Softening of corks

Corks impregnated with sodium silicate solution resist attack by hydrogen chloride and chlorine. 

Rubber stoppers should be occasionally rubbed with a little toluene, which prevents hardening and keeps them clean. A trace of vaseline smeared on a rubber stopper affords considerable protection from the actions of halogens. Rubber stoppers should always be removed from vessels while the latter are still warm, to prevent sticking to the glass. 

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