469 



and being worked hot and dry and revolving more slowlv The 

 action on the raw rubber is curious, with the rolls separated about 

 yV 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 | to I of an Inch 

 thick, to be fed again into the machine. 



The rubber, softened by the heat of the rolls, behave like so 

 much putt)', 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 amount 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 antimonv, lime, vermilion or any of all those substances 

 which the knowledge and experience of the manufacturer indicate 

 as necessarv for the particular class of goods which the rubber is 

 destined to' become. This mixing is done on rollers of exactly the 

 same tvpe 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. I here 



