with lateral connecting channels about 1 ft. apart at an angle
of about 45°, the latex being collected in cups placed at the base
of the vertical channels (fig. 2); the spiral system, in which a
series of spiral grooves are cut all round the trunk, by which means
virtually the entire area of the trunk is tapped. In some instances
a combination of these methods is employed. The V-system is the
oldest, but is being largely superseded by the herring-bone; the
spiral system is more recent and is still on trial.
Instead of the axe or large knives which frequently inflicted serious damage to the trees, special small knives and prickers are now employed so constructed as to avoid injury to the tree through making a larger incision than is necessary, and without penetrating into the wood below the laticiferous layer. It is possible to tap or prick trees daily for a number of years without apparent injury, but the practice of tapping on alternate days appears to be safer and to afford equally satisfactory if not better results. The yield of latex is at first small, but increases with successive tapipings, which appear to stimulate the local production of latex, and finally reaches a maximum.
When the bark has been removed a period of from three to four years must elapse before it is so fully renewed as to render fresh incisions possible. In the case of a tree from seven to ten years old, tapping is so arranged that by the time the last incisions on the original growth are made, the new growths on other portions are at least four years old, and ready for new incisions to be made. Too frequent tapping leads to the production of latex poor in caoutchouc, whilst tapping of trees before they are six or seven years old, and from 20–25 in. in circumference, produces inferior rubber. As a rule, an annual yield of more than 1–2 ℔ of rubber per tree must not be looked for from recent plantations, although much higher yields up to 10–15 ℔ and over per tree are recorded from S. America, and it is therefore probable that with greater experience as to the best methods of tapping and with older trees considerably larger yields may be expected from plantations in the future. An average of 150 trees to the acre (20×15 ft.) and a yield of 112 ℔ of rubber per annum per tree at 2s. 6d. per ℔ gives the result of £28, 2s. 6d. per acre. The cost of production may be assumed to be about 1s. per ℔, to which has to be added the expense of transport. The cost of clearing forest land and planting with rubber in geylon is estimated at about 100 Rs. per acre in the first year, and from 20–30 Rs. per acre in subsequent years until the sixth year, when the plantation would begin to be productive.
The point of next importance is the coagulation of the latex so as to produce rubber in the form and of the quality required by the manufacturer. The primitive methods of coagulation and curing practised in S. America undoubtedly are susceptible of considerable improvement, and certainly waste can be. reduced to a minimum. It is, however, important to remember that rough as these native methods are they result in the production of rubber which commands the highest price. As the removal of the impurities of the latex is one of the essential points to be aimed at, it was thought that the use of a centrifugal machine to separate the caoutchouc as a cream from the watery part of the latex would prove to be a satisfactory process. This method is said to answer well with the latex of Castilloa, but it appears to be inapplicable to the latex of Het/ea, which does not cream readily when centrifugalized.
The plan usually adopted is to collect the latex in rectangular tanks or casks. It is then coagulated by the addition of an acid liquid, acetic acid or lime juice being generally employed, and the mixture allowed to stand. The coagulated rubber separates as a mass of spongy caoutchouc. If the coagulation has been effected in shallow dishes, the rubber is obtained in a thin cake of similar shape known as a “biscuit.”
The rubber thus formed is washed and dried. The coagulated rubber separated from the watery fluid is cut up into small pieces and passed through the grooved rollers of the washing machine, from which it issues in sheets, long crinkled ribbons or “crepe,” which are then dried in hot air chambers or in a vacuum dryer, by which means the water is dissipated at a lower temperature. In order to prevent decomposition of any proteid impurity which may remain incorporated with the rubber, the freshly coagulated rubber is sometimes cured in the smoke of burning wood or a small quantity of an antiseptic such as creosote is added during coagulation.
Plantation rubber comes into commerce in the form of the crinkled ribbons known as crepe, in sheets or biscuits, and sometimes in large blocks made by compressing the crepe rubber. Block rubber is considered to possess certain advantages in securing a constant proportion of water, and in being satisfactory for transport. The best condition and form in which to export rubber cannot be regarded as settled. The probabilities are that in the end the production of a rubber as nearly as possible free from water and impurities and of constant composition will be realized as best meeting the requirements of the modern manufacturer. The need for scrupulous cleanliness in the preparation of rubber is now recognized, and the arrangements of a rubber factory in Ceylon or Malaya are comparable with those of the modern dairy.
In the present transition stage of rubber production it is necessary for the manufacturer in Europe to wash all rubber. He receives both the wild rubber contain in variable quantities of impurity and the purer plantation rubber, tie latter, however, in much smaller amount. The fact that at present washing machinery exists in all European factories and that most of the rubber received needs washing, leads to the greater purity of plantation rubber, except for special purposes, being generally discounted by the manufacturer. As soon as the output of plantation rubber of constant composition has reached much larger dimensions it is probable that the manufacturer will be able to dispense with washing. This will operate to the advantage of plantation rubber and against the wild rubber, so long as the latter is not exported in a purer condition.
So far the Hevea, plantations in Ceylon and the East have not been seriously troubled by insect or fungoid pests, and those which have occurred have succumbed to proper treatment. The most serious trouble has been occasioned in the Malay States by a white thread-like fungus (Fomes semitostus) which attacks the roots of the Hevea tree and eventually kills it. The development of this fungus is greatly promoted by the presence of decaying stumps and wood in the plantation. Vigorous measures are now taken in many plantations to remove all old wood and to extract stumps of old trees, which in the first instance it was considered unnecessary to remove.
2. Manihot Glaziovii belonging to the Euphorbiaceae is the tree of N.E. Brazil which furnishes Ceara or Maniçoba rubber (fig. 3). It is closely related to the Manioc, cassava or tapioca plant (Manihot utilissima) which it resembles when young and exhibits a similar tuberous root system. The tree grows well on dry and rocky soil without rain for a considerable period of the year, and flourishes at high altitudes up to about 4000 ft. It is therefore adapted for conditions which are unsuitable for Hevea. The tree grows about 30 ft. high, with a rounded head of foliage, and greyish-green 3 to 7-lobed palmate leaves, somewhat resembling the leaves of the castor-oil plant in shape and size. The seeds (fig. 3), which are abundant and retain their vitality well, have a hard thick coat. The seeds take a year to germinate, unless the edges near the end bearing the carbuncular projecting are rasped off. Cuttings, if they have a-single bud, strike readily.
Fig. 3.—Manihot Glaziovii. 1, branch with flowers; 2, fruit; 3, seed.
The trees are tapped when they are about five years old. The mode of collecting the rubber is as follows. After brushing away the loose stones and dirt from the root of the tree by means of a handful of twigs, the collector lays down large leaves for the latex to drop upon. He then slices off the outer layer of the bark to the height of 4 or 5 ft. The latex, which exudes slowly and in many tortuous courses, some of it ultimately falling on the ground, is allowed to remain on the tree for several days, until it becomes dry and solid, when it is pulled off in strings, which are either rolled up into balls or put into bags in loose masses, in which form it enters commerce under the name of Ceara “scrap.” Ceara rubber is also exported in the form of lumps and cakes. The annual yield of rubber is rather more than 1 ℔ per tree. The latex coagulates readily, especially if churned or if diluted with water, when a purer rubber is obtained.
The Manihot tree has been widely introduced into other countries, and appears to succeed wherever the rainfall is not excessive. ' In Ceylon and in some parts of India, especially in Madras, it has succeeded well. In W. Africa the tree flourishes, but it is under trial as a rubber producer. The Manihot tree also promises well in E. Africa, Nyasaland and the Mozambique. The pure Ceara rubber, as for example the “biscuits” prepared in Ceylon, is of excellent quality, scarcely if at all inferior to Para. That derived from Brazil, however, is generally inferior, being mixed with wood and dirt. The cultivation and collection of, the rubber being troublesome, it is unlikely to be attended to in those countries in which Hevea is successful.
3. The source of “Ule” rubber exported from Central America, and of the “Caucho” rubber of Peru is Castilloa elastica, Cerv., a lofty tree, N. O. Urticaceae, with a trunk 3 ft. or more in diameter, and large hairy oblong lanceolate leaves often 18 in. long, and 7 in. wide (fig. 4). The tree grows most abundantly in a sporadic manner
