Production—At the commencement of the rainy season the gamboge-collectors start for the forest in search of the trees which in some localities are plentiful. Having found one of the full size they make a spiral incision in the bark round half the circumference of the trunk, and place a joint of bamboo to receive the sap which slowly exudes for several months. When it first issues from the tree, it is a yellowish fluid, which after passing through a viscid state hardens into the gamboge of commerce. >
The trees grow both in the valleys and on the mountains and will yield on an average in one season enough to fill three joints of bamboo 20 inches in length by 1½ inches in diameter. The tree appears to suffer no injury provided the tapping is not more frequent than every other year.[350]
According to Dr. Jamie of Singapore, the gamboge-tree grows most luxuriantly in the dense jungles. The best time for collecting is from February to March or April. The trees, the larger the better, are wounded by a parang or chopping-knife, in various parts of the trunk and large branches, when prepared bamboos are inserted between the root and the bark of the trees. The bamboo cylinders being tied or inserted, are examined daily till filled, which generally takes from 15 to 30 days. Then the bamboos are taken to a fire, over which they are gradually rotated till the water in the gum-resin is evaporated and it gets sufficiently hard to allow of the bamboo being torn off.[351]
Description—The drug arrives in the form of sticks or cylinders 1 to 2½ inches in diameter, and 4 to 8 inches in length, striated lengthwise with impressions from the inside of the bamboo. Often the sticks are agglutinated, or folded, or the drug is in compressed or in shapeless masses. It is when good of a rich brownish orange tint, dense and homogeneous, breaking easily with a conchoidal fracture, scarcely translucent even in thin splinters. Touched with water it instantly forms a yellow emulsion. Triturated in a mortar it affords a brilliant yellow powder, slightly odorous. Gamboge has a disagreeable acrid taste.
Much of the gamboge shipped to Europe is of inferior quality, being of a brownish hue or exhibiting when broken a rough, granular, bubbly surface. Sometimes it arrives imperfectly dried and still soft.
Chemical Composition—Gamboge consists of a mixture of resin with 15 to 20 per cent. of gum. The resin dissolves easily in alcohol, forming a clear liquid of fine yellowish-red hue, and not decidedly acid reaction. It forms darker-coloured solutions with ammonia or the fixed alkalis, and a copious precipitate with basic acetate of lead. Perchloride of iron colours a solution of the resin deep blackish brown.
By fusing purified gamboge resin with potash, Hlasiwetz and Barth (1866) obtained acetic acid and other acids of the same series, together with phloroglucin, C₆H₃(OH)₃, pyrotartaric acid, C₅H₈O₄, and isuvitinic acid, C₆H₃CH₃(COOH)₂.
The gum which we obtained to the extent of 15·8 per cent. by completely exhausting gamboge with alcohol and ether, was found readily soluble in water. The solution does not redden litmus, and is not precipitated by neutral acetate of lead, nor by perchloride of iron, nor by silicate or biborate of sodium. It is therefore not identical with gum arabic.
Commerce—The drug finds its way to Europe from Camboja by Singapore, Bangkok, or Saigon. In 1877 the first place exported 240 peculs, Bangkok in 1875 no less than 346 peculs, value 48,835 dollars; from Saigon there have of late been shipped from 30 to 40 peculs annually (one pecul = 133·3 lbs. = 60·479 kilogrammes).[352]
Uses—Gamboge is a drastic purgative, seldom administered except in combination with other substances.