CANVAS. As exemplifications of hempen canvas, we cannot do better than refer to those important uses of it described under FLOOR CLOTH MANUFACTURE; and SAIL-MAKING. CAOUTCHOU C. This remarkable sub stance is produced by the Siphonia elastica, the Ficus elastica, the Urceola elastica, and many other American and Asiatic plants. It is often termed India rubber, from its use in removing pencil traces from paper. It was in the year 1735 that this substance was first dis covered by De La Condamine to be the inspis sated juice of a tree. In a pure state, it is in sipid and scentless, white, extremely elastic, inflammable, not altered by exposure to the air, insoluble in water and in alcohol, soluble in nether and in the essential oils, acted upon by alkalies, and decomposed by concentrated sulphuric and nitric acids.
In order to obtain caoutchouc, the trees which produce it are pierced in the rainy sea son, upon which a thick juice of a yellowish white colour exudes, which becomes darker by exposure to the air. If this juice be kept in well-corked bottles, it may be preserved for some time without undergoing much change, and it has been imported in this state ; but, however perfectly the atmosphere may be ex cluded, it will ultimately solidify. Heat coa
gulates the juice and separates the caoutchouc : alcohol and acids produce the same effect. If exposed to the air in thin films, it soon dries, losing from one-third to one-half of its weight: and leaving caoutchouc of the usual appear ance. By the natives of South America it is applied in successive coats to the surface of clay models of bottles and of animals, and dried over fires, the smoke of which communi cates to it a dark colour. While the caoutchouc is still soft, various lines are drawn upon it with a blunt tool, which remain permanently impressed. When thewhole has become dry, the clay is crushed and shaken out of the bottles.
The import of ctioutelidue in 1849 amounted td 5328 cwts., and in the first nine mouths of 1850 to 4899 cwts.
The varied Useful purposes to which this singular substance is applied are noticed under INDIA RUBBER MANUFACTURES.