MICRO-GRAVIMETRIC DETERMINATION OF LEAD 2x9 amount of the reagent and also the method of its introduction, (4) the digestion of the filtered precipitate with cont. ammonium hydroxide and the volume of ammonium hydroxide used, (5) the filtration, (6) the wash liquid and method used for washing the precipitate, (7) the temperature and time required to dry the precipitate, the authors have elaborated an exact micro-gravimetric method, applying EMICH'S~ micro-technique and using a porcelain filterstick. EXPERIMENTAL Reagents and standard solution employed were: I. Mercaptobenzothiazole solution, IO/~, in ammonium hydroxide, 240j0. The solution was prepared by dissolving I g of the reagent in IOO ml of ammonium hydroxide, 23%, heating on the water bath to facilitate solution. It is essential to use a fresh solution, i.e. one prepared just before the determination is carried out.
- Standard Pb(NO& p.a. solution (the titre of this solution was determined gravimetrically, using the PbS04 method; it was 3 mg Pb+2 per ml), 3. Ammonium hydroxide, 24%. 4. Ammonium hydroxide, cont.
Remark:
The ammonium hydroxide used must be pure and must not give any silica residue on evaporations.
- Cadmium salt solution, 10%. 6. Bi-distilled water.