Whenever any county jail or jailer’s residence, or both, has been condemned as unfit for county jail purposes, or whenever any county has built a new jail or jailer’s residence, and has not disposed of the old one, the board of county commissioners of said county be and they are hereby authorized to sell and dispose of said old jail or jailer’s residence or both and the real estate thereto belonging at not less than three-fourths of its appraised value, without an election being held for such purpose, such value to be ascertained and determined as hereinafter provided upon such terms and conditions as said board of county commissioners shall deem proper and just, upon first giving thirty days’ notice in the official paper of said county of the time, place, manner and terms and conditions of said sale; and the said board of county commissioners are hereby authorized and empowered to use the funds derived from such sale in the construction, furnishing and equipping of such new jail or jailer’s residence or both, whether built as separate buildings or in conjunction with or as a part of a county courthouse.