284 INDUSTRIAL PLANTS 
with caoutchouc is called vulcanization. By using much 
sulphur and a high degree of heat hard rubber or vulcanite 
is produced. 
The discovery of vulcanization revolutionized the rubber 
industry. Not only were the old uses greatly extended but 
new uses for rubber have so multiplied that caoutchoue now 
ranks among the most important products of the vegetable 
kingdom. The elasticity of soft vulcanized rubber makes it 
invaluable in various articles of dress, for many surgical 
purposes, for elastic bands, solid or pneumatic tires, for 
various parts of machines, and for rubber balls, toys, and in- 
numerable other articles of minor use. Its imperviousness 
to water and air, combined with its flexibility, render it of 
greatest service for waterproof garments or coverings, sub- 
marine diving-dresses, flexible tubes or hose, water-bottles, 
air-cushions, life-preservers, portable boats, ete. Hard rub- 
ber takes a high polish and is very resistant to the action 
of acids and other corrosive fluids. Therefore it makes the 
best possible material for photographer’s developing trays, 
certain parts of fountains pens, telephones, surgical instru- 
ments, etc., while it is a most excellent and inexpensive sub- 
stitute for horn or shell in such articles as combs and handles. 
Both vulcanite and the softer vulcanized rubber are exten- 
sively used for insulation in electric work. Pure rubber on 
account of its remarkable adhesiveness is an indispensable 
part of the best surgeon’s plaster, and of the rubber tape 
used in repairing bicycle tires and in electric wiring. The 
curious erasing power of rubber, whether pure or vulcanized, 
is possessed by no other substance to anything like the same 
degree; hence one of its earliest uses still remains one of the 
commonest and most important. 
Caoutchouce as a raw material bears, as we have seen, some- 
what the same relation to the milky juice of plants that 
cheese bears to the milk of animals. That is to say, it sepa- 
rates from the fluid part as curd from whey, and becomes 
solid by drying. Chemically, however, caoutchouc is quite 
different from the proteid of which cheese mainly consists. 
Pure caoutchouc is a hydrocarbon; in other words, it contains 
only hydrogen and carbon in its composition. Commonly 
