like the main vein in a leaf.
The latex, or milk-like liquid, of the tree, from which the rubber is
taken, flows from these veins and down the center vein into a little
cup which the natives place to receive it. After the little cups are
filled they are gathered and brought into the rubber camp, and there
the latex is coagulated by means of smoke. This is done by the use of
a paddle which is alternately dipped into a bowl of the latex and then
revolved in the smoke from a wood or palm-nut fire. This smoke seems to
have a preservative effect on the rubber as well as drying it out and
causing it to harden on the paddle, each successive layer of the latex
causing the size of the rubber ball or biscuit to increase. When a
biscuit of sufficient size has been thus coagulated it is removed from
the paddle and is ready for shipment to countries where rubber products
are manufactured.
Para rubber is sold in three grades. Fine Para, which is the more
carefully coagulated or smoked rubber; Medium Para, which is rubber
gathered and smoked in the same way as Fine, but which has had
insufficient smoking, and, therefore, more subject to deterioration due
to oxidation, etc.; and Coarse Para, which is rubber gathered from the
drippings from the rubber trees after the cups have been removed. This
latter grade has generally a large percentage of bark and other foreign
substances mixed with it, and is subject to even more deterioration
than is Medium Para, as it is oftentimes not smoked at all.
Another important grade of rubber coming from South America is Caucho.
This tree grows similar to the Para trees and the rubber is gathered
in a similar manner, but is cured by adding to the latex some alkaline
solution and allowing the whole to dry out in the sun. The value of
this rubber can be greatly improved by better methods of coagulation.
From Central America and Mexico comes the Castilloa rubber. This
rubber is gathered from trees in a very similar manner to Para, and is
coagulated by being mixed with juices which are obtained by grinding
up a certain plant which grows in the Castilloa districts. After being
mixed with this plant juice, the Castilloa is spread out in sheets on
bull hides, where it is allowed to dry in the sun, after which the
rubber is rolled up and is ready for shipment. Castilloa is gathered
mostly from wild trees, but in Mexico it has recently been cultivated
to some extent.
From Mexico we also get Guayule. This rubber is obtained from a certain
species of shrub, the shrub being cut down and fed into a grinding or
pebble mill where the branches are crushed and ground and mixed with
water, and the rubber, which is contained in little particles all
through the wood, is worked out, being taken from the pebble mills in
chunks as large as a man’s fist.
From Central Africa and from Borneo come the so-called African gums,
such as Congo, Soudan, Massai, Lapori, Manicoba, Pontianic, etc. Some
of these rubbers are gathered from trees, but most of them from vines
and roots, and the methods of coagulation are varied. Practically all
of them are dried out in the sun. These rubbers are all of lower grade
than the Para rubbers of South America.
[Illustration: BAGS OF CACAO BEANS.]