BS ISO 473:2019 pdf free.Lithopone pigments – General requirements and methods of testing.
Weigh, to the nearest 0,1 mg, about 0,6 g of lithopone 30 %, or about 0,3 g of lithopone 60 %, or about 0,6 g of lithopone 20 %, all previously dried at (105 ± 2) °C, into a beaker and add 25 ml of the hydrochloric acid solution (7.2.2.2). Immediately cover with a watch-glass and boil until the evolution of hydrogen suiphide has ceased [test with the lead acetate paper (7.2.2.9)]. Dilute with 100 ml of water, add 5 ml of the sulphuric acid solution (7.2.2,4).
Boil the solution again and allow the precipitate to settle while hot and filter the supernatant solution through a fine filter paper. Transfer the precipitate to the filter paper and wash with hot water containing some sulphuric acid until a drop of the washings shows no reaction with the potassium hexacyanoferrate(II) solution (7.2.2.11). Fold the filter paper over the precipitate. Transfer it while still wet to a weighed porcelain crucible and ignite it in contact with air at low temperatures and then burn to constant mass at (800 ± 20) °C. The residue is assumed to be barium sulfate. Add a few drops of the sulphuric acid solution (7.2.2.4) to the contents of the crucible. No trace of hydrogen suiphide should be noticeable; otherwise, the sulphuric acid shall be driven off and the residue re-ignited.
Combine the washings with the filtrate. Add a slight excess of the ammonia solution (7.2.2.6) [verify on Congo red paper (7.2.2.8)], followed by the hydrochloric acid solution (7.2.2.4) from a dropping bottle until a small piece of Congo red paper (7.2.2.8), when touched with the solution, just turns to a lasting red-blue or blue-red colour (pH 1,5 to pH 3,0).
If necessary, make up to 150 ml with water, heat the solution to boiling, add 10 drops of the diphenylamine solution (7.2.2,7) and immediately titrate the solution as specified for the standardization of the potassium hexacyanoferrate(II) solution in 7.2.2.11.2.BS ISO 473 pdf download.