PRINCIPAL KINDS OF RUBBER.

Only a few of the principal kinds need be given to show the extent of country covered.

Clonth1 enumerates 13 kinds in South America, 4 in Central America and Mexico, 35 in Africa, 8 in Asia, and 1 in Australia. It is evident that the work of explorers and botanists has been richly rewarded. Each year adds to the list as the new countries are discovered or developed. If the Philippines have no first-class rubber they will be a curious exception to other tropical countries.

Attention is called to the fact that in most cases the exact species of tree or vine is known from which a certain brand of rubber is derived. With gutta-percha, on the contrary, we only know that a few species of trees produce different kinds of gutta-percha, but which particular species produced any one commercial variety we have no way of knowing. The certainty as to the source of the different varieties of rubber is due to three causes: First, mixing can not take place among different varieties unless done when the milk is fresh, before coagulation. Borneo rubber, for example, is generally a mixture of three different vines growing in the same locality. Second, rubber trees being more abundant, better known, and found in more accessible places, can be easily visited and experimented on by botanists and chemists, who can thus deny or corroborate the accounts of the natives. As a rule, too, the native rubber collectors are more civilized than guttapercha collectors. Third, there being a better supply of rubber to meet the demand, the buyers are more exacting against adulterations.

Of all the rubber so far discovered the para rubber, taken from the Amazon Valley, is the best. This is due to its purity (absence of dirt, water, and foreign organic and mineral matter which causes decay), stability (undergoes no decay during long voyages or storages), and physical and chemical properties, such as elasticity, toughness, and readiness to combine with various chemicals, especially sulphur, by which means all kinds of hard rubber are made.

EXTRACTION AND PRESERVATION OF RUBBER.

As has been previously stated, rubber exudes from a wound in the bark of the rubber tree or vine in the form of milk. The two prob1Gummi, Gutta-percha und Balata, Clonth, p. 74.

lems confronting the rubber collector are, first, the best way of extracting the milk from the tree, and, second, treatment to give the milk in order to get the best rubber from it.

1. To most native rubber collectors problem 1 resolves itself into how to get the most milk from the tree in the easiest way and shortest time. Even though they have the sense not to cut down the tree and ring it, as with gutta-percha, yet many are so careless and clumsy in tapping the bark that generally large cuts are made, often the inner wood being cut as well, and the tree is left the prey of insects and borers which generally bring about a lingering death. In this way large tracts of rubber land along the valley of the Amazon and in Central America have suffered greatly, and already reports from reliable sources show that the present supply of the best rubber has to be brought from remote districts of the interior.

In Borneo, Sumatra, and the Malay Peninsula, where the guttapercha collectors are also the rubber collectors, no attempt is made to save the trees and vines. The vines especially are doomed to destruction, for the method consists in tearing them down from the trees, cutting them into short lengths, and suspending the pieces over a receptacle into which the milk may exude. Heat is often applied to one end of the piece to drive the milk out at the other. The method is as complete as it is ruinous. Special attention is called to this method, as we shall probably find it in vogue in the Philippines where rubber vines are known to exist.

Enough scientific experimenting has been done here in the east, especially in Ceylon, Penang, Singapore, and Java, to show conclusively that every variety of rubber tree and vine can be tapped so as to get a large percentage of the rubber actually in the plant and without doing any apparent harm. The method employed differs with the kind of tree to be tapped, but the principle underlying all methods is to so make the incisions in the bark that the greatest number of milk ducts will be cut, while no cutting of nor injury to the inner wood takes place. When the tapping is done at all carefully the wounds are quick to heal, no borers or insects can eat the tree, and the milky supply commences at once to re-form.

2. Treatment of milk in order to get the rubber.-The rubber milk as it flows from the tree has been found to contain roughly (taking the milk from the Para rubber tree for example) 32 per cent rubber, 12 per cent mineral and organic substances (mostly sap), and 56 per cent water. The problem is, therefore, to separate the rubber from the other constituents as cheaply and completely as possible.

It must be remembered that each variety of tree or vine has a milk differing in composition from the figures above. Consequently, the method of extracting the rubber must differ to suit the conditions. The processes tried are almost as many as the different kinds of trees. Some of the principal ways by which the coagulation of the rubber (and hence separation from the other constituents of the milk) is brought about are:

1. A typical heat:

I. THROUGH HEAT.

(a) Smoking. A smudge is made of dry nut husks, and a wooden paddle dipped in the milk and held in the smoke. The heat, acid fumes, and creosote, which all ascend in the smoke, work together to coagulate the rubber, dry it, and also to kill all germs of decay. The resulting rubber, the process being repeated until the paddle is heavily coated, is very pure and stable.

NURSERY OF YOUNG INDIA RUBBER TREES (FICUS ELASTICA).

EXPERIMENTAL GARDENS, BUITENZORG, JAVA. Large trees of same kind in background.