A witness may be impeached by contradictory statements previously made by him as to matters relevant to his testimony and to the case. Before contradictory statements may be proved against him, unless they are written statements made under oath in connection with some judicial proceedings, the time, place, person, and circumstances attending the former statements shall be called to his mind with as much certainty as possible. If the contradictory statements are in writing and in existence, they shall be shown to him or read in his hearing. To lay this foundation, the witness may be recalled at any time. When thus impeached, the witness may be sustained by proof of general good character, the effect of the evidence to be determined by the jury.