47i 



COLD CURE. 



24. Although pure sulphur does not combine with india- 

 rubber at a temparature below 270 F., yet a compound of sulphur 

 with chlorine — namely, mono-chloride of sulphur— does react on 

 rubber, and the sulphur is transferred from the chloride of sulphur 

 to the rubber, and vulcanisation takes place rapidly and complete- 

 ly at ordinary temperatures. This action with pure chloride of 

 sulphur is too violent ; this agent is therefore diluted and a solu- 

 tion of 2-3% 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 cham- 

 ber 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 uncombined or free sulphur 

 is objectionable, or which have been made by accumulation of rub- 

 ber 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 plan- 

 tation 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 nor- 

 mally present in all Para rubber, and which is not soluble in ben- 

 zole. 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 homogeneous 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 solu- 

 tion of samples of rubber in solvents is one test of the purity ot 

 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. 



Final 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 he inclusfon of an account of some of these processes in 



