• Number of votes are necessary to elect a pope: A candidate must receive two-thirds of the vote to be elected. If no one has received the required two-thirds majority, the ballots are set aside, and a new vote begun immediately, with two votes each morning and two each afternoon until a new pope is elected.
• Custom of signaling the election of a pope with white smoke: At the end of each morning and afternoon session of the conclave, the ballots from the two votes are burned together in a furnace near the Sistine Chapel. In the past, wet straw was added to the ballots of an indecisive vote to produce black smoke; dry straw was added to the ballots of a successful vote to produce white smoke, signaling to the crowds in St. Peter's Square the outcome of the conclave's deliberations. In 1978 and 2005, a small vial of chemicals was substituted for the straw to produce the correctly colored smoke.
SOURCE: U.S. Conference of Catholic Bishops; SacredDestinations.com