Wyndham Rowland Dunstan

“ In Africa it seems probable that the production of rubber from vines is likely to be entirely superseded in process of time, and replaced by the plantations of trees which are already being established in those districts in which careful experiment has determined the kind of rubber tree best adapted to the locality. ”

“ During the tropical rain; the soil is liable, to a greater or less extent, to denudation, which becomes very serious when the land slopes; and in any case, the soil is apt to become impoverished by the loss of its soluble constituents. These disadvantages are at their maximum when the rubber trees are quite young. At a later stage the shade of the large trees compensates to a considerable extent for the absence of cover on the ground. Another disadvantage of uncovered soil in a plantation of young rubber trees is that the ground under the heat of a tropical sun rapidly loses its moisture. ”

“ 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. ”

“ It is well known that the Hevea tree usually furnishes very inferior rubber if tapped before it is six or seven years old, and there is evidence to show that the quality of the rubber improves with the age of the tree. The oldest of the plantation trees of Ceylon and Malaya are not much more than twelve years old, whilst it is to be feared that immature trees are often tapped and their latex mixed with that of older trees before coagulation, thus forming inferior rubber. ”

“ 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. ”

“ Many of the trees in the accessible forests of W. Africa have been destroyed by over-tapping and felling. Plantations of Funlumia have been established in several districts, including the Gold Coast and S. Nigeria. The trees are tapped on the “herring-bone” plan and the milk collected in vessels at the base. This is then poured into the hollowed-out trunk of a tree, where it is allowed to stand covered with palm leaves for about a fortnight. The watery portion of the latex soaks into the trunk, and the soft spongy rubber which remains is kneaded and pressed into lumps or balls. ”

“ When the vulcanization of rubber is carried too far, from the presence of a very large proportion of sulphur and an unduly long action of heat, the caoutchouc becomes hard, horn-like, and often black, Rubber hardened by over-vulcanization is largely manufactured under the name of ebonite or vulcanise. It is usually made by incorporating about 40% of sulphur with purified Borneo rubber by means of the usua mixing rollers, shaping the required articles out of the mass thus obtained, and heating for six, eight or ten hours to from 135° to 150°. ”

“ Ever since plantations of Hevea have been made on an increasing scale in the Straits Settlements, the Federated Malay States and in Ceylon, and at the present time rubber plantations form the principal industry in these colonies. ”

“ Para rubber from Brazil generally contains about 15% of water, whilst “plantation” Para is usually nearly dry and contains 1% of water or less. It would appear, however, that the finest “wild” Para rubber as a rule possesses greater tensile strength than the “plantation” rubber. This has been ascribed by some to the presence in “wild” rubber of certain impurities derived either from the latex or introduced during the preparation of the rubber which are thought to enhance the physical properties of the caoutchouc. ”

“ Air goods, such as cushions, beds, gas bags, and so forth, are made of textile fabrics which have been coated with mixed rubber either by the spreading process above described, or by means of heated rollers, the curing being then effected by steam heat. The manufacture of overshoes and fishing boots is an analogous process, only the canvas base is more thickly coated with a highly pigmented rubber of low quality. ”

“ It is a native of India, Burma and the Malay Archipelago and is most abundant, in those regions in which the climate is distinctly humid, and subject to this condition the tree flourishes at high altitudes. In Assam and in upper Burma there are extensive forests of Ficus elastica, but to a large extent the trees have been damaged by careless tapping. Large plantations have been formed by the Government of India both in Assam and Bengal, but most of the rubber exported is still obtained from the forest trees. ”

“ A large number of plantations in British Malaya and Ceylon are now actively exporting increasing quantities of rubber. Hevea seedlings were also introduced into India, but did not apparently succeed except in Burma and S. India. It may be estimated that between one and two million acres of land in the different countries referred to have been already appropriated for rubber plantations. Plantations are also being formed in British, French and German possessions in W. Africa and in the Congo, also in the tropical ortions of Australia. ”

“ 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 tree has been planted in other countries, but has so far not received much attention. It will grow on a dry sandy soil, dislikes much moisture, and needs no shade.
Forsteronia gracilis of Guiana is a climbing plant which also belongs to the Apocynaceae. Like the Forsteronia floribunda of Jamaica it yields rubber of good quality. Ficus Vogelii of W. Africa yields rubber of variable quality. The production of rubber by this tree merits further investigation, as it grows readily in nearly every district of W. Africa and the Sudan. ”

“ Under certain conditions, as when latex is allowed to stand or is centrifugalized, a cream is obtained consisting of the liquid globules, which may be washed free from proteid without change, but, either by mechanical agitation or by the addition of acid or other chemical agent, the liquid gradually solidifies to a mass of solid caoutchouc. ”

“ Each year should therefore show an increase in the production of plantation rubber. No trustworthy estimate of the rate of the increase of production can, however, be formed, as several uncertain economic factors have to be taken into account. ”

“ 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. ”

“ Rollers are made to adhere to their metal spindles by the intervention of a layer of ebonite, and after vulcanization they are turned. In order to make spongy or porous rubber, some material is incorporated which will give off gas or vapour at the vulcanizing temperature,—such as carbonate of ammonia, crystallized alum, and finely ground damp sawdust. Uncombined sulphur is injurious, and often leads to the decay of vulcanized goods, but an excess of sulphur is generally required in order to ensure perfect vulcanization. ”

“ At higher temperatures the viscous liquid suffers decomposition with the formation of various liquid hydrocarbons, principally members of the terpene series. Similar products are also formed by heating gutta-percha which closely resembles caoutchouc in its chemical structure.
Rubber slowly absorbs oxygen when exposed to air and light, the absorption of oxygen being accompanied by a gradual change in the characteristic properties of rubber, and ultimately to the production of a hard, inelastic, brittle substance containing oxygen. Ozone at once attacks rubber, rapidly destroying it. ”

“ 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. ”

“ Belting intended for driving machinery is built up of canvas which has been thoroughly friction ed with the soft mixed rubber, and is cured by placing it in a kind of press kept by means of steam at a dry heat of about 140° C. Packing for the stuffing boxes of steam engines is similarly prepared from strips of rubber and friction ed canvas, as also are the so-called insertion sheets, in which layers of rubber alternate with canvas or even wire gauze. ”

“ Tubes are generally made up around mandrels and allowed throughout the curing to remain imbedded pulverized French chalk, which affords a useful support for many articles that tend to lose their shape during the process. Of late years a considerable amount of seamless tubing has been made much in the same way as lead piping by forcing the mixed rubber through a die and curing as above. ”

“ Although the cost of transport from the remote forest regions of some districts is a serious consideration, this is not likely to be operative in reducing production until there has been a considerable and permanent fall in price, by which time new areas in those countries in which planting is now taking place will probably have come into bearing. ”

“ 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. ”

“ The tree is tapped either in the same manner as the Hevea, or by encircling the tree with a simple spiral cut at an inclination of 45°, or by two parallel spirals if the tree be large. At the bottom of the spiral an iron spout about 4 in. long is driven into the tree, and the milk is received in iron pails. A tree 20 to 30 ft. high to its first branches, and about 4 ft. in diameter, is expected to yield annually 20 gallons of milk, each gallon giving about 2 ℔ of rubber. In the evening the milk is strained through a wire sieve and transferred to barrels. ”

“ The vines grow upon forest trees, and the stems are periodically tapped. There are numerous species of these climbing plants, of which the most important as furnishing good rubber are Landolphia owariensis (see fig. 7) , which occurs throughout W. Africa and the Sudan, Landolphia Heudelotii of W. Africa, and Landolphia Kirkii and L. Dawei, which are found in the forests of E. Africa. Other species of Landolphia, including Landolphia florida, abundant in both E. and W. Africa, furnish rubber of inferior quality. ”

“ For this reason proposals have been made to plant in the place of weeds low-growing leguminous plants, the growth of which will not only prevent impoverishment and loss of soil during the rains and conserve moisture in the heat, but will also have the effect of enriching the soil in nitrogenous constituents through the power leguminous plants possess of absorbing nitrogen from the air through nodules on their roots. ”

“ 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. ”