hard rubber

rubber vulcanized with a large amount of sulfur, usually 25–35 percent, to render it stiff and comparatively inflexible.

Origin of hard rubber

First recorded in 1855–60

His hand reached upward and lifted the hard-rubber receiver from the hook.

Whispering Wires |Henry Leverage
We have, then, a glass or hard-rubber jar containing two lead plates and a solution consisting of water and sulphuric acid.

ABC of Electricity |William Henry Meadowcroft
He took one step forward as Loris swished across the sitting-room, lifted the hard-rubber receiver and voiced a soft, “Hello!”

Whispering Wires |Henry Leverage
He groped along the wall for the electric switch, and found only the shank of it—the hard-rubber button having disappeared.

The Destroying Angel |Louis Joseph Vance

The touch key ended in a hard-rubber knob which could be brought in contact with the skin of the subject.

Harvard Psychological Studies, Volume 1 |Various

hard rubber

a hard fairly inelastic material made by vulcanizing natural rubber See vulcanite