The City may accept gifts, devises or bequests of money or property, hereafter called donations, to the library trust fund. Donations to the City for the city library or for library purposes shall be considered given to the library trust fund unless a contrary intent of the donor is evidenced. All donations shall be subject to approval by the council. Donations may be accepted on such conditions as may be approved by the council. Without limiting the lawful conditions which may be approved by the council, donations may be accepted on the condition that the principal amount be retained and invested and only the income expended for the benefit of the Beaverton City Library.