469 
and being worked hot and dry and revolving more slowly. The 
action on the raw rubber is curious, with the rolls separated about 
^ of an inch a mass of washed rubber is thrown upon the machine, 
it is squeezed into a uniform sheet which is folded over on itself 
by the workman, and a slab of rubber produced i to § of an inch 
thick, to be fed again -into the machine. 
The rubber, softened by the heat of the rolls, behave like so 
much putty, accumulating on the inturning faces of the rollers, 
heaving and seething as it is made to flow over itself, and gradu- 
ally being worked through into a thin sheet, which adheres to the 
more slowly moving roll, the one next the workman. As this sheet 
comes round, wound on the roll, the workman with a stumpy knife 
slices it through, and peels it off, folding it over upon itself to 
repeat the operation of being sucked through the roll over and over 
again. In its passage reports as of saloon pistols are heard, as the 
air imprisoned in the folds of rubber is compressed, and finally 
bursts through the writhing mass of distended and flowing rubber, 
reluctant to pass through the narrow cleft to freedom. In this 
torturing process the fine hard cure South American Para rubber 
shows its superior quality and remains tougher and harder than 
plantation rubber when perfectly masticated. But even with 
South American Para the elasticity and nerve are lost, the rubber 
has no spring and can be bent and torn, indented and cut, and is 
compliant to any shape which is impressed upon it. The colour 
has changed, in the case of plantation rubber from the pale yellow 
or brown to a dirty grey, and the whole nature of the material has 
undergone a metamorphosis : but what this change really consists 
of no one can now tell, 
MIXING. 
21. The masticated rubber is ready now to be mixed with the 
hundred and one ingredients with which it is to be compounded. 
The requisite amoutu of sulphur in fine powder is added, with zinc 
oxide, red lead, plumbago, asbestos, powdered pumice, recovered 
rubber, rubber substitutes, rubber of other grades and qualities, 
sulphide of anti ony, lime, vermilion or any of all those substances 
which the knowledge and experience of the manufacturer indicate 
as necessary for the particular class of goods which the rubber is 
destined to become. This mixing is done on rollers of exactly the 
same type as used in masticating, but the rolls are kept cooler. 
The rubber is put on the machine and the ingredients sprinkled on 
it as it passes through the rolls, they are folded between layers of 
the rubber, and, after repeated working through the rollers, become 
thoroughly incorporated and most intimately mixed into “ dough ” 
of which each factory has many types and the precise compositions 
of which are the secrets of each firm. The dough thus compound- 
ed is rolled up and stored for future use. 
VULCANISATION. 
22. Vulcanisation is the name given to the act of combining 
ndia-rubber and sulphur chemically into a new substance. There 
