Hello,
I found in Lillie (1965 ), page 445 the procedure for Arsenic.  Copied below:

    For As fix in 10% formalin containing 2.5% copper sulfate for 5 days.  Wash 24 hours in running water.  Imbed in paraffin.  Deparaffinized sections present green granules of Scheele's green (CuHAsO3) which, though insoluble in water, is dissolved by acids and by ammonium hydroxide.  By substituting cupric acetate for the sulfate, the green granular paris green or cupric acetoarsenite is produced.  Its solubilities are similar (Castel's method, Bull. Histol. Appliq. 13:106, 1936).  Lillie suggested a light safranin counterstain.

Hoped this helped!
Lynette