RUBBER MANUFACTURE. 115 



of storage room and facilitating drying. Burgess describes a 

 washing machine suitable for plantation use as follows : 



" This machine consists essentially of two steel rollers which 

 revolve on horizontal axes parallel to one another ; the distance 

 between the surface of the two rollers can be adjusted and varies 

 from | inch to practical contact. The rollers revolve at different 

 speeds and are driven by power transmitted by belt and pulley 

 through gear wheels to the rollers themselves. The axes of the 

 two rollers may be on the same horizontal plane, more usually 

 one is slightly above the other. A stream of water flows over 

 the surface of the rollers all the time they are in use. When the 

 machine is used, freshly coagulated lumps of rubber are put in 

 between the rollers, which are separated about -|- inch. The 

 rubber is passed through several times, the rollers being gradually 

 approximated to each other, and the rubber becomes compacted, 

 and to some degree hardened. At the same time, the effect of 

 the differential rate of movement of the two roller surfaces is to 

 subject the rubber to a shearing stress, which stretches and tears 

 it to pieces, and it is here that the peculiar property of rubber is 

 clearly seen. The elastic stretching and rebound kick out any 

 gross mechanical impurity that may be present, and when the 

 machine is used on scrap rubber, there is a perfect shower of dirt, 

 pieces of bark, and wood thrown out from the front of the 

 machine. Freshly cut or torn surfaces of the rubber re-unite and 

 emerge as a continuous sheet. At the same time the stream of 

 water thoroughly washes out any impurity soluble in water that 

 may be left in the rubber. The final product is a coherent but 

 granular sheet of rubber, the thickness of which can be regulated 

 by the distance left between the rollers." 



Washed rubber was not well received when first placed on 

 the market, as manufacturers stated they preferred to perform 

 the washing themselves, but that there is now a good demand for 

 this form of rubber is demonstrated by the sale reports. It is 

 not so liable to arrive on the market in a heated or tacky con- 

 dition as unwashed rubber, which is certainly an important point 

 in its favour, but whether the removal of a portion of the so- 

 called organic impurities does not affect the resiliency of the 

 product is still an open question. Very thin sheets are not well 

 received by buyers, and it is considered that a thickness of about 

 inch should be aimed at. 



