if 225 so 1 350 60 3i 600 70 4 750 80 54 1,60 0 90 5 LOW 90 Modern tire equipment includes a gauge which indicates the amount of pressure in the tire and thus over-inflation or the equally clan- f Goodrich under-inflation are avoided. Consult rich Rubber Company's 'Wonder Book of Rubber) (Akron, Ohio, 1917) and Dykes mobile Encyclopedia' (Saint Louis, annually). RUBBER-TREES, the sources of chouc (q.v.) or India-rubber (q.v.) are botan iially various and widely distributed in the wanner parts of the world. They belong to the four allied groups Moracece, Ruphorbiaces, Aetocorpacece, and Afreelnacter, but not all the members of these families yield caoutchouc, while a similar juice may be obtained from cer tain outside plants. This substance (latex) is one of those, like the 'milk)) of the milkweeds and many others, which are elaborated in the green surface cells and conducted through the plant, for its nourishment by the lactiferous canals. In the rubber plants they run just be neath the bark and often carry the sticky juice in excess, so that tin the gigantic trunks of tropical fig-trees? as Kerner says, ((the latex often wells up in large quantities from rifts in the bark which have arisen spontaneously and thickens into long strings and ropes of In dia-rubber hanging down like a Mantle)) A rough test of whether a tree-juice has the true properties of caoutchouc is to rub some of it between the fingers until it exhibits the recog nized elastic threads; inferior Juices of other trees are sometimes mingled with it by native gatherers as adulterants and these may in some cases nearly ruin the whole package, by de veloping other qualities in coagulation, as for instance those of gutta-percha (q.v.).
The caoutchouc-yielding trees occur in all tropical regions, but are different botanically in each region. The principal commercial supply and the best is obtained from the valley of the Amazon and is known to the trade as Para rub ber; but all other ports of northern South America ship it in large quantities. That which comes from the valleys of the Amazon and Orinoco (Brazil, Guiana and Venezuela) Is chiefly the product of the euphorbiaceous genus Hevea and especially. of H. brasiliensis, a tree often 60 feet in height, branching from the base, which, with two or three similar species, grows abundantly in the hot steaming lowlands along the river courses; the juice is obtained by tap ping the trees by means of incisions in the bark in the evening and collecting the. deposition next morning. Each tree will yield about six ounces in three days and then must be allowed to rest. The main resources in Guiana are the species H. maryensis and paucif olio, the former of which is called by the natives That exported from Maranhlo is similar. The Ceara. rubber is derived from a smaller euphor biaceous tree (Manikat glasiovii), which grows over a large area in that part of Brazil and is tapped when about two years old. The Per nambuco or Mangabeira rubber is the product of a small, drooping tree (Hancornia speciosa) of the family Apocyonacece, which grows on the hills and yields the edible fruit for the sake of which it is frequently cultivated in orchards. This is a comparatively poor sort of rubber. Nearly all the crude rubber above mentioned is exported to Europe. The United States derives its supply mainly from Colombia, Ecuador, Central America and Mexico. This is mainly the product of a tree (Castilloa dos tics) of the family Artocarpaces related to the breadfruit. It is a lofty tree with a trunk i sometimes three feet or more in diameter and large, hairy, oblong leaves, which grows in the rich soil of wet, low-lying, heavily forested valleys. With some allied species it flourishes from Mexico and Cuba to the mountains of Venezuela and the Andes, which separate it from the heveas of Brazil• It reaches its larg est size and best condition in Panama and Nicaragua. Honduras rubber is good, but some of that from Guatemala is inferior.
The Asiatic supply comes from various ports in Assam (via Calcutta), and eastward to Bor neo and is chiefly produced by the rubber-fig (Ficus elastica). A large variety of other
plants and trees in the Malayan and Papuan region yield rubber, some of which is excellent and of growing importance commercially, and everywhere the early rough and wasteful methods of obtaining the product are being corrected. It is also obtained in northern Aus tralia, in Fiji and in various neighboring islands. More than 100 different trees are known to give rubber-making juices in com mercial quantities, while in a great many others, as lettuce, poppy, milkweed and others, it is present in small quantities. The juice of the Brazilian Hevea trees is said to yield about 30 per cent of pure rubber; but a product of less than 15 per cent is not regarded as com mercially profitable.
Africa is now the principal source of the wild rubber supply of the world next to Central and South America. The bulk of that from the west coast and equatorial region is obtained from various climbing shrubs belonging to or allied to the apocyonaceous genus Yokes, few of which are well known to botanists. In Li beria and somewhat elsewhere are rubber-bear ing figs; and a large part of the extensive product of Madagascar and the Mozambique coast is derived from a Walbergia, species of which also give much of the caoutchouc re ceived from the Malayan Islands, Cultivation of Rubber Treear-Attempts have been made in most countries, where suit able conditions prevail, to propagate the rubber trees in plantations of prescribed dimensions, and capable of rational supervision by experts, rendering the planter independent of native de linquencies and assuring annual crops of first quality for an indefinite number of years. It has been demonstrated that the rubber tree can produce, under proper management, a regular and increasing crop, for each year of its natural life, without being injured. Many thousands of acres of rubber are rapidly being developed in Mexican plantations in the tropical coast lands from the country round the Isthmus of Tehuantepec southward into Guatemala. Frog rem has been retarded on account of lack of previous knowledge or precedent in the business, Yet the difficulties seem to have been sur mounted, and it is now demonstrated that the rubber tree can be artificially cultivated when conditions under which its growth is stimulated are understood. In Chiapas, the numerous river bottoms afford the character of soil re, quired, favorable atmospheric conditions and abundance of rain-fall. The rubber lands of this region are covered with thick tropical forest growth, which it is necessary to clear. The rubber tree shoots, raised from seed in neighboring nurseries and about a foot high, are planted in the clearings generally to the number of 200 trees to the acre. At six years of age the tree is tapped, yielding a small first crop.. Hundreds of thousands of every age are growing in strength and luxuriance, with a prospect of affording an ever-increasing supply of the crude product annually. The Central American rubber tree will not flourish in swamps, though moisture is a prime requisite Hence the saying; rubber tree must have its feet dry and its head damp' Extensive ex periments have been made with various kinds of rubber plants ; but the Castilloa has been found to be the best adapted to soil and other condi tions obtaining in Mexico and Guatemala. Rubber can be gtown in commercial quantities in practically all the states of southern Mexico, where it is sometimes cultivated near the ex treme limit of 3,000 feet above sea-level. How ever the best rubber trees grow there at from 300 to 1,000 feet altitude. The altitude it affects varies in different lands, preferably but little above sea-level, but in some localities 1,000, 1,500, or even 3,000 feet above tide water. The tubber plant so commonly grown as an orna mental house plant is the East Indian fig (Ficus elastics).