During the period when the legislature is not in session, no expenditure shall be charged against the legislative appropriation for the expenses of the legislature, exclusive of appropriations included therein for the office of the legislative budget assistant to the house and senate finance committees, and the office of the director of legislative services, without the authorization and approval of the president of the senate in the case of expenditures for the senate and the speaker of the house in the case of expenditures for the house. Authority is also granted hereby to the president of the senate and the speaker of the house to purchase supplies and equipment and to cause payment of expenses incidental to the operation and business of the legislature while the legislature is not in session. Such purchasing or payments shall be a charge upon the legislative appropriation, except such expenses as are otherwise specifically provided for by law.