CHAPTER X. 

 RUBBER MANUFACTURE. 



PROPERTIES OF RUBBER. 



BEFORE dealing with the various methods of preparing rubber 

 from the latex, let us endeavour to describe some of its physical 

 and chemical properties. No other solid body can be compared 

 with it in regard to elasticity, which may be augmented by 

 slightly raising its temperature. When the temperature is 

 lowered to zero it becomes hard and brittle, but regains its 

 elasticity on the temperature being raised. If, however, this be 

 increased to 293 Fahr., it assumes a permanent sticky con- 

 sistency, while, if the temperature be still further raised to 360 

 Fahr., it melts and turns to a dark oily liquid. Rubber is a bad 

 conductor of both heat and electricity, but when acted upon by 

 oxygen, ozone, or light, it may be converted into a good con- 

 ductor of both these forces. It has the power of expanding 

 when heated, and contracting when submitted to a lowered 

 temperature. If, however, raw rubber be raised to a temperature 

 of about 240 Fahr. and then allowed to cool slowly, it loses all its 

 powers of contractility, but no perceptible changes are produced in 

 its other properties. It is upon this characteristic that the rubber 

 thread industry is largely dependent. Rubber is extremely perme- 

 able towater,and this fact is often taken advantage of for fraudulent 

 purposes. It is compressible, and Blossom states that a blow of 

 100 tons diminished the volume of a cube of rubber, of about 35 

 inches square, by 10 per cent. Beadle and Stevens state that* the 

 physical properties of raw rubber are improved by exposure to 

 comparatively low temperatures. They found that samples of 

 block plantation rubber placed in an ice-chest for a week showed 

 a tensile strength of 780 as against 500 previous to being placed 

 in the ice-chest, 



* Chemical News, 22nd Nov. 1907. 



