The Collaborative International Dictionary of English v.0.48:

James's powder \James"'s pow`der\ (Med.)
   Antimonial powder, first prepared by Dr. James, an English
   physician; -- called also fever powder.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Antimonial \An`ti*mo"ni*al\, a.
   Of or pertaining to antimony. -- n. (Med.) A preparation or
   medicine containing antimony.
   [1913 Webster]

   Antimonial powder, a consisting of one part oxide of
      antimony and two parts phosphate of calcium; -- also
      called James's powder.
      [1913 Webster]