INDIGO. 
as caoutchouc, by making incisions in the bark with a 
chopping knife, collecfciiig the thin, white, milky fluid 
which exudes in large vessels, and allowing it to evaporate 
in the srni or over a fire. The solid residiuuii, which is 
the guttapercha of commerce, is finally softened in hot 
water, and pressed into the form of slabs. 
Guttapercha has , many properties in common with 
caoutchouc, being completely insoluble in water, tena- 
cious, but not elastic, and an extremely bad conductor of 
caloric and electricity. The name of vegetable leather, 
which has been applied to it, gives a good idea both of its 
appearance and tenacity. 
Its uses are manifold. It serves for water-pipes, for vessels 
fit for the reception of alkaline or acid liquids which would 
corrode metal or wood, for surgical implements, for boxes, 
baskets, conibs, and a variety of other articles. The wonder 
of the age, submarine telegraphy, could hardly have been 
realised without it, as it is only by being cased iu so 
isolating a substance, and one so impermeable by water, 
that the metallic wire is able to transmit the galvanic 
stream through tho depths of ocean from land to land. 
Of all the dyeing substances which the tropical zone 
produces in siicb endless variety, none is more important 
iu a commercial point of view than indigo. Various 
species of plants producing this bcautifol cerulean colour 
are found growing Bpontaneously in the warmer countries 
of both hemispheres, but the Imligoftra tinctoria is most 
generally cultivated. The knotty shrubby plant rises 
about two feet from the ground ; the leaves are winged 
like those of the acacia, smooth and soft to the touch, 
furrowed above, and of a darker colour on the upper than 
the under side. Tlie small reddish flowers which grow in 
ears from the axillaj of the leaves have no smell, and are 
succeeded by long crooked brown pods, which contain 
small yellow seeds. The plant re(juirea a smooth rich soil, 
well tilled, and neither too dry nor too moist. A child of 
the sun, it cannot be advantageonsly cultivated anywhere 
