India Rubber

—An elastic gummy substance derived from the milky juice of a variety of tropical trees and plants. The juice resembles cream as it i ues from incisions made in the bark. The best rubber, known as Para, comes from Brazil, Bolivia and Peru. Many other grades are obtained from South America and Africa, while succe ful attempts at cultivation have taken place in Ceylon, and the Straits Settlements. India rubber has valuable insulating properties, and is largely used in covering electric cables, etc. a As good india rubber is expensive, a large number of substitutes have been tried for insulating purposes. Some of them are fibrous in construction, and are impregnated with an insulating oil. Their specific resistances are lower than those of rubber, but this is not a serious drawback providing the coating be sufficiently thick. These substitutes are not impervious to moisture and require a waterproof covering, which usually consists of a lead sheathing.