1911 Encyclopædia Britannica/Gutta Percha
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 tree—probably a Bassia—from 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 100 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 are white, and the seeds are contained in an ovoid berry about 1 in. long.
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 93°–119° longitude, where the temperature ranges from 66° to 90° 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 information seems to point to the possibility of growing the tree in Ceylon and on the west coast of Africa.
Preparation of Gutta 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 occurs in the leaves of the tree to the extent of about 9% of the dried leaves, and this may be removed from the powdered leaves by the use of appropriate solvents, but the process is not practicable commercially. The latex flows slowly where an incision is made through the bark, but not nearly so freely, even in the rainy season, as the india-rubber latex. On this account the Malays usually fell the tree in order to collect the latex, which is done by chopping off the branches and removing circles of the bark, forming cylindrical channels about an inch wide at various points about a foot apart down the trunk. The latex exudes and fills these channels, from which it is removed and converted into gutta by boiling in open vessels over wood fires. The work is usually carried on in the wet season when the latex is more fluid and more abundant. Sometimes when the latex is thick water is added to it before boiling.
The best results are said to be obtained from mature trees about thirty years old, which furnish about 2 to 3 ℔ of gutta. Older trees do not appear to yield larger amounts of gutta, whilst younger trees are said to furnish less and of inferior quality. The trees have been so extensively felled for the gutta that there has been a great diminution in the total number during recent years, which has not been compensated for by the new plantations which have been established.
Uses of Gutta Percha.—The Chinese and Malays appear to have been acquainted with the characteristic property of gutta percha of softening in warm water and of regaining its hardness when cold, but this plastic property seems to have been only utilized for ornamental purposes, the construction of walking-sticks and of knife handles and whips, &c.
The brothers Tradescant brought samples of the curious material to Europe about the middle of the 17th century. It was then regarded as a form of wood, to which the name of “mazer” wood was given on account of its employment in making mazers or goblets. A description of it is given in a book published by John Tradescant in 1656 entitled Musaeum Tradescantianum or a Collection of Rarities preserved at South Lambeth near London. Many of the curiosities collected from all parts of the world by the Tradescants subsequently formed the nucleus of the Ashmolean Museum at Oxford which was opened in 1683, but the specimen of “mazer wood” no longer exists.
In 1843 samples of the material were sent to London by Dr William Montgomerie of Singapore, and were exhibited at the Society of Arts, and in the same year Dr José d’Almeida sent samples to the Royal Asiatic Society. Gutta percha was also exhibited at the Great Exhibition of 1851.
Dr Montgomerie’s communication to the Society of Arts led to many experiments being made with the material. Casts of medals were successfully produced, and Sir William Siemens, in conjunction with Werner von Siemens, then made the first experiments with the material as an insulating covering for cable and telegraph wires, which led to the discovery of its important applications in this connexion and to a considerable commercial demand for the substance.
The value of gutta percha depends chiefly on its quality, that is its richness in true gutta and freedom from resin and other impurities which interfere with its physical characters, and especially its insulating power or inability to conduct electricity.
The chief use of gutta percha is now for electrical purposes. Other minor uses are in dentistry and as a means of taking impressions of medals, &c. It has also found application in the preparation of belting for machinery, as well as for the construction of the handles of knives and surgical instruments, whilst the inferior qualities are used for waterproofing.
Commercial Production.—The amount of gutta percha exported through Singapore from British and Dutch possessions in the East is subject to considerable fluctuation, depending chiefly on the demand for cable and telegraph construction. In 1886 the total export from Singapore was 40,411 cwt., of which Great Britain took 31,666 cwt.; in 1896 the export was 51,982 cwt. of which 29,722 cwt. came to Great Britain; while in 1905, 42,088 cwt. were exported (19,517 cwt. to Great Britain). It has to be remembered that the official returns include not only 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 1896–1906 the best qualities of gutta percha fetched from 4s. to about 7s. per ℔. Gutta percha, however, is used for few and special purposes, and there is no free market, the price being chiefly a matter of arrangement between the chief producers and consumers.
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 out into threads, but is still inelastic. On cooling again the gutta resumes its hardness without becoming brittle. In this respect gutta percha differs from india-rubber or caoutchouc, which does not become plastic and unlike gutta percha is elastic. This property of softening on heating and solidifying when cooled again, without change in its original properties, enables gutta percha to be worked into various forms, rolled into sheets or drawn into ropes. The specific gravity of the best gutta percha lies between 0.96 and 1. Gutta percha is not dissolved by most liquids, although some remove resinous constituents; the best solvents are oil of turpentine, coal-tar oil, carbon bisulphide and chloroform, and light petroleum when hot. Gutta percha is not affected by alkaline solutions or by dilute acids. Strong sulphuric acid chars it when warm, and nitric acid effects complete oxidation.
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 have a 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 C10H16. It is therefore isomeric with the hydrocarbon of caoutchouc and with that of oil of turpentine. Accompanying this are at least two oxygenated resinous constituents—albane C10H16O and fluavil C20H32O—which can be separated from the pure gutta by the use of solvents. Pure gutta is not dissolved by ether and light petroleum in the cold, whereas the resinous constituents are removed by these liquids. The true gutta exhibits in an enhanced degree the valuable properties of gutta percha, and the commercial value of the raw material is frequently determined by ascertaining the proportion of true gutta present, the higher the proportion of this the more valuable is the gutta percha. The following are the results of analyses of gutta percha from trees of the genus Dichopsis or Palaquium:—
| Gutta per cent. | Resin per cent. | ||
| Dichopsis (or Palaquium) | oblongifolia | 88.8 | 11.2 |
| ” ” ” | gutta | 82.0 | 18.0 |
| ” ” ” | 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 hydrocarbons, isoprene (C5H8) and caoutchoucine or dipentene (C10H16), 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 or sliced 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 80 to 100 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 constituent of gutta percha. The properties of balata correspond with its composition, and it may therefore be classed as an inferior gutta percha. Balata fetches from 1s. 6d. to 2s. 8d. per ℔.
Among the inferior substitutes for gutta percha may be mentioned the evaporated latices derived from Butyrospermum Parkii (shea-butter 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 ℔, 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 with linseed and other oils, resins, &c., in some cases incorporated with inferior grades of gutta percha.
For further information respecting gutta percha, and for figures of the trees, the following works may be consulted: Jumelle, Les Plantes à caoutchouc et à gutta (Paris, Challamel, 1903); Obach, “Cantor Lectures on Gutta Percha,” Journal of the Society of Arts, 1898. (W. R. D.)