The proceeds of the sale of any real estate owned by the Commonwealth when sold by any department, board or commission thereof, with the specific authority of the General Assembly as provided by existing law, together with any rentals derived therefrom while the same shall have been owned by the Commonwealth, shall be paid into the General Fund of the State Treasury, unless said real estate shall have been purchased with funds paid either wholly or mainly out of special funds, in which event said proceeds of sale or rentals shall be paid to and credited to the proper special fund.
71 P.S. § 768