CAOUTCHOUC', Gum ELASTIC, or INDIA RUBBER, a substance which, on account of its peculiar properties, is extensively used in the arts, and of which the use is continually and rapidly increasing. It is one of the products of the wonderful chemistry of nature, found in the milky juices of plants, and most abundantly in the natural orders ,noracece, artocarpacee, euphorbiacece, apocynacea', asclepiadacece. and papayacece. It exists in the milky juice of plants growing in temperate climates; but it is only in tropical and subtropical countries that it occurs so abundantly as to be of economical importance. Its uses to the plants in which it is elaborated have not been ascertained; and the con jectures of theorists on this subject are not supported by arguments sufficient to give them much probability. In the milky juice, the C. is diffused in the form of minute globules, and not, strictly speaking, in solution; and when the juice is extracted from the plant, and allowed to stand for a short time, these globules separate from the watery part of it, and form a sort of cream on the top, or, in close vessels, appear throughout it as a flaky coagulum. C., as well as some of its useful and curious properties, must have been known in America at a very early period, because balls made of the gum of a tree, lighter and bouncing better than the wind-balls of Castile, are mentioned by Herrera when speaking of the amusements of the natives of Hayti, in his account of Columbus' second voyage. In a book published in Madrid in 1615, Juan de Torquemada mentions the tree which yields it in Mexico, describes the mode of collecting the gum, and states that it is made into shoes; also that the Spaniards use it for waxing their canvas cloaks to make them resist water. More exact information regarding C. was afterwards fur nished by de la Condamine, who visited South America in 1735, but it is curious to note that some of the purposes for which india- rubber is most extensively used at the present time are the same as those for which it was employed in South America nearly three centuries ago. It was at first known by the name of elastic gum, and received that of india-rubber from the discovery of its use for rubbing out black-lead pencil marks, for which purpose it began to be imported into Britain in small quantities about the end of last c., being much valued by artists, and sold at a high price. Even before this
time its employment for the manufacture of flexible tubes for the use of surgeons and chemists had been successfully attempted; but the expensive character of the solvents then known for It, prevented its general application to any purpose in the arts. It was not till 1820 that its employment began to extend beyond the rubbing out of pencil marks, although in the meantime the quantity imported had considerably increased. Its application to the manufacture of water-proof cloth first gave it commercial impor tance. About the same time a method was discovered of fabricating articles of various kinds by casting C. in molds. Its elasticity and flexibility, its insolubility in water, and its great impenetrai6lity to gases and fluids in general, have now been found to adapt it to a great variety cf uses; but for by far the greater number of its applications it is now employed in the vulcanized state.
The C. of commerce is obtained most largely from South America, but considerable quantities are also procured from British India, the Indian archipelago, the west coast of Africa, and the Mauritius. During the year 1872, the actual imports of this material :Tato Great Britain were: Cwts.
7.F'rom Brazil..... ..... 68,143 " New Gran;6.n., Ecuador, and Central America..... 16,390 • " British Indic 13,855 Strait Settlements 15,296 West Coast of Africa . . ........ . 14,135 Mauritius.... 10,433 Other Countries 18,862 Total 157,114 In 1852, the total imports were only 15,269 cwts.; in 1862, 59,703 cwts.: and in 1876, 157,509 cwts. The average annual yield of Brazil for the five years preceding 1871, accordiog to a table sent from that country to the Vienna exhibition of 1873, was about 5,000,000 kilogrammes. The value of the 159,753 cwts. of C. Imported in 1877 was £1,484,794.