Nickel salts are particularly toxic.
Copper and cobalt salts are toxic.
Chemicals and Solutions:
0.1M Cobalt chloride
0.1M Copper sulfate
0.1M Nickel nitrate
0.1M Sodium carbonate
0.1M Sodium hydroxide
Mix nickel nitrate solution with sodium carbonate solution to form a green ppt. of nickel carbonate.
Mix copper sulfate solution with sodium carbonate solution to form a blue ppt. of copper carbonate.
Mix cobalt chloride solution with sodium carbonate solution to form a purple ppt. of cobalt carbonate.
Use excess carbonate, to assure that precipitation of the toxic metal ion.
Carbonate salts are insoluble with the exception of those containing alkali metal ions and ammonium ions.