may be stated approximately to have been from 10d. to 1s.
per ℔. The cost of collecting “wild” rubber is less easy to
state with any approach to accuracy, since the cost varies in
different districts of S. and Central America, but the average
cost is stated not to be less than 1s. per ℔. In Africa the cost
of collection is much less, but the rubber is generally of inferior
quality.
The market price of commercial rubber is determined by the current price of “fine Para” from S. America. This is subject to considerable fluctuation, :and varied in 1900 to 1908 from 2s. 10d. to 5s. 9d. a ℔. As much as 6s. 9d. per ℔ was given for specially prepared “plantation Para.” Towards the latter part of 1904 the price of fine Para reached a high level and then considerably declined, reaching in 1907–8 a lower figure than had been recorded since 1900. At the beginning of 1908 the price gradually rose again to the neighbourhood of 4s. a ℔. During 1909, without any serious decline in production, the price rapidly rose, owing to extraordinary causes, to about 10s. a ℔, and in the early part of 1910 rose to over 12s. a ℔, and subsequently fell to about half this price. Having regard to the present cost of producing “plantation” rubber, and to the probability that, apart from a possible increase in the price of labour, this cost is susceptible of further reduction, it may be concluded that rubber production will continue to be profitable even should a considerable fall in market value take place.
The Principal Rubber Trees, their Cultivation, and the Preparation of Rubber.—Most commercial rubber is derived from natural supplies, from the wild rubber trees of S. and Central America, India and Africa. Each year, however, the output of “plantation” rubber will show a considerable increase, and it is to be expected that ultimately this will form the chief source of supply, unless unforeseen circumstances should arise to interfere with the development of the plantation industry, which has been vigorously started chiefly with European capital in the tropical possessions of Great Britain, France and Germany. The best rubber is now obtained from large trees, of which the following are the more important:—
1. “Para” rubber, which takes the first position in the market, is derived from species of Hevea, principally Hevea brasiliensis, of which there are enormous forests in the valleys of the Amazon and its tributaries, and also in Peru, Bolivia, Venezuela and Guiana. In Brazil alone it is stated that the rubber area amounts to at least one million sq. m. The tree has been recently planted with great success especially in Ceylon and Malaya (Plate figs. 11 and 12).
2. “Ceara” or Maniçoba rubber is derived from species of Manihot, chiefly Manihot Glaviovii, a native of S. America especially abundant in Brazil, and successfully introduced into other countries (Plate fig. 13). The latex of this tree flows less freely than that of Hevea brasiliensis, and the collection of large quantities of the latex is attended with considerable difficulty. The latex is therefore usually allowed to coagulate on the tree, as it slowly exudes from the incision. On this account it is often exported in strings or “scrap” and not usually in biscuits or balls. Partly for this reason and partly because pieces of wood and dirt are apt to be included with the scrap, the market value of Ceara rubber is usually less than that of Para. The plantations of Manihot established in E. Africa, Ceylon and S. India have, however, begun to furnish a better quality of Ceara rubber, which is often prepared in biscuit form. Other species of Manihot are also under trial, and some give promise of good results, especially M. dichotorna and M. heptaphylla.
3. The “Ule” rubber of Central America and British Honduras originates from Castilloa elastica. In S. America its natural occurrence appears to be limited to west of the Andes, but the tree is abundant in Mexico, Guatemala and Nicaragua. The rubber comes into commerce in thick strips or sheets or as “scrap.” The rubber is usually dark in colour and is often contaminated with proteid impurities derived from the latex. Ule rubber is generally inferior in strength to Para and commands a lower price. The Castilloa tree has been experimentally planted in Ceylon, the West Indies and other countries (Plate fig. 14).
Other trees occurring in America which furnish rubber of secondary commercial importance are Hancornia speciosa, yielding the Mangabeira rubber of Brazil, and species of Sapium furnishing the Colombian rubber and much of the rubber of Guiana (derived from Sapium Jenmani), which is scarcely inferior to the rubber of Para.
4. “Rambong” or Assam rubber is the produce of Ficus elastica, commonly known as the indiarubber tree and cultivated in Europe as an ornamental plant. This tree, indigenous to Asia, attains large dimensions in India, Celon and the Mala Archipelago (Plate fig. 15). It furnishes most of the rubber of, India, Sumatra and ]ava. Although intrinsically of excellent quality, Rambong rubber, owing to the careless method of collection practised 'by the natives which leads to the inclusion of much impurity, usually fetches a lower price than Para. The tree has been introduced into W. Africa and Egypt, but has not proved very successful in Africa as a rubber producer.
5. “Lagos” rubber is the produce of the African rubber tree Funtumia elastica, which is indigenous to Africa from Uganda to W. Africa (Plate fig. 16). It is known as the silk rubber tree, probably on account of the silky hairs which are attached to the seeds. The latex, which is usually coagulated by standing or by heating, is obtained from incisions in the bark of the tree. The rubber is of good quality, though, owing to the method of preparation adopted, the product is often impure and discoloured, and consequently usually brings a lower price than the best rubbers of commerce.
6. Besides the trees described above, a number of climbing plants or vines belonging to the Apocyanaceae secrete a latex which furnishes rubber of good quality. These vines are less satisfactory than trees as rubber producers, owing to the readiness with which they are injured and destroyed by careless tapping, and to the difficulty of regulating these methods in the case of vines distributed over enormous areas of forest. Of these vines the most important are the species of Landolphia which occur throughout tropical Africa, including the Sudan, Congo, Mozambique and Madagascar, the principal of which are Landolphia owariensis and L. Heudelotii, common throughout W. Africa, and L. Kirkii and L. Dawei in E. Africa. The rubber is obtained by incising the stems of the vines and coagulating the latex by exposure, by admixture with acid vegetable juices or by heating. Landolphia rubber is usually roughly prepared and in consequence commands a low price. The vines of species of Clitartdra and Carpodinus in W. Africa also furnish good rubber, as do the Forsteronia gracitis of British Guiana and Forsteronia fioribunda of Jamaica. Vines resembling Landolphias are widely distributed in Asia. Among these are species of Willughbeia and Leuconotis, from which much of the rubber exported from Borneo is derived; Parameria glandulifera, common in Siam and Borneo, and Urceola esculenta and Cryptostegia grandiflora, both common in Burma.
Among other sources from which rubber is commercially obtained may be mentioned the Guayule plant (Parthenium argentatum) of Mexico, and the “Ecanda” plant of Portuguese W. Africa, from the tuberous roots of which rubber is extracted by the natives. The “Ecanda” plant has been named Raphionacme utilis. The root rubber prepared by the natives of the Congo and the S. Sudan is extracted partly from the roots of Landolphia or from the rhizomes of Landotphia Thollortii or Carpodirtus lanceotatus. It is obtained by breaking up the roots or rhizomes in hot water and separating the rubber, and machines have now been devised for this purpose. Little is at present known of the large rubber tree of Tonkin (Bleckrodea tonkinensis), the latex of which is stated to furnish excellent rubber.
Sources of Commercial Rubber
1. Para Rubber is so named from the Para province of Brazil, from the principal town of which, also known as Para, most of the rubber is shipped. This rubber is obtained chiefly from Hevea brasiliensis, Müll. Arg., a large euphorbiaceous tree upwards of 60 ft. in height, and having trifoliate leaves, the leaflets being lanceolate and tapering at both ends (fig. 1). The trunk reaches about 8 ft. in circumference. The flowers are usually pale green. The fruit is a capsule containing three seeds rather larger than cobnuts, having a brown smooth surface figured with black patches. The seeds readily lose their vitality, and on this account need special care in transport. They should be loosely packed in dry soil or charcoal. These seeds have been examined at the Imperial Institute, and the kernels have been found to contain nearly half their weight (48%) of an oil resembling linseed oil and applicable for the same purposes. The residue or “cake” left after expression of the oil is apparently nutritious and may prove to be of value for feeding animals. There is present in the seeds, an enzyme which rapidly decomposes the oil if the seeds are crushed and kept, setting free a fatty acid and glycerin. As the seeds are very abundant, they will probably be utilized commercially as soon as the demand for planting has subsided.
In Brazil the trees are found in different districts, but flourish best on rich alluvial clay slopes by the side of rivers, where there is a certain amount of drainage, and the temperature reaches from 89° F; to 94° F. at noon and is never cooler than 73° F. at night, while rain falls during about six months and the soil and atmosphere are moist throughout the year. The genus Hevea was formerly called Siphonia, and the tree named Pao de Xerringa by the Portuguese, from the use by the Omaqua Indians of squirts or syringes made from a piece of pipe inserted in a hollow flask-shaped ball of rubber. The trees are not generally tapped until they are ten to fifteen years old, as young trees yield inferior rubber. If carefully conducted, tapping does not injure the tree. The latex is collected in the so-called dry season between June and February. The trees are tapped in the early morning when the latex is most readily obtained.
