Cracking a hydrocarbon

You can find instructions for this experiment at http://www.rsc.org/learn-chemistry/resource/res00000681/cracking-hydrocarbons Liquid paraffin (a mixture of alkanes of chain length C20 and greater) is vaporised and passed over a hot pumice stone catalyst. A gaseous product is obtained which is flammable and which will decolorise bromine water and acidified permanganate ions. The same apparatus and method can be used to dehydrate ethanol.