In all precincts wherein two election boards shall have been appointed, the receiving board shall attend at the opening of the polls, shall open the polls, and shall proceed with the election. The counting board shall attend at the voting place not later than three hours after the opening of the polls, and shall take charge of the ballot box containing the ballots theretofore cast in that precinct. They shall retire to a partitioned room or space in the voting place and there proceed to count and tabulate the ballots cast, as they shall find them deposited in the ballot box. The receiving board shall continue to receive the vote of electors in the other box, until such time as the counting board shall have finished counting and tabulating the ballots cast in the first ballot box. The county board shall, before exchanging the ballot boxes as herein provided, seal the ballots counted by it in envelopes to be provided for the purpose, which shall not be opened until the two boards shall together proceed with counting, tabulating and summarizing the votes as by this chapter provided. The two boards shall then exchange the first box for the second box, and so continue until the hour of closing the polls arrives.