1) Trying of Impeachments 2) The Confirming of Appointments 3) The Ratification fo Treaties
the senate
I assume you mean the US Senate. From the Constitution: "The Vice President of the United States shall be President of the Senate, but shall have no Vote, unless they be equally divided."
The power of impeachment is vested in the United States Congress. The House of Representatives is the only body that can bring impeachment charges against an official. Only the Senate can act as a court for an impeachment.
The United States Constitution provides that the House of Representatives "shall have the sole Power of Impeachment." (Article I, section 2) and that "the Senate shall have the sole Power to try all Impeachments .... [but] no person shall be convicted without the Concurrence of two-thirds of the Members present." (Article I, section 3)
The Senate has the sole power to hold the trial
Article I, Section 3 of the Constitution of the United States of America:The Senate shall have the sole power to try all impeachments. When sitting for that purpose, they shall be on oath or affirmation. When the President of the United States is tried, the Chief Justice shall preside: And no person shall be convicted without the concurrence of two thirds of the members present. The House of Representatives reserves the sole power to impeach members of the House.
This is because of the Great Compromise which states that the Senate shall be based on equality but the House shall be based on the population of the states.
The Senate shall have the sole power to try all impeachments. Basically, the House serves as a grand jury that may indict an office holder. The Senate conducts the actual trial. The framers intentionally split these duties between the houses because the House is less exclusive. The Senate members serve longer terms (less elections) and are for that reason more resistant to the frequent whims of the people and thus are less likely to convict office holders and remove them from office based on fickle passions and witch-hunts. The thought is that Senators are more reasoned. An indictment can be conducted by passionate congressmen because their decisions are checked by the cool deliberation of the Senate.
Normally it is the Vice President who is ex officio the President of the Senate. But most of the time it is the President Pro Tempore of the majority party who often delegates the power to the newer members of the house. In response to the answer above ^, Article 1 Section 3 of the Constitution states: The Vice President of the United States shall be President of the Senate, but shall have no Vote, unless they be equally divided.
"He shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur"...
Article 2 section 2 of the US constitution "He shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur; and he shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for, and which shall be established by Law: but the Congress may by Law vest the Appointment of such inferior Officers, as they think proper, in the President alone, in the Courts of Law, or in the Heads of Departments."
to break a tie in the senate