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and the faults which underlie it can be easily removed. But before 

 doing this the problem to be solved and the material under treat- 

 ment should be furthur considered. The wet slabs of freshly 

 coagulated rubber are composed of the following ingredients. 

 Rubber, proteid, oils, and resins making up the solid matter, and 

 a watery liquid full of those impurities — the gum, sugar, salts and 

 excess of acetic acid — which were present in solution in the latex 

 during coagulation. 



While the slabs are rolled and pressed, much of the watery 

 liquid is expelled, but a limit is quickly reached and when the 

 slabs are set apart to dry there is usually fifty per cent or more 

 of this watery liquid with the impurities dissolved in it still ad- 

 herent to the rubber "sponge." On drying the water itself evapo- 

 rates but leaves behind in the rubber whatever gum, sugar, salts 

 or other soluble matter it previously contained. 



These are impurities which can and should be removed from 

 rubber- — -the other impurities, the oils, resins and coagulated pro- 

 teid which are not soluble in water, cannot be removed and may 

 be neglected. The rubber slabs in their wet condition begin to 

 putrefy and become most offensive, and during the long period 

 of drying much attention is required to keep them moderately free 

 from mould. This is entirely due to those impurities which were 

 soluble in water and which are being dried up inside the rubber 

 slab. The rubber itself undergoes no appreciable change and it 

 is doubtful whether it is in any way eventually damaged by the 

 putrefaction which occurs in drying. At the same time by spoil- 

 ing the pretty appearance of the rubber sheets, the mould and 

 decomposition products detract from the price the dry rubber 

 commands, and it is a source of annoyance and very disagreeable 

 to the rubber producer. 



The slabs take a long time to dry because the outside film 

 which quickly dries seals the inner portions, and slabs which are 

 half an inch thick are not dry at the end of many months. As 

 the slabs dry the colour changes from white to grey and finally 

 when dry the rubber is transparent. A sheet of rubber may be 

 taken to be dry when the grey colour is no longer apparent in 

 a freshly cut surface. 



All raw rubber before it is vulcanised by combination with sul- 

 phur, is very sensitive to heat, a temperature of I50°F. renders para 

 rubber quite sticky on the surface, and a higher temperature utterly 

 destroys the " nerve" of it. It is consequently very injudicious to 

 use any artificial heat in hastening the drying of rubber. If some 

 artificial heat were absolutely necessary a very carefully regulated 

 temperature never exceeding I20°F. would probably not cause any 

 evident damage, but bearing in mind the fact that a temperature of 

 I50°F. does produce marked damage the sound policy is, I feel 

 sure, to avoid artificial heat altogether. I may here mention that I 

 have subsequently visited many plantations and seen rubber being 

 dried with the aid of heat and in no case did I fail to find some 

 rubber that had been clearly overheated. Fortunately it is possible 



