This section is from the book "The National Capitol. Its Architecture Art And History", by George C. Hazelton, Jr. Also available from Amazon: The National Capitol Its Architecture Art and History.
The Vice-President-elect takes the oath of office, customarily administered by the Vice-President, just preceding the inauguration of the President. This ceremony takes place in the Senate Chamber, over which he is to preside, in the presence of the President, President-elect, Senate and House. The Presidential party then proceed to the platform, prepared to the east of the Capitol, for the inaugural exercises. In this chamber also, all treaties made by the United States with foreign powers are ratified, and nominations for appointments made by the President confirmed. Here, near the close of the Rebellion and during the reconstruction period, the Senate hotly debated the 13th, 14th and 15th Amendments of the Constitution, before they were submitted by Congress to the Legislatures of the States.