220 Chronicles of Science. [ April, 
of a pale yellow colour; it becomes black by exposure to the air. 
Inferior kinds of india-rubber are blacker than others, and contain a 
sticky, resinous fluid, which can be squeezed out. Other sorts are 
white and hard when dry, resembling gutta-percha in that they 
become elastic when heated gently. The first person to advocate 
the use of india-rubber for erasing pencil-marks (whence has arisen 
its name) was the great Dr. Priestley, and at the end of the last 
century you might buy a square inch of india-rubber for 3s.! The 
vast variety of uses to which india-rubber has now been put has 
caused it to be searched for and discovered in every quarter of the 
globe ; and though the principal supply is still from America, it 
has been found in use among the natives of Asia, Africa, and even 
Australia, and is now imported thence. Of the American india- 
rubber, the original and best is procured from Hevea Guayanensis (St- 
phonia elastica), and other species of the same Euphorbiaceous genus: 
it is known as Para-rubber. Pernambuco rubber is the product of 
Hancorma, an Apocynaceous genus, and is an excellent sort. Cowma, 
another Apocynaceous plant, yields a hard, white, gutta-percha-like 
substance, which is sometimes sold as “ rubber milk.” The Castzlloa 
elastica, belonging to the same natural order as the nettle, is the 
plant which yields the somewhat inferior “rubber” of Central 
America. Guatemala rubber is the worst kind, and is quite black 
and resinous. The juice of the Castilloa is not coagulated by heat, 
but by the juice of a vine-like plant, which grows in the same 
forests, and is called “ Achuca.” Species of Micrandra and Stpho- 
campylos (Kuphorbiaceze) yield small quantities of “rubber,” of 
good elasticity. The Asiatic “rubber” has a different appearance 
to the American, and is much inferior, on account of its frequent 
impurities. From Penang, Sumatra, Malay Peninsula, and Borneo 
a “rubber” is imported, the produce of Urceola elastica (Apo- 
cynacez), discovered in 1798, but its value till lately was only 2d. 
a pound, whilst Para fetched half-a-crown ; its value is now about 
half that of the Para. From Assam the rubber brought is the 
produce of the Ficus elastica, which we so often see now as a 
drawing-room plant. In Java, species of Ficus (Urticacese) and 
Vahea gummifera (Apocynacex) yield a good “rubber.” The 
African india-rubber is brought from Mauritius and from the West 
Coast ; that from Mauritius is probably imported from Madagascar, 
where Vahea and Ficus grow; that from the West Coast is im- 
ported in casks, in the form of balls, slabs, and “tongues.” It has 
a very foul smell, and is only valued at 11d.a pound—the cheapest 
of any. By some this is believed to be produced by Sycomorus 
Guineensis (Urticacez), whilst others believe that it exudes from 
some Apocynaceous plant, at present not known. Fragments of 
rubber have been received from Australia, but it is not known what 
plant produced them. 
