Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/862

836 836 INDIA- 11 U B B E R as a product of Asia until 1798, when a plant, afterwards named Urceola elastica, Iloxb., was discovered to yield it by Mr J. Howison, a surgeon of Prince of Wales Island, and soon afterwards Assam rubber was traced by Dr Roxburgh to Fiats elastica, Roxb. It was not, however, until the beginning of the 18th century that the india- rubber industry really commenced. The rapid progress which this has made during the last twenty years may be perceived by a glance at the following table : Imported into England in the year 1830, 464 cwts. 1840, 6,640 ,, ,, ,, ,, 1850, 7,616 ,, ,, 1870, 152,118 ,, 1879, 150,601 It has been computed that in 1870 there were in Europe and America more than 150 manufactories, each employ ing from 400 to 500 operatives, and consuming more than 10,000,000 K&amp;gt; of caoutchouc. The imports into the United States have largely increased during the last few years. Botanical Sources, Modes of Preparation, &c. Notwithstanding the fact that caoutchouc-yielding trees are found in a large belt of countries around the globe, in cluding at least 500 miles on each side of the equator, yet the demand for the best qualities of india-rubber is in excess of the supply. The varieties which are almost exclusively used when great elasticity and durability are required are the Para, Ceara, and Madagascar rubbers. The principal forms of caoutchouc which are imported into Great Britain may be grouped under four heads, the order in which they are here placed indicating their respective values : South American Pard, Ceara, Per- nambuco, Maranhao, Cartagena, Guayaquil ; Central American West Indian, Guatemala ; African Mada gascar, Mozambique, West African ; Asiatic Assam, Borneo, Rangoon, Singapore, Penang, and Java. Of all these, the most important is the Para, the imports of which, according to Messrs Hecht, Levis, & Kahn, have increased from 1670 tons in 1857 to 8000 tons in 1879. For this rubber and the Mozambique variety the demand in- increases every year, an unerring indication of their value. FIG. 1. ffevea brasiliensis. I. SOT-TIT AMERICAN. Pard rubber is obtained chiefly from -^;&amp;lt;, Mull. Arg., a largo euphorbiaceous tree - i i. ] -})(, ] raiirjijn? from the base, and having ffevea b) trifoliate leaves, the leaflets being lanceolate and tapering at both ends (figs. 1, 2). Other species of ffevea, as well as Micrandra siphonoides and M. minor, Beuth., all of which grow abundantly iu the moist steamy valleys of the Amazon and its tributaries, are also used indiscriminately by the natives to furnish Para rubber. These trees are found in different districts, but all flourish best oil rich alluvial clay slopes by the side of rivers, where there is a certain amount of drainage, and the temperature reaches from 89 to 94 at noon and is never cooler than 73 D at night, while rain is rarely absent for ten days together. The genus Hevea was for merly called Siphonia, and the tree named Pao de Xcrringa 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 caoutchouc is collected in the so-called dry season between August and February. The trees are tapped in the evening, and the juice is collected on the following morning. To obtain the juice a deep horizontal incision is made near the base of the tree, and then from it a vertical one, extending up the trunk, with others at short distances in an oblique direction. Small shallow cups made from the clayey soil and dried in the sun are placed below the in cisions 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 juice, of which each tree yields only about 6 ounces in three days, has a strong ammoniacal odour, which rapidly goes off, and in consequence of the loss of ammonia it will not keep longer than a day unchanged, hence when it has to be carried to a distance from the place of col lection 3 per cent of liquid am monia is added. The juice is said by Bruce Warren to yield half its weight of caout chouc, but 32 pel- cent. appears to be the usual quantity. To ob tain the rubber the juice is heated in the following man ner. A piece of wood about 3 feet long, with a flat tened clay mould at one end of it, is dipped in the milk, or this is poured over it as evenly as pos sible. The milk is then carefully dried by turning the mould round and round in a i, i

tamed by heating certain oily palm nuts, those of Attalea excelsa being much pre ferred, and the vapour being confined within certain limits by the narrowness of the neck of the pot in which the nuts are heated. Each layer of rubber is allowed to become firm before adding an other; a practised hand can make 5 or 6 ft in an hour. From what ever cause, 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 &quot; biscuits.&quot; They rarely con tain more than 15 per cent, 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 com mercial quality called &quot; negrohead,&quot; and often contain- 25 to 35 per cent, of impurity. An intermediate quality is known as &quot;eutre- fine. &quot; Para rubber is said to be sometimes adulterated with the juice of the Majandaruba tree (Mimusops data), which might ac count for the great differences that have been occasionally observed in the behaviour of Para rubber in certain stages of manufacture, the coagulated juice of the Mimttsops genus resembling gutta perdu rather than caoutchouc. Previous to 1860 Para rubber was exported only in small quan tities, and then chiefly in the form of shoes ; this variety ceased to be sent over in 1852. Occasionally &quot;negrohead &quot; has been im ported in grotesque forms of animals, &c., and the better qualities in the shape of small bottles moulded in soft clay which has been afterwards washed out by water. -^- Jl^rea bra-sififnsis. a, mal; flower, mid 6, female flower (both enlarged, and with the floral envelope re- moved); c, ripe fruit, am! &amp;lt;/, seed (both natural size).