How do you detect presence of nickel in chocolates?

v Take a small piece of the chocolate and crush it into fine powder. Put it into a test tube and add a little hydrochloric acid .

v Add some water and boil it till the chocolate melts to form a solution.

v To the solutions obtained, add ammonium chloride and ammonium hydroxide.

v Now take a little amount of the solution and pass hydrogen sulphide gas through it using kipp's apparatus . Formation of a black colour indicates the presence of group four cations.

v Now to the filtrate, add small amount of dimethyl glyxime. If a rose red coloured precipitate is obtained in a scarlet red solution, then presence of Nickel (Ni2+) is confirmed.