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Encyclopedia Britannica - Main :: GUI-HAN |
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GUTTA PERCHA , the name applied to the evaporated milky fluid or latex furnished by several trees chiefly found in the islands of the Malay Archipelago. The name is derived from two Malay words, getah meaning gum, and pertja being the name of the treeprobably a Bassiafrom which the gum was (erroneously) supposed to be obtained. Botanical Origin and Distribution.The actual tree is known to the Malays as taban, and the product as getah taban. The best gutta percha of Malaya is chiefly derived from two trees, and is known as getah taban merah (red) or getah taban sutra (silky). The trees in question, which belong to the natural order Sapotaceae, have now been definitely identified, the first as Dichopsis gutta (Bentham and Hooker), otherwise Isonandra gutta (Hooker) or Palaquium gutta (Burck), and the second as Dichopsis oblongifolia (Burck). Allied trees of the same genus and of .the same natural order yield similar but usually inferior products. Among them may be mentioned species of Payena (getah soondie). Gutta percha trees often attain a height of 70 to loo ft. and the trunk has a diameter of from 2 to 3 ft. They are stated to be mature when about thirty years old. The leaves of Dichopsis, which are obovate-lanceolate, with a distinct pointed apex, occur in clusters at the end of the branches, and are bright green and smooth on the upper surface but on the lower surface are yellowish-brown and covered with silky hairs. The leaves are usually about 6 in. long and about 2 in. wide at the centre. The flowers
The geographical distribution of the gutta percha tree is almost entirely confined to the Malay Peninsula and its immediate neighbourhood. It includes a region within 6 degrees north and south of the equator and 93119 longitude, where the temperature ranges from 66 to 900 F. and the atmosphere is exceedingly moist. The trees may be grown from seeds or from cuttings. Some planting has taken place in Malaya, but little has so far 'been done to acclimatize the plant in other regions. Recent
Preparation of Gutla Percha.The gutta is furnished by the greyish milky fluid known as the latex, which is chiefly secreted in cylindrical vessels or cells situated in the cortex, that is, between the bark and the wood (or cambium). Latex also gutta percha of various grades of quality but also other inferior products sold under the name of gutta percha, some of which are referred to below under the head of substitutes. The value of gutta percha cannot therefore be correctly gauged from the value of the imports. In the ten years 18961906 the best qualities of gutta percha fetched from 4s. to about 7s. per lb. Gutta percha, however, is used for few and special
chief
Characters and Properties.Gutta percha appears in commerce in the form of blocks or cakes of a dirty greyish appearance, often exhibiting a reddish tinge, and just soft enough to be indented by the nail. It is subject to considerable adulteration, various materials, such as coco-nut oil, being added by the Malays to improve its appearance. The solid, which is fibrous in texture, hard and inelastic but not brittle at ordinary temperature, becomes plastic when immersed in hot water or if otherwise raised to a temperature of about 65 -66 C. in the case of gutta of the first quality, the temperature of softening being dependent on the quality of the gutta employed. In this condition it can be drawn
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When exposed to air and light, gutta percha rapidly deteriorates, oxygen being absorbed, producing a brittle resinous material. Chemical Composition.Chemically, gutta percha is not a single substance but a mixture of several constituents. As the proportions of these constituents in the crude material are not constant, the properties of gutta percha are subject to variation. For electrical purposes it should havea high insulating power and dielectric strength and a low inductive capacity; the possession of these properties is influenced by the resinous constituents present. The principal constituent of the crude material is the pure gutta, a hydrocarbon of the empirical formula
Gutta Resin per cent. per cent. Dichopsis (or Palaquium) oblongifolia 88.8 11.2 gutta 82.0 18o polyantha 49.3 50'7 pustulata . 47'8 52.2 Maingayi . 24.4 75.6 The hydrocarbon of gutta percha, gutta, is closely related in chemical constitution to caoutchouc. When distilled at a high temperature both are resolved into a mixture of two simpler hydro-carbons, isoprene (Colds) and caoutchoucine or dipentene (Cloths), and the latter by further heating can be resolved into isoprene, a hydrocarbon of known constitution which has been produced synthetically and spontaneously reverts to caoutchouc. The precise relationship of isoprene to gutta has not been ascertained, but recently Harries has further elucidated the connexion between gutta and caoutchouc by showing that under the action of ozone both break up into laevulinic aldehyde and hydrogen peroxide, but differ in the proportions of these products they furnish. The two materials must therefore be regarded as very closely related in chemical constitution. Like caoutchouc, gutta percha is able to combine with sulphur, and this vulcanized product has found some commercial applications. Manufacture of Gutta Percha.Among the earliest patents taken out for the manufacture of gutta percha were those of Charles Hancock, the first of which is dated 1843. Before being used for technical purposes the raw gutta percha is cleaned by machinery whilst in the plastic state. The chopped orsliced material is washed by mechanical means in hot water and forced through a'sieve or strainer of fine wire gauze to remove dirt. It is then kneaded or " masticated " by machinery to remove the enclosed water, and is finally transferred whilst still hot and plastic to the rolling-machine, from which it emerges in sheets of different thickness. Sometimes chemical treatment of the crude gutta percha is resorted to for the purpose of removing the resinous constituents by the action of alkaline solutions or of light petroleum. Substitutes for Gutta Percha.For some purposes natural and artificial substitutes for gutta percha have been employed. The similar products furnished by other plants than those which yield gutta percha are among the more important of the natural substitutes, of which the material known as "balata " or " Surinam gutta percha," is the most valuable. This is derived from a tree, Mimusops balata (bullet tree), belonging to the same natural order as gutta percha trees, viz. Sapotaceae. It is a large tree, growing to a height of 8o to 10o ft. or more, which occurs in the West Indies, in South America, and is especially abundant in Dutch and British Guiana. The latex which furnishes balata is secreted in the cortex between the bark and wood of the tree. As the latex flows freely the trees are tapped by making incisions in the same fashion as in india-rubber trees, and the balata is obtained by evaporating the milky fluid. Crude balata varies in composition. It usually contains nearly equal proportions of resin and true gutta. The latter appears to be identical with the chief
Among the inferior substitutes for gutta percha may be mentioned the evaporated latices derived from Butyrospermum Park ii (sheabutter tree of West Africa or karite of the Sudan), Calotropis gigantea (Madar tree of India), and Dyera costulata of Malaya and Borneo, which furnishes the material known as " Pontianac. All these contain a small amount of gutta-like material associated with large quantities of resinous and other constituents. They fetch only a few pence per lb, and are utilized for waterproofing purposes. Various artificial substitutes for gutta percha have been invented chiefly for use as insulating materials. These often consist of mixtures of bitumen
For further information respecting gutta percha, and for figures of the trees, the following works may be consulted: Jumelle, Les Plantes a caoutchouc et a gutta (Paris, Challamel, 1903) ; Obach, " Cantor Lectures on Gutta Percha, Journal of the Society of Arts, 1898. (W. R. D.) End of Article: GUTTA PERCHA If you wish, you can link directly to this article.
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