Gums, Resins. 212 [Sept 190tt 



the ends of the rolls and prevent contamination with grease and oil from the 

 bearings. There is great uniformity of pattern and general arrangement of these 

 washing mills in all the factories, the differences are in the form of grooving and 

 roughening of the surfaces. The rollers which produce the smoothest and most 

 uniform sheets are those in which the grooves are nearly obliterated, and in which 

 the surface has become rough with the natural wear of the metal ; rolls in this 

 condition would, I think, be most effective with freshly coagulated latex on 

 an estate, 



DRYING. 



19. The rubber in the washed or crepe form is wet not only with surface 

 moisture but with water held in the substance of the rubber itself. It is usually 

 dried by hanging up the strips in dark rooms warmed to about 90° P., an operation 

 taking about a week or ten days. In no case did I notice any artificial circulation 

 of the air to accelerate the drying. A few manufactories have adopted vacuum 

 drying, which I have already described and discussed. There is no sign, however, 

 of this process ousting the older fashioned method of simple air drying. 



MASTICATING RUBBER. 



20. The next process through which the washed and dried rubber passes 

 is that of mastication, during which the rubber is torn, stretched, heated, and 

 generally kneaded about until the toughness and elasticity, so characteristic of it 

 hitherto, are destroyed, and the rubber becomes plastic. 



The masticating machine consists of two steel rollers with smooth polished 

 faces, which revolve on horizontal axes in the same horizontal plane. The distance 

 between the two rolls can be adjusted until they are brought into contact with one 

 another. The rolls may be any convenient size, and are usually about 3 feet in 

 length and 12 to 18 inches in diameter. They are hollow and heated by injected 

 steam, and may be driven at even or differential speeds. The machine, in fact, is in 

 many respects similar to a rubber-washing machine, but differs in the rollers 

 being smooth and being worked hot and dry and revolving more slowly. The 

 action on the raw rubber is curious, with the rolls separated about ?h 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 | of an inch thick, to be fed again into the machine. 



The rubber, softened by the heat of the rolls, behaves like so much putty, 

 accumulating on the inturning faces of the rollers, heaving and seething as it is 

 made to flow over itself, and gradually 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 clef b 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. 



