Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/865

839 INDIA-RUBBER 839 to Vahca, a few only of the species being known to botanists. In Angola, under the name of &quot;Licomgue,&quot; in Golungo Alto and Cazengo, it is collected from Landolphia owaricnsis, Pal. de Beauv. ; from L. ftorida, Benth. , in Angola and Liberia, and from L. Hendclatii, D. C., in Senegal. At Kew there also exists a speci men of india-rubber from the west coast of Africa obtained from an undescribed species of Carpodinus with hairy leaves and stems. In the basin of the Gaboon and Congo it is obtained, according to Du Chaillu, from a climbing plant called N dambo, which gives its name to dambonite, a peculiar substance contained in this kind of rubber (see p. 840). That some African caoutchouc is yielded by species of Ficus there can be no doubt. In Sierra Leone it is collected from Ficus Brasii, R. Br. In Liberia, according to Mr Thomas Christy, the finest rubber is obtained from Urostigma Vogdii, Miq., a tall tree with large handsome leaves, and lower qualities of rubber from other species, and from LaiuLolpliia florida, Benth. In Angola on the west, and at Inhambane on the east coast, rubber is also obtained from species of Ficus. In the island of Reunion caoutchouc is said to be obtained from Periploca grceca, L. IV. ASIATIC. The rubbers which enter English commerce from Asia include the Assam, Borneo, Rangoon, Singapore, Penang, and Java kinds. Assam rubier is imported chiefly from Calcutta in baskets made of split rattans, weighing about 3 cwt. each, and covered with a gunny bag. The rubber is glossy, of a bright pink colour and mottled appearance, and occurs in the form either of small balls pressed together or of irregular masses called &quot;slabs&quot; or &quot;loaf&quot; rubber. The former, being more liable to adulteration, are less in demand by manufacturers. The imports into Liverpool in 1879 were 7000 cwts. Assam rubber is obtained from Ficus clastica, Roxb., a plant too well known as a window ornament to need de scription. A portion also is collected from Urostigma laccifcra, Miq. Ficus clastica grows in the tropical rocky valleys of the Himalayas, between 70 3 and 80 E. long., where there is always a hot moist atmosphere, the temperature rising to 98 F. in the shade. The trees are tapped in the most careless manner. In the lower portion of the tree and in the large aerial roots, diagonal cuts pene trating to the wood are made, from 6 to 18 inches long, and in an elliptical form so as to be about 3 inches across the centre. The milk is received either in holes made in the ground or in leaves folded in the form of a funnel, that from the smaller cuts on the, branches (for the collectors scarify every portion within reach) being allowed to dry on the tree. About 50 oz. of the milk collected in August gives 15 oz. of caoutchouc, but the percentage sometimes falls as low as 10 per cent. From February to April the milk is more scanty, but richer in caoutchouc, and is consequently best col lected at that time. The milk is coagulated by pouring it into boil ing water and stirring it until it is sufficiently firm to be carried about without being clammy ; sometimes it is pressed, ngain boiled, and dried in the sun. In this way the &quot;loaf&quot; rubber in irregular masses is formed. The small &quot;balls&quot; are formed of the strings of rubber which have been allowed to dry on the tree. Assam, rubber, although fairly elastic, is much depreciated in value by the careless mode of collection, and often loses, by washing at the manufactory, as much as 35 per cent, of dirt, consisting of clay, sand, or birk. The exportation of caoutchouc from British India, exclu sive of the Straits Settlements and Ceylon, in 1879 amounted to 9973 cwts., of which 7000 are estimated to have been produced in Assam. About three-fourths of the rubber exported from India goes to Great Britain, and the remainder to the United States. In consequence of the reckless destruction of the trees, the culti vation of Ficus clastica has been commenced in Assam. It is calcu lated that the trees can be tapped at the age of twenty-five years, and that after fifty years they will yield 40 ft of caoutchouc each (worth 3, 4s.) every three years, it being injurious to their health to tap tli em more frequently. Palaij rubber is the product of Cryptostegia grandi flora, R. Br., an asclepiadaceous plant common on the coast of India ; and from If^illui/hbeia cduUs, Roxb., and W, martabanica, D. C., a rubber is obtained in Chittagong ; neither of these, however, is known in Britain as a commercial variety. Borneo rubber conies to the Liverpool market in the form of balls or shapeless masses, internally of a white or pinkish colour, and very porous and spongy, the pores being usually filled with salt water, in consequence of which it often loses 20 to 50 per cent, of its weight in drying. The imports into Great Britain amounted in 1879 to 5000 cwts. Although Borneo rubber was first made known in 1798, it was not imported into England as an article of trade till 1864, when it appeared under the name of gutta susn, i.e., in Malayan, milk-gum. The plant which yields Borneo rubber was identified by Roxburgh as Urccola clastica, Roxb., an apocynaceous climbing plant with a trunk as thick as a man s body, and having a soft thick bark. Mr F. W. Burbidge, who recently visited the island, states that there are three varieties of the rubber plant, known to the natives as &quot;petabo, &quot; which yields the finest caoutchouc ; &quot; menoougan,&quot; which yields the largest quantity; and &quot;sera pit,&quot; from which the commonest rubber is obtained. The petabo variety, according to specimens at Kew, is referred to a species of Lcuconotis-. The rubber is obtained by cutting the plant into pieces varying from a few inches to 2 or 3 feet long, and allowing the juice to drain into buckets or jars, heat being sometimes applied to one end of the pieces when the juice ilows slowly. The milk is coagulated by salt water. The Borneo rubber plant is probably one of the plants that would repay cultivation, as it grows rapidly, yields a supply of sap in three years, and after planting requires no atten tion. In Sumatra, caoutchouc is obtained from Willughbcia firma, and is exported to Holland, but this variety is not known in England. Malacca rubber, which is not met with in English commerce, is said to be obtained from Urccola clastica, Roxb. Rangoon rubber, and those of Penang and Java, are imported into England in small quantities only, and are irregular in appearance. From its physical characters, a portion at least of Rangoon rubber is believed to be the produce of a species of Ficus, probably F. hispida, L. Another caoutchouc-yielding plant, Urccola (Chavan- nesia) esculcnta, Benth., belonging to the Apocijnaccae, has, how ever, been recently discovered in Burmah, some specimens of which at the age of five years have stems 6 inches in diameter, while the crown covers an area of 200 square feet. It has been recommended for plantations as an available source of rubber, the cost of cultiva tion being very slight after the first year, and the profit commenc ing in seven years, at which age the yield is calculated to be 3| It). Penang rubber in character resembles the Assam, and may be also supposed to be obtained from a species of Ficus. Dr &quot;Wallich, how ever, has stated that its source is an asclepiadaceous plant, Cynan- churn ovalifolium, Wright. Java rubber is stated by Dr De Vrij to be obtained from Ficus clastica. Like the Assam rubber it is dark and glossy, but it is of a deeper tint, and has occasional reddish streaks. It is said to be prepared by allowing the juice to dry on the incisions made in the tree. Singapore, Java, and Penang rubbers are much alike in char acter, and may be classed with the Assam rubber, having a firm texture, mottled appearance, and bright polished surface, but vary ing in colour in a single sample from light yellowish-white to dark brown. Java rubber is also exported to France. Caoutchouc is obtained in the Malay archipelago from Alstonia costulata, Miq.; and Alstonia scholaris, R. Br. , is likewise reported to yield it. In Fiji it has been obtained from Alstonia plumosa, Labill. In North Australia caoutchouc has been prepared from Ficus macrophylla, Desf. , and F. rubiginosa, Dcsf. ; the last-named plant has been recommended by Baron Miiller as suitable for cul tivation, being a hardy species. None of the above rubbers are as yet known in British commerce as regular articles of trade. Bibliography. Collins, in Journal of Botany, 1868 ; Journ. Soc. Arts, vol. xviii. p. 86 ; Bevan, British Manufacturing Industries, 1877, p. 97-105, and Report on Caoutchouc, 1872; Markham, in Journ. Soc. Arts, p. 475, 1876; Ulngniicur Unircrscl, vol. ii. p. 187 ; Bernardin, Classification de, 100 Caoutchoucs ct Guitaperchas, Ghent, 1872 ; Christy, Nero Commercial Plants ; Kurz, Forest Flora of British Burmah, vol. ii. p. 1S4. (E. M. II.) Chemistry, Manufacture, and Industrial Uses. The remarkable body known as india-rubber is com posed of carbon and hydrogen alone, but its exact chemical nature is not by any means known with certainty. The analyses of Faraday indicate that its ultimate composition is 87 5 per cent, of carbon and 12-5 per cent, of hydrogen ; but there appears to be good ground for regarding the substance as a polymer of the group C 10 H S, or as (C 10 H 8 ). There are, however, no data for estimating the value of x in this case. It will be noticed, too, that the formula given requires considerably less hydrogen than the propor tion indicated by Faraday s analysis ; but the difficulties of obtaining such a body as caoutchouc in a fit condition for analysis are so great as to render this discrepancy a matter of comparatively small import. The action of cold and heat on india-rubber presents many points of interest. When exposed to a temperature approaching C., it gradually loses its softness and ready extensibility, and finally becomes rigid and inelastic ; but its normal condi tion may be restored by submitting it either to a tempera ture of 35 or 40 C., or to a tension sufficient to stretch it to about twice its natural length. In the latter case it is probable that the change is really due to heat arising from the physical disturbance consequent upon the act of stretching. The effects of heat are more complex and varied than those of cold; ami with caoutchouc at an