RUBBER PLANTING 213 



petrol, chloroform, carbon bisulphide and other solvents. 

 The rubber is more easily taken up by the solvent 

 after it has been mechanically kneaded in the rolling 

 or masticating machines, than in the untreated condition. 

 Weber considered that all these solutions should more 

 properly be regarded as solutions of the so-called 

 solvent in the india-rubber. 



The mechanical strength of rubber which has once 

 been dissolved is greatly inferior to that of the crude 

 rubber. For this reason cut sheet rubber is superior 

 for many purposes to sheet which has been "spread" 

 from a solution. This fact renders it doubtful whether 

 synthetic rubber can ever be made equal in physical 

 properties to natural rubber. The mechanical kneading 

 to which raw rubber is subjected in the course of 

 manufacture has also a marked effect upon its physical 

 properties. 



The value of rubber for many purposes depends 

 largely upon its chemical indifference, i.e. upon its want 

 of power to enter into combination with many other 

 chemical substances. Raw rubber undergoes slow 

 oxidation on exposure to the air, and it enters rapidly 

 into combination with ozone. Dilute acids and alkalies 

 have little or no effect upon it, but it is rapidly destroyed 

 by the action of strong sulphuric or nitric acid, or by 

 exposure to the action of chlorine, bromine or iodine. 

 The only compounds of rubber which have been at all 

 closely studied are those with sulphur, with the halogens 

 and with ozone. 



