The principal uses to which Indian rubber is applied by us are, for the effacing of black-lead marks; for flexible syringes, tubes, and other instruments used by surgeons and chemists; and for the formation, by means of turpentine or linseed oil, of a varnish for air-balloons. Various experiments have been made to dissolve this substance, so that it may assume its naturally elastic state, under any figure that may be required. This has been effected by means of ether, but the process is too expensive for common use. A simple method of forming tubes of it is to split a piece of cane and to put between the pieces a slip of whalebone. If the Indian rubber be cut into slips, and twisted closely round the cane, and the heat of boiling water be applied, the whole will become united into one piece or tube, from which the whalebone first, and afterwards the cane, may easily be separated. It has been proved that cloth of all kinds may be made impenetrable by water, if impregnated with the fresh juice of the Indian rubber tree; and that boots, gloves, and other articles, made of cloth thus prepared, may be joined without sewing, and only by moistening the edges with the juice. These are not only more durable, but retain their shape better than such as are made of the juice without any connecting substance. It has lately been ascertained that, in Prince of Wales's Island, and also in Sumatra, there are trees of a class and order totally different from that above described, which yield a juice similar to this, and applicable to all the same purposes. 254. _The CASTOR-OIL PLANT_ (Ricinus palma christi) _is a native both of the East and West Indies, and has a stem from five to fifteen or sixteen feet in height, and large bluish-green leaves, divided into seven lobes, serrated and pointed, the footstalks long, and inserted into the disk._ _The flowers are produced in a terminating spike, and the seed-vessels are covered with spines, and contain each three flattish oblong seeds._ It is to the seeds of this plant that we are indebted for the drug called _castor-oil_. This is sometimes obtained by pressing the seeds, in the same way as is practised with respect to oil of almonds (152). But the mode chiefly adopted in the West Indies, whence we principally import it, is first to strip the seeds of their husks or pods, and then to bruise them in a mortar; afterwards they are tied in linen bags, and boiled in water until the oil which they contain rises to the surface; this is carefully skimmed off, strained to free it from any accidental impurities, and bottled for use. The oil which is obtained by boiling is considered more mild than that obtained by pressure, but it sooner becomes rancid. The mildest and finest of the Jamaica castor-oil is limpid, nearly colourless, and has scarcely more taste or smell than good olive-oil. The uses of castor-oil in medicine are well known.