Picric acid or 2-Amino-4,6-dinitrophenol or the Sodium salt and Sodium polysulfide solution heated to 110 ℃, and return, until the sample to dye inspection standard. If necessary, use the empty oxygen precipitation and filter.
Properties and Applications
red light black. In the Sodium sulfide solution solubility is very good, for red black; In concentrated sulfuric acid for the blue black, dilution after precipitation.
