Several books speak about dispensational truth extensively:

E.W. Bullinger, The Foundations of Dispensational Truth (London, England: Samuel Bagster & Sons, Ltd. Reprint, 1972).

Charles H. Welch, Dispensational Truth, 4th (revised) ed. (London, England: The Berean Publishing Trust, 1981).

Stuart Allen, The Early and Pastoral Epistles of Paul (London, England, The Berean Publishing Trust, 1977).