This rubber, called after the name used by the natives in Borneo, is of a low type containing a very high proportion of resin. It has, however, taken a prominent place in the rubber market in consequence of the recent high prices of purer kinds. Jelutong rubber comes chiefly from Borneo and Sumatra, and is derived from large forest trees of the genera Dyera and Alstonia. These are abundant in certain districts, mainly in swampy places, and may attain a circumference of as much as 20 feet Much damage has already been done by native methods of collection, but steps have recently been taken by the governments concerned to safeguard the life of the trees. Large factories have also been opened for producing purified rubber by the use of resin solvents. Schidrowitz states that the trees can be tapped 40 times in a year without damage, and that as much as 100 lbs. of latex can be obtained from a single tree. The method of tapping recommended is done with a gouge in the form of a wide V.
The export of Jelutong in 1910 is said to have exceeded 25,000 tons. The crude product contains only 12 to 14 per cent of actual rubber. There is also 30 to 40 per cent, or more of water, and the remainder is chiefly resin. This so-called rubber may be used directly in combination with a certain proportion of a purer grade for the manufacture of inferior classes of goods, or the resin may be more or less completely extracted by the use of solvents.