Oct. 1906.] 



293 



Saps and Exudations. 



chloride of sulphur to the rubber, and vulcanisation takes place rapidly and 

 completely at ordinary temperatures. This action with pure chloride of sulphur 

 is too violent; this agent is therefore diluted and a solution of 2— 3% of chloride 

 of sulphur in carbon bisulphide is used. The article to be vulcanised is immersed 

 in this solution, and left for a few minutes, the time varying with the thickness 

 of the rubber ; it is removed, drained, and finally washed with water. The chamber 

 in which this dipping takes place must be specially arranged to prevent the 

 fumes of the solution, which are poisonous and corrosive, coming into contact 

 with the workmen. This cold cure is used for goods which from their nature would 

 be damaged by exposure to the temperature required for heat vulcanisation, and 

 also for goods in which the presence of uneombined or free sulphur is objectionable, 

 or which have been made by accumulation of rubber by dipping in rubber solution, 

 as is the case with teats for infants' bottles, and in some surgical goods. 



SOLUTION MAKING. 



25. In dissolving rubber for making solution or pastes for spreading on 

 fabrics, benzole is the solvent generally used. The process is simple, the washed dry 

 rubber is soaked in the solvent and then ground up with the solvent in enclosed 

 boxes, in which are several pairs of small rollers which thoroughly mix the rubber 

 and solvent, and according to the relative amounts of rubber and solvent produce 

 a solution free from lumps. If a solution of plantation rubber be made by 

 shaking rubber and benzole in a glass bottle, a turbid instead of a transparent 

 solution results. This is due to a small quantity of a resinous body which is always 

 normally present in all Para Rubber, and which is not soluble in benzole. The 

 effect of the mechanical rolling in solution making in the factory, is to largely 

 break up and incorporate the flakes of this resin and render the whole homogenous 

 and transparent. Thorough mastication of the rubber also tends to produce this 

 same result, and rubber after complete mastication is far more inclined to dissolve 

 to a clear solution in rubber solvents than simple sheet, biscuit, or crepe rubber. 

 This point I mention because the solution of samples of rubber in solvents is 

 one test of the purity of rubber, and the presence of this insoluble resin, which 

 appears large in bulk, but which is in reality only a small fraction of a per cent., is 

 apt to prove disconcerting to the person making the test. 



PINAL MECHANICAL PROCESSES. 



26. The detailed mechanical manufacture of the actual rubber goods of 

 commerce can only have an indirect interest to the rubber grower ; but though 

 indirect, it is, I consider, sufficiently great to justify the inclusion of an account of 

 some of these processes in this report. Much of my time was spent in acquiring 

 knowledge of these details in the various factories I visited. These facts must be 

 remembered in order to properly understand the final manufacture of rubber goods. 

 The dough of masticated rubber, mixed with sulphur and other ingredients, is 

 plastic and has lost the original elasticity of rubber. It can be cut and moulded, 

 stamped into shapes, bent and twisted, just as putty, clay, or a dough of flour 

 and water may. Rubber dough and masticated rubber are self-adhesive, and cut 

 surfaces can be joined firmly together by simple pressure, and if the surfaces be 

 brushed over with benzole the pressure required to form a very fine junction is of 

 the slightest. On heating the dough and masticated rubber which contains sulphur, 

 a chemical change takes place and a chemical compound of rubber and sulphur is 

 formed which possesses the original elasticity and toughness of the raw rubber, 

 but in a great and more perfect degree. This chemical change is called vulcani- 

 sation of the rubber, and it is the final process to which practically all manufactured 

 rubber goods are put. It must never be forgotten that raw rubber and vulcanised 

 rubber are quite different and distinct substances, their chemical compositions are 



