THE NATURAL HISTORY AND COLLECTION OF INDIA RUBBER.
African india rubber is mostly exported from the west coast. The belt
of country producing it extends nearly across the continent. Those
who are familiar with the india rubber plants of our conservatories
are apt to think of the gum as the product of trees, but in Africa
it is largely yielded by climbing plants of very numerous varieties,
belonging generally to the Landolphia species. It is collected by
the natives by careless or desultory methods, probably less advanced
than the ways followed by the South Americans. Possibly its marked
inferiority may be partly attributed to this. It is also supposed by
many that, were the gathering restricted to the vine producing the
best gum, better results would follow. As it is now all gums are mixed
indiscriminately. African gum is of very inferior quality.
The African india rubber vines grow often in dark moist ravines, where
no valuable product other than themselves could be cultivated. They
are entirely wild. The vines when cut exude an abundance of sap,
which differs from the South American product in its quickness of
coagulation. As it escapes from the wound it at once solidifies and
prevents the further escape of juice. The negroes are said to employ
the following highly original method of collecting it. They make long
gashes in the bark. As fast as the milky juice comes out they wipe it
off with their fingers and wipe these in turn on their arms, shoulders,
and body. In this way they form a thick covering of inspissated juice
or caoutchouc over the upper part of their body. This from time to
time is removed by peeling. It is then said to be cut up and boiled
in water. This is one account. According to others the natives remove
a large piece of bark, so that the juice runs out and is collected in
holes in the earth or on leaves. Wooden vessels are said to be used
elsewhere. Sometimes the juice is said to be collected upon the arms,
the dried caoutchouc coming off in the shape of tubes. A clew to the
inferiority of African india rubber is afforded by the statement that
too deep a cut liberates a gum which deteriorates the regular product
if it mixes with it. The drying of the gum is thought to have much to
do with its quality and it is highly probable that this affects the
African product. Some samples seem to be partly decomposed they are
so highly offensive in odor. The South American rubber is often dried
in thin layers, one over the other, by a smoky fire, which may have
an antiseptic effect upon the newly coagulated caoutchouc. No such
process as far as known is used in Africa.
The African india rubber appears under different names in commerce.
From the Congo region lumps of no particular shape called “knuckles”;
from Sierra Leone smooth lumps, “negro-heads,” and “balls” made up
of small scrap; from the Portuguese ports “thimbles,” “nuts,” and
“negro-heads;” from the gaboon “tongues;” and from Liberia “balls”
are received. It is all characterized by great adhesiveness and low
elasticity.
From Assam, Java, Penang, and Rangoon there is considerable gum
exported. It is supposed to be the product of trees of the _ficus_
species, in all these places, as it is known to be in Java and Assam.
In the latter place rigid restrictions are imposed as far as possible
upon the gathering. In the case of wild trees scattered through the
forest the carrying out of these restrictions is not practicable. The
trees are cut with knives in long incisions through the bark and the
juice is collected in holes dug in the ground, or often in leaves
wrapped up into a conical form, somewhat as grocers form their wrapping
paper into cornucopia shape for holding sugar, etc.
It has seemed reasonably certain that the india rubber producing plants
might be cultivated with profit, and it is as certainly to be feared
that without such cultivation they will become extinct. Efforts have
been made in the direction of raising them artificially but without
much success. In Assam numerous experiments have been made to propagate
the india rubber bearing _ficus_ tree.
A good instance of the ill effects of carelessness in the original
gathering of the crop is afforded by the Bornese collectors. The source
of Borneo india rubber is a variety of creepers. These are cut down and
divided into short sections from a few inches to a yard in length. The
sap oozes out from the ends. To accelerate its escape the pieces are
sometimes heated at one end. It is coagulated by salt water. Sometimes
a salt called _nipa_ salt, obtained by burning a certain plant (_nipa
fruticans_), is used for the purpose. In either case it is coagulated
into rough balls and masses. These masses are heavily charged with the
salt water, often containing as much as fifty per cent., and rarely
much less than twenty per cent.
[Illustration: TREE FELLED FOR COLLECTION OF INDIA RUBBER.]
Central America and Panama are great producers of the gum. In Panama
the custom of felling the trees is often adopted. In this case
grooves are cut around the prostrate trunk, and under each groove as
the trunk lies on the ground a vessel is placed to collect the sap.
Its coagulation is often effected by leaving it for a couple of weeks
standing at rest in a hole, excavated on the surface of the ground,
and covered over with leaves. The caoutchouc separates under these
conditions. A quicker method, but one yielding an inferior product,
is obtained by adding to the fresh juice some bruised leaves of a
plant (_ipomæa bona nox_) which acts something like acid upon milk,
in separating the desired solid matter or caoutchouc. A jelly like
accretion saturated with blackish water is thus obtained. By working
it together a blackish liquid is caused to escape, and comparatively
pure gum is gradually obtained. As much as one hundred pounds of india
rubber may be obtained from a single tree where this destructive system
is employed. Further north, where a better counsel has prevailed, the
trees are only tapped, and the india rubber hunter is satisfied if from
a tree eighteen inches in diameter he obtains twenty gallons of sap,
giving fifty pounds of gum. Even where tapping is done the tree is
often destroyed by carelessness or ignorance.
Two systems are followed in Nicaragua. The operator ascends by a ladder
if he has one, or in any case climbs as high as he well can and begins
to make a long incision. Sometimes he carries one long straight cut
clear down to the ground. This is made the starting point for a number
of side cuts, short, and running diagonally into it. This is also one
of the Brazilian methods. The Nicaraguan sometimes also makes two
spiral incisions, one right-handed and the other left-handed, crossing
each other as they descend so as to divide the surface of the tree
into roughly outlined diamonds. In either case the juice flows down
to an iron spout, placed at the bottom of the tree, which spout leads
to an iron pail. The milk is gathered and passed through a sieve, and
coagulated in barrels by the _ipomæa_ plant as before mentioned. This
gives three grades of rubber. The bulk is obtained from the barrels and
is called often _méros_; the small lump which forms in the spout is
rolled into a ball and called _cabezza_; the dried strips pulled out of
the cuts is of very good quality and is called _bola_ or _burucha_.
From Brazil is exported the famous Para india rubber. This is of very
high quality, and is greatly esteemed by all manufacturers. No process
can make a poor gum give a really good product. The system of gathering
it varies. Sometimes the tree is cut into by gashes from an axe, such
gashes extending in a row all around the trunk. Under each gash a small
clay cup is luted fast with some fresh mixed clay. These collect from
a tablespoonful of juice upward, which is collected, and the cups are
removed on the same day. The next day a second row of cuts is made
below the others, and the same process is repeated. This is continued
until from a point as high as a man can reach, down to the ground the
tree is full of cuts. Sometimes a gutter of clay is found partly around
the trunk with gashes above it. In other cases a vine is secured around
the tree and a collecting gutter is worked with it for a basis.
[Illustration: TREE TAPPED FOR INDIA RUBBER.]
The juice is coagulated in a smoky fire. A bottomless jar is placed
over the fire and some palm nuts are mixed with the fuel. The mould,
which is often a canoe paddle, is smeared with clay to prevent adhesion
and is then heated. A cup of juice is poured over it, and after the
excess has dropped off it is moved about rapidly over the smoke and
hot air which ascends from the mouth of the jar. This series of
operations is repeated until the coating is quite thick; it may be as
much as five inches. After solidifying over night it is cut open and
the paddle or mould is removed. After a few days drying it is sent to
market. With all the heating, during which it sweats profusely, it
still retains fifteen per cent. of water.
[Illustration: INDIAN DRYING AND SMOKING INDIA RUBBER.]
India rubber sap may be coagulated by an aqueous solution of alum. The
process has been tried in Brazil, and is used to a considerable extent
in Pernambuco. It was proposed by an investigator named _Strauss_, and
the process is still called by his name. One objection is that it gives
a very wet product, and apparently one of inferior value to the smoked
gum.
The feeling that india rubber suffers in the gathering has been so
much felt that it has been recently suggested that if possible the
uncoagulated juice should be exported to Europe there to be worked up
from the beginning.