Firefighters install chimney over Sistine Chapel ahead of conclave to elect new pope

Vatican firefighters were seen on the roof of the Sistine Chapel installing the chimney, a key moment in the preparation for the May 7 conclave.

After every two rounds of voting in the Sistine Chapel, the ballots of the cardinals are burned in a special furnace to indicate the outcome to the outside world.

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If no pope is chosen, the ballots are mixed with cartridges containing potassium perchlorate, anthracene (a component of coal tar) and sulphur to produce black smoke.

But if there is a winner, the burning ballots are mixed with potassium chlorate, lactose and chloroform resin to produce the white smoke.