We got this practical back yesterday, which we are doing on a semi-microscale basis. The parafin is cracked over porcelain fragments in a test tube. On cleaning up, we noticed that a number of the rubber bungs holding the delivery tubes were damaged. The damage appears to be dissolving, not heat damage, as the bungs were still tacky / runny at the end that fits into the test tube some hours later, especially the ones where the glass tube does not project much beyond the end of the bung. I suspect the reaction products are condensing as they hit the cooler glass of the delivery tube and dissolving the bungs? I'm not keen to waste money replacing bungs every few times this practical runs, so is there an alternative? Would cork bungs work, or be too porous to safely contain the gaseous cracking products, for example? (possibly a daft question, but our chemistry-specialist technician is off at present).