The Action of Metals, &€., on India-rubber. 281 



to collect the rubber under the rollers and pass it repeatedly 

 through them till it attains the necessary degree of softness, 

 so that as it becomes over-masticated it becomes soft and 

 sticky, a point to which any experienced workman would 

 not bring it. About four minutes is required for proper 

 mastication, but one of us prepared some rubbers which were 

 masticated for 15 and 2ij^ minutes respectively, and after 

 spreading these on cloth we had a piece of the same cloth 

 covered with properly masticated rubber (masticated during 

 4 minutes). All these were then placed in an incubator at 

 150° Fah. for a fortnight, but the sample of over-masticated 

 rubber did not shew any sign of decay after that time, and 

 to-day, six months after the experiment was made, the one 

 appears quite as good as the other. The over-masticated 

 rubber, had, when first produced, a slightly greater "tacky" 

 feel than the properly masticated rubber, and this tackiness 

 appeared not to have become greater or less after the lapse 

 of six months. 



Peroxide of Hydrogen. 



The curious effect, or rather absence of effect, which 

 chromic acid had upon india-rubber led us to make an 

 experiment to find whether peroxide of hydrogen would 

 oxidise and destroy it. We placed sheets of rubber both in 

 alkaline and in acid solutions of that reagent for one month, 

 and found that after that time the elasticity and strength of 

 the sheets so treated remained unimpaired, a result which 

 appears quite as surprising as the chromic acid result. 

 Some years ago one of us found that ozone exercised a 

 most injurious influence on india-rubber, especially when it 

 was left in a stretched condition, and it might naturally be 

 expected that peroxide of hydrogen would have exercised 

 an equally injurious influence on it. 



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