How Crude Rubber Is Treated.
_Washing._--When the crude rubber arrives at the factory of the rubber
manufacturer, it is generally stored in bins in dark and fairly cool
store-rooms, where it is kept until ready to be used. The rubber passes
directly from the storage bins to the wash-room, where it is cut up
into small pieces, put into large vats of warmed water and allowed
to soak, in order to soften it sufficiently to be broken down in the
machines. It is then fed into a cracker, a machine consisting of two
rolls with projections on their surfaces shaped like little pyramids,
the two rolls revolving with a differential, one going considerably
faster than the other, and being adjustable, so that they can work
close together or with some distance between them. The rubber is fed
between these rolls and broken down into a coarse, spongy mass. Water
flows on to the rubber during the process, bringing down sand, dirt,
bark, and the many other foreign materials which come mixed with the
rubber. The rubber is put through this machine a number of times, until
it is worked into a uniform condition. Some of the rubbers, like the
Ceylons and Paras, will sheet out into a coarse sheet by being put
through this machine; others, like the majority of the African rubbers,
will fall apart and come down in chunks and have to be fed into the
machine with a shovel.
[Illustration: PREPARING CRUDE RUBBER FOR MAKING TIRES