SECTION 2 MANNER AND TERMS OF SALE. None of the lands granted to the state for educational purposes shall be sold otherwise than at public auction to the highest bidder, the value thereof, less the improvements shall, before any sale, be appraised by a board of appraisers to be provided by law, the terms of payment also to be prescribed by law, and no sale shall be valid unless the sum bid be equal to the appraised value of said land. In estimating the value of such lands for disposal, the value of the improvements thereon shall be excluded: Provided, That the sale of all school and university land heretofore made by the commissioners of any county or the university commissioners when the purchase price has been paid in good faith, may be confirmed by the legislature.