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Originally appearing in Volume V23, Page 801 of the 1911 Encyclopedia Britannica.
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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, Mull. 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. I). 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. To obtain the latex, deep incisions are made near the base of the tree extending up the trunk. Small shallow cups are placed below the incisions to receive the milk, each cup being attached by sticking a piece of soft clay to the tree and pressing the cup against it. The latex, of which each tree yields only about 6 oz. in three days, has a strong ammoniacal odour, which rapidly disappears, and in consequence of the loss of ammonia the latex will not keep for longer than a day unchanged; hence when it has to be carried to a distance from the place of collection, 3 % of ammonia solution is added. The latex usually furnished about 30% of rubber. To obtain the rubber, the latex is usually treated in the following mariner. A piece of wood about 3 ft. long, with a flattened end forming a kind of paddle, is dipped in the milk, or this is poured over it as evenly as possible. The milk is then carefully dried by turning the mould round and round in the smoke produced by burning wood mixed with certain oily palm nuts; those of Attalea excelsa are considered best, the smoke being confined within certain limits by the narrowness of the neck of the pot in which the nuts are heated. The creosote and other products from the smoke no doubt act antiseptically and prevent to a large extent the subsequent putrefaction of the proteids retained by the coagulated rubber. Each layer of rubber is allowed to become firm before forming another; a practised hand can make 5 or 6 lb in an hour. In some districts a stout stick is substituted for the paddle, on which the rubber as it coagulates is wound cylindrically. The rubber thus prepared is the finest that can be obtained. The cakes when completed are, in order to remove them from the mould, slit open with a sharp knife, which is kept wet, and are hung up to dry. The flat rounded cakes of rubber made in this manner are known in the London market as " biscuits. " They retain about 15 % of moisture. The scrapings from the tree, which contain fragments of wood, are mixed with the residues of the collecting pots and the refuse of the vessels employed, and are made up into large rounded balls, which form the inferior commercial quality called " negrohead, " and often contain 25 or 35 % of impurity. The yield of rubber varies, but it is stated on an average to be to lb of rubber per tree, and if care-fully tapped one tree will yield this amount for many years in succession. Plantations of Hevea brasiliensis.—Hevea brasiliensis was introduced to Ceylon and Singapore from seedlings raised at Kew from Brazilian seed, specially collected by Mr H. A. Wickham in S. America. The seedlings rapidly developed and in most places in which they were planted grew into large trees which furnished satisfactory latex when tapped in their sixth or seventh year. 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. Successful plantations of Hevea have also been established in Java, Sumatra and Borneo. Many of these plantations have not yet reached the productive stage—that is, the sixth or seventh year. 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 alreadyappropriated 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 portions of Australia. In certain districts of British W. Africa the Hevea which has been planted promises well, especially in the Gold Coast, where good yields of latex are stated to have been obtained. It may be useful to summarize here the experience which bas bee5-gained in the formation of plantations of Hevea and in the production of rubber. Hevea brasiliensis as a rule flourishes to the greatest extent at Ios-, altitudes on rich soil capable of retaining moisture. The nature of the soil appears, however, to be of secondary importance, provided that it is able to hold moisture and that climatic conditions of high and even temperature with considerable rainfall and absence of wind are satisfied. Although the tree is sensitive to such conditions. it appears to possess a certain capacity of adaptation which should be borne in mind. Generally a low altitude is desirable, but good results have been obtained in Ceylon in sheltered positions at elevations of 3000 ft. and over, although at higher altitudes the growth of these trees appears to be slower. In many plantations besides catch crops (cassava, sesame, ground-nuts, &c.) other crops, such as tea, coffee, cocoa and tobacco, are grown with rubber. It is improbable, except in the early stages of the rubber tree, that this procedure will succeed ; the rubber will ultimately dominate the position to the detriment and ultimate extinction of the other crop, whilst the growth of the rubber tree will be retarded. A partial exception may perhaps be made in the case of cocoa, when the two plants are placed not too closely in about equal numbers. In these circumstances it appears that satisfactory results may be obtained from both crops, at any rate for a certain number of years. The experience of planters. in general is in favour of the complete removal of weeds from a rubber plantation. This practice, which involves periodical weeding, adds considerably to the cost of maintaining plantations, and, although justified so far by results, possesses several other disadvantages. During the tropical rains 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 soi+ 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. 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. Among the plants which are being tried for this purpose are various species of Crotolaria, passion-flower, and the well-known sensitive plant of the East. The success of the method cannot yet be judged, but the experiment is one which deserves very full trial. One of the most important subjects in connexion with rubber plantations is the method to be adopted in tapping the trees for latex. The native methods in vogue in Brazil and Mexico are primitive and often injurious to the tree. At present it cannot be said that finality has been reached on the subject of the best method, giving a good return of latex with a minimum of damage to the tree. A method at one time largely adopted was to make a series of V-shaped incisions on four sides of the tree to a height of about 6 ft. from the base —that is, within the reach of an ordinary man without the need for ladder or scaffolding; the latex obtained from the upper part of the tree is said to furnish less rubber FIG. 2: Tapping, herring-bone system and of poor quality. The latex is collected in cups placed at the apex of each V. Other systems are the herring-bone plan of a vertical channel with lateral connecting channels about i 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 tappings, 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 2o—25 in. in circumference, produces inferior rubber. As a rule, an annual yield of more than 1—2 lb of rubber per tree must not be looked for from recent plantations, although much higher yields up to so—15 lb 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 11 lb of rubber per annum per tree at 2s. 6d. per lb gives the result of £28, 2s. 6d. per acre. The cost of production may be assumed to be about Is. per Ib, to which has to be added the expense of transport. The cost of clearing forest land and planting with rubber in Ceylon is estimated at about ioo Rs. per acre in the first year, and from 2o—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 Hevea, 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 receivesboth the wild rubber containing variable quantities of impurity and the purer plantation rubber, the 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 (Fames 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 Manitoba 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 with-out 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 FIG. 3.—Manihot Glaziovii. I, branch their vitality well, have with flowers; 2, fruit; 3, seed. a hard thick coat. The seeds take a year to germinate, unless the edges near the end bearing the caruncular projecting are rasped off. Cuttings, if they have a single bud, strike readily. 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 I lb 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 mariner in the dense moist forests of the basin of the Rio San Juan, where the rain falls for nine months in the year. It prefers rich fertile soil on the banks of watercourses, but does not flourish in swamps. It is found also in Costa Rica, Guatemala, Honduras, Mexico, Cuba and Hayti, and in Panama with another species of Castilloa, and on the W. coast of S. America down to the slopes of Chimborazo; the Cordilleras of the Andes separating the Castilloas from the Heveas of Brazil. In Nicaragua the latex is collected in April, when the old leaves begin to fall and the new ones are appearing, during which time the latex is richest. 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 lb of rubber. In the evening the milk is strained through a wire sieve and transferred to barrels. The 1, leaf ; 2, twig with the addition of the alkaline juice of male flowers; 3, twig the " achete " plant, or of another with female flowers; plant called " coasso." The strained 4, seed; 4, nat. size. juice of either of these plants, ob- tained by bruising the moistened herb and subsequent expression, is added to the milk in the proportion of about i pint to the gallon. In British Honduras an alkaline decoction prepared from the Moon plant (Caloniclyon speciosum) is used for the same purpose. If these plants are not procurable, two parts of water are added to one of the milk, and the mixture allowed to stand for twelve hours. The coagulum is next flattened out by a wooden or iron roller to get rid of the cavities containing watery liquid, and the sheets are then hung up for fourteen days to dry, when they weigh about 2 lb, the sheets being usually % to k in. thick and 20 in. in diameter. When coagulated in water, the mass is placed in vats in the ground and allowed to dry, this taking place in about a fortnight. It is then rolled into balls. That which dries on the incisions in the tree is called " bola " or " burucha," and is said to be highly prized in New York. The loss of Nicaragua rubber in drying is estimated at 15%. It is exported chiefly from San Juan del Norte, or Grey Town, and the larger proportion goes to the United States. The Castilloa tree appears to be suitable for cultivation only in districts where the Para rubber would grow equally well. The tree is ready for tapping at about the same age as Hevea and the average yield of rubber is about the same. Since the latex " creams " readily the rubber can be separated from the latex by centrifugalizing, and its quality and market value thus enhanced. Much of the native Castilloa rubber is of inferior quality. The tree has been introduced into S. India, Ceylon and the W. Indies, where it has succeeded well, especially in Trinidad and Tobago. It is also under trial in E. and W. Africa and Nyasaland. Several other species of Castilloa than C. elastica are known to furnish rubber, but little has been recorded as to their advantages. 4. Funtumia elastica (formerly known- as Kickxia or 'Kixia elastica) is the W. African (Ire or Irai or Lagos) rubber tree, which belongs to the Apocynaceae, a natural order which includes the Landolphia vines as well as other rubber producers. It is a large forest tree of upright habit extending to 6o or 70 ft. in height and 3 to 4 ft. in diameter. The bright green, glabrous leaves are broad and oblong, about 6 in. in length (see fig. 5). The flowers are yellow, and the seeds enclosed in a pod are long and thin with numerous long silky fibres attached to them, which enable the seeds to be readily carried by the wind. The trees are common throughout the central regions of E. and W. Africa (from Uganda to Sierra Leone). The botanical name is taken from a W. African native name for a rubber tree—" Funtum." Many of the trees in the accessible forests of W. Africa have been destroyed by over-tapping and felling. Plantations of Funtumia 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. In some districts the collected milk is heated alone or diluted with water, to coagulate the rubber, but if heated alone an inferior rubber is apt to result owing to overheating. The Funtumia latex can also be coagulated by the astringent infusion of Bauhinia leaves or by exposing it in shallow dishes, when the liquid " creams." The yield of rubber is stated as a rule to be less than that of Para. The rubber, if properly prepared, is of excellent quality, and the tree deserves further attention, especially in those regions of W. Africa which are unsuited to Hevea. Funtumia africana furnishes a very inferior rubber, which is highly resinous. 5. Ficus elastica is the tree which produces Rambong or Assam rubber. It is well known in Europe as a small ornamental tree, but in the tropics it attains very large dimensions, and develops a system of branching roots which act as buttresses to the large trunk (see fig. 6). It is a native of India,' Burma and the Malay Archipel- ago, 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 ex-tent 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 ex-ported is still ob- tained from the forest trees. It has been found that although the tree grows well in many different countries and different localities, it only furnishes a satisfactory yield of rubber in mountainous districts, such as those of Assam and certain parts of Ceylon and Java. The trees are tapped when about ten years old, and as a rule annually furnish from 5–10 lb of rubber per tree. The latex flows fairly well, but is usually allowed to dry on the tree. The rubber, if of good quality, sells at prices only slightly inferior to that of Para. When the plantations of Ficus in India are in full bearing it is possible that this tree may attract more attention, since the plantation rubber is likely to be of superior quality owing to the greater care taken in its preparation. It seems at present doubtful, however, whether the establishment of plantations of Ficus will be profitable under ordinary conditions in India. In addition to the trees described above there are numerous plants of some importance as rubber producers. Among these may be mentioned the Landolphia vines, which are still the chief source of African rubber. 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 2, section W. Africa and the Sudan, Landolphia Heudelotii of W. Africa, and Landolphia Kirkii and L. Dawei, which are found in the forests P'IG. 7.—Landolphia owariensis. 1, twig with flowers; 2, fruit. of E. Africa. Other species of Landolphia, including Landolphia florida, abundant in both E. and W. Africa, furnish rubber of inferior quality. Among other shrubs and vines which yield rubber of fair quality may be mentioned Willughbeia edulis and Urceola elastica and Paranieria glandulifera, which occur in Burma and Malaya. The Sapiums of Colombia and Guiana are large trees resembling Hevea, and certain species furnish good rubber, especially the Sapium Jenmani of Guiana. Most of the native Sapiums have been destroyed by reckless tapping, and the merits of this genus have been somewhat overlooked and deserve reinvestigation. The same applies to certain species of Hevea, other than H. brasiliensis, which are known to produce good rubber in tropical America. Pernambuco or Mangabeira rubber is obtained from Hancornia speciosa, Gom., an apocynaceous tree common on the S. American plateau in Brazil from Pernambuco to Rio de Janeiro, at a height of 3000 to 5000 ft. above the sea. It is about the size of an ordinary apple tree, with small leaves like the willow, and a drooping habit like a weeping birch, and has an edible fruit like a yellow plum called " mangaba," for which, rather than for the rubber, the tree is cultivated in some districts. Only a small quantity of this rubber comes to England, and it is not much valued, being a " wet " rubber. It is produced in " biscuits " or " sheets." The caoutchouc is collected in the following manner: about eight oblique cuts are made all round the trunk, but only through the bark, and a tin cup is fastened at the bottom of each incision by means of a piece of soft clay. The cups when full are poured into a larger vessel, and solution of alum is added to coagulate the latex. In two or three minutes coagulation takes place, and the rubber is then exposed to the air on sticks, and allowed to drain for eight days. About thirty days afterwards it is sent to market. Pernambuco rubber, as is the case with most rubbers coagulated by saline solutions, contains a large quantity of water. 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. Specimens of the best known and of many of the lesser known rubbers are included in the Colonial and Indian Collections and Sample Rooms of the Imperial Institute, and many of the authentic specimens have been chemically and technically examined in the Scientific and Technical Department of the Institute and commercially valued. Reports on many of the lesser known rubbers have been published in the Bulletin of the Imperial Institute.

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