If only ions from the Cu-As group are present begin on page 190, note 2. This procedure will precipitate the ions of this group and separate them into the subgroups. Go to Procedure 7 and 11 from here. After the Group 2 ions have been separated from the remaining cations, they are further divided into two subgroups. This separation is based on the formation of by See Procedure 6 on p. 196.
Ammonium sulfide is added to the preceding precipitate and the sulfides dissolve.
Repeated treatments and washings important here. This is because HgS is extremely with a K sp of . The other ions dissolve via the to produce . It contains a good as well as a good . Lead sulfate will precipitate in .