Vulcanised Indiarubber consists of indiarubber mixed with 44 per cent oxide of zinc and 4 per cent of sulphur. An excess of sulphur injures the material, causing it to become brittle with age.
This material is used chiefly for jointing pipes, for valves, etc.
A rough way of testing its quality is to throw a piece into water; if it sinks, it probably contains an injurious excess of sulphur.
A good sample should stand a dry heat of 270° Fahr. for 1 hour and a moist heat of 320° Fahr. for 3 hours.
1 Patentees' Circular.